Excitation dynamics in GaAs quantum wells

Abstract

The dynamics of excitons is studied using time?resolved photoluminescence. We deduce experimentally, for the first time, the intrinsic homogeneous linewidth of free excitons in GaAs quantum wells. The scattering rate of excitons is directly estimated from temperature?dependent linewidth measurements. A theoretical model is presented that correlates the observed photoluminescence linewidth, and hence the scattering rate, to the measured spin relaxation rate of excitons. We show that quantum confinement enhances the spin relaxation rate of weakly scattered electrons by more than two orders of magnitude over that of the bulk. The spin?exchange energy is experimentally determined for the first time for GaAs quantum wells. The radiative recombination rate of excitons in GaAs quantum wells is very large due to the macroscopic polarization of the exciton?polariton. Thermalization and scattering reduce the coherence volume of this polarization, resulting in a temperature? and intensity?dependent photoluminescence lifetime. We derive a theoretical model which is shown to explain the experimental results on the radiative lifetimes.