Carbon doping for AlGaAs/GaAs heterojunction bipolar transistors by molecular-beam epitaxy

Carbon doping in GaAs is investigated using solid-source molecular-beam epitaxy. The proportion of inactive C atoms in GaAs layers is found to increase when the free-carrier concentration is higher than about 1018/cm3. The current gain of AlGaAs/GaAs heterojunction bipolar transistors decreases rapidly with increasing base doping. The gradient of this tendency is much steeper than for inverse base doping, indicating the introduction of additional nonradiative recombination centers in heavily doped regions. A high current gain of 300 is achieved with a base doping of 2.5×1018/cm3.