Plenarvorträge - DPG-Tagungen

Halbleiterphysik Mittwoch
HL 29.9 Mi 17:15 H13
Rashba spin precession of two-dimensional holes — •Michele
Governale 1,2 , Marco G. Pala 3,2 , Jürgen König 4,2 , and Ulrich
Zülicke 5,2 — 1 Scuola Normale Superiore, Pisa, Italy — 2 Institut für
Theoretische Festkörperphysik, Universität Karlsruhe, Germany —
3 Dipartimento di Ingegneria dell’Informazione, Università degli studi di
Pisa, Italy — 4 Institut für Theoretische Physik III, Ruhr-Universität
Bochum, Germany — 5 Institute of Fundamental Sciences, Massey
University, New Zealand
Spin-orbit coupling due to structural inversion asymmetry plays an
important role in the field of phase-coherent spintronics.
We present a study of spin precession due to Rashba spin splitting[1]
of holes[2] in semiconductor quantum wells. Based on a simple analytical
expression that we derive for the current modulation in a broad
class of experimental situations of ferromagnet/nonmagnetic semiconductor/ferromagnet
hybrid structures, we conclude that the Datta-Das
spin transistor[3] (i) is feasible with holes and (ii) its functionality is not
affected by integration over injection angles.
The current modulation shows a universal oscillation period, irrespective
of the different forms of the Rashba Hamiltonian for electrons and
holes. The analytic formulas approximate extremely well exact numerical
calculations of a more elaborate Kohn–Luttinger model.
[1] E. I. Rashba, Fiz. Tverd. Tela (Leningrad) 2, 1224 (1960)
[Sov. Phys. Solid State 2, 1109 (1960)].
[2] R. Winkler, Phys. Rev. B 62, 4245 (2000).
[3] S. Datta and B. Das, Appl. Phys. Lett. 56, 665, (1990).
HL 29.10 Mi 17:30 H13
ZnMnSe–Spinaligner on inverted GaAs/AlGaAs–2DEGs — •T.
Leeb 1 , M. Döppe 1 , M. Reinwald 1 , H.-P. Tranitz 1 , D. Weiss 1 , W.
Wegscheider 1 , P. Grabs 2 , G. Schmidt 2 , and L. Molenkamp 2 —
1 Institut für Experimentalphysik, Universität Regensburg, D-93040 Regensburg,
Germany — 2 Physikalisches Institut, Universität Würzburg,
D-97074 Würzburg, Germany
The optical detection of spin injection in ZnBeMnSe/GaAs/AlGaAs–
semiconductor heterostructures represents a convincing, however, indirect
result of voltage driven spin transfer across a semiconductor interface.
In contrast, spin injection into a two dimensional electron gas
(2DEG) has not yet been clearly proven in magnetotransport experiments.
We have fabricated n-doped Zn1−x−yBexMnySe–spinaligner contacts
on an inverted GaAs/AlGaAs–2DEG–structure which was applied
to avoid barriers along the current path. The GaAs surface preparation
and the conditions of the ZnMnSe growth initiation are crucial for achieving
a low barrier electronic structure at the ZnMnSe/GaAs–interface. A
strong Zeeman splitting in the conduction band of the Mn–doped II–VI
semiconductor is observed in photoluminescence measurements at small
external magnetic fields. This verifies the spin aligning capability of the
ZnMnSe contact due to a strongly reduced transmission coefficient for
HL 30 Photovoltaik II
minority spin electrons. Magnetotransport measurements have been performed
on a microstructured Hall contact geometry which was developed
according to theoretical considerations concerning spin equilibration between
quantum hall edge channels. This work is supported by DFG via
SFB 348 and by BMBF 13N8282.
HL 29.11 Mi 17:45 H13
InAs-LEDs für Spininjektionsexperimente — •P. Grabs 1 ,
I. Chado 1 , R. Fiederling 1 , A. Slobodskyy 1 , C. Gould 1 , G.
Schmidt 1 , L. W. Molenkamp 1 , C. J. Meining 2 und B. D.
McCombe 2 — 1 Physikalisches Institut, Experimentelle Physik 3,
Universität Würzburg, Am Hubland, 97074 Würzburg — 2 University at
Buffalo, The State University of New York, Buffalo, New York 14260
InAs ist dank seiner hohen Elektronenbeweglichkeit und der starken
Spin-Bahn-Kopplung ein interessantes Material für Spininjektionsexperimente.
Mit Cd1−xMnxSe, einem verdünnten magnetischen Halbleiter
(DMS), der gitterangepasst auf InAs gewachsen werden kann, steht ein
passender Spinaligner zur Verfügung.
