Semi-conductor

Semi-conductor

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.

Doping

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

Donor

Pentavalent impurities are called donor.

Acceptor

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

Rectifier

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

Nanotechnology

Study of science of small is called nanotechnology.