Doping of semi-conductors
Doping is the introduction of impurities in semi-conductors to alter their electronic properties. The impurities are called dopants. Doping heavily may increase their conductivity by a factor greater than a million.
Intrinsic and extrinsic semi-conductors
An intrinsic semi-conductor is one which is pure enough such that the impurities in it do not significantly affect its electrical behavior.Intrinsic semi-conductors increase their conductivity with increase in temperature unlike metals.An extrinsic semi-conductor is one which has been doped with impurities to modify its number and type of free charge carriers present.