Question

A p-n junction diode is forward biased. As a result,

• A. both the potential barrier height and the width of depletion layer decrease.
• B. both the potential barrier height and the width of depletion layer increase.
• C. the potential barrier height decreases and the width of depletion layer increases.
• D. the potential barrier height increases and the width of depletion layer decreases.

Hint:

In a forward-biased p-n junction, the applied voltage reduces the built-in potential barrier, lowering its height and allowing the depletion layer to shrink as majority carriers diffuse across the junction.

Answer 1

The Correct Option is A

Step 1: Understand the p-n junction under forward bias.
In a p-n junction diode, a potential barrier exists at the junction due to the separation of charges, creating a depletion layer where mobile charge carriers are absent. The potential barrier height is typically around 0.7 V for silicon diodes at equilibrium (no bias). Step 2: Analyze the effect of forward bias.
When a p-n junction is forward biased, the positive terminal of the external voltage is connected to the p-side, and the negative terminal to the n-side. This reduces the electric field opposing the diffusion of majority carriers: - The applied voltage opposes the built-in potential barrier, effectively reducing the potential barrier height. - As the potential barrier decreases, the electric field across the depletion region weakens, allowing majority carriers (electrons from the n-side and holes from the p-side) to diffuse across the junction more easily. Step 3: Determine the effect on the depletion layer width.
The width of the depletion layer is related to the electric field and the potential barrier. In forward bias: - The reduction in the potential barrier reduces the electric field across the junction. - This causes the depletion layer to shrink, as the space charge region narrows due to the increased diffusion of carriers. Step 4: Summarize the effects.
- The potential barrier height decreases because the forward bias opposes the built-in potential. - The width of the depletion layer decreases because the reduced electric field allows the depletion region to contract. Step 5: Match with the options.
Both the potential barrier height and the width of the depletion layer decrease, which matches option (A).