Berlin 2005 – wissenschaftliches Programm
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HL: Halbleiterphysik
HL 17: Poster Ib
HL 17.57: Poster
Freitag, 4. März 2005, 16:30–19:00, Poster TU F
Optical orientation of electron spins in GaAs quantum wells — •Stefan Pfalz1, Roland Winkler1, Tobias Nowitzki1, Dirk Reuter2, Andreas Wieck2, Daniel Hägele1, and Michael Oestreich1 — 1Universität Hannover, Institut für Festkörperphysik, Abteilung Nanostrukturen, Appelstraße 2, 30167 Hannover, Germany — 2Lehrstuhl für Angewandte Festkörperphysik, Ruhr-Universität Bochum, Universitätsstraße 150, 44780 Bochum, Germany
We present a detailed experimental and theoretical analysis of the optical orientation of electron spins in GaAs/AlAs quantum wells. Using time and polarization resolved photoluminescence excitation spectroscopy, the initial degree of electron spin polarization is measured as a function of excitation energy for a sequence of quantum wells with well widths between 63 Å and 198 Å. The experimental results are compared with an accurate theory of excitonic absorption taking fully into account electron-hole Coulomb correlations and heavy-hole light-hole coupling. We find in wide quantum wells that the measured initial degree of polarization of the luminescence follows closely the spin polarization of the optically excited electrons calculated as a function of energy. This implies that the orientation of the electron spins is essentially preserved when the electrons relax from the optically excited high-energy states to quasi-thermal equilibrium of their momenta. Due to initial spin relaxation, the measured polarization in narrow quantum wells is reduced by a constant factor that does not depend on the excitation energy.