Origin of excitonic luminescence in quantum wells: Direct comparison of the exciton population and Coulomb correlated plasma models

Abstract

We report on the origin of the excitonic luminescence in quantum wells. This study is carried out by time-resolved photoluminescence experiments performed on a very high quality InGaAs quantum well sample in which the photoluminescence contributions at the energy of the exciton and at the band edge can be clearly separated and traced over a broad range of times and densities. This allows us to compare the two conflicting theoretical approaches to the question of the origin of the excitonic luminescence in quantum well: the model of the exciton population and the model of the Coulomb correlated plasma. We measure the exciton formation time and we show the fast exciton formation and its dependence with carrier density. We demonstrate, by comparing the temperature dependence of $1s$ and $2s$ excitonic transitions, that excitons provide the dominant contribution to the luminescence signal. Furthermore, our analysis gives evidence that the Coulomb correlated plasma contribution to the luminescence signal might be neglected for densities, temperatures, and time scales actually used in time-resolved experiments.