# Wetting layer

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A '''wetting layer''' is an monolayer of [atom](/source/atom)s that is [epitaxially](/source/Epitaxy) grown on a flat surface. The atoms forming the wetting layer can be semimetallic elements/compounds or metallic alloys (for thin films). Wetting layers form when depositing a lattice-mismatched material on a crystalline substrate. This article refers to the wetting layer connected to the growth of self-assembled quantum dots (e.g. [InAs](/source/Indium_arsenide) on [GaAs](/source/Gallium_arsenide)). These [quantum dots](/source/quantum_dots) form on top of the wetting layer. The wetting layer can influence the states of the quantum dot for applications in [quantum information](/source/quantum_information) processing and [quantum computation](/source/quantum_computation).

==Process==

The wetting layer is epitaxially grown on a surface using [molecular beam epitaxy](/source/molecular_beam_epitaxy) (MBE).  The temperatures required for wetting layer growth typically range from 400-500 degrees [Celsius](/source/Celsius). When a material ''A'' is deposited on a surface of a lattice-mismatched material ''B'', the first atomic layer of material ''A'' often adopts the lattice constant of ''B''. This mono-layer of material ''A'' is called the wetting layer. When the thickness of layer ''A'' increases further, it becomes energetically unfavorable for material ''A'' to keep the lattice constant of ''B''. Due to the high strain of layer ''A'', additional atoms group together once a certain critical thickness of layer ''A'' is reached. This island formation reduces the [elastic energy](/source/elastic_energy).<ref>{{Cite journal | last1 = Lee | first1 = S. | last2 = Lazarenkova | first2 = O. | last3 = Von Allmen | first3 = P. | last4 = Oyafuso | first4 = F. | last5 = Klimeck | first5 = G. | title = Effect of wetting layers on the strain and electronic structure of InAs self-assembled quantum dots | doi = 10.1103/PhysRevB.70.125307 | journal = Physical Review B | volume = 70 | issue = 12 | year = 2004 | article-number = 125307 |arxiv = cond-mat/0405019 |bibcode = 2004PhRvB..70l5307L | s2cid = 13994641 }}</ref> Overgrown with material ''B'', the wetting layer forms a [quantum well](/source/quantum_well) in case material ''A'' has a lower [bandgap](/source/band_gap) than ''B''. In this case, the formed islands are [quantum dots](/source/quantum_dots). Further [annealing](/source/Annealing_(metallurgy)) can be used to modify the physical properties of the wetting layer/[quantum dot](/source/quantum_dot)<ref name="SanguinettiMano2008">{{cite journal|last1=Sanguinetti|first1=S.|last2=Mano|first2=T.|last3=Gerosa|first3=A.|last4=Somaschini|first4=C.|last5=Bietti|first5=S.|last6=Koguchi|first6=N.|last7=Grilli|first7=E.|last8=Guzzi|first8=M.|last9=Gurioli|first9=M.|last10=Abbarchi|first10=M.|title=Rapid thermal annealing effects on self-assembled quantum dot and quantum ring structures|journal=Journal of Applied Physics|volume=104|issue=11|year=2008|pages=113519–113519–5|issn=0021-8979|doi=10.1063/1.3039802|bibcode=2008JAP...104k3519S |doi-access=free}}</ref>
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==Properties==
The wetting layer is a close-to mono-atomic layer with a thickness of typically 0.5 [nanometer](/source/nanometer)s.  The electronic properties of the [quantum dot](/source/quantum_dot) can change as a result of the wetting layer.<ref name="LeeLazarenkova2004">
{{cite journal|last1=Lee|first1=Seungwon|last2=Lazarenkova|first2=Olga L.|last3=von Allmen|first3=Paul|last4=Oyafuso|first4=Fabiano|last5=Klimeck|first5=Gerhard|title=Effect of wetting layers on the strain and electronic structure of InAs self-assembled quantum dots|journal=Physical Review B|volume=70|issue=12|year=2004|article-number=125307 |issn=1098-0121|doi=10.1103/PhysRevB.70.125307|arxiv=cond-mat/0405019|bibcode=2004PhRvB..70l5307L |s2cid=13994641 }}
</ref><ref name="KarraiWarburton2004">
{{cite journal|last1=Karrai|first1=Khaled|last2=Warburton|first2=Richard J.|last3=Schulhauser|first3=Christian|last4=Högele|first4=Alexander|last5=Urbaszek|first5=Bernhard|last6=McGhee|first6=Ewan J.|last7=Govorov|first7=Alexander O.|last8=Garcia|first8=Jorge M.|last9=Gerardot|first9=Brian D.|last10=Petroff|first10=Pierre M.|title=Hybridization of electronic states in quantum dots through photon emission|journal=Nature|volume=427|issue=6970|year=2004|pages=135–138|issn=0028-0836|doi=10.1038/nature02109|pmid=14712271 |bibcode=2004Natur.427..135K |s2cid=4424992 }}
</ref><ref name="ShahzadehSabaeian2014">{{cite journal|last1=Shahzadeh|first1=Mohammadreza|last2=Sabaeian|first2=Mohammad|title=The effects of wetting layer on electronic and optical properties of intersubband P-to-S transitions in strained dome-shaped InAs/GaAs quantum dots|journal=AIP Advances|volume=4|issue=6|year=2014|page=067113|issn=2158-3226|doi=10.1063/1.4881980|bibcode=2014AIPA....4f7113S |doi-access=free}}</ref> Also, the [strain](/source/strain_(chemistry)) of the [quantum dot](/source/quantum_dot) can change due to the wetting layer.<ref name="SunLu2012">
{{cite journal|last1=Sun|first1=Chao|last2=Lu|first2=Pengfei|last3=Yu|first3=Zhongyuan|last4=Cao|first4=Huawei|last5=Zhang|first5=Lidong|title=Wetting layers effect on InAs/GaAs quantum dots|journal=Physica B: Condensed Matter|volume=407|issue=22|year=2012|pages=4440–4445|issn=0921-4526|doi=10.1016/j.physb.2012.07.039|bibcode=2012PhyB..407.4440S }}</ref>

==Notes==
<references/>

==External links==
*[https://arxiv.org/search/?query=%22wetting+layer%22&searchtype=all&abstracts=show&order=-announced_date_first&size=50 Wetting layer on arxiv.org]
*[https://www.ifkp.tu-berlin.de/menue/arbeitsgruppen/agdaehne/forschung/inas_and_ingaas_quantum_dots group website of M. Dähne]

{{Semiconductor laser}}

Category:Quantum electronics
Category:Thin film deposition

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Adapted from the Wikipedia article [Wetting layer](https://en.wikipedia.org/wiki/Wetting_layer) by Wikipedia contributors ([contributor history](https://en.wikipedia.org/wiki/Wetting_layer?action=history)). Available under [Creative Commons Attribution-ShareAlike 4.0 International](https://creativecommons.org/licenses/by-sa/4.0/). Changes may have been made.