Plenarvorträge - DPG-Tagungen

Halbleiterphysik Donnerstag
HL 42 Quantenpunkte und -drähte: Optische Eigenschaften II
Zeit: Donnerstag 15:15–16:30 Raum: H13
HL 42.1 Do 15:15 H13
Investigations of electrically contacted single quantum dots —
•U. Scholz 1 , R. Schmidt 1 , M. Vitzethum 1 , R. Fix 1 , S. Malzer 1 ,
C. Metzner 1 , P. Kailuweit 2 , D. Reuter 2 , A. Wieck 2 , M.C.
Hübner 3 , S. Stufler 3 , A. Zrenner 3 , and G.H. Döhler 1 —
1 Technische Physik I, Universität Erlangen-Nürnberg — 2 Angewandte
Festkörperphysik, Ruhr-Universität Bochum — 3 AG Nanostructure
Optoelectronics, Universität Paderborn
We investigate single quantum dots (QDs) embedded in the intrinsic
region of a micro-LED. The active area of the LED is defined by the
intersection of a p- and a n-doped stripe. The bottom stripe is defined
by focussed ion beam implantation (FIB) which easily provides the necessary
lateral resolution of a few 100 nm. The perpendicular top stripe is
fabricated by wet chemical etching to µm or sub-µm width. As the dot
densities of our samples are typically less than 10 9 cm −2 , the active area
of the LED, on the average, contains one QD. We find single QD spectra
in EL measurements. Extremely sharp recombination lines are observed
up to the third excited state (f-shell). Within the different shells several
emission peaks are visible, which can be attributed to differently charged
excitons. All the lines show a pronounced red shift with increasing bias
voltage due to the Stark effect. Polarisation resolved measurements suggest
for the p-shell an anisotropy of the lateral confinement potential. We
will also discuss voltage dependent photo current measurements and the
application for a single photon turnstile device.
HL 42.2 Do 15:30 H13
Inelastic light scattering of few-electron collective excitations in
charge-tunable artificial atoms — •T. Brocke 1 , A. Stührk 1 , M.-
T. Bootsmann 1 , M. Tews 2 , B. Wunsch 2 , D. Pfannkuche 2 , Ch.
Heyn 1 , W. Hansen 1 , D. Heitmann 1 , and C. Schüller 1 — 1 Institut
für Angewandte Physik und Zentrum für Mikrostrukturforschung, Universität
Hamburg, Jungiusstraße 11, D-20355 Hamburg — 2 I. Institut
für Theoretische Physik, Universität Hamburg, Jungiusstraße 9, D-20355
Hamburg
We report the investigation of electronic excitations in InGaAs selfassembled
quantum dots using resonant inelastic light scattering. By applying
a voltage between a metallic front gate and a back electrode, the
dots can be charged with N = 1...6 electrons. We observe excitations,
which are identified as transitions of electrons from the s to the p shell
(s-p transitions) and from the p- to the d-shell (p-d transitions) of the
quasiatoms. We find that the s-p transition energy decreases and the observed
band broadens, when the p shell is filled with 1 to 4 electrons. By
a theoretical model, which takes into account the full Coulomb interaction
in the few-electron artificial atom, we can confirm the experimental
results to be an effect of the Coulomb interaction in the quantum dot.
This project is funded by the DFG via SFB 508 and SCHU1171/2.
HL 42.3 Do 15:45 H13
Nahfeld-Photolumineszenz einzelner InGaAs-Quantenpunkte
bei tiefen Temperaturen — •Christian Griesche, Kai Hodeck
und Mario Dähne — Technische Universität Berlin, Institut für
Festkörperphysik, Hardenbergstr. 36, 10623 Berlin
Spektroskopische Untersuchungen einzelner InGaAs-Quantenpunkte
mit Optischer Rasternahfeld-Mikroskopie (SNOM) bei 80 K zeigten unter
variierender Anregungsintensität im Signal des Grundzustandsübergangs
neu auftretende Linien. Diese wurden der Bildung von Trionen und Biexzitonen
zugeordnet und weisen eine sehr hohe Bindungsenergie für Exzitonenkomplexe
aus [1].
HL 43 III-V Halbleiter II
Um dieses Phänomen anhand detaillierter Messungen mit höherer
spektraler Auflösung genauer zu analysieren, wurde ein neues
Tieftemperatur-SNOM für den Betrieb bei 4 K aufgebaut. Durch eine
innovative Versuchsanordnung wird hierbei ein zuverlässiger Betrieb
trotz des extrem geringen Platzangebots im Kryostaten gewährleistet.
