Observation of exchange interaction effects under optical orientation of excitons in AlGaAs

Exciton luminescence in AlGaAs layers is studied under interband excitation by circularly polarized light. Curves of luminescence depolarization in a transverse magnetic field (Hanle effect) exhibit peaks arranged symmetrically about a point $H=0$. It is shown that this effect is attributable to crossings of fine-structure levels in the magnetic field. The exchange splitting of bulk exciton levels and also recombination and spin-relaxation times are determined from a comparison between theoretical and experimental dependences.