In solid state physics (and related applied fields), the band gap is the energy difference between the top of the valence band and the bottom of the conduction band in insulators and semiconductors. It is often spelt "bandgap".
The band gap of a semiconductor is important for a number of reasons. An intrinsic (pure) semiconductor's conductivity is strongly dependent on the band gap. This is because the only available carriers for conduction are the electrons which manage to get enough thermal energy to be excited from the valence band into the conduction band. From Fermi-Dirac statistics, the probability of these excitations occurring is proportional to:
- exp is the exponential function
- Eg is the band gap energy
- k is Boltzmann's constant
- T is temperature
|Common materials at room temperature|
The difference between semiconductors and insulators is rather ambiguous. Indeed, according to one definition, a semiconductor is a type of insulator. In general, a material with a sufficiently large band gap will be an insulator. The figure of 3 eV is sometimes given. Mobility also plays a role in determining a material's informal classification.
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