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In intrinsic semiconductor, when an electron moves from valence band to conduction band, hole is formed in place of that electron. Why does that not happen in case of n type semiconductor when 5th electron of pentavalent impurity moves to conduction band?

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  • \$\begingroup\$ in short: a hole is in the crystal lattice. The 5th electron of the donor doesn't belongs to the lattice (weakly bounded), thus, doesn't creates a hole when it moves. \$\endgroup\$ – pasaba por aqui Jul 7 '17 at 16:08
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When you dope a semiconductor the dopants contribute a mobile charge to the semiconductor of one type and this leaves behind an immobile charge of the opposite charge, this is the ionized dopant atom. If you heat a semiconductor, or expose it to photons of a high enough energy you can generate electron-hole pairs. Since this charge is not created from the ionization of a dopant atom, there is no fixed charge.

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