There are two types of impurities added in a intrinsic semiconductor which are as follows 1.Donor Impurity 2.Acceptor Impurity
1.Donor Impurity – These are pentavalent which means they have five valence electron. Four valence electron out of five elctrons are utilized to form four covalent bond with Silicon or Germanium. Fifth valence electron thus enter the conduction band very easily,thus this impurity are also called as donor impurity while doping is called as donor doping. It is used to manufacture N-type semiconductor Eg:Arsenic,Phosphorus,Antimony
2.Acceptor Impurity These are Trivalent which means they have three valence electron. All the three elctrons are utilized to form three covalent bond with Silicon or Germanium. Thus fourth covalent bond remains incompelete resulting in a vacancy called as hole.this hole act as a positive charge carrier,thus this impurity are also called as Acceptor impurity while doping is called as Acceptor doping. It is used to manufacture P-type semiconductor Eg:Boron,Gallium,Indium