The cause of potential barrier in p-n junction diode is

The correct answer is Option (4) → positive space charge and negative space charge regions at the junction

When the junction forms, electrons diffuse from the n side to the p side and holes from the p side to the n side. They leave behind immobile ions: a layer of positive donor ions on the n side and a layer of negative acceptor ions on the p side.

These space charge regions set up an electric field from the n side to the p side, which opposes further diffusion; the potential difference across them is the barrier potential.

Option (1) the depletion of positive charge near the junction — Incorrect. The region is depleted of mobile carriers, but it is the uncovered charges of both signs that create the barrier, not one sign alone.

Option (2) concentration of holes and electrons at the junction — Incorrect. The junction region is actually emptied (depleted) of free electrons and holes.

Option (3) depletion of negative charge near the junction — Incorrect. As with option (1), one sign alone does not produce the barrier; both space charge layers are needed.

NCERT (2026-27):
p-n Junction Formation – “… As the electrons continue to diffuse from n → p, a layer of positive charge (or positive space-charge region) on n-side of the junction is developed.”

p-n Junction Formation – “… As the holes continue to diffuse, a layer of negative charge (or negative space-charge region) on the p-side of the junction is developed.”

Summary – “… When such a junction is made, a ‘depletion layer’ is formed consisting of immobile ion-cores devoid of their electrons or holes. This is responsible for a junction potential barrier.”