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In solid-state physics, the valence band and conduction band are the bands closest to the Fermi level, and thus determine the electrical conductivity of the solid. In nonmetals, the valence band is the highest range of electron energies in which electrons are normally present at absolute zero temperature, while the conduction band is the lowest range of vacant electronic states.
The band gap (usually given the symbol ) gives the energy difference between the lower edge of the conduction band and the upper edge of the valence band. Each semiconductor has different electron affinity and band gap values. For semiconductor alloys it may be necessary to use Vegard's law to calculate these values.
The name "valence band" was coined by analogy to chemistry, since in semiconductors (and insulators) the valence band is built out of the valence orbitals. In a metal or semimetal, the Fermi level is inside of one or more allowed bands. In semimetals the bands are usually referred to as "conduction band" or "valence band" depending on whether ...
Based on the energy eigenvalues, conduction band are the high energy states (E>0) while valence bands are the low energy states (E<0). In some materials, for example, in graphene and zigzag graphene quantum dot, there exists the energy states having energy eigenvalues exactly equal to zero (E=0) besides the conduction and valence bands. These ...
At the junction of two different semiconductors there is a sharp shift in band energies from one material to the other; the band alignment at the junction (e.g., the difference in conduction band energies) is fixed. At the junction of a semiconductor and metal, the bands of the semiconductor are pinned to the metal's Fermi level.
Band diagram of semiconductor-vacuum interface showing electron affinity E EA, defined as the difference between near-surface vacuum energy E vac, and near-surface conduction band edge E C. Also shown: Fermi level E F, valence band edge E V, work function W.
A quasi Fermi level is a term used in quantum mechanics and especially in solid state physics for the Fermi level (chemical potential of electrons) that describes the population of electrons separately in the conduction band and valence band, when their populations are displaced from equilibrium.
This allows electrons to gain energy and thereby move through a conductor, such as a metal, if an electric potential difference is applied to the material. If no such states are available, the material is an insulator. Most insulators have a large band gap. This occurs because the "valence" band containing the highest energy electrons is full ...