Book of abstracts, "Jaszowiec" 2011 - Instytut Fizyki PAN

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This work relates to Department of the Navy Grant N62909-11-1-1076 issued by Office of 

Naval Research Global. The United States Government has a royalty-free license throughout 

the world in all copyrightable material contained herein. 

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Skład własny (Ł. Cywi�ski, podzi�kowania dla T. Słupi�skiego) 

Druk i oprawa: Drukarnia Zalesie, 05-501 Piaseczno, ul. Norwida 10 

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PREFACE 

The 40 th “Jaszowiec” International School and Conference on the Physics of 

Semiconductors continues the tradition of annual meetings of the international and Polish 

semiconductor communities. For the third time the event will be held in the mountain resort 

Krynica-Zdrój on June 25 th – July 1 st , 2011. The first thirty seven meetings took place in the 

village Jaszowiec in another part of Polish mountains. For years, the name “Jaszowiec” has 

become the symbolic trademark of the conference and, therefore, it is still kept. 

The scope of the conference covers essentially all research fields in semiconductor 

physics, including technology, experiment, theory and modeling. During the present 

conference particular attention will be paid to the physics of semiconductor devices, and a 

special day-long symposium “Physics and modeling of devices” has been organized. 

The Conference is preceded by the School (tutorial session), addressed mainly to 

undergraduate and graduate students, and young scientists. The School will be held on June 

25 th -26 th . During the School outstanding scientists will give four lectures providing an 

introduction to important fields in semiconductor physics. The scientific program of the 

school and conference consists of 25 invited lectures, and 194 contributed papers (18 chosen 

for oral presentation and 176 posters). The School and Conference will be attended by 

approximately 250 participants. 

This booklet contains the detailed program and abstracts of all presentations that will 

be given during the event. The invited and contributed papers will be published in a special 

volume of Acta Physica Polonica A. 

The International School and Conference is organized by two institutes of the Polish 

Academy of Sciences: Institute of Physics and Institute of High Pressure Physics; two 

institutes of the Faculty of Physics, University of Warsaw: Institute of Experimental Physics 

and Institute of Theoretical Physics; Foundation “Pro Physica”, and Committee on Physics of 

the Polish Academy of Sciences. The financial support of the organizing institutions as well 

as of the U.S. Army Forward Element Command-Atlantic, Research Division (USARFEC-A) 

and the U.S. Navy Office of Naval Research Global is gratefully acknowledged. 

Current information can be found on the conference web page: 

www.ifpan.edu.pl/jaszowiec . 

I would like to thank the members of the International Advisory Committee and the 

Program Committee for their contribution to the scientific program of the School and 

Conference. I would like also to express my gratitude to Łukasz Cywi�ski, the Secretary of 

the Conference, to Jacek Szczytko, the Chairman of the School, as well as other members of 

the Organizing Committee, Agnieszka J�drzejewska and Maciek Zaj�czkowski for their 

enthusiasm and excellent work. 

I wish all the participants of the meeting scientifically inspiring days and joyful social 

life. Have a pleasant stay in Krynica. 

Chairman of the Conference 

Czesław Skierbiszewski

40th _______________________________________________________________ 

"Jaszowiec" 2011 International School and Conference on the Physics of Semiconductors 

Saturday, June 25 th , 2011 

9:20 -- 9:30 Jacek Szczytko – School opening address 

INVITED LECTURES (SaI1, SaI2) 

9:30 – 12:30 Detlef Hommel (University of Bremen, Germany) 

Modern technologies for semiconductor epitaxy and nano-processing 

15:00 – 18:00 Aldo Di Carlo (University of Rome “Tor Vergata”, Italy) 

Physical simulation of electronic devices 

19:00 Barbecue (on the terrace of the ‘Geovita’ hotel) 

Sunday, June 26 th , 2011 

INVITED LECTURES (SuI1, SuI2) 

9:30 – 12:30 Gerhard Abstreiter (Walter Schottky Institut and Institute for Advanced 

Study TU München, Germany) 

Physics and Technology of Arsenide Based Quantum Dots and Nanowires 

15:00 – 18:00 Debdeep Jena (University of Notre Dame, USA) 

Tutorial: Engineering of Electric Fields in Nitride-Based Semiconductors 

20:30 – 21:30 Concert – chamber music performed by young artists, 

laureates of international music competitions 

Angelika Kumi�ga (violin) 

Agata B�k (cello) 

Michał Kubarski (accordion) 

21:30 Welcoming glass of wine 

5

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40th "Jaszowiec" 2011 International School and Conference on the Physics of Semiconductors 

Monday, June 27 th , 2011 

8:50 -- 9:00 Czesław Skierbiszewski – Conference opening address 

INVITED TALKS (MoI1 … MoI4) 

9:00 – 10:00 Joerg Wrachtrup (University of Stuttgart, Germany) 

Coherent optical control of the NV center in diamond 

10:00 – 10:10 Break 

10:10 – 11:10 Tomasz Dietl (Institute of Physics, Polish Academy of Sciences) 

Understanding and exploiting magnetism of semiconductors 

11:10 – 11:40 Coffee break 

11:40 – 12:40 Łukasz Kłopotowski (Institute of Physics, Polish Academy of Sciences) 

Charging Effects in Self Assembled CdTe Quantum Dots 

12:40 – 12:50 Break 

12:50 – 13:50 Grzegorz S�k (Wrocław University of Technology, Poland) 

Optical properties of strongly in-plane asymmetric epitaxial 

nanostructures 

CONTRIBUTED TALKS (MoO1 … MoO6) 

19:15 – 19:30 P. Utko, R. Ferone, I.V. Krive, R.I. Shekhter, M. Jonson, M. Monthioux, 

L. Noe, J. Nygård 

Coupling between electronic and vibrational excitations in carbon 

nanotubes filled with C60 fullerenes 

19:30 – 19:45 A. Urba�czyk, F.W M. van Otten, R. Nötzel 

Solid-state self assembly: a route to hybrid metal-semiconductor epitaxial 


19:45 – 20:00 M. Galicka, P. Kacman, R. Buczko 

First-Principles Study of Doped III–V nanowires 

20:00 – 20:10 Break 

20:10 – 20:25 F. Schuster, P. Kopyt, P. Lukasik, W. Gwarek, D. Coquillat, F. Teppe, 

B. Giffard, W. Knap 

Terahertz Detectors Based on Low Cost 130 nm Silicon Field Effect 

Transistors 

20:25 – 20:40 P. Wojnar, E. Janik, S. Kret, A. Petrouchik, M. Goryca, T. Kazimierczuk, 

P. Kossacki, G. Karczewski, T. Wojtowicz 

Growth of optically active CdTe quantum dots in ZnTe nanowires 

20:40 – 20:55 J.M. Schneider, B.A. Piot, I. Sheikin, G.A. Goncharuk, P. Vasek, 

P. Svoboda, Z. Vyborny, L. Smrcka, M. Orlita, M. Potemski, D.K. Maude 

Electronic properties of graphite 

21:05 – 23:00 MONDAY POSTER SESSION (MoP1 … MoP60) 

6

40th _______________________________________________________________ 


Tuesday, June 28 th , 2011 

INVITED TALKS (TuI1 … TuI4) 

9:00 – 10:00��Alex Greilich��(Technische Universität Dortmund, Germany) 

Optical control of one and two spins in interacting quantum dots 

10:00 – 10:10 Break 

10:10 – 11:10 Shaffique Adam (National Institute of Standards and Technology, USA) 

Graphene Transport Properties 

11:10 – 11:40 Coffee Break 

11:40 – 12:40 Arkadiusz Wójs (Wrocław University of Technology, Poland) 

Theoretical search for non-Abelian statistics in fractional quantum Hall 

states 

12:40 – 12:50 Break 

12:50 – 13:50 Dmitry Krizhanovskii (University of Sheffield, UK) 

Polariton condensation in dynamic acoustic lattices 

CONTRIBUTED TALKS (TuO1 … TuO6) 

15:30 – 15:45 K. Nogajewski, K. Karpierz, M. Grynberg, W. Knap, R. Gaska, J. Yang, 

M.S. Shur, J. Łusakowski 

Resonant Terahertz Absorption by Magnetoplasmons in Grating-Gate 

GaN/AlGaN-based Field-Effect Transistors 

15:45 – 16:00 K. Milowska, M. Birowska, J.A. Majewski 

Structural and electronic properties of functionalized graphene 

16:00 – 16:15 O. Proselkov, W. Stefanowicz, S. Dobkowska, J. Sadowski, T. Dietl, 

M. Sawicki 

Analysis of the magnetic anisotropy in ultrathin GaMnAs 

16:15 – 16:25 Break 

16:25 – 16:40 M. Goryca, P. Plochocka, P. Wojnar, T. Kazimierczuk, M. Potemski, 

P. Kossacki 

Spin-lattice relaxation of a single Mn 2+ ion in a CdTe quantum dot 

16:40 – 16:55 T. Kazimierczuk, M. Goryca, P. Wojnar, A. Golnik, P. Kossacki 

Magnetophotoluminescence of CdTe/ZnTe Quantum Dots: G-factor and 

Diamagnetic Shift Variation in a Single Dot 

16:55 – 17:10 T. Jakubczyk, W. Pacuski, A. Golnik, C. Kruse, D. Hommel, H. Hilmer, 

R. Schmidt-Grund, J.A. Gaj 

Control over CdTe Quantum Dots Emission using ZnTe-based Micropillar 

Cavities 

17:30 – 19:15 TUESDAY POSTER SESSION (TuP1 … TuP58) 

20:00 Conference Banquet 

7

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Wednesday, June 29 th , 2011 

INVITED TALKS (WeI1 … WeI4) 

9:00 – 10:00 Tomas Jungwirth (Institute of Physics, Academy of Sciences of the Czech 

Republic) 

Spintronics with antiferromagnetic materials 

10:00 – 10:10 Break 

10:10 – 11:10 Ewelina M. Hankiewicz (Universitaet Wuerzburg, Germany) 

Transport in topological insulators 

11:10 – 11:40 Coffee Break 

11:40 – 12:40 James Speck (University of California, Santa Barbara) 

Progress in Nonpolar and Semipolar GaN Materials and Devices 

12:40 – 12:50 Break 

12:50 – 13:50 Yasushi Nanishi (Ritsumeikan University, Japan, and Seoul National 

University, Korea) 

Recent Progress of DERI process for growth of InN and Related Alloys 

CONTRIBUTED TALKS (WeO1 … WeO6) 

19:15 – 19:30 N. Gonzalez Szwacki, J. A. Majewski, T. Dietl 

Properties of TM pairs in the bulk and at the surface of GaN with and 

without Si or Mg codoping 

19:30 – 19:45 A. Bonanni, W. Stefanowicz, M. Sawicki, T. Devillers, B. Faina, T. Li, 

T.E. Winkler, D. Sztenkiel, A. Navarro-Quezada, M. Rovezzi, R. Jakieła, 

A. Meingast, G. Kothleitner, T. Dietl 

Experimental Probing of Exchange Interactions Between Localized Spins 

in a Dilute Magnetic Insulator (Ga,Mn)N 

19:45 – 20:00 M. Birowska, C. �liwa, K. Milowska, J.A. Majewski, T. Dietl 

Origin of uniaxial magnetic anisotropy in (Ga,Mn)As 

20:00 – 20:10 Break 

20:10 – 20:25 E. Calleja, A. Bengoechea-Encabo, S. Albert, M.A. Sanchez-García, 

F. Barbagini, E. Luna, A. Trampert, U. Jahn, P. Lefebvre 

Understanding the Selective Area Nucleation and Growth of GaN 

20:25 – 21:40 S.P. Łepkowski, I. Gorczyca 

Influence of composition and atomic arrangement on elastic properties of 

wurtzite InGaN and InAlN alloys 

20:40 – 20:55 H. Turski, M. Siekacz, M. Sawicka, G. Cywi�ski, C. Cheze, S. Grzanka, 

Z. Wasilewski, P. Perlin, G. Muzioł, J. Pawłowska, I. Grzegory, 

C. Skierbiszewski 

InGaN laser diodes operating at 450-460 nm grown by RF-Plasma MBE 

21:05 – 23:00 WEDNESDAY POSTER SESSION (WeP1 … WeP58) 

8

40th _______________________________________________________________ 


Thursday, June 30 th , 2010 

SYMPOSIUM 

"Physics and modeling of devices " 

INVITED TALKS (ThI1 …ThI9) 

9:00 – 9:30 Maciej Bugajski (Institute of Elektron Technology, Warsaw, Poland) 

Quantum Cascade Lasers 

9:30 – 10:00 Wladek Walukiewicz (Lawrence Berkeley National Laboratory,USA) 

New Concepts and Materials for Solar Power Conversion Devices 

10:00 – 10:10 Break 

10:10 – 10:40 Danek Elbaum (Institute of Physics, Polish Academy of Sciences) 

ZnO biosensing 

10:40 – 11:10 Katarzyna Holc (Institute of High Pressure Physics, Warsaw, Poland) 

Nitride laser diodes 

11:10 – 11:30 Coffee break 

11:30 – 12:00 Detlef Hommel (University of Bremen, Germany) 

Application of CdSe quantum dots for single photon emitters at room 

temperature 

12:00 – 12:30 Wojciech Knap (University of Montpellier, France) 

THz emitters based on GaN/AlGaN HEMTs 

12:30 -- 13:00 Tomasz Stobiecki (AGH University of Science and Technology, Kraków, 

Poland) 

Spin transfer torque in TMR and GMR nanostructures for spintronic 

devices 

15:00 – 15:30 Jan Dziuban (Wrocław University of Technology, Poland) 

Si-based MEMS devices 

15:30 – 16:00 Zbigniew Ku�nicki (Ecole Nationale Superiere de Physique, Illkirch- 

Graffenstaden) 

Giant photoconversion on silicon drived materials 

16:00 Czesław Skierbiszewski – Closing address 

19:00 Farewell dinner 

9

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MONDAY POSTER SESSION (MoP1 …MoP60) 

1. K.A. Kolwas, G. Grabecki, S. Trushkin, Ł. Cywi�ski, M. Aleszkiewicz, T. Dietl, G. 

Springholz, G. Bauer 

Nonlocal transport in PbTe/PbEuTe microstructures 

2. M. Szot, L. Kowalczyk, E. Smajek, B. Taliashvili, P. Dziawa, W. Knoff, A. Reszka, V. 

Domukhovski, E. Łusakowska, P. Dłu�ewski, M. Wiater, T. Wojtowicz, T. Story, M. 

Bukała, R. Buczko, P. Kacman 

Optical transitions in PbTe/CdTe quantum wells grown by molecular beam epitaxy on 

GaAs (001) and BaF2 (111) substrates 

3. A. Woło�, A. Drabinska, M. Kaminska, G. Strzelecka, A. Hruban, A. Materna, M. Piersa, 

Z. Wilamowski 

Properties of three-dimensional topological insulators studied by microwave resonance 

spectroscopy 

4. A. Duzynska, A. Kaminska, H. Teisseyre, E. Przezdziecka, D. Dobosz, Z.R. Zytkiewicz, 

A. Kozanecki, J.D. Fidelus, A. Durygin, V. Drozd, R. Hrubiak, A. Suchocki 

Analysis of Optical Properties and Pressure Dependence of the Energy Gap of ZnO 

Layers, Bulk and Nano-Powders 

5. A. Radzvilavicius, E. Anisimovas 

Defect structure of two-dimensional Wigner crystals 

6. A. Korbecka, J.A. Majewski 

Gauge invariant computational scheme for heterostructures in magnetic field 

7. M. Bukała, P. Sankowski, R. Buczko, P. Kacman 

Modeling PbTe-based low dimensional structures 

8. A. Hruban, A. Materna, W. Dalecki, G. Strzelecka, M. Piersa, E. Jurkiewicz-Wegner, R. 

Diduszko, M. Romaniec, W. Orłowski 

Topological insulators – materials for fundamental researches and perspective 

applications 

9. M. Chwastyk, P.T. Ró�a�ski, M. Zieli�ski 

Atomistic calculation of screened Coulomb interactions in semiconductor 


10. M. Birowska, K. Milowska, J.A. Majewski 

Van der Waals Density Functionals in Materials Science 

11. T. Gro�, E. Malicka, A.W. Pacyna, H. Duda, J. Krok-Kowalski 

Hopkinson-Like Effect in Single-Crystalline CdCr2Se4 Semiconductor 

12. Ł. Wachnicki, B.S. Witkowski, S. Gierałtowska, E. Janik, M. Godlewski, E. Guziewicz 

Optical and structural characterization of zinc oxide nanostructures obtained by 

Atomic Layer Deposition method 

10

40th _______________________________________________________________ 


13. V.V. Khomyak, M.I. Ilaschuk, O.A. Parfenyuk, V.V. Brus, Z.D. Kovalyuk 

Electrical properties of surface-barrier structures n-Zn1-xCdxO/ p-CdTe 

14. E.A. Wolska, D. Sibera, B.S. Witkowski, S.A. Yatsunenko, I. Pełech, U. Narkiewicz, M. 

Godlewski 

Photoluminescence and chromaticity properties of ZnO nanopowders obtained by a 

microwave solwothermal method 

15. T. Š�epka, D. Gregušová, R. Kúdela, Š. Gaži, V. Cambel 

Technology and testing the mechanical properties of the InGaP/GaAs/InGaP 

microcantilevers 

16. M.A. Borysiewicz, E. Dynowska, V. Kolkovsky, J. Dyczewski, E. Kami�ska, A. 

Piotrowska 

ZnO thin films of different crystalline structures grown on Si (100) substrates by 

reactive DC sputter deposition 

17. W. Knoff, M.A. Pietrzyk, B.A. Orłowski, B. Taliashvili, T. Story, R.L. Johnson 

Comparison of the valence band of amorphous and crystalline GeTe and (Ge,Mn)Te 

layers 

18. A. Pietnoczka, R. Bacewicz, T. Słupi�ski, S.H. Wei, M. Jie, J. Antonowicz, T. Drobiazg 

Local Structure Study of GaAs:Te Using Te K-edge X-ray Absorption Fine Structure 

19. A. Taube, K. Korwin-Mikke, R. Mroczy�ski, S. Gierałtowska, A. Łaszcz, I. Pasternak, 

M. Sochacki, M. Zychowska, J. Dyczewski, M. Zdrojek, E. Dynowska, A. Piotrowska 

Thermal Stability of HfO2/SiO2 Gate Stack on Silicon Substrate 

20. M. Iwi�ska, D. Pier�ci�ska, K. Pier�ci�ski, A. Szerling, P. Karbownik, M. Bugajski 

Investigation of thermal properties of AlGaAs/GaAs Quantum Cascade Lasers by 

thermoreflectance spectroscopy 

21. P. Łach, M.G. Brik, I. Sildos, A. Kami�ska, A. Suchocki 

Luminescence properties of Sm 3+ in different phases of TiO2 

22. L.A. Karachevtseva, S.Ya. Kuchmii, O.A. Lytvynenko, F.F. Sizov, O.J. Stronska, A.L. 

Stroyuk 

Investigation of electro-optical properties of 2D macroporous silicon 

23. G.V. Lashkarev, A.M. Yaremko, V.A. Karpyna 

Investigation of multi-phonon excitations in ZnO textured crystalline films by Raman 

spectroscopy 

24. M.L. Peres, V.A. Chitta, D.K. Maude, N.F. Oliveira Jr., P.H. Rappl, A.Y. Ueta, E. 

Abramof 

Rashba effect in n-type PbTe/Pb1-xEuxTe Quantum Wells 

11

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25. I.I. Shtepliuk, G.V. Lashkarev, O.Yu. Khyzhun, V.V. Khomyak, V.I. Lazorenko, I.I. 

Timofeeva, L.A. Klochkov, B. Kowalski, A. Reszka 

Enhancement the intensity of ultraviolet luminescence of ZnO film upon doping 

isovalent impurity of cadmium 

26. V.V. Brus, Z.D. Kovalyuk, P.D. Maryanchuk 

Optical Properties of TiO2 – MnO2 Thin Films Prepared by the Electron-Beam 

Evaporation Technique 

27. S. Gierałtowska, Ł. Wachnicki, B.S. Witkowski, T.A. Krajewski, M. Godlewski, E. 

Guziewicz 

Properties of high-k oxides grown by Atomic Layer Deposition method for transparent 

electronics 

28. E. Maci��ek, T. Gro�, A.W. Pacyna, T. Mydlarz, J. Krok-Kowalski 

High Spin-Low Spin Transitions in Cu0.2Co0.76Cr1.83Se4 Semiconductor 

29. D. Shevchenko, J. Mickevi�ius, G. Tamulaitis, N. Starzhinskiy, K. Katrunov, V. 

Ryzhikov 

Photoluminescence Study of ZnSe Scintillating Crystals Doped with Isovalent 

Tellurium and Oxygen 

30. K. Olender, T. Wosi�ski, A. M�kosa, P. Dłu�ewski, V. Kolkovsky, G. Karczewski 

Native Deep-Level Defects in MBE-Grown p-Type CdTe 

31. P. Urbanowicz, E. Tomaszewicz, T. Gro�, H. Duda, Z. Kukuła 

Residual Paramagnetism at High-Temperature CuEu2W2O10 and Cu3Eu2W4O18 

Semiconductors 

32. M.V. Radchenko, G.V. Lashakrev, M.E. Bugaiova, V.I. Sichkovskyi, V.I. Lazorenko, 

L.A. Krushynskaya, Y.A. Stelmakh, W. Knoff, T. Story 

Ferromagnetic nanocomposite Co-Al2O3 as a spintronic material with engineered 

magnetic properties 

33. D.M. Bercha, K.E. Glukhov, M. Sznajder, S.A. Bercha 

The role of electron subsystem in the phase transition process in a layered CuInP2S6 

crystal 

34. A..I. Dmitriev 

Van der Waals surface of InSe as a standard nanorelief in the metrology of 

nanoobjects 

35. A. Kaminska, C.G. Ma, M.G. Brik, A. Kozanecki, M. Bo�kowski, E. Alves, A. Suchocki 

Crystal field analysis of the Yb 3+ energy level scheme in III-V semiconductors 

36. J. Weszka, M. Doma�ski, J. Jurusik, B. Hajduk, M. Chwastek, H. Bednarski 

Studies of Electric Transport Properties of Single Layer Devices Based on the 

Polyazomethine Thin Films 

12

40th _______________________________________________________________ 


37. R. Jarimavi�iu-te.-Žvalioniene., I. Prosy�evas, Ž. Kaminskiene., S. Lapinskas 

Optical properties of black silicon with precipitated silver and gold nanoparticles 

38. I.P. Koziarskyi, P.D. Marianchuk, E.V. Maistruk, D.P. Koziarskyi 

Optical Properties of Crystals (3HgSe)0.5(In2Se3)0.5, (3HgS)0.5(In2S3)0.5, 

(3HgS)0.5(Al2S3)0.5, (3HgSe)0.5(Al2Se3)0.5, Doped with Mn or Fe 

39. N.S. Yurtsenyuk 

Self-Compensation Mechanism in Semi-Insulating CdMnTe:Sn Crystals Intended for 

X/�-Ray Detectors 

40. J. Krok-Kowalski, G. Władarz, T. Gro�, H. Duda, A.W. Pacyna, K. Nikiforov, P. Rduch 

Influence of Cu, Ga and Au Dopants and Technology Conditions on the Magnetic 

Interactions in HgCr2Se4 Single Crystals 

41. A.I. Ievtushenko, G.V. Lashkarev, V.I. Lazorenko, Z.J. Horvath, M.G. Dusheyko 

The Photodetectors with Vertical Integration Based on ZnO Films 

42. A.I. Ievtushenko, G.V. Lashkarev, V.I. Lazorenko, O.Y. Khyzhun, L.O. Klochkov, O.I. 

Bykov, V.M. Tkach, V.A. Baturin, A.Y. Karpenko 

Features of the Properties for Nitrogen Doping and Al-N Codoping of ZnO Films 

43. A.I. Ievtushenko, G.V. Lashkarev, V.I. Lazorenko, L.O. Klochkov, O.I. Bykov, O.M. 

Kutsay, S.P. Starik, V.A. Baturin, A.Y. Karpenko 

Influence of Oxygen Pressure on the Properties of AZO Films 

44. H. Duda, E. Malicka, T. Gro�, A. G�gor, R. Sitko, J. Krok-Kowalski, P. Rduch 

Thermoelectric Power of CuCrxVySe4 p-Type Spinel Semiconductors 

45. H. Duda, P. Rduch, E. Malicka, T. Gro�, A. G�gor 

Critical Behaviour of the 3D-Heisenberg Ferromagnetic 

46. J.M. Sajkowski, M.A. Pietrzyk, D. Dobosz, M. Stachowicz, A. Droba, E. Przezdziecka, 

A. Wierzbicka, A. Kozanecki 

Optical properties of ZnO/ZnMgO single quantum wells grown by molecular beam 

epitaxy 

47. B.A. Orłowski, S.P. Dziawa, A. Reszka, K. Gas, S. Mickievicius, S. Thiess, W. Drube 

Electronic structure of CdTe/PbEuTe/CdTe 

48. D. Ziółkowska, K.P. Korona, M. Kami�ska, S.H. Wu, M.S. Chen 

Raman Spectroscopy of LiFePO4 and Li3V2(PO4)3 Cathode Materials for Lithium-Ion 

Battery Applications 

49. M. Hosatte, M.Ł. Basta, B.S. Witkowski, Z.T. Ku�nicki, M. Godlewski 

Multi-interface layered P-doped silicon structures for third generation photovoltaics 

50. M. Stachowicz, E. Przezdziecka, D. Dobosz, M.A. Pietrzyk, J.M. Sajkowski, A. Droba, 

A. Wierzbicka, A. Kozanecki 

Optical Properties of Thin ZnO Layers Grown by MBE 

13

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51. K. Gas, E. Dynowska, E. Janik, A. Kami�ska, S. Kret, J.F. Morhange, I. Pasternak, M. 

Wiater, W. Zaleszczyk, R. Hołyst, E. Kami�ska, T. Wojtowicz, W. Szuszkiewicz 

ZnO-based Nanotubes Obtained by the Oxidation of ZnTe and ZnTe/Zn Nanowires 

52. D. �ak, W. Nakwaski 

Composition-dependent thermal resistance of multilayered structures taking into 

account phonon reflection, scattering and tunneling 

53. A. Reszka, B.A. Orłowski, M.A. Pietrzyk, A. Szczerbakow, S. Mickievicius, S. 

Balakauskas, R.L. Johnson 

Pb1-xGexTe surface with Sm 2+ and Sm 3+ doping 

54. H. Bednarski, J. Weszka, M. Doma�ski, V. Cozan 

Studies of Optical Properties of Protonated Poliazomethine Thin Films 

55. A.V. Atrashchenko, V.P. Ulin, V.P. Evtikhiev 

The reasons of destruction of nanoporous GaAs matrix fabricated by electrochemical 

etching 

56. E. Malicka, T. Gro�, A.W. Pacyna, H. Duda, J. Krok-Kowalski 

Effect of Substitution of Ti for Cd in CdCr2Se4 p-Type Semiconductor 

57. K. Dybko , M. Szot, T. Story, G. Karczewski, S. Schreyeck, C. Schumacher, K. Brunner 

and L. W. Molenkamp 

Thermoelectric power in epitaxial Bi2Se3/Si(111) layers 

58. M. Zapalska and T. Doma�ski 

Diamagnetism of the pre-paired electronic systems: the flow equation study 

59. N. Gonzalez-Szwacki, J.A. Majewski 

Quantum Monte Carlo vs. Density Functional Methods for the prediction of relative 

energies of small Si-C clusters 

60. M. Koba and P. Szczepa�ski 

Analysis of a Spatial Hole Burning Effect in a Square and Triangular Lattice Photonic 

Crystal Laser 

14

40th _______________________________________________________________ 


TUESDAY POSTER SESSION (TuP1 …TuP58) 

1. T. Smole�ski, Ł. Cywi�ski, M. Goryca, P. Kossacki 

Exciton and Mn spin dynamics in a nonresonantly coupled pair of (Cd,Mn)Te 

quantum dots 

2. J. Kobak, W. Pacuski, T. Kazimierczuk, J. Suffczy�ski, T. Jakubczyk, A. Golnik, 

P. Kossacki, M. Nawrocki, J.A. Gaj, C. Kruse, D. Hommel 

Three-dimensional anisotropy studies of CdTe quantum dots 

3. K. Grodecki, W. Strupi�ski, A. Wysmołek, R. St�pniewski, J.M. Baranowski 

Probing electron concentration in epitaxial graphene using Raman spectroscopy 

4. M. Zieli�ski, G.W. Bryant, N. Malkova, J. Sims, W. Jaskolski, J. Aizpurua 

Dynamical control of excitonic fine structure with nanomechanical strain 

5. K. Roszak, T. Novotný 

Non-Markovian noise at the Fermi-edge singularity in quantum dots 

6. M. Czapkiewicz, J. Wróbel, V. Kolkovsky, P. Nowicki, M. Aleszkiewicz, M. Wiater, 

T. Wojtowicz 

Transport and Spin Properties of CdTe/CdMgTe Quantum Point Contacts 

7. M. Kozub, P. Machnikowski 

The Role of Strong Coupling in the Superradiance of Ensembles of Quantum Dots 

8. M. Szymura, Ł. Kłopotowski, P. Wojnar, K. Fronc, T. Kazimierczuk, G. Karczewski, 

T. Wojtowicz 

Photoluminescence Linewidth Analysis of Single CdMnTe Quantum Dots 

9. M. Koperski, T. Kazimierczuk, M. Goryca, A. Golnik, J.A. Gaj, M. Nawrocki, 

P. Wojnar, P. Kossacki 

Statistical Study of the Inter-Dot Excitation Transfer in CdTe/ZnTe Quantum Dots. 

10. Ł. Marcinowski, M. Krzy�osiak, K. Roszak, P. Machnikowski, R. Buczko, J. Mostowski 

Phonon influence on the weak measurement of double quantum dot spin states. 

11. P. Kaczmarkiewicz, A. Musiał, G. S�k, P. Podemski, J. Misiewicz, P. Machnikowski 

Influence of Carrier Trapping on the Optical Properties of InAs/InP Quantum Dashes 

12. K. Dziatkowski, D. Ratchford, T. Hartsfield, X. Li, Y. Gao, Z. Tang 

CdSe/ZnS Colloidal Quantum Dots with Alloyed Core/Shell Interfaces: 

a Photoluminescence Dynamics Study 

13. K. Kukli�ski, Ł. Kłopotowski, K. Fronc, P. Wojnar, T. Wojciechowski, M. Czapkiewicz, 

J. Kossut, G. Karczewski, T. Wojtowicz 

Spectroscopy of Indirect Excitons in Vertically Stacked CdTe Quantum Dot Structures 

15

_______________________________________________________________ 


14. W. Abdussalam, A. Sitek, P. Machnikowski 

Collective spontaneous emission from pairs of quantum dots: the role of coupling and 

system geometry 

15. K. Korzekwa, P. Machnikowski 

Tunneling transfer protocol in a quantum dots chain immune to inhomogeneity 

16. A. Musial, G. Sek, A. Marynski, P. Podemski, J. Andrzejewski, J. Misiewicz, A. Loeffler, 

S. Hoefling, S. Reitzenstein, J.P. Reithmaier, A. Forchel 

Thermal Quenching of Photoluminescence from epitaxial InGaAs/GaAs Quantum 

Dots with High Lateral Aspect Ratio 

17. P. Schillak, G. Czajkowski 

Excitonic Magnetoabsorption of Cylindrical Quantum Disks 

18. P. Karwat, A. Sitek, P. Machnikowski 

Spontaneous emission from double quantum dots: collective effects and carrier- 

phonon kinetics 

19. P. Łach, A. Reszka, G. Karczewski, P. Wojnar, T. Wojtowicz, A. Kami�ska, A. Suchocki 

Cathodoluminescence studies of the II – VI semiconducting quantum dots grown by 

molecular beam epitaxy 

20. E. Zielony, E. Popko, Z. Gumienny, P. Kamyczek, A. Henrykowski, J. Jacak, G. 

Karczewski 

Raman spectroscopy of CdTe/ZnTe quantum dots 

21. J. Bara�ski, T. Doma�ski 

Quantum interference in charge transport via the quantum dots coupled between 

the metallic and superconducting leads 

22. H. Bednarski, J. Spałek 

Bound magnetic polaron molecule in diluted magnetic semiconductors within the 

Heitler-London approximation 

23. M. Zału�ny, A. Kozłowski 

Intersubband polaritons in strongly pumped microcavities 

24. M.S. Mukhin, Y.V. Terent'ev, L.E. Golub, M.O. Nestoklon, B.Y. Meltser, 

A.N. Semenov, V.A. Solov'ev, A.A. Sitnikova, A.A. Toropov, S.V. Ivanov 

Magneto-Optical Studies of Narrow Band-Gap Heterostructures with Type II Quantum 

Dots InSb in an InAs Matrix 

25. K.H. Gawarecki, P. Machnikowski 

Phonon-assisted tunneling between hole states in double quantum dots 

26. I. Bragar, K. Gawarecki, P. Machnikowski 

Intermediate band formation for electrons and holes in an inhomogeneous chain of 

quantum dots 

16

40th _______________________________________________________________ 


27. O. Rancova, E. Anisimovas 

Modelling of 1D-2D structural transitions in small Yukawa clusters 

28. P. Kowalski, P. Machnikowski 

Efficient Coulomb mixing between single- and biexciton states in InAs nanocrystals 

29. K. Gołasa, M. Molas, J. Borysiuk, Z.R. Wasilewski, A. Babi�ski 

Strongly disordered wetting layer in the InAs/GaAs self-assembled quantum dots 

system 

30. M. Molas, K. Gołasa, J. Łusakowski, T. Wojtowicz, A. Babi�ski 

Optical transformation of zero-dimensional confinement in the CdTe/CdMgTe multiple 

quantum wells 

31. M. Kozub, A. Musiał, G. S�k, J. Misiewicz, V. Zürbig, J.P. Reithmaier 

Optical Properties of InGaAs Quantum Dots on (100) GaAs Substrates Formed by 

Droplet Epitaxy 

32. M. Molas, K. Gołasa, T. Kazimierczuk, J. Łusakowski, T. Wojtowicz, A. Babi�ski 

Magnetooptical study of excitons confined in potential fluctuations in the 

CdTe/CdMgTe quantum well 

33. A. Ballester, J.M. Escartín, J.L. Movilla, M. Pi, J. Planelles 

Mixed Correlation Phases In Elongated Quantum Dots 

34. J. Ebeling, T. Aschenbrenner, S. Figge, D. Hommel 

Simulation and Realization of Photonic Crystals in Light Emitting Devices 

35. E. Zielony, E. Popko, Z. Gumienny, G. Karczewski 

Electro-optical characterization of Ti/Au-ZnTe Schottky diodes with CdTe quantum 

dots 

36. J. Jadczak, L. Bryja, A. Wójs, G. Bartsch, D.R. Yakovlev, M. Bayer, M. Potemski 

Magneto-photoluminescence studies of many body scattering processes in two- 

dimensional hole gas 

37. H. Videlier, N. Dyakonova, F. Teppe, C. Consejo, W. Knap, J. Lusakowski, 

D. Tomaszewski, J. Marczewski, P. Grabiec 

Spin related effect in Si-MOSFETs THz Photoresponse 

38. N. Dyakonova, A. ElFatimy, Y. Meziani, D. Coquillat, W. Knap, F. Teppe, P. Buzatu, 

L. Varani, H. Marinchio, J. Torres, P. Nouvel 

THz emission related to hot plasmons and plasma wave instability in field effect 

transistors 

39. M. Białek, M. Czapkiewicz, K. Fronc, J. Wróbel, V. Umansky, M. Grynberg, 

J. Łusakowski 

A Comb-Like Shape of the Cyclotron Resonance Line in GaAs/AlGaAs 

Heterostructure 

17

_______________________________________________________________ 


40. J. Przybytek, M. Gryglas-Borysiewicz, M. Baj 

Impurity-Related Noise in Si �-doped Single-Barrier GaAs/AlAs/GaAs Resonant 

Tunneling Devices 

41. F. Teppe, C. Consejo, J. Torres, B. Chenaud, P. Solignac, Z.R. Wasilewski, M. Zholudev, 

N. Dyakonova, D. Coquillat, A. El Fatimy, W. Knap 

Current Driven Terahertz Detection of Quantum Cascade Laser Emission by Plasma 

Waves in Nano-Transistors 

42. G. K�pisty, K. Grodecki, W. Strupi�ski, A. Wysmołek, R. St�pniewski, J.M. Baranowski 

Influence of SiC substrate orientation on epitaxial graphene quality studied by Raman 

spectroscopy 

43. M. Syperek, B. Bujko, J. Jadczak, M. Kubisa, L. Bryja, J. Misiewicz 

Fermi edge and band-to-band recombination dynamics in n-doped GaAs/AlGaAs 

quantum well 

44. M. Kozubal, M. Gryglas-Borysiewicz, J. Przybytek, J. Borysiuk, M. Baj, R. St�pniewski, 

A. Wysmołek, W. Strupi�ski, J. Baranowski 

Magnetotransport Studies of Graphene Exposed to Water Vapours 

45. K. Grodecki, J.A. Błaszczyk, A. Dominiak, W. Strupi�ski, A. Wysmołek, 

R. St�pniewski, A. Drabi�ska, M. Sochacki, J.M. Baranowski 

Interaction of epitaxial graphene with SiC substrates studied by Raman spectroscopy 

46. K. Nogajewski, H. Boukari, P. Kopyt, W. Gwarek, T. Wojtowicz, H. Mariette, 

M. Grynberg, J. Łusakowski 

Antenna-Equipped Field Effect Transistors on CdTe/CdMgTe Quantum Wells as 

Terahertz Detectors 

47. A.D. Chegodaev, D.K. Loginov 

Effect of homogeneous electric field on exciton dispersion in wide quantum well 

48. V.Ya. Roshko 

Theoretical Analysis of Optical Losses in CdS/CdTe Solar Cells 

49. M.Kubisa, K.Ryczko and J.Misiewicz 

Anisotropy of B=0 spin splitting of holes in symmetric GaAs/Ga(1-x)AlxAs quantum 

wells 

50. J. Szczytko, P. Arcade, E. Papis, A. Bara�ska, B. Pi�tka, J. Łusakowski 

Terahertz Properties of Gold Layers on GaAs 

51. P. Sznajder, B. Pi�tka, J. Szczytko, J. Łusakowski 

Towards Optically Tunable Terahertz Plasmonic Detectors 

52. I. Grigelionis, K. Fobelets, B. Vincent, J. Mitard, B. DeJaeger, E. Simoen, D. Jaworski, 

J. Łusakowski 

Mobility of Holes in Nanometer Ge-on-Si p-type Metal-Oxide-Semiconductor Field- 

Effect Transistors at Low Temperatures 

18

40th _______________________________________________________________ 


53. Paweł Utko, Morten H. Madsen, Trine Berthing, Sara Bonde, Claus B. Sorensen, 

Karen L. Martinez, Jesper Nygard 

Vertical InAs nanowires as biological probes 

54. M. �ciesiek, T. Jakubczyk, W. Pacuski, A. Golnik, P. Kossacki, C. Kruse, D. Hommel 

Towards better light-confinement in pillar cavities 

55. M. Rawski, J. �uk, A. Drozdziel, K. Pyszniak, M. Turek 

Investigation of ion-implanted SiC properties by means of a light absorption technique 

56. P. Kamyczek, E. Placzek-Popko, Łukasz Gelczuk, Maria D�browska-Szata 

SiC Schottky barrier diode studied by admittance spectroscopy 

57. P. Sitarek, K. Ryczko, J. Misiewicz, D. Reuter, A. Wieck 

Optical transitions between confined and unconfined states in p-type asymmetric 

GaAs/InGaAs/AlGaAs QW structures 

58. K. Tahy, W. S. Hwang, J.L. Tedesco, R.L. Myers Ward, P.M. Campbell, C.R. Eddy Jr., 

D.K. Gaskill, H. Xing, A. Seabaugh, D. Jena 

Sub-10 nm Epitaxial Graphene Nanoribbon FETs 

19

_______________________________________________________________ 


WEDNESDAY POSTER SESSION (WeP1 …WeP58) 

1. C. �liwa, T. Dietl 

Thermodynamic and thermoelectric properties of (Ga,Mn)As 

2. M. Sobanska, K. Klosek, Z.R. Zytkiewicz, J. Borysiuk, A. Wierzbicka, A. Reszka, E. 

Lusakowska 

Plasma-assisted molecular beam epitaxy of GaN on Si (111) substrates 

3. J. Plaziak, J. Higersberger, J.A. Majewski 

Role of Interface Carrier Transport in Electrical Characteristics of Light Emitting 

Devices Based on Heterostructures 

4. A. Łusakowski, P. Bogusławski, W. Knoff, T. Story 

Influence of crystal structure and hole concentration on magnetic anisotropy of 

GeMnTe 

5. I. Ulfat, L. Ilver, J. Sadowski 

High-resolution study of valence band maximum for (GaMn)As 

6. J. Suffczy�ski, K. Gałkowski, P. Ka�mierczak, J. Papierska, M. Furman, W. Pacuski, 

A. Golnik, A.M. Witowski, J.A. Gaj, W. Stefanowicz, M. Sawicki, M. Łukasiewicz, 

E. Guziewicz, M. Godlewski 

Low temperature grown (Zn,Co)O studied in the band-gap spectral region 

7. J. Levrat, G. Rossbach, A. Dussaigne, H. Teisseyre, I. Grzegory, M. Bockowski, 

T. Suski, R. Butte, N. Grandjean 

Nonpolar III-nitride microcavities for polariton lasing 

8. W. Bardyszewski, S.P.. Łepkowski 

Symmetry of the top valence band states in GaN/AlGaN quantum wells and its 

influence on the polarization of emitted light 

9. D. Sztenkiel, T. Dietl 

Tunnelling effects in (Ga,Mn)As based heterostructures 

10. M. Lopuszynski, J.A. Majewski 

Modelling of Ordering Phenomena in Nitride Semiconducting Alloys 

11. M. Welna, R. Kudrawiec, M. Motyka, J. Misiewicz, R. Kucharski, M. Zaj�c, R. 

Doradzi�ski, R. Dwili�ski 

Infrared Spectroscopy of GaN Crystals Obtained by Ammonothermal Method 

12. M. Latkowska, R. Kudrawiec, G. S�k, J. Misiewicz, J. Ibán~ez, M. Henini, 

M. Hopkinson 

Micro-photoluminescence of GaInNAs layers: Thermal quenching of individual 

exciton lines 

13. M. Fandrich, G. Kunert, T. Aschenbrenner, S. Figge, C. Kruse, D. Hommel 

20

40th _______________________________________________________________ 


Nitride based sensors with Ga- and N-polarity 

14. V.Kh. Le, K. Swiatek, M. Pawlowski, R.R. Galazka 

Zinc vacancy induced ferromagnetic interaction in semimagnetic semiconductor 

(Zn,Mn)Te 

15. S. Dobkowska, W. Stefanowicz, O. Proselkov, R. �uberek, J. Sadowski, T. Dietl, 

M. Sawicki 

Magnetic Properties of (Ga,Mn)As near Metal-Isolator Transition 

16. M. Sakowicz, N. Gauthier, R. Leonelli, C. Silva, H. Nguyen, K. Cui, S. Zhang, Z. Mi 

Time-Resolved Photoluminescence of InGaN/GaN Dot-in-a-Wire Heterostructures on 

Si(111) 

17. M. Bajda, F. Dybała, A. Bercha, W. Trzeciakowski, J.A. Majewski 

Wide range wavelength tuning of InGaAsP/InP laser diodes 

18. M. Gryglas-Borysiewicz, J. Przybytek, M. Baj, A. Kwiatkowski, P. Juszy�ski, D. Wasik, 

P. Dziawa, J. Sadowski 

Transport properties of GaMnAs layers 

19. C. Chèze, M. Sawicka, M. Siekacz, H. Turski, A. Feduniewicz-Zmuda, G. Cywinski, B. 

Grzywacz, S. Grzanka, I. Dziecielewski, B. Lucznik, M. Bockowski, C. Skierbiszewski 

Group III-nitrides growth on N-polar substrates 

20. J. Binder, K.P. Korona, J. Borysiuk, M. Kaminska, M. Baeumler, K. Köhler, L. Kirste 

Absorption and Emission Properties of Light Emitting Diode Structures Containing 

GaInN/GaN QWs 

21. B.J. Kowalski, R. Nietuby�, J. Sadowski 

Mn contribution to the valence band of Ga1-xMnxSb 

22. M. Baranowski, M. Latkowska, M. Syperek, R. Kudrawiec, J. Misiewicz, T. Sarmiento, 

J.S. Harris 

Time resolved photoluminescence studies for GaInNAsSb quantum wells emitting at 

1.3 µm 

23. A. Kafar, J. Goss, S. Sta�czyk, R. Czernecki, M. Leszczynski, T. Suski, P. Wi�niewski, 

P. Perlin 

InGaN laser diodes with passive absorber section 

24. W. Szuszkiewicz, F. Ott, J.Z. Domagała, E. Dynowska, J. Sadowski 

Evidence of a new magnetic order in short-period (Ga,Mn)As/GaAs SLs 

25. Z. Wi�niewski, K. Izdebska, P. Sybilski, Z.R. �ytkiewicz, M. Soba�ska, K. Kłosek, 

A. Reszka, B.J. Kowalski, A. Suchocki 

Application of n-GaN layers grown by MBE for light-induced water splitting and 

hydrogen generation 

26. M. Sarzynski, J. Goss, M. Leszczynski, A. Reszka, B. Kowalski, P. Perlin, T. Suski 

21

_______________________________________________________________ 


Broad optical gain spectrum in III-N quantum structures 

27. M.I. Łukasiewicz, A. Cabaj, M. Godlewski, E. Guziewicz, A. Wittlin, M. Jaworski, 

A. Woło�, Z. Wilamowski 

Microwave techniques investigations of (Zn,Co)O films grown by Atomic Layer 

Deposition 

28. O. Yastrubchak, T. Andrearczyk, J. Sadowski, J. �uk, T. Wosi�ski 

Band-structure analysis from photoreflectance spectroscopy in (Ga,Mn)As 

29. K. Klosek, M. Sobanska, Z.R. Zytkiewicz, H. Teisseyre, E. Lusakowska, A. Wierzbicka, 

P. Nowakowski, L. Klopotowski 

Influence of nitrogen plasma parameters on growth of GaN by plasma-assisted 


30. T.A. Krajewski, P. Stallinga, E. Zielony, P. Kruszewski, K. Go�ci�ski, Ł. Wachnicki, 

S. Figge, D. Hommel, E. Guziewicz, M. Godlewski 

Deep defects in ZnO/GaN heterostructure analyzed by the admittance spectroscopy 

31. T.A. Krajewski, A.J. Zakrzewski, G. Łuka, Ł. Wachnicki, S. Gierałtowska, 

B.S. Witkowski, P. Kruszewski, E. Łusakowska, R. Jakieła, E. Guziewicz, M. Godlewski 

Electrical characterization of the ZnO-based Schottky diodes for possible sensor 

applications 

32. T. Zakrzewski, P. Bogusławski 

Ab initio calculations of transition metal impurity levels in III-V semiconductors 

33. P. Juszy�ski, D. Wasik, M. Baj, J. Przybytek, M. Gryglas-Borysiewicz, J. Sadowski 

Anisotropy of GaMnAs thin film. Planar and Anomalous Hall measurements. 

