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 {~}120 to {~}170 fs as carrier density decreases from 7×{}10¹⁷ to 2×{}10¹⁶ 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. {} 1996 The American Physical Society.