Practice portal › Semiconductor Electronics › Intrinsic and Extrinsic Semiconductors
Asked in RS Academy GUJCET booklet · Doping and carrier concentration
Idea: where a dopant's level sits inside the forbidden gap tells you which type the crystal is.
A pentavalent (donor) impurity puts its level just below the conduction band, only about 0.01 to 0.05 eV under it, so its spare electrons reach the conduction band easily. That is n-type.
A trivalent (acceptor) impurity puts its level just above the valence band. Electrons from the valence band step up into it and leave holes behind in the valence band. That is p-type.
The figure shows one impurity level immediately above the top of the valence band, occupied by electrons, with holes left in the valence band below it.
So the crystal is a p-type semiconductor.
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