Question

Zener diode is used in reverse bias. When its reverse bias is increased, how does the thickness of the depletion layer change?

Answer 1

Hint: A zener diode is a heavily doped diode. The junction potential of the zener diode increases as the zener diode is connected in reverse biased condition. When the reverse biased voltage increases across the zener diode the width of the depletion layer increases.

Complete step-by-step solution:

The zener diode always operates in reverse biased condition. That is, when the reverse biased voltage increases across the zener diode the width of the depletion layer increases. As a result the width of the depletion layer becomes wider. This also reduces the majority carrier current across the zener diode. And on the other hand minority current carriers increase. We have already said that when the reverse biased voltage increases across the zener diode the width of the depletion layer increases. But there is a limit in which the depletion layer can widen. Whenever the limit is crossed once there will be rapid increase in current with the small increase in voltage.
Therefore when the reverse biased voltage increases across the zener diode the width of the depletion layer increases.

Note: A zener diode is a heavily doped diode. For a wide range of current the breakdown voltage for a zener diode will be a constant. When a zener diode is used in the forward biased condition it will act as a normal diode. For a Silicon diode the width of the depletion layer ranges for a micrometer to tens of micrometer.