Phonon broadening of excitons in GaAs/${\mathrm{Al}}_{\mathit{x}}$${\mathrm{Ga}}_{1\mathrm{-}\mathit{x}}$As quantum wells

We have made transmission and reflectivity measurements of the temperature-dependent exciton linewidths for high-quality GaAs/${\mathrm{Al}}_{0.3}$${\mathrm{Ga}}_{0.7}$As quantum wells with well widths ranging between 28 and 340 Å and also for bulk GaAs. The LO-phonon contributions to the linewidths are found to depend only weakly on the well width. Detailed microscopic calculations of the well-width dependence of these linewidths have been made and are shown to be in quantitative agreement with experiment. These calculations provide a physical explanation of the weak dependence of the linewidth on the well width.