Spin dynamics in indirect band-gap quantum wells and quantum dots

Abstract

In this thesis, semiconductor quantum wells (QWs) and quantum dots (QDs) with an indirect band gap in momentum space are investigated with regard to their fine structure and the related spin dynamics. Indirect nanostructures are being developed because of their very long recombination times, which make them interesting for spintronic applications. Here, the focus is on a fascinating but barley studied, quantum mechanical property: The absence of exchange interaction, which, despite the spatial proximity of electron and hole, is caused by their distance in momentum space. Polarized photoluminescence measurements show that due to the lack of exchange interaction, the fine structures of indirect excitons in the studied GaAs/AlAs QW and (In,Al)As/AlAs QDs are fully degenerate. Depending on the ratio of the exciton recombination time and the spin relaxation time, different related effects are observed as spin dynamics between dark and bright states, optical orientation and the hyperfine interaction of the X electron with the nuclei. The comparison of experimental results with theoretical models reveals important structure parameters as the heavy-hole g factor, the spin relaxation time and the hyperfine constant of the X electron. Moreover, the impact of the high energetic direct state on the indirect QD excitons, which limits their optical orientation, is investigated.