Exciton localization, photoluminescence spectra, and interface roughness in thin quantum wells

The combination of conventional photoluminescence (PL), PL-excitation (PLE), and micro-PL spectroscopies is used to study the influence of interface roughness on luminescence properties of thin GaAs/${\mathrm{Al}}_{0.3}$${\mathrm{Ga}}_{0.7}$As single quantum wells (QWs). The QWs were prepared under different growth conditions, resulting in different interface roughness. We discuss the splitting of PL spectra into two (or more) main lines, the pronounced fine structure of the micro-PL spectra and the low-energy shift of the PL lines with respect to the PLE spectrum in terms of a phenomenological interface model. For low temperatures exciton localization due to interface fluctuations with different length scales determines most of the luminescence features. One consequence is a strong suppression of the PLE signal on the low-energy side of the spectra. Therefore in this case the PLE spectrum cannot be used as a measure for the absorption strength or as an indicator for impurity bound excitons. \textcopyright{} 1996 The American Physical Society.