Time-resolved picosecond absorption spectroscopy of the layered compound gallium selenide

The picosecond excite-and-probe absorption technique was used to study the relaxation process of photogenerated hot carriers in $\epsilon$-GaSe at room temperature. The time dependence of the carrier temperature to relax to the lattice temperature was calculated from the absorption kinetic data. The carriers cooled at the rate of 30 K/ps. The dominant relaxation mechanism of the photogenerated hot carriers in GaSe is attributed to the emission of nonpolar optical phonons $A_1^{\prime \mathrm{}\left(1\right)\mathrm{}}$. A smaller value for the deformation potential extracted from the measurements is attributed to the screening of hole-phonon interaction by the photogenerated carrier density.