Valence and conduction bands

<h2 id="band-gap">Band gap</h2>
<p class="note">Main article: <a href="/facts/Band_gap/IjIeh95l">Band gap</a></p>
<p>In semiconductors and insulators the two bands are separated by a <a href="/facts/Band_gap/IjIeh95l">band gap</a>, while in <a href="/facts/Electrical_conductor/BSuyupLP">conductors</a> the bands overlap. A band gap is an energy range in a solid where no electron states can exist due to the <a href="/facts/Quantization_(physics)/fvs2Jwpn">quantization</a> of energy. Within the concept of bands, the energy gap between the valence band and the conduction band is the band gap.<a class="footnote-ref" id="fnref:1" href="#fn:1"><sup>1</sup></a> Electrical conductivity of non-metals is determined by the susceptibility of electrons to be excited from the valence band to the conduction band.
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<h2 id="electrical-conductivity">Electrical conductivity</h2>
<i>Semiconductor band structure</i><i>See <a href="/facts/Electrical_conduction/akyCKvMy">electrical conduction</a> and <a href="/facts/Semiconductor/zFf3mGTE">semiconductor</a> for a more detailed description of band structure.</i>
<p>In solids, the ability of electrons to act as <a href="/facts/Charge_carrier/wpjjql4x">charge carriers</a> depends on the availability of vacant electronic states. This allows the electrons to increase their energy (i.e., <a href="/facts/Accelerate/UVDmjYvR">accelerate</a>) when an <a href="/facts/Electric_field/tt4MooBs">electric field</a> is applied. Similarly, holes (empty states) in the almost filled valence band also allow for conductivity.
</p><p>As such, the <a href="/facts/Electrical_conductivity/akyCKvMy">electrical conductivity</a> of a solid depends on its capability to flow electrons from the valence to the conduction band. Hence, in the case of a semimetal with an overlap region, the electrical conductivity is high. If there is a small band gap (Eg), then the flow of electrons from valence to conduction band is possible only if an external energy (thermal, etc.) is supplied; these groups with small Eg are called <a href="/facts/Semiconductors/zFf3mGTE">semiconductors</a>. If the Eg is sufficiently high, then the flow of electrons from valence to conduction band becomes negligible under normal conditions; these groups are called <a href="/facts/Insulator_(electricity)/SfSXkrh5">insulators</a>.
</p><p>There is some conductivity in semiconductors, 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 <a href="/facts/Electron_hole/YymdTv9d">hole</a> they left behind in the valence band. The hole is an empty state that allows electrons in the valence band some degree of freedom.
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<h2 id="band-edge-shifts-of-semiconductor-nanoparticles">Band edge shifts of semiconductor nanoparticles</h2>
<p>The edge shifting of size-dependent conduction and/or valence band is a phenomenon being studied in the field of <a href="/facts/Quantum_dot/K5Ytv8Yw">semiconductor nanocrystals</a>. The radius limit of occurrence of the semiconductor nanocrystal is the effective <a href="/facts/Bohr_radius/vvP1lghl">Bohr radius</a> of the nanocrystal. The conduction and/or valence band edges shift to higher energy levels under this radius limit due to discrete optical transitions when semiconductor nanocrystal is restricted by the exciton. As a result of this edge shifting, the size of the conduction and/or valence band is decreased. This size-dependent edge shifting of conduction and/or valence band can provide plenty of useful information regarding the size or concentration of the semiconductor nanoparticles or band structures.<a class="footnote-ref" id="fnref:2" href="#fn:2"><sup>2</sup></a>
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<h2 id="see-also">See also</h2>
<ul><li><a href="/facts/Electrical_conduction/akyCKvMy">Electrical conduction</a> for more information about conduction in solids, and another description of band structure.</li>
<li><a href="/facts/Fermi_liquid/BubT8nPx">Fermi sea</a></li>
<li><a href="/facts/HOMO%2fLUMO/XyofpH0p">HOMO/LUMO</a></li>
<li><a href="/facts/Semiconductor/zFf3mGTE">Semiconductor</a> for a full explanation of the band structure of materials.</li>
<li><a href="/facts/Valleytronics/UbNzK72G">Valleytronics</a></li></ul>

<h3>Citations</h3>

<h3>General references</h3>
<ul><li>Kittel, Charles (2005). <i><a href="/facts/Introduction_to_Solid_State_Physics_(Kittel_book)/AHYGtnuX">Introduction to Solid State Physics</a></i>. Wiley. <a href="/facts/ISBN_(identifier)/15AdSPa9">ISBN</a> 0-471-41526-X.</li>
<li>Kornic, Steve (11 April 1997). <a href="https://web.archive.org/web/20210304065130/http://www.chembio.uoguelph.ca/educmat/chm729/band/val1.htm">"The Valence Band"</a>. Chembio. Archived from <a href="http://www.chembio.uoguelph.ca/educmat/chm729/band/val1.htm">the original</a> on 4 March 2021. Retrieved 8 December 2021.</li>
<li>Nave, Carl R. (Rod) (1999). <a href="http://hyperphysics.phy-astr.gsu.edu/hbase/solids/band.html">"Band Theory for Solids"</a>. Hyperphysics. Retrieved 8 December 2021.</li></ul>
<h2 id="external-links">External links</h2>
<ul><li><a href="https://web.archive.org/web/20080515210419/http://www.ee.byu.edu/cleanroom/EW_ternary.phtml">Direct Band Gap Energy Calculator</a></li></ul>

<h2 id="references">References</h2>

<ol>
<li id="fn:1"><p>Cox, P. A. (1987). The electronic structure and chemistry of solids. Oxford [Oxfordshire]: Oxford University Press. ISBN 0-19-855204-1. OCLC 14213060. <a href="0-19-855204-1" target="_blank">0-19-855204-1</a> <a href="#fnref:1" class="footnote-back-ref">↩</a></p></li>
<li id="fn:2"><p>Jasieniak, Jacek; Califano, Marco; Watkins, Scott E. (2011-06-22). "Size-Dependent Valence and Conduction Band-Edge Energies of Semiconductor Nanocrystals". ACS Nano. 5 (7): 5888–5902. doi:10.1021/nn201681s. ISSN 1936-0851. PMID 21662980. <a href="https://dx.doi.org/10.1021/nn201681s" target="_blank">https://dx.doi.org/10.1021/nn201681s</a> <a href="#fnref:2" class="footnote-back-ref">↩</a></p></li>
</ol>

Valence and conduction bands open-in-new

Valence and conduction bands