- Valence band
solids, the valence band is the highest range of electronenergies where electrons are normally present at absolute zero. In semiconductors and insulators, there is a band gapabove the valence band, followed by a conduction bandabove that. In metals, the conduction band has no energy gap separating it from the valence band (basically, this is correct only for semimetals. All solids have forbidden energy levels between the energy bands). The rest of this article refers to the valence band in semiconductors and insulators.for a more detailed description of band structure."
Semiconductors and insulators owe their low conductivity to the properties of the valence band in those materials. It just so happens that the number of electrons is precisely equal to the number of states available up to the top of the valence band. There are no available states in the band gap. This means that when an
electric fieldis applied, the electrons cannot increase their energy (i.e., accelerate) because there are no states available to the electrons where they would be moving faster than they are already going.
There is some conductivity in insulators, however. This is due to thermal excitation—some of the electrons get enough energy to jump the band gap in one go. Once they are in the conduction band, they can conduct electricity, as can the hole they left behind in the valence band. The hole is an empty state that allows electrons in the valence band some degree of freedom.
It is a common misconception to refer to electrons in insulators as "bound"—as if they were somehow attached to the nucleus and could not move. Electrons in insulators are free to move. They are also delocalized, having no well-defined position within the sample.
Semiconductorfor a full explanation of the band structure of materials.
Electrical conductionfor more information about conduction in solids, and another description of band structure.
* [http://www.chembio.uoguelph.ca/educmat/chm729/band/val1.htm Chembio]
* [http://hyperphysics.phy-astr.gsu.edu/hbase/solids/band.html Hyperphysics]
* [http://www.ee.byu.edu/cleanroom/EW_ternary.phtml Direct Band Gap Energy Calculator]
Wikimedia Foundation. 2010.
Look at other dictionaries:
valence band — valentinė juosta statusas T sritis fizika atitikmenys: angl. valence band vok. Valenzband, n; Valenzzone, f rus. валентная зона, f pranc. bande de valence, f … Fizikos terminų žodynas
valence band — valentinė juosta statusas T sritis chemija apibrėžtis Energijos lygmuo, kuriame yra valentiniai kristalo elektronai. atitikmenys: angl. valence band rus. валентная зона … Chemijos terminų aiškinamasis žodynas
valence band — noun The highest range of electron energies in an insulator or semiconductor that can be populated; it corresponds to the valence electrons of the constituent atoms … Wiktionary
valence band — noun Date: 1953 the range of permissible energy values that are the highest energies an electron can have and still be associated with a particular atom of a solid material compare conduction band … New Collegiate Dictionary
Valence Band — The highest energy band in a semiconductor that can be filled with electrons … Energy terms
valence band — noun : the range of permissible energy values that are the highest energies an electron can have and still be associated with a particular atom of a solid material compare conduction band herein … Useful english dictionary
valence band edge — valentinės juostos kraštas statusas T sritis fizika atitikmenys: angl. valence band edge vok. Valenzbandkante, f rus. край валентной зоны, m pranc. bord de la bande de valence, m … Fizikos terminų žodynas
Valence — may refer to:In molecules, atoms, or subatomic particles* Valence (chemistry) * Valence bond theory in chemistry * Valence shell in chemistry * Valence band in physics * Valence quarks (see quark model) in particle physics In other sciences*… … Wikipedia
Band — may refer to a specific group: * Band (music), a company of musicians * School band, a group of student musicians who rehearse and perform instrumental music together * Band (radio), a range of frequencies or wavelengths used in radio… … Wikipedia
Band gap — This article is about solid state physics. For voltage control circuitry in electronics, see Bandgap voltage reference. In solid state physics, a band gap, also called an energy gap or bandgap, is an energy range in a solid where no electron… … Wikipedia