Choose the correct order for the formation of p-n junction diode.(A)…

The correct answer is Option (4) → (A) → (C) → (B) → (D)

When a p-type and an n-type region are joined, the sequence of events is fixed by cause and effect.

(A) diffusion current — comes first. Because of the concentration gradient, holes diffuse from p to n and electrons from n to p.

(C) formation of space charge region — comes next. The carriers that leave uncover immobile ionised acceptors on the p-side and ionised donors on the n-side, forming the depletion layer.

(B) drift current — comes after that. The electric field of the space charge region pushes carriers back across the junction, opposite to the diffusion.

(D) creation of a barrier potential — is reached last. Drift grows until it balances diffusion, and the potential difference across the depletion layer then stays constant.

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 – “… Initially, diffusion current is large and drift current is small. As the diffusion process continues, the space-charge regions on either side of the junction extend, thus increasing the electric field strength and hence drift current. … The loss of electrons from the n-region and the gain of electron by the p-region causes a difference of potential across the junction of the two regions. … Since this potential tends to prevent the movement of electron from the n region into the p region, it is often called a barrier potential.”