Polarization Conversion in MoS 2 Flakes
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XVIII INTERNATIONAL SYMPOSIUM “NANOSTRUCTURES: PHYSICS AND TECHNOLOGY”, MINSK, REPUBLIC OF BELARUS, SEPTEMBER, 2020. EXCITONS IN NANOSTRUCTURES
Polarization Conversion in MoS2 Flakes L. V. Kotovaa,*, A. V. Platonova,**, A. V. Poshakinskiya,***, and T. V. Shubinaa,**** a Ioffe
Institute, St. Petersburg, 194021 Russia *e-mail: [email protected] **e-mail: [email protected] ***e-mail: [email protected] ****e-mail: [email protected]
Received July 24, 2020; revised July 24, 2020; accepted July 24, 2020
Abstract—We have studied experimentally a series of samples of layered MoS2 flakes with thicknesses varying from 1 to 10 μm and observed their strong in-plane optical anisotropy, which we attribute to the effects of strain in combination with fluctuations in the direction of the C-axis. This optical anisotropy allows us to convert the polarization of transmitted light from linear to circular with the degree up to 15%. Keywords: polarization, transition metal dichalcogenides, multilayer flakes DOI: 10.1134/S1063782620110160
INTRODUCTION In recent years, the two-dimensional (2D) semiconductor atomically thin materials are attracting growing attention of researchers. In particular, the prospects for creating van der Waals heterostructures are associated with such systems [1]. The most striking representative of 2D semiconductors is graphene, whose exceptional properties and its successful application in electronics, energy units, and sensors have inspired interest in other layered materials. In the last decade, the family of 2D semiconductors has been replenished with monomolecular layers of transition metal dichalcogenides (TMD) of the MX2 type, where M is a metal (Mo, W) and X is a dichalcogen (S, Se, Te). Unlike graphene, they have a pronounced optical band gap. The uniqueness of their band structure lies in the fact that with a decrease in thickness to the limit of a monolayer, the band gap structure transforms from indirect to direct. Among 2D semiconductors, the molybdenum disulfide (MoS2) occupies a special place as the most resistant to external influences and easily synthesized. Its band gap decreases from 1.8 eV in the monolayer (direct semiconductor [2]) to 1.3 eV in a bulk sample (indirect one). This allows the use of thin MoS2 films in LEDs [3], phototransistors [4] and solar cells [5]. Further applications of TMD involve a thorough study of optical effects, which are mainly associated with excitons—electron-hole pairs coupled by the Coulomb interaction [6]. In this material, the exciton
binding energy reaches hundreds of meV, and the radiation time is only a few picoseconds [7]. With the development of exfoliation and synthesis technologies, TMD thin films and various nanostructures were prepared and studied by many groups [8]. However, polarization phenomena in TMD were out of the focus of research interest. Our work is aimed at the study of the polarization properties of multilayer MoS2 films and their links with morphology and crystal imperfections. RESULTS AND DISCUSSION To qu
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