Base transit time of a heterojunction bipolar transistor (HBT) with Gaussian doped base under high-level of injection

Base transit time for an npn SiGe HBT has been analysed assuming Gaussian doped base considering doping dependent mobility. Band-gap narrowing (BGN) effects due to heavy doping, due to presence of Germanium and due to change in the density of states (DOS) have also been considered. The presence of Ge has been incorporated by using a different saturation velocity for the SiGe alloy. A generalized profile for Ge mole fraction distribution is used, where Ge profile variation has been illustrated by varying a single parameter for box, trapezoidal and triangular forms. Base transit time of SiGe HBT has been calculated for these three Ge profiles under high level of injection.