This article is about solid state physics. For voltage control circuitry how to minimize pdf size electronics, see Bandgap voltage reference. This article is about the electronic bandgap found in semiconductors.
For the photonic band gap, see photonic crystal. In solid-state physics, a band gap, also called an energy gap or bandgap, is an energy range in a solid where no electron states can exist.
It is the energy required to promote a valence electron bound to an atom to become a conduction electron, which is free to move within the crystal lattice and serve as a charge carrier to conduct electric current. Therefore, the band gap is a major factor determining the electrical conductivity of a solid. Substances with large band gaps are generally insulators, those with smaller band gaps are semiconductors, while conductors either have very small band gaps or none, because the valence and conduction bands overlap.