Propagation dynamics of exciton spins in a high‐density semiconductor quantum dot system

Abstract

AbstractWe study propagation dynamics of exciton spins in a system composed of high‐density self‐assembled quantum dots (QDs) of CdSe and a diluted magnetic semiconductor (DMS) layer of ZnMnSe, where spin‐polarized excitons are generated in the DMS layer and are subsequently injected into the QDs. The degree of circular polarization, P, of excitonic photoluminescence at 5 T in the coupled QDs shows a rapid increase with increasing delay time after a linearly polarized pulsed excitation, indicating the exciton‐spin injection from the ZnMnSe to CdSe‐QDs. The P value tends to decay gradually because of the exciton‐spin relaxation in the QDs after the injection. The spin‐polarized excitons in the QD ensemble migrate simultaneously from the QDs with higher exciton energies to those with lower exciton energies, where the exciton‐spins relax inside each dot during the migration. Therefore, the observed P values in the QD emission band are affected by this feeding of the relaxed spins. (© 2009 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)