Plenarvorträge - DPG-Tagungen

Halbleiterphysik Montag
abhängigkeit der ZnO-Valenzbandstruktur im Vergleich zur experimentell
bestimmten Vergrößerung der Spin-Bahn-Wechselwirkung ∆so und
der Kristallfeldaufspaltung ∆cf. 2
[1] R.R.Reeber, J. Appl. Phys. 41, 5063 (1970)
[2] N.Ashkenov et al., eingereicht bei Phys. Rev. B
HL 12.88 Mo 16:30 Poster A
Room temperature UHV bonding of Si to GaAs — •Alin Mihai
Fecioru, Stephan Senz, and Ulrich Goesele — Max-Planck-
Institut für Mikrostrukturphysik, 06120 Halle
The traditional method of wafer bonding of Si to GaAs at room temperature
followed by heating to high temperatures is not possible due to
the difference in the thermal expansion coefficients of the two materials.
Our interfaces were obtained by ultrahigh vacuum (UHV) wafer bonding
at room temperature, without any intermediate layer. The cleaning
of Si wafers was done with RCA solution followed by HF tip. In the UHV
the hydrogen is thermally desorbed at 480 ◦ C. A UV/ozone treatment is
applied to GaAs wafers in order to remove organic contamination. This
induces the formation of a complex oxide which will be thermally desorbed
at 450 ◦ C in UHV. An atomic hydrogen induced modification of
Ga2O3 into Ga2O enhances the process.
Electrical properties of n-GaAs (100)/ p-Si (100) interfaces were investigated
by temperature dependent current-voltage measurements. A
high concentration of electrically active defects is observed at the interface.
Additional tunneling contributions (for highly doped samples) cause
a high leakage current.
HL 12.89 Mo 16:30 Poster A
a-Si/SiOx Bragg-Reflektoren auf mikro-strukturierten Halbleitern
— •Rüdiger Schmidt-Grund 1 , Thomas Nobis 1 , Bernd
Rheinländer 1 , Volker Gottschalch 2 , Helmut Herrnberger 2
und Marius Grundmann 1 — 1 Universität Leipzig, Fakultät für Physik
und Geowissenschaften, Institut für Experimentelle Physik II, Linnéstr.
5, 04103 Leipzig — 2 Universität Leipzig, Fakultät für Chemie und Mineralogie,
Linnéstr. 3, 04103 Leipzig
Laterales Bragg-Confinement von Mikroresonator-Lichtemittern
erhöht das Verhältnis der Zahl der axial resonanten Moden zur Zahl
der spontan emittierten lateralen Moden. Hoch reflektierende Si/SiOx
Bragg-Reflektoren (BR) eignen sich gut zur Verbesserung des optischen
Confinements in mikro-strukturierten Resonatoren.
Sowohl Metall-, a-Si- und SiOx-Einzelschichten als auch a-Si/SiOx BR
wurden mittels PECVD für den Wellenlängenbereich von (500 - 830)
nm mit kleiner Paarzahl N (typisch N = 4,5) auf Glas-, InP- und GaAs-
Substraten mit verschiedenen 3-dimensionalen und gekrümmten Strukturen
abgeschieden. Die optischen Eigenschaften wurden mittels der neuen
Methode der detektions-fokalen räumlich-aufgelösten spektroskopischen
Ellipsometrie und der Methode der konfokalen räumlich-aufgelösten spektroskopischen
Ellipsometrie untersucht. Aus der Modell-Analyse der ellipsometrisch
gemessenen Spektren der Mueller-Matrix konnten das Reflexionsvermögen
(R) und die Schichtdicken berechnet und Rückschlüsse auf
die Probengeometrie gezogen werden. Das aus der ellipsometrischen Analyse
berechnete R wurde mit dem R, welches mittels konfokaler Mikro-
Reflexion bestimmt wurde, verglichen.
HL 12.90 Mo 16:30 Poster A
Free-charge carrier properties in AlGaAs/GaAs superlattices
investigated by magnetooptic ellipsometry — •Claas von Middendorff
1 , Tino Hofmann 1 , Gunnar Leibiger 2 , and Mathias
Schubert 1 — 1 Fakultät für Physik und Geowissenschaften, Institut
für Experimentelle Physik II, Universität Leipzig,Linnéstraße 5, 04103
Leipzig — 2 Fakultät für Chemie und Mineralogie, Halbleiterchemie, Universität
Leipzig, Linnéstraße 3, 04103 Leipzig
Far-infrared magnetooptic ellipsometry is employed to determine the
electron effective mass, the mobility and concentration in Si-doped
AlGaAs/GaAs-superlattices at temperatures ranging from 70 to 290 K.
We observe a directional dependence of the free-charge carrier mobility.
As expected for a system of reduced dimensionality the in-plane mobility
is much larger than its out-of-plane component. The parameters
are determined by modelling the observed magneto-optic birefringence
originating from the far-infrared free-charge carrier excitations in the
AlGaAs/GaAs-heterojunctions without any need for additional electrical
measurements.
