Intrinsic Semiconductor:- It is pure semi-conducting material and no impurity atoms are added to it. In the intrinsic semiconductor, number of free electrons in the conduction band and the number of holes in valence band is exactly equal and very small indeed.
Extrinsic Semiconductor:- It is prepared by doping a small quantity of impurity atoms to the pure semi conducting material. In the extrinsic Semiconductor, number of free electrons and holes is never equal. There is excess of electrons in n-type semi-conductors and excess of holes in p-type semiconductors.
Intrinsic Semiconductor is a pure form of the semiconductor as there is no addition of impurity takes place. An example of intrinsic semiconductors is Silicon (Si) and Germanium (Ge).
Extrinsic Semiconductor is obtained, when a small quantity of Tetravalent or Pentavalent impurity like Arsenic (As), Aluminum (Al), Phosphorus (P), Galium (Ga), Indium (In), Antimony (Sb) etc. is added in pure semiconductor, an .