Question

What is meant by 'doping' in a semiconductor?

Answer 1

Hint Semiconductors are the materials which have conductivity more than insulators but less than conductors. The band gap in case of semiconductors is very small, so doping is done in order to increase the conductivity.

Complete answer:
The electrical conductivity of a solid is defined as its ability to conduct electric current pass through it. On the basis of the value of electrical conductivity of solids they have been and semiconductors. Conductors allow the maximum portion of electricity pass through it whereas insulators don't allow electricity to pass through it. Semiconductors have electrical conductivity which is intermediate between conductors and insulators.
A semiconductor which is obtained by heating an insulator is called intrinsic semiconductor. When we cannot work with pure intrinsic semiconductors we have certain impurities. Adding certain impurity under certain conditions is known as doping. Silicon and germanium act as insulators at low temperatures. These elements can be made to behave as semiconductors by doping that is either heating it or by adding impurities like boron or phosphorus. The impurities added are known as dopants. The semiconductor which is obtained by adding impurities is called extrinsic semiconductor.
n-type extrinsic semiconductors are produced when phosphorus is added to silicon or germanium crystals. The phosphorus added to crystal is impure. The alternative of phosphorus is arsenic.
p-type extrinsic semiconductors are produced when boron is added to silicon or germanium crystals. The boron added to the crystal is an impurity.
The main purpose of doping is to increase the electrical conductivity of semiconductors.

Note: Silicon and germanium crystals are semiconductors. By increasing the number of dopants then, the number of charge carriers also increases. Therefore the current flow also increases. While doping we should add dopant in excess otherwise sometimes an electrically neutral structure is formed.