Plenarvorträge - DPG-Tagungen

Halbleiterphysik Montag
diated by the waveguide underneath. The coupling leads to a strong
and spectrally narrow reduction of the absorption within the plasmon
spectrum [1]. We can measure the dispersion of these 2-dimensional
metallic photonic crystals. Changing the structure to 1-dimensional gold
nanowires allows even stronger coupling. Polaritons with a normal mode
splitting of more than 250 meV are formed [2]. Furthermore, we demonstrate
control of the dephasing times in the particle plasmons and quan-
tum beats in the 20 fs range by varying the geometric arrangement [3]. A
number of possible applications of these novel systems will be presented.
This work was financially supported by DFG and BMBF.
[1] S. Linden et al., Phys. Rev. Lett. 86, 4688 (2001).
[2] A. Christ et al., Phys. Rev. Lett. 91, 183901 (2003).
[3] K. Schubert et al., phys. stat. sol. (c) 0, 1412 (2003).
HL 3 Quantenpunkte und -drähte: Herstellung und Charakterisierung
Zeit: Montag 10:15–13:15 Raum: H17
HL 3.1 Mo 10:15 H17
Mix-and-Match Prozess zur Herstellung verzweigter elektronischer
Wellenleiter unter Verwendung von elektronenstrahlsensitivem
Calixaren und konventionellem Fotolack — •Michael
Knop 1 , Mirja Richter 1 , Ulrich Wieser 1 , Ulrich Kunze 1 , Dirk
Reuter 2 und Andreas D. Wieck 2 — 1 Lehrstuhl für Werkstoffe
und Nanoelektronik, Ruhr-Universität Bochum, D-44780 Bochum —
2 Lehrstuhl für Angewandte Festk örperphysik, Ruhr-Universität Bochum,
D-44780 Bochum
Es wird ein Verfahren zur Herstellung nanoskaliger, modulationsdotierter
GaAs/Al1−xGaxAs- Feldeffektstrukturen beschrieben.
Im ersten Prozessschritt wird eine Wellenleiterstruktur durch
Niederenergie-Elektronenstrahlithographie im Negativresist Calixaren
definiert. Zur Minimierung des Proximity-Effektes verwenden wir eine
Beschleunigungsspannung von 2 kV. Im zweiten Prozessschritt wird
durch UV-Lithographie die Mesa- und Kontaktstruktur des Transistors
in einem konventionellen Fotolack erzeugt. Die entstandene Kombination
aus Calixaren und Fotolack wird in einem einzigen nasschemischen
Ätzschritt in die Heterostruktur übertragen. Auf diese Weise lassen sich
minimale Strukturabmessungen von etwa 20 nm erzeugen. Die Wellenleiter
werden durch Transportmessungen charakterisiert.
HL 3.2 Mo 10:30 H17
Threedimensional Kinetic Monte Carlo Simulation of Formation
of Microstructures in Liquid Droplets — •Michael Block 1 ,
Roland Kunert 1 , Eckehard Schöll 1 , Torsten Boeck 2 , and
Thomas Teubner 2 — 1 Institut für Theoretische Physik, Technische
Universität Berlin, Hardenbergstr. 36, 10623 Berlin — 2 Institut für
Kristallzüchtung Berlin, Max-Born-Str. 2, 12489 Berlin
We simulate the epitaxy of Indium droplets on a glass surface and
the crystallization of Silicon inside these droplets utilizing kinetic Monte
Carlo methods. The influence of the growth temperature, the flux of
incoming particles, the surface coverage, and in particular an energy parameter
(comparable to the surface binding energy) upon the morphology
of growth is analysed. According to the experimental conditions of crystallization,
a temperature gradient and diffusion in spherical droplets is
included. The simulations result in the formation of pyramidal structures
in agreement with the experiment. The dependence of their shape and
the conditions of formation on the growth parameters is investigated in
detail.
HL 3.3 Mo 10:45 H17
NANOENGINEERING OF LATERAL STRAIN-
MODULATION IN QUANTUM WELL HETEROSTRUC-
TURES — •Jörg Grenzer 1 , S.A. Grigorian 1 , S. Feranchuk 1 ,
U. Pietsch 1 , U. Zeimer 2 , J. Fricke 2 , H. Kissel 2 , A. Knauer
2 , and M. Weyers 2 — 1 University of Potsdam, Institute of Physics,
Am Neuen Palais 10, 14469 Potsdam, Germany — 2 Ferdinand-Braun-
Institut fuer Hoechstfrequenztechnik, Albert-Einstein-Str. 11, 12489,
Berlin, Germany
We have developed a method to design a lateral band-gap modulation
in a single quantum well heterostructure (SQW). The lateral strain variation
is induced by patterning of a stressor layer grown on top of the SQW
which itself is not patterned. The 3D strain distribution is calculated using
linear elasticity theory implemented trough a finite element method
(FEM). The local variation of the band-gap energy is derived from the
strain distribution with the help of the deformation potential approach.
