continued...

As a continuation of the semiconductors, i will be covering the "dopes" today.

Doping:

The ability of conductivity of semiconductors can be controlled by doping the materials with impurities. The number of impurity atoms added may be by the thousand or million folds. The term low doping means small number of atoms added in the order of one per 100 million atoms. High doping is that of bigger number of atoms added in one per ten thousand atoms. Other than the number of atoms of impurities added, the type of impurity also affects conductivity. Varying the number and type of impurity atoms may be done in thousands or millions folds too.

Dopants

The materials chosen as suitable dopants depend on the atomic properties of both the dopant and the material to be doped. Generally, dopants that produce desired controlled changes are either electron donors or acceptors.

This may sound very technical but let me attempt to explain what a donor is.

This is the process of doping a semiconductor with an impurity which has more protons per atom (more electrons per atom). The atoms in a semiconductor will form bonds with neighbouring atoms in such a manner that each atom sees a “closed shell”. Since the donor atom introduces an additional electron, this electron is loosely bound; it is more free to move than the electrons which form the closed shell. This additional electron is easily put into the conduction band and can therefore conduct electricity easily. A donor-doped semiconductor is called an N-type semiconductor because it has negative charge carriers.

In other words, when a doping material is added, it gives away (donates) weakly-bound outer electrons to the semiconductor atoms. The purpose of N-type doping is to produce an abundance of mobile or “carrier” electrons in the material.