Atmospheric and Long-term Aging Effects on the Electrical Properties of Variable Thickness WSe2 Transistors

Anna N. Hoffman; Michael G. Stanford; Cheng Zhang; Ilia N. Ivanov; Akinola D. Oyedele; Maria Gabriela Sales; Stephen J. McDonnell; Michael R. Koehler; David G. Mandrus; Liangbo Liang; Bobby G. Sumpter; Kai Xiao; Philip D. Rack

doi:10.1021/acsami.8b12545

Atmospheric and Long-term Aging Effects on the Electrical Properties of Variable Thickness WSe₂ Transistors

Anna N. Hoffman, Michael G. Stanford, Cheng Zhang, Ilia N. Ivanov, Akinola D. Oyedele, Maria Gabriela Sales, Stephen J. McDonnell, Michael R. Koehler, David G. Mandrus, Liangbo Liang, Bobby G. Sumpter, Kai Xiao, Philip D. Rack

Research output: Contribution to journal › Article › peer-review

40 Scopus citations

Abstract

Atmospheric and long-term aging effects on electrical properties of WSe₂ transistors with various thicknesses are examined. Although countless published studies report electrical properties of transition-metal dichalcogenide materials, many are not attentive to testing environment or to age of samples, which we have found significantly impacts results. Our as-fabricated exfoliated WSe₂ pristine devices are predominantly n-type, which is attributed to selenium vacancies. Transfer characteristics of as-fabricated devices measured in air then vacuum reveal physisorbed atmospheric molecules significantly reduced n-type conduction in air. First-principles calculations suggest this short-term reversible atmospheric effect can be attributed primarily to physisorbed H₂O on pristine WSe₂, which is easily removed from the pristine surface in vacuum due to the low adsorption energy. Devices aged in air for over 300 h demonstrate irreversibly increased p-type conduction and decreased n-type conduction. Additionally, they develop an extended time constant for recovery of the atmospheric adsorbents effect. Short-term atmospheric aging (up to approximately 900 h) is attributed to O₂ and H₂O molecules physisorbed to selenium vacancies where electron transfer from the bulk and adsorbed binding energies are higher than the H₂O-pristine WSe₂. The residual/permanent aging component is attributed to electron trapping molecular O₂ and isoelectronic O chemisorption at selenium vacancies, which also passivates the near-conduction band gap state, p-doping the material, with very high binding energy. All effects demonstrated have the expected thickness dependence, namely, thinner devices are more sensitive to atmospheric and long-term aging effects.

Original language	English
Pages (from-to)	36540-36548
Number of pages	9
Journal	ACS Applied Materials and Interfaces
Volume	10
Issue number	42
DOIs	https://doi.org/10.1021/acsami.8b12545
State	Published - Oct 24 2018

Funding

*E-mail: [email protected]. ORCID Anna N. Hoffman: 0000-0003-2899-0889 Michael G. Stanford: 0000-0001-9663-1138 Cheng Zhang: 0000-0001-6531-4703 Ilia N. Ivanov: 0000-0002-6726-2502 Akinola D. Oyedele: 0000-0001-5596-5238 Liangbo Liang: 0000-0003-1199-0049 Bobby G. Sumpter: 0000-0001-6341-0355 Kai Xiao: 0000-0002-0402-8276 Author Contributions P.D.R. conceived of the experimental plan and managed the project. A.N.H. performed the device fabrication and electrical and Raman characterization. M.G.S., C.Z., I.N.I., A.D.O., and K.X. facilitated device fabrication training and helped with the electrical and Raman measurements; M.G.S. and S.J.M. performed XPS measurements; L.L. and B.G.S. did the DFT calculations; M.R.K. and D.G.M. grew the WSe2 bulk crystals. The manuscript was written through contributions of all authors. All authors have given approval to the final version of the manuscript. This manuscript has been authored by UT-Battelle, LLC under Contract No. DE-AC05-00OR22725 with the U.S. Department of Energy. The United States Government retains and the publisher, by accepting the article for publication, acknowledges that the United States Government retains a nonexclusive, paid-up, irrevocable, world-wide license to publish or reproduce the published form of this manuscript, or allow others to do so, for United States Government purposes. The Department of Energy will provide public access to these results of federally sponsored research in accordance to the DOE Public Access Plan. Notes The authors declare no competing financial interest.