34. G. Staszczak, A. Khachapuridze, S. Grzanka, R. Piotrzkowski, R. Czernecki, P. Perlin, 

T. Suski 

Interplay between internal and external electric field studied by photoluminescence in 

InGaN/GaN light emitting diodes 

35. M. Baranowski, M. Latkowska, R. Kudrawiec, M. Syperek, J. Misiewicz, 

G.S. Karthikeyan, S. Jong-In, K.L. June 

Influence of antimony on the optical quality of GaInN:Sb multi quantum wells 

36. J. Sadowski, A. Siusys, P. Dziawa, A. Reszka, B.J. Kowalski 

Properties of Mn-doped GaAs Nanowires and GaAs/(Ga,Mn)As Core-Shell Nanowire 

Structures Grown by MBE on GaAs(111)B Substrates 

37. I.A. Kowalik, M.A. Nin~o, A. Locatelli, T. OnurMente�, A. Navarro-Quezada, 

M. Rovezzi, A. Bonanni, T. Dietl, D. Arvanitis 

Room temperature nano-magnetism of (Ga,Fe)N films: element specific spectroscopy 

and microscopy 

38. L. Marona, S. Grzanka, P. Wisniewski, T. Suski, M. Leszczynski, R. Czernecki, 

M. Bockowski, S.P. Najda, P. Perlin 

22

40th _______________________________________________________________ 


The non-radiative recombination rate in InGaN laser diodes during the aging 

39. L. Janicki, M. Gladysiewicz, R. Kudrawiec, M. Rudzi�ski, R. Kucharski, M. Zaj�c, 

J. Misiewicz, W. Strupinski, R. Doradzi�ski, R. Dwili�ski 

Electromodulation Spectroscopy of GaN/AlGaN Quantum Wells Grown on Polar and 

Non-polar GaN Substrates Obtained by Ammonothermal Method 

40. E.P. Smakman, R. vanVoornveld, J.G. Keizer, J.K. Garleff, P.M. Koenraad 

Spin-Polarized STM with Fe-Coated W Tips and Bulk Cr Tips 

41. B.S. Witkowski, Ł. Wachnicki, E. Guziewicz, M. Godlewski 

Cathodoluminescence measurements at liquid helium temperature of monocrystalline 

ZnO layers 

42. T. Andrearczyk, I. Krogulec, T. Wosi�ski, T. Figielski, A. M�kosa, Z. Tkaczyk, 

J. Wróbel, J. Sadowski 

Towards electrically controllable read-write devices based on ferromagnetic 

semiconductors 

43. J.B. Gosk, Z. Werner, C. Pochrybniak, M. Barlak, J. Szczytko, A. Twardowski 

Magnetic properties of Mn-ion implanted and plasma pulse treated Si 

44. G. Muzioł, M. Siekacz, H. Turski, C. Skierbiszewski 

Simulations of optical modes in InGaN based laser diodes operating at 455 nm 

45. M. Woi�ska, K. Madrak, J. Szczytko, J. Gosk, A. Majhofer, D. Pociecha, E. Górecka, 

A. Twardowski 

Monte-Carlo simulations and magnetic studies of ferromagnetic nanocomposites 

46. J. Szczytko, J. Szydlowska, N. Gonzalez Szwacki, K. Dziatkowski, P. Gizi�ski, A. Kaim, 

A. Twardowski 

Di-TEMPO amine for molecular spintronics – model of p-shell magnetism 

47. M. Baranowski, M. Latkowska, R. Kudrawiec, J. Misiewicz 

Hopping excitons in GaInNAs alloys: Radiative versus non-radiative recombination at 

various temperatures 

48. J.Z. Domagala, B. Lucznik, H. Teisseyre, M. Bockowski, I. Grzegory 

Structural characterization of the nonpolar substrate grown by multistep hydride vapor 

phase epitaxy. 

49. Ł. Gluba, O. Yastrubchak, H. Krzy�anowska, J.Z. Domagała, T. Andrearczyk, J. �uk, 

J. Sadowski, T. Wosi�ski 

Investigation of fundamental parameters of low doped (Ga,Mn)As epitaxial layers 

50. P. Kamyczek, E. Popko, Z. Gumienny, E. Zielony, S.Grzanka, R. Czernecki, T. Suski 

Admittance spectroscopy in GaN p-n junction 

51. Pawel Kempisty, Pawel Strak, Stanislaw Krukowski 

23

_______________________________________________________________ 


Role of hydrogen in the ammonia based growth of GaN and InGaN - ab initio study 

52. S.P. Lepkowski, W. Bardyszewski, H. Teisseyre 

Effect of the built-in strain on the in-plane optical anisotropy of m-plane GaN/AlGaN 

quantum wells 

53. J. Papierska, J.-G. Rousset, A. Golnik, W. Pacuski, M. Nawrocki, J. A. Gaj, 

J. Suffczynski, I. Kowalik, W. Stefanowicz, M. Sawicki, T. Dietl, A. Navarro-Quezada, 

B. Faina, Tian Li, A. Bonanni 

Magnetooptical properties of (Ga,Fe)N layers 

54. Maria Ptasi�ska, Jacek Piechota, Jakub Sołtys, Stanisław Krukowski 

Gas Phase Reactions during GaN Growth by MOVPE Method – Ab initio Study 

55. Konrad Sakowski, Leszek Marcinkowski, Szymon Grzanka, Elzbieta Litwin- 

Staszewska, Stanislaw Krukowski 

Simulations of Gallium Nitride luminescent devices with extension of standard 

nonradiative recombination model 

56. Pawel Strak, Pawel Kempisty, Konrad Sakowski, Stanislaw Krukowski 

Density Functional Theory (DFT) simulations of the physical properties of AlN/GaN 

multiple quantum wells (MQWs) 

57. Z. R. Zytkiewicz, P. Dluzewski, J. Borysiuk, M. Sobanska, K. Klosek, B. Witkowski, 

P. Nowakowski, J. Dabrowski 

Plasma-assisted MBE growth and characterization of GaN nanocolumns on Si (111) 

substrates 

58. Zbigniew R. Zytkiewicz, Pawel Strak, Stanisław Krukowski 

Crossing Size Limits of Bulk III-V Crystals Feasible by Liquid Phase Electroepitaxy 

24

40th _______________________________________________________________ 

"Jaszowiec" 2011 International School and Conference on the Physics of Semiconductors SaI1 

Modern technologies for wide-gap semiconductor epitaxy 

and nano-processing 

Detlef Hommel 

Institute of Solid State Physics, University of Bremen, Germany 

An overview will be given on the growth and application of wide bandgap 

semiconductors like group-III nitrides and group-II selenides and tellurides. It will be shown 

that different epitaxial methods have to be used for different materials (MBE for II-VI and 

mostly MOVPE for nitrides). In this respect homo- and heteroepitaxy will be compared as 

well. 

The growth mechanisms for CdSe and InGaN quantum dots differ significantly and 

both have not much common with the well known Stranski-Krastanov growth mode. This will 

be discussed in detail. 

As an important tool for nano-processing a focused ion beam (FIB) tool will be 

presented. Such a dual beam system with a Ga-source for nanostructuring, an electron source 

for imaging, an integrated e-beam lithography and sources for insulator and metal deposition 

on a nanometer scale allows to design novel device structures. 

Approaches to grow fully monolithic microcavities based on selenides, nitrides and 

tellurides will be presented. Using the FIB micropillars can be designed out of such planar 

structures with interesting physical properties. Introducing quantum dots into the cavity one 

can obtain efficient sources for single photon emission up to room temperature. 

25

SaI2 _______________________________________________________________ 


Physical simulation of electronic devices 

Aldo Di Carlo 

Dept. of Electronics Engineering, University of Rome “Tor Vergata”, Rome, Italy 

Physical Simulation is a fundamental step for the design and fabrication of 

commercially available and research developed electronic devices.[1] Since ’80 several 

Technology Computer Aided Design (TCAD) tools has been developed to this end, starting 

from the seminal work of R. Dutton at Stanford University. Nowadays, the need for faster 

and better performing electronic devices with higher integration density has been driving 

almost since the dawn of semiconductor technology a steady trend of scaling down the device 

dimensions. This led to an incredible increase in computing power and memory capacity, 

quantified by the well-known Moore’s law. Due to this downscaling, the dimensions of the 

active region of conventional metal–oxide–semiconductor field-effect transistors (MOSFETs) 

have already reached the nanometer scale. This makes device simulation very challenging and 

new theoretical framework should be considered. [2] 

Hand in hand with device scaling, new devices exploiting quantum mechanical effects for 

their functioning have been proposed, e.g., transistors based on quantum wires, dots, or 

molecules. Quantum dots and wires have also gained much attention for their use in 

optoelectronic devices for lasing or single photon emission or as color tunable and white-light 

emitters. The electronic, optical, and transport properties of the active regions of such highly 

scaled or new devices cannot be described by classical or semiclassical theories. A fully 

quantum mechanical treatment has to be used instead. [3] 

In this lecture, I will review the methods for electronic device simulation starting from the 

common picture based on drift-diffusion equation up to quantum mechanical based 

approaches for both continuum and atomistic models. A review of available TCAD tools will 

be given. 

Fig. 1 

Simulation of GaN based nanocolumn LED. 

Electrostatic potential and current flow lines 

around the intrinsic part of the column. 

(a) The classical results. 

(b)The self-consistent Quantum/driftdiffusion 

results, showing also the contours of the electron 

and hole densities at half of the mean density 

inside the intrinsic region. (from Ref. 2) 

[1] S. Selberherr, Analysis and Simulation of Semiconductor Devices, Springer, (1984). 

[2] M. Auf der Maur et al. IEEE Trans. Electron Devices 58, 1425 (2011) 

[3] A. Pecchia and A. Di Carlo, Rep. Prog. Phys., vol. 67, no. 8, pp. 1497–1561, (2004). 

26

40th _______________________________________________________________ 

"Jaszowiec" 2011 International School and Conference on the Physics of Semiconductors SuI1 

Physics and Technology of Arsenide Based Quantum Dots and Nanowires 

Gerhard Abstreiter 

Walter Schottky Institut and Institute for Advanced Study 

TU München, 85748 Garching 

Optical control of charges, spins, excitons and photons has been achieved in recent years in 

semiconductor nanostructures. They are therefore excellent candidates for demonstrating 

basic principles of quantum information technology. I will discuss the basic optical properties 

and recent results on electro-optic control of single self-assembled InGaAs quantum dots. 

This includes results on spin storage and spin lifetimes of electrons and holes [1, 2] in dot 

ensembles, as well as single charge and spin control and readout [3]. In the second part of my 

lecture I will also discuss recent results on MBE grown GaAs and InAs based nanowire 

hetero-structures with new functionalities [4 - 9]. 

[1] M. Kroutvar et al., Nature 432, 81 (2004) 

[2] D. Heiss et al., Phys. Rev. B 76, 24136 (2007) 

[3] D. Heiss et al., Phys. Rev. B 82, 245316 (2010) 

[4] A. Fontcuberta i Morral et al., Small 4, 899 (2008) and APL 92, 063112 (2008) 

[5] M. Heigoldt et al., J. Mater. Chem. 19, 840 (2009) 

[6] D. Spirkoska et al., Phys. Rev. B 80, 245325 (2009) 

[7] I. Zardo et al., Phys. Rev. B 80, 245324 (2009) 

[8] S. Hertenberger et al., J. Appl. Phys. 108, 114316 (2010) 

[9] M. Soini et al., Appl. Phys. Letters 97, 263107 (2010) 

27

SuI2 _______________________________________________________________ 


Tutorial: Engineering of Electric Fields in Nitride-Based Semiconductors 

Debdeep Jena 

Associate Professor of Electrical Engineering University of Notre Dame, 

Notre Dame, IN 46556 USA 

djena@nd.edu, http://www.nd.edu/~djena 

The built-in polarization fields in III-Nitride semiconductor heterostructures play 

fundamental and crucial roles in many electronic and optical phenomena exhibited by these 

semiconductors. In addition, they strongly influence the design and performance of electronic 

and optical devices fabricated from III-Nitride heterostructures. The goals of this tutorial are – 

1) To introduce the concept of electronic polarization in semiconductors 

2) To explore its influence on electronic and optical properties 

3) To explore details of how charge electrostatics and transport are affected 

4) To explore how optical transitions and emission properties are influenced, 

5) To apply them to electronic and optical devices of the present, and 

6) To discuss open problems, and what is possible in the future using polarization. 

Specifically, the concept of polarization will be traced down to its microscopic origin in 

charge dipoles in the highly polar III-Nitride semiconductor crystals. We will discuss how the 

macroscopic properties emerge from the microscopic picture. The effect of dipoles on charge 

transport, electrostatics, and optical transition matrix elements will be described. We will 

study how the fields emerging from the polarization can be used to design ‘traditional’ highperformance 

electronic and optical devices such as high electron mobility transistors 

(HEMTs), light-emitting diodes (LEDs) and lasers. The discussion will cover both the ‘good’ 

and ‘bad’ effects of polarization in such devices. 

We will also discuss various “novel” device applications of polarization physics in III- 

Nitride semiconductor heterostructures. Some of these include polarization-induced Zenerinterband 

tunneling and p-type doping for applications in light emitting devices. The wellknown 

concept of “lattice-- matching” in III-V semiconductor heterostructures will be 

extended to include the idea of “Polarization-- matching” and the opportunities of such 

concepts will be discussed. 

28

40th _______________________________________________________________ 

"Jaszowiec" 2011 International School and Conference on the Physics of Semiconductors MoI1 

�� 

Coherent optical control of the NV center in diamond 

Jörg Wrachtrup 

3rd� Physics Institute and Research Center SCOPE, University of Stuttgart, D-70659 

Stuttgart, Germany 

29

MoI2 _______________________________________________________________ 


Understanding and exploiting magnetism of semiconductors 

Tomasz Dietl 

Laboratory for Cryogenic and Spintronic Research, 

Institute of Physics, Polish Academy of Sciences and 

Institute of Theoretical Physics, University of Warsaw 

Triggered by a theoretical model of ferromagnetism mediated by valence band 

holes put forward a dozen years ago, the search for compounds combining the resources 

of semiconductors and ferromagnets has evolved into an important and challenging field 

of materials science. This endeavour has been fuelled by continual demonstrations of 

remarkable low-temperature functionalities found for ferromagnetic structures of 

(Ga,Mn)As, p-(Cd,Mn)Te, are related materials -- now transferred to elemental 

ferromagnets -- as well as by abundant experimental observations and theoretical 

modellings of ferromagnetic features persisting up to high temperatures in a number of 

magnetically doped semiconductors and oxides without any valence band holes or even 

in materials nominally undoped with transition metals. 

In the talk, a broad overview of recent breakthrough experimental and theoretical 

developments will be given emphasizing that, from the one hand, they disentangle 

controversies and puzzles accumulated over the last decade and, on the other, offer new 

outstanding research prospects [1]. More specifically, it will be shown how element 

specific and spin sensitive contemporary nanocharacterization methods help to asses the 

real structure of materials down to the atomic scale and, thus, to build a sensible 

theoretical understanding of macroscopic properties, including the origin of low- and 

high-temperature ferromagnetism in semiconductors. Recent experiments that 

demonstrate the influence of the electric field and current on magnetism and the 

generation of current by time-dependent magnetization will be discussed in a broad 

context of spin physics and spintronic applications. 

[1] See, T. Dietl, “A ten-year perspective on dilute magnetic semiconductors and oxides”, 

Nature Mater. 9, 965 (2010). 

30

40th _______________________________________________________________ 

"Jaszowiec" 2011 International School and Conference on the Physics of Semiconductors MoI3 

Charging Effects in Self Assembled CdTe Quantum Dots 

Łukasz Kłopotowski 

Institute of Physics, Polish Academy of Sciences al. Lotników 32/46, Warszawa, Poland 

Semiconductor quantum dots (QDs) are often referred to as artificial atoms. This 

analogy stems mostly from zero dimensional density of states hindering interactions between 

these nanostructures and the environment. In fact, QDs are more than atom-like 

structures: they can be easily incorporated into semiconductor devices enabling studies 

of properties impossible to achieve in atom particles. These phenomena are related to 

a possibility of controllable feeding the dots with charge carriers one by one: an effect 

resulting from a Coulomb blockade. Such deterministic charging not only allows to study 

effects related to Coulomb interaction between carriers, but has proved to be essential 

in discoveries of phenomena requiring a particular QD charge state: creation of dynamic 

nuclear polarization, coherent qubit operations, creation of Mahan excitons, to name just 

a few. 

Most studies on charge tunability of QDs were done in InGaAs system. On the other 

hand, II - VI QDs possess a few interesting advantages over their better known counterparts: 

they can be easily doped with magnetic ions and exhibit stronger excitonic 

interactions. Combining these features with a possibility to prepare a II - VI QD in 

a given charge state can result for instance in electrical control over magnetism on a 

nanoscale. 

In this talk, we report on our recent achievements in studies of charging effects in 

self assembled CdTe QDs [1]. By studying QD photoluminescence (PL), we show charge 

tunability in dots embedded in a field-effect structure. Exploiting the vertical electric 

field resulting from biasing the device, we study the quantum confined Stark effect to 

gain insight into Coulomb interactions and changes of charge distribution upon tuning 

the QD occupancy. In particular, we find that the electron wave function is stiffer than the 

hole wave function – an effect which we subsequently confirm with analysis of PL lifetimes 

of different QD occupancies. We demonstrate that the confinement in our dots is far from 

the strong confinement limit. This in turn results in Coulomb correlations dominating 

over confinement. A fingerprint of this phenomenon is a universal shape of the QD PL 

spectrum featuring the same transition sequence – an effect entirely different from the 

InGaAs system, where confinement conditions totally determine the PL spectrum. We 

conclude with presenting an outlook for future studies involving magnetically doped dots 

and different approaches for extending the tunability in this system. 

[1] Ł. Kłopotowski et al. Phys. Rev. B 83, 155319 (2011). 

31

MoI4 _______________________________________________________________ 


Optical properties of strongly in-plane asymmetric epitaxial nanostructures 

Grzegorz Sęk 

Institute of Physics, Wrocław University of Technology 

Wybrzeże Wyspiańskiego 27, 50-370 Wrocław, Poland 

Strongly laterally asymmetric nanostructures have already been proven advantageous in 

both laser applications, offering higher gain and broader spectral tunability, or fundamental 

studies of solid state quantum electrodynamics (QED), due to enhanced exciton oscillator 

strength. On the other hand, such structures are believed to have selective and geometrydriven 

polarization properties. However, our spectroscopic measurements on self-assembled 

structures of two material systems but similar geometries (lateral aspect ratio of about 3-5) 

demonstrated significantly different properties. 

For InAs elongated structures (called dashes) on InP substrate the linear-polarizationresolved 

photoluminescence measurements have shown the degree of polarization (DOP) at 

the level of 30% for high excitation conditions and/or at elevated temperatures. A systematic 

increase of the DOP has been observed for the enlarged dash height and eventually exceeded 

90% for very tall structures called columnar quantum dashes. The dependence, tending to 

saturate for larger heights, has been reproduced theoretically by both analytical considerations 

assuming the heavy - light hole bands mixing as the primary factor responsible for the 

polarization properties and by full 8 band kp calculations including strain. Unexpectedly 

however, low temperature single dot study revealed exciton to biexciton lifetimes ratio of 

about 2 and biexciton binding energy below 0.5 meV, both together characteristic for the 

strong confinement regime. In addition, rather small exciton fine structure splitting in the 

range of 60 – 200 µeV has been detected, comparable to values reported for common selfassembled 

dots. All these facts suggest the occurrence of an additional exciton localization 

within the structures, e.g. on local size or content fluctuations, causing a decreased 

confinement anisotropy. This has further been supported by an observed decrease of the DOP 

down to about 10% at low temperatures and low excitation. The calculated temperature 

dependence of the DOP reproduced this feature very well after taking into account a 

fluctuation of the dash cross-sectional size. The latter confirmed that the low temperature 

emission originates from excitons trapped on potential fluctuations with the localization 

energy of about 5 meV. 

Quite an opposite behavior has been found for In0.3Ga0.7As/GaAs extended quantum 

dots. On one hand, single dot study, QED experiments on a dot inside a pillar microresonator 

and time-resolved spectroscopy have shown large oscillator strengths and weakened quantum 

confinement manifested in a small value of the exciton to biexciton lifetime ratio (below 1) 

and a decreased (as compared to standard quantum dots) exciton radiative lifetime (~ 300 ps). 

Further, we observed no fingerprints of any localization effects in the polarization-resolved 

experiments versus temperature and excitation, which agrees with a very smooth morphology 

of these structures when compared to the InP-based ones. The DOP is only about 6% despite 

the shape asymmetry and similar light hole contribution to valence band states as in InP-based 

structures (based on 8 band kp calculations). This is caused by a shallow electron confining 

potential making them (and hence the entire exciton) to experience less anisotropic 

confinement potential. Furthermore, exciton localization within the wetting layer enhancing 

their radiative lifetime to almost 1 ns has been observed. This appeared to be responsible for 

strong temperature sensitivity of the wetting layer - quantum dot energy transfer efficiency 

and the appearance of a low-energy sideband emission accompanying the biexciton, being a 

fingerprint of its interaction with excitons from the wetting layer. 

32

40th _______________________________________________________________ 

"Jaszowiec" 2011 International School and Conference on the Physics of Semiconductors MoO1 

Coupling between electronic and vibrational excitations in 

carbon nanotubes filled with C60 fullerenes 

Pawel Utko 1 , Raffaello Ferone 2,3 , Ilya V. Krive 3,4 , Robert I. Shekhter 3 , Mats 

Jonson 3,5,6 , Marc Monthioux 7 , Laure Noé 7 , and Jesper Nyg˚ard 1 

1 Niels Bohr Institute & Nano-Science Center, University of Copenhagen, 

DK-2100 Copenhagen, Denmark 

2 Department of Physics, Lancaster University, Lancaster LA1 4YB, UK 

3 Department of Physics, University of Gothenburg, SE-412 96 Göteborg, Sweden 

4 B. I. Verkin Institute for Low Temperature Physics and Engineering, 

61103 Kharkov, Ukraine 

5 School of Engineering and Physical Sciences, Heriot-Watt University, 

Edinburgh EH14 4AS, UK 

6 School of Physics, Konkuk University, Seoul 143-701, Korea 

7 CEMES-CNRS, B.P. 94347, F-31055 Toulouse Cedex 4, France 

Filling single wall carbon nanotubes with C60 fullerenes yields hybrid structures [1], 

the so-called C60 fullerene peapods, which can offer enhanced functionality with respect 

to empty tubes. Prospective nanoelectronic applications of such composites include data 

storage devices, single electron transistors and spin-qubit arrays for quantum computing. 

However, the extent to which the electronic properties of peapods are affected by 

entrapped fullerenes is still unclear. Even though theoretical investigations predict dramatic 

changes in the electronic band structure of the nanotube, the experimental results 

remain equivocal. 

Here, we investigate the effect of the C60 fullerenes on the low-temperature electron 

transport via peapod quantum dots [2] operated in the regime of weak electronic coupling 

Γ between energy states of the dot and its electrical leads. Compared with empty nanotubes, 

we find an abnormal temperature dependence of Coulomb blockade oscillations, 

indicating the presence of a nanoelectromechanical coupling between electronic states of 

the nanotube and mechanical vibrations of fullerenes. This provides a useful method to 

detect the C60 presence and to probe the interplay between electrical and mechanical 

excitations in peapods, which thus emerge as a new class of nanoelectromechanical systems. 

We note that other types of devices for which a coupling to mechanical vibrations 

plays a crucial role in electrical transport are suspended nanotubes, as well as molecular 

conductors and transistors. 

[1] B. W. Smith, M. Monthioux, and D. E. Luzzi, Nature 396, 323 (1998). 

[2] P. Utko, R. Ferone, I. V. Krive, R. I. Shekhter, M. Jonson, M. Monthioux, L. Noé, 

and J. Nyg˚ard, Nature Commun. 1, 37 (2010). 

33

MoO2 _______________________________________________________________ 


Solid-state self assembly: a route to hybrid metal-semiconductor epitaxial 


Adam Urba�czyk, Frank W.M. van Otten and Richard Nötzel 

COBRA Research Institute, Departament of Applied Physics, Eindhoven Univeristy of 

Technology, The Netherlands 

� 

� 

Recently there has been a lot of research interest in metallic nanostructures for 

confining light at deeply subwavelength dimensions utilizing surface plasmons. Such 

plasmonic nanostructures are currently finding applications in fields of sensing and energy 

conversion. Combining them with optically active media such as semiconductor quantum dots 

(QDs) could lead to even more exciting applications in the field of nanophotnics and 

nanoelectronics, where the metal-QD hybrid structures could be used as ultrasmall light 

sources or switching elements. In order to obtain such hybrid structures in reproducible and 

scalable manner one has to control the metal-QD separation with single nanometer precision 

owing to extreme light confinement due to surface plasmon resonance (SPR). Recently our 

group demonstrated a promising approach to solve this problem by utilizing solid-state selfassembly. 

Here we report alignment of epitaxial nanocrystals of Ag and In on isolated InAs 

QDs and one dimensional QD arrays obtained by molecular beam epitaxy (MBE). By 

changing the process conditions the SPR wavelength of the metal nanocrystals can be easily 

tuned over wide range in order to match the emission wavelength of the QDs. 

Photoluminescence (PL) measurements reveal large enhancement of the emitted light 

intensity as compared to a reference structure without metal. What is more, in those hybrid 

nanostructures PL polarization is modified, evidencing electromagnetic character of the 

interaction between the metal nanocrystals and the QDs. 

� 

Figure 1. Atomic force microscope image of a Ag nanocrystas aligned on a single near-surface 

InAs QD and a reference structure with bare near surface QDs. 

34

40th _______________________________________________________________ 


First-Principles Study of Doped III–V nanowires 

M. Galicka 1 , P. Kacman 1 and R. Buczko 1 

1 Institute of Physics PAS, al. Lotników 32/46, 02-668 Warsaw, Poland 

GaAs and InAs nanowires (NWs) are considered as one of the most interesting structures for 

nanoelectronics and nanophotonics. Their potential application in novel electronic devices 

requires, however, controllable p-type and n-type conductivity. The specific growth conditions 

for NWs, their crystal structure and orientation of their side facets lead sometimes to different 

incorporation of dopants than known for planar layers. For example, GaAs epitaxial layers are 

typically p-type doped with Be and n-type doped with Si ions. In contrast, in GaAs NWs 

although Si doping leads sometimes to n-type, but most often p-type conductivity is observed 

in Si-doped GaAs NWs [1,2]. The problem of doping of NWs has become now a major 

challenge to the growers of one-dimensional III-V semiconductor structures. 

To explain the observed phenomena we study theoretically the properties of GaAs and 

InAs NWs, in which one cation/anion is substituted by a dopant ion. Since the III-V 

semiconductor NWs can grow in both, zinc-blende (ZB) and wurtzite (WZ) structures, we 

check whether the crystal structure of the wire has an impact on the doping level and the 

distribution of impurities in the NW and, most important, on the electronic properties of the 

doped NWs. The calculations show that the distribution of impurities in the wires as well as 

the conductivity depend crucially on the crystal structure. 

We consider ZB NWs oriented along (111) axis and WZ NWs along (0001) axis. These 

growth directions are chosen because they are the most energetically preferred for both GaAs 

and InAs NWs [3]. Using ab initio methods based on the density functional theory we have 

calculated the formation and segregation energies for GaAs and InAs NWs doped with 

different ions. In GaAs NWs, we consider Be atom, which substitutes a cation and should lead 

to p-type conductivity and Si atom which substitutes either anion (p-type) or cation (n-type). 

The formation energies for Si in GaAs NWs calculated for various sets of chemical potentials 

suggest that the energy needed for substituting the anion and the cation, and thus the type of 

conductivity obtained by Si-doping, can be different in ZB and WZ wires. As-grown InAs 

NWs have usually high concentration of electrons in the conduction band. Thus, in InAs NWs 

we show, by comparing the formation energies, that among Be, Zn or Si impurities, which can 

be used to obtain p-type wires, Be is preferred. 

The segregation energy shows where the dopants prefer to stay – it is defined as the 

difference between the energy of a NW with the impurity ion in a given position in the wire 

and in its center. It has been obtained that in ZB structures the impurities prefer to stay at the 

side surfaces of the NW. In WZ NWs the positions inside the wire are preferred. For all kinds 

of impurities studied, the segregation energy in WZ NWs is much smaller than in ZB NWs, 

thus, the distribution of impurities in WZ wires should be much more homogenous. 

To study the electronic properties we have calculated the density of states of the doped 

NWs. In contrast to the formation and segregation energies, which have been calculated for 

wires with the surfaces not saturated by foreign ions, the density of states has been obtained 

for wires with side surfaces fully passivated by hydrogen atoms. 

[1] M. Hilse et al., Appl. Phys. Lett. 96, 193104 (2010) 

[2] J. Dufouleur et al., Nano Lett. 10, 1734 (2010) 

[3] M. Galicka, et al., J. Phys: Condens. Matter 20, 454226 (2008) 

Work supported by EC network SemiSpinNet (PITN-GA-2008-215368). 

35

MoO4 _______________________________________________________________ 


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36

40th _______________________________________________________________ 


Growth of optically active CdTe quantum dots in ZnTe nanowires 

� 

P. Wojnar 1 , E. Janik 1 , S. Kret 1 , A. Petrouchik 1 , M. Goryca 2 , 

T. Kazimierczuk 2 , P. Kossacki 2 , G. Karczewski 1 and T. Wojtowicz 1 

� 

1 Institute of Physics, Polish Academy of Sciences, Al Lotników 32/46, 02-668 Warsaw, Poland 

2 Institute of Experimental Physics, University Warsaw, ul Ho�a 69, 00-681 Warsaw, Poland 

Quantum dots consisting of nanometer sized insertions of low energy gap semiconductor in large 

energy gap nanowire have recently risen a great interest because of their emerging applications as 

single photon sources at room temperature [1], biological markers, nanobarcodes [2] and also in view 

of electronic coupling of several quantum dots. 

In this work the growth and optical properties of CdTe 

quantum dots in ZnTe nanowires are reported. The structure is 

grown by molecular beam epitaxy in the vapor-liquid-solid 

growth mechanism induced by gold catalysts. Nanometer sized 

droplets of gold/gallium eutectic are formed on GaAs substrate 

by thermal treatment of a 1 nm thick gold layer deposited in a 

separate growth process. Subsequently, ZnTe nanowires with 

the length of about 1.5 �m are grown at relatively high 

substrate temperature of 420°C. For the deposition of the CdTe 

insertion, the temperature is decreased to 380°C, which is still 

a too high temperature for the epitaxial growth and, therefore, 

ensures that CdTe growth occurs in the axial direction of the 

nanowire. Deposition time of CdTe is set to 60s. The further 

growth of 200 nm ZnTe nanowire segment takes place at 

380°C. 

Photoluminescence measurements performed at 5 K show 

clearly that the presence of CdTe insertions in the ZnTe 

nanowires results in the appearance of a strong emission in the 

2.0 eV – 2.2 eV energy region. When the excitation spot 

Figure Low temperature micro- 

photoluminescence of the ZnTe 

nanowires with CdTe insertions – 

(a) “as grown” sample - several objects 

excited simultaneously (b) nanowires 

dispersed on silicon – only one 

emission line present, 9 K, excitation: 

532 nm (2.33 eV), 100 �W 

diameter is reduced to the size of the order of 1 �m, this broad 

band splits into several sharp lines with the spectral width of 

the order of 2 meV, figure a. Those lines are related to the 

emission from individual quantum dots in nanowires as 

confirmed by our further study. In order to better resolve the 

individual emission lines, the nanowires are removed from the 

GaAs substrate in a ultrasonic methanol bath and dispersed on 

a silicon substrate, figure b. 

The emission lines exhibit a relatively large degree of linear 

polarization ranging from 70% to 95% depending on the particular line. This effect is due to large 

contrast of the dielectric constant of the nanowire and the surrounding and, thus, confirms that the 

emissions come from an object placed inside a nanowire. On the other hand, photon correlation 

measurements prove the zero dimensional character of studied objects. A clear antibunching at the zero 

delay time between arriving of two subsequent photons from the same emission line is observed 

confirming that these individual objects cannot emit simultaneously two photons at the same energy. 

Moreover, the power dependence of the emission and the cross-correlation measurements allow us to 

indentify biexcitonic emissions with binding energies ranging from 7 - 12 meV 

The research has been supported by the European Union within European Regional Development Fund through Innovative 

Economy grant (POIG.01.01.02-00-008/08) and “support for the creation of joint research infrastructure of scientific 

institutions.” - POIG.02.02.00-00-003/08 

[1] A. Tribu et al., NanoLett., 8, 4326 (2008) 

�� 

37

MoO6 

_______________________________________________________________ 


Electronic properties of graphite 

J. M. Schneider 1,2 , B. A. Piot 2 , I. Sheikin 2 , N. A. Goncharuk 3 , P. Vaˇsek 3 , P. Svoboda 3 , Z. Výborný 3 , L. Smrčka 3 , 

M. Orlita 2 , M. Potemski 2 , and D. K. Maude 2 

1 Instituto de Física, Universidade de São Paulo, PB 66318, 05315-970 São Paulo, SP, Brazil 

2 Grenoble High Magnetic Field Laboratory, Centre National de la Recherche Scientifique, 38042 Grenoble, France 

3 Institute of Physics, Academy of Science of the Czech Republic, 162 53 Prague 6, Czech Republic 

Despite more than 50 years of reserach, graphite is not yet fully understood. From the viewpoint of graphene, a 

single layer of carbon atoms set in a honeycomb lattice, graphite can be considered as a quasi-two-dimensional (2D) 

system consisting of a macroscopic stack of graphene layers. A fundamental question concerns the link between 

the coupling of the graphene layers and the dimensionality of the electronic system in graphite. According to the 

Slonczewski, Weiss, and McClure (SWM) band structure calculations of graphite the weak coupling leads to the form 

of the in-plane dispersion depending upon the momentum kz in the direction perpendicular to the layers. The carriers 

occupy a region along the H-K-H edge of the hexagonal Brillouin zone. The Fermi surface of graphite reveals two 

extremal majority charge carriers cross sections: Electrons at the K point (kz = 0) and holes at kz = 0.35. For both 

types of charge carriers the in-plane dispersion is parabolic (massive fermions). Only at the H point (kz = 0.5) the 

in-plane dispersion is linear, similar to that of charge carriers in graphene (massless Dirac fermions). However, the 

extremal cross section at the H point is negligible (minority charge carriers) and does not contribute significantly to 

the electronic properties of graphite. 

This work represents a review of recent studies of the electronic properties of graphite using the Shubnikov-de Haas 

(SdH) and the de Haas -van Alphen (dHvA) effect at millikelvin temperatures [1, 3–5]. Because of the low temperatures 

used, both the SdH and the dHvA effect are much richer than previously published data. Quantum oscillations 

are observed for both majority electrons and holes with an orbital quantum number up to almost N = 100. The 

high quality of the data allows a detailed investigation of the fine structure of the Fermi surface [1]. Using both the 

semiclassical model and the full magnetic field Hamiltonian we show that these oscillations are fully consistent with 

the three-dimensional (3D) SWM bandstructure calculations of graphite. At magnetic fields B > 2 T, a significant 

deviation from the 1/B periodicity occurs. A self-consistent calculation of the Fermi energy shows that the deviation 

from the 1/B periodicity is caused by a considerable movement of the Fermi energy when the quantum limit is approached. 

This seriously questions the validity of using the high-field data to extract the phase of the Shubnikov-de 

Haas oscillations and hence the nature of the charge carriers [2, 3]. The detailed information of the band structure 

of graphite and the movement of the Fermi energy in magnetic field allows to examine the spin splitting of quantum 

features. We show that an effective g-factor value of g ∗ = 2.5 is required to explain the data [4]. 

We performed dHvA measurements to make a complete map of the Fermi surface of graphite. For tilt angles θ < 60 ◦ , 

the fundamental frequencies of both the electrons and holes follow almost exactly a 1/cos(θ) dependence (quasi-2D 

behavior). For θ > 60, a clear deviation from the quasi-2D behavior is observed. The deviation is a signature of 

the dispersion along kz and unequivocally demonstrates the 3D character of the Fermi surface which arises from the 

coupling between the graphene layers. Furthermore, the observation of quantum oscillations at θ = 90 ◦ is a direct 

proof that the Fermi surface of graphite is closed. Additionally, the θ = 90 ◦ data reveals minority holes with a Dirac 

like energy spectrum much like as for charge carriers in graphene [5]. 

References 

[1] J. M. Schneider, Phys. Rev. Lett. 102, 166403 (2009). 

[2] I. A. Luk’yanchuk and Y. Kopelevich, Phys. Rev. Lett. 97, 256801 (2006). 

[3] J. M. Schneider, Phys. Rev. Lett. 104, 119702 (2010). 

[4] J. M. Schneider et al, Phys. Rev. B 81, 195204 (2010). 

[5] J. M. Schneider, to be submitted to Phys. Rev. Lett. 

38

40th _______________________________________________________________ 

"Jaszowiec" 2011 International School and Conference on the Physics of Semiconductors MoP1 

Nonlocal transport in PbTe/PbEuTe microstructures 

K. A. Kolwas 1 , G. Grabecki 1,2 , S. Trushkin 1 , Ł. Cywiński 1 , M. Aleszkiewicz 1 , 

T. Dietl 1,3 , G. Springholz 4 , G. Bauer 4 

1 Instytut Fizyki PAN, al. Lotnikow 32/46, PL-02-668 Warszawa, Poland 

2 Wydział Matematyczno-Przyrodniczy, Szkoła Nauk Ścisłych, UKSW, ul. Wóycickiego 1/3, 

PL 01-938 Warszawa, Poland 

3 Instytut Fizyki Teoretycznej, UW, ul.Hoża 69 PL 00-681 Warszawa, Poland 

4 Institut für Halbleiter-und-Festkörperphysik, Johannes Kepler University, 

Altenbergerstr. 69, A-4040 Linz, Austria) 

Heterostructures of narrow-gap semiconductors have recently received a renewed attention, due to the discovery 

of Quantum Spin Hall phase in HgTe/HgCdTe quantum wells [1], the fingerprint of which is the presence of 

large quantized nonlocal voltage signals due to the edge currents [2]. However, even in the topologically trivial 

phase, a large nonlocal voltage signal has been seen in Hall bar structures of HgTe [3] due to the presence of 

Spin Hall Effect (SHE) in the ballistic regime [4]. 

Heterostructures of IV-VI compounds (Pb,Eu,Sn)Te are another attractive candidates in which one can 

search for physics related to the crucial influence of the spin-orbit coupling on the electronic structure of 

relevant bands. In contrast to HgTe case, there is no inversion asymmetry (because of rock-salt crystal structure) 

and the Dresselhaus splitting is absent. The huge dielectric constant of PbTe (e0 > 1000) makes it an ideal 

material in which quantum ballistic transport effects can be observed [5]. 

We have fabricated, by means of the e-beam 

lithography techniques, multi-probe quantum wires (see 

Fig. 1 inset) based on an MBE-grown PbTe quantum 

well (QW), of the thickness of 12 nm, embedded 

between 

Pb1-xEuxTe barriers, deposited on BaF2 substrates. The 

wires were equipped with side gates for tuning the 

electron concentration. The wire widths W were as 

narrow as 1 mm, and their lengths L = 5 mm. The electron 

mobility in the initial QW was 5 m 2 /Vs, which 

corresponds to the electron mean free path le = 3 mm. 

Therefore, W < le < L , and our structures were in quasiballistic 

regime. The application of negative voltage to 

the gates has led to the total depletion of the wires. The 

measured resistance was then above 10 7 Ohms. 

The low-temperature transport measurements have 

shown characteristic negative magnetoresistance maxima 

which were almost temperature independent in the range 

Fig. 1: Local magnetoresistance of structure T < 20 K (Fig. 1). We assign it to the suppression of the 

shown in the inset. 

electron non-specular backscattering by the wire 

boundaries [6]. 

Nonlocal resistance measurements have been performed in order to search for the signatures of the SHE and 

the inverse SHE [3, 4]. The obtained signal at B = 0 is at least one order of magnitude larger than the value 

expected from the classical van der Pauw formula. However, it is suppressed by the magnetic field with a 

dependence distinctly correlated with the local magnetoresistance. This suggests that the nonlocal resistance may 

be related to non-specular boundary scattering in our wires. 

Acknowledgments: This work was supported by Ministry of Science (Poland) under Grant 

No. 1247/B/H03/2008/35 and under Iuventus Plus grant No. IP2010 006070. 

References 

[1] Markus König et al., Science 318, 766 - 770 (2007). 

[2] Andreas Roth et al., Science 325, 294 - 297 (2009). 

[3] C. Brune et al., Nature Physics 6, 448 - 454 (2010). 

[4] E. M. Hankiewicz et al., Phys. Rev. B 70, 241301 (2004). 

[5] G. Grabecki et al., Phys. Rev. B 72, 125332 (2005). 

[6] C. W. J Beenakker and H. van Houten, Cond-Mat/0412664 (2004). 

39

MoP2 _______________________________________________________________ 


Optical transitions in PbTe/CdTe quantum wells grown by molecular beam 

epitaxy on GaAs (001) and BaF2 (111) substrates 

M. Szot,* L. Kowalczyk, E. Smajek, B. Taliashvili, P. Dziawa, W. Knoff, A. Reszka, 

V. Domukhovski, E. Łusakowska, P. Dłu ewski, M. Wiater, T. Wojtowicz, T. Story, 

M. Bukała, R. Buczko, P. Kacman 

Institute of Physics, Polish Academy of Sciences, Al. Lotników 32/46, 02-668 Warsaw, Poland 

IV-VI narrow band gap semiconductors PbTe, PbSe, and PbS constitute materials system 

alternative to III-V semiconductors in the area of mid-infrared lasers and detectors. The 

attractiveness of PbTe/CdTe heterosystem results, inter alia, from a very strong confinement 

of electrons in PbTe caused by large difference in the energy gaps of these semiconductors 

( Eg=1.2 eV at 300 K) and from low Auger recombination rate in PbTe. Additionally, PbTe 

and CdTe exhibit excellent matching of their lattice parameters at room temperature, even 

tough they crystallize in different cubic lattices: zinc blende (a0=6.48 Å) for CdTe and rock 

salt (a0=6.46 Å) for PbTe. Such features are strongly desirable for efficient optoelectronic 

devices operating at room temperature. In this paper, we undertake experimental and 

theoretical studies of ground-state photoluminescence (PL) from PbTe/CdTe quantum wells 

grown along different crystal directions by molecular beam epitaxy (MBE). 

The PbTe/CdTe QWs were grown by the MBE on (001) oriented GaAs and (111) oriented 

BaF2 substrates with thick (1÷4 µm) high quality CdTe buffer layers. The structural quality of 

the heterostructures was examined by x-ray diffraction (XRD) and cross-sectional TEM and 

SEM electron microscopy techniques. The PbTe/CdTe heterostructures with the best crystal 

quality were obtained for the growth at low temperatures (about 260 °C). The XRD rocking 

curve width parameter below 200 arcsec was found for both PbTe and CdTe. For multiple- 

QWs diffraction satellites up 7 th order were observed. The single- and multiple-QWs (3 

repetitions of a basic PbTe/CdTe bilyer) were grown with the thicknesses of PbTe quantum 

wells varying from 4 to 20 nm and 60 nm thick CdTe barriers. 

The optical properties of the heterostructures were examined by the PL measurements using 

1064 nm line of YAG:Nd pulsed laser for excitation. For both (001) and (111) PbTe QWs we 

observed relatively narrow and strong PL which we attribute to the ground-state transitions in 

the PbTe well. The PL energy at T=4 K shifts from 310 meV to 460 meV for (001) PbTe 

QWs with thickness varying from 20 nm to 4 nm, respectively. For a given quantum well 

thickness of 12 nm, the PL energy observed for (111) PbTe QW grown on BaF2 is about 70 

meV lower than for (001) PbTe well. The observed blue shift of the PL line is in good 

agreement with our theoretical analysis of the influence of quantum size effect on the groundstate 

electronic transitions in the PbTe wells. Both studied growth directions were considered 

theoretically. Our calculations were performed within two methods: tight-binding and 

effective mass approximation. The dependence on band offsets in the conduction and valence 

band in the type-I band alignment at the PbTe/CdTe interface was studied. The strong 

effective mass anisotropy and strain induced change of the band gap in PbTe were taken into 

account. The latter effect results from the large difference between PbTe and CdTe 

temperature expansion coefficients. 

This work was partially supported by the European Union within the European Regional 

Development Fund, through the Innovative Economy grant (POIG.01.01.02-00-108/09). 

40

40th _______________________________________________________________ 


Properties of three-dimensional topological insulators 

studied by microwave resonance spectroscopy 

A. Wolos, 1,2 A. Drabinska, 1 M. Kaminska, 1 G. Strzelecka, 3 A. Hruban, 3 A. Materna, 3 

M. Piersa, 3 Z. Wilamowski 2 

1 Faculty of Physics, University of Warsaw, ul Hoza 69, 00-681 Warsaw, Poland. 

2 Institute of Physics, Polish Academy of Sciences, Al. Lotnikow 32/46, 02-668 Warsaw, 

Poland. 

