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Topic: Conduction band


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  Conduction band - ArticleWorld   (Site not responding. Last check: 2007-10-03)
Conduction band refers to the area across which valence electrons move in order to accommodate a higher energy state.
When the valence band electrons have sufficient energy to jump a so-called ‘forbidden gap’ and onto the conduction band, an electronic current is possible.
The probability is directly proportional to, where Eg stands for the energy of the band gap, k stands for Boltzmann’s constant and T denotes the temperature of the semiconductor material.
www.articleworld.org /index.php/Conduction_band   (399 words)

  
 Band Theory for Solids
In insulators the electrons in the valence band are separated by a large gap from the conduction band, in conductors like metals the valence band overlaps the conduction band, and in semiconductors there is a small enough gap between the valence and conduction bands that thermal or other excitations can bridge the gap.
Most solid substances are insulators, and in terms of the band theory of solids this implies that there is a large forbidden gap between the energies of the valence electrons and the energy at which the electrons can move freely through the material (the conduction band).
The increase in conductivity with temperature can be modeled in terms of the Fermi function, which allows one to calculate the population of the conduction band.
hyperphysics.phy-astr.gsu.edu /hbase/solids/band.html   (623 words)

  
 UW-Madison MRSEC   (Site not responding. Last check: 2007-10-03)
The band of unoccupied orbitals is known as the conduction band.
Conduction occurs when electrons are promoted from the valence band to the conduction band, where they can move throughout the solid.
The band gap energy, Eg, shown as the double-headed arrow, is the separation between the top of the valence band and the bottom of the conduction band.
mrsec.wisc.edu /Edetc/background/LED/band.htm   (326 words)

  
 Band gap
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.
An intrinsic (pure) semiconductor's conductivity is strongly dependent on the band gap.
Band gap decreases with increasing temperature, in a process related to thermal expansion[?].
www.ebroadcast.com.au /lookup/encyclopedia/ba/Bandgap.html   (280 words)

  
 Energy band formation
The band structure is in general divided into several bands, band 1, band 2, band 3 and so on.
The inclusion of band structure in Monte Carlo simulations is discussed in Shichijo and Hess.
In the case of very high field transport, which requires the better physical model of the full band structure, it is also possible to use a hybrid approach which treats the less energetic particles with the non-parabolic band formulation.
www.mtmi.vu.lt /pfk/funkc_dariniai/quant_mech/bands.htm   (1339 words)

  
 Chapter 19. Electrical Properties
The precise location of the bands and band gaps depends on the type of atom (e.g., Si vs. Al), the distance between atoms in the solid, and the atomic arrangement (e.g., carbon vs. diamond).
Electrical conduction requires that electrons be able to gain energy in an electric field; this is not possible in these materials because that would imply that the electrons are promoted into the forbidden band gap.
Conduction in insulators is by electrons in the conduction band and by holes in the valence band.
www.virginia.edu /bohr/mse209/chapter19.htm   (2258 words)

  
 Electrical conduction Summary
Conduction is well-described by Ohm's Law, which states that the current is proportional to the applied electric field.
Bands which are completely full of electrons cannot conduct electricity, because there is no state of nearby energy to which the electrons can jump.
A solid with filled bands is an insulator, but at finite temperature, electrons can be thermally excited from the valence band to the next highest, the conduction band.
www.bookrags.com /Electrical_conduction   (1542 words)

  
 Chapter 4: Energy Bands   (Site not responding. Last check: 2007-10-03)
The electronic conductivity of a material is determined by the properties of its constituent atoms or molecules, and by the manner in which they are arranged in the lattice (1).
The valance band consists of electrons that, because they have relatively low energy, are associated with individual atoms or molecules: the conduction band contains more energetic electrons that are free to move throughout the material in response to applied electromagnetic energy.
If the valance and conduction bands are separated by a small gap, then, at typical temperatures, thermal activity will deplete the valance band and populate the conduction band; such a material is a conductor.
www.ortho.lsuhsc.edu /Faculty/Marino/EL/EL4/Energy.html   (661 words)

  
 Basic Electricity Tutorial - Band Theory
The farther the electron is from the nucleus and the fewer neighbors an electron has in the valance band the smaller the gap is between the valance band and the conductive band.
This means less energy is required to move it to the conduction band where it then becomes a free electron and is able to participate in the conduction process.
In metals the gap is non existent and the valance band and the conduction band overlap slightly.
www.electricalknowledge.com /basicelectricity2.asp   (326 words)

