Solid State Electronic Devices, 7th Edition

7.4 Minority Carrier Distributions and Terminal Currents

In this section we examine the operation of a BJT in more detail. We begin our analysis by applying the techniques of previous chapters to the problem of hole injection into a narrow n-type base region. The mathematics is very similar to that used in the problem of the narrow base diode (Prob. 5.40). Basically, we assume holes are injected into the base at the forward-biased emitter, and these holes diffuse to the collector junction. The first step is to solve for the excess hole distribution in the base, and the second step is to evaluate the emitter and collector currents (I_E, I_C) from the gradient of the hole distribution on each side of the base. Then the base current (I_B) can be found ...