Relaxation processes of hot holes in germanium and GaAs studied by picosecond infrared spectroscopy

Abstract

Relaxation processes of holes in p-type Ge and GaAs are investigated with picosecond infrared pulses in the wavelength range from 0.8 to 12 μm. The transient inter-valence band absorption of Ge studied in spectrally and temporally resolved measurements reveals subpicosecond carrier-carrier and inter-valence band scattering of the excited holes, followed by the picosecond cooling of hot heavy holes via emission of optical phonons. Photogenerated non-equilibrium split-off holes give rise to a short-lived population inversion between the split-off and the light hole band, resulting in a transient gain around 260 meV. In p-type GaAs, ultrafast recombination of holes with shallow acceptors is directly observed for the first time. Carrier capture occurs on a time scale of several tens of picoseconds, following a non-exponential kinetics. Emission of longitudinal-optical phonons by free holes is found to be the dominant mechanism of recombination, directly populating the acceptor ground state.