Forward bias applied to a p-n junction diode

The correct answer is Option (3) → decreases the electric field in the depletion region

In forward bias the applied voltage opposes the built-in potential of the junction. The effective barrier becomes \( V_0 - V \), so the barrier height falls, the depletion region becomes narrower and the field across it becomes weaker.

Option (1) widens the depletion region — Incorrect. Forward bias narrows the depletion region; it widens in reverse bias.

Option (2) increases the number of donors on the n-side — Incorrect. The number of donors is fixed by doping; a bias voltage does not change it.

Option (3) decreases the electric field in the depletion region — Correct. The applied field is opposite to the built-in field, so the net electric field in the depletion region decreases.

Option (4) increases the potential difference across the depletion region — Incorrect. The potential difference across the depletion region falls from \( V_0 \) to \( V_0 - V \); it rises only in reverse bias.

NCERT (2026-27):
p-n Junction Diode Under Forward Bias – “… The direction of the applied voltage (V) is opposite to the built-in potential V₀. As a result, the depletion layer width decreases and the barrier height is reduced [Fig. 14.13(b)]. The effective barrier height under forward bias is (V₀ − V).”