Plenarvorträge - DPG-Tagungen

Halbleiterphysik Dienstag
its origin in the formation of a recombination active boron- and oxygenrelated
metastable defect centre. The formation process of this defect is
investigated on Cz-Si solar cells as a function of an applied voltage in
the dark at temperatures ranging from 298 to 373 K. We show that the
defect formation is not only a consequence of illumination or the application
of a forward bias voltage but also occurs at elevated temperatures
in the dark. Taking into account that the application of a reverse bias
partly suppresses the defect formation, our results provide clear experimental
evidence that a recombination-enhanced mechanism correlated
with the total recombination rate is the driving force of the formation of
the metastable defect.
HL 24.5 Di 18:45 H15
Topological Features and Luminescence of Cu(InGa)Se2 Absorbers
with Sub-Micron Lateral Resolution — •Levent Gütay,
Richard Fuhrmann, and Gottfied Heinrich Bauer — Institute
of Physics, Carl von Ossietzky University Oldenburg
In a confocal microscope with sub-micron resolution we have
simultaneously recorded optical reflection and photoluminescence of
Cu(InGa)Se2 absorbers and layer structures [1]. The optical reflection
provides not a direct information on structural topological properties
such as grain boundaries but is composed of photons reflected from the
illuminated surface and weightened by a step-like acceptance function of
the microscope aperture. Furthermore the reflection signal vs. topology
is not unambiguous since in a wavy topology with spatial wave vector k
as analyzed e.g. by afm-scans, the optical reflection measures intensities
and may show maximum signal for reflection from tops and from valleys
as well; the according pattern consequently contains wave vectors with
2k. We have created artificial optical reflection patterns by converting
HL 25 Heterostrukturen II
numerically afm-topology into 2D reflection. We compare 2D Fourier
transforms of experimental with those of calculated reflection patterns
and correlate laterally resolved pl-yields with topological features in the
k-space.
[1] K. Bothe, G.H. Bauer, T. Unold, Thin Solid Films 362, 453 (2001)
HL 24.6 Di 19:00 H15
Admittance spectroscopy on single crystalline chalcopyrite thin
films — •A. Dietz 1 , J. Cieslak 1 , J. Eberhardt 1 , M. Gossla 1 ,
Th. Hahn 1 , H. Metzner 1 , N. Rega 2 , U. Reislöhner 1 , S. Siebentritt
2 , and W. Witthuhn 1 — 1 Friedrich-Schiller-Universität Jena, Institut
für Festkörperphysik, Max-Wien-Platz 1, 07743 Jena — 2 Hahn-
Meitner-Institut, Glienicker Str. 100, 14109 Berlin
Thin films of the chalcopyrite semiconductors CuInS2 (CIS), CuGaS2
(CGS) and CuGaSe2 (CGSe) were grown heteroepitaxially on Si- (CIS,
CGS) and GaAs-substrates (CGSe), respectively. For the growth of the
sulphur compounds, Molecular Beam Epitaxy (MBE) from elemental
sources was utilized, while CGSe was deposited via metal organic vapour
phase epitaxy (MOVPE).
After deposition, the samples were etched in KCN. Various metals including
Al, Ti, Ni, Cr, Ag, and a Ga/In-eutectic were tested for their
contact properties on the chalcopyrite epilayers. Schottky contacts were
obtained by the evaporation of Al, while Ni gave reliable ohmic contacs.
Thermal admittance spectroscopy (TAS) was performed on these samples
to reveal their shallow doping. The TAS spectra show typically one large
capacitance step representing a p-type dopant. The results are compared
to those obtained for polycrystalline CGSe layers in solar cells.
Zeit: Dienstag 18:00–19:15 Raum: H14
HL 25.1 Di 18:00 H14
Band offset determination of InGaAsN quantum well structures
employing surface photovoltage — •Massimo Galluppi, Gheorghe
Dumitras, Lutz Geelhaar, and Henning Riechert — Infineon
Technologies, Corporate Research Photonics, 81730 Munich, Germany
The band offset of semiconductor quantum well (QW) structures is
one of the most important parameters one needs to know in order to predict
the properties of electronic or optoelectronic devices based on such
structures. The here presented method is based on surface photovoltage
(SPV) experiments [1].The band offset and the band alignment result
directly from examining the SPV spectrum. In contrast to conventional
techniques, this method has the advantage that no fitting procedures are
needed and that the exact knowledge of the potential across the QW is
not required.
