Dynamical processes of high-density excitons in GaSe crystals

Dynamical processes of high-density excitons and their relaxation mechanisms in GaSe crystals have been investigated in real and momentum spaces by observing resonant luminescence spectra of the excitons in the time- and space-resolved regimes. Temporal profiles of the luminescence show remarkable excitation-density dependence. The temporal profiles have been well explained by a nonlinear rate equation including a two-exciton scattering process and localization to shallow trapping states at high density. Above a certain excitation density, spatial propagation becomes remarkable owing to the suppression of localization due to site-filling effects, giving the group velocity similar to1.0 x 10(8) cm/s. The other characteristic features of the exciton dynamics at high density appear as inelastic scattering processes on recoil luminescence bands in the time- and space-resolved spectra. From these results, detailed scattering and relaxation mechanisms of the excitons in this material at high density have been clarified in the momentum space.