Spin relaxation in intrinsic GaAs quantum wells: Influence of excitonic localization

We have investigated exciton spin relaxation in GaAs quantum wells by picosecond time-resolved photoluminescence spectroscopy, in order to determine the origin of spin-relaxation processes and their dependence on excitonic localization. The studies have been done as a function of excitation and detection energy, lattice temperature, and carrier density. The excitation-energy dependence of the polarization decay time indicates that exchange interaction is the leading spin-relaxation mechanism at low temperature. However, we have not been able to explain the high-temperature (T≥50 K) dependence of the polarization decay time with either the D’yakonov-Perel’ mechanism or with the exchange interaction. We have also found that spin relaxation is strongly affected by excitonic localization.