Effect of majority carrier current on the base transit time of a BJT for exponential doping

The main objective of this paper is to show that majority carrier current needs to be taken into account in determining base transit time. In previous analytical works for base transit time, majority carrier current in the base was neglected. In this paper both drift and diffusion currents for electron and hole are considered in obtaining minority carrier profile n(x). In the model, it is assumed that the lateral injection of base current into the active base region is occurred from a source function, g. The energy-bandgap-narrowing effects due to heavy doping, velocity saturation as well as doping and field dependent mobility are considered.