Abstract

Trapping of free carriers by shallow impurities in III-V compounds represents an important relaxation process of electrons and holes and is of particular relevance for charge transport in semiconductor devices. In this paper, we report the first direct, time-resolved study of the recombination of free holes with ionized acceptors in p-type GaAs. The experiments which were performed with zinc-doped GaAs crystals at lattice temperatures between 10 and 70 K are based on the following pump-probe scheme: The intense excitation pulse in the mid-infrared promotes holes which are initially bound to the (neutral) acceptor atoms, to the valence bands, i. e. free carriers are created by photoionization of the impurity atoms. The relevant absorption band and the spectral position of the pump pulses are shown in Fig. 1(a). After excitation, the (negatively charged) acceptors give rise to a new transient absorption in the near infrared (Fig. 1b), the deionization band which is due to transition from the ground state of the ionized acceptor to the conduction band.^[1] The strength of this enhanced absorption is determined by the momentary density of ionized acceptors that is identical to the density of free holes. Thus the decay of the deionization band monitored by near-infrared probe pulses directly reveals the kinetics of hole-acceptor recombination.

© 1992 IQEC