What is meant by doping in semiconductor?

Hint: Doping is the introduction of impurities into an intrinsic semiconductor, deliberately, for the purpose of modulating its structural, and electrical properties.

Complete step by step answer:
The process of adding impurities in one type of semiconductor which is named as extrinsic semiconductor to make it usable is called Doping.
Pure Germanium and Silicon are sometimes used as semiconductors. These semiconductors must have controlled the quantity of impurities added to them. Addition of impurities changes the ability of the conductor and it acts as a semiconductor. This process of adding an impurity to a pure material or intrinsic substance is called doping. Also, the impurity added is called a dopant. After doping, an intrinsic material becomes an extrinsic material and then after doping these materials becomes good to use.

Following are some reasons for doping:
1.Doping improves conductivity of semiconductor
2.Doping improves characteristics of semiconductor
3.Doping make semiconductors flexible for different applications

When the impurities are added to silicon or germanium without modifying their crystal structure, an N-type material is produced and When an intrinsic semiconductor is doped with Trivalent impurity it becomes a P-Type semiconductor.
Doping of silicon with any impurity must not change the crystal structure or the bonding process. Silicon can be doped with two most important materials; they are boron and phosphorus. Other materials are aluminium, indium and arsenic, antimony. The extra electron of impurity atom does not participate in a covalent bonding. These electrons are loosely packed together by their originator atoms.

Note: Extrinsic semiconductors are formed as a result of doping. This can be simplified as follows:
1.Impurities + Intrinsic semiconductor = Extrinsic semiconductor
2.Aluminium + Silicon = Extrinsic semiconductor