Editing Epitaxy (section)

==Methods==
{{See also|Epitaxial wafer}}

===Vapor-phase===
[[Image:CBE im1.png|right|500px|thumb|Figure 1: Basic processes inside the growth chambers of a) MOVPE, b) MBE, and c) CBE.]]
Homoepitaxial growth of semiconductor thin films are generally done by [[Chemical vapor deposition|chemical]] or [[physical vapor deposition]] methods that deliver the precursors to the substrate in gaseous state. For example, '''silicon''' is most commonly deposited from [[silicon tetrachloride]] (or [[germanium tetrachloride]]) and [[hydrogen]] at approximately 1200 to 1250&nbsp;°C:<ref name="Morgan&Board">{{cite book|last1=Morgan|first1=D. V.|last2=Board|first2=K.|title=An Introduction To Semiconductor Microtechnology|url={{google books |plainurl=y|id=yQ5TAAAAMAAJ|page=23}} |date=1991|publisher=John Wiley & Sons|location=Chichester, West Sussex, England|isbn=978-0471924784|page=23|edition=2nd}}</ref>
:SiCl<sub>4(g)</sub> + 2H<sub>2(g)</sub> ↔ Si<sub>(s)</sub> + 4HCl<sub>(g)</sub>

where (g) and (s) represent gas and solid phases, respectively. This reaction is reversible, and the growth rate depends strongly upon the proportion of the two source gases. Growth rates above 2 micrometres per minute produce polycrystalline silicon, and negative growth rates ([[etching (microfabrication)|etching]]) may occur if too much [[hydrogen chloride]] byproduct is present. (Hydrogen chloride may be intentionally added to etch the wafer.){{Cn|date=April 2023}} An additional etching reaction competes with the deposition reaction:
:SiCl<sub>4(g)</sub> + Si<sub>(s)</sub> ↔ 2SiCl<sub>2(g)</sub>

Silicon VPE may also use [[silane]], [[dichlorosilane]], and [[trichlorosilane]] source gases. For instance, the silane reaction occurs at 650&nbsp;°C in this way:
:SiH<sub>4</sub> → Si + 2H<sub>2</sub>

VPE is sometimes classified by the chemistry of the source gases, such as [[hydride VPE]] (HVPE) and [[MOVPE|metalorganic VPE]] (MOVPE or MOCVD).

The reaction chamber where this process takes place may be heated by lamps located outside the chamber.<ref>{{cite web | url=https://www.chiphistory.org/89-applied-materials-series-7600-epitaxial-reactor-system | title=Applied Materials Series 7600 Epitaxial Reactor System - the Chip History }}</ref> A common technique used in [[compound semiconductor]] growth is [[Molecular-beam epitaxy|molecular beam epitaxy]] (MBE). In this method, a source material is heated to produce an [[evaporate]]d beam of particles, which travel through a very high [[vacuum]] (10<sup>−8</sup> [[pascal (unit)|Pa]]; practically free space) to the substrate and start epitaxial growth.<ref>A. Y. Cho, "Growth of III\–V semiconductors by molecular beam epitaxy and their properties," Thin Solid Films, vol. 100, pp. 291–317, 1983.</ref><ref>{{Cite journal |last=Cheng |first=K. Y. |date=November 1997 |title=Molecular beam epitaxy technology of III-V compound semiconductors for optoelectronic applications |journal=Proceedings of the IEEE |volume=85 |issue=11 |pages=1694–1714 |doi=10.1109/5.649646 |issn=0018-9219}}</ref> [[Chemical beam epitaxy]], on the other hand, is an ultra-high vacuum process that uses gas phase precursors to generate the molecular beam.<ref name=Tsang1989>{{cite journal | last=Tsang | first=W.T. | title=From chemical vapor epitaxy to chemical beam epitaxy | journal=Journal of Crystal Growth | publisher=Elsevier BV | volume=95 | issue=1–4 | year=1989 | issn=0022-0248 | doi=10.1016/0022-0248(89)90364-3 | pages=121–131| bibcode=1989JCrGr..95..121T }}</ref>

Another widely used technique in microelectronics and nanotechnology is [[atomic layer epitaxy]], in which precursor gases are alternatively pulsed into a chamber, leading to atomic monolayer growth by surface saturation and [[chemisorption]].

===Liquid-phase===
Liquid-phase epitaxy (LPE) is a method to grow semiconductor crystal layers from the melt on solid substrates. This happens at temperatures well below the melting point of the deposited semiconductor. The semiconductor is dissolved in the melt of another material. At conditions that are close to the equilibrium between dissolution and deposition, the deposition of the semiconductor crystal on the substrate is relatively fast and uniform. The most used substrate is indium phosphide (InP). Other substrates like glass or ceramic can be applied for special applications. To facilitate nucleation, and to avoid tension in the grown layer the thermal expansion coefficient of substrate and grown layer should be similar.

