If a p-n junction is forward biased, then what is the direction of diffusion and drift current across the junction?
Answer & explanation
Correct answer: option 2
The correct answer is Option (2) → Diffusion - from p to n side, Drift - from n to p side
The two currents across a junction have different causes: the diffusion current is due to the concentration difference of the majority carriers, and the drift current is due to the electric field of the depletion region acting on the minority carriers.
Holes diffuse from the p side to the n side and electrons diffuse from the n side to the p side. Both motions give a conventional current from p to n.
The junction field points from the n side to the p side, so it drives the minority carriers to give a current from n to p.
Forward bias makes the diffusion current much larger than the drift current, but it does not change their directions.
NCERT (2026-27):
p-n Junction Formation – “… During the formation of p-n junction, and due to the concentration gradient across p-, and n- sides, holes diffuse from p-side to n-side (p → n) and electrons diffuse from n-side to p-side (n → p). This motion of charge carries gives rise to diffusion current across the junction. … The motion of charge carriers due to the electric field is called drift. Thus a drift current, which is opposite in direction to the diffusion current (Fig. 14.10) starts.”