3 Institute of Electronic Materials Technology, ul. Wolczynska 133, 01-919 Warsaw, Poland. 

Bismuth selenide and telluride, as well as other related materials have been recently 

proposed as three-dimensional topological insulators with a single Dirac cone on the surface 

[1]. This class of materials is predicted to show an insulating bulk gap together with gapless 

surface states. Occurrence of the topological surface states has been confirmed by angleresolved 

photoemission spectroscopy [2]. There are, however, only a few reports in literature 

concerning experimental observation of electric transport in the conducting surface, owing to 

large number of bulk carriers (either electrons or holes) originating from crystal defects. In 

order to override presence of highly conductive bulk states shading electric properties of the 

surface, we propose to apply a contactless method basing on a standard electron spin 

resonance (ESR) spectrometery. 

In this communication we discuss results of microwave resonance experiments 

performed on Bi2Te3, Bi2Se3, and Bi2Te2Se crystals grown by vertical Bridgman method in 

Institute of Electronic Materials Technology, Warsaw. The experiment was performed using 

Bruker ELEXSYS E580 spectrometer operating in X- and Q-bands. Semiconducting samples 

placed in a cavity of a standard ESR spectrometer show, in addition to spin resonance spectra, 

also spectral features related to sample conductivity. Using this technique, we have earlier 

investigated Shubnikov-de Haas oscillations, cyclotron resonance or coupled plasmoncyclotron 

resonance in two dimensional electron gas (2DEG) in GaN-based heterostructures 

[3] and in Si-based quantum wells. 

First results obtained for bismuth selenide and telluride samples show a broad 

resonance line dependent only on the component of the external magnetic field perpendicular 

to the sample plane. This feature is characteristic for the cyclotron-related resonances in two 

dimensional electron gas. The relation of the observed resonance line to the topological 

surface states, together with parameters of the 2DEG (concentration and mobility) derived 

from the resonance will be discussed. 

[1] H. Zhang et al. Nature Phys. 5, 438 (2009). 

[2] Y. Xia et al. Nature Phys. 5, 398 (2009). 

[3] A. Wolos et al. Phys. Rev. B 76, 045301 (2007). 

41

MoP4 _______________________________________________________________ 


Analysis of Optical Properties and Pressure Dependence of the Energy Gap of 

ZnO Layers, Bulk and Nano-Powders 

A. Duzynska 1,* , A. Kaminska 1 , H.Teisseyre 1,2 , E. Przezdziecka 1 , D. Dobosz 1 , 

Z.R. Zytkiewicz 1 , A. Kozanecki 1 , J. D. Fidelus 1,2 , A. Durygin 3 , V. Drozd 3 , R. Hrubiak 3 , 

A. Suchocki 1,4 

1 Institute of Physics, Polish Academy of Sciences, Al. Lotników 32/46, 02-668 Warsaw, Poland 

2 Institute of High Pressure Physics, Polish Academy of Sciences, Sokołowska 29/37, 01-142 Warsaw, Poland 

3 CeSMEC, Florida International University, University Park, Miami, FL 33199, USA 

4 Institute of Physics, University of Bydgoszcz, Weyssenhoffa 11, 85-072, Bydgoszcz, Poland 

* Corresponding author: A. Duzynska, e-mail address duzyn@ifpan.edu.pl 

Nowadays zinc oxide (ZnO) is a promising wide-band-gap semiconductor for 

optoelectronic applications, especially in the blue and ultraviolet spectral ranges. An important 

factor affecting mechanical, electric and optical properties of ZnO are methods/conditions of 

growth as well as its crystal form. 

In this project we have studied pressure dependence of the near band gap 

photoluminescence (using the diamond anvil cell technique) of several various samples: 

- two zinc oxide thin layers grown by plasma-assisted molecular beam epitaxy (PA-MBE) on 

sapphire substrates (thickness of the layers: 1µm and 200 nm), 

- bulk ZnO crystal grown by vapor-phase deposition during industrial process of production of 

zinc white, 

- two samples of hexagonal ZnO nano-powders (size of crystallite: 1µm and 65 nm) grown by 

plasma technique. 

We also investigated the stability and the volume behaviour under hydrostatic pressure by 

X-ray powder-diffraction of bulk crystal using synchrotron radiation. The values the bulk moduli 

(B0), and their pressure derivative (B0’), before and after phase transition from wurtzite (B4) to 

rock salt (B1) structure were obtained from these measurements. We found that for wurtzite 

structure B0 is equal to (156 ± 13) GPa and for rock salt phase B0 = (180 ± 59) GPa. In zinc oxide 

the B4-B1 transition has been earlier reported at ~ 10 GPa. However, the change of nanoscale 

grain size has a huge influence on the characteristic of phase transition. We supposed that in the 

case of nano-powders a tetragonal intermediate (iT) appears at the B4/B1 interface and a 

hexagonal intermediate (iH) is also showed as an effect of axial compression [1]. These results 

are visible in our experimental data of pressure dependence of the energy gap EG (≈ EPL), 

especially for nano-powder with 65 nm crystallite size. Moreover experimental band gap 

pressure coefficients for bulk crystal and films grown on sapphire are about 20 meV/GPa, but for 

nano-powders are lower, about 15 meV/GPa. This effect will be also discussed. 

The photoluminescence is quenched at about 10 GPa for ZnO bulk materials as results of 

transition from direct to indirect gap in the rock salt structure. Nonetheless for smaller size nanopowder 

the photoluminescence vanishes at 20 GPa. The origin of this phenomenon will be 

analysed in this work. 

References: 

1. S. E. Boulfelfel and S. Leoni, Phys. Rev. B. 78, 125204 (2008). 

Acknowledgement: This work was partly supported by the European Union within European Regional Development 

Fund, through the Innovative Economy grants (POIG.01.01.02-00-008/0 and POIG.01.01.02-00-108/2009/2) and 

the project no N N202 010134 of Polish Ministry of Science and Higher Education. 

42

40th _______________________________________________________________ 


Defect structure of two-dimensional Wigner crystals 

A. Radzvilavičius and E. Anisimovas 

Department of Theoretical Physics, Vilnius University, Saul˙etekio al. 9-III, LT-10222 

Vilnius, Lithuania 

As the density and temperature of the electron gas is lowered beyond a certain critical 

value, the potential Coulomb energy dominates the kinetic energy and particles tend to 

crystallize. The lowest energy structure of a two-dimensional system thus corresponds to 

the perfect hexagonal Wigner lattice [1]. Finite-size clusters, however, are usually formed 

due to the presence of an external confinement. In many experimental realizations, such 

structures are trapped by a symmetric parabolic potential; these include, but are not 

limited to, micro-metric charged spheres in low-temperature dusty plasmas and electrons 

in semiconductor quantum dots [2]. The structural properties of finite two-dimensional 

Wigner clusters strongly depend on the system size and energetic state. 

In the present contribution, we report the results of 

the numerical Monte Carlo and minima hopping [3] experiments, 

and analyze the structural properties of twodimensional 

Wigner clusters, consisting of classical point 

charges, confined by an external parabolic potential trap. 

Systems of up to N = 1000 particles are considered. 

Thenumberofmetastableconfigurations,corresponding 

to the local minima of the potential energy, grows 

very rapidly with the number of particles. Structurally 

different states are realized with different probabilities. 

By analyzing the number and probabilities of metastable 

configurations we conclude that the configurational uncertainty 

(entropy), grows faster than exponentially – as 

the logarithm of the factorial of the number of particles 

N [4]. 

Small crystals exhibit near-circular symmetry – shell 

structure, induced by the external confinement. Ground 

Figure 1: The triangulated 

structure and defects of 600particle 

Wigner cluster. 

states of larger clusters correspond to a few circular shells at the exterior and an ordered 

hexagonal core. Due to the necessity to satisfy Euler’s theorem and to lower strain energy 

of the lattice, the presence of intrinsic topological defects is unavoidable; these are mainly 

located in the transition region between the circular surface and ordered interior, at the 

six corners of a near-perfect hexagon (figure 1). The number of defective vertices in 

six defect groups grows non-uniformly with the system size. A few distinct species of 

defects are distinguished: disclinations, dislocations, lengthy grain boundaries, unique 

triangular vacancies and interstitial sites. Large pentagonal rosette defects (see figure) 

are also observed in large clusters. As the energy of the metastable state grows, the 

orientational symmetry of the crystal is lost. Long grain boundaries in the interior, large 

numberofdislocationsandnear-surfacecomplexestendtoappearinthehighlymetastable 

configurations. 

[1] E. Wigner, Phys. Rev. 46, 1002 (1934), 

[2] A. V. Filinov, M. Bonitz and Yu. E. Lozovik, Phys. Rev. Lett. 86, 3851 (2001), 

[3] S. Goedecker, J. Chem. Phys. 120, 9911 (2004), 

[4] A. Radzvilavičius and E. Anisimovas, J. Phys.: Condens. Matter 23, 075302 (2011). 

43

MoP6 _______________________________________________________________ 


Gauge invariant computational scheme for heterostructures in magnetic field 

Anna Korbecka and Jacek A. Majewski 

Institute of Theoretical Physics, Faculty of Physics, University of Warsaw, 

ul. Hoża 69 PL-00-681, Poland 

Multiband k·p models together with the envelope function theory have become a standard 

approach for studies of the electronic structure of not only bulk semiconductors but also their 

heterostructures, other low-dimensional forms, and semiconductors in the translational symmetry 

breaking magnetic field. This continuum scheme proved to be very useful for modeling of 

semiconductor nanostructures, albeit not free from flaws. In applications of this method for 

structures where the translational symmetry is broken, the corresponding component of the wave 

vector is substituted by differential operator. Together with the fact that parameters of the k·p 

Hamiltonian are position dependent, it leads to the situation where the operators representing 

individual components of the total matrix operator are not hermitian. Therefore, these operators are 

modified (so-called ‘symmetrization’ is performed) to acquire hermitian form. It solves some of the 

severe problems, however the ‘symmetrization’ procedure is not unique and very often leads to 

unphysical spurious solutions [1] and nonphysical outcomes for the heavy-hole subbands [2]. The 

problem has been disputed hotly for a long time in semiconductor physics without a final solution 

on the horizon. In the meantime, the new approach has emerged that is based on the so-called Burt’s 

exact envelope function theory [3] and formulates the whole operator matrix in a proper form 

instead of ‘symmetrizing’ its individual components [4], i.e., the whole matrix of operators is 

hermitian, however, its individual operator components are not. This procedure of B.A. Foreman is 

not plagued by spurious solutions problem and gives in most cases physically reasonable results, 

which can be, however, quite different from ones obtained within the standard approach. In 

addition, it has been recently proved [2] that the Foreman’s scheme is the only one that guarantees 

the gauge invariance of the k·p Hamiltonian for semiconductor low-dimensional structures in the 

constant magnetic field. 

We have implemented Foreman’s theory for low dimensional semiconducting systems in 

magnetic field into nextnano 3 simulation package [5] together with the magnetic p-d exchange 

interaction [6] and interface corrections for systems without mirror symmetry (e.g., no-common 

atom systems like InAs/GaSb). The Hamiltonian has been solved on discrete lattice. This allows us 

for reliable studies of the Landau level formation in the valence bands in non-magnetic 

heterostructures (GaAs/AlGaAs, InGaAs/GaAs, InAs/GaSb) and also heterostructures with 

modulated magnetization (such as (Ga,Mn)As/AlGaAs and (Ga,Mn)Sb/InAs). The scheme deals 

also with the doped structures, by including the electrostatic potential obtained from the Poisson’s 

equation self-consistently into Foreman’s k·p Hamiltonian. 

In particular, we have computed the electronic structure of GaAs/Al0.33Ga0.67As [001] and 

[311] heterostructures in the magnetic field. The obtained results help to interpret experiments on gfactor 

in 2D-hole gases [6] and the intrinsic photo-induced anomalous Hall effect [7]. 

[1] E. P. Pokalitov, V. A. Fonoberov, V. M. Fomin, and J.T. Devreese, Phys. Rev. B. 64, 245328 (2001). 

[2] T. Andlauer, R. Morsch, P. Vogl, Phys. Rev. B. 78, 075317 (2008). 

[3] M. G. Burt, J. Phys. Condens. Matter 4, 6651 (1992). 

[4] B. A. Foreman, Phys. Rev. B. 48, 4964 (1993); ibid. 56, R12 748 (1997). 

[5] http://www.nextnano.de 

[6] D.A. Vasyukov, A.S.Plaut, M.Henini, Physica E 42, 964 (2010). 

[7] D.A. Vasyukov, A.S.Plaut, M.Henini, L.N.Pfeiffer, K.W.West, C.A.Nicoll, I.Farrer, and D.A. Ritchie, 

Physica E 42, 940 (2010). 

44

40th _______________________________________________________________ 


Modeling PbTe-based low dimensional structures 

M. Bukała 1 , P. Sankowski 2 , R. Buczko 1 and P. Kacman 1 

1 Institute of Physics, Polish Academy of Sciences, Warsaw 02-668, Poland 

2 Institute of Informatics, University of Warsaw, Warsaw 02-097, Poland 

We present a theoretical study of various PbTe low dimensional structures. First, we 

consider rock-salt PbTe inclusions in zinc-blende CdTe matrix as well as of zinc-blende CdTe 

nano-clusters in rock-salt PbTe matrix i.e. structures with possibly improved thermoelectric 

properties. Next, we model PbTe-based 2D heterostructures, in which quantum spin-Hall 

phase is expected. For these purposes a tight-binding parameterisation for PbTe has been 

obtained, which, in contrast to all available in literature parameterisations, leads not only to 

proper values of the energy gaps but also to adequate effective masses in the valence and 

conduction bands. Our tight-binding model includes the sp3 atomic orbitals with spin-orbit 

interactions and accounts for the nearest neighbour and next near neighbour interactions. We 

have checked on 2D PbTe/CdTe heterostructures that such tight-binding description and the 

effective mass approach lead to similar energy structures. 

The aim of the former research is to show how introducing nanostructures of different 

size and shape changes the electron density of states near the Fermi level and thus can be used 

to optimize the thermoelectric power Seeback coefficient. We have considered the Fermi level 

situated near the top of the valence band (in p-type) as well as at the bottom of the conduction 

band (in n-type). We have studied structural and electronic properties of PbTe quantum wires 

in the CdTe matrix, and CdTe anti-wires and CdTe anti-dots in the PbTe matrix. For structures 

with less than 500 atoms in the unit cell, all atomic positions in the model nanostructures, in 

particular at the interfaces, have been calculated using first principles methods with relaxation 

and re-bonding allowed. The obtained relaxed atomic positions have been further used in the 

calculations of electron density of states of the studied structures, which are performed within 

the tight-binding approximation. In larger structures the relaxation has not been taken into 

account. 

Our calculations show that all kinds of inclusions can lead to shape and size dependent 

changes of the density of states at the Fermi level. Thus, the electronic contribution to the 

Seebeck coefficient can be optimized by changing the shape, size, density as well as the 

spatial arrangement of the inclusions. 

The same tight-binding model, supported by effective mass approach, have been used to 

study the PbTe-based 2D heterostructures. In particular, it has been shown that states related 

to the interfaces can appear in PbSnTe/PbTe structure, in which the Sn content leads to band 

inversion. By changing the Sn content and the diameter of the heterostructure, we are looking 

for systems, in which such states may lead to the spin-Hall effect. 

The work was partially supported by the European Union within the European Regional 

Development Fund, through grant Innovative Economy (POIG.01.01.02-00-108/09) 

45

MoP8 _______________________________________________________________ 


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46

40th _______________________________________________________________ 


Atomistic calculation of screened Coulomb interactions in semiconductor 

nanostructures. 

M. Chwastyk, P. T. Różański, and M. Zieliński 

Instytut Fizyki UMK, ul. Grudziądzka 5, 87-100 Toruń, Poland 

Dielectric screening of Coulomb interactions affects optical and electronic properties 

of semiconductor nanostructures including multi-exciton generation rates in colloidal 

nanocrystals [1], excitonic spectra and self-energy corrections in nanopillar or graphene 

quantum dots [2,3]. Using tight-binding approach we compare several methods of accounting 

for dielectric screening in atomistic calculation including semi-classical approximation [4], 

Thomas-Fermi approach [5] and real-space dielectric matrix inversion [6]. We propose an 

efficient method in which dielectric screening can be decomposed into contribution from 

volume and surface-polarization terms, further screened by microscopic Thomas-Fermi like 

contribution. We illustrate our approach by calculating electronic and optical properties of 

several different spherical semiconductor nanocrystals differing in size and composition. We 

compare results obtained with proposed approach and real-space dielectric matrix inversion 

and study role of different approximation used in calculation. We discuss possibility 

generalizing our model for a multi-million atom systems like self-assembled quantum dots. 

[1] Z. Lin, A. Franceschetti, and M.T. Lusk, arXiv:1009.0417 

[2] Y. M. Niquet et al., Phys. Rev. B 73, 165319 (2006). 

[3] D. Guclu, P. Potasz, and P. Hawrylak Phys. Rev. B 82, 155445 (2010). 

[4] A. Franceschetti and M. C. Troparevsky, Phys. Rev. B 72, 165311 (2005). 

[5] S. Lee et al., Phys. Rev. B 63, 195318 (2001). 

[6] F. Trani, D. Ninno, and G. Iadonisi, Phys. Rev. B 76, 085326 (2007). 

47

MoP10 _______________________________________________________________ 


Van der Waals Density Functionals in Materials Science 

Magda Birowska, Karolina Milowska, and Jacek A. Majewski 

Faculty of Physics, University of Warsaw, ul. Hoża 69, 00-681 Warszawa, Poland 

The density functional theory (DFT) has revolutionized materials science making it possible 

to quantitatively predict numerous properties of materials. However, exact in principle, the DFT 

relies on various approximations to the exchange and correlation functionals that are nowadays 

prerequisites for practical implementations of DFT. In spite of a long list of successes, the local 

density approximation (LDA) or generalized gradient approximation (GGA) that are commonly 

used in so-called ab-initio calculations have as well many flaws. One of its weaknesses is rather 

poor description of Van der Waals (VdW) type of bonding in solids. The best example is the 

geometry unit cell geometry of graphite. Whereas the atomic distances in the carbon planes with 

strong covalent bonds are excellently predicted by LDA or GGA, the distances between the 

planes, which are determined by Van der Waals type of interactions, are not. Therefore, recently 

new correlation functionals have emerged that take into account polarization effects and could 

improve the description of Van der Waals forces [1,2]. 

In this communication, we present the results of theoretical studies of various systems with 

considerable role of VdW forces where the new functionals have been employed. The results of 

test studies for graphite are very promising, providing the solution to the long standing problem 

and giving the distance between the carbon layers equal to 3.349 Å (with DRSLL functional [1]) 

or 3.345 Å (with LMKLL one [2]) in excellent agreement with experimental value of 3.36 Å 

(LDA and GGA lead to distances equal to 3.117 Å and 3.425 Å, respectively). However, in the 

studies we focus on graphene single-, bi-, and multi-layers, either free standing or bound in an 

incommensurable way to silicon carbide substrate. We consider also functionalized graphene 

layers. The correct description of the structural and electronic properties of these systems is of 

crucial importance for the quickly developing electronics based on graphene. In our studies of 

materials we have used the numerical package SIESTA with implemented VdW functionals and 

the standard LDA and GGA ones. This facilitates the direct comparison of the material 

properties obtained within both approaches. We find differences in the electronic structures of 

these systems and their energetics. In particular, we find that the potential barriers in these 

systems calculated with VdW functional and standard approaches in many cases differ 

considerably. It is of crucial importance, particularly if one uses atomistic ab initio methods as a 

starting point for multi-scale modeling of materials and determines effective potentials on the 

basis of DFT calculations. 

This paper has been supported by the project “SiCMAT” (POIG.01.03.01-14-155/09-00). 

[1] M. Dion, H. Rydberg,E. Schoder, D. C. Langreth, and B. I. Lundqvist, Phys. Rev. Lett. 92, 

246401 (2004) 

[2] K. Lee, E. Murray, L. Kong, B. I. Lundqvist and D. C. Langreth, arXiv:1003.5255v1 (2010). 

48

40th _______________________________________________________________ 


Hopkinson-Like Effect in Single-Crystalline CdCr2Se4 Semiconductor 

T. Groń 1 , E. Malicka 2 , A.W. Pacyna 3 , H. Duda 1 and J. Krok-Kowalski 1 

1 University of Silesia, Institute of Physics, ul. Uniwersytecka 4, 40-007 Katowice, Poland 

2 University of Silesia, Institute of Chemistry, ul. Szkolna 9, 40-006 Katowice, Poland 

3 The Henryk Niewodniczański Institute of Nuclear Physics, Polish Academy of Sciences, 

ul. Radzikowskiego 152, 31-342 Kraków, Poland 

The magnetization of many compounds shows a peak near the Curie temperature, TC, 

when heating the sample in a fixed (small) magnetic field [1]. This behavior is commonly 

called the Hopkinson effect [2]. The accepted explanation [3] of the Hopkinson effect is based 

only on domain wall motion. This mechanism is obviously inapplicable to the case of singledomain 

particles. However, a thermomagnetic effect which is quite similar to the Hopkinson 

effect has been experimentally observed in most of the amorphous magnetic materials as well 

as in some spin glasses where the existence of multi-domain particles is questionable or even 

practically impossible [2]. In Nd2Fe14B-type ribbons the existence of a maximum in the 

thermomagnetic curves of thermally demagnetized samples in low fields was connected with 

the processes of irreversible rotation of magnetic moments of non-interacting uniaxial single 

domain particles according to the Stoner-Wohlfarth model [2,4]. 

Magnetization, ac and dc magnetic susceptibility of the p-type CdCr2Se4 semiconductor 

[5] were measured in the zero-field-cooled mode using a Lake Shore 7225 dc 

magnetometer/ac susceptometer at 4.3 K and in applied external magnetic fields up to 60 kOe, 

and a Faraday type Cahn RG automatic electrobalance in the temperature range 4.5-400 K and 

' 

" 

at 1 kOe, respectively. The in-phase c ( T) 

and out-of-phase c ( T) 

components of the ac 

1 

fundamental susceptibility were recorded in the temperature range 4.5-160 K using an 

oscillating field Hac = 1 Oe with frequency of 120 Hz for external magnetic fields Hdc = 0, 100 

Oe, 200 Oe, 450 Oe and 1 kOe. The signals of the second (c2) and third (c3) harmonics were 

detected at the same temperature range, for the same amplitude and frequency as the ac c1 

measurements without an external static magnetic field. 

The dc magnetic measurements showed ferromagnetic order with a Curie temperature 

TC = 130 K and a saturation magnetization of 5.91 µB/f.u. at 4.5 K and at 60 kOe. The ac 

' 

magnetic measurements revealed a spectacular peak at 450 Oe and 1 kOe in the c 1( 

T) 

curve 

near TC, similar to the Hopkinson peak. The increasing dc magnetic field suppresses the 

' 

magnetic susceptibility intensity of c ( T) 

and slightly shifts the Hopkinson peak to higher 

1 

" 

temperatures. A small and positive value of c1( T) 

below TC indicating a small energy loss 

correlates rather with strong spin fluctuations than with spin rearrangement processes. This is 

consistent with zero values of second and third harmonic ac susceptibility in the temperature 

range of 4.5-160 K, suggesting the lack of short-range magnetic interactions. One can 

conclude that the peaks in the thermomagnetic curves at 450 Oe and 1 kOe can be 

qualitatively explained with the aid of the Hopkinson-like effect. 

This work is partly founded from science Grant No. N N204 145938. 

[1] J. Hopkinson, Proc. R. Soc. London 48, 1 (1890). 

[2] O. Popov, and M. Mikhov, J. Magn. Magn. Mater. 75, 135 (1988). 

[3] M. Kersten, Z. Angew. Phys. 8, 313 (1956). 

[4] E.C. Stoner, and E.P. Wohlfarth, Phil. Trans. R. Soc. A 240, 599 (1948). 

[5] H.W. Lehmann, Phys. Rev. 163, 488 (1967). 

49 

1

MoP12 _______________________________________________________________ 


Optical and structural characterization of zinc oxide 

nanostructures obtained by Atomic Layer Deposition method 

Ł. Wachnicki 1 , B. S. Witkowski 1 , S. Gierałtowska 1 , E. Janik 1 , M. Godlewski 1,2 , 

E. Guziewicz 1 

1 Polish Academy of Sciences, Institute of Physics, al. Lotników 32/46, Warszawa 02-668, 

Poland 

2 Cardinal Stefan Wyszynski University, College of Science, Department of Mathematics and 

Natural Sciences, Warszawa, Poland 

Zinc oxide has been extensively investigated in the past few years mainly 

because of a large variety of potential applications. For example, it can be used 

in light-emitting diodes and transistors, as gas sensors, and transparent 

conductive oxide in solar cells. 

Among many applications, ZnO is also a prospective material for sensor 

technology, where developed surface morphology is very important. In this 

work we present growth of ZnO nanostructures using ALD. As a substrate we 

used gallium arsenide with gold eutectic mixture prepared on the surface at 

600°C. To obtain eutectic solution we spread gold thin film on a GaAs substrate 

and then annealed the sample in a nitrogen gas flow. Au-Ga droplets where 

formed in this way. The so-prepared substrate was used for growth of ZnO 

nanostructures in the ALD system. We applied deionized water and zinc 

chloride as an oxygen and zinc precursors, respectively. The eutectic mixture 

plays a role of a catalyst for the ZnO nanostructures growth. Au-Ga droplets 

flow on the front of growth forcing the growth of ZnO nanostructures. Optical 

and structural characterization was investigated by photoluminescence, scanning 

electron microscope (SEM) and atomic force microscope (AFM). SEM images 

show ZnO nanorods in a form of crystallites of up to 1 m length and 100 nm 

diameters. It is the first demonstration of ZnO nanostructures growth by ALD 

using VLS (vapour-liquid-solid) approach. 

The research was supported by the European Union within European Regional 

Development Fund, through grant Innovative Economy (POIG.01.01.02-00- 

008/08). 

50

40th _______________________________________________________________ 


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MoP14 _______________________________________________________________ 


Photoluminescence and chromaticity properties of ZnO nanopowders 

obtained by a microwave solwothermal method 

E. Wolska 1 , D. Sibera 2 , B.S. Witkowski 1 , S.A. Yatsunenko 1 , I. Pełech 2 , 

U. Narkiewicz 2 , M. Godlewski 1,3 

1 Institute of Physics, Polish Academy of Sciences, Al. Lotników 32/46, 

02-668 Warsaw, Poland 

2 Institute of Chemical and Environment Engineering, West Pomeranian University of 

Technology, K. Puławskiego 10, 70-322 Szczecin, Poland. 

3 Dept. of Mathematics and Natural Sciences College of Science, 

Cardinal S. Wyszy ski University, Dewajtis 5, 01-815 Warsaw, Poland 

ZnO is one of the most intensively studied wide band gap semiconducting material. 

Different applications of ZnO in transparent electronics, optoelectronics, photovoltaics 

and spintronics were demonstrated recently, which explains the increasing interest in this 

material. Moreover, new applications in medicine and biology are predicted. It is claimed 

that ZnO nanopowders can be used as luminescence markers for such applications. 

Luminescence markers are promising materials to be used for early recognition of many 

of diseases, including cancer. 

In the present work we discuss growth and properties of ZnO nanopowders obtained by a 

microwave solvothermal method. We compare properties of nanopowders obtained by 

two methods. In the first process as a zinc precursor we used zinc nitrate hexahydrate 

(Zn(NO3)2 6H2O) dissolved in distilled water. In the second process we used zinc nitrate 

hexahydrate and ethanol. For each of these two processes we performed growth at five 

different values of pressure in the microwave reactor during the solvothermal synthesis. 

The so-obtained powders were studied as-grown or after annealing at 750 o C in the air 

atmosphere. 

Each type of the samples were characterized with photoluminescence, 

cathodoluminescence and their size was determined from SEM and XRD investigations. 

The growth processes were optimized to obtain the brightness light emission and, in some 

cases, the best chromaticity. The latter study was motivated by possibility of white color 

emission of ZnO upon UV excitation. 

We discuss relations between synthesis parameters in the solvothermal microwave 

processes and optical properties of the samples obtained. 

The research was partially supported by the European Union within European Regional 

Development Fund, through grant Innovative Economy (POIG.01.01.02-00-008/08). 

52

40th _______________________________________________________________ 


Technology and testing the mechanical properties of the 

InGaP/GaAs/InGaP microcantilevers 

Tomáš Ščepka, Dagmar Gregušová, Róbert Kúdela, Štefan Gaži and Vladimír 

Cambel 

Institute of Electrical Engineering, Slovak Academy of Sciences, Dúbravská cesta 9, SK- 

84104 Bratislava, Slovakia 

Microcantilevers are at the heart of atomic force microscopes and also perspective for 

future chemical and biological sensing applications. Most of the commercially produced 

cantilevers are made of silicon or silicon nitride. However, microcantilever probes based on 

III-V semiconductor materials and their heterostructures can be equipped with novel 

functionalities through the incorporation of electronic and opto-electronic devices designed 

directly on them. 

GaAs is the most used III-V material for cantilever probe development thanks to its 

optoelectronic properties, high mobility of electrons, sufficient mechanical properties and 

high piezoresistivity (values higher than those of silicon) [1]. Application of mature 

deposition methods, such as metal organic chemical vapor deposition, allows for the 

formation of sandwich layers whose thickness can be defined with extreme precision. 

This work is a first step towards sensors with improved sensitivity and integrability. 

We focus on the fabrication and initial mechanical testing of microcantilevers based on an 

InGaP/GaAs/InGaP heterostructure (Fig. 1.). The heterostructure consists of a GaAs layer, 

that determined the cantilever thickness. The layer is embedded between two InGaP etch-stop 

layers [2]. All layers are lattice matched to a thinned semi-insulating GaAs (100) substrate. 

The front-side patterning was accomplished using optical photolithography, Ar ion milling of 

InGaP layer, and wet chemical etching of GaAs. The substrate was at first thinned to ~250 µm 

and then cantilevers were released via back-side bulk micromachining in two solutions. The 

1H2SO4:8H2O2:1H2O mixture was used as a fast etchant 

which was followed by a finer 1H3PO4:2H2O2:8H2O 

etchant. The experimental cantilevers presented here 

were designed as simple rectangles, nominally 100-300 

µm long and 35-65 µm wide, with a thickness of 0.1, 0.2, 

0.5, 1, and 2 µm. We have investigated the influence of 

geometrical dimensions, especially thickness of GaAs 

layer, on the fabrication process and mechanical 

properties of the cantilevers. To determine the resonance 

frequencies, a detection system of an Atomic Force 

Microscope (NT-MDT NTEGRA) was used. The 

measured resonance frequencies of the cantilevers 

correspond with theoretical values. 

This work is the result of the ESF project implementation, CENTE - 2 nd stage, ITMS code 

26240120019, supported by the R&D Operational Program funded by the ERDF. 

[1] K. Hjort et al., J. Micromech. Microeng. 4, 1-13 (1994). 

[2] D. Gregušová et al., J. Micromech. Microeng. 20, 097001 (2010). 

53 

Figure 1. SEM micrograph of 

fabricated microcantilever.

MoP16 _______________________________________________________________ 


ZnO thin films of different crystalline structures grown on Si (100) 

substrates by reactive DC sputter deposition 

Michał A. Borysiewicz 1 , El bieta Dynowska 1,2 , Valery Kolkovsky 2 , Jan Dyczewski 2 , 

Eliana Kami ska 1 , Anna Piotrowska 1 

1 Institute of Electron Technology, Al. Lotników 32/46, 02-668 Warsaw, Poland 

2 Institute of Physics, Polish Acad. of Sci., Al. Lotników 32/46, 02-668 Warsaw, Poland 

ZnO is considered an advantageous material in the transparent electronics, 

optoelectronics and photovoltaics due to its wide band-gap of 3.37 eV and high exciton 

binding energy of about 60 meV. Most research on ZnO thin films is performed on layers 

deposited on sapphire substrates. The sapphire has the advantage of having a crystalline 

structure matching that of the ZnO, but also a disadvantage of a large lattice mismatch of 

~18%. Therefore, to grow high-quality ZnO thin films on sapphire substrates, buffer layers 

have to be introduced [1-3]. On the other hand, in order to enable the integration of electronic 

and optoelectronic elements on one chip and take advantage of the high quality, large wafer 

sizes and low price, ZnO growth on silicon (100) substrates should be studied, regardless of 

the lattice mismatch to ZnO. 

This work reports on the structure of thin ZnO films on Si (100) substrates deposited 

using room-temperature reactive DC sputtering from a Zn target in an Ar-O2 mixture. Films 

grown in several deposition processes are compared. The power fed to the Zn target was kept 

at 75 W and the total gas pressures and amounts of oxygen in the gas mixture were changed 

between the processes. The structure of the films was studied by means of X-ray diffraction in 

the -2 geometry and scanning electron microscopy of the surface as well as the crosssections. 

The stoichiometry was estimated using Rutherford backscattering spectrometry. 

Transport properties were determined through Hall effect measurements. The 

characterisations were carried out after deposition and after subsequent 15 minutes-long 

annealing processes in an RTP furnace in O2 flow at 400 o C, 600 o C and 800 o C. We found, that 

by varying the parameters of the growth accordingly, films with very different structures 

could be produced. In particular, growth in oxygen-poor conditions resulted in porous 

polycrystalline structures (Fig. 1) potentially suited for applications in chemical sensors or 

dye-sensitized solar cells and growth in oxygen-rich conditions led to the formation of dense 

columnar films (Fig. 2) which may be applied in LEDs. 

This study was partially supported by the European Union within European Regional 

Development Fund, through grant Innovative Economy (POIG.01.03.01-00-159/08, 

"InTechFun"). 

Fig. 1. Fig. 2. 

[1] B. Pecz et al., J. Appl. Phys. 100, 103506 (2006) 

[2] M.W. Cho et al., Semicond. Sci. Technol. 20, S13–S21 (2005) 

[3] M.A. Borysiewicz et al., Acta Phys. Pol. A 119, 333 (2011) 

54

40th _______________________________________________________________ 


Comparison of the valence band of amorphous and crystalline 

GeTe and (Ge,Mn)Te layers 

W. Knoff 1 , M.A. Pietrzyk 1 , B.A. Orłowski 1 , B. Taliashvili 1 , T. Story 1 , R.L. Johnson 2 

1 Institute of Physics, PAS, Al. Lotników 32/46, 02-668 Warsaw, Poland 

2 Institute of Experimental Physics, University of Hamburg, Luruper Chaussee 149, 

D-22761 Hamburg, Germany 

(Ge,Mn)Te belongs to the IV-VI family of diluted magnetic semiconductors and attracts 

considerable attention due to its ferroelectricity and carrier-induced ferromagnetism governed 

by the RKKY indirect exchange mechanism. GeTe is also known as a phase change material 

exhibiting at the nanosecond scale a transformation from an amorphous to a polycrystalline 

phase, accompanied by insulator to metal transition. In (Ge,Mn)Te layers this structural 

transformation results also in paramagnet to ferromagnet transition. The aim of this work is to 

compare electronic structure of amorphous (a-) and crystalline (c-) GeTe and Ge0.9Mn0.1Te 

semiconductors using resonant photoemission spectroscopy (RPES) method. 

GeTe and (Ge,Mn)Te layers were grown on BaF2 (111) substrates by molecular beam epitaxy 

technique using effusion cells with GeTe, Mn, and Te2. For the growth of amorphous and 

crystalline GeTe and (Ge,Mn)Te layers, the substrate temperature was kept at room 

temperature and at T=250 0 C, respectively. Mn content in the layers was determined by energy 

dispersive X-ray fluorescence analysis. No evidence of crystalline phases was found in 

a-GeTe and a-(Ge,Mn)Te layers by X-ray diffraction (XRD) measurements. GeTe and 

(Ge,Mn)Te layers deposited at higher temperature (T=250 0 C) grow epitaxially and are 

monocrystalline with [111] growth direction. For GeTe and (Ge,Mn)Te layers the 

photoemission spectra were measured in the photon energy range 45-60 eV. The three-peak 

structure related to 4p and 5p Te orbitals (about 2.6 eV), Ge 4s orbitals (7.6 eV), and Te 5s 

orbitals (12 eV) was experimentally observed in the valence band of both c-GeTe and a-GeTe 

[1-3]. The spectra obtained for c-(Ge,Mn)Te and a-(Ge,Mn)Te in the energy range 

corresponding to the transition from Mn 3p to Mn 3d states reveal the same structure of peaks 

and Mn 3d orbitals contribution at 4 eV. 

Intensity (arb.u.) 

a) 

c-GeTe 

a-GeTe 

hυ = 50 eV 

0 5 10 15 

Binding Energy (eV) 

0 5 10 15 20 25 

Binding Energy (eV) 

Fig.1 The valence band photoemission spectra of amorphous and crystalline GeTe (figure a) and (Ge,Mn)Te 

(figure b). The spectrum of (Ge,Mn)Te was measured at the energy corresponding to the Mn 3p-3d threshold. 

[1] N.J. Shevchik, J. Tejada, W.W. Langer, M. Cardona, Phys. Rev. Lett., 30 659 (1973). 

[2] B.J. Kowalski, M.A. Pietrzyk, W. Knoff, et al., Physics Procedia 3 1357 (2010). 

[3] M.A. Pietrzyk, B.J. Kowalski, B.A. Orłowski, et al., Acta Phys. Pol. A 112, 275 (2007). 

c-(Ge,Mn)Te 

a-(Ge,Mn)Te 

hν=51 eV 

This work was partially supported by the EC Network SemiSpinNet (PITN-GA-2008-215368). 

55 

Intensity (arb.u.) 

b)

MoP18 _______________________________________________________________ 


Local Structure Study of GaAs:Te Using Te K-edge X-ray Absorption Fine 

Structure. 

A. Pietnoczka 1 , R. Bacewicz 1 , T. Słupi ski 2 , S. H. Wei 3 , M. Jie 3 , J. Antonowicz 1 , 

T. Drobiazg 1 

1 Faculty of Physics, Warsaw University of Technology, ul. Koszykowa 75, 00-662 Warsaw, 

Poland 

2 Faculty of Physics, University of Warsaw, Ho a 69, Warsaw 00-681, Poland 

3 NREL, 1617 Cole Blvd., Golden, CO 80401, USA 

The annealing of heavily doped GaAs:Te can significantly change the value of the free 

electron concentration in a reversible manner. These changes of electrical properties are 

accompanied by the structural changes of GaAs:Te solid solution.[1] In this contribution we 

present an attempt to determine local changes around Te atoms for different states of the 

GaAs:Te crystals caused by the annealing corresponding to different electron concentrations. 

Extended X-ray Absorption Fine Structure (EXAFS) and X-ray Absorption Near Edge 

Structure (XANES) techniques have been employed to investigate the local structure around 

tellurium atom and its valence. Tellurium K-edge absorption has been measured in a 

fluorescence method at the X1 beamline in the HASYLAB. The samples were kept at the 

temperature of 80 K in order to minimize the thermal disorder. 

Various models of Te defect complex have been used to fit the data for low 

concentration state: VGa- TeAs complexes [2], TeAs+ TeAs pairs [1], as well as several DX-like 

configurations of tellurium. DX configurations have been calculated using density functional 

theory (DFT). The EXAFS and XANES spectra for different Te location have been simulated 

and compared with the experimental data. Multi-parameter fitting of the EXAFS data 

provided information on the local structure around Te (the bond lengths, the coordination 

numbers and Debye-Waller factor). The charge state of Te has been determined from the 

XANES data. The EXAFS and XANES were useful for ruling out the possibility of existence 

GaTe and Ga2Te3 precipitations. 

The XAFS results have been compared with the studies of structural disorder using the 

X-ray diffuse scattering. 

References: 

[1] T.Słupi ski, E.Zieli ska-Rohozi ska, Thin Solid Films 367, 227 (2000). 

[2] D.T.J. Hurle, J. Appl. Phys. 85, 6957 (1999). 

56

40th _______________________________________________________________ 


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MoP20 _______________________________________________________________ 


Investigation of thermal properties of AlGaAs/GaAs Quantum 

Cascade Lasers by thermoreflectance spectroscopy 

Małgorzata Iwi ska 1,2 , Dorota Pier ci ska 1 , Kamil Pier ci ski 1 , 

Anna Szerling 1 , Piotr Karbownik 1 , Maciej Bugajski 1,2 

1 Institute of Electron Technology, al. Lotników 32/46, 02-668 Warsaw, Poland 

2 Faculty of Physics, WUT, ul. Koszykowa 75, 00-662 Warsaw, Poland 

Abstract 

Quantum Cascade Lasers (QCLs) are semiconductor unipolar devices in 

which intersubband transitions of carriers lead to lasing. The QCL design’s 

characteristic feature is the active regions cascading scheme. The wavelength of 

emitted radiation in QCLs depends mainly on the width and the depth of quantum 

wells and to the less extend on the material. QCLs emit wavelengths within the 

infrared region of the spectrum and which covers most of molecules’ absorption 

bands. This makes them ideal sources for trace gases detection, air pollution 

monitoring, human’s exhaled breath monitoring or biomedical imaging. Most of 

QCL applications require devices operating at room temperature (RT), often in 

CW mode, which is not an easy task to achieve. 

For full exploitation of QCLs application potential understanding of 

thermal management in the devices is necessary. For CW RT operation the active 

region temperature has to be kept under control. Its value depends on such 

parameters as the pulse frequency, the pulse width, device mounting technology 

and the heat sink temperature. The excessive temperature of the active region 

causes escape of the electrons from the upper laser level to continuum states and 

thermal backfilling of the lower laser level, both processes deteriorating device 

performance by lowering the laser gain. 

The AlGaAs/GaAs QCLs investigated in this work are designed and 

fabricated at the Institute of Electron Technology in Warsaw [1]. The aim of the 

study was to determine the main factors influencing temperature rise in QCLs and 

to optimise their thermal properties. The measurements included temperature 

dependence of light current (I-V) characteristics and measurements of temperature 

distributions within devices. The latter were obtained by spatially resolved 

thermoreflectance measurements [2,3], which is the technique allowing for high 

resolution temperature mapping on working devices. 

1. K. Kosiel, M. Bugajski, A. Szerling, J. Kubacka-Traczyk, P. Karbownik, E. Pruszy ska- 

Karbownik, J. Muszalski, A. Łaszcz, P. Romanowski, M. Wasiak, W. Nakwaski, I. 

Makarowa, P. Perlin , Photonics Letters of Poland, vol.1, 16-18, (2009) 

2. M. Bugajski, T. Piwoñski, D. Wawer, T. Ochalski, E. Deichsel, P. Unger, B. Corbett, 

Materials Science in Semiconductor Processing, vol.9, 188-197 (2006) 

D. Wawer, T. J. Ochalski, T. Piwo ski, A. Wójcik-Jedli ska, M. Bugajski, H. Page, phys. 

stat. sol. (a) 202, 1227–1232 (2005) 

58

40th _______________________________________________________________ 


Luminescence properties of Sm 3+ in different phases of TiO2 

P. Łach 1 , M. G. Brik 2 , I. Sildos 2 , A. Kamińska 1 , and A. Suchocki 1,3 

1 

- Institute of Physics, Polish Academy of Sciences, al. Lotników 32/46, 02-668, Warsaw, 

Poland 

2 

- Institute of Physics, University of Tartu, Riia 142, Tartu 51014, Estonia 

3 

- Institute of Physics, Kazimierz Wielki University, Weyssenhoffa 11, Bydgoszcz 85-072, 

Poland 

Titanium dioxide (TiO2) belongs to the wide-gap (3.0-3.2 eV) semiconductors and it 

has a very good performance as a photocatalyst and an oxygen sensor. Recently, it has been 

considered as a host suitable for doping with rare (RE) ions. In particular, samarium-doped 

titania reveals interesting phenomena like intense host-emission, high sensitivity of the 

emission on the ambient gas and enhanced photocatalytic activity [1]. 

We have carried out studies of the photoluminescence of Sm 3+ -doped TiO2 within the 

temperature range 10 – 300 K in order to show the energy levels of the trivalent impurity ion 

in two different phases of titania. The anatase TiO2 crystallizes in I41/amd space group, in a 

tetragonal structure, the lattice parameters are equal to 3.7850 and 9.5140 Ǻ. The rutile TiO2 

crystallizes in the P42/mnm space group and lattice parameters are equal to 4.593 and 2.959 

Ǻ. In order to obtain crystalline titania powder in both of these two phases our samples were 

annealed: up to 700°C and at 1100 °C for anatase and rutile phases, respectively. Thanks to 

that we have obtained a maximum of Sm emission intensity [2], which depends on the 

ambient around the samples. The best luminescence signals were observed during the 

measurements in the atmospheric oxygen. We have used the over band-gap excitation in both 

cases. The PL intensity of rutile titania was much lower than in the corresponding anatase 

TiO2 at room temperature. In the two cases we have also observed the PL spectra at low 

temperatures. Unfortunately in argon atmosphere our samples have not given any signals. 

An example of PL spectrum of Sm 3+ in TiO2 at room temperature under the band-toband 

excitation of the anatase structure is presented below. 

PL intenity [au] 

0,007 

0,006 

0,005 

0,004 

0,003 

0,002 

0,001 

0,000 

6 H7/2 

6 H5/2 

6 H9/2 

6 H11/2 

500 550 600 650 700 750 

Wavelength [nm] 

Sm 3+ in anatase TiO 2 

λ exc = 325 nm 

T=300K 

In order to check the influence of high pressure on the photoluminescence properties 

of both phases titanium oxide doped with Sm we have used the intra-center excitation (488 

nm) in a diamond anvil-cell at low temperature. Pressure coefficients of the various 

luminescence lines were established. Pressure dependence of the crystals field parameters f 

Sm 3+ ions were calculated on this basis. 

Acknowledgements: This work was partly supported by the European Union within European Regional 

Development Fund, through the Innovative Economy grant POIG.01.01.02-00-108/2009/3 

References: 

[1] M.G. Brik et al., Physica B 405 (2010) 2450-2456 

[2] V. Kiisk et al., J. Phys. D: Appl. Phys. 42 (2009) 125107 

59

MoP22 _______________________________________________________________ 


Investigation of electro-optical properties of 2D macroporous silicon 

structures with surface nanocrystals 

Lyudmila A. Karachevtseva a , Stepan Ya. Kuchmii b , Oleg A. Lytvynenko a , 

Fedor F. Sizov a , Olena J. Stronska a , Alexandr L. Stroyuk b 

a V. Lashkaryov Institute of Semiconductor Physics of NASU, Kyiv, Ukraine 

b L.V. Pisarzhevskii Institute of Physical Chemistry of NASU, Kyiv, Ukraine 

One of the perspective materials for the development of 2D photonic structures is 

macroporous silicon that can be obtained by the method of photoanodic etching. In view of 

the potential barrier on a macropore surface or heterojunction on «macropore-nanocoating» 

boundary, one should take into account processes on the local surface centres at energies 

below that of the indirect interband transition. 

