Semiconductors are mainly two types.
1. Intrinsic semiconductor
2. Extrinsic semiconductor
INTRINSIC SEMICONDUCTORS
A semiconductor is an extremely pure form is known as an intrinsic semiconductor
Ex: Pure Germanium, Pure Silicon
Intrinsic semiconductors even at room temperature hole electron pairs are created. When an electric field is applied across an intrinsic semiconductor the current conduction takes place by electrons and holes. Hence semiconductor conductance consists of the movement of electrons and holes in opposite directions in the conduction and valence bands respectively. Alternatively, an intrinsic semiconductor may be defined as one in which the number of conduction electrons is equal to the number of holes.
EXTRINSIC SEMICONDUCTORS
The intrinsic semiconductor has little current conduction capability at room temperature. For getting good conducting properties, some suitable impurity or doping agent is added. Such type of semiconductors is called extrinsic or impure semiconductors. The process of adding impurity to a semiconductor is called doping. The purpose of adding impurity is to increase either the number of free electrons or holes in a semiconductor crystal. Depending upon the type of impurity added , extrinsic semiconductors are classified into.
( a ) n-type semiconductor
( b ) p-type semiconductor.