  
 Chem 101 (SEAS) Conduction Properties
For compounds where the separation in energy of the bonding and antibonding orbitals is large, the broadening of the levels in the solid state is insufficient to cause overlap of the resultant bands.
Conduction requires transfer of electrons to the conduction band across the very large band gap.
As the separation of the bonding and antibonding bands decreases the band gap decreases.
www.seas.upenn.edu /~chem101/sschem/conduction.html   (770 words)

  
 The photodiode
Although there may be an infinite number of bands in the band structure of a given material, there are two bands that are of particular significance in determining the electronic and optical properties of a material.
In semiconductor and insulator materials, this is the gap between the valence band and the conduction band.
Both bands can contribute to the conduction of current, but the conductivity is low, because the number of unoccupied states in the valence band and the number of occupied state in the conduction band is small.
electron9.phys.utk.edu /optics421/modules/m4/photodiode.htm   (1304 words)

  
 band gap
In a semiconductor, such as silicon, the energy difference between the highest valence band and the lowest conduction band.
The band gap energy is the amount of energy (in electron volts) required to free an outer shell electron from its orbit about the nucleus to a free state, and thus promote it from the valence to the conduction level.
To free an electron, the energy of a photon must be at least as great as the band gap energy.
www.daviddarling.info /encyclopedia/B/AE_band_gap.html   (379 words)

  
 Band Gap   (Site not responding. Last check: 2007-10-03)
The band gap of a semiconductor is the minimum energy required to move an electron from its bound state to a free state where it can participate in conduction.
The band structure of a semiconductor gives the energy of the electrons on the y-axis and is called a "band diagram".
Once the electron is in the conduction band, it is free to move about the semiconductor and participate in conduction.
www.udel.edu /igert/pvcdrom/SEMICON/EG.HTM   (289 words)

  
 Semiconductors
Conduction is equally possible in the valence band.
In a semiconductor, the distance between the valence band and the conduction band is fairly small.
Also, the band gap to cross between the valence and conduction band is very large.
nobelprize.org /educational_games/physics/semiconductors/19.html   (309 words)

  
 Striking Effects of Nitrogen in Semiconductor Alloy Explained
The band gap is the difference in energy between a semiconductor's valence band, which is filled with electrons, and its conduction band, which is empty.
(Bands are not physical locations but energy levels, analogous to the energy levels of electron orbitals around an atomic nucleus.) Since charge cannot flow in a completely full band or a completely empty one, pure semi-conductors are usually insulators at low temperatures.
Different colors of modulated light revealed the unmistakable signature of two conduction bands; in agreement with Walukiewicz's model, the conduction bands initially moved closer and then grew farther apart as the pressure was gradually increased.
www.lbl.gov /Science-Articles/Archive/nitrogen-solar-cell.html   (1277 words)

  
 LED
As electrons continue to come into the conduction band, they will be pushed to the p-type side of the p-n junction, which has more space to hold electrons (you can think of the "positive" side attracting the negatively-charged electrons).
Electrons falling from the higher-energy band of orbitals (conduction band) to the lower-energy band of orbitals (valence band) in the p-type semiconductor results in the atoms going from a higher-energy state to a lower-energy state (i.e., becoming more stable).
As the electrons cross the band gap, energy related in magnitude to the size of the band gap is released in the form of light.
www.chemistry.wustl.edu /~courses/genchem/Tutorials/LED/LED.htm   (788 words)

  
 Britney's Guide to Semiconductor Basics
Metals conduct electricity easily because the energy levels between the conduction and valence band are closely spaced or there are more energy levels available than there are electrons to fill them so very little energy is required to find new energies for electrons to occupy.
Often, we are interested in transitions that occur near the bottom of the conduction band minimum to valence band maximum; In this case, the is useful to draw the bandstructure energy as a function of position, setting the wavevector k =0.
The bands in a semiconductor material are approximated by parabolic functions of k close to the bandedges.
britneyspears.ac /physics/basics/basics.htm   (2065 words)

  
 Diamonds | American Museum of Natural History
Both diamond and graphite have important applications in electronics: Diamond may be used as either an insulator (nonconductor) or a semiconductor, and graphite is commonly used as a conductor.
A substance is an electrical conductor if very little energy is required to move an electron from its bonded condition -- in the so-called valence band -- to a mobile condition in the conduction band.
In nonconductors (insulators) a large energy barrier exists between the valence band and the conduction band.
www.amnh.org /exhibitions/diamonds/electric.html   (174 words)

