If the forward voltage in a p-n junction diode is increased, the width of the depletion region
Answer & explanation
Correct answer: option 2
The correct answer is Option (2) → Decreases
The depletion region is the layer around the junction that has lost its free carriers and holds the fixed ions that create the barrier potential.
In forward bias the applied voltage opposes the barrier potential. The effective barrier becomes \( V_0 - V \), more electrons and holes cross the junction, and the uncovered ion layer becomes thinner. A larger forward voltage lowers the barrier further, so the depletion region becomes narrower.
Why the other options are incorrect
Option (1) Increases — Incorrect. The width increases in reverse bias, when the applied voltage adds to the barrier potential.
Option (3) No change — Incorrect. The width depends on the effective barrier \( V_0 - V \), so it does change with the applied voltage.
Option (4) Fluctuates — Incorrect. A steady forward voltage gives a steady width; there is nothing to make it fluctuate.
Note: The same question was also asked in CUET (UG) 2023 on 07-06-2023 (Slot 3), and a similar question in CUET (UG) 2026 on 24-05-2026 (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)].”