MICROSCOPIC MECHANISMS GOVERNING EXCITON-DECAY KINETICS IN TYPE-II GAAS ALAS SUPERLATTICES/

We have measured the time- and space-resolved evolution of type-II exc itons in GaAs/AlAs superlattices with various AlAs layer thicknesses, at temperatures ranging from 1.8 to 30 K. Our photoluminescence (PL) t ime decay and transport results demonstrate that the exciton-decay kin etics at low temperatures are entirely determined by intrinsic radiati ve recombination, whereas at higher temperatures, the PL time decays a re dominated by nonradiative defect trapping processes. We show that t hese nonradiative decays do not occur within the layers but are instea d localized at the heterointerfaces. The measured lifetimes at 30 K ar e consistent with our model calculations based on this interpretation. Furthermore, the superlattice and interface-disorder-induced Gamma-X mixing potentials are determined from our low-temperature exciton life times to be 1.3 and 0.2 meV, respectively.