Page 959 - Basic Electrical Engineering

(b) A reverse-biased p–n junction

In reverse biasing, the battery connection is reversed, i.e., the negative
terminal of the battery is connected to the p-side and the positive terminal is

connected to the n-side of the p–n junction as shown in Fig. 14.7. Electrons
from the n-side are attracted to the positive terminal of the battery and the

holes from the p-side get attracted to the negative terminal of the battery.
Since the holes of the p-side are attracted by the negative terminal and the
electrons of the n-side are attracted by the positive terminal of the battery, the

depletion layer gets widened as the applied voltage is gradually increased.
The barrier voltage also gets gradually increased and as such the possibility

of the majority charge carriers crossing the barrier is reduced to zero. Due to
minority charge carriers a negligibly small current of the order of micro

amperes will flow as shown in Fig. 14.7 (b). A reverse-biased, p–n junction,
therefore, offers very high resistance to current flow. The number of minority

charge carriers are small and a very small reverse voltage is required to pull
all the minority charge carriers by the two terminals of the applied voltage
across the junction. Any further increase in reverse voltage does not increase

the negligible small reverse current produced. Hence, this very small amount
of reverse current is also referred to as reverse saturation current.