Why a hole is not formed when 5th electron of pentavalent impurity moves to conduction band in n type semiconductor?
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.