Editing Gallium arsenide (section)

===Solar cells and detectors===
Gallium arsenide is an important semiconductor material for high-cost, high-efficiency [[solar cell]]s and is used for single-crystalline [[thin-film solar cell]]s and for [[multi-junction solar cells]].<ref>{{cite journal |last1=Yin |first1=Jun |last2=Migas |first2=Dmitri B. |last3=Panahandeh-Fard |first3=Majid |last4=Chen |first4=Shi |last5=Wang |first5=Zilong |last6=Lova |first6=Paola |last7=Soci |first7=Cesare |date=3 October 2013 |title=Charge Redistribution at GaAs/P3HT Heterointerfaces with Different Surface Polarity |journal=The Journal of Physical Chemistry Letters |volume=4 |issue=19 |pages=3303–3309 |doi=10.1021/jz401485t}}</ref>

The first known operational use of GaAs solar cells in space was for the [[Venera 3]] mission, launched in 1965. The GaAs solar cells, manufactured by Kvant, were chosen because of their higher performance in high temperature environments.<ref>{{cite book |author1=Strobl, G.F.X. |title=High-Efficient Low-Cost Photovoltaics: Recent Developments |author2=LaRoche, G. |author3=Rasch, K.-D. |author4=Hey, G. |publisher=Springer |year=2009 |isbn=978-3-540-79359-5 |chapter=2: From Extraterrestrial to Terrestrial Applications |doi=10.1007/978-3-540-79359-5 |chapter-url=https://cds.cern.ch/record/1338850}}</ref>  GaAs cells were then used for the [[Lunokhod programme|Lunokhod rovers]] for the same reason.{{citation needed|date=September 2023}}

In 1970, the GaAs heterostructure solar cells were developed by the team led by [[Zhores Alferov]] in the [[USSR]],<ref>Alferov, Zh. I., V. M. Andreev, M. B. Kagan, I. I. Protasov and V. G. Trofim, 1970, ‘‘Solar-energy converters based on p-n Al<sub>x</sub>Ga<sub>1−x</sub>As-GaAs heterojunctions,’’ ''Fiz. Tekh. Poluprovodn. 4'', 2378 (''Sov. Phys. Semicond. 4'', 2047 (1971))</ref><ref>[https://web.archive.org/web/20090225094509/http://www.im.isu.edu.tw/seminar/2005.11.16.pdf Nanotechnology in energy applications]. im.isu.edu.tw. 16 November 2005 (in Chinese) p. 24</ref><ref>[http://nobelprize.org/nobel_prizes/physics/laureates/2000/alferov-lecture.pdf Nobel Lecture] by [[Zhores Alferov]] at nobelprize.org, p. 6</ref> achieving much higher efficiencies. In the early 1980s, the efficiency of the best GaAs solar cells surpassed that of conventional, [[crystalline silicon]]-based solar cells. In the 1990s, GaAs solar cells took over from silicon as the cell type most commonly used for [[photovoltaic array]]s for satellite applications. Later, dual- and triple-junction solar cells based on GaAs with [[germanium]] and [[indium gallium phosphide]] layers were developed as the basis of a triple-junction solar cell, which held a record efficiency of over 32% and can operate also with light as concentrated as 2,000 suns. This kind of solar cell powered the [[Mars Exploration Rover]]s [[Spirit rover|Spirit]] and [[Opportunity rover|Opportunity]], which explored [[Mars]]' surface. Also many [[Solar car racing|solar car]]s utilize GaAs in solar arrays, as did the Hubble Telescope.<ref>{{Cite web |title=Hubble's Instruments Including Control and Support Systems (Cutaway) |url=https://hubblesite.org/contents/media/images/4521-Image |access-date=2022-10-11 |website=HubbleSite.org |language=en}}</ref>

