Effects of emitter-base junction gradation on the minority-carrier transport in the base region of bipolar junction transistors

The effects of emitter-base junction gradation, mobility gradients, and electric field gradients on the injected minority-carrier density distributions in the base region of narrow-base transistors are analyzed. It is shown that the collector current of transistors having a graded emitter-base junction deviates from the ideal characteristics. The factors which contribute to this departure are analyzed in this paper. It is also shown that the emitter-base forward bias voltage affects the transit time significantly in narrow-base transistors, even when high injection level conditions are absent.