Editing Gallium arsenide (section)

==Preparation and chemistry==
In the compound, gallium has a +3 [[oxidation state]]. Gallium arsenide [[single crystal]]s can be prepared by three industrial processes:<ref name="Moss" />
* The vertical gradient freeze (VGF) process.<ref>{{cite book |author1=Scheel, Hans J. |title=Crystal Growth Technology |author2=Tsuguo Fukuda. |publisher=Wiley |year=2003 |isbn=978-0471490593}}</ref>
* Crystal growth using a horizontal zone furnace in the [[Bridgman-Stockbarger technique]], in which gallium and arsenic vapors react, and free molecules deposit on a seed crystal at the cooler end of the furnace.
* Liquid encapsulated [[Czochralski process|Czochralski]] (LEC) growth is used for producing high-purity single crystals that can exhibit semi-insulating characteristics (see below). Most GaAs wafers are produced using this process.

Alternative methods for producing films of GaAs include:<ref name="Moss" /><ref>{{cite book |author1=Smart, Lesley |title=Solid State Chemistry: An Introduction |author2=Moore, Elaine A. |publisher=CRC Press |year=2005 |isbn=978-0-7487-7516-3}}</ref>
* [[Chemical vapor deposition|VPE]] reaction of gaseous gallium metal and [[arsenic trichloride]]: 2 Ga + 2 {{chem|AsCl|3}} → 2 GaAs + 3 {{chem|Cl|2}}
* [[MOCVD]] reaction of [[trimethylgallium]] and [[arsine]]: {{chem|Ga(CH|3|)|3}} + {{chem|AsH|3}} → GaAs + 3 {{chem|CH|4}}
* [[Molecular beam epitaxy]] (MBE) of [[gallium]] and [[arsenic]]: 4 Ga + {{chem|As|4}} → 4 GaAs or 2 Ga + {{chem|As|2}} → 2 GaAs

Oxidation of GaAs occurs in air, degrading performance of the semiconductor. The surface can be passivated by depositing a cubic [[gallium(II) sulfide]] layer using a tert-butyl gallium sulfide compound such as ({{chem|<sup>t</sup>|BuGaS)|7}}.<ref>"Chemical vapor deposition from single organometallic precursors" A. R. Barron, M. B. Power, A. N. MacInnes, A. F.Hepp, P. P. Jenkins {{US patent|5300320}} (1994)</ref>

===Semi-insulating crystals===
In the presence of excess arsenic, GaAs [[Boule (crystal)|boules]] grow with [[crystallographic defect]]s; specifically, arsenic antisite defects (an arsenic atom at a gallium atom site within the crystal lattice). The electronic properties of these defects (interacting with others) cause the [[Fermi level]] to be [[Fermi level pinning|pinned]] to near the center of the band gap, so that this GaAs crystal has very low concentration of electrons and holes. This low carrier concentration is similar to an intrinsic (perfectly undoped) crystal, but much easier to achieve in practice. These crystals are called "semi-insulating", reflecting their high resistivity of 10<sup>7</sup>–10<sup>9</sup> Ω·cm (which is quite high for a semiconductor, but still much lower than a true insulator like glass).<ref name="DD-2012">McCluskey, Matthew D. and Haller, Eugene E. (2012) ''Dopants and Defects in Semiconductors'', pp. 41 and 66, {{ISBN|978-1439831526}}</ref>

===Etching===
Wet etching of GaAs industrially uses an oxidizing agent such as [[hydrogen peroxide]] or [[bromine]] water,<ref>{{cite book |author1=Brozel, M. R. |title=Properties of Gallium Arsenide |author2=Stillman, G. E. |publisher=IEEE Inspec |year=1996 |isbn=978-0-85296-885-7}}</ref> and the same strategy has been described in a patent relating to processing scrap components containing GaAs where the {{chem|Ga||3+}} is complexed with a [[hydroxamic acid]] ("HA"), for example:<ref>"Oxidative dissolution of gallium arsenide and separation of gallium from arsenic" J. P. Coleman and B. F. Monzyk {{US patent|4759917}} (1988)</ref>
:GaAs + {{chem|H|2|O|2}} + "HA" → "GaA" complex + {{chem|H|3|AsO|4}} + 4 {{chem|H|2|O}}
This reaction produces [[arsenic acid]].<ref>{{cite journal |last1=Lova |first1=Paola |last2=Robbiano |first2=Valentina |last3=Cacialli |first3=Franco |last4=Comoretto |first4=Davide |last5=Soci |first5=Cesare |date=3 October 2018 |title=Black GaAs by Metal-Assisted Chemical Etching |url=https://discovery.ucl.ac.uk/id/eprint/10059695/ |journal=ACS Applied Materials & Interfaces |volume=10 |issue=39 |pages=33434–33440 |doi=10.1021/acsami.8b10370 |issn=1944-8244 |pmid=30191706 |s2cid=206490133}}</ref>