Abstract
Nominally undoped p-type GaAs with an unusually low shallow donor concentration has been grown by molecular beam epitaxy. The effect of the As/Ga flux ratio on the residual shallow donor and acceptor concentrations and defect density in this material was investigated by analyzing low temperature photoluminescence (PL) spectra. The PL spectra are indicative of low shallow donor concentrations, since they exhibit a single, narrow (FWHM=0.4 meV) free exciton peak and essentially no donor-related peaks. For increasing As/Ga flux ratio the donor concentration decreases, the defect concentration increases, and the acceptor concentration goes through a minimum. These results can be explained by a model based on the incorporation of Si and C into As and Ga sites and the formation of a carbon–Ga vacancy defect complex.
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