Spatial evolution of inelastic scattering of high-density excitons in GaSe crystals

Spatial evolution of heavily photo-created excitons in GaSe single crystals has been studied by observing space- and time-resolved photoluminescence. At an early stage, the free-exciton recombination band shows a blue-shift with broadening due to the phase-space filling effect and the increment of the exciton self-energy. Recoil luminescence bands due to the exciton–exciton and exciton-carrier scattering shifts to the lower and higher energy sides with increasing exciton density and by separating a detecting position from the center of the exciting laser spot, respectively. These results are consistently explained by the expansion of the high-density exciton masses in the real space and by their k-space relaxation accompanying intra-band inelastic scattering under the energy and momentum conservation law.