Reabsorption of the excitonic luminescence in direct band gap semiconductors

We investigate here the influence of reabsorption on the excitonic luminescence spectrum of AgGa${\mathrm{Se}}_2$, CuGa${\mathrm{S}}_2$, and ZnSe under excitation by an electron beam and a He-Cd laser (in the case of ZnSe only). We develop a simple and new theoretical model to analyze our experimental data; it shows that reabsorption should be taken into account in most of our luminescence experiments at 77 K. We believe that such a study provides an interesting method to determine free-exciton energies when they correspond to large absorption coefficients. We have also studied the excitonic luminescence of ZnSe at liquid-helium temperature but, in this case, there is no reabsorption and we think that this is due to strong polariton effects.