SPIN DYNAMICS OF EXCITON-STATES IN GAAS/ALGAAS MULTIPLE-QUANTUM WELLS

We report an experimental study of the excitonic spin relaxation dynamics in GaAs/AlGaAs Multiple Quantum Wells (MQW) presenting interface roughness by time and polarization resolved luminescence spectroscopy. The relaxation is found to occur mainly when the excitons are in the free state, before their localization. The initial polarization rare P(0) is found to depend strongly on the energy as it approaches 100% for a nearly resonant heavy hole exciton (XH) excitation whereas it is negative (≃ -12%) for a light hole exciton (XL) resonant excitation. We discuss the role of both band mixing and excitonic oscillator strength to explain these results. A significant energy shift (up to 2 meV) between the exciton spectra of opposite helicity is also observed. The time evolution of this energy shift is well correlated to the depolarization dynamics. © 1993 Academic Press. All rights reserved.