Question

what is extrinsic semiconductor

Answer 1

impure or doped semiconductor

number of free electron in conduction band is not equal to the number of holes in valence band.

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Answer 2

An Extrinsic Semiconductor is a SemiConductor doped by a specific impurity which is able deeply modify it's electrical properties making it suitable for electronic appliancations ( Diodes, Transistors etc ).

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