The electrical conductivity
is determined by the mobility of the free electrons in the band model. The band model consists of the valence band and the conduction band.
. The free electrons move in the conduction band. Thehighest mobility of free electrons is at absolute zero at 0 Kelvin
. In order to transport free electrons from the valence band to the conduction band in semiconductors, the electron energy must exceed the level of the valence band. This can be done by applying an electric field to bridge the energetic difference determined by the band gap.