Abstract
A method for identifying and quantifying acceptor contamination in semi-insulating (SI) GaAs is described. The method has been applied to commercial SI GaAs and to NRL zone-refined ingots. Results indicate that carbon is not the only acceptor present in significant concentrations in typical SI GaAs. Zinc is present in essentially all samples and is the dominant shallow acceptor in a significant fraction of the commercial material studied. The method consists of moving the Fermi level to the ground state of the shallowest acceptor present, usually carbon, by diffusing copper into the material. An infrared transmission measurement identifies the neutral acceptors from their electronic 1s-2p intrasite excitation. The strength of the absorption is proportional to the neutral acceptor concentration. Sensitivities are greatest for shallow acceptors where neutral acceptor concentrations as low as 5×1012 cm−3 can be identified and quantified.
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