Analytical modelling of InGaP/GaAs HBTs

Heterojunction Bipolar Transistors with GaAs base and InGaP emitter have increasingly become important since they have great potential for numerous low- and high-frequency microwave circuit applications due to their high linearity, good reliability and nearly ideal current-voltage characteristics. Current gain and transit time are two important factors for determining the performance of these devices as amplifiers and as switches. Switching speed is mainly determined by transit time of minority carriers across a device and forward transit time is an important component of the total transit time. An analytical model is developed here to predict the variation of current gain and forward transit time with composition of InGaP emitter, as well as with emitter and base doping profile. Dependence of band gap and diffusion constants on composition of InGaP emitter is also considered in the analysis. Performance of these devices is compared with that of AlGaAs/GaAs and Si/SiGe HBTs.