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 nn and pn 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 np and pp represent the electron and hole densities in a P-type semiconductor after doping
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