Analysis of base transit time for a bipolar junction transistor considering base current

Consideration of base current makes the analytical modeling of base transit time for a bipolar junction transistor intractable, as such model requires knowledge of the majority hole current density, the recombination mechanism in the base and the injection of carriers from the base contact. All these effects along with bandgap narrowing, velocity saturation, Webster effect etc. makes the differential equation for minority carrier density third order or higher, nonlinear, non-homogeneous and of variable-coefficient. In this work, all these difficulties have been successfully overcome and therefore, an analytical model has been developed. The model results show that the consideration of base current increases the base transit time up to 5 - 8% even in the low-injection condition.