Question: When a p-n junction diode is forward biased, what happens to the barrier height and the depletion layer width?

Step 1 (Governing Principle): [0.25 Mark]

In a p-n junction, the barrier potential ($V_B$) is created by the electric field of the depletion region, which opposes the flow of majority charge carriers. When an external voltage $V$ is applied in forward bias, 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 Logical Deduction): [0.5 Mark]

• The applied forward bias voltage ($V$) opposes the internal barrier potential ($V_B$).
• The effective barrier height becomes $(V_B - V)$, which is less than the original barrier height ($V_B$).
• Due to the repulsion of majority carriers (holes in p-side, electrons in n-side) toward the junction, the depletion region is pushed and compressed.
• Consequently, the width of the depletion layer ($w$) decreases as the majority carriers are forced to cross the junction.

Step 3 (Final Concluded Answer): [0.25 Mark]

Since both the barrier height and the depletion layer width decrease under forward bias, the correct option is (C).

💡 EL10 Concept Insight: Think of the depletion layer as a "wall" between two rooms; forward biasing is like pushing on both sides of the wall simultaneously, which makes the wall thinner and easier to climb over!