Microscopic mechanisms governing exciton-decay kinetics in type-II GaAs/AlAs superlattices

Abstract

We have measured the time- and space-resolved evolution of type-II excitons in GaAs/AlAs superlattices with various AlAs layer thicknesses, at temperatures ranging from 1.8 to 30 K. Our photoluminescence (PL) time decay and transport results demonstrate that the exciton-decay kinetics at low temperatures are entirely determined by intrinsic radiative recombination, whereas at higher temperatures, the PL time decays are dominated by nonradiative defect trapping processes. We show that these nonradiative decays do not occur within the layers but are instead localized at the heterointerfaces. The measured lifetimes at 30 K are consistent with our model calculations based on this interpretation. Furthermore, the superlattice and interface-disorder-induced \ensuremath{\Gamma}-X mixing potentials are determined from our low-temperature exciton lifetimes to be 1.3 and 0.2 meV, respectively.