Semiconductor Pn Junction

Introduction to semiconductor pn junction:

We take a silicon (p-Si) semiconductor wafer and add a small quantity of pentavalent impurity, this converts p-Si to n-Si. There are several processes by which a semiconductor can be formed. The wafer now consists of p-region and n-region and a junction between p- and n-region .This is how pn junction semiconductor is formed. I like to share this Natural Sources of Radiation with you all through my article.

Two improtant processes take place during the formation of a p-n junction semiconductor:

Difffusion
Drift.
In the n-type semiconductor, the concentration of electrons is more than the concentration of holes. Similarly in p-type semiconductor , the concentration of holes is more than the concentration of electrons.

Diffusion Current of Pn Junction Semiconductor:

During the formation of p-n junction , due to difference in concentration across p- and n- regions , holes move from p-side to n-side ( p n) and electrons move from n-side to p-side(n`->` p).This motion of charge carriers gives rise to diffusion current across the junction. Understanding temperature equation is always challenging for me but thanks to all math help websites to help me out.

When an electron moves from n`->` p, it leaves behind a hole on the n-side.This hole(positive charge) is immovable as it is bonded to the surrounding atoms. As the electrons continue to move from n`->` p, a layer of positive charge ( or positive space-charge region) on the n-side of the junction is developed.

Similarly , when a hole  moves from p`->` n, it leaves behind an electron on the n-side.This electron(negative charge) is immovable as it is bonded to the surrounding atoms. As the holes continue to move from p `->` n, a layer of negative charge ( or negative space-charge region) on the p-side of the junction is developed.

Drift Current of Pn Junction Semiconductor:

An electric field  from positive charge to negative charge develops as a result of the positive space-charge region on n-side of the junction and negative space charge region on the p-side of the junction. And as a result of this electric field, an electron on p-side of the junction is moved to n-side and a hole on n-side moves to p-side.The motion of charge carriers due to this electric field is called drift.Thus the drift current, which is opposite to the diffusion current starts.

In the begining, diffusion current is large and drift current is small. As the process of diffusion continues, charge regions on either side of the junction extend, thus increasing the electric field strength and so the drift current.This process continues till the diffusion current equals the drift current.