SPECTROSCOPY OF SPIN-POLARIZED EXCITONS IN SEMICONDUCTORS

Excitons in semiconductors can be spin-polarized under optical selecti ve excitation by polarized radiation (optical orientation) or due to s pin relaxation and sublevel mixing in an external magnetic field. The paper deals with optical phenomena where spin-polarized excitons gener ated 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 a ccount 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 in termediate states in resonant Raman scattering by spin flips of holes bound to accepters in GaAa/AlGaAs multiple quantum wells. The analysis of polarized Raman spectra permits to make decisive conclusions conce rning microscopic mechanisms of the observed scattering prosesses. Fin ally, the doubly-resonant 2a-1s LO-assisted secondary emission observe d in CdTe/CdMnTe quantnm-well structures is described as a process wit h spin-polarized hot 1s-excitons acting as real intermediate states,