Effect of recombination lifetime and velocity saturation on Ge profile design for the base transit time of Si/SiGe HBTs

In this paper, a fully analytical base transit time model for a SiGe-base HBTs with various shapes of germanium profiles in the base region considering both finite recombination lifetime and finite saturation velocity. The design of optimal Ge profile to minimize base transit time in the base can be achieved by using our model. The base structure for optimization has a linear ramp over the central portion of the base, similar to Winterton' s structures, and this Ge profile has been also used in Si/SiGe HBT fabrication.