Band Gap
The energy range in a solid where no electronic quantum states can exist, separating the top of the valence band from the bottom of the conduction band.
Governing formula
E_g = E_c - E_v = h ν_threshold
SI unit
eV (Electron-Volts)
In depth
The band gap E_g dictates a material's optical and electrical properties. Metals have overlapping bands (E_g = 0), semiconductors have narrow band gaps (E_g < 3 eV), and insulators have wide band gaps (E_g > 3 eV). In direct bandgap semiconductors, electron transitions occur without momentum change.
Examples in the real world
Gallium Arsenide (GaAs, E_g = 1.42 eV) utilized in high-efficiency optoelectronic lasers and solar cells.