Current gain of narrow-base transistors

It is shown that the total number of impurities per cm² in the quasi-neutral base region of narrow-base transistors and their current-gain β strongly depend upon the emitter-base voltage V_BE. The computed results demonstrate that the β of these transistors falls considerably with V_BE increase, even in the absence of high-injection effects. The analysis also shows that the collector current of narrow-base transistors increases slower than exp (V_BE/V_T) giving rise to a non-ideality factor greater than one. It is concluded that narrow-base transistors with higher base resistivities are more susceptible to these effects.