Engineering the interface chemistry for scandium electron contacts in WSe2 transistors and diodes

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dc.contributor.authorSmyth, Christopher M.
dc.contributor.authorWalsh, Lee A.
dc.contributor.authorBolshakov, Pavel
dc.contributor.authorCatalano, Massimo
dc.contributor.authorSchmidt, Michael
dc.contributor.authorSheehan, Brendan
dc.contributor.authorAddou, Rafik
dc.contributor.authorWang, Luhua
dc.contributor.authorKim, Jiyoung
dc.contributor.authorKim, Moon J.
dc.contributor.authorYoung, Chadwin D.
dc.contributor.authorHinkle, Christopher L.
dc.contributor.authorWallace, Robert M.
dc.contributor.funderHorizon 2020en
dc.contributor.funderScience Foundation Irelanden
dc.contributor.funderNational Science Foundationen
dc.contributor.funderSemiconductor Research Corporationen
dc.date.accessioned2019-09-09T11:48:18Z
dc.date.available2019-09-09T11:48:18Z
dc.date.issued2019-07-24
dc.description.abstractSc has been employed as an electron contact to a number of two-dimensional (2D) materials (e.g. MoS2, black phosphorous) and has enabled, at times, the lowest electron contact resistance. However, the extremely reactive nature of Sc leads to stringent processing requirements and metastable device performance with no true understanding of how to achieve consistent, high-performance Sc contacts. In this work, WSe2 transistors with impressive subthreshold slope (109 mV dec−1) and I ON/I OFF (106) are demonstrated without post-metallization processing by depositing Sc contacts in ultra-high vacuum (UHV) at room temperature (RT). The lowest electron Schottky barrier height (SBH) is achieved by mildly oxidizing the WSe2 in situ before metallization, which minimizes subsequent reactions between Sc and WSe2. Post metallization anneals in reducing environments (UHV, forming gas) degrade the I ON/I OFF by ~103 and increase the subthreshold slope by a factor of 10. X-ray photoelectron spectroscopy indicates the anneals increase the electron SBH by 0.4–0.5 eV and correspondingly convert 100% of the deposited Sc contacts to intermetallic or scandium oxide. Raman spectroscopy and scanning transmission electron microscopy highlight the highly exothermic reactions between Sc and WSe2, which consume at least one layer RT and at least three layers after the 400 °C anneals. The observed layer consumption necessitates multiple sacrificial WSe2 layers during fabrication. Scanning tunneling microscopy/spectroscopy elucidate the enhanced local density of states below the WSe2 Fermi level around individual Sc atoms in the WSe2 lattice, which directly connects the scandium selenide intermetallic with the unexpectedly large electron SBH. The interface chemistry and structural properties are correlated with Sc–WSe2 transistor and diode performance. The recommended combination of processing conditions and steps is provided to facilitate consistent Sc contacts to WSe2.en
dc.description.sponsorshipSemiconductor Research Corporation (NEWLIMITS Center and NIST through award number 70NANB17H041)en
dc.description.statusPeer revieweden
dc.description.versionPublished Versionen
dc.format.mimetypeapplication/pdfen
dc.identifier.articleid045020en
dc.identifier.citationSmyth, C. M., Walsh, L. A., Bolshakov, P., Catalano, M., Schmidt, M., Sheehan, B., Addou, R., Wang, L., Kim, J., Kim, M. J., Young, C. D., Hinkle, C. L. and Wallace, R. M. (2019) 'Engineering the interface chemistry for scandium electron contacts in WSe2 transistors and diodes', 2D Materials, 6(4), 045020. (17pp.) DOI: 10.1088/2053-1583/ab2c44en
dc.identifier.doi10.1088/2053-1583/ab2c44en
dc.identifier.eissn2053-1583
dc.identifier.endpage17en
dc.identifier.issued4en
dc.identifier.journaltitle2D Publishingen
dc.identifier.startpage1en
dc.identifier.urihttps://hdl.handle.net/10468/8476
dc.identifier.volume6en
dc.language.isoenen
dc.publisherIOP Publishingen
dc.relation.projectinfo:eu-repo/grantAgreement/EC/H2020::MSCA-COFUND-FP/713567/EU/Cutting Edge Training - Cutting Edge Technology/EDGEen
dc.relation.projectinfo:eu-repo/grantAgreement/SFI/SFI Research Centres/12/RC/2278/IE/Advanced Materials and BioEngineering Research Centre (AMBER)/en
dc.relation.projectinfo:eu-repo/grantAgreement/NSF/Directorate for Engineering::Division of Electrical, Communications & Cyber Systems/1407765/US/Understanding the Nature of Interfaces in Two Dimensional Electronic Devices(UNITE)/en
dc.relation.urihttps://iopscience.iop.org/article/10.1088/2053-1583/ab2c44
dc.rights©Original content from this work may be used under the terms of the Creative Commons Attribution 3.0 licence. Any further distribution of this work must maintain attribution to the author(s) and the title of the work, journal citation and DOI.en
dc.rights.urihttps://creativecommons.org/licenses/by/3.0/en
dc.subjectMetal contacten
dc.subjectTransistoren
dc.subjectWSe2en
dc.subjectScandiumen
dc.subjectInterfacial chemistryen
dc.subjectAnnealen
dc.subjectX-ray photoelectron spectroscopyen
dc.titleEngineering the interface chemistry for scandium electron contacts in WSe2 transistors and diodesen
dc.typeArticle (peer-reviewed)en
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