Ellipsometry and optical spectroscopy of low-dimensional family TMDs

• Published in: Semiconductor Physics Quantum Electronics & Optoelectronics
• Date: 2017
• Main Authors: Kravets, V.G., Prorok, V.V., Poperenko, L.V., Shaykevich, I.A.
• Format: Article
• Language: English
• Published: Інститут фізики напівпровідників імені В.Є. Лашкарьова НАН України 2017
• Online Access: https://nasplib.isofts.kiev.ua/handle/123456789/214956
• Journal Title: Digital Library of Periodicals of National Academy of Sciences of Ukraine
• Cite this: Ellipsometry and optical spectroscopy of low-dimensional family TMDs / V.G. Kravets, V.V. Prorok, L.V. Poperenko, I.A. Shaykevich // Semiconductor Physics Quantum Electronics & Optoelectronics. — 2017. — Т. 20, № 3. — С. 284-296. — Бібліогр.: 43 назв. — англ.

Here, we report a comprehensive study of the fundamental optical properties of two-dimensional materials. These properties have been ascertained using spectroscopic ellipsometry, optical spectroscopy of Raman scattering, and photoluminescence. We have focused on the optical properties of the chemically exfoliated layered TMDs: MoS₂, MoSe₂, WS₂, and WSe₂. The complex refractive index and optical conductivity within the region 1 to 4.5 eV were extracted, which led to the identification of many unique interband transitions at high symmetry points in the electron band structure. The positions of the so-called A and B excitons in monolayers are found to shift upwards in energy as compared with those of the bulk form and have a smaller separation because of the decreased interactions between the layers. For monolayer TMDs, the valence-band spin-orbit splitting at the K point was estimated from the energy difference between the A and B exciton peaks. Our findings of the spin-orbit coupling of ∼0.16, ∼0.26, ∼0.37, and ∼0.55 eV in monolayers MoS₂, MoSe₂, WS₂, and WSe₂, respectively. All these findings not only extend our understanding of the novel electronic structures of mono- and few-layer TMDs but also provide a foundation for future technological applications of optoelectronic and spintronic device components.