Plenarvorträge - DPG-Tagungen

Halbleiterphysik Donnerstag
20GPa. In the investigated GaAs0.915N0.085 sample the phase transition
indicated by the disappearance of the GaAs-like phonons takes place at
about 19GPa. Up to that pressure, the pressure coefficients of the optical
phonons are similar to those of GaAs. The LVM shifts to higher
frequencies at a significantly higher rate. This behaviour can be understood
assuming that the pressure induced changes of the bond lengths
are the same as in pure GaAs. It can be shown that the anharmonicity
of the Ga-N bonds in Ga(As,N) is smaller than in GaN.
HL 43.2 Do 15:30 H14
Zirkular photogalvanischer Effekt bei Interband-Anregung in
Quantentrögen — •Petra Schneider 1 , S.D. Ganichev 1 , V.V.
Bel’kov 2 , C. Back 1 , M. Oestreich 3 , J. Rudolph 3 , D. Hägele 3 ,
L.E. Golub 2 , W. Wegscheider 1 und W. Prettl 1 — 1 Institut für
Experimentelle und Angewandte Physik, Universität Regensburg, 93041
Regensburg — 2 A. F. Ioffe Physico-Technical Institute, 194021 St. Petersburg,
Russland — 3 Institut für Festkörperphysik, Universität Hannover,
30167 Hannover
Der zirkular photogalvanische Effekt konnte zum ersten Mal bei
Interband-Anregung nachgewiesen werden. Die Messung wurde an
p-leitenden (113)A MBE-gewachsenen GaAs/AlGaAs Quantentrögen
durchgeführt. Die spektrale Abhängigkeit des Photostroms wurde zusammen
mit dem Polarisationsgrad im Energiebereich von 1.45 bis 1.8 eV gemessen.
Ergebnisse bzgl. der Spinrelaxationszeiten bei Raumtemperatur
in dem untersuchten Spektralbereich werden präsentiert.
HL 43.3 Do 15:45 H14
Determination of the nitrogen distribution in GaInNAs/GaAs
quantum wells by transmission electron microscopy and correlation
with spectroscopic data — •M. Hetterich 1 , A. Grau 1 ,
D. Litvinov 2 , A. Rosenauer 2 , D. Gerthsen 2 , Ph. Gilet 3 , and L.
Grenouillet 3 — 1 Institut für Angewandte Physik and Center for Functional
Nanostructures (CFN), Universität Karlsruhe, D-76131 Karlsruhe,
Germany — 2 Laboratorium für Elektronenmikroskopie and CFN, Universität
Karlsruhe, Germany — 3 LETI/DOPT/SLIR, CEA-Grenoble,
38054 Grenoble cedex 9, France
We report on a new technique for the determination of the nitrogen
concentration in GaInNAs heterostructures by transmission electron
microscopy and correlate the obtained results with spectroscopic data
(temperature-dependent photoluminescence and photoreflectance spectroscopy).
Two almost identical samples grown by gas-source molecular
beam epitaxy on GaAs (001) were investigated, containing InGaAs and
GaInNAs quantum wells, respectively. Both samples had the same nominal
well thickness and In concentration. They only differed in the nitrogen
content. The In concentration profile of the InGaAs/GaAs quantum
wells was determined by composition evaluation of lattice fringe analysis
(CELFA) based on the chemical sensitivity of the (002) reflection in
the zincblende structure. The N concentration in the GaInNAs wells was
HL 44 Poster II
then evaluated by the comparison of CELFA results obtained for both
samples. The presented technique may be useful for future investigations
into the mechanisms behind the influence of annealing on the optical
properties of GaInNAs quantum wells.
HL 43.4 Do 16:00 H14
Real-time growth monitoring using multichannel-RAS —
•Ch. Kaspari, F. Poser, S. Weeke, and W. Richter for the
NanOp collaboration — Technische Universität Berlin, Institut für
Festkörperphysik, Sekr. PN 6-1, Hardenbergstraße 36, D-10623 Berlin
Since its development by Berkovits, Aspnes and co-workers in the
1980ies, reflectance anisotropy spectroscopy (RAS) has become an important
in situ-technique to investigate the epitaxial growth of semiconductor
surfaces and interfaces. However, for growth monitoring on a
sub-second time scale one is usually restricted to transient measurements
at one single photon energy.
We have developed a special RAS setup that is capable of measuring
transients at eight different photon energies simultaneously in the spectral
range between 1.4 and 4.5 eV, thus allowing for a simple 8-point
RAS spectrum every 100 ms. This technique was used to investigate fast
growth processes in III-V-MOVPE, e.g. oxide desorption, GaAs buffer
growth and N/As group V switching processes.
