Spectroscopy of spin-polarized excitons in semiconductors

Excitons in semiconductors can be spin-polarized under optical selective excitation by polarized radiation (optical orientation) or due to spin relaxation and sublevel mixing in an external magnetic field. The paper deals with optical phenomena where spin-polarized excitons generated in semiconductor nanostructures play an important role. Firstly, both optical orientation and optical alignment of excitons in type II GaAs/AlAs superlattices are considered and effects of the anisotropic electron-hole exchange interaction and external magnetic field on the photoluminescence polarization are analyzed. Secondly, magnetic-field-induced anticrossing of excitonic sublevels is discussed taking into account the axial and anisotropic exchange splittings, spin-relaxation and difference in the lifetimes of radiative and non- radiative exciton states. Next, the localized and bound excitons are shown to act as intermediate states in resonant Raman scattering by spin flips of holes bound to acceptors in GaAs/AlGaAs multiple quantum wells. The analysis of polarized Raman spectra permits to make decisive conclusions concerning microscopic mechanisms of the observed scattering processes. Finally, the doubly-resonant 2s-1s LO-assisted secondary emission observed in CdTe/CdMnTe quantum-well structures is described as a process with spin-polarized hot 1s- excitons acting as real intermediate states.