Editing Gallium arsenide (section)

==Electronics==
===GaAs digital logic===
GaAs can be used for various transistor types:<ref name="Fisher1995">{{cite book |author1=Dennis Fisher |url=https://books.google.com/books?id=KSKJ56kvcSYC&q=source-coupled-fet-logic&pg=PA61 |title=Gallium Arsenide IC Applications Handbook |author2=I. J. Bahl |publisher=Elsevier |year=1995 |isbn=978-0-12-257735-2 |volume=1 |page=61}} 'Clear search' to see pages</ref>
* [[Metal–semiconductor field-effect transistor]] (MESFET)
* [[High-electron-mobility transistor]] (HEMT)
* [[Junction field-effect transistor]] (JFET)
* [[Heterojunction bipolar transistor]] (HBT)
* [[Metal–oxide–semiconductor field-effect transistor]] (MOSFET)<ref>{{cite book |last1=Ye |first1=Peide D. |title=Fundamentals of III-V Semiconductor MOSFETs |last2=Xuan |first2=Yi |last3=Wu |first3=Yanqing |last4=Xu |first4=Min |date=2010 |publisher=[[Springer Science & Business Media]] |isbn=978-1-4419-1547-4 |editor-last1=Oktyabrsky |editor-first1=Serge |pages=173–194 |chapter=Atomic-Layer Deposited High-k/III-V Metal-Oxide-Semiconductor Devices and Correlated Empirical Model |doi=10.1007/978-1-4419-1547-4_7 |editor-last2=Ye |editor-first2=Peide |chapter-url=https://books.google.com/books?id=sk2SrZH3xEcC&pg=PA173}}</ref>

The HBT can be used in [[integrated injection logic]] (I<sup>2</sup>L).

The earliest GaAs logic gate used Buffered FET Logic (BFL).<ref name="Fisher1995" />

From {{circa|1975}} to 1995 the main logic families used were:<ref name="Fisher1995" />
* Source-coupled FET logic (SCFL) fastest and most complex, (used by TriQuint & Vitesse)
* Capacitor–diode FET logic (CDFL) (used by Cray for [[Cray-3]])
* Direct-coupled FET logic (DCFL) simplest and lowest power (used by Vitesse for VLSI gate arrays)

===Comparison with silicon for electronics===
====GaAs advantages====
Some electronic properties of gallium arsenide are superior to those of [[silicon]]. It has a higher [[saturation velocity|saturated electron velocity]] and higher [[electron mobility]], allowing gallium arsenide transistors to function at frequencies in excess of 250&nbsp;GHz.<ref name="waferworld">{{Cite web |title=What Are the Applications of Gallium Arsenide Semiconductors? {{!}} Wafer World |url=https://www.waferworld.com/post/what-are-the-applications-of-gallium-arsenide-semiconductors |access-date=2024-09-27 |website=www.waferworld.com |language=en}}</ref> GaAs devices are relatively insensitive to overheating, owing to their wider energy band gap, and they also tend to create less [[noise (physics)|noise]] (disturbance in an electrical signal) in electronic circuits than silicon devices, especially at high frequencies. This is a result of higher carrier mobilities and lower resistive device parasitics. These superior properties are compelling reasons to use GaAs circuitry in [[mobile phone]]s, [[communications satellite|satellite]] communications, microwave point-to-point links and higher frequency [[radar]] systems. It is also used in the manufacture of [[Gunn diode]]s for the generation of [[microwave]]s.{{citation needed|date=September 2023}}

Another advantage of GaAs is that it has a [[direct band gap]], which means that it can be used to absorb and emit light efficiently. Silicon has an [[indirect band gap]] and so is relatively poor at emitting light.{{citation needed|date=September 2023}}

As a wide direct band gap material with resulting resistance to radiation damage, GaAs is an excellent material for outer space electronics and optical windows in high power applications.<ref name="waferworld" />

Because of its wide band gap, pure GaAs is highly resistive. Combined with a high [[dielectric constant]], this property makes GaAs a very good substrate for [[integrated circuit]]s and unlike Si provides natural isolation between devices and circuits.  This has made it an ideal material for [[monolithic microwave integrated circuit]]s (MMICs), where active and essential passive components can readily be produced on a single slice of GaAs.