GaAs-based devices hold the world record for the highest-efficiency single-junction solar cell at 29.1% (as of 2019). This high efficiency is attributed to the extreme high quality GaAs epitaxial growth, surface passivation by the AlGaAs,<ref>{{Cite journal |author=Schnitzer, I. |last2=Yablonovitch |first2=E |last3=Caneau |first3=C |last4=Gmitter |first4=T.J |display-authors=1 |year=1993 |title=Ultrahigh spontaneous emission quantum efficiency, 99.7 % internally and 72 % externally, from AlGaAs/GaAs/AlGaAs double heterostructures |journal=Applied Physics Letters |volume=62 |issue=2 |page=131 |bibcode=1993ApPhL..62..131S |doi=10.1063/1.109348 |s2cid=14611939}}</ref> and the promotion of photon recycling by the thin film design.<ref>{{Cite journal |author=Wang, X. |last2=Khan |first2=M.R |last3=Gray |first3=J |last4=Alam |first4=M.A. |last5=Lundstrom |first5=M.S |display-authors=1 |year=2013 |title=Design of GaAs Solar Cells Operating Close to the Shockley–Queisser Limit |journal=IEEE Journal of Photovoltaics |volume=3 |issue=2 |page=737 |doi=10.1109/JPHOTOV.2013.2241594 |s2cid=36523127}}</ref> GaAs-based [[photovoltaics]] are also responsible for the highest efficiency (as of 2022) of conversion of light to electricity, as researchers from the [[Fraunhofer Institute for Solar Energy Systems]] achieved a 68.9% efficiency when exposing a GaAs [[thin film]] photovoltaic cell to monochromatic laser light with a wavelength of 858 nanometers.<ref>{{Cite web |date=28 June 2021 |title=Record Efficiency of 68.9% for GaAs Thin Film Photovoltaic Cell Under Laser Light - Fraunhofer ISE |url=https://www.ise.fraunhofer.de/en/press-media/press-releases/2021/record-efficiency-68-9-percent-for-gaas-thin-film-photovoltaic-cell.html |access-date=2022-10-11 |website=Fraunhofer Institute for Solar Energy Systems ISE |language=en}}</ref>

Today, multi-junction GaAs cells have the highest efficiencies of existing photovoltaic cells and trajectories show that this is likely to continue to be the case for the foreseeable future.<ref>{{Citation |last=Yamaguchi |first=Masafumi |title=High-Efficiency GaAs-Based Solar Cells |date=2021-04-14 |work=Post-Transition Metals |editor-last=Muzibur Rahman |editor-first=Mohammed |url=https://www.intechopen.com/books/post-transition-metals/high-efficiency-gaas-based-solar-cells |access-date=2022-10-11 |publisher=IntechOpen |language=en |doi=10.5772/intechopen.94365 |isbn=978-1-83968-260-5 |s2cid=228807831 |editor2-last=Mohammed Asiri |editor2-first=Abdullah |editor3-last=Khan |editor3-first=Anish |editor4-last=Inamuddin |doi-access=free}}</ref> In 2022, [[Rocket Lab]] unveiled a solar cell with 33.3% efficiency<ref>{{Cite web |date=10 March 2022 |title=Rocket Lab unveils space solar cell with 33.3% efficiency |url=https://isolarparts.com/ko/blogs/nwes2/rocket-lab-unveils-space-solar-cell-with-33-3-efficiency |access-date=2022-10-12 |website=solarparts |language=ko}}</ref> based on inverted metamorphic multi-junction (IMM) technology. In IMM, the lattice-matched (same lattice parameters) materials are grown first, followed by mismatched materials. The top cell, GaInP, is grown first and lattice matched to the GaAs substrate, followed by a layer of either GaAs or GaInAs with a minimal mismatch, and the last layer has the greatest lattice mismatch.<ref>{{Cite web |last1=Duda |first1=Anna |last2=Ward |first2=Scott |last3=Young |first3=Michelle |date=February 2012 |title=Inverted Metamorphic Multijunction (IMM) Cell Processing Instructions |url=https://www.nrel.gov/docs/fy12osti/54049.pdf |access-date=October 11, 2022 |website=National Renewable Energy Laboratory}}</ref> After growth, the cell is mounted to a secondary handle and the GaAs substrate is removed. A main advantage of the IMM process is that the inverted growth according to lattice mismatch allows a path to higher cell efficiency.

