Optical studies of Sm-doped ZnO and monolayer transition metal dichalcogenide thin film

• Main Author: 陳軍翰
• Other Authors: 劉祥麟
• Format: Others
• Language: zh-TW
• Published: 2018
• Online Access: http://ndltd.ncl.edu.tw/handle/2sn28u

碩士 === 國立臺灣師範大學 === 物理學系 === 106 === We investigated the samarium (Sm) doping effects on the optical properties of ZnO thin films and reported the temperature dependence spectroscopic ellipsometry studies of monolayer transition metal dichalcogenides thin films such as MoS2, MoSe2, WS2, and WSe2. Room temperature Raman scattering spectrum of undoped ZnO thin film shows two phonon modes at approximately 99.1 cm-1 and 437.9 cm-1, displaying symmetries of E2(low) and E2(high). With increasing Sm doping, E2(low) mode shows a blueshift. By contrast, E2(high) mode shows a redshift. Furthermore, the intensities of these two phonon modes decrease and become completely diminished for the 3% Sm doped sample. The intensities of optical transmission spectra show an increase in the ultraviolet region and the band gap energy shows a blueshift as the Sm contents increases. We attributed this feature to the Burstein-Moss effect for 3% and 5% doped samples and the band characteristics of ternary Zn1-xSmxO alloys for 8% and 10% doped samples. The temperature dependent refractive index and extinction coefficient spectra of monolayer transition metal dichalcogenides thin films were extracted from the ellipsometry parameters. Room temperature optical absorption spectra of these materials show two excitonic transitions (denoted as A and B excitons). They originate from the spin-split direct gap transitions at the K points of the Brillouin zone. Several high energy absorptions are associated with the electronic transitions at the Λ and M points. With increasing temperature, the intensity of refractive index decreases and the absorption structures show a redshift. Notably, the valence spin-orbit coupling is temperature independent.