Relaxation processes of hot holes in Ge and GaAs investigated by ultrafast infrared spectroscopy

Abstract

Relaxation phenomena of holes in p-type Ge and GaAs are studied by ultrafast infrared spectroscopy in the wavelength range from 0.8 to 10 mu m. In germanium, carriers are excited to the split-off band by 250 fs pulses and the subsequent scattering dynamics is measured via the transient intervalence band absorption. The excited carriers undergo intervalence band scattering within 100 fs and thermalize with time constants around 700 fs. In contrast, equilibration among unexcited holes proceeds within 100 fs. Inelastic carrier-carrier collisions via the dynamically screened Coulomb interaction are the main mechanism of thermalization. In GaAs, we monitor the picosecond recombination of free holes with shallow accepters. After infrared photoionization of impurity atoms, hole capture occurs within several 10-11 S-1. Emission of single longitudinal optical phonons represents the predominant process by which the impurity ground state is repopulated.