Base transit time of a Heterojunction Bipolar Transistor with Gaussian doped base

Base transit time for an npn SiGe HBT is calculated assuming Gaussian doped base and a generalized trapezoidal Ge profile considering field dependent mobility in excess to doping dependent mobility and diffusivity. Band-gap narrowing (BGN) due to heavy doping, due to presence of Ge and due to change in the density of states (DOS) are also considered. For presence of Ge, a different saturation velocity has been used. Ge profile variation has been incorporated by a single parameter. Base transit time of SiGe HBT is calculated and computed for different Ge contents. The calculated base transit time shows similar variations as found in literature for BJT.