Question

The increase in the width of the depletion region in a p-n junction diode is due to :

• A. forward bias only
• B. reverse bias only
• C. both forward bias and reverse bias
• D. increase in forward current

Answer 1

The Correct Option is B

The increase in the width of the depletion region in a p-n junction diode is primarily due to the application of reverse bias. Let's explore why this is the case and examine each option provided:

1. Understanding the depletion region: The depletion region in a p-n junction diode is formed by the diffusion of charge carriers (electrons and holes) across the junction. This region is devoid of free charge carriers and is occupied by immobile ions, which create an electric field opposing further diffusion.
2. Effect of reverse bias: When a reverse bias is applied to a p-n junction, the external voltage increases the potential barrier. This leads to an increase in the electric field across the depletion region, causing more charge carriers to be swept away from the junction, hence widening the depletion region.
3. Effect of forward bias: In contrast, when a forward bias is applied, it reduces the potential barrier. This allows more charge carriers to recombine at the junction, thereby decreasing the width of the depletion region.
4. Analysis of options:
   • Forward bias only: Forward bias reduces the width of the depletion region, not increases it. Hence, this option is incorrect.
   • Reverse bias only: Reverse bias increases the width of the depletion region, making this the correct choice.
   • Both forward bias and reverse bias: As explained, forward bias decreases the width of the depletion region, so this option is incorrect.
   • Increase in forward current: This is irrelevant to the width of the depletion region; hence it is incorrect.

Thus, the correct answer is reverse bias only.