Dependency of Heterojunction Transistors' speed on various physical parameters: A comparative study of SiGe & AlGaAs HBTs

It is very essential to find out how the speed of a Heterojunction Bipolar Transistor (HBT) depends on different physical parameters of the transistor as the device has become indispensable in modern ultrafast circuits. As the speed of an HBT is a very strong function of its base transit time, here we investigate its dependency on minority carrier injection, base width, base emitter voltage, peak base doping concentration and slope of base doping for an AlGaAs HBT. The analytical model of base transit time of this AlGaAs HBT is based on SIGe model as found in literature. Comparison of base transit time obtained from similar simulation for SIGe and AlGaAs HBT has been presented in this work.