Optical absorption in 2D photonic macroporous silicon structures was investigated 

taking into account the linear electro-optical effect. The spectral dependence of optical 

absorption in the near-IR area (impurity absorption) has oscillating structure and varies under 

the “3/2” law at long wavelengths. This correlates with frequency dependence of the 

imaginary part of permittivity for optical transitions between impurity levels and the allowed 

bands of a crystal in an electric field (the impurity Franz-Keldysh effect) [1]. The 

experimental absorption spectra of macroporous silicon agree well with the corresponding 

spectral dependences of the electro-optical energy and the imaginary part of permittivity in 

the weak electric field approximation, thus confirming realization of the impurity Franz- 

Keldysh effect. The electric field of the reflected electromagnetic wave at the grazing angle of 

light incidence onto macropore surface changes effectively a local surface electric field. 

The near-IR light absorption oscillations for 2D macroporous silicon structures with 

microporous silicon and as well as CdTe, ZnO surface nanocrystals were investigated taking 

into account electro-optical effect within the strong electric field approximation. Wellseparated 

oscillations with one order amplitude at spectral ranges of the surface bonds were 

observed. An analysis of the experimental absorption spectra is carried out within the model 

of the resonant electron scattering on impurity states in the strong electric field with 

difference between two resonant energies equaled to Wannier-Stark ladder [2]. The model of 

the resonant electron scattering on impurity states in an electric field of heterojunction 

«silicon-nanocoating» on macropores surface and the realization of Wannier-Stark effect on 

the randomly distributed surface bonds were considered. The Wannier-Stark ladders are not 

destroyed by impurities due to the longer scattering lifetime relatively the oscillation period 

of an electron in an external electric field at all investigated spectral region for macroporous 

silicon structures with CdTe and ZnO surface nanocrystals. 

[1] L.A. Karachevtseva, V.I. Ivanov, O.O. Lytvynenko, K.A. Parshin, O.J. Stronska, Appl. 

Surf. Sci. 255(5), 3328 (2008). 

[2] L. Karachevtseva, S. Kuchmii, O. Lytvynenko, F. Sizov, O. Stronska, A. Stroyuk, Appl. 

Surf. Sci. 257, 3331 (2011). 

60

40th _______________________________________________________________ 


Investigation of multi-phonon excitations in 

ZnO textured crystalline films by Raman spectroscopy 

George V. Lashkarev 1 , Anatoliy M. Yaremko 2 , Vitaliy A. Karpyna 1 

1 I.N.Frantsevich Institute for Problems of Material Science, National Academy of Sciences of 

Ukraine, 3 Krzizhanovsky st., Kyiv, Ukraine 

2 V.E.Lashkarev Institute for Semiconductor Physics, National Academy of Sciences of 

Ukraine, 45 Prospect Nauky, Kyiv, Ukraine 

ZnO is a direct bandgap semiconductor (Eg = 3.37eV at RT) which has got much 

attention due to its ability to generate ultraviolet (UV) radiation. A large binding energy of 

excitons (~60 meV) favors to excitonic transitions at room and higher temperatures. Besides 

ZnO has a strong enough constant of electron- (exciton) phonon interaction (EPI) what 

promtes 8-9 phonon replicas observed in Raman spectrum of this crystal. Investigation of 

photoluminescence (PL) and Raman scattering (RS) spectra are essential for understanding 

the mechanism of light generation and absoorption. In the series of papers the phonon replicas 

in ZnO were revealed in PL and Raman investigations but without theoretical consideration. 

ZnO films were deposited by radio frequency reactive magnetron sputtering on sapphire 

(0001) substrate. To grow textured films of high structural perfectness we used layer-by-layer 

growth mode described in [1]. This growth mode was realized by several stage of deposition 

at which next ZnO layer grow on the previously grown one, in result, ZnO films of improved 

quality is formed. The resonant Raman scattering is a powerful method for the investigation 

of elementary excitations in crystals. Raman measurements were carried out in backscattering 

geometry (z(x,x)z� polarization at which z direction oriented parallel to the c-axis) at room 

temperature using Horiba Jobin Yvon T64000 system, equipped with an Olympus confocal 

optical microscope. The experiment was performed in the wavenumber range from 200 to 

5000 cm -1 with a spectral resolution < 2 cm -1 . 

Multi-phonon structure of RS spectra can be 

Intensity, arb.units 

50 

40 

30 

20 

10 

A LO 

1 

ZnO:Cu/sapphire 

2A LO 

1 

3A LO 

1 4ALO 

5A 

1 

LO 

1 

7A LO 

1 

6A LO 

1 

8A LO 

1 

0 

0 

0 1000 2000 3000 4000 5000 

Raman shift, cm -1 

50000 

40000 

30000 

20000 

10000 

Intensity, arb. units 

Fig.1. Comparison of 

experimental RS spectra 

(curve 1) of ZnO:Cu film with 

calculated one (curve 2). 

1 

2 

explained in the frames of theoretical approach developed 

in [2]. To consider the RS we have to study the response 

of the system on electromagnetic field in the second order 

of perturbation theory. Fig.1 shows experimental RS 

spectrum and theoretical result. It is seen that positions of 

maxima of experimental spectrum are well enough 

described by theoretical dependences. In particular, we 

can see that number of maxima is eight, which is 

practically the same as for good quality bulk crystal [3]. 

The numerical calculations show also that character of 

spectrum, i.e. the number of maxima and distribution of 

intensity different line is very sensitive to constant of EPI. 

The theoretical consideration allows determining 

following main parameters, described LO phonons in RS: 

energy �LO=72 meV, constant of EPI �� 0,1 = 0.2 eV, damping constant � = 10 meV. 

[1] A.I. Ievtushenko, V.A. Karpyna, V.I. Lazorenko, et.al., Thin Solid Films 518 4529 (2010) 

[2] Yaremko A.M., V.M. Dzhagan, V.O. Yukhymchuk, et.al., J. Mol. Struct., 976 205 (2010) 

[3] J. F. Scott, Phys. Rev. B, 2 1209 (1970) 

The authors are grateful to V. Strelchuk for Raman measurements of ZnO films 

61

MoP24 _______________________________________________________________ 


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Properties of high-k oxides grown by Atomic Layer Deposition method for 

transparent electronics 

S. Gierałtowska 1 , Ł. Wachnicki 1 , B.S. Witkowski 1 , T.A. Krajewski 1 , M. Godlewski 1,2 , 

E. Guziewicz 1 

1 Polish Academy of Sciences, Institute of Physics, al. Lotników 32/46, Warszawa 02-668, 

Poland 

2 Cardinal Stefan Wyszynski University, College of Science, Department of Mathematics and 

Natural Sciences, Warszawa, Poland 

Transparent electronics is nowadays an emerging technology for the next generation of 

electronic structures, including IC (integrated circuit), recent devices with 45nm node and 

smaller cross-bar memories and transistors for e-paper applications. The essential materials 

used in semiconductor manufacturing processes are high-k oxides gate dielectrics. The 

introduction of high-k for gate dielectrics is one of several strategies allowing further 

miniaturization of microelectronic components, colloquially referred to as extending the 

Moore's Law. 

Our research was focused on the optimization of technological parameters for composite 

layers of high-k oxides that include hafnium oxide (HfO2) and aluminum oxide (Al2O3). We 

obtain high quality thin films using Atomic Layer Deposition at low temperature (60°C – 

150°C). Growth parameters are elaborated for the maximum smoothness and amorphous 

microstructure required for gating. To fabricate thin film transistors (TFTs) and active 

elements of cross-bar memories, we deposit ZnO (zinc oxide) as an active channel and high-k 

oxides as gate dielectric at low temperature, both grown by the ALD technique. I-V 

characteristics of our TFT structure will be shown. The combination of low temperature and 

transparency processing makes the ZnO-TFT with high-k dielectric very promising for the 

next generation of invisible and flexible electronics. 

The research was partially supported by the European Union within European Regional 

Development Fund, through grant Innovative Economy (POIG.01.01.02-00-008/08). 

65

MoP28 _______________________________________________________________ 


High Spin-Low Spin Transitions in Cu0.2Co0.76Cr1.83Se4 Semiconductor 

E. Maciążek 1 , T. Groń 2 , A.W. Pacyna 3 , T. Mydlarz 4 and J. Krok-Kowalski 2 





4 International Laboratory of High Magnetic Fields and Low Temperatures, 

ul. Gajowicka 95, 53-529 Wrocław, Poland 

Electrical and magnetic studies carried out on single-crystalline CuxCoyCrzSe4 spinels 

showed ferromagnetic ordering and p-type metallic conductivity for y = 0.06, 0.1 and 0.11 as 

well as a ferrimagnetic behaviour and n-type electrical semiconductivity for y = 0.23 [1]. 

Later, structural and electrical investigations carried out on polycrystalline Cu1-xCoxCr2Se4 

spinels in the compositional range 0.0 ≤ x ≤ 1.0 revealed a transformation from cubic to 

monoclinic structure above x = 0.4 as well as metallic-type conductivity with high values of 

activation energy for x ≤ 0.5 and polaron semiconducting with low activation energy for x ³ 

0.8 [2]. Recently, X-ray diffraction studies on the single phase Cu1-xCoxCr2Se4 samples (x = 0, 

0.2, 0.8, 1) proved the existence of the cubic spinel-type structure for x ≤ 0.2 and the 

monoclinic Cr3S4-type one for x ³ 0.8 [3]. Magnetization and magnetic susceptibility of the 

CuxCoyCrzSe4 polycrystals measured in the zero-field-cooled mode showed a transition from 

ferromagnetic order via ferrimagnetic one to antiferromagnetic-like behaviour with increasing 

Co content. This transition was accompanied with a lowering symmetry from cubic to 

monoclinic and for the latter the spin crossover phenomenon occurred [4]. 

Magnetization, dc and ac magnetic susceptibility of Cu0.2Co0.76Cr1.83Se4 were measured 

in the zero-field-cooled mode using a vibrating sample magnetometer with a step motor at 4.2 

K and in applied external magnetic fields up to 150 kOe, a Faraday type Cahn RG automatic 

electrobalance in the temperature range 4.2-370 K and at 800 Oe, and a Lake Shore 7225 ac 

' 

" 

susceptometer, respectively. The in-phase c 1( 

T) 

and out-of-phase c1( T) 

components of the ac 

fundamental susceptibility were recorded in the temperature range 4.2-170 K simultaneously 

as a function of temperature in an oscillating field Hac = 1 Oe with frequency of 120 Hz. The 

signals of the second (c2) and third (c3) harmonics associated with nonlinear susceptibilities 

were detected as a function of temperature using an oscillating field of 5 Oe with frequency of 

120 Hz without the applied external magnetic field. 

' 

Two spectacular peaks were observed on the c1( T) 

curve at 128 K and 147 K which 

corresponded to the strong fall of the dc magnetic susceptibility. At the same temperatures 

these peaks were observed on the curves of the second and third harmonics of magnetic 

susceptibility. Taking into account also a low value of the magnetization of 0.22 µB/f.u. at 4.2 

K and at 140 kOe as well as a hysteresis between 15 kOe and 60 kOe one can conclude that in 

the Cu0.2Co0.76Cr1.83Se4 semiconductor the high spin-low spin transitions may be populated 

and cross over in thermal equilibrium. 

[1] T. Groń, E. Maciążek, J. Heimann, J. Kusz, I. Okońska-Kozłowska, K. Bärner, and Ch. 

Kleeberg, Physica B 254, 84 (1998). 

[2] E. Maciążek, A. Molak, and T. Goryczka, J. Alloys Compd. 441, 222 (2007). 

[3] V. Svitlyk, and Y. Mozharivskyj, Inorg. Chem. 48, 5296 (2009). 

[4] E. Maciążek, T. Groń, A.W. Pacyna, T. Mydlarz, B. Zawisza, and J. Krok-Kowalski, Acta 

Phys. Pol. A 119, (2011). 

66

40th _______________________________________________________________ 


Photoluminescence Study of ZnSe Scintillating Crystals Doped with 

Isovalent Tellurium and Oxygen 

D. Shevchenko 1 , J. Mickevi ius 1 , G. Tamulaitis 1 

N. Starzhinskiy 2 , K. Katrunov 2 , V. Ryzhikov 2 

1 Institute of Applied Research and Semiconductor Physics Department, 

Vilnius University, Sauletekio Ave. 9-III, LT-10222 Vilnius, Lithuania 

2 Institute for Scintillation Materials, 60 Lenin Ave., 61001 Kharkov, Ukraine 

Recently, zinc selenide has attracted considerable attention as a promising scintillating 

material for ionizing radiation detection. Compared to conventional CsI(Tl) scintillators, 

ZnSe –based scintillators have these advantages: considerably lower hygroscopicity, lower 

afterglow level, high light yield, and higher radiation stability (by 3 to 4 orders of magnitude). 

Thus, scintillators based on ZnSe semiconducting compounds are an attractive choice for 

applications in medical and industrial tomography, X-ray introscopy and many others. 

Operating photoemission band in the ZnSe scintillators results from optical transition 

involving deep-defect states. Deep-level-related radiative recombination efficiency can be 

improved by doping with isovalent impurities and subsequent thermal annealing in Zn vapor. 

Introduction of the isovalent impurities promote formation of thermally stable complex 

defects, which act as radiative recombination centers. Subsequent annealing in Zn vapor 

enhances the concentration of the complex defects. Therefore it is important to understand 

radiative and non-radiative recombination mechanisms and their relation with the crystal 

growth conditions. 

The study of deep-level-related photoluminescence was carried out in the ZnSe crystals 

doped with isovalent tellurium and oxygen. Doping of ZnSe by Te was accomplished by 

mixing tellurium into the melt for crystal growth. Two methods of doping with oxygen were 

used: ZnSe(O) sample was doped with O by annealing finelly ground row material in oxygenrich 

atmosphere, while ZnSe(O, Al) sample was doped with oxygen by mixing Al2O3 into the 

melt for crystal growth. Undoped ZnSe samples were also studied for reference. After growth, 

all the samples under study were annealed in Zn vapor in identical conditions. 

Photoluminescence (PL) spectra were measured under steady-state conditions using CW 

He-Cd laser as an excitation source. The wavelength dependence of the absolute quantum 

yield was measured using an integrating Ulbricht sphere. Monochromated light of a halogen 

lamp was used for PL excitation. 

It was determined that photoluminescence quantum yield depends on excitation photon 

energy. The quantum yield rapidly decreases when the excitation photon energy is increased 

above the ZnSe band gap. The highest quantum yield (~ 22 %) is observed in the sample 

doped with tellurium and annealed in Zn vapor. The quantum yield of this sample was by a 

factor of 2 higher than that in other crystals. The observed dependence of the quantum yield 

on excitation wavelength is explained by nonradiative carrier recombination on crystal surface 

and direct excitation of donor-acceptor pair luminescence in ZnSe crystal volume. 

The study of PL spectra showed that the deep–level–related photoemission efficiency 

can be also enhanced by doping with oxygen. PL intensity of ZnSe(O, Al) scintillating crystal 

is by a factor of 16 higher than that of ZnSe(O) scintillator. The photoluminescence spectra 

consist of two strongly overlapped bands due to recombination via M- and SA-type complex 

defects. Annealing results in an increase of PL intensity by factor of ~3 and a red-shift of the 

PL band, compared with those in unannealed crystals. 

67

MoP30 _______________________________________________________________ 


Native Deep-Level Defects in MBE-Grown p-Type CdTe 

Karolina Olender, Tadeusz Wosiński, Andrzej Mąkosa, Piotr Dłużewski, 

Valery Kolkovsky and Grzegorz Karczewski 

Institute of Physics, Polish Academy of Sciences, 02-668 Warsaw, Poland 

We present results of investigation of deep-level defects in p-type CdTe layers grown by 

the molecular-beam epitaxy (MBE) technique. The CdTe layers of 5 µm thickness were doped 

with nitrogen and grown on (001)-oriented p+-type, Zn-doped GaAs substrate. Prior to 

deposition of the investigated CdTe:N film, the GaAs substrate was covered with thin, 3monolayer-thick, 

undoped ZnTe layer to reduce the strong lattice mismatch between CdTe and 

GaAs and to stabilize the growth in the [001] direction. 

Deep-level transient spectroscopy (DLTS) was used to identify a set of deep electronic 

states in the band gap of p-CdTe layer employing Schottky barriers, obtained by sputtering 

aluminum. Room-temperature free carrier concentration in the CdTe layers was 

2.4 × 10 16 cm -3 , as found from capacitance–voltage measurements recorded at a frequency of 

1 MHz. 

DLTS measurements, carried out in the temperature range from 90 to 400 K, showed 

five hole traps, at low concentrations of the order of 10 13 cm -3 , called H1 to H5. Explicit 

saturation of the dependence of DLTS-signal amplitude on the filling-pulse time was observed 

for the H2 and H3 traps. They were characterized by the exponential kinetics of carrier 

capture, which means that the observed DLTS peaks originate from isolated point defects or 

impurities. The H2 trap, with the activation energy for hole emission of 0.46 eV, most likely is 

the same trap, which we observed as a minority-carrier trap in n-type CdTe:I layer [1]. We 

attributed this trap to the Cd vacancy, VCd. The H3 trap, with the activation energy of 0.75 eV, 

has been tentatively ascribed to the complex formed of VCd and the Te antisite defect, TeCd. 

In the case of H1 and H4 traps the dependence of DLTS-signal amplitude on the filling- 

pulse time, observed over the range of four orders of magnitude of the time, was logarithmic. 

It suggests that the observed traps are related to the hole states of dislocations. Thorough 

analysis of the dependence of DLTS-peak shape on the filling time allowed us to determine 

the type of electronic states associated with these dislocations. The H1 trap, with the 

activation energy of 0.22 eV, is characteristic of localized states. On the other hand, the H4 

trap, with the activation energy of 0.49 eV, was assigned to the bandlike states of dislocations. 

Probably, an electron emission from the same dislocation states was observed in our DLTS 

experiments for n-type CdTe:I epitaxial layers [1]. We attributed both the H1 and H4 traps to 

threading dislocations, generated at the mismatched interface with the substrate and 

propagated through the CdTe layer. 

Finally, the H5 trap, displaying the logarithmic capture kinetics, has been associated 

with acceptor states at the CdTe surface. We observed a strong influence of electric field on 

the DLTS-peak position of this trap and its apparent activation energy. Measurements of the 

electric-field dependences of hole emission rates, performed at various temperatures, allowed 

us to determine the mechanism responsible for the field-induced enhancement of hole 

ionization rate from the traps as the phonon-assisted tunnelling. 

This work has been partially supported by the Polish Ministry of Science and Higher 

Education under Grant No. N N515 0719 37. 

[1] K. Olender, T. Wosinski, A. Makosa, S. Kret, V. Kolkovsky and G. Karczewski, Semicond. 

Sci. Technol. 26, 045008 (2011). 

68

40th _______________________________________________________________ 


Residual Paramagnetism at High-Temperature Semiconductors 

CuEu2W2O10 and Cu3Eu2W4O18 

P. Urbanowicz 1 , E. Tomaszewicz 2 , T. Groń 1 , H. Duda 1 and Z. Kukuła 1 


2 West Pomeranian University of Technology, Department of Inorganic and Analytical 

Chemistry, Al. Piastów 42, 71-065 Szczecin, Poland 

CuEu2W2O10 and Cu3Eu2W4O18 were synthesized by the solid-state reaction method 

using CuWO4 and Eu2WO6 as the starting materials. The CuEu2W2O10 and Cu3Eu2W4O18 

compounds crystallize in the monoclinic and triclinic system, respectively [1]. Copper 

tungstate, CuWO4, belongs to the triclinic distorted wolframite type structure [2–4] in which 

every metal ion is surrounded by six oxygen ions. It has a potential technological significance 

(scintillation detectors, optical fibres). Thin film of CuWO4 is expected to be a promising 

positive electrode material for high-performance rechargeable lithium batteries [5,6]. On the 

other hand, doped and undoped rare-earth metal molybdates and tungstates (e.g., Eu2WO6) are 

host candidates for luminescent applications. They are used for a fabrication of white lightemitting 

diodes showing high stability, energy-saving and safety [7,8]. In the case of Eu2WO6 

narrower multiplet widths comparable to the thermal energy cause a weak temperature 

dependence of the magnetic susceptibility without the Curie-Weiss region as well as a low ntype 

conduction [9]. 

The magnetic susceptibility of the powder compounds under study was measured in the 

temperature range 2-300 K in the applied external magnetic fields H = 5 kOe using a SQIUD 

Magnetometer of the Quantum Design MPMS – XL – 5 type. The electrical resistivity has been 

measured by a four-probe dc method using the apparatus with Keithley K181 digital 

multimeters. The thermoelectric power was measured by a differential method using the 

temperature difference of about 2 K. For electrical measurements the powder samples were 

compacted to disc form (10mm in diameter and 1–2 mm thick) using a pressure of 1.5GPa 

and they were next sintered through 2 h at 873 K. 

The electrical and magnetic measurements of CuEu2W2O10 and Cu3Eu2W4O18 showed a 

residual paramagnetism, i.e. a low value of the magnetic susceptibility and its weak 

temperature dependence as well as a semiconducting behaviour at high temperatures. We 

have also found that the effective magnetic moment increases gradually from 0.5 µB at 2 K to 

5 µB at 300 K, suggesting a transition from the low spin (LS) state of Eu 3+ ions to their LS and 

high spin (HS) mixed states, as the effective number of Bohr magnetons (peff = 9.80 for S = 3, 

HS) has not been reached. It means that only 50 % conversion of the molecules from LS to 

HS occurred. This work is partly founded from science Grant No. N N209 336937. 

[1] E. Tomaszewicz, J. Typek, and S.M. Kaczmarek, J. Therm. Anal. Calorim. 98, 409(2009). 

[2] L. Kihlborg, and L. Gebert, Acta Crystallogr. B 26, 1020 (1970). 

[3] S. Klein, and H. Weitzel, J. Appl. Crystallogr. 8, 54 (1975) (in German). 

[4] P.F. Schofield, K.S. Knight, S.A.T. Redfern, and G. Cressey, Acta Crystallogr. B 53, 102 

(1997). 

[5] L.G. Van Uitert, and S.T. Preziosi, J. Appl. Phys. 33, 2908 (1962). 

[6] R.H. Gillette, Rev. Sci. Instrum. 21, 294 (1950). 

[7] S. Neeraj, N. Kijima, and A.K. Cheetham, Chem. Phys. Lett. 387, 2 (2004). 

[8] T. Kim, and S. Kang, J. Lumin. 122–123, 964 (2007). 

[9] P. Urbanowicz, E. Tomaszewicz, T. Groń, H. Duda, A.W. Pacyna, and T. Mydlarz, Physica 

B 404, 2213 (2009). 

69

MoP32 _______________________________________________________________ 


Ferromagnetic nanocomposite Co-Al2O3 as a spintronic material with 

engineered magnetic properties 

M.V. Radchenko 1 , G.V. Lashkarev 1 , M.E. Bugaiova 1 , V.I. Sichkovskyi 1 , 

V.I. Lazorenko 1 , L.A. Krushynskaya 2 ,Y.A. Stelmakh 2 , W. Knoff 3 , T. Story 3 

1 I.M. Frantsevych Institute for Problems of Material Science, National Academy of Sciences 

of Ukraine, 3 Krzhizhanovskogo str., Kyiv, Ukraine 

2 E.O.Paton Electric Welding Institute, Academy of Sciences of Ukraine, 68 Antonowich str., 

Kyiv, Ukraine 

3 Institute of Physics, Polish Academy of Sciences, Al. Lotników 32/46, Warsaw, Poland 

Ferromagnetic cobalt nanoparticles (NP) embedded in alumina matrix constitute a new class 

of two-phase spintronic materials - ferromagnetic nanocomposites (FMNC). FMNC attract 

attention as artificially developed materials permitting efficient engineering of their magnetic 

and magnetotransport properties These materials are closely related to inhomogeneous diluted 

magnetic semiconductors containing ferromagnetic clusters. In this work, we study magnetic 

and electrical characteristics of Cox(Al2O3)100-x (x

40th _______________________________________________________________ 


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71

MoP34 _______________________________________________________________ 


Van der Waals surface of InSe as a standard nanorelief in the metrology of 

nanoobjects 

Dmitriev A. I. 

. I. M. Frantsevich Institute for Problems of Material Science, National Academy of 

Sciences of Ukraine, Krzhizhanivskogo st. 3, 03680 Kyiv, Ukraine, FAX: +38424-2131. 

E-mail: dmitr. kiev@gmail.com 

Development of new high technologies and new materials leading to the fundamental 

improvment of the technical level of production largely dependents on the level of metrological 

support. Intensive development of nanotechnology requires high-precision measurements on 

atomic and molecular levels by creating the metrological system for measurements, at the first 

turn, the length in the nanometer scale. Such measurements require standard samples of 

nanorelief surface. 

At present, the nanorelief surface of highly oriented pyrolytic graphite (HOPG) is used for 

this purpase. Simultaneously with the scanning of an unknown surface the scan of the well- 

known surface of graphite (the period of the hexagonal crystal lattice: a = 2,464 ± 0,002 Ǻ) is 

carried out. Software recognition of atoms image of the graphite allows to generate a control 

signal for correcting the microscope manipulator. When cleaving HOPG many stages with 

dimensions less than 2x2 mm are formed. They are used as a model of nanorelief They appear 

at fracture of graphite planes, oriented not toward cleavage. Graphite planes have structural 

defects associated with dislocations. Different types of dislocations manifest themselves in the 

topography of the surface in many ways. Over time, the accumulation of the adsorbate on the 

surface, results in poor quality images. 

Semiconductor InSe belongs to a group of layered compounds A3B6.Each layer of this 

crystal consists of atomic groups Se-In-In-Se with strong covalent bonds in the layer. Se atoms 

of neighboring layers are linked by weak Van der Waals (VdW) forces and form VdW surface. 

High chemical stability and the absence of dangling bonds (defects) prevents the appearance of 

the adsorbat. Low surface roughness of cleaved surface at the areas up to 5x5 mm allows to 

use the VdW surface of InSe single crystals as the standard nanorelief. This is evidenced by 

the researches of morphology for VdW surface by scanning tunneling microscopy [1] in which 

images with atomic resolution were obtained. A single crystal InSe, grown by vertical 

Bridgman-Stockbarger method. The crystal has -g-polytype rhombohedral structure . with 

periods a = 4.003 Å, and c = 24.9553 Å (in hexagonal axes). 

Thus InSe is appropriate standard nanorelief for probe microscopy. 

1. Physics of the Solid State,53, 3, 622 (2011). 

72

40th _______________________________________________________________ 


Crystal field analysis of the Yb 3+ energy level scheme in III-V 

semiconductors 

A. Kami�ska 1 , C.-G. Ma 2 , M.G. Brik 2 , A. Kozanecki 1 , M. Bo�kowski 3 , E. Alves 4 , 

A. Suchocki 1,5 

1 Institute of Physics, Polish Academy of Sciences, 02-668 Warsaw, Poland 

2 Institute of Physics, University of Tartu, Riia 142, Tartu 51014, Estonia 

3 Institute of High Pressures Physics ‘Unipress’, Polish Academy of Sciences, 01-142 Warsaw, 

Poland 

4 Instituto Tecnologico e Nuclear, Estrada Nacional 10, 2686-953 Sacavém, Portugal 

5 Institute of Physics, University of Bydgoszcz, Weyssenhoffa 11, 85-072 Bydgoszcz, Poland 

Rare earths (RE) doped semiconductors are nowadays attracting a lot of attention due 

to their unique optical and electrical properties and high potential of these materials in new 

optoelectronic device applications, for instance in electrically-pumped light-emitting diodes 

or lasers [1]. Among the RE doped III–V semiconductors InP:Yb is one of the most 

intensively studied material. Recently an important effort has been devoted also to study the 

optical properties of ytterbium doped GaN [2, 3]. These materials reveal strong Yb-related 

luminescence at about 1 �m. Yb 3+ ions (4f 13 electron configuration) have a simple energy 

level scheme, which consists of two states only: 2 F7/2 and 2 F5/2 separated by about 

10 000 cm -1 . Such a scheme excludes excited state absorption and all related energy losses. 

From this point of view, Yb 3+ ion is now the most promising for use as a non-Nd lasing center 

in the infrared spectral region. 

In the present work we report on combination of the high-pressure measurements with 

use of diamond anvil cell (DAC) of the luminescence spectra of InP:Yb 3+ and GaN:Yb 3+ 

crystals with ab initio calculations of the electronic and optical properties of these systems. 

The CASTEP module [4] of the Materials Studio was used to calculate the electronic and 

optical properties at ambient and elevated pressure. In addition, crystal field analysis of 

splitting of the 2 F7/2 and 2 F5/2 states has been performed, with an aim of assigning all features 

of the experimental luminescence spectra. 

A thorough analysis of the pressure behavior of the Yb 3+ luminescence lines in InP 

reveals interesting effects, namely: after 6 GPa blue shift of the luminescence tends to 

saturation, which was explained by pressure-induced shift of the InP valence band 

approaching the energies of the Yb 4f-4f transitions. This overlap behaves exactly as the 

luminescence lines with pressure. An analysis of the pressure dependence of the Yb 3+ 

luminescence in GaN and fitting the trigonal crystal field Hamiltonian to the experimental 

data allowed to determine the ambient pressure values of crystal field parameters, spin orbit 

parameter and their pressure coefficients. 

Acknowledgements: This work was partly supported by the European Union within 

European Regional Development Fund, through the Innovative Economy grant 

(POIG.01.01.02-00-108/2009/2) and the project No. N N202 203838 of Polish Ministry of 

Science and Higher Education. 

References: 

[1] J. H. Park et al., J. Appl. Phys. 98, 056108 (2005). 

[2] W.M. Jadwisienczak et al., Opt. Mater. 23, 175 (2003), 

[3] T. Koubaa et al., J. Alloys Compd. 496, 56 (2010). 

[4] M. D. Segall et al., J. Phys.: Condens. Matter 14, 2717 (2002). 

73

MoP36 

_______________________________________________________________ 


Studies of Electric Transport Properties of Single Layer Devices 

Based on the Polyazomethine Thin Films 

J. Weszka, M. Domański, J. Jurusik, B. Hajduk, M. Chwastek, 

and H. Bednarski 

Centre of Polymer and Carbon Materials, Polish Academy of Sciences, 34 M. 

Curie-Sk̷lodowska Str., 41-819 Zabrze, Poland 

Organic semiconductors (OS) have been known since a many years for their great potential 

applications in opto-electronic devices. Among the conjugated polymers, poly(pphenylenevinylene) 

(PPV) and its derivatives (like MEH-PPV) belong to the family 

of more extensively studied OSs and are known as revealing good properties for optoelectronic 

applications. Poly (p-phenyleneazomethine) (PPI), much less known and studied 

polymer than PPV, being its iso-elctronic counterpart and having nearly the same 

electronic structure, though containing nitrogen atoms in the backbone, has appeared to 

be very promising for optoelectronic applications, too [1,2]. 

Single-layer organic devices have been produced based on chemical vapour deposited, 

in a homemade technological set-up [3]. Polyazomethine thin films were grown via polycondensation 

process of aromatic diamine and dialdehyde and sandwiched between metal 

electrodes with different work functions. The choice of the electrodes has appeared to 

influence greatly the device properties. For these reasons various pairs of electrode materials 

were used from ITO, Al and Au in order to check practically conditions of Schottky 

barrier formation and their applicability for photovoltaic devices. Metallic electrodes were 

thermally evaporated under vacuum of 10 −6 Tr, otherwise glass substrates covered with 

ITO layer were used. 

To verify quality of the as-prepared devices current-voltage characteristics have been 

taken as well as measurements of the current dependence on time were performed. Results 

have been analysed in terms of the unified device model for single layer organic light 

emitting diodes or photovoltaic cells with charge injection, transport and space charge 

effects [4]. The model describes both injection limited and space charge limited current 

flow and the transition between them. Determined by us relatively high value of the 

Schottky barrier height (higher then 0.5 eV) suggests that the current flow in the asprepared 

devices is injection charge limited, which is further supported by the net injected 

charge being relatively small. Therefore, for small bias voltage in the injection limited 

regime the thermionic emission is the dominant injection mechanism. 

Relatively low currents density, in comparison to those reported for PPV, recorded 

for our studied PPI based devices is attributed to the presence of surface states on the 

side of high work function electrode rather than to steric differences in the backbones of 

the two polymers. This is consistent with the results we obtained on MEH-PPV devices 

prepared for comparison reasons. 

[1] A. Iwan and D. Sek, Prog. Polym. Sci. 33 (2008) 289-345. 

[2] J. Weszka, H. Bednarski and M.Domanski, J. Chem. Phys. 131 (2009) 024901. 

[3] J. Weszka, M. Domanski, B. Jarzabek, J. Jurusik, J. Cisowski, A. Burian, Thin 

Solid Films 516 (2008) 3098. 

[4] P.S. Davids, I.H. Campbell, and D.L. Smith, J. Appl. Phys. 82 (1997) 6319. 

74

40th _______________________________________________________________ 


Optical properties of black silicon with precipitated silver and gold 

nanoparticles 

R. Jarimavi i t -Žvalionien 1 , I. Prosy evas 1 , Ž. Kaminskien 1 , S. Lapinskas 2 

1 Institute of Materials Science, Kaunas University of Technology, Savanoriu pr. 271, Kaunas, Lithuania 

2 Institute of Applied Research, Vilnius University, Sauletekio str. 10, Kaunas, Lithuania 

Black silicon (BS) is a new generation material which may be useful for many 

applications, such as lasers, gas sensors, solar cells and etc. Black silicon (BS) is a type of porous 

silicon with low light reflectance and high light absorbance values. BS layers are especially 

useful and important in solar energy conversion. Forming BS layers on silicon increase the 

effective area and light absorbance as well as solar conversion efficiency. Another new way to 

increase solar energy conversion is use surface plasmons, i.e., collective surface oscillations of 

conducting electrons in metal nanostructures that tend to trap optical waves near their surface. 

Plasmonics is a rapidly emerging subfield of nanotechnologies, which gives a possibility to 

control and guide light interaction with matter more effectively. Noble metals like silver and 

gold are ideal for this purpose as they do not have many interband transitions and do not absorb 

much light as a result. By combining black silicon with precipitated plasmonic nanoparticles in 

active layer has the potential to increase light interaction with matter more effectively and can 

revolutionary change the market of solar cells. 

Etching of silicon and formation of porous surfaces can be performed by many different 

methods. But the most simple in use is chemical metal assisted etching. In this work the porous 

silicon plates were prepared by wet chemical metal assisted method in a 1-minute single step 

liquid etch based upon catalysis by silver nanoparticles formed in a solution containing HF, V2O2 

and AgNO3. Processing time was reduced to 10 seconds by heating the samples at 80 o C. For 

synthesis of plasmonic nanoparticles silver nitrate (AgNO3) and chloroauric acid (HAuCl4) were 

used. 

Scanning electron microscope (SEM) analysis was done in order to evaluate the form and 

size of formed pores before precipitation of plasmonic nanoparticles and morphology of surface 

of porous silicon after precipitation. Optical properties of black silicon samples were investigated 

with UV-VIS and FTIR spectrometers and reflectance spectra were recorded during porous 

silicon formation at different times. 

SEM analysis of PS exhibited oval-shaped pores with Ø 150 – 200 nm and Ø 50 – 100 

nm in samples with longer and shorter processing times respectively. SEM analysis of BS with 

precipitated nanoparticles has revealed non-uniform distribution of gold and silver nanoparticles 

(Ø 70 - 150 nm) on BS surface and inside of pores. Reflectance analysis of BS has revealed that 

reflectance decreases with increase of processing time, herewith with pores depth, and increases 

after precipitation of nanoparticles in both cases. This phenomenon is still under investigation, 

but in general we can conclude, that formation of BS was successful and precipitation of 

nanoparticles on its surface gives a possibility to control reflectivity of BS surfaces and increase 

photo efficiency through enhanced plasmonic properties of gold and silver nanoparticles. 

75

MoP38 _______________________________________________________________ 


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76

40th _______________________________________________________________ 


Self-Compensation Mechanism in Semi-Insulating CdMnTe:Sn Crystals 

Intended for X/γ-Ray Detectors 

N.S. Yurtsenyuk, L.A. Kosyachenko, V.M. Sklyarchuk, 

O.L. Maslyanchuk, E.V. Grushko 

Chernivtsi National University, Optoelectronics Department, 58012 Chernivtsi, Ukraine 

Cd1-xMnxTe is a typical diluted magnetic semiconductor with the zinc-blende structure 

within the 0 < x < 0.77 range. Owing to its unique magnetic and magneto-optic properties, 

Cd1-xMnxTe crystals can be used in many device applications, such as Faraday rotators, 

optical isolators, solar cells, magnetic field sensors and substrates for the epitaxial growth of 

Hg1-xCdxTe and Hg1-xZnxTe [1]. More recently, Cd1-xMnxTe offers several potential 

advantages over Cd1-xZnxTe as a material for room-temperature X/γ-ray detectors [2,3] that 

are widely used in science, medicine, industry, environment monitoring and other fields. 

Cd1-xMnxTe has a wide range of tunability of the band gap due to the large compositional 

influence of manganese. The band gap range 1.7 eV to 2.2 eV, required for substantiating an 

“ideal” radiation detector performance, can be realized with a relatively low (< 50%) amount 

of Mn compared with that of Zn in Cd1-xZnxTe (up to 70%) [4]. In fact, the energy band gap 

of Cd1-xMnxTe increases about 13 meV per atomic percent of Mn compared with 6.7 meV of 

Zn in Cd1-xZnxTe. Another important advantage is that the segregation coefficient of Mn in 

CdTe is approximately 1 compared with 1.35 for Zn, that is, Cd1-xMnxTe crystals can have a 

more homogenous distribution of Mn throughout the ingot. These notable characteristics of 

Cd1-xMnxTe increase the possibility of growing uniform large-volume stoichiometric crystals 

that can potentially be fabricated into different high-quality devices. 

In this work we study the conductivity mechanism of Cd1-xMnxTe single crystals doped 

by Sn. It is known that the introduction of Sn in the CdTe, as well as in other II-VI 

semiconductors, accompanied by the formation of complexes and self-compensation of 

conductivity and leads to a semi-insulating state of the semiconductor, which is very 

important from the standpoint of its use in X/γ-ray detectors. We set a goal to find the 

ionization energy of the level responsible on electrical conductivity Ei of the material and the 

degree of its compensation ξ = Na/Nd. The band gap and its temperature dependence 

(necessary for calculations) were found from the optical transmission curves in the range of 

the absorption edge of semiconductor. Based on the experimental dependences of the 

electrical characteristics of the material and statistics of electrons and holes, we have 

succeeded in determining Ei and ξ. Such a degree of compensation reveals to be close to 

100%. This is a direct confirmation of self-compensation, which provides semi-insulating 

state of the semiconductor. It seems that the obtained results lead to the conclusions which are 

important for technology. 

[1] J.K. Furdyna, J. Appl. Phys. 64(4), R29 (1988). 

[2] A. Burger, K. Chattopadhyay, H. Chen, J.-O. Ndap, X. Ma, S. Trivedi, S.-W. Kutcher, R. Chen, 

and R.-D. Rosemeier. J. Cryst. Growth 198/199, 872 (1999). 

[3] A. Mycielski, A. Burger,M. Sowinska, M. Groza, A. Szadkowski, P. Wojnar, B.Witkowska, 

W.Kaliszek, and P. Siffert, Phys. Stat. Sol. (c) 2, 1578 (2005). 

[4] J.E. Toney, T.E. Schlesinger, and R.B. James, Nucl. Instr. & Meth., A428, 14 (1999). 

77

MoP40 _______________________________________________________________ 


Influence of Cu, Ga and Au Dopants and Technology Conditions on the 

Magnetic Interactions in HgCr2Se4 Single Crystals 

J. Krok-Kowalski 1 , G. Władarz 1 , T. Groń 1 , H. Duda 1 , A.W. Pacyna 2 , K. Nikiforov 3 and 

P. Rduch 1 

1 University of Silesia, Institute of Physics, ul. Uniwersytecka 4, 40-007, Katowice, Poland 



3 Physico-Mathematical Faculty, K. Tsiolkovski State Pedagogical University, 

St. Razin str. 26, Kaluga 248023, Russia 

It is well known, that in the ferromagnetic spinel compound HgCr2Se4 (where TC and 

CW are of order 100 K and 150 K respectively) the divalent Hg 2+ ions occupy tetrahedral 

positions only, whereas trivalent Cr 3+ ions are located only in octahedral positions. 

Ferromagnetic coupling of the magnetic moments in this compound is realized via 

superexchange magnetic interactions [1]. It is also well known, that the full substitution in the 

tetrahedral positions of the divalent Hg 2+ ions by the monovalent, e.g. Cu + ions, leads to both 

the mixed valence of the chromium ions (it means, Cr 3+ and Cr 4+ in the ratio 1:1) and to the 

appearance and domination of the another mechanism of the magnetic coupling giving very 

strong ferromagnetic coupling, namely double exchange interaction. In this case both TC and 

CW become of order of 400 K [2,3]. However, the substitution of the Hg 2+ ions by the 

trivalent ions, e.g. Ga 3+ , leads to the collinear antiferromagnetism being the result of the 

superexchange interaction only, with the concentration of Ga 3+ ions up to 50%. The one aim 

of this work is to investigate how influences the substitution of Hg 2+ ions by Cu + , Au 2+ and 

Ga 3+ ions on the magnetic ordering in the sample, when the concentration of the substituting 

ions is lower than 10 %. The another one concerns of the influence of technology conditions 

on magnetic ordering in the sample. 

Using the chemical transport method the single crystals of HgCr2Se4 doped with copper 

(7%), gallium (8%) and gold (2%) were obtained. Additionally, the two non doped single 

crystals of HgCr2Se4 were obtained, in different synthesis conditions. One of them was 

synthesized with the deficiency of Hg (this procedure the produces vacancies), another one 

with Hg excess (this procedure brings to elimination of vacancies). For all crystals under 

study both the dc and ac magnetic susceptibility was measured in the temperature range of 

4.2 – 250 K. The dc measurements were carried out with the use of the Cahn magnetic 

balance and SQUID susceptometer, whereas the ac measurements were carried out with the 

use of the Lake Shore 7225 magnetometer. 

As it follows from the obtained results, substitution monovalent Cu + ions and divalent 

Au 2+ ions in place of Hg 2+ ions causes the increase of the Curie temperature in comparison 

with the Curie temperature of undoped HgCr2Se4. Substitution of Hg 2+ ions by trivalent Ga 3+ 

ions causes the lowering of TC. On the other hand, ZFC and FC measurements of the 

magnetic susceptibility shows that in the samples containing Cu + and Ga 3+ some trace 

frustration of magnetic interactions in spite of their ferromagnetic ordering occurs. Similar 

effect have been observed for single crystal synthesized with the deficiency of Hg. The latter 

effect is caused by the occurrence of vacancies generated in the sample by the technological 

process. 

[1] P.K. Baltzer, P.J. Wojtowicz, M. Robbins, and E. Lopatin, Phys. Rev. 151, 367 (1966). 

[2] F.K. Lotgering, Proc. Int. Conf. on Magnetism, Nottingham England, (1964) 533. 

[3] J. Krok, J. Spałek, J. Juszczyk, and J. Warczewski, Phys. Rev. B 28, 6499 (1983). 

78

40th _______________________________________________________________ 


The Photodetectors with Vertical Integration Based on ZnO Films 

A.I. Ievtushenko 1 , G.V. Lashkarev 1 , V.I. Lazorenko 1 , Zs.J. Horvath 2,3 , M.G. Dusheyko 4 

1 Frantsevich Institute for Problems of Materials Science, NASU, Kyiv, Ukraine 

2 Research Institute for Technical Physics and Materials Science, HAS, Budapest, Hungary 

3 Institute of Microelectronics and Technology, Budapest, Hungary 

4 National Technical University of Ukraine “KPI”, Kyiv, Ukraine 

ZnO is a wide-band (Eg 3.3 eV) direct-gap material which attracts a great attention to 

the development of the photodetectors for near-ultraviolet range. It is an electronic analog of 

GaN, but ZnO have economic and ecological benefits in comparison with GaN. There are 

many papers devoted to the formation detectors of a planar configuration [1]. One of the 

promising directions of microelectronics is the development and study of devices with a 

vertical structure. The reason is that in this vertical configuration of electrodes the 

interelectrode distance can be easily reduced without using expensive lithography processes. 

Therefore, the purpose of this report is devoted to the study of technological aspects for the 

deposition of ZnO films as well as the investigation of the photoelectrical properties of 

structures with vertical configuration of the electrodes. 

Early we reported the positive role of nitrogen in ZnO for UV detectors [2]. Therefore, 

the undoped and nitrogen doped ZnO films with different concentrations of the nitrogen were 

deposited by magnetron sputtering on n-Si and ITO/glass substrates. Structural and optical 

properties of the films were examined by XRD, EDX and optical measurements. Aluminum 

as ohmic contact to Si and Ni as Schottky contact to ZnO were deposited by electron beam 

evaporation with thickness control. Ni/ZnO/n-Si/Al and Ni/ZnO/ITO layered structures of 

photodetectors were obtained. Current-voltage curves of photodiodes were studied in dark and 

under visible and UV irradiations using Keithley-236 Source Measure Unit. Features of the 

current-voltage characteristics and leakage current mechanisms are discussed. It was found an 

increase of photosensitivity with increasing nitrogen concentration in nitrogen doped ZnO 

films for all types of vertical structures. The maximum enhancement of reverse current under 

UV irradiation was two orders of magnitude. The influence of deposition technology of ZnO 

films on the photoelectrical properties of detectors as well as the effect of nitrogen 

incorporation will be presented. Prospects for the application of ZnO photodetectors with 

vertical integration and requirements for their design will be discussed. 

[1] K. Liu, M. Sakurai, M. Aono Sensors, 10, pp.8604-8634 (2010). 

[2] A.I. Ievtushenko, G.V. Lashkarev, V.I. Lazorenko, et al. Phys. Stat. Sol. ( ), 207, 7, pp. 

1746–1750 (2010). 

