Characterization of residual carbon in semi-insulating GaAs

Abstract

We have found that undoped semi-insulating GaAs substrates convert from semi-insulating to strongly conducting p-type behavior following high-temperature annealing (830 and 885 °C) for long periods of time (22–60 h). Remarkably similar results have been obtained for both liquid-encapsulated Czochralski and horizontal Bridgman undoped semi-insulating GaAs synthesized by various manufacturers. Hole concentrations measured at room temperature are about p=9.1×1015 and 3.6×1016 cm−3 after 830 and 885 °C anneals, and p is uniform throughout the 380 to 510 μm substrate thickness for 885 °C anneals. Hall-effect measurements of carrier freeze-out indicate that residual carbon acceptors are the dominant shallow-acceptor species. Conversion to p type appears to arise from out-diffusion of EL2 deep donors and from formation of an additional acceptor-type native defect which also results from arsenic out-diffusion during annealing.