One of the first GaAs [[microprocessor]]s was developed in the early 1980s by the [[RCA]] Corporation and was considered for the [[Strategic Defense Initiative|Star Wars program]] of the [[United States Department of Defense]]. These processors were several times faster and several orders of magnitude more [[Radiation hardening|radiation resistant]] than their silicon counterparts, but were more expensive.<ref>{{cite book |author1=Šilc, Von Jurij |url=https://archive.org/details/processorarchite0000silc |title=Processor architecture: from dataflow to superscalar and beyond |author2=Robič, Borut |author3=Ungerer, Theo |publisher=Springer |year=1999 |isbn=978-3-540-64798-0 |page=[https://archive.org/details/processorarchite0000silc/page/34 34] |url-access=registration}}</ref> Other GaAs processors were implemented by the [[supercomputer]] vendors [[Cray]] Computer Corporation, [[Convex Computer|Convex]], and [[Alliant Computer Systems|Alliant]] in an attempt to stay ahead of the ever-improving [[CMOS]] microprocessor. Cray eventually built one GaAs-based machine in the early 1990s, the [[Cray-3]], but the effort was not adequately capitalized, and the company filed for bankruptcy in 1995.

Complex layered structures of gallium arsenide in combination with [[aluminium arsenide]] (AlAs) or the alloy [[Aluminium gallium arsenide|Al<sub>x</sub>Ga<sub>1−x</sub>As]] can be grown using [[molecular-beam epitaxy]] (MBE) or using [[metalorganic vapor-phase epitaxy]] (MOVPE). Because GaAs and AlAs have almost the same [[lattice constant]], the layers have very little induced [[Strain (chemistry)|strain]], which allows them to be grown almost arbitrarily thick.  This allows extremely high performance and high electron mobility [[High-electron-mobility transistor|HEMT]] transistors and other [[quantum well]] devices.

GaAs is used for monolithic radar power amplifiers (but [[Gallium nitride|GaN]] can be less susceptible to heat damage).<ref name="at-2016-radar">{{Cite web |date=2016-06-09 |title=A reprieve for Moore's Law: milspec chip writes computing's next chapter |author-last1=Gallagher|author-first1=Sean|url=https://arstechnica.com/information-technology/2016/06/cheaper-better-faster-stronger-ars-meets-the-latest-military-bred-chip/ |access-date=2016-06-14 |website=Ars Technica}}</ref>

====Silicon advantages====
Silicon has three major advantages over GaAs for integrated circuit manufacture. First, silicon is abundant and cheap to process in the form of [[silicate]] minerals. The [[economies of scale]] available to the silicon industry has also hindered the adoption of GaAs.{{citation needed|date=September 2023}}

In addition, a Si crystal has a very stable structure and can be grown to very large diameter [[boule (crystal)|boule]]s and processed with very good yields. It is also a fairly good thermal conductor, thus enabling very dense packing of transistors that need to get rid of their heat of operation, all very desirable for design and manufacturing of very large [[Integrated circuit|IC]]s. Such good mechanical characteristics also make it a suitable material for the rapidly developing field of [[nanoelectronics]]. Naturally, a GaAs surface cannot withstand the high temperatures needed for diffusion; however a viable and actively pursued alternative as of the 1980s was ion implantation.<ref name="Morgan&Board">{{cite book |last1=Morgan |first1=D. V. |title=An Introduction To Semiconductor Microtechnology |last2=Board |first2=K. |date=1991 |publisher=John Wiley & Sons |isbn=978-0471924784 |edition=2nd |location=Chichester, West Sussex, England |page=137}}</ref>

