P-N junction is an arrangement made by a close contact of n-type semiconductor and p-type semiconductor.
It is a single crystal of Germanium(Ge) or silicon(Si) dopped in such a manner that one half portion of it acts as p-type semiconductor and the other half as n-type semiconductor. Hear the term junction implies the boundary or region of transition between n-type and p-type semiconductor materials.
Formation Of Depletion Region In P-n Junction
In an n-type semiconductor, the concentration of electrons is more than that of holes. Similarly, in p-type semiconductor, the concentration of holes is more than that of electrons.
During formation of P-N junction and due to the concentration gradient across p and n sides, holds diffuse from p-side to n-side and electrons diffuse from n-side to p-side.
As holes diffuse from p to n side they leave behind negative accepter ions, which setup a layer of negative charge on the p side of the junction. Similarly, as the electron diffuse from n to p side, they leave behind positive donor ions which setup a layer of positive charge on the n side of the junction. This setups and electric field near the junction from n to p side.
The region on either side of the junction which becomes depleted (free) from the mobile charge careers is called depletion reason or depletion layer.
The accumulation of negative charges in the p region and positive charges in the n region setup a potential difference across the junction. This acts as a barrier and is called barrier potential VB.
Only those electrons and holes which have energy atleast eVB are able to cross the barrier and some diffusion take place. This diffusion of majority charge careers across the junction gives rise to an electric current from p to n side and is called diffusion current.