Alternate Definitions for band gap

Definition: The energy it takes to excite an electron from the top of the valence band to the bottom of the conduction band. Among other things, this dictates what wavelengths of light are absorbed by a material.

Example: The band gap of Si is 1.1 eV, so it starts absorbing in the infrared spectrum but also absorbs higher-energy visible and UV light.

Definition: The energy difference between the valence band and the conduction band in a semiconductor material.

Example: Gallium Arsenide (GaAs) has a relatively small band gap of 1.4 eV, making it suitable for high-frequency electronic devices.