HL 43.5 Do 16:15 H14
Optical cross sections of the deep defect centers in low temperature
grown GaAs — C. Steen 1 , C. Metzner 1 , R. Schmidt 1 , P.
Kiesel 2 , S. Malzer 1 , and •G.H. Döhler 1 — 1 Institut für Technische
Physik I, FAU Erlangen-Nürnberg, Erlangen, Germany — 2 Palo Alto
Research Center Incorporated, Palo Alto, California
“Low Temperature Grown GaAs”(LT-GaAs) grown by molecular beam
epitaxy (MBE) at low substrate temperatures (190 ◦ C - 300 ◦ C) contains
a high concentration of (non-stoichiometric) excess As, which is incorporated
as EL2-like point defects (AsGa) and As precipitates. At low
temperatures, where the thermal emission rates are negligible, the occupation
of the deep defects can be changed optically. A determination
of the (wavelength-dependent) optical cross sections is possible if initial
conditions can be adjusted where all defects are depleted or filled, respectively.
We have determined the optical cross sections σn and σp of
the defects in LT-GaAs. We have used a p-i-n structure with a thin, only
a few nm thick, layer of LT-GaAs embedded in the i-region of a n-i-p
diode. By applying a reverse bias we are able to control the charge in the
LT-GaAs layer [1]. The charge of the LT-GaAs layer is directly correlated
with the channel conductance Gnn of the (thin) top n-layer. The optical
cross sections for both electrons and holes were deduced by determining
the initial slope of the Gnn change when the illumination starts. The
results were confirmed by the determination of the ratio of σn and σp
deduced from the steady Gnn value under illumination.
[1] K.-F.-G. Pfeiffer et al., Appl. Phys. Lett. 77, 2349 (2000)
Zeit: Donnerstag 16:30–19:00 Raum: Poster A
HL 44.1 Do 16:30 Poster A
Unified Description of Spin-Polarized Electron Transport in
Ferromagnet-Semiconductor Structures — •U. Wille and R.
Lipperheide — Abteilung Theoretische Physik (SF5), Hahn-Meitner-
Institut Berlin, Glienicker Str. 100, D-14109 Berlin, Germany
Generalizing our recent work [PRB 68, 115315 (2003)] on electron
transport in semiconductor structures, we develop a unified description
of ballistic and diffusive spin-polarized transport in ferromagnetsemiconductor
structures. A “thermoballistic” current is introduced, in
which electrons move ballistically in the band edge potential of the semiconductor,
and are thermalized at certain randomly distributed equilibration
points. Spin relaxation is allowed to occur in the ballistic intervals
between the equilibration points. An integral equation for the density spin
polarization in the semiconductor is derived. For constant band edge potential,
this equation can be converted to a differential equation, which
is identical to the spin diffusion equation, except that the spin diffusion
length is renormalized by the factor (1+τ/τs) −1/2 , where τ and τs are the
momentum and spin relaxation times, respectively. The ballistic element
in the unified description gives rise to discontinuities in the chemical
potential at the ferromagnet-semiconductor interfaces. The spin polarization
injected into the semiconductor and the position dependence of
the polarization inside the semiconductor are obtained for any value of
the ratio τ/τs.
HL 44.2 Do 16:30 Poster A
Herstellung einer lateralen Py/GaSb/InAs Spinventil-
Geometrie — •M. Wahle 1 , T. Last 1 , S.F. Fischer 1 , U. Kunze 1 ,
C. Schwender 2 und H. Fouckhardt 2 — 1 Werkstoffe und Nanoelektronik,
Ruhr-Universität Bochum, 44780 Bochum — 2 FB Physik, TU
Kaiserslautern, 67653 Kaiserslautern
Für den elektrischen Nachweis der Spinakkumulation in einem Halbleiter
in lateraler Spinventil-Geometrie wird eine GaSb(5 nm)/InAs(15
nm)/AlSb(20 nm)-Heterostruktur mit hochremanenten Permalloy-(Py)-
Elektroden kontaktiert. Aufgrund der Ausbildung einer Schottky-
Barriere zwischen Py und GaSb kann diese als Tunnelbarriere zum
InAs-Transportkanal dienen. Mittels Magnetotransportmessungen wurden
die Elektronendichte n ≈ 1.5·10 12 cm −2 und die mittlere Beweglichkeit
µ ≈ 30000 cm 2 /Vs des 2DEGs im InAs bestimmt. Die Herstellung
der lateralen Nanostrukturen erfolgt in drei Schritten. Eine Isolation
des Ferromagnet-Halbleiter Kontaktes von der Metallkontaktierung wird
durch Aufsputtern von 200 nm SiO2 erzielt. In einem optischen Lithographieschritt
wird ein 20 µm breites Kontaktfenster zum GaSb geöffnet. Die