Plenarvorträge - DPG-Tagungen

Halbleiterphysik Donnerstag
HL 44.49 Do 16:30 Poster A
PAC Untersuchungen an Seltenen Erden Sonden in GaN und
ZnO — •R. Nédélec 1 , R. Vianden 1 und die ISOLDE Kollaboration
2 — 1 Helmholtz - Institut für Strahlen- und Kernphysik, Nußallee
14–16, 53115 Bonn — 2 ISOLDE, CERN, CH-1211 Genève 23
Halbleiter mit großer Bandlücke, wie die Gruppe-III-Nitride und Zinkoxid,
haben in den letzten zehn Jahren enorm an Bedeutung gewonnen.
Für die Anwendung in der Optoelektronik sowie Hochleistungs- und
Hochtemperaturelektronik ist eine Strukturierung der Bauelemente mittels
Ionenimplantation von Vorteil.
Nach Dotierung von Halbleitern mit großer Bandlücke (insbesondere
GaN [1]) mit verschiedenen Seltenen Erden konnten Lumineszenzeffekte
in unterschiedlichen Wellenlängenbereichen des sichtbaren Spektrums
beobachtet werden.
Wir zeigen erste Ergebnisse der Untersuchungen zum Ausheilprozess
der Implantationsschäden sowie der temperaturabhängigen Messungen
mit der Methode der gestörten γ-γ-Winkelkorrelation (PAC). Dazu verwenden
wir die 91–1094keV Kaskade der PAC-Sonde 172-Lu(172-Yb).
[1] A.J. Steckl, J.M. Zavada, MRS Bulletin, Sept. 1999, p. 33
HL 44.50 Do 16:30 Poster A
Photoluminescence of GaAs/AlGaAs heterostructures grown in
a manganese contaminated MBE system — •Klaus Wagenhuber,
Hans-Peter Tranitz, Matthias Reinwald, and Werner
Wegscheider — Institut für Experimentelle und Angewandte Physik,
Universität Regensburg, Universitätsstr. 31, D-93053 Regensburg
Photoluminescence is a highly sensitive tool for the detection of residual
impurities in semiconductor crystals. We used this technique to determine
the quality of modulation doped single interface (MDSI) Al-
GaAs/GaAs structures. The samples were grown in an MBE chamber,
which is also used for the epitaxy of GaMnAs layers. Manganese on a
gallium-site forms a shallow acceptor level at about 0.11 eV above the
top of the GaAs valence Band. Due to free-to-bound and donor-acceptor
pair transitions a characteristic emission band appears at a well-known
position of the luminescence spectrum. Our samples exhibit bright and
narrow excitonic recombination lines in the PL-signal but even at high
excitation densities no manganese peak could be observed. That leads
to the conclusion that these layers are, to a high degree, free of the unwanted
manganese impurity. Magneto-transport measurements show low
temperature electron mobilities in excess of 5 · 10 6 cm 2 /Vs and thus confirm
these results.
This work is supported by BMBF Verbundprojekt ” Spinelektronik und
Spinoptoelektronik in Halbleitern“
HL 44.51 Do 16:30 Poster A
Phonon modes and infrared dielectric functions of Cu-, Fe-,
Ga-, Li-, N-, P-, Sb-doped ZnO thin films — •Carsten Bundesmann,
Mathias Schubert, Holger von Wenckstern, Michael
Lorenz, Evgeni Kaidashev, and Marius Grundmann — Fakultät
für Physik und Geowissenschaften, Institut für Experimentelle Physik II,
Universität Leipzig, Linnéstraße 5, 04103 Leipzig
Raman spectroscopy and mid-infrared spectroscopic ellipsometry was
applied to study Cu-, Fe-, Ga-, Li-, N-, P-, Sb-doped ZnO thin films
deposited on differently orientated sapphire substrates using the pulsed
laser deposition technique. Raman spectroscopy reveals additional modes
related to the different dopant species, while spectroscopic ellipsometry
allows the determination of wave numbers and broadening parameters
of the ZnO-type phonon modes, and free charge carrier parameters. The
broadening parameters are closely related to the thin film quality. Furthermore,
infrared spectroscopic ellipsometry can be used to determine
crystal orientation as shown for ZnO thin films grown on a-plane oriented
sapphire.
