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Semiconductors are materials which have a conductivity between conductors (generally metals) and nonconductors or insulators (such as most ceramics). Semiconductors can be pure elements, such as silicon or germanium, or compounds such as gallium arsenide or cadmium selenide

The addition of impurities to semiconductor materials is called doping- This technique leads to change the conducting nature of the material- There are tWO types of impurities, and one is the donor impurities- One of the major characteristics of donor

impurity is that it donates electrons to the semiconductor to increase its conductivity. Donor—type elements must have 5 Valence electrons, four for bonding with the semiconductor elements such as Si and Ge, and one electron left to act as a

donor. The other type is the acceptor impurities- One of the major characteristics of acceptor impurity is that it accepts electrons from the semiconductor elements to increase its conductivity. Acceptor—type elements must have 3 valence electrons, so as to produce a de?cit of one electron (or presence of a hole) to act as an acceptor impurity.

Therefore

There are two types of impurities, and one is the donor impurities. Donor-type elements must have 5 valence electrons, four for bonding With the semiconductor elements such as Si and Ge, and one electron left to act as a donor. The other type is the acceptor impurities- Acceptor—type elements must have 3 valence electrons, so as to produce a de?cit of one electron (or presence of a hole) to act as an acceptor impurity.