ACCEPTOR ASSESSMENT AND THE ROLE OF CARBON IN SEMIINSULATING GAAS

A method for identifying and quantifying acceptor contamination in sem i-insulating (SI) GaAs is described. The method has been applied to co mmercial 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 commer cial material studied. The method consists of moving the Fermi level t o the ground stare of the shallowest acceptor present, usually carbon, by diffusing copper into the material. An infrared transmission measu rement identifies the neutral accepters from their electronic 1s-2p in trasite excitation. The strength of the absorption is proportional to the neutral acceptor concentration. Sensitivities are greatest for sha llow accepters where neutral acceptor concentrations as low as 5x10(12 ) cm(-3) can be identified and quantified. (C) 1997 American Institute of Physics.