“A semiconductor in which impurity is added at controlled rate to make it conductive is known as Extrinsic semiconductor.”
As intrinsic semiconductor is not useful for the preparation of various electronic devices ,since it is capable of conducting little current at room temperature. So to make it conductive small amount of suitable impurity is added .Then it will become an impure semiconductor which is conductive and this impure semiconductor is known as in extrinsic semiconductor.
Now, what is doping?
Doping is a process in which impurities added to a semiconductor to make it conductor.
” the process by which an impurity is added to a semiconductor is known as doping”
Purpose of doping:
The purpose of adding impurity in the semiconductor crystal is to increase the number of free electron or holes to make it conductive
If pentavalent impurity is added to a pure semiconductor a large number of free electron will exist in a semiconductor. But when trivalent impurity is added to a pure semiconductor then a large number of holes will exist in it.
Depending upon the type of impurity, Extrinsic semiconductor is classified as
where, n-type semiconductor are also known as Donor impurities
and p-type semiconductor are also known as acceptor impurities .