Explain the forward and reverse characteristics of a Zener diode.

Hint: A zener diode is a type of diode that can operate in the reverse breakdown region. An ordinary diode operating in this region will be destroyed due to excessive current. But the case for the zener diode is not like that of other diodes. The zener diode operated in the reverse voltage region will have a relatively constant voltage across it, regardless of the value of current through the device. Thus the zener diode is used as a voltage regulator.

Complete answer:
A zener diode is a diode that can operate in the reverse breakdown region. An ordinary diode operated in this region will be destroyed due to excessive current. But the case for the zener diode is not like that of other diodes.

A zener diode is usually heavily doped because here we have to reduce the reverse breakdown voltage. This causes a very thin depletion layer. As a result, a zener diode will have a sharp reverse breakdown voltage. This is clear from the reverse characteristics of zener diodes shown in figure below. Note that the reverse characteristics drop in an almost vertical manner at reverse voltage.

As the curve reveals, two things happen when breakdown voltage is reached. That is, the diode current increases rapidly and the reverse voltage across the diode remains almost constant.

Note:
In other words, the zener diode operated in the reverse voltage region will have a relatively constant voltage across it, regardless of the value of current through the device. Thus the zener diode is used as a voltage regulator. Thus a zener diode operates in the reverse breakdown region. An ordinary diode operated in this region will be destroyed due to excessive current. But the case for the zener diode is not like that of other diodes.