The electronic band structure of MoS2, MoSe2, WS2, and WSe2, crystals has been studied at various hydrostatic pressures experimentally by photoreflectance (PR) spectroscopy and theoretically within the density functional theory (DFT). In the PR spectra direct optical transitions (A and B) have been clearly observed and pressure coefficients have been determined for these transitions to be: αA = 2.0 ± 0.1 and αB = 3.6 ± 0.1 meV/kbar for MoS2, αA = 2.3 ± 0.1 and αB = 4.0 ± 0.1 meV/kbar for MoSe2, αA = 2.6 ± 0.1 and αB = 4.1 ± 0.1 meV/kbar for WS2, αA = 3.4 ± 0.1 and αB = 5.0 ± 0.5 meV/kbar for WSe2. It has been found that these coefficients are in an excellent agreement with theoretical predictions. In addition, a comparative study of different computational DFT approaches has been performed and analyzed. For indirect gap the pressure coefficient have been determined theoretically to be −7.9, −5.51, −6.11, and −3.79, meV/kbar for MoS2, MoSe2, WS2, and WSe2, respectively. The negative values of this coefficients imply a narrowing of the fundamental band gap with the increase in hydrostatic pressure and a semiconductor to metal transition for MoS2, MoSe2, WS2, and WSe2, crystals at around 140, 180, 190, and 240 kbar, respectively.
Details
- Pressure Coefficients for Direct Optical Transitions in MoS2, MoSe2, WS2, and WSe2 Crystals and Semiconductor to Metal Transitions
- Dybala, F. (Author)
- Polak, M. P. (Author)
- Kopaczek, J. (Author)
- Scharoch, P. (Author)
- Wu, Kedi (Author)
- Tongay, Sefaattin (Author)
- Kudrawiec, R. (Author)
- Ira A. Fulton Schools of Engineering (Contributor)
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Digital object identifier: 10.1038/srep26663
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Identifier TypeInternational standard serial numberIdentifier Value2045-2322
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The final version of this article, as published in Scientific Reports, can be viewed online at: https://www.nature.com/articles/srep26663
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Dybała, F., Polak, M. P., Kopaczek, J., Scharoch, P., Wu, K., Tongay, S., & Kudrawiec, R. (2016). Pressure coefficients for direct optical transitions in MoS2, MoSe2, WS2, and WSe2 crystals and semiconductor to metal transitions. Scientific Reports, 6(1). doi:10.1038/srep26663