A collector current model for InAlAs/InGaAsSb/InGaAs double heterojunction bipolar transistors with non-ideal effects

A collector current model incorporating electron diffusion in the base and thermionic emission at the abrupt B–E heterojunction is derived and applied to InGaAsSb heterojunction bipolar transistors (HBTs). Parameters extracted from the model include effective base doping concentration, conduction band discontinuity (ΔEC) at the base-emitter junction, and emitter resistance. The calculated current from the model is consistent with the measured result. It is found that a high collector current ideality factor is resulted from a nonzero ΔEC and a low effective base doping concentration. Moreover, a nonzero ΔEC makes the high-injection effect almost invisible in collector current characteristics, even if it actually exists.