Briefly explain the two important processes that occur during the formation of a p-n junction.

Two important processes are in the formation of p-n junction.

Diffusion: During the formation of p-n junction, due to 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 carriers give rise to diffusion current across the junction.

Drift: 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. Due to this field an electron on p-side of junction moves to n-side and a hole on n-side of the junction moves to p-side. The motion of charge carriers due to the electric field is called drift and constitutes drift current.