Editing Epitaxy (section)

===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]].