Wir berichten über das MBE-Wachstum und die Charakterisierung
von asymmetrischen LEDs mit einer p-Barriere aus AlSb1−xAsx, einem
InAs-Quantentrog und Cd1−xMnxSe als n-Barriere und Spininjektor.
Die zirkulare Polarisation des emittierten Lichts einer solchen LED kann
als Maß für die Effizienz der Spininjektion dienen. Es werden Ergebnisse
von Elektrolumineszenz- und Transportmessungen an den Strukturen
gezeigt.
Diese Arbeit wird unterstützt durch das DARPA SPINS Program.
HL 29.12 Mi 18:00 H13
Spin polarization due to Rashba spin-orbit and boundary
scattering — •Kai Dittmer 1 , Jun-Ichiro Ohe 1,2 , and Bernhard
Kramer 1 — 1 1. Institut für Theoretische Physik, Universität Hamburg
— 2 Physics Department of Sophia University (Tokio)
We calculate spin resolved transport properties of a three terminal [1]
fork-shaped structure with spin-orbit coupling of the Rashba type. For
the calculation of the conductance we apply the transfer matrix method
for the Ando model of the Rashba hamiltonian in the ballistic regime. The
conductance is computed as a function of the Fermi energy for different
values of the spin-orbit coupling constant and for different geometrical
structures and sizes of the model. We observe high polarization and transmission
in the conductance in certain regions of the Fermi energy that
can be explained by spin-orbit and boundary scattering [2]. The dependence
of the spin polarization of the current in different regions of the
sample and the corresponding probability density of the scattering states
is investigated. The possibility of observing the effects in experiment is
discussed.
[1] Kiselev and Kim, Appl. Phys. Lett. 78, 775 (2001); J. Appl. Phys.
94, 4001 (2003).
[2] Chen et al., cond-mat/0308569
Zeit: Mittwoch 15:15–16:45 Raum: H14
HL 30.1 Mi 15:15 H14
Photospannung bei Ladungsträgerinjektion von Farbstoffmolekülen
in transparente Löcher- und Elektronenleiter — •B.
Mahrov 1 , Th. Dittrich 2 , G. Boschloo 1 , L. Dloczik 2 und A.
Hagfeldt 1 — 1 Department of Physical Chemistry, University of Uppsala,
Box 579, 75123 Uppsala, Sweden — 2 Hahn-Meitner-Institut, SE2,
Glienicker Str. 100, D-14109 Berlin, Germany
Transiente und spektrale Photospannung (PV) wurde für Ladungsträgerinjektion
von Farbstoffmolekülen (Ru(dcbpyH2)2(NCS)2) in transparente
Löcher- (CuSCN, CuI, CuAlO2) und Elektronenleiter (TiO2,
SnO2:F) untersucht. Das PV-Signal steigt innerhalb von 10 ns bis 10
µs und die effektiven Lebensdauern variieren zwischen 100 ns und 1 ms
je nach verwendetem Substrat und Mechanismus der Ladungstrennung.
Die Injektionseffizienz ist für Löcher und Elektronen von der gleichen
Größenordnung. Die Injektionsschwelle ist stark vom Substrat abhängig
und liegt zwischen 1.2 und 1.9 eV.
HL 30.2 Mi 15:30 H14
Influence of Film Texture on Grain Boundary Activity in
Cu(In,Ga)Se2 Films — •G. Hanna 1 , N. Ott 2 , H.P. Strunk 2 ,
T. Glatzel 3 , S. Sadewasser 3 , U. Rau 1 , and J.H. Werner 1 —
1 Institut für Physikalische Elektronik, Universität Stuttgart, Pfaffenwaldring
47, 70569 Stuttgart — 2 Institut für Werkstoffwissenschaften
VII, Universität Erlangen Nürnberg — 3 Hahn Meitner Institut, Berlin
A preferred (220/204) crystallographic orientation (texture) of
Cu(In,Ga)Se2 (CIGS) absorber layers is beneficial for the performance
of finished CIGS solar cells as compared to (112) textured CIGS layers
[1,2]. We study the laterally resolved electronic properties of CIGS thin
films with different textures by means of Cathodoluminescence (CL)
mapping, measured in a transmission electron microscope, and Kelvin
Probe Force Microscopy (KPFM). The (220/204) textured samples have
a very homogenous lateral CL-intensity whereas the (112) textured
samples exhibit strong contrasts in the CL-signal. The line scans of the
work function Φ across grain boundaries (GBs) measured with KPFM
exhibit a dip of more than 300 meV across the GB at a (112)-textured
sample while a (220/204) sample shows no comparable dip of Φ at the
GB but rather small spikes. Both measurement methods show that
the superior properties of CIGS solar cells with (220/204)-textured