For a given vertical layer structure we optimized the geometrical parameters
to provide a nanostructure with maximum lateral band-gap
variation.
Experimentally such a structure was realized by etching a surface grat-
ing into a InGaP stressor layer grown on top of a InGaAs-SQW. The 3D
strain distribution and the band-gap variation are probed by X-ray grazing
incidence diffraction and photoluminescence (PL), respectively. We
found a splitting of the PL line of about 50 meV as predicted by FEM.
A planarization of the grating structure during a second epitaxy reduced
the induced band-gap variation. However, for the planar structure we
found still a splitting of larger than 22 meV.
HL 3.4 Mo 11:00 H17
Shape transition during growth of InAs/GaAs quantum dots
— •Peter Kratzer 1 and Quincy Liu 2 — 1 Fritz-Haber-Institut der
Max-Planck-Gesellschaft, Berlin — 2 Hahn-Meitner-Institut, Berlin
Recent STM studies have revealed that free-standing MBE-grown InAs
quantum dots on GaAs(001) appear in at least two varieties, as flat structures
mainly bounded by (137) facets [1], or also as larger objects with
an aspect ratio > 0.3, showing a variety of bounding facets [2]. We investigate
theoretically the energetics associated with these island shapes,
employing a hybrid approach [3]: surface energies and surface stress are
calculated using density functional theory, taking into account the specific
atomic structure. The bulk elastic energy in both the islands and the substrate
is calculated within continuum elasticity theory, using the finiteelement
method. We find that the flat island shape with (137) facets is
energetically preferable for small island volumes, while the steeper shape
becomes energetically lower for larger islands. Tensile surface stress and
the associated lowering of the surface energy on strained facets plays a
decisive role in this cross-over. We discuss implications of our findings for
the growth kinetics of InAs islands, in particular for the two-dimensional
growth mode of new atomic layers on the strained side facets of the island.
[1] J. Marquez et al., Appl. Phys. Lett. 78, (2001) 2309
[2] G. Costantini et al., Appl. Phys. Lett. 82, (2003) 3194
[3] E. Pehlke et al., Appl. Phys. A 65, (1997) 525
HL 3.5 Mo 11:15 H17
InAs quantum dots grown on the GaAs(2, 5, 11)A and B surfaces:
a STM and PL study — •Yevgeniy Temko, Takayuki
Suzuki, Ming Chun Xu und Karl Jacobi — Fritz-Haber-Institut
der Max-Planck-Gesellschaft, Faradayweg 4-6, D-14195 Berlin
InAs quantum dots (QDs) were grown by molecular beam epitaxy on
GaAs(2, 5, 11)A [1] and B surfaces. By atomically resolved in situ scanning
tunnelling microscopy we determine the main bounding facets on
the QDs. On both substrates the QDs are faceted by 110-, 111-surfaces
and a rounded region formed by vicinal (001) stacking. The latter becomes
faceted on large islands. There is no mirror symmetry on the QDs
in agreement with substrate symmetry. Besides this similarity there are
also differences: On the (2, 5, 11)A substrate the QDs shape is elongated
whereas those on the GaAs(-2,-5,-11)B are rather rounded similar to the
InAs QDs grown on GaAs(113)A and B [2,3,4]. The size distribution of
the islands on the B face is much sharper than on the A face which is also
confirmed by the low-temperature photoluminescence measurements.
[1] L.Geelhaar, J.Marquez, P.Kratzer, and K.Jacobi, Phys. Rev. Lett. 86,
3815 (2001)
[2] T.Suzuki, Y.Temko, and K.Jacobi, Appl. Phys. Lett. 80, 4744 (2002)
[3] Y.Temko, T.Suzuki, and K.Jacobi, Appl. Phys. Lett. 82, 2142 (2003)
[4] Y.Temko, T.Suzuki, M.C.Xu, and K.Jacobi, Appl. Phys. Lett. 83,
3680 (2003)