The effects of photoexcited free carriers on exciton dynamics in GaAs/AlGaAs quantum wells

We report on the effect of photogenerated free carriers on the spectral diffusion and on the LO-phonon Raman scattering of resonantly excited excitons. This is observed by an exciton population redistribution between localized states and by a decrease in the Raman scattering intensity under an extremely weak, additional, above bandgap excitation. We interpret these effects by a new channel for exciton transfer induced by free carrier -exciton scattering that adds up to the phonon assisted exciton tunneling between the states that arise from interface roughness.