Classification of Semiconductor

CLASSIFICATION OF SEMICONDUCTOR

1. Intrinsic semiconductor

A pure semiconductor is called intrinsic semiconductor. At the room temperature, the valance electrons may acquire sufficient energy to enter the conduction band to form free electrons. Under the influence of the electricfield, these electrons constitute electric current.

2. Extrinsic Semiconductor

Pure silicon or germanium (intrinsic semiconductor) has little use except in the manufacture of heat and light sensitive resistance. The process of adding impurity to a pure semiconductor is called doping. The characteristics of semiconductor materials can be significantly altered by doping impurity atoms into relatively pure semiconductor. The added impurity is called dopant and its presence in crystal can significantly change the electrical properties of the material. A doped semiconductor is called extrinsic semiconductor. There are two types of extrinsic semiconductor: n‒type and p‒type.

(i) n‒type semiconductor

The n‒type semiconductor is formed by doping pentavalent impurity atoms like arsenic, antimony or phosphorus at a very low level in silicon/germanium. This process creates excess unbond electrons in conduction band.

(ii) p‒type semiconductor

A small amount of trivalent impurities such as aluminium or boron is added into the pure semiconductor to get the p‒type semiconductor. The impurity atoms that accept the electrons from valance band creating holes are called acceptor atoms.