The second major advantage of Si is the existence of a native oxide ([[silicon dioxide]], SiO<sub>2</sub>), which is used as an [[Insulator (electricity)|insulator]]. Silicon dioxide can be incorporated onto silicon circuits easily, and such layers are adherent to the underlying silicon. SiO<sub>2</sub> is not only a good insulator (with a [[band gap]] of 8.9 [[electron volt|eV]]), but the Si-SiO<sub>2</sub> interface can be easily engineered to have excellent electrical properties, most importantly low density of interface states. GaAs does not have a native oxide, does not easily support a stable adherent insulating layer, and does not possess the dielectric strength or surface passivating qualities of the Si-SiO<sub>2</sub>.<ref name="Morgan&Board" />

[[Aluminum oxide]] (Al<sub>2</sub>O<sub>3</sub>) has been extensively studied as a possible gate oxide for GaAs (as well as [[indium gallium arsenide|InGaAs]]).

The third advantage of silicon is that it possesses a higher [[Electron hole|hole]] mobility compared to GaAs (500 versus 400&nbsp;cm<sup>2</sup>V<sup>−1</sup>s<sup>−1</sup>).<ref>Sze, S. M. (1985). ''Semiconductor Devices Physics and Technology''. John Wiley & Sons. Appendix G. {{ISBN|0-471-87424-8}}</ref> This high mobility allows the fabrication of higher-speed P-channel [[field-effect transistor]]s, which are required for [[CMOS]] logic. Because they lack a fast CMOS structure, GaAs circuits must use logic styles which have much higher power consumption; this has made GaAs logic circuits unable to compete with silicon logic circuits.

For manufacturing solar cells, silicon has relatively low [[Molar absorptivity|absorptivity]] for sunlight, meaning about 100 micrometers of Si is needed to absorb most sunlight. Such a layer is relatively robust and easy to handle. In contrast, the absorptivity of GaAs is so high that only a few micrometers of thickness are needed to absorb all of the light. Consequently, GaAs thin films must be supported on a substrate material.<ref name="adv">[https://web.archive.org/web/20100211014421/http://www.eere.energy.gov/solar/tf_single_crystalline.html Single-Crystalline Thin Film]. US Department of Energy</ref>

Silicon is a pure element, avoiding the problems of stoichiometric imbalance and thermal unmixing of GaAs.<ref>{{cite book |last1=Cabrera |first1=Rowan |url=https://books.google.com/books?id=EeTEDwAAQBAJ&dq=Silicon+is+a+pure+element,+avoiding+the+problems+of+stoichiometric+imbalance+and+thermal+unmixing+of+GaAs&pg=PA35 |title=Electronic Devices and Circuits |date=2019 |publisher=EDTECH |isbn=9781839473838 |page=35 |access-date=20 January 2022}}</ref>

Silicon has a nearly perfect lattice; impurity density is very low and allows very small structures to be built (down to [[5 nm process|5&nbsp;nm]] in commercial production as of 2020<ref>{{Cite web |last=Cutress |first=Dr Ian |title='Better Yield on 5nm than 7nm': TSMC Update on Defect Rates for N5 |url=https://www.anandtech.com/show/16028/better-yield-on-5nm-than-7nm-tsmc-update-on-defect-rates-for-n5 |access-date=2020-08-28 |website=www.anandtech.com}}</ref>). In contrast, GaAs has a very high impurity density,<ref>{{cite book |last1=Schlesinger |first1=T.E. |url=https://doi.org/10.1016/B0-08-043152-6/00612-4 |title=Encyclopedia of Materials: Science and Technology |date=2001 |publisher=Elsevier |isbn=9780080431529 |pages=3431–3435 |chapter=Gallium Arsenide |doi=10.1016/B0-08-043152-6/00612-4 |access-date=27 January 2021}}</ref> which makes it difficult to build integrated circuits with small structures, so the 500&nbsp;nm process is a common process for GaAs.{{Citation needed|date=May 2016}}

Silicon has about three times the thermal conductivity of GaAs, with less risk of local overheating in high power devices.<ref name="at-2016-radar" />