When a forward bias is applied to a pn-junction, it
Answer & explanation
Correct answer: option 3
The correct answer is Option (3) → lowers the potential barrier.
In forward bias the p-side is joined to the positive terminal, so the applied voltage V opposes the built-in barrier potential \( V_{0} \).
\( V_{\mathrm{barrier}} = V_{0} - V \)
The barrier is lowered, the depletion layer becomes narrower, and many more majority carriers can diffuse across the junction, so the current rises.
Why the other options are incorrect
Option (1) raises the potential barrier. — Incorrect. Raising the barrier is what reverse bias does.
Option (2) reduces the majority carrier current to zero. — Incorrect. Forward bias increases the majority carrier (diffusion) current; it is reverse bias that makes it very small.
Option (4) increases the width of depletion layer. — Incorrect. The depletion layer becomes narrower in forward bias; it widens in reverse bias.
Note: A similar question was also asked in CUET (UG) 2023 on 02-06-2023 (Slot 2).
NCERT (2026-27):
p-n Junction Diode Under Forward Bias – “When an external voltage V is applied across a semiconductor diode such that p-side is connected to the positive terminal of the battery and n-side to the negative terminal [Fig. 14.13(a)], it is said to be forward biased.”
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 ).”