Excitonic properties of weakly coupled GaAs single quantum wells investigated with high-resolution photoluminescence excitation spectroscopy

Photoluminescence spectra of three weakly coupled GaAs quantum wells are measured as a function of the excitation energy with a high resolution of both the excitation and the detection energy. The spectra exhibit fine structures corresponding to island terraces as well as superfine structures associated with the coexistence of free and bound excitons. We present direct evidence for the transfer of carriers, excitons or exciton energy between the growth islands of the same well and adjacent wells. The relative occupation of free and bound exciton states depends strongly on temperature, carrier density, and excitation energy. A qualitative model, which explains these experimental results as a consequence of interwell interaction of excitons, is suggested.