Complex designs of Al<sub>x</sub>Ga<sub>1−x</sub>As-GaAs devices using [[quantum well]]s can be sensitive to infrared radiation ([[QWIP]]).

GaAs diodes can be used for the detection of X-rays.<ref>[http://ppewww.physics.gla.ac.uk/preprints/97/05/psd1/psd1.html Glasgow University report on CERN detector]. Ppewww.physics.gla.ac.uk. Retrieved on 2013-10-16.</ref>

==== Future outlook of GaAs solar cells ====
Despite GaAs-based photovoltaics being the clear champions of efficiency for solar cells, they have relatively limited use in today's market. In both world electricity generation and world electricity generating capacity, solar electricity is growing faster than any other source of fuel (wind, hydro, biomass, and so on) for the last decade.<ref>{{Cite journal |last1=Haegel |first1=Nancy |last2=Kurtz |first2=Sarah |date=November 2021 |title=Global Progress Toward Renewable Electricity: Tracking the Role of Solar |journal=IEEE Journal of Photovoltaics |publication-date=20 September 2021 |volume=11 |issue=6 |pages=1335–1342 |doi=10.1109/JPHOTOV.2021.3104149 |issn=2156-3381 |s2cid=239038321 |doi-access=free}}</ref> However, GaAs solar cells have not currently been adopted for widespread solar electricity generation. This is largely due to the cost of GaAs solar cells - in space applications, high performance is required and the corresponding high cost of the existing GaAs technologies is accepted. For example, GaAs-based photovoltaics show the best resistance to gamma radiation and high temperature fluctuations, which are of great importance for spacecraft.<ref>{{Cite journal |last1=Papež |first1=Nikola |last2=Gajdoš |first2=Adam |last3=Dallaev |first3=Rashid |last4=Sobola |first4=Dinara |last5=Sedlák |first5=Petr |last6=Motúz |first6=Rastislav |last7=Nebojsa |first7=Alois |last8=Grmela |first8=Lubomír |date=2020-04-30 |title=Performance analysis of GaAs based solar cells under gamma irradiation |url=https://www.sciencedirect.com/science/article/pii/S0169433220300854 |journal=Applied Surface Science |language=en |volume=510 |pages=145329 |bibcode=2020ApSS..51045329P |doi=10.1016/j.apsusc.2020.145329 |issn=0169-4332 |s2cid=213661192}}</ref> But in comparison to other solar cells, III-V solar cells are two to three orders of magnitude more expensive than other technologies such as silicon-based solar cells.<ref name="Horowitz-2018">{{Cite report |url=http://dx.doi.org/10.2172/1484349 |title=A Techno-Economic Analysis and Cost Reduction Roadmap for III-V Solar Cells |last1=Horowitz |first1=Kelsey A. |last2=Remo |first2=Timothy W. |date=2018-11-27 |doi=10.2172/1484349 |osti=1484349 |last3=Smith |first3=Brittany |last4=Ptak |first4=Aaron J. |s2cid=139380070}}</ref> The primary sources of this cost are the [[Epitaxy|epitaxial growth]] costs and the substrate the cell is deposited on.

GaAs solar cells are most commonly fabricated utilizing epitaxial growth techniques such as [[Metalorganic vapour-phase epitaxy|metal-organic chemical vapor deposition]] (MOCVD) and [[Hydride vapour phase epitaxy|hydride vapor phase epitaxy]] (HVPE). A significant reduction in costs for these methods would require improvements in tool costs, throughput, material costs, and manufacturing efficiency.<ref name="Horowitz-2018" /> Increasing the deposition rate could reduce costs, but this cost reduction would be limited by the fixed times in other parts of the process such as cooling and heating.<ref name="Horowitz-2018" />

