Carrier cooling and exciton formation in GaSe

Abstract

The initial cooling of hot carriers and the subsequent exciton formation in GaSe are studied by time-resolved photoluminescence (PL) using femtosecond up-conversion techniques. From the time-resolved PL spectra of this layered III-VI semiconductor two different energy relaxation channels are derived. After an initial subpicosecond cooling due to Fröhlich-type interaction of carriers with longitudinal optical $E^{\prime }{(2\mathrm{}}^2)$ phonons a slower regime follows, which is dominated by deformation potential interaction with the nonpolar optical $A_1^{\prime }{(1\mathrm{}}^2)$ phonons. The coupling constant for nonpolar optical phonon scattering is derived. The subsequent formation of excitons is studied at different carrier densities and detection energies. A cross section for the free-exciton formation is determined based on a rate equation model.