When p-n junction is forward biased how the depletion layer width decreases and in reverse biased how it increases???
A pn junction is said to be forward biased if the positive terminal of the external battery is connected to p side and the negative terminal is the n side.
In forward biasing, the applied voltage mostly drops across the depletion region and the voltage drop across the p side and n side of the pn junction is negligibly small. This is due to the fact that resistance of depletion region is very high as it has no free charge carriers.
The majority carriers , electrons in the n region are repelled by negative terminal of the battery and move towards the junction. Similarly holes from p region move towards junction. The positive terminal of p region attracts electrons from n region and vice versa. As a result diffusion of majority carriers takes place across the junction which makes the junction thinner.
Thus the electric current is called forward current and it is due to majority carriers.
A pn junction is said to be reverse biased when positive terminal of the battery is connected to n side and vice versa. There is no conduction across the junction due to majority carriers however a few minority carriers cross the junction after being accelerated by high reverse biased voltage. This is called reverse current.
Since the large increase in voltage shows small increase in reverse current the resistance of pn junction is high to the flow of current when reverse biased.
Hence the width of depletion region if large.