Correct Option: (A) both the potential barrier height and the width of depletion layer decrease.

Step 1 (Governing Principle): [1/3 Mark]

In a p-n junction diode, the potential barrier ($V_B$) is created by the electric field of the depletion region, which opposes the diffusion of majority charge carriers. When an external forward bias voltage ($V$) is applied, the positive terminal of the battery is connected to the p-side and the negative terminal to the n-side.

Step 2 (Step-by-Step Working): [1/3 Mark]

• The applied forward bias voltage ($V$) creates an electric field that opposes the internal junction electric field ($E_i$).
• The net potential barrier height becomes: $$V_{net} = V_B - V$$
• Since $V > 0$, the effective potential barrier height ($V_{net}$) decreases.
• Because the barrier height is reduced, the depletion region is no longer able to maintain its original width ($w$). The majority carriers are pushed towards the junction, effectively narrowing the depletion layer: $$w \propto \sqrt{V_B - V}$$

Step 3 (Final Concluded Answer): [1/3 Mark]

As the forward bias voltage ($V$) increases, the potential barrier height ($V_B - V$) decreases and the width of the depletion layer ($w$) decreases, allowing current to flow across the junction. Therefore, Option (A) is the correct choice.

💡 EL10 Concept Insight: Think of the depletion layer as a "speed bump" for electricity; when you forward bias the diode, you are essentially flattening that speed bump, making it much easier for the current to flow through.