Exciton-Carrier Scattering in Gallium Selenide

Detailed investigation of the luminescence features due to the recombination of the exciton-free-carrier process in GaSe is presented. This process shows a well-resolved luminescence line and it is an efficient recombination process in this semiconductor, even at low temperatures. We report accurate photoluminescence spectra measured at 2 K as a function of the excitation intensity, of the excitation energy, and of the lattice temperature from 2 to 200 K. To discriminate between the different kinds of free carriers participating in exciton-carrier scattering in GaSe, we have computed the temperature dependence of the scattering probability of the direct excitons with different carriers: direct electrons, indirect electrons, and holes; we have found that the most probable exciton-carrier scattering process is that involving the coexistence of direct electron and hole collisions. Line shape of the exciton-carrier scattering as a function of the carrier temperature has been calculated and fitted to the experimental luminescence spectra from 2 to 200 K and a very good agreement is found. From the absorption spectra of GaSe, we obtained a direct estimate of the excitonic polarizability.