Picosecond capture of photoexcited holes by shallow acceptors in p-type GaAs

Ultrafast recombination of holes with shallow acceptors in a III-V semiconductor is directly observed for the first time, by means of picosecond infrared spectroscopy. Neutral impurities in p-doped GaAs at low temperature are photoionized by picosecond infrared excitation. The recombination of free holes with negatively charged acceptors—monitored via absorption changes below the band edge—occurs on a time scale of several tens of picoseconds, following a nonexponential kinetics. Emission of longitudinal-optical phonons by the free holes is found to be the dominant mechanism of recombination.