Electron volt (eV) is a unit for small energies. It is the energy that an electron has when it is accelerated with one volt. One electron volt is equal to the energy of `1.6021764*10^-19` joules (J).
The specification in electron volts is mainly used for semiconductors and compound semiconductors, and describes the energy required to overcome the band gap. Depending on the semiconductor, this can be less than 1 eV, but can also be several electron volts. For example, the band gap of silicon( Si) is 1.1 eV, that of gallium nitride( GaN) 3.4 eV.