Stoichiometry-dependent deep levels in p-GaAs prepared by annealing under excess arsenic vapor pressure

In order to obtain the precise energy spectrum of stoichiometry-dependent deep levels, we apply the photocapacitance (PHCAP) method under constant capacitance conditions on the various p-GaAs crystals prepared by 67 h annealing at 900°C under excess arsenic vapor pressure followed by rapid cooling. The present PHCAP investigation reveals the deep acceptor levels at 0.48, 0.71, 0.92, and 1.02 eV above the valence band, respectively, and shows that these deep acceptor levels could be detected commonly in various kinds of p-GaAs crystals with regardless of the sort of doped acceptor impurities and the concentrations. In addition, the dependencies of the level density mentioned above are also studied as a function of the arsenic vapor pressure being applied during annealing and of the carrier concentration. These dependencies of the level density are specified into three categories in conjunction with the carrier concentration and with the dependencies of the level density on the arsenic vapor pressure. From the experimental results of the present PHCAP investigation on p-GaAs and of the previously reported results on n-GaAs, it is shown that the excess arsenic atoms in GaAs crystal play a major role on the formation of stoichiometry-dependent deep levels in p-type GaAs crystals.