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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 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 ...
The band offsets are determined by two kinds of factors for the interface, the band discontinuities and the built-in potential. These discontinuities are caused by the difference in band gaps of the semiconductors and are distributed between two band discontinuities, the valence-band discontinuity, and the conduction-band discontinuity.
For intrinsic semiconductors (undoped), the valence band is fully filled with electrons, whilst the conduction band is completely empty. The Fermi level is thus located in the middle of the band gap, the same as that of the surface states, and hence there is no charge transfer between the bulk and the surface. As a result no band bending occurs.
a is the atomic spacing (lattice constant) found in an actual crystal lattice of carbon atoms (diamond lattice) so the band structure at that spacing is the one found in diamond. At that spacing the orbitals form two bands, called the valence band and conduction band, with an energy gap of 5.5 electron volts (eV) between them.
The conduction band edge may also be indicated in an insulator, simply to demonstrate band bending effects. E V: The valence band edge likewise should be indicated in situations where electrons (or holes) are transported through the top of the valence band such as in a p-type semiconductor.
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.
BMSs can be described by three energy gaps, the spin-flip gap Δ2 in valence band (VB), band gap Δ1 and spin-flip gap Δ3 in conduction band (CB). [2] Up to now, bipolar magnetic semiconductors, together with half-metal and spin gapless semiconductor, have been viewed as three important classes of spintronic materials. [3] [4]