79

MoP42 _______________________________________________________________ 


Features of the Properties for Nitrogen Doping and Al-N Codoping of ZnO 

Films 

A.I. Ievtushenko 1 , G.V. Lashkarev 1 , V.I. Lazorenko 1 , O.Y. Khyzhun 1 , L.O. Klochkov 1 , 

O.I. Bykov 1 , V.M. Tkach 2 , V.A. Baturin 3 , A.Y. Karpenko 3 


2 Bakul Institute for Superhard Materials, Kyiv, Ukraine 

3 Institute of Applied Physics, Sumy, Ukraine 

Now zinc oxide is almost the most investigated material in the world because of its 

physical, ecological and economic benefits which make it promising one for photonic, 

optoelectronic and acoustooptic devices, etc. However the properties of ZnO films strongly 

depend on the concentration of various defects appearing at the stages of film growth and 

further processes in as-grown ZnO films. 

The nitrogen in ZnO is an acceptor impurity and widely used in attempts to obtain 

stable p-type conductivity in ZnO. However, based on our previous studies, we think that 

nitrogen doping leads to the passivation of oxygen vacancies of ZnO and therefore increase 

the photosensitivity, response speed and stability of photodetectors on their basis. Little 

known fact is the effect of increasing the concentration of nitrogen in ZnO films on their 

physical properties by using the increase of nitrogen pressure in the chamber at magnetron 

deposition. It is promising to investigate the way of increasing of nitrogen solubility in ZnO 

by using Al-N codoping. 

ZnO:N films with different nitrogen concentration were deposited on Si, SiNx and 

quartz substrates by magnetron sputtering using Zn, Zn:0.7%Al and Zn:1.4%Al targets. The 

investigations of XRD, AFM, PL, X-ray photoelectronic and EDX spectroscopy were carried 

out. In this report the influence of different types of nitrogen doping on the transformation of 

the structure, optical properties and morphology of ZnO:N films will be presented. 

80

40th _______________________________________________________________ 


Influence of Oxygen Pressure on the Properties of AZO Films 

A.I. Ievtushenko 1 , G.V. Lashkarev 1 , V.I. Lazorenko 1 , L.O. Klochkov 1 , O.I. Bykov 1 , 

O.M. Kutsay 2 , S.P. Starik 2 , V.A. Baturin 3 , A.Y. Karpenko 3 


2 Bakul Institute for Superhard Materials, Kyiv, Ukraine 

3 Institute of Applied Physics, Sumy, Ukraine 

New oxide materials are very attractive for replacement of existing traditional ones in 

various fields of electronics and optoelectronics. Particularly the problems of creation the 

transparent conductive electrodes based on them attract more attention. 

The major drawback of widely-used ITO is a limited world reserve of indium. 

Opposite to ITO, zinc oxide has ecological and economical benefits and its components are 

widely distributed in Earth. Therefore, doped with aluminum (AZO), gallium (GZO) or 

indium (IZO) ZnO films are the best suited candidates to replace ITO. The development of 

technology for deposition of transparent conductive electrodes based on AZO films will have 

the commercial future. 

Therefore the high quality aluminum doped ZnO films were deposited on glass 

substrates by layer by layer deposition method at a magnetron sputtering of Zn:1.4%Al target. 

The report presents the results of oxygen pressure influence on structural, morphological, 

electrical and optical properties of AZO films. It is demonstrated that optimal oxygen pressure 

of 0.03 Pa in the deposition chamber leads to the following AZO films characteristics: the 

resistivity is about 10 -3 Ohm cm, transparency - 95% and roughness - 6 nm. Our results on 

investigation of AZO films magnetron deposition technology will be discussed as well as the 

prospects of their applications. 

81

MoP44 _______________________________________________________________ 


Thermoelectric Power of CuCrxVySe4 p-Type Spinel Semiconductors 

H. Duda 1 , E. Malicka 2 , T. Groń 1 , A. Gągor 3 , R. Sitko 2 , J. Krok-Kowalski 1 and P. Rduch 1 



3 Institute of Low Temperature and Structure Research, Polish Academy of Sciences, 

ul. Okólna 2, 50-950 Wrocław, Poland 

Detailed studies of the thermoelectric power, electrical conductivity, structural and 

magnetic properties carried out on polycrystalline CuCrxVySe4 spinels with x = 1.79, 1.64 and 

1.49 and y = 0.08, 0.22 and 0.45, respectively, are presented. Powder samples of the 

CuCrxVySe4 spinel series were prepared by annealing stoichiometric mixtures of high purity 

( 99.99 %) elements: Cu, Cr, V and Se. A precise atomic content determination of each 

sample with the aid of the energy-dispersive X-ray spectrometry (EDXRF) showed that the 

polycrystals of the CuCrxVySe4 spinel system revealed the cation deficiencies in the 

octahedral sites because x + y 

y 

2. A Rietveld refinement of the spinels under study was done 

using an X'Pert PRO X-ray diffractometer and a Jana-2000 program package. The electrical 

conductivity has been measured with the four-probe dc method using the apparatus with 

Keithley K181 digital multimeters. The thermoelectric power was measured with a 

differential method using the temperature gradient T of about 2 K. The electrical and thermal 

contacts between the sample and the copper rods were maintained with a silver lacquer 

mixture (Degussa Leitsilber 200). Magnetization and magnetic susceptibility were performed 

using a Faraday type Cahn RG automatic electrobalance at magnetic field up to 7 kOe. The 

electrical and magnetic measurements were done in the temperature ranges 77-432 K and 77- 

550 K, respectively. 

All the compounds under study crystallize in regular system of a normal spinel type 

MgAl2O4 structure with the space group symmetry Fd3m. With increasing V content a lattice 

parameter slightly increases from 1033.66(4) pm for y = 0.08 to 1033.71 (5) for y = 0.45 

while the positional anion parameter decreases from 0.2574(3) for y = 0.08 to 0.2568(3) for y 

= 0.45. The CuCrxVySe4 spinels are ferromagnets for that a Curie temperature TC and a 

paramagnetic Curie-Weiss temperature decrease as the V content increases, i.e. from TC = 

406 K and = 383 K for y = 0.08, via TC = 351 K and = 380 K for y = 0.22 via to TC = 282 

K and = 277 K for y = 0.45. The electrical conductivity measurements revealed the change 

of the hole conductivity character from the semiconductive into the metallic one close to TC. 

The thermoelectric power analysis was done with the aid of the modified Matoba, Anzai and 

Fujimori semi-empirical formula [1] including magnetic contribution [2]. The results of 

thermopower analysis of the spinels under study show that the intensity of the magnon drag 

component is smaller in comparison with the single crystal sample of comparable V-content 

[2]. The magnon excitations, usually driven by the double exchange mechanism, are observed 

only at low temperatures. At higher temperatures the contribution to total thermopower 

originates mainly from the phonon component. At high temperatures, the diffusion component 

dominates and, according to the Mott formula, it is proportional to temperature. The non-zero 

value of the so-called impurity component of the thermopower described by the T 1/2 law 

suggests the presence of cation deficiencies in the octahedral sites. 


[1] M. Matoba, S. Anzai, and A. Fujimori, J. Phys. Soc. Jpn. 63, 1429 (1994). 

[2] E. Malicka, T. Groń, D. Skrzypek, A.W. Pacyna, D. Badurski, A. Waśkowska, S. Mazur, 

and R. Sitko, Philos. Mag. 90, 1525 (2010). 

82

40th _______________________________________________________________ 


Critical Behaviour of the 3D-Heisenberg Ferromagnetic 

Semiconductors CdxCeyCr2Se4 

H. Duda 1 , P. Rduch 1 , E. Malicka 2 , T. Groń 1 and A. Gągor 3 



3 Institute of Low Temperature and Structure Research, Polish Academy of Sciences, 

ul. Okólna 2, 50-950 Wrocław, Poland 

The pure CdCr2Se4 end member of the CdxCeyCr2Se4 spinel system combines the p-type 

semiconducting and ferromagnetic properties with a Curie temperature TC = 142 K and a 

Curie-Weiss temperature qCW = 190 K [1]. Magnetization of CdCr2Se4 reaches the full 

saturation of 5.98 µB per molecule [2] and the ferromagnetic properties are the result of 

dominance of large and positive the nearest-neighbour Cr-Cr interactions [3]. Various 

theoretical models of the critical phenomena, the mean-field, the three-dimensional (3D) 

Heisenberg, the 3D-Ising and the tricritical mean-field model used to explain the critical 

properties showed that the CdCr2Se4 was in best accordance with the 3D-Heisenberg model 

for which the critical exponents: β = 0.36, γ = 1.38 and δ = 4.8 [4,5]. 

The CdxCeyCr2Se4 spinel single crystals under study have a normal cation distribution, 

the Cd and Ce ions being located at the tetrahedral sites, while the Cr ions at the octahedral 

ones. Electrical and magnetic measurements revealed the semiconducting properties and a 

ferromagnetic order with TC = 132 K which insensibly decreases as the Ce content increases 

as well as a strong reduction of magnetic moment from 5.8 µB for y = 0.03 to 1.93 µB for y = 

0.13. The critical exponents of CdxCeyCr2Se4 single crystals were studied by measuring 

isothermal dc-magnetization around the paramagnetic-ferromagnetic (PM-FM) phase 

transition. Isothermal magnetization was measure with the aid of a Quantum Design System 

(MPMS XL) in the magnetic field up to 20 kOe and in the temperature range 125-140 K. 

The critical exponents (TC, β, γ and δ) were determined by analyzing the magnetization 

data in terms of various research techniques including modified Arrott plot [6], Kouvel-Fisher 

method [7], and critical isotherm analysis. Here β and γ are the critical exponents for the 

temperature dependence of the spontaneous magnetization just below TC and inverse initial 

susceptibility just above TC, respectively. In addition, the critical exponent δ is determined 

separately from the isothermal magnetization at TC. The critical exponent values are found to 

be consistent with the Widom scaling relation δ = 1 + γ/β, implying the critical exponents are 

reliable. The critical exponents characterizing the PM-FM transition are: β = 0.367 ±0.013, γ 

= 1.389 ±0.025 and δ = 4.763 ±0.043 at TC = 131 K for the sample Cd0.96Ce0.03Cr2Se4 and β = 

0.350 ±0.003, γ = 1.202 ±0.026 and δ = 4.487 ±0.095 at TC = 134 K for the sample 

Cd0.84Ce0.13Cr2Se4. These values of critical exponents concerning CdxCeyCr2Se4 system are 

close to the theoretical ones predicted by the 3D-Heisenberg model for CdCr2Se4. 


[1] P.K. Baltzer, H.W. Lehmann, and M. Robbins, Phys. Rev. Lett. 15, 493 (1965). 

[2] R.C. LeCraw, H. von Philipsborn, and M.D. Sturge, J. Appl. Phys. 38, 965 (1967). 

[3] P.K. Baltzer, M. Robbins, and P.J. Wojtowicz, J. Appl. Phys. 38, 953 (1967). 

[4] L. Zhang, J. Fan, L. Li, R. Li, L. Ling, Z. Qu, W. Tong, S. Tan, and Y. Zhang, A Letters 

Journal Exploring the Frontiers of Physics (EPL) 91, 57001 (2010). 

[5] W. Zarek, Acta. Phys. Pol. A 52, 657 (1977). 

[6] A. Arrott, and J.E. Noakes, Phys. Rev. Lett. 19, 786 (1967). 

[7] J.S. Kouvel and M.E. Fisher, Phys. Rev. Lett. 136, A1626 (1964). 

83

MoP46 _______________________________________________________________ 


Optical properties of ZnO/ZnMgO single quantum wells grown by 


J.M. Sajkowski, M.A. Pietrzyk, D. Dobosz, M. Stachowicz, A. Droba, E.Przezdziecka, 

A.Wierzbicka, A. Kozanecki, 

Institute of Physics Polish Academy of Sciences, Al. Lotników 32/46 02-668, Warsaw, Poland 

In this work the high quality ZnMgO layers and ZnO/ZnMgO quantum wells (QWs) showing 

no phase separation were grown on (0001) sapphire substrates. ZnMgO layers and 

ZnO/ZnMgO heterostructures were grown at temperatures 445 - 460°C. No specific buffer 

layers were deposited on sapphire. Prior to growth the substrates were annealed in the growth 

chamber in oxygen (p=1,4*10 -5 Torr) at 600° C, and then a ~100 nm ZnMgO (Mg contents 10 

- 20%) barrier layer was grown. Then the growth was interrupted for couple of minutes and 

after this a ZnO wells with different thicknesses were grown. Finally, ZnMgO capping layers 

of the same composition as the ZnMgO barrier were deposited. After growth the structures 

were characterized using X-ray diffraction for the analysis of their crystalline quality and 

AFM was used for surface morphology studies. AFM images revealed very good flatness of 

the surface – rms value was 1-2 nm. 

We present results of optical spectroscopy for a series of ZnO/ZnMgO single quantum wells 

of different widths using photoluminescence. Temperature dependent PL spectra were 

measured within a temperature range of 4-300K. We observed a blue shift of excitonic 

emission in comparison with bulk ZnO values which demonstrates quantum confinement in 

the ZnO wells with thicknesses smaller than 4 nm. We also demonstrate that excitonic 

emission from QWs is dominated by excitons bound to donors. The characteristic energy of 

PL decay of the dominant excitonic lines agrees well with the values of localization energies 

of excitons to donor centers. For wider ZnO wells the quantum confined Stark effect shifts the 

PL spectra below the band gap of ZnO. This is a direct consequence of the very large built-in 

electric field developed in ZnO/ZnMgO QWs grown along the polar c-direction. 

Acknowledgement: Work supported in part within European Regional Development Fund, 

through grant Innovative Economy (POIG.01.01.02-00-008/08). 

84

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Electronic structure of CdTe/PbEuTe/CdTe 

B.A. Orlowski 1 , S. P. Dziawa 1 , A. Reszka 1 , K. Gas 1 , S. Mickievicius 2 , S. Thiess 3 , 

W. Drube 3 . 

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Top part of the semiconductor nanostructure CdTe/Pb0.95Eu 0.05Te/CdTe with Pb0.95Eu 0.05Te 

buried under thin layer of CdTe (the layer transparent for part of photoemitted electrons) was 

studied with application of High Energy X-ray Photoemission Spectroscopy. The Energy 

Distribution Curves (EDC) corresponding to the valence band and core levels electrons of the 

buried layer and top cover CdTe layer were measured with application of synchrotron 

radiation of high energy h = 3510eV to obtain big escape depth of electrons photoemitted 

from buried layer. The measured peaks corresponding to the buried layer atoms were 

observed in the valence band region and in the high binding energy region for core levels 

Pb4f, Pb3d and Eu 3d. For top cover layer the contribution of valence band, Cd4d and 

Cd3d core levels were obtained. Measured Te4d, Te 3d and Te4d spectra possesses 

contribution as well from buried as from the top cover layer. 

The nanostructure was grown by MBE deposition method in the Institute of Physics, Polish 

Academy of Sciences in Warsaw [1]. The CdTe buffer layer was evaporated on GaAs wafer 

and Pb0.95Eu0.05Te layer of 6nm thick, evaporated on it. The layer of Pb0.95Eu 0.05Te was 

covered by CdTe layer of thickness 22 nm. The structure was exposed to the air and 

photoemission spectra were performed ex situ using the Tunable High Energy X-ray 

Photoemission Spectrometer at HASYLAB, Hamburg [2]. After sputtering of CdTe top layer 

the photoemission signal of buried layer elements remarkably increases (see Fig.1, Pb5d). 

Main parameters of the electronic structure of CdTe/Pb0.95Eu 0.05Te/CdTe were determined. 

Intensity [a. u.] 

1 . 4 

1 . 2 

1 . 0 

0 . 8 

0 . 6 

0 . 4 

0 . 2 

0 . 0 

C d T e / P b E u T e / C d T e 

H I G H E N E R G Y X P S 

h ν = 3 5 1 0 e V 

S p u t t e r i n g 

2 n d 

1 s t 

n o 

v b 

C d 4 d 

P b 5 d 

T e 4 d 

- 1 0 0 1 0 2 0 3 0 4 0 5 0 

B i n d i n g E n e r g y [ e V ] 

Fig.2. Set of EDC’s of the valence band, Cd4d, Pb5d and Te4d electrons region and measured after following 

steps of cleaning of the sample by sputtering CdTe 22nm top layer. 

The authors acknowledge support by MSHE of Poland research Projects DESY/68/2007 and by the European 

Community FP6 Programme "Integrating Activity on Synchrotron and Free Electron Laser Science" at DESY. 

1. M. Szot, L. Kowalczyk, E. Smajek, V. Domukhovski, J. Domagała, E. Łusakowska, B. Taliashvili, 

P. Dziawa, W. Knoff, W. Wiater, T. Wojtowicz, T. Story, Acta Phys. Pol. 114, 1397 (2009). 

2. Th. Eickhoff, V. Medicherla, W. Drube, Jour.Electr. Spectr.Rel. Phen. 137-140, 85-88 (2004) 

orbro@ifpan.edu.pl 

85 

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86

40th _______________________________________________________________ 


Multi-interface layered P-doped silicon structures for third generation 

photovoltaics 

Mikael Hosatte 1 , Marek Basta 1 , Bartłomiej S. Witkowski 2 , Zbigniew T. Kuznicki 

1 and Marek Godlewski 2 

1 Photonic Systems Laboratory, Pole Api, Blvd. Sebastien Brandt, 67414 Illkirch- 

Graffenstaden, France 

2 Institute of Physics, Polish Academy of Sciences, Al. Lotnikow 32/46, 02-668 Warszawa, 

Poland 

Nanoscale Si-layered systems represent an attractive way to enlarge optical and electrical 

functions in Si optoelectronic, photonic and PV technology. Physical interactions transform 

the initial Si material to a new Si-based metamaterial. The device architecture also plays a 

role in specific nonlinear features. The seemingly paradoxical behavior requires a better 

insight into understanding the mechanisms determining the macroscopic performance. We 

report here some specific optical and electrical properties resulting from the complexity of 

different test structures. Optoelectronic properties of nanostructured materials can differ 

greatly comparing to those of bulk, or even thin film. The complexity of low-dimensional 

interactions renders impossible to directly use the description of the phenomena developed for 

previous device generations [1]. This is particularly true for Multi-interface Novel Devices 

(MINDs) which results mainly from the superposition of a PN junction [2], a nanoscale 

system [3] and a multi-interface architecture. In MINDs, whose collection efficiencies have 

been improved since the first generation, the buried substructure is presented as a 

metamaterial layer because it exhibits physical properties different than bulk silicon. In 

particular, it allows low energy-carrier multiplication. 

a) b) 

Figure 1. Architecture of MIND test structure (a) and SEM measurement showing buried nanoscale 

substructure as well as metamaterial layer (b) 

[1]P. Havu, V. Havu, M.J. Puska, M.H. Hakala, A. Foster, and R.M. Nieminen, “Finiteelement 

implementation for electron transport innanostructures”,J.Chem. Phys.124, 054707 

(2006) 

[2]C.T Sah, R.N. Noyce, W. Shockley, Proc. IRE 45, 1228 (1957). (2001). 

[3]Z. T. Kuznicki, Multi-interface novel devices, model with a continuous substructure, “3 rd 

Generation Photovoltaics for High Efficiency through Full Spectrum Utilization”, ed. A. 

Luque& A. Marti (Institute of Physics Publishing, Bristol, UK, 2003) pp. 165-195. 

87

MoP50 _______________________________________________________________ 


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88

40th _______________________________________________________________ 


ZnO-based Nanotubes Obtained by the Oxidation of ZnTe 

and ZnTe/Zn Nanowires 

K. Gas 1* , E. Dynowska 1 , E. Janik 1 , A. Kami ska 2 , S. Kret 1 , J.F. Morhange 3 , 

I. Pasternak 4 , M. Wiater 1 , W. Zaleszczyk 1 , R. Hołyst 2 , E. Kami ska 4 , T. Wojtowicz 1 , 

W. Szuszkiewicz 1 

1 Institute of Physics PAS, Al. Lotników 32/46, Warsaw, Poland 

2 Institute of Physical Chemistry, PAS, ul. Kasprzaka 44/52, Warsaw, Poland 

3 Institut des Nanosciences de Paris, UMR 7588, UMPC, 4 Place Jussieu, Paris, France 

4 Institute of Electron Technology, Al. Lotników 32/46, Warsaw, Poland 

One-dimensional (1D) semiconductor nanostructures like, e.g., nanowires (NWs) or 

nanobelts recently attracted a great deal of attention due to their potential application in 

electronic and optoelectronic nanodevices. Among many materials ZnO is particularly 

intensively studied due to its wide, direct energy gap (3.37 eV at 295 K) and large exciton 

binding energy of 60 meV. The non-intentionally doped ZnO usually exhibits n-type 

conductivity and it is difficult to convert it to p-type. The lack of p-type ZnO is the major 

obstacle in possible device applications of this material. Contrary to ZnO, ZnTe can be 

relatively easy highly p-type doped. Moreover, as it was already shown thermal oxidation of 

nitrogen-doped ZnTe allows to obtain p-type ZnO [1], therefore one possible way to produce 

p-type, ZnO-based NW structure would be through the oxidation of p-type ZnTe NWs. In this 

paper we report a successful fabrication of the ZnO-containing nanotubes obtained by thermal 

oxidation. For this purpose MBE-grown ZnTe and ZnTe/Zn core/shell NWs were oxidized by 

annealing in flowing O2 gas using both a rapid thermal annealing apparatus and a furnace. 

Some samples were annealed in flowing Ar gas for a comparison. 

Scanning and transmission electron microscopy (SEM and TEM, respectively) 

demonstrated tubular character and some changes in the NWs’ morphology after the oxidation 

process. The TEM analyses also revealed that the nanotubes are built of small ZnO and TeO2 

crystallites with random crystallographic orientations. The average inner diameter of the 

nanotubes is about 40 nm whereas their outer diameter can reach up to 100 nm (measured in 

the central part of the NW). We determined the chemical composition of the samples using 

energy dispersive X-ray spectroscopy. Complementary information on the structure properties 

of the NWs was obtained by X-ray diffraction, the optical properties of the NWs were also 

investigated by Raman scattering. The influence of the technological conditions on the 

evolution of the nanostructures is shown and discussed. The results of our studies suggest that 

the most probable mechanism of formation of such tubular nanostructures consists of two 

major steps. Firstly, the ZnTe is partially decomposed by the reaction with oxygen both at the 

surface of the NW and along its axis at the center of the NWs. Due to very fast oxygen 

diffusion along the [111] direction a creation of a cavity starts in the central part of the NW. 

Next, the Zn from the surface produce the ZnO shell and the remaining Te aggregate into 

small nanocrystals, which decorate the hollow inner part of the ZnO NW [2] or (after an 

oxidation) form TeO2. 

The studies were partially supported by the European Union within European 

Regional Development Fund, through grant Innovative Economy (POIG.01.01.02-00-008/08). 

* Corresponding author, e-mail address: kgas@ifpan.edu.pl 

[1] E. Prze dziecka et al., Semicond. Sci. Technol. 22, 10 (2007). 

[2] P. Lu, D.J. Smith, phys. stat. sol. (a) 107, 681 (1988). 

89

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Composition-dependentthermalresistanceofmultilayeredstructurestakingintoaccountphononreflection,scatteringandtunneling. 

DariuszŻak 1,2 ,WłodzimierzNakwaski 2 

1 InstituteofElectronTechnology, 

al.Lotników32/46,02-668Warsaw,Poland. 

2 PhotonicsGroup,InstituteofPhysics,TechnicalUniversityofLodz, 

ul.Wolczanska219,90-924Lodz,Poland. 

Abstract 

Developmentinthesynthesisandprocessingofnanoscaledevicescreatesthe 

demandtopredicttheirthermalproperties.Nowadays,superlatticestructures 

arebasecomponentsoflightemittingandlightdetectingdevicesinmiddleof 

infra-redspectrumrange.Thermalpropertiestakeimportantplaceindesigning 

process.Heatspreadinginmultilayersstructuresismuchdifferentthanthatin 

bulkmaterials.Mainpartofheattransportinthosestructures,isgovernedby 

thephonontransport.Thepresenceofmultipleinterfacesinmultilayerstructuresimpairssignificantlythephonontransportofheat,whichresultsinthe 

reducedthermalconductivitiesofthelayersandamountstoincreasedthermal 

resistivityofthedevices.Thebehaviourofthephonon/heattransportinthe 

presenceofinterfacesisachallengeinanalyticaldescription.Inthisarticlea 

semi-analyticalexpressionbasedontheacousticmismatchmodelandthediffuse 

mismatchmodelisproposed,thatpredictsthethermalconductivityofsuperlatticestructuresatroomtemperaturesaccurately.ThemodelwasusedtopredictthethermalconductivitiesofSi/Ge,Si/Si0.3Ge0.7.Si/Gesuperlatticestructuresconsistof60,80,100,200,300periodsandhavedifferentlayerssizeratio 

foreachsample.AllSi/Si0.3Ge0.7superlatticestructureswithperiodwidths 

300˚A,150˚A,75˚A,45˚Aare3µmthinkandhave2:1layerratio.Theobtained 

calculationsofthermalconductivityinrangeoftemperaturefrom200Kto300K 

areingoodagreementwiththeexperimentaldata.Thebehaviourofthermal 

conductivityinthepresentsofchangingnumbersofinterfacespredictedbythis 

modelisconfirmedbymeasurements. 

1 

90

40th _______________________________________________________________ 


Pb1-xGexTe surface with Sm 2+ and Sm 3 + doping 

A. Reszka 1 , B.A. Orlowski 1 , M.A. Pietrzyk 1 , A. Szczerbakow 1 , S. Mickievicius 2 , 

S. Balakauskas 2 , R.L. Johnson 3 

1 Institute of Physics, Polish Academy of Sciences, Al. Lotników 32/46, 02-668 Warsaw, 

Poland 

2 Semiconductor Physics Institute, A. Gostauto 11, 2600 Vilnius, Lithuania 

3 Institut für Experimentalphysik, Universität Hamburg, Luruper Chaussee 149, 22761 

Hamburg, Germany 

In the present work we report the experimental results of resonant photoemission study 

of single crystal Pb1-xGexTe surface doped with Sm. Doping of IV-VI semiconductors with 

rare earth atoms turns these materials into diluted magnetic semiconductors, exhibiting 

a number of specific properties [1]. 

The main goals of the presented studies were: 

– Determination of Sm 4f electrons contribution to the valence band of Sm/Pb1-xGexTe. 

– Verification of Sm ions charge states (Sm 2+ and Sm 3+ ) to determine their structure 

and binding energies. 

– Investigation of the changes of Sm 2+ /Sm 3+ ratio during the process of Sm incorporation into 

the host lattice. 

The Pb1-xGexTe (x=0.03) samples were grown by the Bridgman method in the Institute 

of Physics Polish Academy of Sciences in Warsaw. The photoemission experiments were 

performed at the FLIPPER II beam line in HASYLAB in Hamburg, Germany. 

Typical feature of rare-earth photoemission spectroscopy (PES) is a characteristic 

behaviour of its intensity related to strongly localized 4f-shell electrons. Therefore, the PES 

investigations of Sm/Pb1-xGexTe were carried out for the varying photon energy through the 

region corresponding to Sm 4d 4f Fano resonance (h = 130-160 eV) [2]. In order to get 

a clean surface for experiment the sample was sputtered by Ar + ions to remove possible oxide 

contaminations and annealed at the temperature 300 ºC under UHV conditions. Samarium 

was deposited on the top of Pb1-xGexTe sequentially to obtain 1, 3 and 7 ML capping layers. 

Afterwards sample was annealed at 250 ºC for 0.5, 1.5 and 6.5 hours to incorporate Sm atoms 

into Pb1-xGexTe crystal matrix. After each deposition and annealing processes the set of 

energy distribution curves (EDC) spectra was measured. Deposited samarium ions occur as 

Sm 2+ and Sm 3+ at the surface. Annealing led to the decrease of Sm 2+ /Sm 3+ ratio indicating 

change in the interaction of Sm ions with their neighbourhood. 

The authors acknowledge support by MSHE of Poland research Projects DESY/68/2007 and by the 

European Community via the Research Infrastructure Action under the FP6 Structuring the European 

Research Area" Programme (through the Integrated Infrastructure Initiative "Integrating Activity on 

Synchrotron and Free Electron Laser Science") at DESY. Partially supported by Innovative Economy 

(POIG.01.01.02-00-108/09) and (POIG.01.01.02-00-008/08) 

[1] T. Story. Semimagnetic Semiconductors Based on Lead Chalcogenides. 

Lead Chalcogenides: Physics and Applications. Taylor & Francis, New York 2002. 

[2] U. Fano, Phys. Rev. B 23 (1961) 1866. 

91

MoP54 

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Studies of Optical Properties of Protonated Poliazomethine 

Thin Films 

H. Bednarski 1 , J. Weszka 1 , M. Domański 1 and V. Cozan 2 

1 Centre of Polymer and Carbon Materials, Polish Academy of Sciences, 34 M. 


2 Petru Poni Institute of Macromolecular Chemistry, Aleea Gr. Ghica Voda 41 A , 

700487 Iasi, Romania 

The poly(p-phenyleneazomethine) (PPI) belongs to alternately conjugated polymers 

revealing semiconducting properties, thus belonging to the family of organic semiconductors. 

PPI is isoelectronic counterpart of poly(p-phenylene-vinilene) (PPV), which is well 

known for its wide applications in organic optoelectronics. Having nearly the same π electron 

system as PPV [1], the PPI differ structurally in the presence of nitrogen atoms. This 

structural feature opens an additional way of chemical doping, by nitrogen atoms lone 

pair protonation. Doping of conjugated polymers is a well established way of influencing 

on important electronic, opto-electronic and mechanical properties of semiconducting 

polymers. 

Doping of poliazomethines is realized mainly based on acid chemistry. Such a technique 

makes the process complex and difficult to control. Apart from intentional protonation 

always exist possibility of occurrence of unwanted side reactions like hydrolysis, decomposition 

etc. [2]. Moreover, the routine experimental methods such as IR, UV-vis, provide 

only averaged quantities, thus microscopic details are not fully resolved. Generally, the 

microscopic mechanism of protonation of polyazomethines is not well understood and 

many reported results are unclear. 

The purpose of this work is twofold, namely experimental studies of optical properties 

of protonated poliazomethine thin films, as well as theoretical studies of protonation 

mechanism of this important group of materials. Performed theoretical calculations are 

aimed to rationalize observed experimental finding such as a red shift of the maximum of 

the absorption band due to protonation. 

[1] J. Weszka, H. Bednarski and M.Domanski, J. Chem. Phys. 131 (2009) 024901. 

[2] A. Iwan and D. Sek, Prog. Polym. Sci. 33 (2008) 289-345. 

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The reasons of destruction of nanoporous GaAs matrix 

fabricated by electrochemical etching 

A. V. Atrashchenko 1 , V. P. Ulin 1 , V. P. Evtikhiev 1 

1 Ioffe Physical-Technical Institute of the Russian Academy of Sciences, 

Politekhnicheskaya 26, 194021, St Petersburg, Russia 

The goal of the present study is to find out the reasons of the destruction of porous 

matrices based on n-type GaAs oriented in (100) created by using anodic electrochemical 

etchinganddefineparametersoftheporouslayers(poresdiameter, wallsthickness, depth, 

period of branching) for further application of such matrices in nanocomposite materials 

(matrixes with filled with metals or alloys (Ga, In, Ga-Au, In-Au)) [1,2]. 

Aperspectivetechniqueofcreatingsuchmatricesisthemethodofanodicelectrochemical 

etching which allows one to obtain nanoporous matrices on large areas. Experiments 

in [3,4] show that a creation of nanoporous matrices by electrochemical etching method 

meets with a problem of destruction of porous layer with the increasing of the etching 

depth. 

Based on previously obtained data [4] and carried out experiments in this paper there 

were suggested three hypotheses explaining the destruction of the porous layer with the 

increasing of depth. 1) During the etching occurs a catastrophic heating which leads to a 

change of the electrical parameters of the reaction. The temperature measurements made 

while executing every experiment has refuted this hypothesis. 2) There is a different speed 

of movement of the electrochemical reaction (relative to the front of etching) in different 

halides. To check this hypothesis we changed the electrolyte composition by leaving only 

one halide. This led to predictable changes in the pores parameters [5], but didn’t remove 

the problem of porous layer destruction. Occasionally we found that with the increasing 

of the pore size the undamaged layer depth increases. 3) Mechanical destruction of the 

porous layer is due to high pressure of products of the etching. In etching form the 

products whose volume is larger than etched volume. The products go outside through 

nanochannels. The increase of the nanochannel length leads to drastic amplification of 

resistance to the products outlet. At some moment a pressure of the etching products on 

a pore walls exceeds the value of the tensile strength so that the pressure at the front of 

pore formation is higher than one in the middle of the porous layer. This explains why 

at stopping of the etching, when the destruction starts, we can see the destruction only 

at the front of etching. 

We have defined the reason of the porous matrices destruction while increasing of the 

porous layer depth by anodic electrochemical etching which is a mechanical destruction 

of the pores walls due to amplification of the etching products pressure on the walls. 

We have defined the limits of the parameters variation for subsequent usage them as a 

medium for creation of nanocomposite metal-semiconductor A3B5 materials: the pores 

diameter is from 20 nm to 70 nm (up to 200 nm in fluoride electrolytes with an abrupt 

decrease of the structural order), the walls thickness lies within 10-20 nm, the depth of 

branching ranges from 150 nm to 1200 nm. We have outlined the methods allowing one 

to increase the porous layers depth by varying pulse current while etching. 

[1] J. B.Pendry, Phys. Rev. Lett. 85, 3966 (2000); 

[2] M. G. Silveirinha, C. A. Fernandes, Phys. Rev. B 78, 033108 (2008); 

[3] M. Christophersen et al., Phys. Stat. Sol. (a) 197, 197, (2003); 

[4] V. P. Ulin, S. G. Konnikov,Semiconductors 41, 832 (2007); 

93

MoP56 _______________________________________________________________ 


Effect of Substitution of Ti for Cd in CdCr2Se4 p-Type Semiconductor 

E. Malicka 1 , T. Groń 2 , A.W. Pacyna 3 , H. Duda 2 and J. Krok-Kowalski 2 





The CdCr2Se4 spinel combines the p-type semiconducting and ferromagnetic properties 

with Curie temperature TC = 142 K and Curie-Weiss temperature qCW = 190 K [1,2]. 

Magnetization of CdCr2Se4 reaches the full saturation of 5.98 µB per molecule [3]. The 

ferromagnetic properties of CdCr2Se4 are a result of dominating interactions between the 

nearest-neighbour chromium ions and of weaker superexchange couplings between the more 

distant chromium ones [4]. The Cr 2p XPS spectra of CdCr2Se4 showed the spin-orbit 

splitting between the final Cr 2p3/2 and Cr 2p1/2 states of 9.5 eV. The Cr 2p3/2 states are split 

into two peaks at 574.2 and 575.2 eV. The peak separation with the binding energy difference 

ΔE about 1 eV is typical of the 3d 3 elements with localized magnetic moment of 3 µB [5]. 

CdCr2Se4 crystallizes in the cubic structure (Fd3m). The X-ray refinements showed that the 

(Cd) ions have a preference to be located in the tetrahedral sites and the [Cr] ions prefer to be 

located in the octahedral sites of the spinel structure [6]. 

Chemical composition and structure refinement gave the sample composition and cation 

distribution according to the spinel formula: (Cd0.88Ti0.08)[Cr2]Se4. Magnetization, ac and dc 

magnetic susceptibility of (Cd0.88Ti0.08)[Cr2]Se4 were measured in the zero-field-cooled mode 

using a Lake Shore 7225 dc magnetometer/ac susceptometer at 4.3 K and in applied external 

magnetic fields up to 60 kOe, and a Faraday type Cahn RG automatic electrobalance in the 

temperature range 4.3-300 K and at 1 kOe and 2 kOe, respectively. 

The dc magnetic measurements of (Cd0.88Ti0.08)[Cr2]Se4 showed ferromagnetic order 

with Curie temperature TC = 129 K and Curie-Weiss temperature qCW = 138 K. Saturation 

magnetization of 4.73 µB/f.u. at 4.3 K and at 60 kOe seems to be strongly reduced in 

comparison with the CdCr2Se4 matrix. Such considerable lowering of magnetic moment 

induced by titanium substitution could be explained with only a transition of the certain 

number of Cr ions from the high-spin states to the low-spin states. Additionally, the ac 

magnetic measurements revealed a spectacular peak at 450 Oe and 1 kOe in the real part of 

the first harmonic susceptibility curve near TC, similar to the Hopkinson peak. Zero-value of 

its imaginary part below TC indicates a lack of the energy loss connected with the spin 

rearrangement processes. This is consistent with zero values of second and third harmonic ac 

susceptibility in the temperature range of 4.5-160 K, suggesting the lack of short-range 

magnetic interactions. 


[1] H.W. Lehmann, Phys. Rev. 163, 488 (1967). 

[2] P.K. Baltzer, H.W. Lehmann, and M. Robbins, Phys. Rev. Lett. 15, 493 (1965). 

[3] R.C. LeCraw, H. von Philipsborn, and M.D. Sturge, J. Appl. Phys. 38, 965 (1967). 

[4] P.K. Baltzer, M. Robbins, and P.J. Wojtowicz, J. Appl. Phys. 38, 953 (1967). 

[5] V. Tsurkan, St. Plogmann, M. Demeter, D. Hartmann, and M. Neumann, Eur. Phys. J. B 

15, 401 (2000). 

[6] T. Groń, A. Krajewski, J. Kusz, E. Malicka, I. Okońska-Kozłowska, A. Waśkowska, Phys. 

Rev. B 71, 035208 (2005). 

94

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Thermoelectric power in epitaxial Bi2Se3/Si(111) layers 

K. Dybko , M. Szot, T. Story and G. Karczewski, 

Institute of Physics, Polish Academy of Sciences, 

Al. Lotników 32/46, 02-668 Warszawa, Poland 

S. Schreyeck, C. Schumacher, K. Brunner and L.W. Molenkamp 

! " 

Bi2Se3 belongs to the class of three-dimensional topological insulators characterized 

by a bulk insulating state and conducting two-dimensional surface states with linear Diraclike 

dispersion. As grown Bi2Se3 samples are usually n-type due to inevitably present charged 

Se vacancies. Consequently, the conductivity of the system consists of parallel bulk and 

surface states conductivities. The observation of the surface states electrical properties 

requires minimalization of the bulk states contribution. It has been demonstrated in high field 

magnetotransport experiment [1] that beyond magnetic field corresponding to quantum limit 

for 3D carriers the clear Shubnikov de Haas oscillations of 2D character appear. This high 

field signature of surface states unambiguously proved the coexistence of both conducting 

channels in bulk samples. 

Here we study how the surface states affect thermoelectric properties of the whole 

electronic system in Bi2Se3. The samples were grown by molecular beam epitaxy on 

reconstructed (7x7)–(111) surface of Si semi-insulating substrate. Typically, samples are 100 

nm thick and have electron concentration of the order of 10 19 cm -3 . The Seebeck effect was 

measured over the temperature range of 10-300 K in ab-plane of the samples. The magnitude 

of the thermoelectric power decreases smoothly with lowering temperature until around 80 K, 

where it develops into a broad peak with maximum at 45-50 K. The absolute height of this 

peak is within 10 percent equal to the room temperature value (-60 V). The observed 

anomaly could be attributed to the theoretically predicted enhancement of the thermopower 

for surface states of topological insulators [2,3]. Here we measure the sum of individual 

contributions to the thermopower originating from bulk and surface states weighted by their 

electrical conductivities. Therefore, we also consider an alternative explanation that the 

effect is due to phonon drag, which may lead to the enhancement of the low temperature 

thermopower in semiconductors. 

[1] J.G. Analytis et al. , Nature Phys. 6, 960 (2010). 

[2] R. Takahashi and S. Murakami, Phys. Rev. B 81, 161302 (2010). 

[3] P. Ghaemi, R.S.K. Mong and J.E. Moore, Phys. Rev. Lett. 105, 166603 (2010). 

95

MoP58 

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Diamagnetism of the pre-paired electronic systems: 

the flow equation study 

M. Zapalska and T. Domański 

Institute of Physics, M. Curie Sk̷lodowska University, 20-031 Lublin, Poland 

Magnetic ordering of the electronic systems can originate from a variety of mechanisms. 

It can be explained for instance by the energetic reasons (Pauli paramagnetism), assigned 

to the orbital effects (diamagnetism) or to the mutual electron-electron interactions which 

through the exchange coupling induce either the ferromagnetic or antiferromagnetic order. 

Among these phenomena the particular version of ordering (perfect diamagnetism) 

appears whenever the Fermi liquid becomes unstable towards the electron pair formation 

and the system becomes superconducting. It is well known that superconductivity goes 

hand in hand together with the perfect diamagnetism (Meissner effect). In his seminal 

paper P.W. Anderson explained this in terms of the Anderson-Higgs mechanism when the 

phasal Goldstone mode is swallen producing the massive term A 2 . 

Recent studies of the Princeton group [L. Li et al, Phys. Rev. B 81, 054510 (2010) by 

means of the high-presission torque magnetometry reveiled that in cuprate materials the 

remarkable diamagnetic response survies to temperatures much higher than critical Tc. It 

is expected that apparantly the preformed electron pairs (which above Tc are not capable 

to establish the long-range coherence) are responsible for such residual diamagnetism. We 

shall analyze this problem using the nonperturbative flow equation technique designed 

within the numerical renormalization group scheme. 

96

40th _______________________________________________________________ 


Quantum Monte Carlo vs. Density Functional Methods for the prediction of 

relative energies of small Si-C clusters 

Nevill Gonzalez Szwacki and Jacek A. Majewski 

Faculty of Physics, University of Warsaw, ul Hoża 69, 00-681 Warszawa, Poland 

In many systems, prediction of the structural properties requires correct description of 

the electron correlation, clearly exceeding the accuracy of the available exchange correlation 

functionals in the density functional theory (DFT). This is also the case in small systems with 

very non-homogenous distribution of electronic charge, like for example Si–C clusters, which 

play an important role are in technological processes, such as chemical vapor deposition used 

for fabrication of SiC thin films. The simulation of the growth processes is out of scope of abinito 

methods and has to be done using effective approaches after ‘coarse graining’ procedure. 

The quality of the effective potentials is crucial for reliability of the predictions. Therefore, 

the effective potentials are usually fitted to the results of the first-principles calculations for 

building blocks of a material. 

Numerous experimental and theoretical studies have been performed to investigate 

equilibrium geometries, vibrational frequencies, and relative energies of small SinCm cluster 

isomers [1,2]. Most of the calculations employed standard approximations to the DFT. 

In order to examine the accuracy of various DFT exchange-correlation (XC) 

functionals in predicting the relative energies of cluster isomers and to provide new 

benchmark data, we have performed diffusion quantum Monte Carlo (DMC) calculations for 

small SinCm clusters. We compare our DMC results with DFT ones obtained using the local 

density approximation (LDA), Perdew-Burke-Ernzerhof generalized gradient approximation 

(GGA), and the popular B3LYP hybrid Hartree-Fock/DFT functional. On the basis of our 

DMC results for Si-C clusters, we conclude that LDA and GGA XC functionals are not 

reliable for predicting the relative stability of various isomers of covalent SiC clusters, 

B3LYP does a little bit better, and generally the errors of various methods are completely 

unsystematic. This is illustrated in Fig. 1, where we plotted the energy (relative to the 

average) of four SinCm isomers. In particular, it is easily seen that the LDA approximation 

underestimates the relative energy of the planar (1) and (2) clusters, whereas the GGA 

approximation is unable to capture correctly the relative energy of the 3D clusters (2) and (3). 

The present studies clearly demonstrate that 

the determination of the effective potentials 

on the basis of DFT calculations with 

approximated exchange-correlation 

functionals can be misleading and 

computational schemes going beyond this 

approximation are very desirable. 

This paper has been supported by the project 

“SiCMAT” (Innovative Economy, 

POIG.01.03.01-14-155/09-00) 

[1] M. Bertolus, F. Finocchi, and P. Millie, J. Chem. Phys. 120, 4333 (2004). 

[2] C. R. Hsing et al., Phys. Rev. B 79, 245401 (2009). 

97

MoP60 _______________________________________________________________ 


Analysis of a Spatial Hole Burning Effect in a Square and 

Triangular Lattice Photonic Crystal Laser 

Marcin Koba 1,2 , and Pawe̷l Szczepański 1,2 

1 Warsaw University of Technology, Koszykowa 75, 00-662 Warsaw, Poland 

2 National Institute of Telecommunications, Szachowa 1, 04-894 Warsaw, Poland 

In this paper we present an approximate analysis of the nonlinear operation of the 

two-dimensional (2D) photonic crystal (PC) lasers taking into account nonlinear effects 

(gain saturation, spatial hole burning). 

Our analysis is conducted for the laser with an active medium that is confined in 

the square region with circular holes arranged in square or triangular Bravais’ lattice. 

The analysis is based on two-dimensional coupled wave equations [1]-[4] for TE and TM 

modes, modified by introduction of nonlinear gain and energy theorem developed earlier 

forvarioustypesoflaser[5], includingDFBstructures[6]-[8]. Similarly, aswehavedonein 

e.g. [6]-[8] the field distributions appearing in the energy theorem (including nonlinearity) 

were approximated by those existing in the linear structure (i.e. at threshold). 

Following our derivation presented in [4],[9],[10] we introduce an approximate equations 

describing the small signal gain coefficient α0 as a function of system parameters, 

where we have introduced power saturation and spatial hole burning effects. We use these 

equations to calculate laser characteristics illustrating hole burning effect impact on cw 

operation of square and triangular lattice PC laser structure above the threshold. With 

thehelpofthepresentedtechniqueitispossibletocalculatetheoptimalcouplingstrength 

providing maximal power efficiency of the given 2D photonic laser structure. 

[1] K. Sakai, E. Miyai, and S. Noda, Opt. Express 15, 3981 (2007). 

[2] K. Sakai, E. Miyai, and S. Noda, IEEE J. Quantum Electron. 46, 788 (2010). 

[3] K. Sakai, J. Yue, and S. Noda, Opt. Express 16, 6033 (2008). 

[4] M. Koba, P. Szczepanski, and T. Kossek, IEEE J. Quantum Electron. 47, (13) 2011. 

[5] L. Wosińska, P. Szczepański, and W. Woliński, Opto-Electron. Rev. 1, 26 (1992). 