  
 NSM Archive - Silicon Germanium (SiGe) - Band structure
is the effective mass of the density of states in one valley of conduction band.
Both the valence and conduction band degeneracy are lifted by the uniaxial [001] strain component, which leads to the following splittings (Van de Walle and Martin, (1986)):
The conduction band degeneracy are lifted by the uniaxial [001] strain component, which leads to the following splittings (Van de Walle and Martin, (1986)):
www.ioffe.rssi.ru /SVA/NSM/Semicond/SiGe/bandstr.html   (1173 words)

  
 Conductors, Insulators, and Semi-Conductors
The conduction band is composed of the excited energy states of a substance, and it contains electrons that have been thermally or otherwise excited from the valence band.
The electrons in the conduction band are able to freely move about the substance and conduct electricity if an external electric field is applied.
In conductors, the valence band and the conduction band overlap.
www.phy.duke.edu /courses/217/MottScatteringReport/node18.html   (523 words)

  
 Material grabs more sun TRN 042104
A bandgap is the energy required to push an electron from a material's valence band to the conduction band where electrons are free to flow.
The researchers found that in the case of zinc-manganese-tellurium, instead of splitting the conduction band, introduced oxygen molecules "formed their own band well separated from the original conduction band," said Walukiewicz.
The difference between the material's valence band and first conduction band, or the amount of energy needed to push an electron from one to the other, provided a bandgap that absorbs photons that contain 1.8 electron volt.
www.trnmag.com /Stories/2004/042104/Material_grabs_more_sun_042104.html   (739 words)

  
 Types of Recombination   (Site not responding. Last check: 2007-10-03)
Any electron which exists in the conduction band is in a meta-stable state and will eventually fall back to a lower energy position in the valance band.
However, for photovoltaic devices which for terrestrial applications are made out of silicon, it is unimportant since silicon's band gap is an "indirect" band gap which does allow a direct transition for an electron in the valence band to the conduction band.
Therefore, if an energy is introduced close to either band edge, recombination is less likely as the electron is likely to be re-emitted to the conduction band edge rather than recombine with a hole which moves into the same energy state from the valence band.
www.udel.edu /igert/pvcdrom/SEMICON/RECTYPE.HTM   (419 words)

  
 DAMOCLES: Numerical algorithms -- Band structure and scattering rates
The inclusion of the spin-orbit interaction -- necessary for the valence bands -- has required a re-working of the band structure and the nonlocal approximation has been adopted for the valence bands of those materials for which hole transport has been implemented.
This is one of the reasons why the conduction bands using nonlocal pseudopotential are being recalculated and implemented in DAMOCLES (still in progress).
Values labeled 'intra-band 1' are relative to intra-band transitions within the lowest-lying conduction band, those labeled 'inter-band and intra-high-bands' are relative to all other transitions, intraband within higher-energy bands and all inter-band processes.
www.research.ibm.com /DAMOCLES/html_files/numerics.html   (2537 words)

  
 Doped Semiconductors   (Site not responding. Last check: 2007-10-03)
The application of band theory to n-type and p-type semiconductors shows that extra levels have been added by the impurities.
The addition of donor impurities contributes electron energy levels high in the semiconductor band gap so that electrons can be easily excited into the conduction band.
The addition of acceptor impurities contributes hole levels low in the semiconductor band gap so that electrons can be easily excited from the valence band into these levels, leaving mobile holes in the valence band.
hyperphysics.phy-astr.gsu.edu /hbase/solids/dsem.html   (258 words)

  
 Energy bands
The splitting results in an energy band containing 2N states in the 2s band and 6N states in the 2p band, where N is the number of atoms in the crystal.
An important feature of an energy band diagram, which is not included on the simplified diagram, is whether the conduction band minimum and the valence band maximum occur at the same value for the wavenumber.
For instance, for a single band minimum described by a longitudinal mass and two transverse masses the effective mass for density of states calculations is the geometric mean of the three masses.
ece-www.colorado.edu /~bart/book/book/chapter2/ch2_3.htm   (3344 words)

  
 Radiative Transitions
(a) intrinsic (valence band to conduction band) transition, (b) extrinsic (deep donor to conduction band) transition, (c) extrinsic (deep acceptor to valence band) transition, (d) extrinsic (deep acceptor to conduction band) transition.
The rate that electrons will be absorbed is determined by the number of unoccupied states in the conduction band, the number of occupied states in the valence band and density of photons of energy equal to the transition energy.
The important part of this equation is that the probability of finding an electron in the conduction band has to be greater than the probability of finding an electron in the valence band or alternatively, there must be a population inversion.
www.mtmi.vu.lt /pfk/funkc_dariniai/rad_transitions.htm   (1036 words)

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