Semi conductor are those materials whose electrical conductivity, at room temperature, lies in between that of insulator and conductor. Germenium and Silicon are two important semiconductor. In a crystal lattice of semi-conductor, some of the electrons become free from bond formation. At the sites of these electrons a deficiency of electron exists which acts as a virtual positive charge. These virtual positive charges are called holes. Semi-conductors are used in electronics industry.
Semi-conductors are of two types :
1. Intrinsic Semi-Conductor
2. Extrinsic Semi-Conductor

Intrinsic Semi-Conductor

A semi conductor in an extremely pure form is known as intrinsic semi conductor. At absolute zero, an intrinsic semi conductor is a perfect insulator, (conductivity = zero).

Extrinsic Semi-Conductor

If a measured and small amount of chemical impurity is added to intrinsic semi-conductor, it is called extrinsic semi-conductor or doped semi conductor. As a result of doping, there is large increase in its conductivity.

Extrinsic semi conductor are of two types :
I.     N-type semi-conductor
II.   P-type semi-conductor

N-type semi-conductor

An extrionic semi conductor in which electrons are majority charge carrier is called N type semi conductor. Such a semi conductor is made by doping a pure semi conductor with pentavalent impurity like Arsenic, Antimony & Phosphorus.

P-type semi-conductor

An extrinsic semi conductor in which holes are the majority charge carrier is called a P type semi conductor. Such a semi conductor is made by doping a pure semi conductor with trivalent impurity like Gallium, Indium, Boron and Aluminium.


Adding of chemical impurity to a pure semi conductor is called doping. The amount and type of impurity is closely controlled.


Pentavalent impurities are called donor.


Trivalent impurities are called acceptor.
The electrical conductivity of a semi conductor increases with the increase in temperature.


Rectifier is a device which converts alternating current into direct current.


Study of science of small is called nanotechnology.