Phonon sideband of photoluminescence as a probe of exciton states in a quantum well

We report a novel technique to probe the length scale of exciton localization, by disorder, in semiconductor quantum wells (QW's). The method is based on the study of longitudinal-optic (LO) phonon satellites of exciton photoluminescence. It is applied to the (In,Ga)As/InP QW system, in which we observe coupling to LO modes of both (In,Ga)As and InP. For a QW with weak disorder, in a magnetic field, the method probes the most localized states of the quantum Hall system.