Influence of exciton localization on recombination line shapes: ${\mathrm{In}}_{\mathit{x}}$${\mathrm{Ga}}_{1\mathrm{-}\mathit{x}}$As/GaAs quantum wells as a model

We present an approach for the optical interband density and for luminescence line shapes of quantum-well excitons by considering the localization of the excitonic center of mass due to potential fluctuations. The localization-induced violation of the K=0 selection rule effects considerably the high-energy side of the recombination line shape. Perfect agreement between line-shape simulations and photoluminescence spectra of ${\mathrm{In}}_{\mathit{x}}$${\mathrm{Ga}}_{1\mathrm{-}\mathit{x}}$As/GaAs quantum wells is obtained over the full temperature range from T=2 K up to 120 K. Furthermore, by introducing a quantitative measure of the degree of localization we find the exciton motion restricted to about 13 nm in the present case.