What is meant by doping? How does it affect a semiconductor?

Doping: The process through which an impurity is added to semiconductor is termed as doping. A semiconductor to that an impurity at controlled rate is added to make this conductive is termed as an extrinsic semiconductor. The reason of adding impurity into the semiconductor crystal is to raise the number of free electrons or holes to make this conductive. When pentavalent impurity is added to a pure semiconductor a large number of electrons will exist in this. If a trivalent impurity is added many of holes will exist into the semiconductor.