| AVS 65th International Symposium & Exhibition | |
| Spectroscopic Ellipsometry Focus Topic | Monday Sessions |
| Session EL+AS+EM-MoM |
| Session: | Application of SE for the Characterization of Thin Films and Nanostructures |
| Presenter: | Baokun Song, Huazhong University of Science & Technology, China |
| Authors: | B.K. Song, Huazhong University of Science & Technology, China H.G. Gu, Huazhong University of Science & Technology, China M.S. Fang, Huazhong University of Science & Technology, China Y.L. Hong, Shenyang National Laboratory for Materials Science Institute of Metal Research Chinese Academy of Sciences, China W.C. Ren, Shenyang National Laboratory for Materials Science Institute of Metal Research Chinese Academy of Sciences, China X.G. Chen, Huazhong University of Science & Technology, China S.Y. Liu, Huazhong University of Science & Technology, China |
| Correspondent: | Click to Email |
Recently, two-dimensional (2D) WSe2 has become a popular choice for nanoelectronic, optoelectronic, and valleytronic devices due to its layer-modulated bandgap, high mobility (~200cm2V-1s-1) and on-off ratio (108), and large spin-orbit coupling effect. The performance of those novel WSe2-based devices strongly depends on the intrinsic optical properties of WSe2, which exhibit an intriguing layer dependency. Therefore, the accurate and quantitative characterization of the layer-dependent optical properties of WSe2 is essential to the optimal design of those related devices.
In this work, the dielectric function, bandgaps, and critical points (CPs) of WSe2 ranging from monolayer to bulk have been comprehensively investigated and analyzed by spectroscopic ellipsometry over an ultra-broad band (0.73-6.42eV). The dielectric function of high-quality uniform WSe2 specimens prepared by chemical vapor deposition were firstly obtained from the ellipsometric spectra. Then the bandgaps of the WSe2 films were determined from their corresponding absorption coefficient spectra. We experimentally observed that the bandgaps of the WSe2 films change from 1.63eV in monolayer to 1.21eV in bulk. Moreover, by using the CPs analysis, a series CPs (A-H) in the dielectric function spectra were precisely distinguished and many of them were rarely reported before. The positions of CPs (A-E) exhibit an obvious red shift when the layer number increases, while the CPs (F-H) exhibit a slight blue shift. The former phenomenon can be partly interpreted as the decaying geometrical confinement of excitons, while the underlying reasons for the latter merit further studies. These novel and advanced optical features will promote the fundamental understanding of the electronic structures and the development of WSe2-based devices.