[1] C. Bundesmann et al., Appl. Phys. Lett. 83, 1974 (2003)
HL 44.52 Do 16:30 Poster A
Well-width dependent electron spin dephasing in (110) GaAs
QWs — •Stefanie Döhrmann 1 , Maik Begoin 1 , Dieter Schuh 2 ,
Max Bichler 2 , Daniel Hägele 1 , and Michael Oestreich 1
— 1 Universität Hannover, Institut für Festkörperphysik, Abteilung
Nanostrukturen, Appelstr. 2, 30167 Hannover — 2 Technische Universität
München, Walter-Schottky-Institut, Am Coulombwall, 85748 Garching
Recently the electron spin in semiconductors has become a focus of
intense research in the context of spintronics. A prime condition for the
development of potential applications is the understanding of spin decoherence
in semiconductor structures. We have measured spin dephasing
times in (110) GaAs quantum wells (QWs) in dependence on well width
in a temperature range from 6 to 300 K. The sample under investigation
is an undoped, wedge shaped GaAs/AlGaAs multiple quantum well
grown on (110) oriented substrate. The electron spin dephasing times
were determined by means of time and polarization resolved photoluminescence
spectroscopy using a synchroscan streakcamera for detection.
HL 44.53 Do 16:30 Poster A
Electron spin dephasing in biased GaAs quantum wells —
•Joachim Fritzsche 1 , Jörg Rudolph 1 , Daniel Hägele 1 , Markus
Beck 2 , Stefan Malzer 2 , Gottfried Döhler 2 und Michael
Oestreich 1 — 1 Institut für Festkörperphysik, Universität Hannover,
Appelstr. 2, D-30167 Hannover — 2 Institut für Technische Physik I, Universität
Erlangen-Nürnberg, Erwin-Rommel-Str. 1, D-91058 Erlangen
Electron spin dephasing times are of basic interest in the course of
”spintronics” and its potential for applications. One important spindephasing
mechanism depends on electron hole exchange interaction which
is determined by the overlap of electron and hole wavefunctions and,
therefore, can be tuned by external electric fields.
We measure electron spin dephasing times in a biased GaAs quantum
well in dependence of temperature and electric field applied perpendicular
to the layers. The sample consists of a single undoped 20 nm
GaAs quantum well sandwiched between 100 nm Al0.35Ga0.65As barriers.
Electron and holes are excited by ps-pulses of an 80 MHz mode-locked
Ti:Sapphire laser. Electron spin dephasing times are determined by time
and polarization-resolved photoluminescence which is detected by a
synchroscan streakcamera.
HL 44.54 Do 16:30 Poster A
Charge carriers in columnar nanostructures of porous GaAs and
InP using micro-Raman scattering — •Pavel Prunici 1 , Gert
Irmer 1 , Jochen Monecke 1 , and Ivan Tiginyanu 2 — 1 Institut für
Theoretische Physik, TU Bergakademie Freiberg, Bernhard-von-Cotta-
Str. 4, D-090596 Freiberg, Germany — 2 Institute of Applied Physics,
Technical University of Moldova, Boulevard Stefan cel Mare 168, MD-
2004 Chisinau, Moldova
Raman scattering spectra of columnar nanostructures of porous GaAs
and InP were investigated at room temperature and at 77 K using different
laser excitation wavelengths in the visible and in the near infrared
region. The samples have two layers with different porosity structures
which were well characterized by scanning electron microscope. In the
case of porous GaAs the cylinders have radii in the range of 50-100 nm
and about 10000 nm long. The radii of the InP cylinders are in the
range of 25-50 nm. The distribution of the charge carriers in individual
cylinders as well as in groups of well-oriented parallel cylinders was studied
using micro-Raman scattering. The bands observed are compared
with calculations predicting coupled LO-phonon-plasmon and coupled
Fröhlich-plasmon modes using a dielectric function derived on the basis
of an appropriate two-dimensional effective-medium theory.
HL 44.55 Do 16:30 Poster A
BxGa1−x−yInyAs und InxGa1−xNyAs1−y als neuartige Absorbermaterialien
in Dünnschichtsolarzellen — •Claudia Krahmer,
Gunnar Leibiger, Helmut Herrnberger und Volker Gottschalch
— Universität Leipzig, Institut für Anorganische Chemie, Linnestr.
3, 04103 Leipzig
(BGaIn)As- und (InGa)(NAs)- Mischkristalle, gitterangepasst
an (001) GaAs-Substrate, sind infolge der Reduzierung der
Bandlückenenergie gegenüber GaAs potentielle Absorbermaterialien
für Dünnschichtsolarzellen.
Mittels MOVPE (Metallorganische Gasphasen-Epitaxie) wurde unter
Verwendung von Trimethylgallium, Trimethylindium, Triethylbor,
Dimethylhydrazin, Diethylzink und Disilan p- und n- leitendes
BxGa1−x−yInyAs und InxGa1−xNyAs1−y bei 550 ◦ C bzw. 560 ◦ C auf GaAs
abgeschieden. Der Einfluss des Zn- und Si- Einbaus auf das epitaktische
Wachstum konnte ermittelt werden.
Die veränderten Solarzelleneigenschaften bei Verwendung von
(InGa)(NAs)- bzw. (BGaIn)As- Absorberschichten werden diskutiert. Als
Vergleich dienten GaAs- Solarzellen verschiedener Struktur, die im Hinblick
auf die Optimierung der Zellen gezüchtet wurden.