Explanation:
When a p-n junction diode is forward biased, the positive terminal of the battery is connected to the p-side (anode) and the negative terminal to the n-side (cathode) of the diode. This creates a forward current flow across the junction.

Depletion Region:
The depletion region is a region near the junction where the mobile charge carriers (electrons in the n-region and holes in the p-region) have been pushed away or neutralized, creating a region devoid of free charge carriers. This region acts as an insulator and prevents the flow of current when the diode is in reverse bias.

Effect of Forward Bias:
When the p-n junction diode is forward biased, the following changes occur in the depletion region:

1. Reduction in Width:
The applied forward bias voltage reduces the potential barrier between the p and n regions. As a result, the depletion region width decreases.

2. Expansion of Space-Charge Region:
With the application of a forward bias, more majority carriers (electrons in the n-region and holes in the p-region) are injected into the depletion region. This leads to the expansion of the space-charge region.

3. Decrease in Barrier Potential:
The forward bias voltage reduces the barrier potential across the junction, allowing the majority carriers to overcome the potential barrier and cross the junction. This decreases the barrier potential.

4. Increase in Diffusion Current:
The decrease in barrier potential and expansion of the space-charge region allow the majority carriers to diffuse across the junction. This results in an increase in the diffusion current.

Conclusion:
When the p-n junction diode is forward biased, the width of the depletion region decreases. This reduction in width allows the majority carriers to easily cross the junction and results in a significant increase in the forward current flow through the diode.