Consider the following statements about a p-n junction diode with a built-in potential \(V_0\) and an applied voltage \(V\):
(A) Under forward bias, the width of the depletion layer decreases.
(B) Under reverse bias, the effective barrier height is \((V_0 - V)\).
(C) Under forward bias, the p-side of the junction is connected to the positive terminal of the battery.
(D) Under reverse bias, the current is of the order of milliampere.
Which of the above statements are incorrect?
Answer & explanation
Correct answer: option 3
The correct answer is Option (3) → (B) and (D) only
A forward bias opposes the built-in potential, so the barrier and the depletion layer shrink. A reverse bias adds to the built-in potential. So both grow, and only a tiny current flows.
(A) Under forward bias, the width of the depletion layer decreases. — Correct statement. The applied voltage opposes \( V_0 \), and the depletion layer narrows.
(B) Under reverse bias, the effective barrier height is \( (V_0-V) \). — Incorrect statement. In reverse bias the applied voltage acts in the same direction as \( V_0 \), so the barrier height becomes \( (V_0+V) \); \( (V_0-V) \) is the forward-bias value.
(C) Under forward bias, the p-side of the junction is connected to the positive terminal of the battery. — Correct statement. This is the forward-bias connection; with the n-side on the positive terminal the junction is reverse biased.
(D) Under reverse bias, the current is of the order of milliampere. — Incorrect statement. The reverse current is very small, of the order of microampere; currents in milliampere flow under forward bias.
NCERT (2026-27):
p-n junction diode under forward bias – “… As a result, the depletion layer width decreases and the barrier height is reduced … The effective barrier height under forward bias is (V0 – V).”
p-n junction diode under reverse bias – “… The direction of applied voltage is same as the direction of barrier potential. As a result, the barrier height increases and the depletion region widens due to the change in the electric field. The effective barrier height under reverse bias is (V0 + V) …”
Summary – “13. By changing the external applied voltage, junction barriers can be changed. In forward bias (n-side is connected to negative terminal of the battery and p-side is connected to the positive), the barrier is decreased while the barrier increases in reverse bias. Hence, forward bias current is more (mA) while it is very small (μA) in a p-n junction diode.”