Nonequilibrium hole relaxation dynamics in an intrinsic semiconductor

The thermalization dynamics of photoexcited nonequilibrium holes is selectively investigated in intrinsic bulk GaAs using a high sensitivity two-wavelength pump-probe technique. The carriers are photoexcited close to the bottom of their respective bands and hole heating is followed by monitoring the absorption saturation due to filling of higher-energy states. The characteristic thermalization time is measured to increase only slightly from similar to 120 to similar to 170 fs as carrier density decreases from 7x10(17) to 2x10(16) cm(-3), indicating that hole heating is dominated by hole-optical-phonon scattering. These results are in good agreement with a simulation of the carrier relaxation based on numerical resolution of the carrier Boltzmann equations including interaction of holes with LO and TO phonons.