HL 12.91 Mo 16:30 Poster A
The Boltzmann Equation in Semiconductor Superlattices —
•Bernhard Rieder and Joachim Keller — Institute of Theoretical
Physics, University of Regensburg, 93040 Regensburg
We model the electron motion in semiconductor superlattices with the
help of the Boltzmann equation in the relaxation time approximation. A
smooth transition from the superlattice to the bulk region of the semiconductor
material is assumed. We derive corrections to the Boltzmann
equation in this transition region, because the model of the boundaries
is crucial for the behavior of the system. Instabilities, which hindered
the application of the superlattices as TeraHertz-source up to now, will
develop there. In experiments these instabilities lead to periodic behavior
of the system. Up to now no realistic model including the boundaries was
set up which reproduces this behavior. With our model we find periodic
behavior and investigate the effect of the electric circuit which is coupled
to the superlattice.
HL 12.92 Mo 16:30 Poster A
The Correlation between Emission Spectra and Atomic Scale
Structure of GaAs/AlGaAs Quantum Wells — •M. Erdmann 1 ,
C. Ropers 1 , M. Wenderoth 1 , L. Winking 1 , T. C. G. Reusch 1 ,
R. G. Ulbrich 1 , S. Malzer 2 , and G. Döhler 2 — 1 IV. Physikalisches
Institut der Universität Göttingen, Tammannstraße 1, 37077
Göttingen — 2 Inst. für techn. Physik, Universität Erlangen-Nürnberg,
Erwin-Rommel-Straße 1, 91058 Erlangen
We have performed cross-sectional Scanning Tunneling Microscopy and
Micro-Photoluminescence experiments on GaAs/AlGaAs quantum wells
and correlated the structural and optical data. The emission spectra were
obtained using a scanning Micro-PL microscope with lateral resolution
of 500 nm. Large X-STM topographs with atomic resolution were converted
into potentials by linear scaling, serving as starting point for a
numerical simulation in Envelope Function approximation of the optical
spectra of the studied real structure. We assume a laterally isotropic
aluminium distribution and use a model recently introduced by Runge
and Zimmermann [2]. In real quantum films, interface fluctuations lead
to localization of excitons in the disorder potential of the quantum well
interfaces [1]. The resulting inhomogeneous broadening of the optical
spectra is quantitatively reproduced by the simulated spectra [3].
[1] A. Zrenner et al., Phys. Rev. Lett. 72 (1994) 3382
[2] R. Zimmermann, F. Große, and E. Runge, Pure Appl. Chem. 69 (1997)
1179
[3] C. Ropers, M. Wenderoth, L. Winking, T.C.G. Reusch, M. Erdmann,
R.G. Ulbrich, S. Malzer and G. Döhler, Phys. Rev. Lett. (submitted)
HL 12.93 Mo 16:30 Poster A
Micro- and nanotubes made of strained metal/semiconductor
double layers — •Olrik Schumacher, Stefan Mendach, Christian
Heyn, Holger Welsch, and Wolfgang Hansen — Institut
für Angewandte Physik, Universität Hamburg, Jungiusstrasse 11, D-
20355 Hamburg, Germany
The method of self-rolling strained semiconductor double layers first
introduced by Prinz [1] enables to build tubes with radii varying between
some nanometers and some microns. Here we show that by
choosing adequate preparation parameters it is also possible to roll
metal/semiconductor double layers into micro- and nanotubes. By evaporating
metals with different layer thicknesses onto InGaAs-layers we
achieve strained double layers resulting in tubes with tuneable diameter.
The dependence between diameter and layer composition as well as the
rolling anisotropy will be shown and compared to conventional semiconductor
tubes. Furthermore possible applications will be discussed.
[1] V. Ya. Prinz et al., Physica E6 (2000) 828-831.
HL 12.94 Mo 16:30 Poster A
FWM-Experimente an dotierten Einzel-Quantumwells —
•Patrick Schröter 1 , Bertram Su 1 , Christian Schüller 1 ,
Max Bichler 2 und Werner Wegscheider 3 — 1 Institut für
Angewandte Physik, Universität Hamburg — 2 Walter-Schottky-Institut,
TU-München — 3 Institut für Angewandte und Experimentelle Physik,
Universität Regensburg
Wir präsentieren die nach unserem Wissen ersten spektral aufgelösten
Vier-Wellen-Misch-Experimente (SR-FWM) an modulationsdotierten
GaAs/AlGaAs-Einzel-Quantumwells. Die optisch dünnen Proben
sind mit einem Gate zur Variation der Ladungsträgerdichte versehen. Die
Experimente wurden in einem optischen 3 He-Magnet-Kryostaten durchgeführt,
der Temperaturen bis 0,4 K und Magnetfelder bis zu 11,5 T er-