Intrinsic semiconductors are a pure form of semiconductors. Extrinsic semiconductors are obtained when an impurity is added to an intrinsic semiconductor.
Intrinsic semiconductors are the ones which are semiconductors by nature. For example silicon and Germanium (group 14 elemets). But these elements are conductors of electricity at high temperatures and at room temperature they are insulators. Even when we provide high temperature they are poorly conducting ie they conduct but it is not enough.
so In order to improve their conductivity we Dope them.(ie we add calculated amount of impurites). On the basis of the impurity added they can be:
compound semiconductors are formed using group 12 and group 16 elements to get an average valence of 4
please refer to Ncert class 12 part 1 page 27-28 after this.