[6] R. Paszkiewicz, A. Tyszka-Zawadzka, and P. Szczepański, Opt. Commun. 270, 314 

(2007). 

[7] P. Szczepański, D. Sikorski, and W. Woliński, IEEE J. Quantum Electron. 25, 871 

(1989). 

[8] P. Szczepanski, Appl. Opt. 24, 3574 (1985). 

[9] M. Koba, and P. Szczepanski, IEEE J. Quantum Electron. 46, 1003 (2010). 

[10] M. Koba, T. Osuch, and P. Szczepanski, J. Mod. Opt. submited for publication. 

98

40th _______________________________________________________________ 

"Jaszowiec" 2011 International School and Conference on the Physics of Semiconductors TuI1 

Optical control of one and two spins in interacting quantum dots 

Alex Greilich, Samuel G. Carter, Danny Kim, Allan S. Bracker and Daniel Gammon 

Naval Research Laboratory, Washington DC 20375, USA 

The interaction between two quantum bits enables entanglement, the two-particle 

correlations that are at the heart of quantum information science. In semiconductor quantum 

dots much work has been focused on demonstrating single spin qubit control using optical 

techniques. However, optical control of two spin qubits remains a major challenge for scaling 

to a full-fledged quantum information platform. Here we combine advances in verticallystacked 

quantum dots with ultrafast laser techniques to achieve optical control of the 

entangled state of two spins. 

We demonstrate ultrafast optical control of two interacting electron or hole spins in 

two separate QDs using optical initialization, single-qubit gates with short pulses, and twoqubit 

gates with longer pulses or through precession in the exchange field. Local 

entanglement between the two spins is inferred from the coherent evolution of superposition 

states as measured in Ramsey fringes. 

The two-qubit gate speeds achieved here are over an order of magnitude faster than in 

other systems. These results demonstrate the viability and advantages of optically controlled 

quantum dot spins for multi-qubit systems. 

[1] Danny Kim, Samuel G. Carter, Alex Greilich, Allan S. Bracker and Daniel Gammon, 

Nature Physics 7, 223 (2011).�� 

99

TuI2 _______________________________________________________________ 


Graphene Transport Properties� 

Shaffique Adam 

Center for Center for Nanoscale Science and Technology, National Institute of Standards and 

Technology 

Arguably, one of the most intriguing properties of graphene transport is the nonvanishing 

``minimum conductivity” at the Dirac point. The carrier density in these single 

monatomic sheets of carbon can be continuously tuned from electron-like carriers for large 

positive gate bias to hole-like carriers for negative bias. The physics close to zero carrier 

density (also called the intrinsic or Dirac region), is now understood to be dominated by 

fluctuations in local disorder potential, breaking the landscape into puddles of electrons and 

holes [1]. I will discuss the competing effects of disorder, electron-electron interactions, and 

quantum interference on graphene’s transport properties and demonstrate that, remarkably, a 

semi-classical effective medium theory captures the physics in the experimentally relevant 

regime [2]. Figure 1 shows a comparison of our theoretical predictions [3] with subsequent 

experimental data from Columbia, Manchester, Maryland and Exeter universities showing 

good agreement. To further test the range of validity of our model, I compare our results to a 

fully quantum-mechanical numerical calculation [4] of the conductivity and find that while 

the two theories are incompatible at weak 

disorder, they are compatible for strong 

disorder. Armed with this success, I will 

discuss how future graphene experiments 

could shed light on some long-standing 

open questions in condensed matter 

physics. 

Figure 1: Comparison of the self-consistent 

theory [3] with experimental data from 

various groups around the world. (See Ref. 

[2] for details). Solid blue line shows the 

Dirac point conductivity for graphene in 

the presence of charged impurities of 

concentration nimp. The dashed line shows the quantum mechanical ballistic result 4e 2 /�h. 

Early results claimed that the conductivity was universal with a value of 4e 2 /h (dotted line). 

References: 

[1] S. Das Sarma, S. Adam, E. H. Hwang, E. Rossi, “Electronic transport in two dimensional 

graphene”, arXiv:1003.4731, Rev. Mod. Phys. (in press). 

[2] S. Adam, “Graphene carrier transport theory”, invited book chapter for Graphene 

Nanoelectronics: metrology, synthesis, properties and applications (Springer book series on 

nanoscience and technology). 

[3] S. Adam, E. H. Hwang, V. Galitski, and S. Das Sarma “A self-consistent theory for 

graphene transport” Proc. Nat. Acad. Sci. USA 104, 18392 (2007). 

[4] S. Adam, P. W. Brouwer, and S. Das Sarma “Crossover from quantum to Boltzmann 

transport in graphene” Phys. Rev. B Rapid Communications 79, 201404 (2009). 

100

40th _______________________________________________________________ 

"Jaszowiec" 2011 International School and Conference on the Physics of Semiconductors TuI3 

Theoretical search for non-Abelian statistics in fractional quantum Hall states 

Arkadiusz Wójs 

Institute of Physics, Wroc�aw University of Technology, Wroc�aw, Poland 

Convincing demonstration of non-Abelian anyon quantum statistics (corresponding to 

the multi-dimensional realization of the braid group, allowed in two spatial dimensions) is a 

major challenge in today’s condensed matter physics. Promising physical systems for this 

quest are sought among correlated many-electron states a high magnetic field, responsible for 

the fractional quantum Hall effect at such Landau level fillings as �=5/2 or 12/5. In particular, 

the 5/2 state is believed to realize a superfluid condensate of p-paired “composite fermions” 

(electrons binding vortices of the many-body wave function) in an effectively compensated 

magnetic field. This hypothetical state, described by the “Pfaffian” wave function of Moore 

and Read, supports elementary charge excitations in form of fractional (e/4) quasiparticles 

which obey non-Abelian anyon quantum statistics. Anticipation of the Pfaffian ground state 

relies mostly on numerics, and it is confronted with rather ambiguous experimental evidence, 

including recent reports of the (unexpected) depolarization of spin at �=5/2. Therefore, the 

focus of this talk will be on available evidence concerning Pfaffian dynamics (more generally, 

non-Abelian quantum statistics) in realistic conditions of the fractional quantum Hall effect. 

We will begin by revisiting the question of spin polarization at �=5/2. The combination 

of exact diagonalization and quantum Monte Carlo in spherical geometry confirms quantum 

ferromagnetism in clean systems, as expected for the Pfaffian phase, but also reveals stability 

of Skyrmions (topological spin excitations) in sufficiently thick systems [1]. As pairing nature 

of the ferromagnetic (Pfaffian) ground state implies that Skyrmions at �=5/2 carry twice the 

charge (e/2) of spinless quasiparticles, the (realistic) lateral disorder aids Skyrmion formation, 

in turn leading to local depolarization – in agreement with its photoluminescence signatures. 

Having established the role of spin we will confine further analysis to the spin-polarized 

channel and turn to the question of adiabatic connection (i.e., essential equivalence) between 

the exact Pfaffian state and the realistic Coulomb ground state. The problem is subtler than at 

�=1/3 (where the famous Laughlin wave function is firmly established), because of a longer 

correlation length, a more fragile gap, and a competition between two- and three-body effects 

(the Pfaffian state being a unique zero-energy ground state of the contact triplet repulsion). 

Since the analysis of overlaps or pair correlation functions computed in the largest tractable 

systems is hardly conclusive, we studied features linked directly to the non-Abelian statistics. 

Specifically, in addition to the neutral boson pair-pair collective mode with the characteristic 

roton dispersion, the Pfaffian ground state should have a neutral fermion excitation associated 

with an unpaired particle (analogous to the Bogoliubov-deGennes excitation of a conventional 

superconductor). In the relevant weakly paired phase, the neutral fermion dispersion should 

have a minimum near the Fermi wave vector. More importantly, the neutral fermion mode is 

predicted to become gapless in the presence of distant quasiparticles – as a consequence of 

their non-Abelian statistics within the Ising model with degenerate fusion channels (1 and �). 

Our calculations confirm [2] these qualitative features, in support of exotic statistics at �=5/2. 

Other issues will include Pfaffian/anti-Pfaffian duality, effects of Landau level mixing 

(e.g., on particle-hole symmetry) [3], and the pairing transition of composite fermions [4]. 

[1] A. Wójs, G. Möller, S. H. Simon, and N. R. Cooper, Phys. Rev. Lett. 104, 086801 (2010). 

[2] G. Möller, A. Wójs, and N. R. Cooper, http://arxiv.org/abs/1009.4956 

[3] A. Wójs, C. T�ke, and J. K. Jain, Phys. Rev. Lett. 105, 096802 (2010). 

[4] A. Wójs, C. T�ke, and J. K. Jain, Phys. Rev. Lett. 105, 196801 (2010). 

101

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Polariton condensation in dynamic acoustic lattices 

D. Krizhanovskii 1 , E. Cerda-Méndez 2 , M.Wouters 3 , K. Biermann 3 , K.Guda 1 , R.Bradley 1 , 

D.Sarker 1 , P. V. Santos 3 , R. Hey 3 and M. S. Skolnick 1 

1 Department of Physics and Astronomy, University of Sheffield, Sheffield, United Kingdom 

2 Paul-Drude-Institut für Festkörperelektronik, Berlin, Germany 

3 ITP, Ecole Polytechnique Fédérale de Lausanne, 1015 Lausanne, Switzerland 

Microcavity polariton condensates 

arising either from Bose-Einstein condensation 

(BEC) or from Optical Parametric Oscillation 

(OPO) exhibit collective superfluid-like 

behavior [1](OPO), spatial and temporal 

coherence (OPO, BEC) and vortices (OPO, 

BEC). Here, we study spatial coherence of 

OPO polariton condensates formed by 

polariton-polariton scattering from the pump in 

external periodic potentials created by Surface 

Acoustic Waves (SAW)[2]. The effect of 

strong polariton-phonon coupling results in 

modulation of the polariton dispersion with 

marked formation of Brillouin zones of period 

k=π/λSAW and energy stop band widths up to ~0.5 

meV (Fig.1a). 

Without SAW the OPO “signal” condensate 

is formed at k=0 above threshold with a coherence 

length of about ~20-25 µm. As the height of the 

SAW potential is increased we observe dramatic 

reduction of the spatial coherence length (Ly) along 

the SAW direction by a factor of 3-4 (Fig.1c), a result of suppressed tunnelling between the 

adjacent SAW minima. A smaller decrease of the coherence length Lx by a factor of 2 

perpendicular to the SAW direction (Fig.1d) is attributed to the increased phase fluctuations, 

predicted theoretically for 1D system of the non-equilibrium OPO. The observed effect 

corresponds to transition from condensate to insulator state. Nevertheless, this is not a Mott 

insulator: the number of particles per potential well is still large compare to the case of 

superfluid-to Mott-insulator transition in cold atom system. Interestingly, at intermediate SAW 

powers the emission peaks at the edges of the 1 st Fig.1 a) Dispersion of polaritons subject to SAW 

potential. b) Image of condensate emission c)-d) 

Spatial coherence length of OPO signal parallel 

(LX) and perpendicular (LY) SAW at different 

pump powers. 

Brillouin zone (Fig.1b), indicating a phase 

difference of π between adjacent condensates. A likely reason for this is an additional scattering 

mechanism between the main pump beam and its diffraction replica. 

By contrast, inter-particle interactions at high densities screen the acoustic potential, 

partially reversing its effect on spatial coherence. Figs.1 c)-d) shows that with increasing 

excitation power the reduction of spatial coherence lengths occurs at higher SAW powers, thus 

indicating efficient screening of SAW potential at low acoustic powers as the polariton density 

is increased. 

Our work on polariton condensation in acoustic lattices provides new technology to 

investigate fundamental effects in hybrid light-matter system, such as coherent transport of 

condensates, creation of entangled states and Josephson tunneling. 

1. A. Amo, et al, Nature 457, 291 (2009) 

Ly (P =140 mW) 

laser 

40 

Ly (P =200 mW) 

laser 

Ly (P =240 mW) 

laser 

30 

Ly (P =300 mW) 

laser 

-5 0 5 10 15 

0 5 10 15 

2. E. A. Cerda-Méndez, D. N. Krizhanovskii et al, Phys. Rev. Lett. 105, 116402 (2010) 

102 

Energy (eV) 

1.5365 

1.5360 

1.5355 

1.5350 

1.5345 

1.5340 

1.5365 

1.5360 

1.5355 

1.5350 

1.5345 

1.5340 

a) 

b) 

-2 -1 0 1 2 

k-vector ky 

c) 

d) 

Ly (P laser =68 mW) 

SAW power (dBm) 

50 

20 

10 

0 

40 

30 

20 

10 

0 

Coherence length L y (µm) 

Coherence length Lx (µm)

40th _______________________________________________________________ 

"Jaszowiec" 2011 International School and Conference on the Physics of Semiconductors TuO1 

Resonant Terahertz Absorption by Magnetoplasmons 

in Grating-Gate GaN/AlGaN-based Field-Effect Transistors 

K. Nogajewski 1 , K. Karpierz 1 , M. Grynberg 1 , W. Knap 2 , R. Gaska 3 , 

J. Yang 3 , M. S. Shur 4 , and J. ̷Lusakowski 1 

1 Faculty of Physics, University of Warsaw, ul. Ho˙za 69, 00-681 Warsaw, Poland 

2 CNRS - Université Montpellier2, Pl. E. Bataillon, 34095 Montpellier, France 

3 Sensor Electronic Technology, Inc., Columbia, South Carolina 29209, USA 

4 Rensselaer Polytechnic Institute, Troy, New York 12180, USA 

An interest to fabricate voltage-tunable detectors of THz radiation based on plasma 

excitations in field-effect transistors (FETs) is marked by an effort to test new types of 

structures and new materials. High electron mobility FETs based on GaN/AlGaN heterostructures 

offer a possibility of high-voltage/high-current THz applications in agressive 

environments. However, to support technical developments, basic physical investigation 

must be carried out on technologically advanced devices. 

The goal of the present work is to describe magnetoplasmon excitations in a twodimensional 

electron gas in a GaN/AlGaN heterostructure. Our experiments were carried 

out on samples that have been recently shown to exhibit gate-voltage tunable plasmon 

resonances at zero magnetic field (B) [1]. The samples were large-area (about 

1.6 mm×1.6 mm) FETs with the gate electrode composed of two interdigitated comb-like 

structures. Five transistors with the gate periodicity between 1.5µm and 4µm were processed 

on a high-quality GaN/AlGaN heterostructure. The metal grating served both as 

a gate electrode controlling the concetration of a two-dimensional electron gas (n) and as 

a coupler between magnetoplasmons and incident THz radiation. 

Transmission ( a.u. ) 

ν FIR = 2.52THz 

−3.5 −3 −2.5 −2 −1.5 −1 −0.5 0 

Gate Voltage ( V ) 

B = 8T 

B = 6T 

B = 4T 

B = 2T 

B = 0T 

Fig. 1: Transmission of 2.52 THz radiation 

through a GaN/AlGaN FET as a function of 

VG and B. Minima correspond to magnetoplasmon 

resonances. 

Bothmagnetoresistanceand magnetotransmission 

measurements were carried 

out at 4.2 K and B up to 10 T as a function 

of the gate polarization (VG). Shubnikov-de 

Haas oscillations of the magnetoresistance 

allowed us to estimate n as 

a function of the gate polarization (VG) 

and then an n-dependent electron quantum 

relaxation time τ. We found that τ 

dependsinanon-monotonicwayonnand 

ranges from 0.03 ps to about 0.1 ps. 

An example of magnetotransmission 

data shown in Fig. 1 gives a clear evidenceofexcitationofmagnetoplamonresonances 

tunable by B and VG. Magnetoplasmons 

frequency, ωmp, can only approximately 

be described by a classical 

formula ωmp = � 

ω2 c +ω2 p. Deviations 

from this dependence are explained as a result of interaction of plasmons in gated and 

ungated parts of the transistor channel. 

This work was partially supported by the JU ENIAC MERCURE project No. 220120. 

[1] A. V. Muravjov et al., Appl. Phys. Lett. 96, 042105 (2010). 

103

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Structural and electronic properties of functionalized graphene 

Karolina Milowska, Magdalena Birowska, and Jacek A. Majewski 

Faculty of Physics, University of Warsaw, ul. Hoża 69, PL-00-681 Warszawa, Poland 

We present extensive ab initio studies in the framework of the density functional theory 

(DFT) of graphene layers functionalized with simple molecules, which provide novel 

predictions for electronic structure of the functionalized graphene mono- and bilayers. The 

calculations reveal that the functionalization of graphene by simple molecules (e.g., such as 

OH, NH, and COOH) causes opening of the electronic band gap, just indicating new 

perspectives for design of field effect transistors (FETs) based on single and bilayer graphene. 

Remarkable electronic, mechanical and thermal properties of graphene have made it a 

promising candidate for a new generation of electronic devices [1]. However, the single and 

bilayer graphene have zero energy band gaps. Therefore, it hinders direct application of these 

systems in FETs. On the other hand, the functionalization of the graphene could change its 

electronic structure. Since quantitatively this effect is rather unknown, we have undertaken 

theoretical studies of this issue. 

In the present paper, we study the effects of functionalization of graphene with simple 

organic molecules (NHn, OH, and COOH) focusing on the stability and band gaps of the 

structures. We perform DFT calculations for graphene supercells with various numbers of the 

attached molecules. Employing the numerical package SIESTA, we completely optimize the 

geometry of the structures getting very good agreement with existing experimental data [2], 

and other theoretical calculations [3]. All studied groups bind covalently to the graphene layer 

implying sp 2 to sp 3 rehybridization and local deformation of the graphene plane. As example 

of our results, below we depict band 

structures of graphene layer 

functionalized with one single 

molecule per 3x3 graphene 

superlattice. The molecules are (a) - 

OH, (b) - NH, (c) – NH2, and (d) – 

COOH. The red dotted lines indicate 

band structure of pure graphene, the 

black ones the electronic structure of 

functionalized graphene. In all cases, 

the zero band gap at K-point of pure graphene opens, being equal to 0.11, 0.12, 0.25, and 0.24 

eV for OH, NH, NH2, and COOH, respectively. Generally, the stability of the functionalized 

graphene layers decreases with the growing concentration of functionalizing molecules. 

Interestingly, for higher (1x1) concentrations of OH, we observe separation of O and H, 

which cover now other sides of the graphene layer. On the other hand, quite naturally, the 

band gap increases with the concentration of the attached molecules, e.g., in the case of 2x2 

cell functionalized with hydroxyl group (graphene’s surface is strongly bent), the band gap 

reaches 1.04 eV. All this shows clearly that the band gap of graphene layers can be tuned 

within fairly large range. Further, it turns out that the functionalized graphene layers exhibit 

magnetic moments, just implying some possible spintronic applications. 

This paper has been supported by the project “SiCMAT” (Innovative Economy, POIG.01.03.01-14-155/09-00). 

1. S. Park, and R. S Ruoff, Nature Nanotech., 4, 217 (2009). 

2. H. B. Su, R. J. Nielsen, A. C. T. van Duin, and W. A. Goddard, Phys. Rev. B 75 134107 (2007). 

3. Jia-An Yan, M. Y. Chou, Phys. Rev. B 82 125403 (2010). 

104

40th _______________________________________________________________ 


Analysis of the magnetic anisotropy in ultrathin GaMnAs 

O. Proselkov 1 , W. Stefanowicz 1 , S. Dobkowska 1 , J. Sadowski 1,2 , 

T. Dietl 1,3 , M. Sawicki 1 

1 Institute of Physics, Polish Academy of Sciences, Warszawa, Poland 

2 MAX-Lab, Lund University, Lund, Sweden 

3 Institute of Theoretical Physics, University of Warsaw, Poland 

(Ga,Mn)As is the main test-bed material for testing concepts of future spintronics devices 

and its magnetic anisotropy is assumed to be reasonably well known both on the ground of 

understanding of the experimental data and on the level of a description its microscopic 

origins. However, some very recent studies have brought new insights into the magnetic 

anisotropy of thin and ultrathin (Ga,Mn)As. Firstly, in very thin (Ga,Mn)As layers, despite an 

adequate high Mn concentration to assure their homogenous metallic character, a blocked 

superparamagnetic response has been found [1]. Then, it was postulated that the strength of 

the ever-present in-plane uniaxial magnetic anisotropy was related to nanometer-scale ripples 

on the (Ga,Mn)As surface [2]. Furthermore, a collapse in the magnitude of the anomalous 

Hall effect was found for thin layers at low temperatures [3]. Finally, a cycloidal spin 

arrangement and the accompanying uniaxial in-plane anisotropy of diagonal [110]/[1-10] 

directions was suggested to form in very thin layers [4]. 

As all these findings indicate that the long celebrated macrospin approach [5] to the 

phenomenological description of the magnetic anisotropy may cease its validity in ultrathin 

layers, an examination of the conditions of its applicability in this technological important 

case is timely and important. Simultaneously, means for assessment of the abovementioned 

concepts are to be defined and tested. For these purposes we investigate in greater detail 

temperature dependence of the magnetic anisotropy of 4 nm Ga0.925Mn0.075As, a layer that 

according do [1] exhibits two types of magnetic responses: a temperature reversible one 

typical for a long-range-coupled magnetization and an irreversible one possessing 

characteristics similar to a blocked superparamagnet. We find that we can self consistently 

describe our findings on the grounds of the macrospin model as in [5] only above a 

temperature at which signatures of blocked superparamagnetic response disappears (25 K in 

this case). Below, the same model yields conflicting results which depend on the magnetic 

history of the sample. However, if applied at this temperature range, this approach implies 

disappearance of magnetic anisotropy at temperatures corresponding to the mean blocking 

temperature of the superparamagnetic part of the layer and a change of sign of the cubic 

anisotropy at the lowest temperatures. The last findings point to a strong coupling between 

these two major constituencies of the magnetic response in such a layers. 

The work was supported in part by the European Research Council through the FunDMS 

Advanced Grant within the "Ideas" 7th Framework Programme of the EC, EC Network 

SemiSpinNet (PITN-GA-2008-215368) and Polish MNiSW 2048/B/H03/2008/34 grant. 

[1] M. Sawicki, et al., Nature Phys. 6, 22 (2010); S. Dobkowska, et al., this conference. 

[2] S. Piano, et al., arXiv:1010.0112. 

[3] D. Chiba et al., Phys. Rev. Lett. 104, 106601 (2010). 

[4] A. Werpachowska and T. Dietl, Phys. Rev. B 82, 085204 (2010). 

[5] K.-Y. Wang, et al., Phys. Rev. Lett., 95, 217204 (2005). 

105

TuO4 _______________________________________________________________ 


Spin-lattice relaxation of a single Mn 2+ ion in a CdTe quantum dot 

M. Goryca 1,2 , P. Plochocka 2 , P. Wojnar 3 , T. Kazimierczuk 1 , M. Potemski 2 

and P. Kossacki 1,2 

1 Institute of Experimental Physics, Faculty of Physics, University of Warsaw, Warsaw, Poland 

2 Grenoble High Magnetic Field Laboratory, CNRS, Grenoble, France 

3 Polish Academy of Sciences, Warsaw, Poland 

From the point of view of miniaturization of magnetic memory devices a quantum dot 

(QD) containing a single magnetic impurity is an interesting system. It has been demonstrated 

that it gives unique possibility to read and manipulate the electronic spin state of the single 

atom [1-3]. Although principles of using such system as a memory device are known, further 

studies of interaction of the magnetic ion with its neighborhood are still needed. Particularly a 

detailed knowledge about the spin-lattice relaxation is of a great importance, as this kind of 

relaxation is a main factor limiting the information storage time. 

In this work we present spectroscopic studies of the spin-lattice relaxation of a single 

Mn 2+ ion embedded in a CdTe/ZnTe QD, performed in high magnetic field. The experiment 

was done in a micro-photoluminescence setup at temperature of about 15 K. The magnetic 

field up to 12 T was produced with a superconductive magnet and applied in the Faraday 

configuration, parallel to the growth axis of the sample. The sample contained a single layer 

of self-assembled QDs. The PL of the QDs was excited using a tunable dye laser in the range 

570−610 nm. The spin-conserving excitation transfer between two QDs [4] was used to inject 

spin-polarized excitons into the QD containing the Mn 2+ ion and to orient its spin [3]. 

The spin-lattice relaxation time of the Mn 2+ ion was determined in two independent 

experiments. In the first one we measured the efficiency of the optical orientation of the Mn 2+ 

ion [3] as function of excitation power and magnetic field. Thus we were able to examine in 

detail the competition between two processes: the optical orientation of the Mn spin by spinpolarized 

excitons injected into the QD and thermalization of the magnetic ion in external 

magnetic field caused by spin-lattice relaxation. When these processes exactly compensate 

each other, i.e. the spin orientation rate is exactly equal to the relaxation rate, then the Mn 2+ is 

completely depolarized. Thus the spin orientation rate can be estimated using the exciton 

injection rate to the QD and probability of the Mn spin flip per one exciton [3]. 

In the second, time-resolved experiment we measured directly the Mn spin relaxation 

time. We used the same mechanism as previously to orient the magnetic ion. Once it reached 

the steady state we turned the excitation off for a certain period. Then we turned the excitation 

on again to probe the Mn spin. By varying the length of the dark period in the range of 20 ns – 

500 µs we were able to measure the relaxation time in the wide range of magnetic fields. 

Both experiments gave the same results within experimental accuracy. The spin-lattice 

relaxation time of the Mn 2+ ion in the QD for low magnetic field (around 1 T) reaches 

hundreds of microseconds and is comparable to the value measured for bulk, diluted 

(Cd,Mn)Te material [5]. It is, however, decreasing rapidly for high magnetic field and at 12T 

reaches value of tens of nanoseconds, which is over two orders of magnitude smaller than the 

one observed for bulk material. Possible origins of this surprising difference include strain 

fields, usually high in structures containing QDs. 

[1] L. Besombes et al., Phys. Rev. Lett. 93, 207403 (2004). 

[2] C. Le Gall et al, Phys. Rev. Lett. 102, 127402 (2009). 

[3] M. Goryca et al, Phys. Rev. Lett. 103, 087401 (2009). 

[4] T. Kazimierczuk et al, Phys. Rev. B 79, 153301 (2009). 

[5] T. Strutz et al., Phys. Rev. Lett. 68, 3912 (1992). 

106

40th _______________________________________________________________ 


Magnetophotoluminescence of CdTe/ZnTe Quantum Dots: 

G-factor and Diamagnetic Shift Variation in a Single Dot 

Tomasz Kazimierczuk 1 , Mateusz Goryca 1,2 , Piotr Wojnar 3 , 

Andrzej Golnik 1 , Piotr Kosacki 1,2 

1 Institute of Experimental Physics, Faculty of Physics, 

University of Warsaw, ul. Hoża 69, PL-00-681 Warsaw, Poland 

2 LNCMI-CNRS (UJF, UPS, INSA), BP 166, 38042 Grenoble Cedex 9, France 

3 Institute Physics, Polish Academy of Science, 

Al. Lotników 32/46, PL-02-668 Warsaw, Poland 

Typically, self-assembled quantum dots (QDs) are characterized by strong confining 

potential, which defines carrier wavefunctions. A flat shape of such QDs lifts the degeneracy 

between light and heavy holes in favor of the latter ones. Due to the selection rules, the 

recombination occurs between an electron and a hole of opposite spin directions. Thus, in the 

magnetic field along growth direction, all transitions with carriers in the ground state exhibit 

Zeeman given by a difference between electron and hole Landé factors. Particularly, the same 

Zeeman splitting should be observed for X, X + , X - , and XX transitions. Such a predictiction 

was tested already in early stages of QD research demonstrating equality between Landé 

factors for neutral and charged exciton with precision better than 1% [1]. 

In this work we present a comparison of magnetic field influence on various excitonic 

transitions in single CdTe/ZnTe QDs. The experiments included PL measurements in 

magnetic field up to 28T applied either 

perpendicular or parallel to the growth direction. 

Recorded data allowed us to extract two basic 

parameters: excitonic Landé factor related to linear 

Zeeman effect and diamagnetic shift related to 

quadratic field dependence. Contrary to the picture 

described previously, we discovered a clear 

systematic difference between g-factors inferred 

from X, X + , and X - transitions in Faraday 

configuration (Fig. 1). Landé factor inferred from 

the XX transition follows exactly values related to 

X transition, as in both cases the spectral effect is 

related to splitting of the same state (being final or 

initial one respectively). The average difference 

between X + and X - g-factors yields 21%. 

Similar but smaller difference between g-factors inferred from different excitonic 

transitions was found in the in-plane field geometry. In such a geometry, qualitatively similar 

behavior was reported for pyramidal InGaAs/AlGaAs QDs [2] and interpreted in terms of 

Coulomb correlations. In our case, such an interpretation is supported by analysis of 

diamagnetic coefficients. The lack of significant systematic difference in diamagnetic shift 

allows us to reject an alternative explanation of g-factor variation by increase/decrease of 

barrier penetration by weakly confined hole. 

[1] J. J. Finley et al., Phys. Rev. B 66, 153316 (2002). 

[2] D. Y. Oberli et al., Phys. Rev. B 80, 165312 (2009). 

107 

g-factor of X + , X - , and XX 

3.0 

2.5 

2.0 

1.5 

XX 

X + 

X - 

1.0 

1.0 1.5 2.0 2.5 3.0 

g-factor of X 

Fig. 1. Correlation between Landé factors 

inferred from different excitonic transitions 

in 24 different dots.

TuO6 _______________________________________________________________ 


ControloverCdTeQuantumDotsEmissionusingZnTe-based 

MicropillarCavities 

T.Jakubczyk 1 ,W.Pacuski 1 ,A.Golnik 1 ,C.Kruse 2 ,D.Hommel 2 , 

H.Hilmer 3 ,R.Schmidt-Grund 3 and J.A.Gaj 1 

1 InstituteofExperimentalPhysics,UniversityofWarsaw,ul.Hoża69,00-681Warsaw, 

Poland 

2 InstituteofSolidStatePhysics,UniversityofBremen,Postfach330440,D-28334, 

Bremen,Germany 

3 InstituteforExperimentalPhysicsII,UniversitätLeipzig,Linnéstr.5,D-04103, 

Leipzig,Germany 

Pillarmicrocavitiescontainingquantumdots(QDs)werereportedassystemsenablingcontroloverspatial,energeticandtemporalaspects[1]oflightemission.Intermsof 

applicationsinquantuminformationprocessing[2],coherentcouplingbetweenlightand 

matterobtainedinsuchsystemsisofprimaryimportance.Inthiscontextanextension 

oftheresearchfromtheGaAs-basedsystemstowiderband-gapII-VIbasedonesispromising.Therobustexcitonicstatesandastrongercarrierconfinementinthesematerials 

extendthefunctionalityrangeofsuchQDsystemstohighertemperatures. 

Inthiscommunicationwereportamicrophotoluminescencestudyofpillarcavities 

basedonsuperlattice-baseddistributedBraggreflectors(DBRs)[3],lattice-matchedto 

ZnTe.Micropillarsofdiametersrangingfrom0.7to5µmwereetchedbyfocusedion 

beam(FIB)outofaplanarmicrocavitybasedontheseDBRsandcontainingasingle 

planeofCdTe/ZnTequantumdots. 

BoththeemissionofasingleQDaswellasemissionof 

anensembleofthemwasusedtoexaminedifferentpropertiesofthestructures.WepresentresultsprovingtheabilityofZnTe-basedpillarstoenhancetheQDsemission(see 

Figure).Furthermore,wepresenttheirabilitytoguidethis 

emissionresultinginanenhancedcollectionrate.ThesefeaturesstronglyindicatethepossibilityofconstructingefficientsinglephotonsourcesbasedonCdTeQDs. 

Toinhibittheunwantedemissionintotheleakymodes 

anewapproachwasused.AlateralDBRmadeofyttriastabilizedzirconiaandaluminawassuccessfullydeposited.Wepresentadetailedphotoluminescencestudyoftheobtainedstructures. 

[1]J.M.Gérard,B.Sermage,B.Gayral,B.Legrand,E.Costard,andV.Thierry-Mieg, 

Phys.Rev.Lett.81,1110 

(1998). 

[2]J. P. Reithmaier, G. S ֒ ek, A. Löffler, C. Hofmann, 

S.Kuhn,S.Reitzenstein,L.V.Keldysh,V.D.Kulakovskii,T.L.Reinecke,andA.Forchel,Nature432,197 

(2004). 

[3]W.Pacuski,C.Kruse,S.Figge,andD.Hommel,Applied 

PhysicsLetters94,191108(2009). 

108

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"Jaszowiec" 2011 International School and Conference on the Physics of Semiconductors TuP1 

Exciton and Mn spin dynamics in a nonresonantly coupled pair 

of (Cd,Mn)Te quantum dots 

T. Smoleński 1 , ̷L. Cywiński 2 , M. Goryca, 1 and P. Kossacki 1 

1 Institute of Experimental Physics, Faculty of Physics, University of Warsaw, ul. Ho˙za 

69, 00-681 Warsaw, Poland 

2 Institute of Physics, Polish Academy of Sciences, Al. Lotników 32/46, 02-668 Warsaw, 

Poland 

It has been shown recently that a spin of a single Mn ion residing inside a quantum 

dot can be optically oriented by circularly polarized light creating spin-polarized excitons 

in the dot [1,2]. In case of experiments in which the absoprtion line corresponding to a 

specific spin state of the Mn was excited resonantly [2], it was argued that the spin relaxation 

of holes (due to phonon scattering and spin-orbit interaction, leading to transitions 

between bright and dark exciton states seen in experiment in Ref. [2]) can explain the 

existence of the Mn optical orientation [3]. 

In experiment from Ref. [1] the spin-polarized excitons were created in the Mn free 

dot which was nonresonantly coupled to an adjacent dot [4] containing a single Mn spin 

[1,5]. The exciton (X) tunnels out of the first dot in a few ps [4], but the timescale on 

which it relaxes to its ground state in the second dot (thereby lowering its energy by 

≈ 0.2 eV) is not precisely know. Depending on whether this relaxation is fast or slow 

compared to the dynamics of the exciton coupled to the Mn spin, different states of the 

X+Mn system are expected to be realized after the relaxation. In order to model both the 

dynamics of the photoluminescence from the second dot, and the Mn spin dynamics (due 

to the sp-d exchange coupling with the exciton), we use the Lindblad generator formalism 

to describe all the relaxation process: the transition from the first dot to the ground 

state of the second dot, the radiative recombination, and the carrier spin relaxation. In 

this way we model both the coherent and the incoherent the processes leading to the 

brightening of dark excitons [5], possible population trapping in the dark state, and Mn 

optical orientation. 

This work was supported by InTechFun (Grant No. POIG.01.03.01-00-159/08), by the 

Homing and the Start programmes of the Foundation for Polish Science supported by the 

EEA Financial Mechanism, and by the Polish Ministry of Science and Higher Education 

as research grants in years 2010-2011. 

[1] M. Goryca, T. Kazimierczuk, M. Nawrocki, A. Golnik, J.A. Gaj, P. Kossacki, P. Wojnar, 

and G. Karczewski, Phys. Rev. Lett. 103, 087401 (2009). 

[2] C. Le Gall, L. Besombes, H. Boukari, R. Kolodka, J. Cibert, and H. Mariette, Phys. 

Rev. Lett. 102, 127402 (2009). 

[3] ̷L. Cywiński, Phys. Rev. B 82, 075321 (2010). 

[4] T. Kazimierczuk, J. Suffczyński, A. Golnik, J.A. Gaj, P. Kossacki, and P. Wojnar, 

Phys. Rev. B 79, 153301 (2009). 

[5] M. Goryca, P. Plochocka,T. Kazimierczuk, P. Wojnar, G. Karczewski, J.A. Gaj, M. Potemski, 

and P. Kossacki Phys. Rev. B 82, 165323 (2010). 

109

TuP2 _______________________________________________________________ 


Three-dimensional anisotropy studies of CdTe quantum dots 

J. Kobak 1 , W. Pacuski 1 , T. Kazimierczuk 1 , J. Suffczy ski 1 , T. Jakubczyk 1 , A. Golnik 1 , 

P. Kossacki 1 , M. Nawrocki 1 , J.A. Gaj 1 , C. Kruse 2 , D. Hommel 2 

1 Institute of Experimental Physics, Faculty of Physics, University of Warsaw, 

ul. Ho a 69, PL-00-681 Warszawa, Poland 

2 Institute of Solid State Physics, University of Bremen, PO.Box 330 440, D-28334 Bremen, 

Germany 

In standard microphotoluminescence study of quantum dots (QDs) optical axis is 

oriented parallel to the growth axis of the sample. Therefore polarization of emitted photons is 

perpendicular to the growth axis of the sample. In this work we present the results of microand 

macro-photoluminescence study of QDs in a configuration with optical axis perpendicular 

to the growth axis. Such measurements were possible since the samples were cleaved and 

their edge was exposed. In our measurements we explore both polarizations parallel and 

perpendicular to the growth axis. 

We studied selforganized CdTe QDs in ZnTe matrix grown by molecular beam 

epitaxy (MBE). Two techniques were used in order to form dots from thin CdTe layer. In the 

first technique the CdTe thin layer was covered by amorphous tellurium at a low temperature. 

Subsequently amorphous tellurium was evaporated at growth temperature before overgrowing 

with ZnTe. In the second technique, the CdTe thin layer was overgrown by ZnTe with high 

Zn content, without changing the temperature. For spectroscopy samples were placed under 

the microscope lens which position was controlled by three xyz piezo translation stages. 

Whole system was immersed in superfluid helium in a magneto-optical cryostat. Lines 

associated to the single QDs we identified with use of single photon correlation 

measurements. 

Two emission bands were observed in the macro-photoluminescence measurements. 

Band seen at lower energy was attributed to quantum dots. This band is strongly polarized in 

direction perpendicular to the growth axis of the sample. Such effect is expected for heavy 

hole excitons. The band located at higher energy was identified as coming from the wetting 

layer. It shows a small degree of linear polarization with a stronger component in direction 

parallel to the growth axis. 

In micro-photoluminescence measurements we have found that more than 99% of 

QDs show the complete polarization perpendicular to the growth axis. This is in agreement 

with macro-photoluminescence results and with prediction done for heavy hole excitons. 

Surprisingly, we have found also sharp emission lines exhibiting a weak polarization degree. 

Moreover, for them the stronger polarization was parallel to the growth axis. Apart from 

polarization properties, such lines exhibit typical properties of QDs: excitation power 

dependence and temporal evolution such as biexciton – exciton cascade observed in photon 

correlation measurements. 

We have done magneto-optical measurements to get a deeper understanding of the 

observed unusual polarization anisotropy. We applied two configurations: with a magnetic 

field in a direction parallel or perpendicular to the growth axis. Results of the polarization 

resolved magnetooptical measurements are discussed in terms of multi-axis anisotropy of 

QDs. 

110

40th _______________________________________________________________ 


Probing electron concentration in epitaxial graphene 

using Raman spectroscopy 

K.Grodecki 1,2 , W.Strupinski 2 , A.Wysmołek 1 , R.Stępniewski 1 , and J.M.Baranowski 2,1 

1 Faculty of Physics, University of Warsaw, Hoża 69, 00-681 Warsaw, Poland 

kacper.grodecki@fuw.edu.pl 

2 Institute of Electronic Materials Technology, Wólczynska 133, 01-919 Warsaw, Poland 

Over the past years, a lot of attention has been attracted to graphene. Its unique 

properties could make it the successor to silicon in electronic applications. Now one of the 

essential problems that must be solved in graphene technology is accurate control of the 

carrier concentration in the structure. Within this communication we would like to let know 

that this problem can be effectively solved by the use of Raman spectroscopy. The Raman 

spectra of graphene-like structures consist of several bands. The most prominent among them 

are so called G and 2D bands. The position of the 2D band is predominantly strain sensitive 

whereas the position of the G band depends both on the intensity and the doping [1, 2]. 

In this communication we show how frequency measurements of G and 2D-band may 

be used to evaluate free carrier concentration in graphene layer. In order to validate this 

method we have examined a set of graphene samples with known electron concentration. 

The measured graphene layers were grown on Si face of 4H-SiC on-axis substrates by 

chemical vapor deposition technique [3]. As determined from the Hall measurements the 

electron concentration of different samples remained between 6x10 12 and 2.4x10 13 cm -2 . 

Micro-Raman measurements were performed at room temperature using single grating 

spectrometer equipped with longpass filters and CCD camera. The size of exciting light spot 

from 532nm Nd:YAG continuous wave laser at the sample surface was approximately 2mm 

in diameter. 

The micro-Raman measurements performed on the samples with different electron 

concentration revealed pronounced shifts of the G and 2D band positions. Basing on the 

strain dependences of these bands from literature data [2] the electron concentration induced 

shift was calculated. This result - 1cm -1 /10 12 cm 2 - remains in compliance with the 

measurements performed within this concentration range for a gated structure freestanding 

graphene measurements [1]. This proves that Raman spectroscopy can be very useful as a fast 

contactless method which allows to determinate the local carrier concentration and strain (up 

to micrometer scale) in graphene structures. 

[1] A. Das, S. Pisana, B.Chakraborty, S. Piscanec, S. K. Saha, U. V. Waghmare, K. S. 

Novoselov, H. R. Krishnamurthy, A. K. Gaim, A. C. Ferrari and A. K. Sood, Nature 

Nanotechnology 3, 210 (2008) 

[2] N. Ferralis, Journal of Materials Science 45, 19, (2011) 

[3] W. Strupinski, K. Grodecki, A. Wysmolek, R. Stepniewski, T. Szkopek, P. E. Gaskell, A. 

Gruneis, D. Haberer, R. Bozek, J. Krupka, and J. M. Baranowski, NANO Letters (2011) DOI: 

10.1021/nl200390e 

111

TuP4 _______________________________________________________________ 


Dynamical control of excitonic fine structure with nanomechanical strain 

M. Zielinski 1 , G. W. Bryant 2 , N. Malkova 2 , J. Sims 3 , W. Jaskolski 1 , J. Aizupura 4 

1 Instytut Fizyki UMK, ul. Grudziądzka 5, 87-100 Toruń, Poland 

2 Atomic Physics Division and Joint Quantum Institute, NIST, 100 Bureau Drive, 

Gaithersburg, Maryland 20899-8423, USA 

3 Information Technology Laboratory, NIST, 100 Bureau Drive, Gaithersburg, Maryland 

20899-8423, USA 

4 Centro Mixto de Fisica de Materiales CSIC-UPV/EHU and Donostia International Physics 

Center, Paseo Manuel Lardizabal 4, Donostia-San Sebastian 20018, Spain 

We show how nanomechanical strain [1,2] can be used to achieve dynamical control 

of electronic and optical properties of semiconductor quantum dots, including exciton fine 

structure of single quantum dots and charge distributions in double quantum dots with 

potential applications in quantum dot based schemes for entangled photon-pair generation and 

manipulating interacting qubits for quantum information processing. 

We use atomistic tight-binding theory [1-4] to describe the response of confined states 

in a self-assembled quantum dot embedded in a nanomechanical cantilever. The internal strain 

due to the lattice mismatch, the external strain and the internal readjustment to minimize the 

applied strain must all be accounted for to model correctly the strain effects [1,2]. We show 

that applied strain can be used to manipulate the fine structure splitting of mechanoexcitons 

by distorting electron and hole charge distributions and rotating hole orientation. Electrons 

and hole levels and charge distributions can shift together or in opposite directions depending 

on how the strain is applied. This gives control for tailoring band gaps and optical response. 

The strain can also be used to transfer electrons and holes between vertically or laterally 

coupled dots, giving a mechanism for manipulating transition strengths and interacting qubits 

for quantum information processing. 

We demonstrate that nanomechanical strain tunes the exchange splittings and rotates 

the polarization of mechanoexcitons, providing energy and phase control of excitons. We 

further demonstrate that nanomechanical strain is a tool to shift electron and hole levels, 

transfer carriers between dots, manipulate mechanoexciton shape, orientation, fine-structure 

splitting and optical transitions rates. 

[1] G.W. Bryant, M. Zielinski, N. Malkova, J. Sims, W. Jaskolski and J. Aizpurua, Phys. Rev. 

Lett. 105, 067404 (2010). 

[2] G.W. Bryant, M. Zielinski, N. Malkova, J. Sims, W. Jaskolski, J. Aizpurua, prepared for 

publication in Phys. Rev. B 

[3] W. Jaskolski, M. Zielinski, G.W. Bryant, J. Aizpurua, Phys. Rev. B 74, 205309 (2006). 

[4] M. Zielinski, M. Korkusinski, and P. Hawrylak, Phys. Rev. B 81, 085301 (2010). 

112

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Non-Markovian noise at the Fermi-edge singularity in quantum 

dots 

Katarzyna Roszak 1 and Tomáˇs Novotný 2 

1 Institute of Physics, Wroc̷law University of Technology, 50-370 Wroc̷law, Poland 

2 Department of Condensed Matter Physics, Faculty of Mathematics and Physics, 

Charles University, 12116 Prague, Czech Republic 

The Fermi-edge singularity is a phenomenon originating from the interaction of conduction 

electrons with localised perturbations and is characterised by a power-law divergence. 

It was first predicted theoretically for X-ray absorption in metals [1] and later 

verified experimentally [2]. The theory then developed [1,3] has been used to describe 

other situations involving a similar Hamiltonian and leading to the same power-law divergence, 

such as resonant tunnelling through localised levels. The proper description of 

the transport set-up is done by an extension of the original Fermi-edge singularity model, 

where no charge transfer between the continuum and the localized level(s) is considered, 

to the interacting resonant level model, which has served recently as an important benchmark 

for novel quantum transport techniques [4]. 

The Fermi-edge singularity in transport through quantum dots occurs in the regime 

where the energy of the quantum dot level(s) is similar to that of one of the leads. The 

change of occupation in the local level(s) during the tunnelling process leads to sudden 

changes in the scattering potential and hence, to truncated singular behaviour of the 

current through the quantum dot at resonance and power-law dependence of the current 

away from resonance [5,6]. As shown in recent experiments [6], noise in this regime 

displays characteristic behaviour (including a super-Poissonian maximum) which cannot 

be accounted for by the Markovian theory. Since the Fermi-edge singularity transport 

setup involves both many-body correlations and quantum coherence it is reasonable to 

expect large non-Markovian corrections in the singularity region. We show that this is 

indeed the case and that including the non-Markovian effects allows us to account for all 

of the qualitative features of the noise. 

[1] G. D. Mahan, Phys. Rev. 163, 612 (1967). 

[2] P. H. Citrin, Phys. Rev. B 8, 5545 (1973). 

