Question

In terms of band theory, what is the difference between a conductor and a semiconductor?

Answer 1

In a semiconductor, each occupied band is fully filled, yet there exists a reduced energy gap between the highest occupied band and the conduction band. In contrast, in a conductor, the highest occupied band is either partially filled or overlaps with the conduction band if it is totally filled.

Answer 2

	Conductor	Semiconductor
1.	The valence band and the conduction band overlap, or the valence band is partially filled.	There is a small energy gap (band gap) between the valence band and the conduction band.
2.	Zero or negligible band gap.	Its band gap is small (~1 eV).
3.	Conductivity decreases slightly with temperature (due to scattering).	Conductivity increases with temperature (more electrons are excited across the gap).
4.	Example: Copper, Silver, Aluminium	Example: Silicon, Germanium