The Physics of Electrical Conduction

• Conductivity arises due to the electrons being delocalized.
• To transport an electron the state must be partially filled / contain an electron only part of the time.

Metals

• In metals, the valence and conduction bands overlap (in terms of energy).

• And, the Fermi level¹ lies within the overlapped region.

• Hence, the electrons flow easily when a voltage is applied.

• Semiconductors have a slightly larger band gap, so we need to heat them up (or do some tricks) to reduce the band gap to allow conduction.

• The band gap for insulators is too high and nothing can reduce it enough for conduction.

Footnotes

1. highest occupied energy level at absolute zero. ↩