A first principles analysis of the effect of hydrogen concentration in hydrogenated amorphous silicon on the formation of strained Si-Si bonds and the optical and mobility gaps

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dc.contributor.authorLegesse, Merid
dc.contributor.authorNolan, Michael
dc.contributor.authorFagas, GĂ­orgos
dc.contributor.funderScience Foundation Irelanden
dc.contributor.funderEuropean Commissionen
dc.date.accessioned2016-07-21T14:49:33Z
dc.date.available2016-07-21T14:49:33Z
dc.date.issued2014-05-28
dc.date.updated2014-09-04T11:10:46Z
dc.description.abstractIn this paper, we use a model of hydrogenated amorphous silicon generated from molecular dynamics with density functional theory calculations to examine how the atomic geometry and the optical and mobility gaps are influenced by mild hydrogen oversaturation. The optical and mobility gaps show a volcano curve as the hydrogen content varies from undersaturation to mild oversaturation, with largest gaps obtained at the saturation hydrogen concentration. At the same time, mid-gap states associated with dangling bonds and strained Si-Si bonds disappear at saturation but reappear at mild oversaturation, which is consistent with the evolution of optical gap. The distribution of Si-Si bond distances provides the key to the change in electronic properties. In the undersaturation regime, the new electronic states in the gap arise from the presence of dangling bonds and strained Si-Si bonds, which are longer than the equilibrium Si-Si distance. Increasing hydrogen concentration up to saturation reduces the strained bonds and removes dangling bonds. In the case of mild oversaturation, the mid-gap states arise exclusively from an increase in the density of strained Si-Si bonds. Analysis of our structure shows that the extra hydrogen atoms form a bridge between neighbouring silicon atoms, thus increasing the Si-Si distance and increasing disorder in the sample.en
dc.description.sponsorshipEuropean Commission (7th Framework ICT-FET-Proactive program, Project: SiNAPS (Contract No 257856)); Science Foundation Ireland (SFI Starting Investigator Research Grant Program, project “EMOIN” grant number SFI 09/SIRG/I1620)en
dc.description.statusPeer revieweden
dc.description.versionAccepted Versionen
dc.format.mimetypeapplication/pdfen
dc.identifier.articleid203711
dc.identifier.citationLegesse, M., Nolan, M. and Fagas, G. (2014) 'A first principles analysis of the effect of hydrogen concentration in hydrogenated amorphous silicon on the formation of strained Si-Si bonds and the optical and mobility gaps', Journal of Applied Physics, 115, 203711. http://scitation.aip.org/content/aip/journal/jap/115/20/10.1063/1.4880395en
dc.identifier.doi10.1063/1.4880395
dc.identifier.endpage203711 (10)en
dc.identifier.issn0021-8979
dc.identifier.issn1089-7550
dc.identifier.journaltitleJournal of Applied Physicsen
dc.identifier.startpage203711 (1)en
dc.identifier.urihttps://hdl.handle.net/10468/2917
dc.identifier.volume115en
dc.language.isoenen
dc.publisherAIP Publishingen
dc.rights© 2014 AIP Publishing LLC. This article may be downloaded for personal use only. Any other use requires prior permission of the author and AIP Publishing. The following article appeared in M. Legesse et al., J. Appl. Phys. 115, 203711 (2014) and may be found at http://dx.doi.org/10.1063/1.4880395en
dc.subjectAmorphous siliconen
dc.subjectAtomsen
dc.subjectChemical bondsen
dc.subjectCrystal atomic structureen
dc.subjectDangling bondsen
dc.subjectElectronic propertiesen
dc.subjectHydrogenen
dc.subjectHydrogenationen
dc.subjectMolecular dynamicsen
dc.subjectUndersaturationen
dc.subjectDangling bondsen
dc.subjectAmorphous semiconductorsen
dc.subjectOptical saturationen
dc.subjectCarrier mobilityen
dc.subjectBond formationen
dc.titleA first principles analysis of the effect of hydrogen concentration in hydrogenated amorphous silicon on the formation of strained Si-Si bonds and the optical and mobility gapsen
dc.typeArticle (peer-reviewed)en
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