Erste Photolumineszenz-Untersuchungen an einzelnen InGaAs-
Quantenpunkten bei tiefen Temperaturen werden derzeit mit diesem
Gerät durchgeführt.
[1] K. Hodeck et. al., phys. stat. sol. (c)0, No.4, 1209 (2003)
HL 42.4 Do 16:00 H13
Excitonic Complexes in Single InGaN Quantum Dots —
•Robert Seguin 1 , Sven Rodt 1 , Andre Strittmatter 1 , Dieter
Bimberg 1 , Eike Hahn 2 , and Dagmar Gerthsen 2 — 1 TU Berlin,
Institut für Festkörperphysik, Sekr. PN 5-2, Hardenbergstr. 36,
D-10623 Berlin, Germany — 2 Laboratorium für Elektronenmikroskopie,
Universität Karlsruhe, D-76128 Karlsruhe, Germany
InGaN quantum dots (QDs) are very promising for future light emitting
devices covering the visible region. But little is known about their
electronic structure like excitonic complexes.
We present results obtained by cathodoluminescence spectroscopy on
single InGaN/GaN QDs grown by MOCVD on Silicon(111) substrate. To
probe single QDs metallic shadow masks are evaporated onto the sample
surface. The QDs consist of In-rich regions within an inhomogenous In-
GaN layer, as is demonstrated by high-resolution cross-section transmission
electron microscopy. The existence of zero-dimensional localization
centers is confirmed by the observation of δ-function like emission lines
at low temperatures and temperature dependent measurements.
The spectral jitter [1] of the various emission lines, enables us to identify
up to 5 lines originating from the same QD. Excitation density and
polarization dependent measurements reveal more information about the
electronic origin of these lines.
[1] V. Türck, S. Rodt, R. Heitz, O. Stier, M. Straßburg, U.W. Pohl, and
D. Bimberg, Physica E 13, 269 (2002).
HL 42.5 Do 16:15 H13
The Nature of the Excitonic Ground State in coupled QD
Molecules — •H. J. Krenner, M. Sabathil, W. Prestel, D.
Schuh, M. Bichler, J. J. Finley, and G. Abstreiter — Walter
Schottky Institut, TUM, Am Coulombwall 3, 85748 Garching
We present a combined theoretical and experimental investigation of
excitonic states in individual QDMs subject to axial electric fields (F).
Theoretical calculations of the interband spectra including a full treatment
of strain and Coulomb interactions, demonstrate that the electron
dot-dot coupling is significantly stronger than for holes. This gives rise
to a field driven transition of the nature of the excitonic ground state
between optically active (direct) and optically inactive (indirect) states.
We have experimentally tested this prediction of a field driven anticrossing
by performing photoluminescence on single QDMs. Over the
field range for which the ground state is predicted to be dark, a characteristic
emission multiplet is observed from each QDM following quasi
resonant excitation into the wetting layer. This structure is attributed to
optically active few particle states in the nominally dark QD, a conclusion
supported by experiments using non-resonant excitation above the
barrier band gap where only one emission line is observed. Furthermore,
indirect excitons are shown to exhibit a strongly anomolous linear Stark
shift consistent with a large intrinsic e-h separation (∼2-3 nm).
Zeit: Donnerstag 15:15–16:30 Raum: H14
HL 43.1 Do 15:15 H14
Raman spectroscopy of Ga(As,N) epitaxial layers under hydrostatic
pressure — •M. Güngerich 1 , P.J. Klar 1 , W. Heimbrodt 1 ,
J. Koch 1 , W. Stolz 1 , M.P. Halsall 2 , and P. Harmer 2 — 1 FB
Physik und WZMW, Philipps-Universität, Marburg, Germany — 2 Dept.
Physics, UMIST, Manchester, United Kingdom
Vibrational modes of GaAs1−xNx layers were studied by Raman spec-
troscopy at hydrostatic pressures up to 20GPa. Lattice vibrations of
Ga(As,N) show a two-mode behaviour typical of a system where the impurity
atoms are considerably lighter than the host atoms. The N atoms
vibrate independently of the GaAs-like phonons and give rise to a local
vibrational mode (LVM) visible in the spectra for x > 0.005. Pure
GaAs is known to undergo a phase transition from the zincblende structure
to an orthorhombic structure in the pressure range between 15 and