Positive and Negative Photoconductivity in Monolayer MoS₂ as a Function of Physisorbed Oxygen

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https://pubs.acs.org/doi/10.1021/acs.jpcc.1c01550

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https://doi.org/10.1021/acs.jpcc.1c01550
 http://hdl.handle.net/11603/25734

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https://orcid.org/0000-0003-1745-3121
 https://orcid.org/0000-0003-3855-3754
 https://orcid.org/0000-0003-4959-1334
 https://orcid.org/0000-0002-1756-1328

Date

2021-04-16

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journal articles
preprints
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Citation of Original Publication

Gustafson, Jon K. et al. Positive and Negative Photoconductivity in Monolayer MoS2 as a Function of Physisorbed Oxygen. The Journal of Physical Chemistry C 2021 125 (16), 8712-8718 DOI: 10.1021/acs.jpcc.1c01550

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This document is the unedited Author’s version of a Submitted Work that was subsequently accepted for publication in The Journal of Physical Chemistry C , copyright © American Chemical Society after peer review. To access the final edited and published work see https://doi.org/10.1021/acs.jpcc.1c01550

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Abstract

We investigate the effect of molecular oxygen on the photoconductivity of monolayer MoS₂ via broad-band time-resolved terahertz spectroscopy. We observe that the photoconductivity of monolayer MoS₂ transitions from negative to positive when the environment of MoS₂ changes from vacuum to atmospheric pressure. We argue that this transition from negative to positive photoconductivity results from physically adsorbed oxygen depleting excess electrons from the n-type MoS₂. We attribute the negative photoconductivity to negative trion formation, in which photoinduced excitons capture excess electrons from the MoS₂. We attribute the positive photoconductivity to negative trion formation as well; however, in this case, photoinduced excitons capture photoinduced defect electrons rather than excess electrons, which have been immobilized by physisorbed oxygen. These results should prove useful to those who look to make sensors and other types of devices out of monolayer MoS₂ as physisorbed gases, particularly oxygen, can dramatically affect the conductivity of the monolayer.