Carbon Doping in Molecular Beam Epitaxy of GaAs from a Heated Graphite Filament.

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 10 sup (17) -10 sup (20) cm sup (-3) were achieved by resistively heating a graphite filament with a direct current power supply. Capacitance-voltage, p/n junction, and secondary ion mass spectrometer 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 heterojuntions were obtained in transistors with a carbon base doping of 1X10 sup (19) 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.