[3] G. D. Mahan, Many-Particle Physics (Kluwer, New York, 2000). 

[4] E. Boulat, H. Saleur, and P.Schmitteckert, Phys. Rev. Lett.101, 140601 (2008). 

[5] H. Frahm, C. von Zobeltitz, N. Marie, and R. J. Haug, Phys. Rev. B74,035329 (2006). 

[6] N. Marie, F. Hohls, T. Lüdtke, K.Pierz, R. J. Haug, Phys. Rev. B 75, 233304 (2007). 

113

TuP6 _______________________________________________________________ 


Transport and Spin Properties of CdTe/CdMgTe Quantum Point Contacts 

M. Czapkiewicz, J. Wróbel, V. Kolkovsky, P. Nowicki, M. Aleszkiewicz, M. Wiater and 

T. Wojtowicz 

Instytut Fizyki PAN, Warszawa, Poland 

The spin properties of one-dimensional (1D) semiconductor devices are more strongly influenced 

by electron-electron interactions as compared to two-dimensional (2D) systems. Up to 

now, however, studies of spin characteristics of 1D transport channels are almost exclusively 

devoted to III-V heterostructures and quantum wells [1]. Here we report on fabrication and 

low temperature magnetotransport measurements of quantum point contacts, patterned from ntype 

CdTe/CdMgTe modulation doped quantum well. We expect that the many-body effects are 

quite important in this material since the effective mass is larger and the dielectric constant is 

smaller as compared to GaAs. 

Two-terminal quantum point contacts 

have been made of high quality 2D electron 

gas with concentration n2D= 4.6×10 11 cm −2 

and mobility µ = 0.2×10 6 cm 2 /Vs. The 

nanojunctions of length L≈0.2 µm and lithographic 

width Wlith = 0.45±0.01 µm are 

patterned by e-beam lithography and deepetching 

techniques. The carrier density in the 

device is controlled by means of V-shaped 

side gates which are separated from the constriction 

area by narrow etched grooves, see 

Fig. 1. The differential conductances G have 

been measured in a He-3 cryostat as a function 

of dc source-drain excitation and inplane 

magnetic field by employing a standard 

low-frequency lock-in technique. 

SG 

5 

10 

15 

µm 

etched grooves 

SG 

Figure 1: Atomic force microscopy image 

of quantum point contact formed by chemical 

etching. The width of nano-junction is controlled 

by side gates (SG). 

Data show that G is quantized vs gate voltage, however, conductance steps are reduced 

down to≈ 0.6×(2e 2 /h) and superimposed on reproducible conductance fluctuations (UCF’s). 

We have also found, that the quantization/UCF patterns change considerably when voltages are 

applied asymmetrically to the side gates. Therefore, we argue that transport in studied devices 

is strongly influenced by short range potential fluctuations present in the junction area. However, 

in spite of a disorder, we have been able to observe the Zeeman splitting of 1D transport 

channels at milikelvin temperatures. By comparing obtained splittings with the nonlinear conductance 

data we have been able to determine the effective Landé factor in the constriction. We 

have found that |g ∗ | = 1.7±0.1 in remarkable agreement with bulk value reported for CdTe, 

independently on 1D level index. We conclude that there is no enhancement of electronic g factor. 

This is an unexpected result, since such enhancement, attributed to exchange interaction, 

was always observed for quantum point contacts and quantum wires made of GaAs [2]. 

We acknowledge the support from the Polish Ministry of Science and Higher Education, 

project number N202/103936 and partial support by the European Union within European Regional 

Development Fund (grant Innovative Economy POIG.01.01.02-00-008/08). 

[1] K.-F. Berggren and M. Pepper, Phil. Trans. R. Soc. A 368, 1141 (2010). 

[2] K. J. Thomas et al., Phys.Rev. B 68, 4846 (1998). 

114

40th _______________________________________________________________ 


The Role of Strong Coupling in the Superradiance of Ensembles 

of Quantum Dots. 

Micha̷l Kozub, Pawe̷l Machnikowski 


We present a theoretical description of spontaneous emision from a dense ensemble 

of self-assembled quantum dots (QDs) in the limit of weak excitation. We show that 

the decay rate of the spontaneous emission from the system depends on the number of 

collectively emitting dots, thus confirming the experimental conclusion [1] on the appearance 

of collective (superradiant) emission in the inhomogeneous ensamble of interacting 

dots. However our simulations indicate that interactions over a common electromagnetic 

reservoir are not sufficiently strong to account for the observed increase of the decay rate. 

We therefore introduce additional terms in the interaction potential to make up for the 

discrepancy between the experiment and our simulations. 

In the experiment [1], the decay rate of the luminescence signal was analysed as a 

function of the size of mesas cut out in a planar ensemble of QDs, that is, of the number 

of dots collectively interacting with the electromagnetic field. The observed decay of luminescence 

after a resonant excitation had an approximately exponential character with 

the decay rate increasing as the mesas became larger. This was interpreted as a collective 

effect, due to long range coupling between the dots. 

In this work we model the ensemble of QDs as a system of interacting and collectively 

emitting two-level atoms. In analogy with the experimental procedure, we study the 

emission of systems of dots with randomly selected transition energies that are randomly 

placed (at a fixed density) on squares of different sizes. The evolution of the system 

is simulated using the equations derived in the Power-Zinau-Wooley picture and in the 

Markov approximation, which corresponds to the method of Ref. [2], generalized to nonidentical 

emitters placed in a dielectric medium. We make the additional assumption that 

at most one exciton is present in the system in the initial state, coherently delocalized 

over all the dots (which corresponds to resonant excitation with a very short pulse). We 

calculate the time dependence of the average number of excitons in the dots for system 

parameters corresponding to the experimental situation [1] and show that the population 

decay indeed has an approximately exponential character with rates very close to 

those observed experimentally. This result could not be achieved for dipole-coupled dots, 

without taking into account another type of QD interaction. We show that including a 

short range tunnel coupling between the dots leeds to an increase of the recombination 

rate which is indistinguishable from that obtained for an artificially enhanced long-range 

dipole coupling. In this way we show that the coupling between the quantum dot emitters 

and the electromagnetic vacuum cannot be held fully responisble for the variation of the 

emission rate as proposed in [1]. 

[1] M. Scheibner et al., Nature Physics, 3, 106 (2007). 

[2] R. H. Lehmberg, Phys. Rev. A, 2, 883 (1970). 

115

TuP8 _______________________________________________________________ 


Photoluminescence Linewidth Analysis 

of Single CdMnTe Quantum Dots 

M. Szymura 1;2 , Ł. Kłopotowski 2 , P. Wojnar 2 , K. Fronc 2 , T. Kazimierczuk 3 , 

G. Karczewski 2 and T. Wojtowicz 2 

1 Department of Mathematics and Natural Sciences, 

Cardinal Stefan Wyszyński University, Warsaw, Poland 

2 Institute of Physics, Polish Academy of Sciences, Warsaw, Poland 

3 Faculty of Physics, University of Warsaw, Warsaw, Poland 

Quantum dots (QDs) doped with transition metal ions are interesting from the point of view of 

both basic studies and applications in quantum information processing. Introducing e.g. Mn, 

substantially changes magnetooptical properties of QDs. In particular, the photoluminescence 

(PL) linewidth (γ) for a CdTe QD is about 200 μeV, while for CdMnTe with 20% of 

manganese increases by a factor of 100. In this report, we present a comprehensive study of 

the PL linewidth performed on a large number of dots differing with respect to size and 

manganese concentration. 

Two kinds of structures with CdMnTe QDs were investigated: those with ZnTe barrier and 

with ZnMnTe barrier. All quantum dots were grown by molecular beam epitaxy (MBE) on 

GaAs substrate. A 4 μm thick buffer CdTe layer was first deposited. Next a ZnTe (and 

ZnMnTe) barrier layer was grown. QDs were developed from 6 monolayers of CdMnTe. PL 

measurements were performed as a function of the magnetic field up to 5T at a temperature of 

2K. We study samples with manganese concentration between 1% to 20%. 

The presence of manganese ions caused giant Zeeman splitting of electronic states of QDs.We 

- 

analyzed two circular polarizations. In practice, the transitions in polarization quickly 

disappear as a result of efficient spin relaxation between the Zeeman split subbands. We 

reproduce the transition energies with a Brillouin function, which allows us to evaluate 

manganese concentration and temperature. 

Broadening of the PL transitions from Mn-containig QDs is due to magnetization fluctuations. 

Therefore, γ depends on magnetic field, QD volume and manganese concentration and 

temperature [1]. At the absence of magnetic field, for a QD with 1.5% manganese we find γ 

≈4.5 meV. As the magnetic field is increased, γ decreases by about a factor of 2 in 5T. This 

decrease manifests the freezing of the magnetic fluctuations in increased magnetic field. We 

reproduce this narrowing of the linewidth with magnetic field with a formula derived from 

fluctuation dissipation theorem [1]. We obtain a good agreement between the results of 

calculations and experiment. Moreover, the above analysis allows us to evaluate the QD 

volume. We find that QDs emitting in higher energies have smaller volume, as expected. 

[1] G. Bacher et al. Phys. Rev. Lett. 89, 127201 (2002). 

116

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Statistical Study of the Inter-Dot Excitation Transfer in CdTe/ZnTe 

Quantum Dots. 

Maciej Koperski 1 , Tomasz Kazimierczuk 1 , Mateusz Goryca 1 , Andrzej Golnik 1 , 

Jan A. Gaj 1 , Michał Nawrocki 1 , Piotr Wojnar 2 and Piotr Kossacki 1 

1 Institute of Experimental Physics, Faculty of Physics, University of Warsaw, 

Hoża 69, 00-681 Warsaw, Poland 

2 Polish Academy of Sciences, Lotników 32/46, 02-668 Warsaw, Poland 

Photoluminescence (PL) experiments are the most basic tool for characterization of 

semiconductor quantum dots (QDs). They provide broad range of information on the 

excitonic complexes, such as neutral excitons (X), trions (X + , X - ) and biexcitons (XX), 

confined in a zero-dimensional system. Measurements of PL spectra as a function of 

excitation laser energy is known as photoluminescence excitation technique (PLE). Features 

in PLE spectra are usually related to excited exciton states or phonon-replica. Additionally, in 

the system of self organized CdTe/ZnTe quantum dots, very sharp resonances at high energy 

are often observed. They were attributed to the efficient excitation transfer between 

neighboring dots [1]. Diverse experiments have been reported, taking advantage of the 

excitation transfer, such as polarization conversion [1] and orientation of the magnetic ion in 

dots with single manganese atom [2]. Despite extensive studies, the detailed mechanism of the 

inter-dot tunneling remains not entirely clear. 

Here we present the results of detailed statistical analysis of the energy distribution of 

resonances detected in PLE spectra. We studied MBE grown samples containing single layer 

of self organized CdTe/ZnTe quantum dots. The samples were placed in a microphotoluminescence 

setup at low temperature (1.5 - 15 K). The PL was excited using a tunable 

dye laser in the range 570−610 nm. During measurements we have selected more than 200 

single quantum dots for which exciton complexes (X, X+, X- and XX) were identified, and 

for which the sharp resonances related to inter-dot transfer were observed. Each resonance 

correspond to the absorption with creation of neutral exciton, after which the exciton is 

transferred to the second dot and subsequently recombines. The difference between energies 

of neutral excitons in the two dots varied in our experiments between 80 meV and 300 meV 

and was mainly limited by the experimental setup. This distance is larger than typical distance 

between s-shell and p-shell groups of lines which yields about 50meV in our case. We 

analyzed the occurrence probability versus the energy distance between neutral exciton line in 

the emitting dot and the exciton energy in the absorbing dot (resonance energy). 

This analysis revealed relatively flat distribution of the resonances, which shows that 

levels participating in the tunneling are not collected in separate groups (p-shell, d-shell etc.). 

This might be interpreted as a result of smearing discrete distribution into continues one due 

to the statistical scatter between different dots or significant broadening of the excited states 

in each emitting dot. In any case, the observed flat distribution suggest that the density of 

states participating in the tunneling is flat or the tunneling occurrence is not limited by the 

presence of excited states in the emitting dot. 

[1] T. Kazimierczuk, J. Suffczyński, A. Golnik, J. A. Gaj, P. Kossacki and P. Wojnar, Phys. 

Rev. B 79, 153301 (2009). 

[2] M. Goryca, T. Kazimierczuk, M. Nawrocki, A. Golnik, J. A. Gaj, P. Kossacki, P. Wojnar 

and G. Karczewski, Phys. Rev. Lett. 103, 087401 (2009) 

117

TuP10 _______________________________________________________________ 


Phonon influence on the weak measurement of double quantum 

dot spin states. 

̷L. Marcinowski 1 , M. Krzy˙zosiak 1,2 , K. Roszak 1 , P. Machnikowski 1 , 

R. Buczko 3 , and J. Mostowski 3 


2 Beijing University of Technology, 100124 Beijing, China 

3 Institute of Physics, Polish Academy of Sciences, 02-668 Warsaw, Poland 

The occupation of a double quantum dot (DQD) can be measured by coupling one of the 

dots to a quantum point contact (QPC) and monitoring the current flowing through the 

QPC [1]. This originates form the interaction between the quantum dot and QPC electrons 

which shifts the energy level in the QPC depending on the dot state influencing the 

tunneling rate through the point contact. A single tunneling event is a weak measurement 

of the dot and provides a small amount of information about the system state. A series 

of tunneling events constitutes a continous measurement process in which the descrete 

current yields a growing amount of information on the system state, but also gradually 

destroys quantum coherence and localizes the state, consistently with the von Neumann 

projection principle. 

The same measurement scheme can be used to distinguish two-electron spin-singlet 

and spin-triplet states in DQDs [2]. This is based on Pauli exclusion: when the spin-triplet 

state requires the electrons to be localized in different dots (only QD ground states are 

taken into account), double dot occupation is allowed for the spin-singlet state. Hence, 

monitoring the fluctuations in the QPC current allows one to perform a measurement in 

the singlet-triplet basis. 

In this work we study the effect of phonon-induced transitions which are present in this 

solid state system [3] on the QPC current and the measurement-influenced evolution of the 

DQD state. In the strong bias regime, when the measurement is possible in the absence 

of phonons [2], phonon-induced relaxation leads to a reduction of the double occupation, 

and hence, to quenching of the current response. In the weak bias case the energy transfer 

from the tunneling electron is insufficient to excite the QD to a doubly occupied state 

and the phonon reservoir serves as a source of noise which makes the excitation possible; 

this is reflected in the current trace. 

[1] T. M. Stace and S. D. Barrett, Phys. Rev. Lett. 92, 136802 (2004). 

[2] S. D. Barrett and T. M. Stace, Phys. Rev. B 73, 075324 (2006). 

[3] K. Roszak and P. Machnikowski, Phys. Rev. B 80, 195315 (2009). 

118

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InfluenceofCarrierTrappingontheOpticalPropertiesof 

InAs/InPQuantumDashes 

P.Kaczmarkiewicz,A.Musiał,G.Sęk,P.Podemski,J.Misiewicz, 

P.Machnikowski 

InstituteofPhysics,WrocławUniversityofTechnology,50-370Wrocław,Poland 

WemodeltheopticalpropertiesofhighlyanisotropicInAs/InPquantumdots,also 

referredtoasquantumdashes(QDashes)[1]. Thosestructuresarecharacterizedbya 

non-uniformshapeandpresenceofwidthfluctuations[2]whichcanprovideadditional 

confinementinthesystem. Trappingofcarriersinthepotentialfluctuationsleadsto 

quantitativeandqualitativechangeintheopticalpropertiesofthesystem.Theexciton 

groundstateexhibitsQD-like(stronglyconfined[3])propertieswhichcanexplainthe 

temperaturedependenceofthedegreeoflinearpolarizationofemittedradiation. 

WeshowhowthetransitionratesdependonQDashshapeparameters(amplitude 

andpositionofthewidening)andcalculateemissionspectraforsingleQDashesandfor 

ensemblesofQDashes. Wealsostudythepolarizationpropertiesofradiationemitted 

bythesystem. WeconfirmthataQDashwidthfluctuationleadstostrongtrapping 

ofcarriers,whichresultsinloweringtheanisotropyofanexcitongroundstateinspite 

ofstrongelongationofthewholestructure. Suchacharacteroftheconfiningpotential 

manifestsitselfintheexperimentalresultsbyaloweredvalueofthedegreeoflinear 

polarizationatlowtemperaturesandlowexcitationconditions. 

TheinvestigationoftheopticalpropertiesofQDashesisimportantfromthepointof 

viewofpossibleapplications.IthasbeenshownthatQDashesmayhaveseveraladvantagesoverothernanostructures,especiallyinlaserapplicationsfortelecommunication[1]. 

Understandingofthepolarizationpropertiesandthereforecarrierconfinementregimeis 

alsoimportantforconstructingpolarization-insensitiveopticalamplifiers[4]. 

Webaseourmodelingoftheelectron-holesystemontheeffectivemassmethodwith 

light-heavyholebandmixingtakenintoaccount[5].Theholestatesareassumedtoconsist 

mostlyofaheavy-holecomponentwithsmalladmixtureoflight-holestates.Thislightholeadmixturedependsontheanisotropyoftheholewavefunctionviathemomentum 

dependenceoftherelevantelementofthe k·pHamiltonian. Interferencebetweenthe 

radiationemittedbythelight-andheavy-holecomponentsleadstotheappearanceof 

apreferredpolarizationaxis,paralleltothestructureelongation. Thepresenceofan 

additionalconfinementduetotheshapefluctuationdecreasestheanisotropyofanexciton 

groundstateandreducestheDOP.Inourmodelingweconsiderthecaseofasingle 

excitonconfinedinaQDash,whichcorrespondstoexperimentalmeasurementsinthe 

weakexcitationregime. Coulombcorrelationsareincludedwithintheconfigurationinteractionscheme. 

[1]J.P.Reithmaier,G.Eisenstein,A.Forchel,Proc.IEEE95,1779(2007). 

[2]H.Deryetal.,J.Appl.Phys.95,6103(2004). 

[3]G.Sęketal.,J.Appl.Phys.105,086104(2009). 

[4]P.Podemskietal.,Appl.Phys.Lett.93,171910(2008). 

[5]P.Kaczmarkiewiczetal.,ActaPhys.Pol.A(inprint). 

119

TuP12 _______________________________________________________________ 


CdSe/ZnS Colloidal Quantum Dots with Alloyed Core/Shell Interfaces: 

a Photoluminescence Dynamics Study 

Konrad Dziatkowski 1,2 , Daniel Ratchford 1 , Thomas Hartsfield 1 , Xiaoqin Li 1 , 

Yan Gao 3 and Zhiyong Tang 3 

1 Department of Physics, University of Texas at Austin, Austin TX 78712, USA 

2 Institute of Experimental Physics – University of Warsaw, 00-681 Warsaw, Poland 

3 National Center for Nanoscience and Technology, 100190 Beijing, P. R. China 

The colloidal semiconducting nanocrystals – and quantum dots (QDs) in particular – 

have been a subject to extensive studies driven by their promising photonic or photovoltaic 

applications. There are numerous features of colloidal QDs, to mention only long term 

photostability, that make them superior to other single emitters, e.g dye molecules. 

Nevertheless, their optical properties are not yet optimal from the viewpoint of technological 

utilization. One of the main unresolved issues with respect to colloidal QDs is fluctuations 

of photoluminescence (PL), or so called “blinking”. Despite intense experimental 

and theoretical research effort, the detailed microscopic mechanism of PL intermittency 

remains obscure, and so far no single theoretical model accounts for all observations [1]. 

The most comprehensive explanation postulates that when a QD is charged, a non-radiative 

Auger ionization suppresses PL and makes the emitter appearing dark [2]. Recently, 

the diminishing of Auger process and, in consequence, quenching of blinking was observed 

in selenium-based ternary QDs, even though these QDs possessed extra charge [3]. 

Subsequent theoretical study claimed this observation to be a general feature of the emitters 

with smoothed quantum confinement potential, since under such conditions the transition 

matrix element for the Auger recombination is greatly reduced [4]. 

This paper reports a comprehensive study of PL dynamics in chemically-synthesized 

CdSe/ZnS QDs with alloyed core/shell interfaces. Due to the softening of the structural 

interface between the core and the shell such emitters manifest a quantum yield of up 

to 80 % [5]. The employed technique of time-correlated single photon counting enabled 

measurements of the decay of exciton luminescence from both the ensemble and individual 

QDs. For decreasing emission wavelength, the ensemble data revealed systematic increase 

of total decay rates with greater variation, as it is expected that smaller emitters are more 

influenced by the surface/interface trap states. In experiments performed on single QDs, 

the PL trajectories exhibited familiar two-state blinking pattern, despite alloying between 

CdSe and ZnS. We suggest that in core/shell QDs with a large band gap offset, as in case 

of CdSe/ZnS system, the compositionally graded energy profile at the interface may not 

be smooth enough to suppress non-radiative Auger recombination and prevent blinking. 

[1] P. Frantsuzov, M. Kuno, B. Janko, and R. A. Marcus, Nature Physics 4, 519 (2008). 

[2] A. L. Efros and M. Rosen, Physical Review Letters 78, 1110 (1997). 

[3] X. Wang, X. Ren, K. Kahen, M. A. Hahn, M. Rajeswaran, S. Maccagnano-Zacher, 

J. Silcox, G. E. Cragg, A. L. Efros, and T. D. Krauss, Nature 459, 686 (2009). 

[4] G. E. Cragg and A. L. Efros, Nano Letters 10, 313 (2010). 

[5] W. K. Bae, K. Char, H. Hur, and S. Lee, Chemistry of Materials 20, 531 (2008). 

120

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Spectroscopy of Indirect Excitons in Vertically Stacked CdTe 

Quantum Dot Structures 

K. Kukliński, ̷L. K̷lopotowski, K. Fronc, P. Wojnar, T. Wojciechowski, 

M. Czapkiewicz, J. Kossut, G. Karczewski, and T. Wojtowicz 

Institute of Physics, Polish Academy of Sciences, Al. Lotników 32/46, 

02–668 Warsaw, Poland 

We show that by means of an electric field we can tune the energy levels in vertical 

single quantum dot (QD) pairs and study transitions related to recombination of indirect 

excitons. 

Embedding QDs in vertical field effect structures enables electrical control of the QDs 

charge state and allows to study properties related to Coulomb interactions. There are 

many reports on studies of direct excitons in single CdTe/ZnTe QDs. However, for this 

material system, no data is reported on indirect excitons, i.e. excitons related to recombination 

of an electron and a hole localized in two separate QDs. Obtaining a controlled 

coupling between two QDs is interesting from the point of view of basic research and for 

realization of a quantum gate, the building block of a quantum computer. 

In this communication, we present the results of spectroscopic studies of indirect excitons 

in vertically stacked QD structures. The QDs were embedded in the insulating 

region of a p–i–Schottky diode grown by molecular beam epitaxy on a GaAs substrate. 

The layer sequence was the following: a 4-µm thick p–doped ZnTe buffer, a 100 nm of 

undoped ZnTe, two QD layers separated by a 4 or 8 nm ZnTe spacer, a 50 nm thick 

ZnTe cap and a 50 nm ZnMgTe blocking barrier. QDs were formed from a 2D CdTe layer 

six monolayers thick. Ohmic contacts were established to the p–type ZnTe and a Al/Au 

Schottky contacts were deposited on top of the sample. Single QD pairs were accessed 

through 200 nm diameter shadow mask apertures. The photoluminescence (PL) signal 

was excited with a 532 nm laser beam focused to a 2 µm spot with a microscope objective. 

PL spectra were measured at 10 K as a function of a bias voltage. 

At zero bias we observe PL transitions from single pairs of QDs. We identify charge 

states from uncoupled dots. As the bias is increased, transitions shift due to the quantum 

confined Stark effect. Evidence of the presence of indirect excitons in the measured PL 

spectra are transitions strongly shifting in the electric field, as a consequence of greater 

value of dipole moment compared with direct excitons. We observe two types of lines: 

these for which Stark shift is about 0.5–1 meV/V and these with 4–7 meV/V. In accordance 

with the above conclusion, we identify the first transitions as related to direct 

excitons, and the latter as indirect. We assume that the dipole moment of the indirect excitons 

is pind = ed, where d is the spacer layer thickness. Therefore, the Stark shift of the 

indirect exciton allows us to calibrate the electric field in our structure. We find that this 

field is a factor of four smaller than expected from a capacitor formula: F = (U−Ubi)/W, 

where U and Ubi is the applied and built–in voltage, respectively, and W is the width of 

the intrinsic region. Having calibrated F, we find that the dipole moment for the direct 

exciton pdir ∼ 1 nm, thus pind ≈ 4(8)pdir. With decreasing reverse bias we observe both 

the red– and blue–shifted indirect exciton transitions. We assume that due to strain– 

enhanced nucleation, the QDs in the top layer are larger than the bottom dots. Basing 

on the band profiles of our structures, we conclude that the blue–shifted transitions are 

related to the recombination of the electron and hole localized in the top and the bottom 

dot, respectively. In turn, red–shifted indirect excitons are associated with the recombination 

of the electron and hole in the bottom and the top dot, respectively. 

121

TuP14 _______________________________________________________________ 


Collective spontaneous emission from pairs of quantum dots: 

the role of coupling and system geometry 

Wildan Abdussalam, Anna Sitek, Pawe̷l Machnikowski 

Institute of Physics, Wroc̷law University of Technology, 50-370 Wroc̷law, Poland 

We study the role of various types of coupling between semiconductor quantum dots 

(QDs) in the collective spontaneous emission of double dot systems. Excitons delocalized 

in closely spaced QDs recombine in a different way than in a single QD due to collective 

interaction of the two emitters with the quantum radiation field [1]. While for noninteracting 

dots this collective effect appears only for almost identical dots (with the 

transition energies within the emission line width), coupling between the dots leads to 

accelerated or slowed down emission even for dots with different transitions energies, 

which is manifested in the linear and non-linear response from these systems [2]. 

In this contribution, we study the spontaneous emission from an exciton confined in 

a double quantum dot. We focus on the similarities and differences between the cases of 

radiative (long-range, dipole) and tunnel coupling between the excitons in the dots. We 

show that for strictly identical dots the oscillating nature of the dipole coupling on long 

distances leads to non-monotonic dependence of the radiative decay rate on the inter-dot 

separation, which is not present in the case of tunnel coupling. However, for a double 

dot system with a realistic, technologically feasible mismatch of transition energies, the 

collective effects disappear completely well before these oscillations become relevant. In 

this case, there is no qualitative difference between the two physically different coupling 

types and the system dynamics in the two cases becomes indistinguishable for appropriate 

values of the coupling parameters. 

We believe that these findings may shed some light on the interpretation of the experiment 

[3] in which enhanced emission was observed in a quantum dot ensemble in which 

the dipole coupling energies on the typical inter-dot distances were much smaller than the 

average transition energy mismatch between the dots. 

[1] A. Sitek, P. Machnikowski, Phys. Rev. B 75, 035328 (2007). 

[2] A. Sitek, P. Machnikowski, Phys. Rev. B 80, 115319 (2009); 80, 115301 (2009). 

[3] M. Scheibner, T. Schmidt, L. Worschech, A. Forchel, G. Bacher, T. Passow, D. Hommel, 

Nature Physics 3, 106 (2007). 

122

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Tunneling Transfer Protocol in a Quantum Dots Chain Immune 

to Inhomogeneity 

Kamil Korzekwa and Pawe̷l Machnikowski 


We propose a quantum dot (QD) implementation of a quantum state transfer channel. 

The proposed channel consists of N vertically stacked QDs with the nearest neighbour 

tunnel coupling, placed in an axial electric field. The QD chain isdoped with oneelectron. 

The terminal QDs are assumed to provide a stronger binding for the electron. In this 

way, the states with electron on the terminal dots are energetically separated from other, 

but remain indirectly coupled via the QD chain. The inhomogeneity of the QD chain 

is included by using normal distribution for the values of tunnel couplings and electron 

energy levels. By applying an external electric field along the chain, the terminal QDs 

are brought to resonance, which leads to an efficient occupation transfer. 

Our proposal requires a global electric field as the only control means, therefore it 

satisfies the requirement of simplicity. We study the conditions of getting the quantum 

state transfer and compare the results with the previously proposed protocol [1]. We show 

that in our model the transfer fidelity for a homogenous QD chain is independent of the 

chains length. We show also that controlling the global electric field is enough to make 

the system resistant to inhomogeneity of both QD energies and tunnel coupling. Within 

our model we use the real QD parameters and show that almost perfect tunneling transfer 

is possible. 

Sinceourprotocolfulfillsthesimplicityrequirementitisexperimentallyfeasible. Since 

thetransferisindependentoftheQDinhomogeneityitcouldbeusedtotransferexcitation 

in a real QD chain. 

a) 

|P| 2 

1 

0.75 

0.5 

0.25 

0 

0 25 50 75 100 

t [ns] 

b) 

|P| 2 

1 

0.75 

0.5 

0.25 

0 

0 25 50 75 100 

Evolution of the occupation of on the initial QD (solid line), the final QD (dashed line) and the 

QDs inside the chain (dotted line) of 10 QDs spin chain. Electron energies in the QD’s normally 

distributed with standard deviation ∆ = 10meV and tunnel couplings J = 10meV. Terminal 

QDs energy E = 50meV a) No external electric field; b) Terminal QDs tuned to resonance by 

an external field. 

[1] A. Wójcik, T. ̷Luczak, P. Kurzyński, A. Grudka, T. Gdala, and M. Bednarska, Phys. 

Rev. A 72, 034303 

123 

t [ns]

TuP16 _______________________________________________________________ 


Thermal Quenching of Photoluminescence from epitaxial InGaAs/GaAs 

Quantum Dots with High Lateral Aspect Ratio 

Anna Musiał 1 , Grzegorz S k 1 , Aleksander Mary ski 1 , Paweł Podemski 1 , 

Janusz Andrzejewski 1 and Jan Misiewicz 1 

Andreas Löffler 2 , Sven Höfling 2 , Stephan Reitzenstein 2 , Johann Peter Reithmaier 2,* 

and Alfred Forchel 2 

1 Institute of Physics, Wrocław University of Technology, Wrocław, Poland 

2 Technische Physik, Universität Würzburg, Wilhelm Conrad Röntgen-Center for Complex 

Material Systems, Am Hubland, D-97074 Würzburg, Germany 

Self-assembled In0.3Ga0.7As quantum dots (QDs) [1] have already been demonstrated as 

good candidates for testing QED phenomena due to enhanced exciton oscillator strength [2] 

being a result of increased structure volume and weaker carrier confinement [3]. 

This report concerns temperature dependence of photoluminescence (PL) in both 

ensemble and single QD regime. At 5K, PL spectra consist of two bands related to the wetting 

layer (WL) and QD ensemble, separated by rather small energy (~ 35 meV) indicated shallow 

confining potentials for holes and electrons. At low temperatures WL emission dominates and 

there is a rather insignificant carrier transfer to the dots because most of the WL states are 

localized [3]. At higher temperatures (> 30K) carriers are released becoming extended into the 

WL plane and carrier redistribution increases the QD emission with respect to the WL one. 

Thermal quenching of PL from QD ensemble reveals activation energy of about 30 meV 

corresponding well with the confinement energy identifying a primary carrier loss mechanism 

– release of carriers to WL. This has also been confirmed at the single QD level. The 

activation energy varies between 15-30 meV reflecting the dot size and hence carrier 

confinement distribution. In case of single QD the impact of WL is stronger, because the 

probability that a carrier returns to the same dot and emits is lower than the probability of 

carrier to get back to any of the dots contributing to the ensemble PL. In a very few cases a 

fingerprint of 2 nd significantly smaller activation energy is observed, suggesting that carrier 

localization inside those structures is not present or localization energy is very low (below 1 

meV - the resolution of the method) meaning that at low temperatures excitons are always 

extended over the entire QD and experience large coherence volume. This was further 

supported by polarization-resolved temperature dependent PL to probe the symmetry of 

confining potential by obtaining the degree of linear polarization. It is low at 5K (~6%) and 

decreases slightly with temperature due to emission from higher energy states reflecting lower 

effective anisotropy [4]. This can be understood as a result of very weak confining potential 

for electrons in agreement with 8 band kp calculations giving DOP values below 10%. 

[1] A. Löffler, J. P. Reithmaier, A. Forchel, A. Sauerwald, D. Peskes, T. Kümmell and G. 

Bacher, J. Cryst. Growth 286, 6 (2006). 

[2] J. P. Reithmaier, G. S k, A. Löffler, C. Hofmann, S. Kuhn, S. Reitzenstein, L. Keldysh, 

V. Kulakovskii, T. Reinecke and A. Forchel, Nature 432, 197 (2004). 

[3] G. S k, A. Musiał, P. Podemski, M. Syperek, J. Misiewicz, A. Löffler, S. Heling, L. 

Worschech and A. Forchel, J. Appl. Phys. 107, 96106 (2010). 

[4] P. Kaczmarkiewiecz, A. Musiał, G. S k, P. Podemski, P. Machnikowski and J. Misiewicz, 

Acta Phys. Pol. A (2011), in press. 

* Currently at: Institute of Nanostructure Technologies and Analytics, Technische Physik, Universität Kassel 

124

40th _______________________________________________________________ 


Excitonic Magnetoabsorption of Cylindrical Quantum Disks 

P. Schillak and G. Czajkowski 

Department of Theoretical Physics, University of Technology and Life Sciences 

Al. Prof. S. Kaliskiego 7, 85-789 Bydgoszcz, Poland 

Potential applications of semiconducting nanostructures in novel optoelectronic devices 

gain the interest in the optical properties of quantum disks, quantum wires and the 

other low-dimensional objects. Here we investigate the influence of excitonic effects on 

the optical properties of quantum disks in the external magnetic field. We propose the 

theoretical approach which enables to calculate the optical functions for low-dimensional 

structureswithcylindricalsymmetryexposedtotheexternalmagneticfielddirectedalong 

the symmetry axis. We consider an interacting electron-hole pair inside the semiconducting 

nanostructure with hard-wall potential of finite height (different for an electron and 

a hole) at the boundaries. The different anisotropic effective masses are taken inside and 

outside the structure. The novelty of our approach is that the six-dimensional eigenvalue 

problem is transformed into the equivalent eigenvalue problem given by the system of the 

coupled two-dimensional second order differential equations. Differential equations are 

solved numerically. As an example, we present in Fig. 1 the magnetic field dependent 

excitonic energy spectrum for the InP disk with the radius R = 8 nm and the height 

d = 4 nm. Additionally, numerical results are compared with experimental data taken 

from the paper by Dewitz et al. [1]. Having the energies and wave functions, we apply 

the real density matrix approach [2,3] 

which gives the optical functions including 

magnetoabsorption and the 

magnetic field dependent dielectric 

tensor for light- and heavy-hole excitons. 

In this approach the linear 

response is described by the set of 

coupledequationsfortwo-pointcorrelation 

function Y(re,rh) and the 

Maxwellianfieldequation. TheconstitutiveequationforY(re,rh)hasa 

form of Schrödinger’s equation with 

a source term, which reflects the 

light-matter interaction. Numerical 

computations were performed 

for In0.55Al0.45As/Al0.35Ga0.65 and 

CdSe quantum disks. Our numerical 

results are in a good agreement 

with experimental data. 

relative energy [meV] 

120 

100 

80 

60 

40 

20 

0 

0 20 40 60 

magnetic field B [T] 

Figure 1: The calculated (full lines) and measured 

(circles) relative positions of energy levels 

as functions of the applied magnetic field. 

[1] C. v. Dewitz, F. Hatami, M. Millot, J. M. Broto, J. Léotin, and W. T. Masselink, 

Appl. Phys. Letters 95, 151105 (2009). 

[2] G. Czajkowski, F. Bassani, and L. Silvestri, Rivista del Nuovo Cimento, 26(5-6), pp. 

1-150 (2003). 

[3] P. Schillak and G. Czajkowski, phys. stat. sol. (c), 5 2495 (2008). 

125

TuP18 _______________________________________________________________ 


Spontaneous emission from double quantum dots: collective 

effects and carrier-phonon kinetics 

Pawe̷l Karwat, Anna Sitek, Pawe̷l Machnikowski 


We study theoretically the evolution of luminescence from a double quantum dot in the 

presence of carrier-phonon interaction. We show that the spontaneous emission from 

this system is determined by the interplay of collective effects, which are due to the 

interaction between the two emitters and their common radiative reservoir, and phononinduced 

transitions (typically on a much shorter time scale). 

The time-resolved luminescence from double quantum dots is an interesting subject of 

study as it yields information on the carrier kinetics under the joint action of two reservoirs: 

electromagnetic vacuum to which the exciton ultimately decays in the spontaneous 

emission (radiative recombination) process and the lattice excitations which may dephase 

the charge states and lead to transitions between the confined states. One of the experiments 

[1] revealed surprising temperature dependence of the luminescence life time which 

first grows as the temperature is increased and then decreases. This enhancement of the 

exciton lifetime with increasing temperature is in striking contrast to the single dot case 

where the life time drops down with temperature, which can easily be associated with 

various possible thermally activated non-radiative channels. 

In this presentation, we model the system kinetics using a Markovian Lindblad generator 

for the spontaneous emission process [2] and a non-Markovian time-convolutionless 

dissipator that accounts for the phonon-related kinetics [3]. We show that the quasiequilibrium 

distribution of the occupations of the two lowest energy eigenstates sets up 

within several picoseconds after the excitation. Since one of these states is more active 

optically (“brighter”) this leads to temperature dependence of the emission rate and to 

non-monotonic dependence of the luminescence life time similar to that observed in the 

experiment. 

[1] C. Bardot, M. Schwab, M. Bayer, S. Fafard, Z. Wasilewski, P. Hawrylak, Phys. Rev. 

B 72, 035314 (2005). 

[2] A. Sitek, P. Machnikowski, Phys. Rev. B 80, 115319 (2009). 

[3] P. Machnikowski, K. Roszak, A. Sitek, Acta Phys. Pol. A 116, 818 (2009). 

126

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Cathodoluminescence studies of the II – VI semiconducting quantum dots 

grown by molecular beam epitaxy 

P. Łach 1 , A. Reszka 1 , G. Karczewski 1 , P. Wojnar 1 , T. Wojtowicz 1 , A. Kamińska 1 , 

and A. Suchocki 1,2 

1 

- Institute of Physics, Polish Academy of Sciences, al. Lotników 32/46, 02-668, Warsaw, 

Poland 

2 

- Institute of Physics, Kazimierz Wielki University, Weyssenhoffa 11, Bydgoszcz 85-072, 

Poland 

Self-assembled quantum dots (QDs) as zero-dimensional structures are very 

intensively studied optically and electrically on account of their shape and small sizes. Our 

QDs consisted of II-VI compounds were grown on (100)-oriented GaAs substrate by Stranski- 

Krastanov mode by molecular beam epitaxy method (MBE). The obtained objects have 

diameter and height of the order of 10 - 40 nm and 1 - 14 nm, respectively. The QDs were 

embedded in a ZnTe matrix with thickness of about 1.5 µm and they were composited of 6 

monolayers. A whole was covered by a thin cap (100 nm). The concentration of the QDs was 

equal to 10 9 – 10 10 of QDs per 1 cm 2 . 

We have measured the cathodoluminescence (CL) spectra of such structures as a 

function of the temperature. The luminescence was excited by electron beam with 

accelerating voltage of the order of 5 – 15 kV. This experiment was carried out for CdTe, 

CdMnTe and CdSe QDs. We have checked behaviour of the CL signals in different places on 

these samples. This dependence shows certain non-uniform distribution of QDs in the 

examined samples. With increase of the temperature the spectra became considerably wider 

and their intensities decreased. It results from excitons redistribution between QDs (the 

carriers were intercepted from a wetting layer to a bigger QD which emits a light in lower 

energies). The possible mechanisms of the temperature luminescence quenching are nonradiative 

exciton recombination due to the Auger effect and disappearance of the quantum 

confinement at higher temperatures. We discuss the both mechanisms in this paper. 

The examples of the results of the photoluminescence (PL) and cathodoluminescence (CL) 

measurements (on the left) and the temperature dependences for CdTe QDs (on the right) are 

presented below for comparison. 

CL intensity [au] 

PL intensity [au] 

40000 

30000 

20000 

10000 

0 

20K 

2,00 2,05 2,10 2,15 2,20 2,25 2,30 

50000 

40000 

30000 

20000 

10000 

0 

Energy [eV] 

70K 

60K 

50K 

40K 

30K 

1,95 2,00 2,05 2,10 2,15 2,20 2,25 2,30 2,35 

Energy [eV] 

T=60K 

T=57K 

T=53K 

T=48K 

T=43K 

T=34K 

T=28K 

T=20K 

T=11K 

CL intensity [au] 

14000 

12000 

10000 

8000 

6000 

4000 

2000 

10 20 30 40 50 60 70 

Temperature [K] 

10 20 30 40 50 60 

In this case we have measured the PL and CL spectra to about 100K. The CdMnTe and CdSe 

QDs have given the CL signals even over 200K. 

Acknowledgement: This work was partially supported by the grant of the Polish Ministry of 

Science and Higher Education for years 2007-2011. 

127 

PL intensity [au] 

14000 

12000 

10000 

8000 

6000 

4000 

2000 

Temperature [K]

TuP20 _______________________________________________________________ 


Raman spectroscopy of CdTe/ZnTe quantum dots 

E. Zielony 1 , E. Popko 1 , Z. Gumienny 1 , P. Kamyczek 1 , A. Henrykowski 1 , J. Jacak 1 , 

G.Karczewski 2 

1 Institute of Physics, Wroclaw University of Technology, Wybrzeze Wyspianskiego 27, 

50-370 Wroclaw, Poland 

2 Institute of Physics, Institute of Physics Polish Academy of Science, al. Lotnikow 32/46, 


Semiconducting low-dimensional structures of CdTe quantum dots embedded in ZnTe matrix 

have been investigated by micro-Raman spectroscopy. A reference ZnTe sample (without 

dots) was also studied for comparison. Both samples were grown by molecular beam epitaxy 

technique on the p-type GaAs substrate. The QD sample consists of 3µm thick p + -type 

ZnTe:N buffer deposited on the p-type GaAs substrate, 1µm undoped ZnTe, a layer of CdTe 

quantum dots and 0.3µm of undoped ZnTe cap. The CdTe self assembled quantum dots were 

grown in the atomic layer epitaxy (ALE) growth mode by deposition of six monolayers of 

CdTe. The process of QD formation was induced by covering the CdTe layers with an 

amorphous tellurium layer and its subsequent thermal desorption [1]. The presence of 

quantum dot structure was confirmed by photoluminescence measurements. The Raman 

measurements have been performed at room temperature with the help of the T64000 Jobin 

Ivon spectrometer configured in the triple subtractive mode of operation. The samples were 

excited by an Ar 2+ laser working at a wavelength of 514.5 nm. The Raman spectra have been 

recorded for different acquisition parameters of the measurement. For the reference and QD 

sample localized longitudinal (LO) phonons of 210cm -1 wavenumber associated with the 

ZnTe layer [2] are observed. In the case of QD sample another broad band corresponding to 

the LO CdTe phonon related to the QD-layer appears at a wavenumber of 160 cm -1 [2]. Such 

behavior does not exhibit the Raman spectra for the reference sample. For both samples 

additionally tellurium - related peaks at wavenumbers around 120 cm -1 and 140 cm -1 are 

detected. It has been noticed that the intensity of CdTe and ZnTe LO phonon peaks decreases 

with increasing time of a laser beam exposition while the signal associated with Te - like 

Raman peaks increases. The latter is caused by the laser damage in the ZnTe layer followed 

by the formation of Te aggregates on the ZnTe surface. The Raman measurements confirm 

the presence of CdTe layer of quantum dots in the investigated material. 

[1] P. Wojnar, J. Suffczynski, K. Kowalik, A. Golnik, M. Aleszkiewicz, G. Karczewski, and 

J. Kossut, Nanotechnology 19, 235403 (2008). 

[2] V. S. Vinogradov, et al., Physics of the Solid State, Vol. 50, No. 1, 2008. 

128

40th _______________________________________________________________ 


Quantum interference in charge transport via the quantum dots 

coupled between the metallic and superconducting leads 

J. Barański and T. Domański 

Institute of Physics, M. Curie Sk̷lodowska University, 20-031 Lublin, Poland 

We analyze the effects of quantum interference observable in the Andreev current 

induced through the double quantum dots coupled between an isotropic superconductor 

and metallic leads. Superconducting properties are transfered on such nanostructures 

due to the proximity effect and they have qualitative influence on the nonequillibrium 

phenomena, especially in a regime of the subgap bias voltage |V | ≤ ∆/|e|. We will 

discuss condictions necesarry for observing the Fano resonances and shall try to account 

for their interplay with the strong correlation effects. 

129

TuP22 _______________________________________________________________ 


Bound Magnetic Polaron Molecule in Diluted Magnetic 

Semiconductors within the Heitler-London Approximation 

Henryk Bednarski 1 and Jozef Spa̷lek 2 

1 Centre of Polymer and Carbon Materials, Polish Academy of Sciences, 34 M. 


2 Marian Smoluchowski Institute of Physics, Jagiellonian University, Reymonta 4, 

30-059 Kraków, Poland 

Recently developed by us a complete microscopic theory of the bound magnetic polaron 

molecule (BMPM) in diluted magnetic semiconductors [1] is reformulated in a reduced 

spin-state space. Namely, we solve the BMPM problem by taking into account the 

Heitler-London form of the two-electron wave function in the four dimensional spin-state 

space (comprising one singlet and three triplet states) and include the thermodynamic 

fluctuations of the magnetization due to the localized 3d spins in the Gaussian form. 

In this manner, the role of covalency effects can be clearly identified and its influence 

analysed in detail. Moreover, within this formulation the quantum aspect of the BMPM 

problem is also accounted for, as it results from quantum-mechanical indistinguishability 

of the two impurity electrons and is contained in the antisymmetric nature of their 

two-electron wave function. Therefore, the formulation of the BMPM theory provides us 

with the opportunity of studying the physical origin of the competition between ferroand 

antiferro-magnetic interactions of the impurity pair of electrons in diluted magnetic 

semiconductors. 

[1] H. Bednarski, J. Spa̷lek, arXiv:0912.0662v4, submitted to Phys. Rev. B. 