Centrifugal liquid-phase epitaxy is used commercially to make thin layers of [[silicon]], [[germanium]], and [[gallium arsenide]].<ref name="Capper2007">{{cite book|last1=Capper|first1=Peter|last2=Mauk|first2=Michael|title=Liquid Phase Epitaxy of Electronic, Optical and Optoelectronic Materials|date=2007|publisher=John Wiley & Sons|isbn=9780470319499|pages=134–135|url={{google books |plainurl=y |id=e5mM5INQK9IC|page=135}}|access-date=3 October 2017|language=en}}</ref><ref name="Farrow2013">{{cite book|author1-link=Robin F. C. Farrow|last1=Farrow|first1=R. F. C.|last2=Parkin|first2=S. S. P.|last3=Dobson|first3=P. J.|last4=Neave|first4=J. H.|last5=Arrott|first5=A. S.|title=Thin Film Growth Techniques for Low-Dimensional Structures|date=2013|publisher=Springer Science & Business Media|isbn=9781468491456|pages=174–176|url={{google books |plainurl=y |id=WM7kBwAAQBAJ|page=192}}|access-date=3 October 2017|language=en}}</ref> Centrifugally formed film growth is a process used to form thin layers of materials by using a [[centrifuge]]. The process has been used to create silicon for thin-film solar cells<ref name="Christensen2015">{{cite web|last1=Christensen|first1=Arnfinn|title=Speedy production of silicon for solar cells|url=http://sciencenordic.com/alternative-energy-environmental-technology-forskningno/speedy-production-of-silicon-for-solar-cells/1419392|website=sciencenordic.com|date=29 July 2015 |publisher=ScienceNordic|access-date=3 October 2017|language=en}}</ref><ref name="Luque2012">{{cite book|last1=Luque|first1=A.|last2=Sala|first2=G.|last3=Palz|first3=Willeke|last4=Santos|first4=G. dos|last5=Helm|first5=P.|title=Tenth E.C. Photovoltaic Solar Energy Conference: Proceedings of the International Conference, held at Lisbon, Portugal, 8–12 April 1991|date=2012|publisher=Springer|isbn=9789401136228|page=694|url={{google books |plainurl=y |id=CKfnCAAAQBAJ|page=694}}|access-date=3 October 2017|language=en}}</ref> and far-infrared photodetectors.<ref name="Katterloher2002">{{cite journal|last1=Katterloher|first1=Reinhard O.|last2=Jakob|first2=Gerd|last3=Konuma|first3=Mitsuharu|last4=Krabbe|first4=Alfred|last5=Haegel|first5=Nancy M.|author5-link=Nancy Haegel|last6=Samperi|first6=S. A.|last7=Beeman|first7=Jeffrey W.|last8=Haller|first8=Eugene E.|editor-first1=Marija |editor-first2=Bjorn F. |editor-last1=Strojnik |editor-last2=Andresen |title=Liquid phase epitaxy centrifuge for growth of ultrapure gallium arsenide for far-infrared photoconductors|journal=Infrared Spaceborne Remote Sensing IX|date=8 February 2002|volume=4486|pages=200–209|doi=10.1117/12.455132|bibcode=2002SPIE.4486..200K|s2cid=137003113}}</ref> Temperature and centrifuge spin rate are used to control layer growth.<ref name="Farrow2013" /> Centrifugal LPE has the capability to create dopant concentration gradients while the solution is held at constant temperature.<ref name="Pauleau2012">{{cite book|last1=Pauleau|first1=Y.|title=Chemical Physics of Thin Film Deposition Processes for Micro- and Nano-Technologies|date=2012|publisher=Springer Science & Business Media|isbn=9789401003537|page=45|url={{google books |plainurl=y |id=fsXoCAAAQBAJ|page=67}}|access-date=3 October 2017|language=en}}</ref>

===Solid-phase===
Solid-phase epitaxy (SPE) is a transition between the amorphous and crystalline phases of a material. It is usually produced by depositing a film of amorphous material on a crystalline substrate, then heating it to crystallize the film. The single-crystal substrate serves as a template for crystal growth. The annealing step used to recrystallize or heal silicon layers amorphized during ion implantation is also considered to be a type of solid phase epitaxy. The impurity segregation and redistribution at the growing crystal-amorphous layer interface during this process is used to incorporate low-solubility dopants in metals and silicon.<ref>{{cite journal |first1=J.S. |last1=Custer |first2=A. |last2=Polman |first3=H. M. |last3=Pinxteren| journal=Journal of Applied Physics |volume= 75 |issue= 6 |pages=2809 |date=15 March 1994 |title=Erbium in crystal silicon: Segregation and trapping during solid phase epitaxy of amorphous silicon|bibcode=1994JAP....75.2809C |doi=10.1063/1.356173 }}</ref>