Question

Why does the width of depletion region increase in reverse bias?

Answer 1

Reverse bias: Reverse bias is when the p-side of the diode is attached to the negative voltage of the battery and the n-side is attached to the positive voltage of the battery.

We can understand this concept by the above diagram of $\mathrm{P}-\mathrm{N}$ junction.

1. By connecting a $\mathrm{P}-$ type and an $\mathrm{N}-$type diode, a $\mathrm{P}-\mathrm{N}$ junction diode is formed, it permits only one direction of current to flow, it blocks the current going in the other direction.
2. It can give free electrons and holes greater energy to pass the junction, where the junction width or the breadth of the depletion layer is reduced.
3. When the battery's positive terminal is connected to the $\mathrm{N}-$type junction during reverse biasing, while the negative terminal is connected to the $\mathrm{P}-$type junction, therefore, the positive terminal attend to pull the electrons (near to the depletion layer) in $\mathrm{N}-$type with regards to itself, whereas the negative terminal pulls the holes with regards to itself which leads in in increase in the width of depletion layer..
4. This occurs because conduction is impossible when reverse bias voltage is applied since the electrons have stepped away from the junction.

Hence, the width of the depletion region in a $\mathrm{P}-\mathrm{N}$ junction diode is increased by reverse bias.