Adding of impurities to semiconductor is doping.
Materials which are used in semiconductor devices are generally of silicon , germanium etc .
The impurities belong to either boron family members like gallium , indium to make p- type semiconductors and to make n-type semiconductors we use
nitrogen famiily members to make n-type semiconductors like phosphorus ,
Doping is done because addition of small qty of them causes dramatic changes in the electrical properties.