Direct observation of exciton localization in a GaAs/AlGaAs quantum well

We present the direct observation of exciton localization in a GaAs/AlGaAs quantum well. We have observed the two-component exponential decay of photoluminescence from heavy-hole excitons when the excitation density is very low. We have confirmed by measuring the lateral spatial motion of excitons that the fast component is attributable to the radiative recombination of free excitons while the slowly decaying component is due to the localized excitons.