Probing excitonic states in suspended two-dimensional semiconductors by photocurrent spectroscopy

A. R. Klots; A. K.M. Newaz; Bin Wang; D. Prasai; H. Krzyzanowska; Junhao Lin; D. Caudel; N. J. Ghimire; J. Yan; B. L. Ivanov; K. A. Velizhanin; A. Burger; D. G. Mandrus; N. H. Tolk; S. T. Pantelides; K. I. Bolotin

doi:10.1038/srep06608

Probing excitonic states in suspended two-dimensional semiconductors by photocurrent spectroscopy

A. R. Klots, A. K.M. Newaz, Bin Wang, D. Prasai, H. Krzyzanowska, Junhao Lin, D. Caudel, N. J. Ghimire, J. Yan, B. L. Ivanov, K. A. Velizhanin, A. Burger, D. G. Mandrus, N. H. Tolk, S. T. Pantelides, K. I. Bolotin

Correlated Electron Materials

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Abstract

The optical response of semiconducting monolayer transition-metal dichalcogenides (TMDCs) is dominated by strongly bound excitons that are stable even at room temperature. However, substrate-related effects such as screening and disorder in currently available specimens mask many anticipated physical phenomena and limit device applications of TMDCs. Here, we demonstrate that that these undesirable effects are strongly suppressed in suspended devices. Extremely robust (photogain > 1,000) and fast (response time > 1 ms) photoresponse allow us to study, for the first time, the formation, binding energies, and dissociation mechanisms of excitons in TMDCs through photocurrent spectroscopy. By analyzing the spectral positions of peaks in the photocurrent and by comparing them with first-principles calculations, we obtain binding energies, band gaps and spin-orbit splitting in monolayer TMDCs. For monolayer MoS₂, in particular, we obtain an extremely large binding energy for band-edge excitons, E_bind ≥ 570 meV. Along with band-edge excitons, we observe excitons associated with a van Hove singularity of rather unique nature. The analysis of the source-drain voltage dependence of photocurrent spectra reveals exciton dissociation and photoconversion mechanisms in TMDCs.

Original language	English
Article number	6608
Journal	Scientific Reports
Volume	4
DOIs	https://doi.org/10.1038/srep06608
State	Published - Oct 16 2014

Funding

We thank Jed Ziegler and Richard Haglund for their help with optical measurements and acknowledge stimulating discussions with Tony Heinz. K.I.B. acknowledges support from ONR-N000141310299, NSF CAREER DMR-1056859, HDTRA1-10-0047, and Vanderbilt University. N.H.T. would like to acknowledge support from DOE/BES and ARO through grant numbers FGO2-99ER45781 and W911NF-07-R-0003-02. Samples for this work were prepared at the Vanderbilt Institute of Nanoscale Science and Engineering using facilities renovated under NSF ARI-R2 DMR-0963361 and NSF EPS1004083. N.J.G., J.Y., D.M., and S.T.P. were supported by US DoE, BES, Materials Sciences and Engineering Division.

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Klots, A. R., Newaz, A. K. M., Wang, B., Prasai, D., Krzyzanowska, H., Lin, J., Caudel, D., Ghimire, N. J., Yan, J., Ivanov, B. L., Velizhanin, K. A., Burger, A., Mandrus, D. G., Tolk, N. H., Pantelides, S. T., & Bolotin, K. I. (2014). Probing excitonic states in suspended two-dimensional semiconductors by photocurrent spectroscopy. Scientific Reports, 4, Article 6608. https://doi.org/10.1038/srep06608

