AlGaAs/GaAs heterojunction bipolar transistors are fabricated using carbon-doped p-type GaAs base regions grown for the first time by flow-rate modulation epitaxy. Because of the much smaller diffusion coefficient of carbon atoms in GaAs than that of beryllium and other p-type impurities, sharp impurity profiles are achieved. The heterojunction bipolar transistors exhibited high current gains up to 40 for a base layer width of 150 nm and base doping of 2.4×1019 cm-3. The electron lifetime in heavily carbon-doped GaAs layers is considerably long, indicating favorable quality of heavily carbon-doped layers.
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