1. Conductor (Metal)
In conductor the conduction band and valence band overlap each other.
2. Insulator
In insulator, The Valence band is completely filled and conduction band is completely empty and the energy gap is large.
In semiconductor, The valence band is totally filled and the conduction band is empty but the energy gap between valence band and conduction band is very small. So at very small temperature electron can jump from valence band to conduction band.


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