Spectral shape of excitons in alloy semiconductors.

The study of low-temperature photoluminescence spectra of Ga47In53As as a function of excitation intensity reveals three distinct features: With decreasing excitation intensity the excitonic line (i) narrows, (ii) shifts to lower energies and (iii) gets increasingly asymmetric. This behavior is more pronounced in samples with a broad excitonic linewidth. At low excitation intensities linewidths of 1.2meV for Ga47In53As grown by chemical beam epitaxy are found. The experimental observations are described in terms of a quantitative, semi-classical model which is based on the migration of carriers to low-energy-sits of the zincblende alloy. An expression for the photoluminescence lineshape of excitons in alloy-semiconductors is given for the first time. The experimental results are well described by this theoretical model.