Electrical Engineering ⇒ Topic : Extrinsic or impurity semiconductors

Extrinsic or impurity semiconductors are those intrinsic semiconductors to which some suitable impurity or doping agent has been added in extremely small amount (about 1 part in 100 million)

Extrinsic semiconductors can be of two types depending on the doping agent

(1)N-type extrinsic semiconductors are those intrinsic or pure crystals which have been doped by a pentavalent element like antimony etc. In such semiconductors, conduction is mostly by electrons

where n_n and p_n represent the electron and hole densities is the N-type semiconductorafter doping

(2)P-type extrinsic semiconductors are those intrinsic semiconductors which have been doped by a trivalent element like boron. In such semiconductors, conduction is mostly by means of hole movement.

where n_p and p_p represent the electron and hole densities in a P-type semiconductor after doping