What is doping ? Why is it essential ? What are different dopants used ?

Explanation

Doping. The process of adding desirable impurity in a controlled manner to a pure semiconductor crystal (Si or Ge) so as to improve the conductivity is called doping.
At room temperature,t he conductivity of an intrinsic semiconductor is very low, and also its conductivity depends on temperature. Thus by adding impurity atom in the semiconductor (i.e. doping), the conductivity of the semiconductor can be controlled as desired.
Two types of dopants are used.
`1.` Pentavalent dopant. If the dopant is an element from `5th` group of periodic table having `5` valence electrons like Sb or As, the semiconductor so produced is called n-type semiconductor.
`2.` Trivalent dopant. If the dopant is an element from `3rd` group of periodic table having `3` valence electrons like In or Ga, the semiconductor so produced is called p-type semiconductor.