Which of the following statements about the depletion region of an unbiased p-n junction are correct?
A. The width of the depletion region is independent of the densities of the dopants.
B. The width of the depletion region is dependent on the densities of the dopants.
C. The electric field in depletion region is produced by the positive and negative ions.
D. The electric field in the depletion region is produced by the electrons in the conduction band and the holes in the valence band.
Choose the correct answer from the options given below:
Answer & explanation
Correct answer: option 4
The correct answer is Option (4) → B and C only
When a p-n junction forms, electrons and holes diffuse across and recombine near the junction. This leaves a thin depletion region containing only immobile ions: positive donor ions on the n-side and negative acceptor ions on the p-side.
(A) The width of the depletion region is independent of the densities of the dopants. — Incorrect. With heavier doping the required ion charge is found in a thinner layer, so the region becomes narrower.
(B) The width of the depletion region is dependent on the densities of the dopants. — Correct. This is the reason given for (A).
(C) The electric field in depletion region is produced by the positive and negative ions. — Correct. The uncovered donor and acceptor ions set up the field (the barrier) across the junction.
(D) The electric field in the depletion region is produced by the electrons in the conduction band and the holes in the valence band. — Incorrect. The region is depleted of mobile charge carriers; free electrons and holes are not what produce its field.
NCERT (2026-27):
p-n Junction Formation – “… When an electron diffuses from n → p, it leaves behind an ionised donor on n-side. This ionised donor (positive charge) is immobile as it is bonded to the surrounding atoms. … Similarly, when a hole diffuses from p → n due to the concentration gradient, it leaves behind an ionised acceptor (negative charge) which is immobile. … This space-charge region on either side of the junction together is known as depletion region as the electrons and holes taking part in the initial movement across the junction depleted the region of its free charges (Fig. 14.10). … Due to the positive space-charge region on n-side of the junction and negative space charge region on p-side of the junction, an electric field directed from positive charge towards negative charge develops.”