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title = "Probing excitonic states in suspended two-dimensional semiconductors by photocurrent spectroscopy",

abstract = "The optical response of semiconducting monolayer transition-metal dichalcogenides (TMDCs) is dominated by strongly bound excitons that are stable even at room temperature. However, substrate-related effects such as screening and disorder in currently available specimens mask many anticipated physical phenomena and limit device applications of TMDCs. Here, we demonstrate that that these undesirable effects are strongly suppressed in suspended devices. Extremely robust (photogain > 1,000) and fast (response time > 1 ms) photoresponse allow us to study, for the first time, the formation, binding energies, and dissociation mechanisms of excitons in TMDCs through photocurrent spectroscopy. By analyzing the spectral positions of peaks in the photocurrent and by comparing them with first-principles calculations, we obtain binding energies, band gaps and spin-orbit splitting in monolayer TMDCs. For monolayer MoS2, in particular, we obtain an extremely large binding energy for band-edge excitons, Ebind ≥ 570 meV. Along with band-edge excitons, we observe excitons associated with a van Hove singularity of rather unique nature. The analysis of the source-drain voltage dependence of photocurrent spectra reveals exciton dissociation and photoconversion mechanisms in TMDCs.",

author = "Klots, \{A. R.\} and Newaz, \{A. K.M.\} and Bin Wang and D. Prasai and H. Krzyzanowska and Junhao Lin and D. Caudel and Ghimire, \{N. J.\} and J. Yan and Ivanov, \{B. L.\} and Velizhanin, \{K. A.\} and A. Burger and Mandrus, \{D. G.\} and Tolk, \{N. H.\} and Pantelides, \{S. T.\} and Bolotin, \{K. I.\}",

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AU - Klots, A. R.

AU - Newaz, A. K.M.

AU - Wang, Bin

AU - Prasai, D.

AU - Krzyzanowska, H.

AU - Lin, Junhao

AU - Caudel, D.

AU - Ghimire, N. J.

AU - Yan, J.

AU - Ivanov, B. L.

AU - Velizhanin, K. A.

AU - Burger, A.

AU - Mandrus, D. G.

AU - Tolk, N. H.

AU - Pantelides, S. T.

AU - Bolotin, K. I.

PY - 2014/10/16

Y1 - 2014/10/16

N2 - The optical response of semiconducting monolayer transition-metal dichalcogenides (TMDCs) is dominated by strongly bound excitons that are stable even at room temperature. However, substrate-related effects such as screening and disorder in currently available specimens mask many anticipated physical phenomena and limit device applications of TMDCs. Here, we demonstrate that that these undesirable effects are strongly suppressed in suspended devices. Extremely robust (photogain > 1,000) and fast (response time > 1 ms) photoresponse allow us to study, for the first time, the formation, binding energies, and dissociation mechanisms of excitons in TMDCs through photocurrent spectroscopy. By analyzing the spectral positions of peaks in the photocurrent and by comparing them with first-principles calculations, we obtain binding energies, band gaps and spin-orbit splitting in monolayer TMDCs. For monolayer MoS2, in particular, we obtain an extremely large binding energy for band-edge excitons, Ebind ≥ 570 meV. Along with band-edge excitons, we observe excitons associated with a van Hove singularity of rather unique nature. The analysis of the source-drain voltage dependence of photocurrent spectra reveals exciton dissociation and photoconversion mechanisms in TMDCs.

AB - The optical response of semiconducting monolayer transition-metal dichalcogenides (TMDCs) is dominated by strongly bound excitons that are stable even at room temperature. However, substrate-related effects such as screening and disorder in currently available specimens mask many anticipated physical phenomena and limit device applications of TMDCs. Here, we demonstrate that that these undesirable effects are strongly suppressed in suspended devices. Extremely robust (photogain > 1,000) and fast (response time > 1 ms) photoresponse allow us to study, for the first time, the formation, binding energies, and dissociation mechanisms of excitons in TMDCs through photocurrent spectroscopy. By analyzing the spectral positions of peaks in the photocurrent and by comparing them with first-principles calculations, we obtain binding energies, band gaps and spin-orbit splitting in monolayer TMDCs. For monolayer MoS2, in particular, we obtain an extremely large binding energy for band-edge excitons, Ebind ≥ 570 meV. Along with band-edge excitons, we observe excitons associated with a van Hove singularity of rather unique nature. The analysis of the source-drain voltage dependence of photocurrent spectra reveals exciton dissociation and photoconversion mechanisms in TMDCs.

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SN - 2045-2322

VL - 4

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ER -

Probing excitonic states in suspended two-dimensional semiconductors by photocurrent spectroscopy

Abstract

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