Page 972 - Basic Electrical Engineering

emitter–base junction must be forward biased while the collector base region
reverse biased as shown in Fig. 14.15 (a) and (b).
The forward bias of the EB junction reduces the width of the depletion

region and the barrier voltage gets reduced.
The reverse bias of the CB junction increases the width of the depletion

region and the barrier voltage gets increased.
Since the EB junction is forward biased, electrons form the majority charge

carriers and would flow from the emitter to the base region. Since the base is
lightly doped, there will be a smaller number of holes present there. Only a

small percentage of electrons from the emitter will recombine with holes in
the base region. Only around two per cent of the electrons from the emitter
recombine with the holes that are present in base region. The reverse bias of

the CB junction causes expansion of the depletion layer. The width of the
base region is thinner than the collector region. Therefore, the depletion

region will penetrate deep into the base region. The electrons from the emitter
region will arrive near the CB depletion region. Due to large CB bias voltage,

electrons will be pulled across the CB junction by the positive terminal of the
collector. The collector thus collects the 98 per cent of the electrons emitted

by the emitter.