Exciton line shapes of GaAs/AlAs multiple quantum wells.

We present a detailed study of the photoluminescence (PL) spectra of GaAs/AlAs multiple-quantum-well structures with well thicknesses of 83.8 and 78.1 \AA{} in the temperature range from 16 to 320 K. We examine the relation of luminescence and absorption, find a part of the heavy-hole exciton line suitable for a detailed comparison with model profiles, and perform a line-shape analysis using Lorentz-Gauss profiles expressed efficiently in terms of the complex probability function. We have observed the Stokes shift (about 4 meV at 16 K, which vanishes fast with increasing temperature) of the PL peak with respect to the center of the exciton absorption, and explain it quantitatively assuming a detailed thermodynamical balance of excitons and radiation. The inhomogeneous broadening of the line is Gaussian and the increase of the homogeneous Lorentzian component is found to be nearly linear in the 50\char21{}320-K region.