Editing Light-emitting diode (section)

== Single-color LEDs ==
[[File:Blue light emitting diodes over a proto-board.jpg|thumb|upright|[[Blue]] LEDs]]
{{external media | width = 210px | float = right | headerimage= [[File:Herb Maruska original blue LED College of New Jersey Sarnoff Collection.png|210px]] | video1 = [https://vimeo.com/109205062 "The Original Blue LED"], [[Science History Institute]]}}

By [[Light-emitting diode physics#Materials|selection of different semiconductor materials]], single-color LEDs can be made that emit light in a narrow band of wavelengths from near-infrared through the visible spectrum and into the ultraviolet range. The required operating voltages of LEDs increase as the emitted wavelengths become shorter (higher energy, red to blue), because of their increasing semiconductor band gap.
{{anchor|blue LED}}

Blue LEDs have an active region consisting of one or more InGaN [[quantum well]]s sandwiched between thicker layers of GaN, called cladding layers. By varying the relative In/Ga fraction in the InGaN quantum wells, the light emission can in theory be varied from violet to amber.

[[Aluminium gallium nitride]] (AlGaN) of varying Al/Ga fraction can be used to manufacture the cladding and quantum well layers for [[ultraviolet]] LEDs, but these devices have not yet reached the level of efficiency and technological maturity of InGaN/GaN blue/green devices. If unalloyed GaN is used in this case to form the active quantum well layers, the device emits near-ultraviolet light with a peak wavelength centred around 365&nbsp;nm. Green LEDs manufactured from the InGaN/GaN system are far more efficient and brighter than green LEDs produced with non-nitride material systems, but practical devices still exhibit efficiency too low for high-brightness applications.{{citation needed|date=March 2016}}

With [[Aluminium gallium nitride|AlGaN]] and [[aluminium gallium indium nitride|AlGaInN]], even shorter wavelengths are achievable. Near-UV emitters at wavelengths around 360–395&nbsp;nm are already cheap and often encountered, for example, as [[black light]] lamp replacements for inspection of anti-[[counterfeiting]] UV watermarks in documents and bank notes, and for [[UV curing#LEDs|UV curing]]. Substantially more expensive, shorter-wavelength diodes are commercially available for wavelengths down to 240&nbsp;nm.<ref>{{cite journal |url=http://www.semiconductor-today.com/features/SemiconductorToday%20-%20Going%20deep%20for%20UV%20sterilization%20LEDs.pdf |journal=Semiconductor Today |title=Going Deep for UV Sterilization LEDs |page=82 |volume=5 |issue=3 |author=Cooke, Mike |date=April–May 2010 |url-status=dead |archive-url=https://web.archive.org/web/20130515030549/http://www.semiconductor-today.com/features/SemiconductorToday%20-%20Going%20deep%20for%20UV%20sterilization%20LEDs.pdf |archive-date=May 15, 2013 }}</ref> As the photosensitivity of microorganisms approximately matches the absorption spectrum of [[DNA]], with a peak at about 260&nbsp;nm, UV LED emitting at 250–270&nbsp;nm are expected in prospective disinfection and sterilization devices. Recent research has shown that commercially available UVA LEDs (365&nbsp;nm) are already effective disinfection and sterilization devices.<ref name="water sterilization">{{Cite journal | last1 = Mori | first1 = M. | last2 = Hamamoto | first2 = A. | last3 = Takahashi | first3 = A. | last4 = Nakano | first4 = M. | last5 = Wakikawa | first5 = N. | last6 = Tachibana | first6 = S. | last7 = Ikehara | first7 = T. | last8 = Nakaya | first8 = Y. | last9 = Akutagawa | first9 = M. | doi = 10.1007/s11517-007-0263-1 | last10 = Kinouchi | first10 = Y. | title = Development of a new water sterilization device with a 365 nm UV-LED | journal = Medical & Biological Engineering & Computing | volume = 45 | issue = 12 | pages = 1237–1241 | year = 2007 | pmid = 17978842 | s2cid = 2821545 | doi-access = free }}</ref>
UV-C wavelengths were obtained in laboratories using [[aluminium nitride]] (210&nbsp;nm),<ref name="aln">{{Cite journal | last1 = Taniyasu | first1 = Y. | last2 = Kasu | first2 = M. | last3 = Makimoto | first3 = T. | doi = 10.1038/nature04760 | title = An aluminium nitride light-emitting diode with a wavelength of 210 nanometres | journal = Nature | volume = 441 | issue = 7091 | pages = 325–328 | year = 2006 | pmid = 16710416 | bibcode = 2006Natur.441..325T| s2cid = 4373542 }}</ref> [[boron nitride]] (215&nbsp;nm)<ref name="BN">{{Cite journal | last1 = Kubota | first1 = Y. | last2 = Watanabe | first2 = K. | last3 = Tsuda | first3 = O. | last4 = Taniguchi | first4 = T. | title = Deep Ultraviolet Light-Emitting Hexagonal Boron Nitride Synthesized at Atmospheric Pressure | doi = 10.1126/science.1144216 | journal = Science | volume = 317 | issue = 5840 | pages = 932–934 | year = 2007 | pmid = 17702939| bibcode = 2007Sci...317..932K | doi-access = free }}</ref><ref name="bn2">{{Cite journal | last1 = Watanabe | first1 = K. | last2 = Taniguchi | first2 = T. | last3 = Kanda | first3 = H. | doi = 10.1038/nmat1134 | title = Direct-bandgap properties and evidence for ultraviolet lasing of hexagonal boron nitride single crystal | journal = Nature Materials | volume = 3 | issue = 6 | pages = 404–409 | year = 2004 | pmid = 15156198 |bibcode = 2004NatMa...3..404W | s2cid = 23563849 }}</ref> and [[diamond]] (235&nbsp;nm).<ref name="dia">{{Cite journal | last1 = Koizumi | first1 = S. | last2 = Watanabe | first2 = K. | last3 = Hasegawa | first3 = M. | last4 = Kanda | first4 = H. | title = Ultraviolet Emission from a Diamond pn Junction | doi = 10.1126/science.1060258 | journal = Science | volume = 292 | issue = 5523 | pages = 1899–1901 | year = 2001 | pmid = 11397942| bibcode = 2001Sci...292.1899K| s2cid = 10675358 }}</ref>