Band Gap

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 exist. In a graph of the electronic band structure of a solid, the band gap generally refers to the energy difference (in electron volts) between the top of the valence band and the bottom of the conduction band which is found in insulators and semiconductors. It is the amount of energy required to free an outer shell electron from its orbit about the nucleus to become a mobile charge carrier, able to move freely within the solid material.