Carbon doping in molecular beam epitaxy of GaAs from a heated graphite filament

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Abstract
Carbon doping of GaAs grown by molecular beam epitaxy has been obtained for the first time by use of a heated graphite filament. Controlled carbon acceptor concentrations over the range of 1017–1020 cm−3 were achieved by resistively heating a graphite filament with a direct current power supply. Capacitance-voltage, p/n junction, and secondary-ion mass spectrometry measurements indicate that there is negligible diffusion of carbon during growth and with post-growth rapid thermal annealing. Carbon was used for p-type doping in the base of Npn AlGaAs/GaAs heterojunction bipolar transistors. Current gains greater than 100 and near-ideal emitter heterojunctions were obtained in transistors with a carbon base doping of 1×1019 cm−3. These preliminary results indicate that carbon doping from a solid graphite source may be an attractive substitute for beryllium which is known to have a relatively high diffusion coefficient in GaAs.