The method was employed to investigate InGaAs and InGaAsN single
QW structures. A good accordance with the results predicted by theory
and measured by conventional experimental techniques was found.
In addition, the dependence of the band offsets on the indium and on
the nitrogen concentration was studied. While the indium concentration
affects both the conduction and the valence band offsets, the nitrogen
concentration changes only the conduction band offset.
[1] Gh. Dumitras et al., PRB 66, 205324 (2002); Gh. Dumitras et al.,
JAP 94, 3955 (2003).
HL 25.2 Di 18:15 H14
Edge magneto plasmons in GaAs and GaN-based heterojunctions
— •Hans Huebl, Thomas Vallaitis, Sebastian T. B. Goennenwein,
and Martin S. Brandt — Walter Schottky Institut, Technische
Universität München, München, Germany
Various processes can influence the microwave properties of lowdimensional
electron systems, such as absorption caused by cyclotron
resonance, spin resonance or quantum oscillations. However, also
collective excitations such as plasmons can be excited in experimental
set-ups used to study these processes. Since absorption by plasmons
can be very strong, it can easily dominate the spectra observed. In
this contribution, we report a detailed investigation of the absorption
caused by edge magneto plasmons (EMPs) in two-dimensional electron
gases (2DEG). EMPs in InGaAs quantum well structures as well as in
GaN-AlGaN heterostructures have been studied, allowing a variation
of the charge carrier density by more than one order of magnitude.
Very good agreement with the theory of Allen et al.[1] is found, while
the more elaborate theory of Volkov and Mikhailov[2] is not required
to account for the experimental data. Therefore, 2DEG samples with
circumferences of > 1 cm or < 50 µm e.g. in checkerboard arrangement
will be necessary to study spin effects.
[1] S. J. Allen, H. L. Störmer and J. C. M. Hwang, PRB28, 4875 (1983)
[2] V. Volkov and S. A. Mikhailov, Landau Level Spectroscopy, ed. by
G. Landwehr and E. I. Rashba, Springer Verlag, Berlin, Chapter 15, p.855
(1991)
HL 25.3 Di 18:30 H14
Strukturuntersuchungen an dünnen InAs/GaAs Schichten
mittels Rastertunnelmikroskopie an Querschnittsflächen
— •Ferdinand Streicher, Holger Eisele, Tai-Yang Kim,
Jan Grabowski, Rainer Timm, Andrea Lenz, Konstantin
Pötschke, Udo W. Pohl, Dieter Bimberg und Mario Dähne
— Technische Universität Berlin, Institut für Festkörperphysik,
Hardenbergstr. 36, D-10623 Berlin
Mittels Querschnitts-Rastertunnelmikroskopie (XSTM) wurde die
Struktur dünner InAs/GaAs Quantentröge (wells) mit atomarer
Auflösung untersucht. Hierbei wurde insbesondere die atomare Anordnung
des InAs in den 0,6 - 1,8 ML dicken Schichten beobachtet.
Ausgehend von lateralen Inhomogenitäten geben die Untersuchungen
Auskunft über Ansätze von Inselbildungen, bevor das Quantenpunktwachstum
bei ca. 1,8 ML einsetzt.
Weiterhin zeigt sich eine Intensivierung des elektrischen Kontrastes in
den XSTM-Bildern mit zunehmender Schichtdicke, was auf die gleichzeitig
wachsende Anzahl von quantisierten Zuständen in der Schicht
zurückzuführen ist.
HL 25.4 Di 18:45 H14
Elektronische Eigenschaften von in-situ geätzten und
überwachsenen GaAs/AlGaAs Grenzflächen — •Stephan
Schulz, Christian Heyn und Wolfgang Hansen — Institut
für Angewandte Physik und Zentrum für Mikrostrukturforschung,
Universität Hamburg, Jungiusstraße 11, 20355 Hamburg
In-situ Trockenätzen und anschließendes MBE-Überwachsen von vorstrukturierten
Substraten bietet vielfältige Möglichkeiten zur Herstellung
neuartiger Quantenstrukturen. Als Ätzprozesse verwenden wir Chemi-