The substrate used to grow these solar cells is usually germanium or gallium arsenide which are notably expensive materials. One of the main pathways to reduce substrate costs is to reuse the substrate. An early method proposed to accomplish this is epitaxial lift-off (ELO),<ref>{{Cite journal |last1=Konagai |first1=Makoto |last2=Sugimoto |first2=Mitsunori |last3=Takahashi |first3=Kiyoshi |date=1978-12-01 |title=High efficiency GaAs thin film solar cells by peeled film technology |journal=Journal of Crystal Growth |language=en |volume=45 |pages=277–280 |bibcode=1978JCrGr..45..277K |doi=10.1016/0022-0248(78)90449-9 |issn=0022-0248 |doi-access=free}}</ref> but this method is time-consuming, somewhat dangerous (with its use of [[hydrofluoric acid]]), and requires multiple post-processing steps. However, other methods have been proposed that use phosphide-based materials and hydrochloric acid to achieve ELO with [[surface passivation]] and minimal post-[[Etching (microfabrication)|etching]] residues and allows for direct reuse of the GaAs substrate.<ref>{{Cite journal |last1=Cheng |first1=Cheng-Wei |last2=Shiu |first2=Kuen-Ting |last3=Li |first3=Ning |last4=Han |first4=Shu-Jen |last5=Shi |first5=Leathen |last6=Sadana |first6=Devendra K. |date=2013-03-12 |title=Epitaxial lift-off process for gallium arsenide substrate reuse and flexible electronics |journal=Nature Communications |language=en |volume=4 |issue=1 |pages=1577 |bibcode=2013NatCo...4.1577C |doi=10.1038/ncomms2583 |issn=2041-1723 |pmid=23481385 |s2cid=205315999 |doi-access=free}}</ref> There is also preliminary evidence that [[spalling]] could be used to remove the substrate for reuse.<ref>{{Cite book |last1=Metaferia |first1=Wondwosen |title=2021 IEEE 48th Photovoltaic Specialists Conference (PVSC) |last2=Chenenko |first2=Jason |last3=Packard |first3=Corinne E. |last4=Ptak |first4=Aaron J. |last5=Schulte |first5=Kevin L. |date=2021-06-20 |publisher=IEEE |isbn=978-1-6654-1922-2 |location=Fort Lauderdale, FL, USA |pages=1118–1120 |chapter=(110)-Oriented GaAs Devices and Spalling as a Platform for Low-Cost III-V Photovoltaics |doi=10.1109/PVSC43889.2021.9518754 |osti=1869274 |chapter-url=https://ieeexplore.ieee.org/document/9518754 |s2cid=237319505}}</ref> An alternative path to reduce substrate cost is to use cheaper materials, although materials for this application are not currently commercially available or developed.<ref name="Horowitz-2018" />

Yet another consideration to lower GaAs solar cell costs could be [[concentrator photovoltaics]]. Concentrators use lenses or parabolic mirrors to focus light onto a solar cell, and thus a smaller (and therefore less expensive) GaAs solar cell is needed to achieve the same results.<ref>{{Cite journal |last1=Papež |first1=Nikola |last2=Dallaev |first2=Rashid |last3=Ţălu |first3=Ştefan |last4=Kaštyl |first4=Jaroslav |date=2021-06-04 |title=Overview of the Current State of Gallium Arsenide-Based Solar Cells |journal=Materials |language=en |volume=14 |issue=11 |pages=3075 |bibcode=2021Mate...14.3075P |doi=10.3390/ma14113075 |issn=1996-1944 |pmc=8200097 |pmid=34199850 |doi-access=free}}</ref> Concentrator systems have the highest efficiency of existing photovoltaics.<ref>{{Cite report |title=Current Status of Concentrator Photovoltaic (CPV) Technology |last1=Philipps |first1=Simon P. |last2=Bett |first2=Andreas W. |date=2015-12-01 |doi=10.2172/1351597 |osti=1351597 |last3=Horowitz |first3=Kelsey |last4=Kurtz |first4=Sarah |doi-access=free}}</ref>

So, technologies such as concentrator photovoltaics and methods in development to lower epitaxial growth and substrate costs could lead to a reduction in the cost of GaAs solar cells and forge a path for use in terrestrial applications.