The substance which contain relatively intermediate level of free electrons (less than conductor and more than that of insulator) is called semiconductor. Germanium and and silicon are the examples of semi-conductor.
Doping: The process of addition of impurities like trivalent (whose valency is three) and pentavalent (whose valency is five) elements in a pure semiconductor is known as doping.
Hole: If an electron gets sufficient energy to jump from the valence band to the conduction band, the vacancy is left in the valance band. This vacency is called hole. It carries no charge but behaves like positive charge.
Types of Semi-condutors:
a. Intrinsic semiconductor: The pure semiconductor like silicon and germanium are called intrinsic semiconductor. It has equal number of electrons and holes.
b. Extrinsic semiconductor: The impure semiconductor which is obtained by doping trivalent or pentavalent elements are called extrinsic semiconductor.
There are two types of Extrinsic Semiconductor:
- N-type semiconductor: The extrinsic semiconductor obtained by doping pentavalent element like phosphorus (P5) is known as n-type semiconductor. In N-type semiconductor, out of five valence electrons, four electrons are shared by silicon while the fifth electron remain unshared. Therefore, majority charge carrier is the hole which meant n-type semiconductor acts like a positive charge. It is donor type of semiconductor.
- P-type Semiconductor: The extrinsic semiconductor obtained by doping trivalent element like aluminum is known as p-type semiconductor. In p-type semiconductor, the three valence electrons of aluminum atom forms covalent bond with the valence electron of three silicon atoms. There is a shortage of one electron in tetrahedral covalent bond. The deficiency of one electron is called hole. It’s majority charge carrier is hole and minority charge carrier is electron. It is a acceptor type of semiconductor.