Keywords

TMD
WSe
ambient
atmosphere
environment
field-effect transistor
transition-metal dichalcogenide

Access to Document

10.1021/acsami.8b12545

Cite this

Hoffman, A. N., Stanford, M. G., Zhang, C., Ivanov, I. N., Oyedele, A. D., Sales, M. G., McDonnell, S. J., Koehler, M. R., Mandrus, D. G., Liang, L., Sumpter, B. G., Xiao, K., & Rack, P. D. (2018). Atmospheric and Long-term Aging Effects on the Electrical Properties of Variable Thickness WSe₂ Transistors. ACS Applied Materials and Interfaces, 10(42), 36540-36548. https://doi.org/10.1021/acsami.8b12545

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title = "Atmospheric and Long-term Aging Effects on the Electrical Properties of Variable Thickness WSe2 Transistors",

abstract = "Atmospheric and long-term aging effects on electrical properties of WSe2 transistors with various thicknesses are examined. Although countless published studies report electrical properties of transition-metal dichalcogenide materials, many are not attentive to testing environment or to age of samples, which we have found significantly impacts results. Our as-fabricated exfoliated WSe2 pristine devices are predominantly n-type, which is attributed to selenium vacancies. Transfer characteristics of as-fabricated devices measured in air then vacuum reveal physisorbed atmospheric molecules significantly reduced n-type conduction in air. First-principles calculations suggest this short-term reversible atmospheric effect can be attributed primarily to physisorbed H2O on pristine WSe2, which is easily removed from the pristine surface in vacuum due to the low adsorption energy. Devices aged in air for over 300 h demonstrate irreversibly increased p-type conduction and decreased n-type conduction. Additionally, they develop an extended time constant for recovery of the atmospheric adsorbents effect. Short-term atmospheric aging (up to approximately 900 h) is attributed to O2 and H2O molecules physisorbed to selenium vacancies where electron transfer from the bulk and adsorbed binding energies are higher than the H2O-pristine WSe2. The residual/permanent aging component is attributed to electron trapping molecular O2 and isoelectronic O chemisorption at selenium vacancies, which also passivates the near-conduction band gap state, p-doping the material, with very high binding energy. All effects demonstrated have the expected thickness dependence, namely, thinner devices are more sensitive to atmospheric and long-term aging effects.",

keywords = "TMD, WSe, ambient, atmosphere, environment, field-effect transistor, transition-metal dichalcogenide",

author = "Hoffman, {Anna N.} and Stanford, {Michael G.} and Cheng Zhang and Ivanov, {Ilia N.} and Oyedele, {Akinola D.} and Sales, {Maria Gabriela} and McDonnell, {Stephen J.} and Koehler, {Michael R.} and Mandrus, {David G.} and Liangbo Liang and Sumpter, {Bobby G.} and Kai Xiao and Rack, {Philip D.}",

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Hoffman, AN, Stanford, MG, Zhang, C, Ivanov, IN, Oyedele, AD, Sales, MG, McDonnell, SJ, Koehler, MR, Mandrus, DG, Liang, L , Sumpter, BG , Xiao, K & Rack, PD 2018, 'Atmospheric and Long-term Aging Effects on the Electrical Properties of Variable Thickness WSe₂ Transistors', ACS Applied Materials and Interfaces, vol. 10, no. 42, pp. 36540-36548. https://doi.org/10.1021/acsami.8b12545

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AU - Stanford, Michael G.

AU - Zhang, Cheng

AU - Ivanov, Ilia N.

AU - Oyedele, Akinola D.

AU - Sales, Maria Gabriela

AU - McDonnell, Stephen J.

AU - Koehler, Michael R.

AU - Mandrus, David G.

AU - Liang, Liangbo

AU - Sumpter, Bobby G.

AU - Xiao, Kai

AU - Rack, Philip D.

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AB - Atmospheric and long-term aging effects on electrical properties of WSe2 transistors with various thicknesses are examined. Although countless published studies report electrical properties of transition-metal dichalcogenide materials, many are not attentive to testing environment or to age of samples, which we have found significantly impacts results. Our as-fabricated exfoliated WSe2 pristine devices are predominantly n-type, which is attributed to selenium vacancies. Transfer characteristics of as-fabricated devices measured in air then vacuum reveal physisorbed atmospheric molecules significantly reduced n-type conduction in air. First-principles calculations suggest this short-term reversible atmospheric effect can be attributed primarily to physisorbed H2O on pristine WSe2, which is easily removed from the pristine surface in vacuum due to the low adsorption energy. Devices aged in air for over 300 h demonstrate irreversibly increased p-type conduction and decreased n-type conduction. Additionally, they develop an extended time constant for recovery of the atmospheric adsorbents effect. Short-term atmospheric aging (up to approximately 900 h) is attributed to O2 and H2O molecules physisorbed to selenium vacancies where electron transfer from the bulk and adsorbed binding energies are higher than the H2O-pristine WSe2. The residual/permanent aging component is attributed to electron trapping molecular O2 and isoelectronic O chemisorption at selenium vacancies, which also passivates the near-conduction band gap state, p-doping the material, with very high binding energy. All effects demonstrated have the expected thickness dependence, namely, thinner devices are more sensitive to atmospheric and long-term aging effects.

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