Semiconductors are the materials whose conductivity lies between insulator and conductors. Their conductivity lies in between insulator and conductors because of the energy band gap. The energy band gap of semiconductor lies in between insulator and conductors. For example for the case of silicon, the semiconductor, the conductivity is 1.1 electron volt.
Types of semiconductors:
Semiconductors are of following two types:
- Intrinsic semiconductors: A pure semi-conductor which is free from any type of impurity is known as a pure semi-conductor. For example: Si and Germanium
The electron configuration of
(atomic number Z = 16) Si – 1S2 252 2P6 352 3P2
(Z = 32) Ge – 1S2 2S2 2P6 352 3P6 3d10 452 4P2
In both the cases, there are 4 valance electrons in the outer most shell, so they make 4 covalent bonds with the neighboring atoms; hence no electron is left free.
But at O Kelvin, there is no movement of electrons so they behave like insulators. But at the room temperature some of the covalent bonds may break up due to which the electron hole pairs are generated which cause conduction. But it must be noted that no. of electrons are always equal to the no. holes in a pure semi-conductor.
Extrinsic semiconductors: A doped semi-conductor is known as an extrinsic semi-conductor. (Doping: The addition of impurity atoms to a pure-semi-conductor (intrinsic semiconductor) is known as doping. It is used to increase the conductivity of a pure semi-conductor. It must be noted that the impurity atom is about 1 in every 1010 atoms.)
Thus this is the meaning of semiconductor and its types.
I will discuss the extrinsic semiconductor and its types in next article. In that article I will also discuss the more difference between intrinsic and extrinsic semiconductors.