130

40th _______________________________________________________________ 


Intersubband polaritons in strongly pumped microcavities 

M. Zału ny and A. Kozłowski 

Institute of Physics, M. Curie-Skłodowska University, Pl. M. Curie-Skłodowskiej 1, 20-031 

Lublin, Poland 

It is well known that resonant microstructures have an important role in the 

enhancement of nonlinear optical processes in multiple quantum well (MQWs) structures. So 

far most research has concentrated on the nonlinear effects connected with excitonic coupling 

to the microcavity (MC) mode [1]. In our recent paper [2] we have discussed theoretically the 

nonlinear intersubband response of the MQWs embedded in MCs. The simplest case, when 

strong probe wave acts alone, has been considered. It has been shown, that in the strongcoupling-regime 

the saturation effect leads to the evolution of the absorption spectra from a 

pair of simple harmonic oscillators to highly anharmonic ones. 

The experimental and theoretical results reported in [1] indicate that in MCs the pumpprobe 

nonlinear excitonic effects [leading to the formation of the so-called Mollow absorption 

spectrum (MAS) [3]] are much more easily observed due to the enhancement of the optical 

field by the MC. Stimulated by this fact in this paper we discuss theoretically the problem of 

the formation of the intersubband MAS in the MQW-MC systems. 

Like in our previous paper, we employ a semiclassical approach based on the transfer 

matrix formalism (TMF) and the so-called sheet model [2,4] (The sheet, modeling the optical 

response of the QW, is characterized by the 2D conductivity.) For simplicity we neglect the 

influence of the electron-electron interaction on the nonlinear intersubband response. It has a 

good justification when the surface electron concentration in QW is relatively small (�10¹¹ 

cm²) and the wavelength of incident radiation is not too large ( �10 m) [5]. To achieve a 

sufficiently strong coupling between intersubband excitation and incident radiation the 

experimentally studied systems usually contain a large number of QWs. Practically, the QWs 

occupy almost the whole space between mirrors. Unfortunately, in such type of systems, 

contrary to those studied in [1], the strength of the optical field acting on each QW is 

different. The numerical simulations reported in this paper are performed taking into account 

also the above mentioned effect. 

The calculations of the angle resolved (probe) absorption spectra are decomposed into 

two sequential stages. First, the pump wave propagation in the system is described neglecting 

the energy transfer between the (strong) pump and (weak) probe waves. The spatial pump 

field distribution in the MC-MQW system is calculated taking into account the saturation 

effect. The case when the response to pump beam has bistable character [2] is also considered. 

At second stage, the linear problem of the probe beam propagation in the system is solved 

taking into account fact the that the Mollow 2D (intersubband) conductivity of each QW [3,6] 

depends on the pump field intensity, at the position of the QW, determined in the first stage. 

For better understanding of the role of the spatial variation of the pump field in the MC we 

also present a simplified approach based on a Fabry-Perot model and the “mean field” 

approximation [2]. 

[1] B. Beveaurd, et al. CR Acad. Sci. IV-Phys., 2, 1439 (2001) and references therein. 

[2] M. Zału ny and C. Nalewajko, J. Appl. Phys. 107, 123106 (2010). 

[3] B. R. Mollow, Phys. Rev. 188,1969 (1969); Phys. Rev. A 5, 227 (1972). 

[4] M. Zału ny and C. Nalewajko, J. Appl. Phys. 99, 026104 (2006. 

[5] R. A. Kaindl, et al., Phys. Rev. B 62, 161308(R) (2001). 

[6] P. Meystre and M. Sargent III, Elements of quantum optics (Springer, Berlin, 1990). 

131

TuP24 _______________________________________________________________ 


Magneto-Optical Studies of Narrow Band-Gap Heterostructures with Type 

II Quantum Dots InSb in an InAs Matrix 

Mikhail S. Mukhin 1 , Yakov V. Terent’ev 1 , Leonid E. Golub 1 , Mikhail O.Nestoklon 1 , 

Boris Ya. Meltser 1 , Alexey N. Semenov 1 , Victor A. Solov’ev 1 , Alla A. Sitnikova 1 , Alexey A. 

Toropov 1 and Sergey V. Ivanov 1 

1 Ioffe Physical-Technical Institute of Russian Academy of Sciences, 26 Polytekhnicheskaya, 

St Petersburg 194021, Russian Federation 

Spin is the only electron internal degree of freedom, and utilizing it in the new 

generation of semiconductor devices is the main goal of semiconductor spintronics. Today 

spintronics focuses mainly on diluted magnetic semiconductors (DMS) where ferromagnetism 

and giant Zeeman splitting can be obtained due to exchange interaction between free carriers 

and Mn ions. Most of the work has been focused on II-VI DMS such as CdMnTe or ZnMnSe 

and some others. Enhanced magnetic properties of these materials exist only at cryogenic 

temperatures due to paramagnetic behavior of the magnetic ions. A lot of recent investigations 

have been focused on doping III-V semiconductors into a DMS state. Although III-V DMS 

demonstrate higher Curie temperature, Mn is much less soluble here than in II-VI 

semiconductors [1]. Another issue is that in III-V compounds magnetic doping harmfully 

affects emission properties and, moreover, changes conductivity to p-type. We have proposed 

a new approach to the problem based on using narrow band-gap III-V compounds possessing 

the largest intrinsic electronic g-factor, which are InSb and InAs [2]. 

Present research is focused on spin-related phenomena in low-dimensional InSb/InAs 

heterostructures and continues our preliminary studies [3]. Magneto-optical investigations of 

type-II InSb QDs in an InAs matrix and their theoretical consideration are reported. In(Sb,As) 

heterostructures incorporating monolayer-scale InSb insertions in the InAs matrix, possessing 

high recombination efficiency, were fabricated by MBE. Circularly polarized 

photoluminescence has been measured in the 

polarization, % 

100 

80 

60 

40 

20 

0 

-20 

T=2K 

B=4T 

0,1 1 10 

Excitation Intensity, W/cm 2 

Faraday geometry, allowing direct probing of the 

electron spin state. Experiments were carried out in 

the temperature range from 2 to 140 K and 

excitation density 0.1 – 20 W/cm 2 . It was found that 

the polarization degree varies form 100% -minus 

up to 15% -plus, depending on the excitation 

intensity and temperature. The physical model of the 

phenomenon is developed, based on the selection 

rules for optical transitions involving heavy holes, 

dependence of the oscillator strength on the excitation density, inherent for indirect in space 

optical transitions that only are allowed here, and an analysis of equilibrium population of 

energy levels. The detailed calculation of the energy spectrum of charge carries, performed 

within a tight-binding approximation, is also presented. The results of the theoretical 

treatment are in good agreement with experimental data. The simulation of the experimental 

data revealed that the oscillator strength of the optical transitions of electrons with the spin 

oriented either along or against the magnetic field vector differs by approximately 1,8 times. 

[1] T.T. Chen, C.H. Chen, W.S. Su et al., J. Appl. Phys. 93, 9655 (2002). 

[2] Ya.V. Terent’ev, A.A. Toropov, B.Y. Meltser et al., Semiconductors 44, 194 (2010). 

[3]Ya.V. Terent’ev, O.G. Lyublinskaya, A.A. Toropov et al., Semiconductors 43, 635 (2009). 

132

40th _______________________________________________________________ 


Phonon-assisted tunneling between hole states in double 

quantum dots 

Krzysztof Gawarecki, Pawe̷l Machnikowski 


In this work, we present a theoretical analysis of hole states in double quantum dots 

(DQDs). The system under consideration, consist two, coupled, vertically stacked dots 

with one trapped hole. We study hole states in a realistic model which takes into account 

the system geometry and strain in the DQD. In present work, we also investigate 

phonon-related processes in such a system. We derive phonon-assisted relaxation between 

two lowest hole states and compare those results with the previous one for electrons [1,2]. 

The relaxation rates are calculated as a function of external axial electric field. Carrierphonon 

couplings via both deformation potential and piezoelectric interactions can be 

predominant for different parameters. As shown previously [3] the ground state in such 

molecule can be antibonding [3], which corresponds to recent experiments[4]. In consequence, 

for some distance between dots (relevant to ground state bonding–antibonding 

transition) relaxation rate can be very small. 

DQDs, can be used for designing quantum-coherent devices, including spin-based 

quantum bits. Information can be encoded on carrier states in such structures. However, 

phonon-related processes are inevitable in a cristal environment and may limit the 

feasibility of implementing quantum control in these systems. In consequence, it is essential 

to understand not only the spectral properties of various kinds of semiconductor 

nanostructures but also the relevant phonon-induced processes. 

Our model [1] is based on a k·p approximation for a single particle in a strained selfassembled 

structure. The local band structure in a such a system is obtained from the 

8-band Hamiltonian with strain-induced terms (Bir-Pikus Hamiltonian).We solve the 4x4 

part (light- and heavy holes with two possible spin orientation) of this hamiltonian. Interation 

with the conduction band, was included via quasi-degenerate perturbation theory. 

Next, we calculate the the valence band edges and the effective mass for heavy and light 

holes as a function of the spatial position. The hole wave functions are calculated within 

a multi-component envelope function approximation combined with a Ritz variational 

method. Finally, the Fermi golden rule is used to obtain the relaxation rates between the 

lowest energy eigenstates. 

[1] K. Gawarecki, M. Pochwa̷la, A. Grodecka-Grad and P. Machnikowski, 

Phys. Rev. B 81, 245312 (2010). 

[2] K. Gawarecki, P. Machnikowski, Acta Phys. Pol. A (in press), arxiv:1007.1577 (2010). 

[3] J.I. Climente et al., Phys. Rev. B 78, 115323 (2008). 

[4] M.F. Doty et al., Phys. Rev. Lett. 102, 047401 (2009). 

133

TuP26 _______________________________________________________________ 


Intermediate band formation for electrons and holes in an 

inhomogeneous chain of quantum dots 

Igor Bragar, Krzysztof Gawarecki, Pawe̷l Machnikowski 


We study the electron and hole states of a chain of non-identical, vertically stacked quantum 

dots (QDs). It has been proposed [1] that inserting such a structure in the intrinsic 

region of a p-i-n junction solar cell could increase the photocurrent due to sequential 

absorption of low energy (below-bandgap) photons. While this idea has been gaining 

growing experimental support in the recent years [2], it still seems unclear whether the 

underlying physics corresponds to the intermediate band concept [3] as the band formation 

in a quantum dot chain may be strongly suppressed by the energy inhomogeneity. 

In this presentation we use a simple model of a tunnel-coupled chain of dots containing 

one electron or one hole. By using the energy and coupling parameters obtained from 

realistic k.p calculations [4], we are able to relate the spectral properties of the chain as 

well as the localization properties of the carrier wave functions to the actual geometry of 

the system (dot sizes and inter-dot separations). We study how the pseudo-band formed 

of the ground states confined in the QDs disintegrates upon increasing the inhomogeneity 

of the electron and hole energies. We discuss the impact of localization on the interband 

absorption from the pseudo-band to extended (bulk) states, which is a prerequisite for the 

functionality of the photovoltaic device. We formulate the conditions for the strength of 

the coupling (hence the dot separation) as compared to the degree of the inhomogeneity 

that must be satisfied in order for the system to support delocalized states. 

[1] V. Aroutiounian, S. Petrosyan, A. Khachatryan, K. Touryan, J. Appl. Phys. 89, 2268 

(2001). 

[2] Y. Okada, T. Morioka, K. Yoshida, R. Oshima, Y. Shoji, T. Inoue, T. Kita, J. Appl. 

Phys. 109, 024301 (2011). 

[3] A. Luque and A. Martí, Phys. Rev. Lett. 78, 5014 (1997). 

[4] K. Gawarecki, M. Pochwa̷la, A. Grodecka-Grad, P. Machnikowski, Phys. Rev. B 81, 

245312 (2010). 

134

40th _______________________________________________________________ 


Modelling of 1D-2D structural transitions in small Yukawa 

clusters 

Olga Rancova, Egidijus Anisimovas 

Department of Theoretical Physics, Vilnius University, Saul˙etekio al. 9, LT-10222 

Vilnius, Lithuania 

We study structural transitions that take place in the simplest finite-size systems and 

are analogous to phase transitions in the macroscopic limit [1]. The model system consists 

of a small number of identical interacting charged particles in an anisotropic trap, where 

the particles form stable ordered structures known as Wigner crystals [2]. These are 

observed in diverse systems as electrons on liquid He, ions in traps, 2D semiconductor 

quantum dots, dusty plasmas, macroscopic model systems [3]. Recent developments of 

experimental techniques allowed direct investigation of structural and dynamic properties 

of systems consisting of just a few or several tens of particles under different external 

conditions that can be modelled numerically. 

In present research we model 1D-2D dimensional structural transition caused by decreasing 

anisotropy of the confining potential that is one of the simplest cases of continuous 

phase transitions. Such dimensional transitions called ”zigzag transitions” are studied 

experimentally and modelled numerically [4, 5]. 

The model system consists of N identical charged particles interacting through pairwiseYukawapotentialVin 

= r −1 exp(−κr)withscreeningparameterκandconfinedby2D 

asymmetric parabolic potential Vc = x 2 +α 2 y 2 . The potential interaction energy strongly 

dominates over the kinetic energy. Thus, we are concerned with the minimization of the 

total potential energy. α > 1 squeezes the confining potential inducing structural transitionsofthesystem. 

ThenumericaltechniquecombiningtheMetropolisprocedureandthe 

Newtonoptimizationmethodisusedtoobtaintheenergeticallyfavourableconfigurations. 

The calculations are performed for different κ changing the value of α. 

In present research we investigate the simplest systems up to N = 9 undergoing 

1D-2D structural transition. Changing the potential parameter α gradually we explore 

dependence of the order parameter of the system 〈y〉, defined as average system width 

in the anisotropy dimension, on the potential anisotropy parameter looking for evidences 

of the phase transition. When α reaches a critical value αc the system order parameter 

drops to zero and we obtain a power-law behaviour of the order parameter 〈y〉 ∝ (αc−α) γ 

in the vicinity of this critical point (γ is a critical exponent). We find that in this area 

γ ≈ 0.5 in all cases investigated. Whereas [5] suggests γ = 0.387 in N = 5,κ = 3 case. 

We obtain that the value of the critical exponent changes when the potential anisotropy 

parameter value departs from the critical point. 

Acknowledgments O. Rancova is funded by Lithuanian Science Council (grant No. 

SF-PD-2009-08-17-0054). 

[1] O. Rancova, E. Anisimovas, and T. Varanavičius, Phys. Rev. E 83, 036409 (2011). 

[2] E. Wigner, Phys. Rev. 46, 1002 (1934); C. C. Grimes and G. Adams, Phys. Rev. 

Lett. 42, 795 (1979); E. Y.Andrei, G. Deville, D. C. Glattli, F. I. B. Williams, E.Paris, 

and B. Etienne, Phys. Rev. Lett. 60, 2765 (1988). 

[3] A. V. Filinov et.al., Phys. Rev. Lett. 86, 3851 (2001); M. Saint Jean et.al., Europhys. 

Lett. 55, 45 (2001); D. Block et.al., Phys. Plasmas 15, 040701 (2008). 

[4] A. Melzer, Phys. Rev. E 73, 056404 (2006). 

[5] T. E. Sheridan and K. D. Wells, Phys. Rev. E 81, 016404 (2010). 

135

TuP28 _______________________________________________________________ 


EfficientCoulombmixingbetweensingle-and 

biexcitonstatesinInAsnanocrystals 

P.Kowalski,P.Machnikowski 

InstituteofPhysics,WrocławUniversityofTechnology,50-370Wrocław,Poland 

Multipleexcitongeneration(impactionization)innanocrystalsisaprocess,inwhich 

absorptionofasinglephotonleadstogenerationofmultipleelectron-holepairs. This 

effecthasbeenobservedexperimentally[1,2]andmayincreasetheefficiencyofsolarcells. 

Whileearlierpapersreportedquantumefficienciesreaching700%[3],laterreportssuggestthatthosefigureswereoverestimatedandtheactualyielddoesnotexceed170%[4]. 

Thiscontroversymightberesolvediftheprocessisbetterunderstoodtheoretically. 

Inourpreviouswork[5]wehaveshownthatcoherenttwo-pairgenerationwithasingle 

absorbedphotonispossibleduetoCoulombindirectmixingofsingle-exciton(onepair) 

andbiexciton(two-pair)configurations.However,forlowenergystatesthisprocessisin 

generalveryinefficientsincethetypicalmagnitudeoftheCoulombmatrixelement(tens 

ofmeV)ismuchsmallerthantheaverageseparationbetweentheenergylevels(hundreds 

ofmeV). 

Forhighenergystatesthespectrumoftwo-pairconfigurationsismuchmoredense.In 

thatrangetypicalseparationofstatescoupledtoasinglepairisontheorderof100meV 

(forthenanocrystalradiusof7nm).Thestrengthofthecouplingstillreaches100meV. 

Hence,weexpectstrongmixingbetweenthe1-pairand2-pairconfigurationswhichcan 

leadtoamoreefficientbiexcitongeneration. 

[1]R.D.Schaller,V.I.Klimov,Phys.Rev.Lett.92,186601(2004). 

[2]R.D.Schaller,J.M.Pietryga,V.I.Klimov,NanoLett.7,3469(2007). 

[3]R.D.Schaller,M.Sykora,J.M.Pietryga,V.I.Klimov,NanoLett.6,424(2006). 

[4]M.TuanhTrinhet.al.,NanoLett.8,1713(2008). 

[5]P.Kowalski,P.Machnikowski,ActaPhys.Pol.114,1187(2008). 

136

40th _______________________________________________________________ 


Strongly disordered wetting layer in the InAs/GaAs self-assembled 

quantum dots system 

K. Gołasa 1 , M. Molas 1 , J. Borysiuk 1 , Z. R. Wasilewski 2 and A. Babiński 1 

1 Faculty of Physics, University of Warsaw, Hoża 69, 00-681 Warszawa, Poland 

2 Institute for Microstructural Sciences, National Research Council, Ottawa, Canada 

A wetting layer (WL) is an inevitable result of the formation of quantum dots (QDs) in 

the Stranski–Krastanow growth mode. It is usually assumed that the WL is a thin, highly 

strained quantum well, on which three-dimensional islands grow. However, in real systems 

the morphology of the WL can be more complex. In particular substantial indium fluctuations 

in the WL, which give rise to confinement of carriers have recently been identified [1]. 

In this communication we address the question of growth conditions necessary to form 

such strongly disordered WL. We investigate two samples A and B grown with different 

parameters using molecular beam epitaxy. While growing both samples, a substrate rotation 

was stopped during the InAs layer deposition in order to obtain a gradient of InAs coverage 

across the wafer. The amount of deposited InAs was chosen in such a way as to have a 

continuous variation of the dot density, starting with just InAs WL to fairly high density of 

InAs QDs on each wafer. In the reference sample A, grown in usual conditions, such the 

procedure resulted in an expected evolution of the low-temperature photoluminescence across 

the wafer. Low InAs coverage resulted in the WL-related emission centred at 1.44 eV, which 

disappeared from the spectrum with increasing intensity of the QDs emission due to 

increasing density of QDs grown. In the 

sample B the scenario was different. The 

lowest InAs coverage resulted in QDs 

emission but no emission from the WL (see 

lowest spectrum in Fig. 1). At the expected 

energy range of the WL-emission several 

sharp lines due to recombination of confined 

single excitons and biexcitons were 

observed. At higher InAs coverage a weak 

emission related to a thin WL (denoted with 

an arrow in Fig. 1) was observed, which 

disappeared at even higher InAs coverage 

leaving just the QDs emission in the 

1,25 1,30 1,35 1,40 1,45 

spectrum. The observed behaviour suggests that the WL does not form a continuous twodimensional 

layer before the onset of the QDs formation in the sample B. Instead, twodimensional 

platelets form, which can confine electrons and holes. With higher InAs coverage 

the platelets merge giving rise to usually observed WL. Our conclusions are supported with 

results of transmission electron microscopic study of the samples morphology. 

We present details of the growth procedure and discus their effect on the morphology 

of the investigated samples. We also discuss possible applications of self-assembled QDs 

grown with no continuous WL. 

[1] A. Babiński, J. Borysiuk, S. Kret, M. Czyż, A. Golnik, S. Raymond and Z. R. Wasilewski, 

Appl. Phys. Lett. 92, 171104 (2008). 

137 

PL intensity [arb.u.] 

Energy [eV] 

WL 

Fig.1. The μ-PL spectra from three positions of 

the investigated sample. 

InAs nominal coverage

TuP30 _______________________________________________________________ 


Optical transformation of zero-dimensional confinement in the 

CdTe/CdMgTe multiple quantum wells 

M. Molas 1,* , K. Gołasa 1 , J. Łusakowski 1 , T.Wojtowicz 2 , and A. Babi ski 1 

1 Faculty of Physics, University of Warsaw, Ho a 69, 00-681 Warszawa, Poland 

2 Institute of Physics, Polish Academy of Sciences, Al. Lotników 32/46, 02-668 Warszawa, Poland 

Zero-dimensional confinement in semiconductor structures, which is crucial for many optoelectronic 

applications, may result from several factors influencing potential energy of carriers. Most intensely 

investigated are quantum dots (QDs) formed in Stranski-Krastanov growth mode [1,2] or due to composition 

fluctuations in thin quantum wells (QWs) [3]. There are, however, systems in which the confinement results 

from a more complicated potential energy pattern [4,5]. In this communication we report on QDs which in our 

opinion fall to the latter category as they can be transformed by optical illumination. 

An active part of the investigated structure consisted of 20 CdTe QWs, each of a 16 nm width, 

separated by a 48 nm-wide Cd0.8Mg0.2Te barriers. Both the QWs and the barriers were uniformly doped with 2 × 

10 16 cm -3 iodine atoms acting as donors. Broad optical emission band related to the QWs was observed around 

1.6 eV. Moreover, a few discrete emission lines were observed at a lower energy. A more detailed analysis of 

these lines, based on excitation power dependence of their intensity and polarization-sensitive measurements of 

their optical anisotropy, allowed for their attribution to 0D-confined neutral excitons and biexcitons. 

A characteristic feature of the observed single-dot spectra was their instability against a high excitation powerdensity. 

Series of spectra in excited with a relatively low (I = 0.1 W) excitation power-density separated by 2 

min exposure to a high power light (I = 350 W) are shown in Fig. 1. It can be appreciated that the spectra 

change as a result of a high intensity illumination (see Fig.1 a - c) and a new lineshape, stable against subsequent 

high-density illumination was obtained (see Fig. 1 c - d). 

An analysis of the observed metastable behaviour of the spectra led us to conclusion that the 

confinement of carriers, responsible for the spectra, results partially from intrinsic electric fields due to ionized 

Luminescence (a.u.) 

d) 

c) 

b) 

a) 

1.535 1.540 1.545 1.550 

Energy (eV) 

1.555 1.560 1.565 

Figure 1. The -PL spectra from one position of the 

investigated sample 

donors and partially due to local potential 

fluctuations inherent to the QW growth process. 

Existence of such mixed QDs (MQDs) have 

previously been proposed on the basis of farinfrared 

spectroscopic measurements of the 

investigated structure [4, 5]. A large (from 20 

eV to nearly 120 eV) dispersion of the optical 

anisotropy of excitons confined in the MQDs 

suggests a substantial asymmetry of the 

respective lateral potential. The observed 

transform-ation of MQDs is proposed to be 

related to ionization of donors which changes 

the potential fluctuations pattern. A longer 

exposure to a high intensity light leads to 

formation of a different potential fluctuations 

pattern which is reflected by a different 

luminescence lineshape. Discussion of obtained 

results in terms of potential fluctuations in doped QW is presented. 

Partial financial support by Polish Ministry of Higher Education contract N N515071937 

is acknowledged. 

[1] M. Bayer, et al, Phys. Rev. B 65, 195315 (2002). 

[2] G. Karczewski, et al, Appl. Phys. Lett. 74, 3011 (1999). 

[3] L. Besombes, et al, phys. stat. sol. (a) 178, 197 (2000). 

[4] K. Karpierz, et al, Acta Phys. Polonica A 112, 237 (2007). 

[5] K. Nogajewski, et al, Acta Phys. Pol. A 114, 1259 (2008). 

* corresponding author : maciej.molas@fuw.edu.pl 

138

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OpticalPropertiesofInGaAsQuantumDotson(100)GaAs 

SubstratesFormedbyDropletEpitaxy 

MichałKozub 1 ,AnnaMusiał 1 ,GrzegorzSęk 1 ,JanMisiewicz 1 , 

VerenaZürbig 2 andJohannPeterReithmaier 2 

1 InstituteofPhysics,WrocławUniversityofTechnology,50-370Wrocław,Poland 

2 InstituteofNanostructureTechnologiesandAnalytics,TechnischePhysik,Universität 

Kassel,Heinrich-Plett-Str.40,34132Kassel,Germany 

Thepresenceofawettinglayer(WL)inalasingsemiconductormicrostructureintroducesanaditionalandunwantedchannelforcarrierlossandnonradiativerelaxation, 

significantlyreducingtheefficiencyofthedevice. However,inacommonIII-Vsystem 

grownbyself-assemblytheexistenceofthewettinglayerisanintrinsicpropertyofthe 

growthmodeandisunlikelytobeavoided.BecauseoftheWLsdeterioratinginfluence, 

techniquesofgrowthoflowdimensionalstructuresaimingtoreducetheWLorevento 

allowthegrowthofnanostructureswithouttheWLatallarebeingsought. 

Weattemptasystematicstudyoftheinfluenceoftemperatureandflowrateonthe 

formationofawettinglayerinanInGaAs/GaAsquantumdot(QD)systemgrownby 

the’dropletepitaxy’method[1,2],andfurtherhowthegrowthconditionchangesaffect 

theopticalpropertiesoftheentirestructure.SeveralQDsamplesgrownattemperatures 

between 410and 500 o Candgrowthratesof80-110nm/hhavebeeninvestigatedby 

photoluminescence(PL)andcontactlesselectroreflectance(CER).Incaseofthelatter, 

duetoenhancedsensitivityofthemodulationtechniqueitwaspossibletofollownot 

onlytheQDs,butalsotheWLsopticaltransitionsalongthevariatinggrowthcondition 

parameters.Ourfindingssuggestthatwithdecreasingthesubstratetemperature,surface 

diffusioncanbeefficientlyreducedthusenablingustohindertheassemblyofthewetting 

layer. TheWL-relatedopticaltransitionsarewellresolvedathighertemperatures(i.e. 

500 o C),furtherfollowedbyacorrespondingCERsignalintensitydropandbroadening, 

tofinallydisappearfortemperaturesaslowas 410 o C.Weassumethatthedecrementof 

growthtemperature(and/orgrowthrate)renderstheWLdiscontinuousandcausesitto 

coverasmallfractionofthesurfaceonlyforthelowesttemperatures(growthrates). 

AsboththechangesinthegrowthconditionsanddisappearanceoftheWLareexpectedtoaffecttheopticalpropertiesofquantumdots,theQDopticaltransitionshave 

alsobeeninvestigatedvsthetechnologicalparameters. Firstofall,thecombinationof 

PLandCERallowedustodeterminethetransitionenergiesrelatedtoQDs.Then,we 

derivetherespectiveactivationenergiesfromPLthermalquenchingmeasurementsina 

temperaturerangefrom5to300Kinordertodetectareductionofthermally-induced 

losseswithdiminishingWL.Eventually,thechangesinthesurfacedensityofthedots 

havebeenstudiedbymeansofPLwiththespatialresolutionofabout1micrometer, 

whichallowedthedisclosureofthesubstructureofemissionpeaksfromtheensemble 

relatedtosinglequantumdotemissionlinesoreventhesplitofspectraintosharplines 

relatedtosingledots. 

[1]N.Koguchi,S.Takahashi,T.Chikyow,J.CrystalGrowth111,688(1991). 

[2]V.Zrbig,A.Gushterov,L.Lingys,M.Benyoucef,J.P.Reithmaier,Int.MBEConf., 

Berlin,Germany(August,2010). 

139

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Magnetooptical study of excitons confined in potential fluctuations in 

the CdTe/CdMgTe quantum well 

M. Molas 1,* , K. Gołasa 1 , T. Kazimierczuk 1 , J.Łusakowski 1 , T.Wojtowicz 2 , 

and A. Babi ski 1 

1 Faculty of Physics, University of Warsaw, ul. Ho a 69, 00-681 Warszawa, Poland 

2 Institute of Physics, PAS, Al. Lotników 32/46, 02-668 Warszawa, Poland 

The low dimensional systems based on quantum dots (QDs) are intensely investigated 

for their applications in efficient light sources and detectors tuned in a wide range of 

wavelengths from near infrared to ultraviolet. A three-dimensional confinement of excitons 

can be achieved in self-assembled QDs [1], on fluctuations at interfaces of thin quantum 

wells (QWs) or in disordered thin QWs [2, 3]. However, it was recently shown that also in 

wider single or multiple doped QWs local potential fluctuations can also lead to the QD-like 

confinement [4, 5]. 

We report on magneto-optical properties of sharp excitonic photoluminescence (PL) 

lines related potential fluctuations, which are observed from a sample with a single QW of a 

modulated thickness. An active part of the sample consisted of a 30.1 nm wide CdTe QW, 

sandwiched between two Cd0.8Mg0.2Te barriers. A 5 nm wide iodine doping layer was added 

in the Cd0.8Mg0.2Te barrier. Results of low-temperature micro-PL measurements, performed 

in magnetic field are presented. 

Optical emission from the QW was observed in energy range between 1.81 eV to 

1.83 eV, which reflected the change in the QW thickness. At lower energy, at several 

positions on the sample a few discrete emission lines were observed. The effect of sample 

temperature, magnetic field, and detection polarisation was studied. Neutral biexcitons and 

excitons confined to a single fluctuation-related QD were identified. We found that the 

optical anisotropy of observed excitonic features ranged from about 10 eV to nearly 

160 eV, which suggests a broad distribution of lateral potential asymmetry. Energy 

dispersion of neutral exciton states amounts to 22 meV, which suggests a substantial 

distribution of the confining potential. The values of effective excitonic Lande factor of 

excitons ranged from |g*| = 1.8 to 2. 

We propose to explain our observations in a model of potential fluctuations in the QW 

resulting from a strongly disordered layer of iodine-doping. In regions of the highest iodine 

surface density the effect of electrostatic potential on the QW is the strongest. Confined 

electronic and hole states in the QW in such regions are strongly affected by the Quantum 

Confined Stark Effect (QCSE), which leads to a local decrease of the QW band-gap. In areas 

with a lower iodine density the effect is weaker and the QW bandgap is only weakly affected. 

Fluctuations of the effective QW bandgap due to the QCSE resulting from fluctuations of 

remote ionized iodine donor density are responsible in our opinion for observed QD-like 

confinement of electrons and holes in the investigated structure. 

[1] For review, see D. Bimberg et al, Quantum Dot Heterostructures (Wiley, New York, 1999). 

[2] L. Besombes, et al, Phys. Stat. Sol. (a) 178, 197 (2000). 

[3] D. Gammon, et al, Phys. Rev. Lett. 76, 3005 (1996). 

[4] K. Karpierz, et al, Acta Phys. Pol. A 112, 237 (2007). 

[5] K. Nogajewski, et al, Acta Phys. Pol. A 114, 1259 (2008). 

* corresponding author : maciej.molas@fuw.edu.pl 

140

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Mixed Correlation Phases In Elongated Quantum Dots 

A. Ballester 1 , J. M. Escartín 2 , J. L. Movilla 1 , M. Pi 2 , and J. Planelles 1 

1 Departament de Química Física I Analítica, Universitat Jaume I, Box 224, E-12080, 

Castelló, Spain 

2 Departament ECM, Facultat de Física, IN2UB, Universitat de Barcelona, E-08028, 

Barcelona, Spain 

Nanorods (NRs) are an elongated variant of quantum dots (QDs) with a highly 

anisotropic confining potential. These nanostructures constitute the bridge between zerodimensional 

QDs and one-dimensional quantum wires (QWs). Nanodumbbells (NDs) are 

another type of elongated structures. These structures are NRs sandwiched between two 

spherical caps, typically of a different material. The theoretical study of colloidal 

semiconductor NRs and NDs is of particular interest because of the ability to synthesize these 

kinds of nanostructures with precise size and shape control [1,2]. 

The unusual long length of the NRs leads to characteristic profiles of the electron 

density distribution in the NR growth direction, which depend on the ratio among the NR 

length and the number of electrons populating the conduction band of the nanostructure. In 

the case of diluted N-electron NRs, the particles are distributed in an ordered way forming a 

Wigner crystal [3]. The Coulomb energy predominates so that correlations dominate the 

electronic structure. In the opposite limit, the particles interact weakly and the kinetic energy 

dominates the Coulomb repulsion. Then, the so-called Fermi-liquid phase appears [4]. The 

transition to the Fermi liquid goes through an intermediate phase (called charge-density wave 

within the local spin-density-functional theory) which can be considered as a partially melted 

Wigner molecule [5]. In this contribution, we present a comprehensive study on the electron 

density distribution in both, NRs under applied electric fields and nanodumbbells. We show 

that two of the above-mentioned phases may coexist simultaneously in the same structure – 

but in different regions – giving rise to new phases that we refer to as mixed correlation 

phases [6]. 

[1] X. Peng, L. Manna, W. Yang, J. Wickham, E. Scher, A. Kadanich, and A. P. Alivisatos, 

Nature (London) 404, 59 (2000); S. Kan, T. Mokari, E. Rothenberg, and U. Banin, Nature 

Mater. 2, 155 (2003). 

[2] J. E. Halpert, V. J. Porter, J. P. Zimmer, and M. G. Bawendi, J. Am. Chem. Soc. 128, 12590 

(2006). 

[3] J. Planelles, M. Royo, A. Ballester, and M. Pi, Phys. Rev. B 80, 045324 (2009). 

[4] V. Filinov, M. Bonitz, and Yu. E. Lozovik, Phys. Rev. Lett. 86, 3851 (2001). 

[5] M. Koskinen, M. Manninen, and S. M. Reimann, Phys. Rev. Lett. 79, 1389 (1997). 

[6] A. Ballester, J. M. Escartín, J. L. Movilla, M. Pi, and J. Planelles, Phys. Rev. B 82, 115405 

(2010). 

141

TuP34 _______________________________________________________________ 


Simulation and Realization of Photonic Crystals in Light 

Emitting Devices 

Jakob Ebeling, Timo Aschenbrenner, Stephan Figge, and Detlef Hommel 

Institute of Solid State Physics, Univerity of Bremen, Germany 

Indium gallium nitride (InGaN) based light emitting diodes (LEDs) have been very 

successful in the blue and green spectral range. However, the light extraction efficiency 

of conventional devices suffers from the total internal reflection at the semiconductor-air 

interface due to the relatively high optical refractive index (GaN: n≈2.5) limiting the numerical 

extraction efficiency of conventional, planar LEDs based on GaN to about 4% [1]. 

To overcome this issue, different concepts have been theoretically studied and partially 

realized. Among these are encapsulation with a lower index material, surface roughening, 

thin-film LEDs and structuring the surface with photonic crystal (PC) structures, 

which are periodic variations of the refractive index at the length scale of the emission 

wavelength. The most common concept of a one-dimensional PC is a distributed Bragg 

reflector (DBR). 

Additionally to LEDs, PCs can be used to improve the properties of laser diodes. 

Commonly known are vertical-cavity surface-emitting laser diodes with DBR mirrors, 

but also distributed feedback (DFB) and DBR-based edge emitting laser diodes have 

been realized [2][3]. 

We present numerical simulations of different types of PCs and their realization on 

various structures. A one-dimensional photonic crystal grating was fabricated by focused 

ion beam (FIB) milling at the resonator ends of an edge-emitting GaN-based laser device 

forming a lateral GaN-air-DBR to enhance the reflectivity of the resonator mirrors. 

Optoelectronic measurements were made to compare devices with and without additional 

gratings. 

Moreover, green emitting InGaN-based quantum dot LED structures were grown on 

sapphire substrates with metal-organic vapour-phase epitaxy. Different two-dimensional 

PCs were structured by FIB milling as well as e-beam lithography with subsequent dry 

etching. The structure surfaces are characterized by scanning electron microscopy and 

atomic force microscopy and a comparison between the two technological methods is 

given. Optical measurements obtained by micro-photoluminescence are used to quantify 

the light extraction enhancement achieved by PC structuring. The results of the different 

structures are compared with each other and with previous simulations. 

[1] C. Wiesmann, K. Bergenek, N. Linder, and U.T. Schwarz, Laser & Photonics Review 

3, 3 (2009). 

[2] D. Hofstetter, R.L. Thornton, L.T. Romano, D.P. Bour, M. Kneissl, and R.M. Donaldson, 

Appl.Phys.Lett. 73, 2158 (1998). 

[3] J. Cho, S. Cho, B.J. Kim, S. Chae, C. Sone, O.H. Nam, J.W. Lee, Y. Park, and T.I. 

Kim, Appl.Phys.Lett. 76, 12 (2000). 

142

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Electro-optical characterization of Ti/Au-ZnTe Schottky diodes with CdTe 

quantum dots 

E. Zielony 1 , E. Popko 1 , Z. Gumienny 1 , G. Karczewski 2 

1 Institute of Physics, Wroclaw University of Technology, Wybrzeze Wyspianskiego 27, 

50-370 Wroclaw, Poland 

2 Institute of Physics, Institute of Physics Polish Academy of Science, al. Lotnikow 32/46, 


In this study the deep level transient spectroscopy (DLTS) and micro-Raman spectroscopy 

techniques have been applied to investigate ZnTe (p-type) – Ti/Au Schottky diodes containing 

a layer of CdTe self-assembled quantum dots (SAQDs). The reference sample was the ZnTe – 

Ti/Au diode without dots. Both samples were grown by molecular beam epitaxy technique. 

The dots were formed in the atomic layer epitaxy (ALE) growth mode by deposition of three 

monolayers of CdTe. Micro-Raman measurements confirmed the presence of CdTe layer of 

quantum dots in the investigated material. A broad band corresponding to the longitudinal 

(LO) CdTe phonon related to the QD-layer has been detected at a wavenumber of 160 cm -1 

[1] in the case of the QD sample. Another peak observed for the wavenumber of 210 cm -1 has 

been assigned to localized LO phonon associated with the ZnTe layer in both samples [1]. 

Moreover two tellurium - related bands at wavenumbers around 120 cm -1 and 140 cm -1 have 

been identified [1]. DLTS measurements for the sample with QDs reveal the presence of two 

hole-related signals with thermal activation energies equal to EH1=0.2eV and EH2=0.4eV. For 

the reference ZnTe-Ti/Au diode only the H2 signal is observed. It may be concluded that the 

H1=0.2 eV level can be assigned to the hole emission from defects accompanying quantum 

dots formation. The 0.4eV trap is attributed to the ZnTe bulk material [2]. 

[1] V. S. Vinogradov, et al., Physics of the Solid State, Vol. 50, No. 1, 2008. 

[2] E. Placzek-Popko, et al., Physica B 404 5173-5176 (2009). 

143

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Magneto-photoluminescence studies of many body scattering processes 

in two-dimensional hole gas 

J. Jadczak1 1 , L. Bryja 1 , A. Wojs 1 , G. Bartsch 2 , D.R. Yakovlev 2 , M. Bayer 2 

and M. Potemski 3 

1 Institute of Physics, Wroclaw University of Technology, Wroclaw, Poland 

2 Experimentelle Physik 2, Technische Universität Dortmund, D-44227 Dortmund, Germany 

3 Grenoble High Magnetic Field Laboratory, CNRS, Grenoble, France 

Fig. 1. PL vs magnetic field for 

the symmetric 15 nm QW. 

The 2D hole gas due to the much higher effective mass 

create a unique possibility to study a variety of many 

body scattering processes, also not observed in n-type 

systems. In this work we report on detailed lowtemperature 

(T=1.8÷4.2K), high-field (B≤28T), polarization-resolved 

magneto-photoluminescence (MPL) studies 

of 2DHG in GaAs quantum wells. In the symmetric 15 

nm wide well with a hole concentration p=1.5x10 11 /cm -2 

we detected in MPL spectra shake-up hole replicas of 

positively charged exciton (trion) on acceptor bound [1] 

and free states (Fig. 1). The former one for the first time. 

In asymmetric samples with different width 

(w=18÷30nm) and concentrations (p=1.4÷2.3x10 11 /cm -2 ) we observed an opposite process 

with hole cyclotron replicas going to higher energies with the magnetic field. The most intriguing 

effect, never reported before, was the observation of a coupling between the free and 

acceptor bound positively charged excitons (Fig. 2). The two 

states: free and bound are brought into resonance by an exchange 

of a quantum of a hole cyclotron energy in a scattering 

process with surrounding 2D holes. For the 22 nm wide 

sample the resonance is observed in magnetic field around 

B=13T. Further to our previous studies [3] we observed, that 

the essential coupling occur between free trion - X + and a 

pair of hole cyclotron replicas of the acceptor bound trion - 

CR-AX + . The coupling can be observed in photoluminescence 

spectra due to a nearly energy degeneracy of all final 

states involve in a radiative recombination. Aided with numerical 

calculations [3] we have explained the existence of 

two hole replicas as the transitions of bright and dark doublet 

states of AX + . The dark state is enabled in an optical 

transition by transfer of an access momentum to one of 2D 

Fig. 2. PL vs magnetic field 

for asymmetric 22 nm QW 

surrounding holes. In three coupling states model we have calculated energy and intensity of 

all observed PL lines and we have obtained a very good agreement with experimental data. 

The coupling is observed in spite of very small coupling constants (determined from experiment) 

only because two replicas are involved. 

[1] L. Bryja et al., Phys. Rev. B 75, 035308 (2007). 

[2] J. Jadczak et al. Acta Physica Polonica (in press) 

[3] A. Wojs, Phys. Rev. B 76, 085344 (2007); Phys. Rev. Lett. 104, 086801 (2010). 

144

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Norm. PhotoVoltaic Response (arb. Units) 

1.5 

1.0 

T = 10K 

Spin related effect in Si-MOSFETs THz Photoresponse 

Hadley Videlier 1 , Nina Dyakonova 1 , Frederic Teppe 1 , Cristophe Consejo 1 , 

Wojciech Knap 1 , Jerzy Lusakowski 2 , Daniel Tomaszewski 3 , Jacek Marczewski 3 , Piotr 

Grabiec 3 

1 Laboratoire Charles Coulomb UMR 5221 CNRS- Université Montpellier 2, 34095 

Montpellier, France 

2 Institute of Experimental Physics, Warsaw University, Warsaw, Poland 

3 Institute of Electron Technology, Al. Lotnikow 32/46, 02-668 Warsaw, Poland 

Photoresponse to sub-terahertz and Terahertz (THz) radiations in Silicon Metal Oxide 

Semiconductor Field Effect Transistors (Si-MOSFETs) has been studied previously [1-3]. The 

obtained values of responsivity and Noise Equivalent Power have shown the potential of Si- 

MOSFETs as sensitive detectors at room temperature [1]. The photovoltaic response 

dependences on the gate length and the gate bias were in good agreement with the Dyakonov- 

Shur plasma wave detection theory [4]. The detection signal results from the rectification of 

high frequency currents induced by the incident radiation in the transistor channel. The 

rectification takes place due to a nonlinear response of the gated two dimensional electron gas 

and a source-drain asymmetry. The main source of nonlinearity is the superposition of two 

radiation-induced effects: i) the modulation of the carrier density in the channel by variations 

of the gate potential and ii) current oscillations due to variations of the drain potential. 

Recently, monolithically integrated THz focal-plane arrays including antennas and amplifiers 

on a single silicon die has been designed to work at room temperature [5]. 

In this work we have studied the effect of high magnetic field on the Si-MOSFETs 

photovoltaic response subjected to sub-terahertz radiation (185-300 GHz ) at low temperature. 

Frequency (GHz) 

400 

300 

200 

100 

0 

0 3 5 8 10 13 15 

B (Tesla) 

!" # $ %$" &$ ' ( 

% ) * + ,$ - 

( . %$ 

185 GHz 

In Figure 1, photovoltaic signal is presented at 10 K 

as a function of applied magnetic field for three 

different incident frequencies. A very well 

0.5 

pronounced structure shifts to higher fields by 

0 2 4 6 8 10 

Magnetic Field (T) 

12 14 16 

increasing incident frequency. The positions of peaks 

is plotted in the inset of Fig.1 where the straight line 

follows equation f = gµ BB 

/ h and g = 2 . The calculation is in good qualitative agreement 

with experiments indicating a possible link between the observed structures in the 

photovoltaic response and a spin related phenomenon. This effect has been studied as a 

function of different parameters as temperature and applied source-drain current. However, a 

full quantitative interpretation of our results requires more complete experimental and 

theoretical developments. 

[1] R. Tauk, F. Teppe, S; Boubanga, et al. Appl. Phys. Lett. 89, 253511 (2006) 

[2] W. Knap, F. Teppe, Y. Meziani, et al. Applied Physics Letters 85 (4) 675-677 (2004) 

[3] W. Stillman, M.S. Shur, D. Veksler, S. Rumyantsev and F. Guarin, El. Lett., V43 (2007) 

[4] M. Dyakonov and M. Shur. El. Dev., IEEE Transactions on, 43(3):380–387 (1996) 

[5] E. Ojefors et al., IEEE Journal of, 44(7):1968–1976 (2009) 

145

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THz emission related to hot plasmons and plasma wave instability in 

field effect transistors 

Nina Dyakonova 1,2 , Abdelouahad El Fatimy 3 , Yahya Meziani 4 , Dominique 

Coquillat 1,2 , Wojciech Knap 1,2 , Frederic Teppe 1,2 , Petre Buzatu 1,2 , Luca Varani 5 , Hugues 

Marinchio 5 , Jeremy.Torres 5 , Pilippe Nouvel 5 

1 Université Montpellier 2, Laboratoire Charles Coulomb UMR 5221, Montpellier, France 

2 CNRS, Laboratoire Charles Coulomb UMR 5221, Montpellier, France 

3 Cardiff School of Physics and Astronomy, Cardiff University, Cardiff, United Kingdom 

4 Departamento de Física Aplicada, Universidad de Salamanca, Salamanca, Spain 

5 IES, UMR CNRS 5214, Université Montpellier 2, Montpellier, France 

The plasma waves in two-dimensional channel can be generated thermally by hot electrons 

(hot plasmons) [1] or can be due to plasma wave instability [2]. The THz emission due to 

radiative decay of non resonant hot plasmons is characterized by broad non tunable spectrum 

and a smooth onset. The mechanism plasma wave instability in a field effect transistor was

Book of abstracts, "Jaszowiec" 2011 - Instytut Fizyki PAN

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