Crystal growth and characterization of niobium incorporated W1-xNbxSe2(0 ≤ x≤ 0.2 ), MoTe2 and WTe2 layered semiconductors

• Main Authors: Pin-Rui Ji, 紀品睿
• Other Authors: Ching-Hwa Ho
• Format: Others
• Language: zh-TW
• Published: 2018
• Online Access: http://ndltd.ncl.edu.tw/handle/zfyf84

碩士 === 國立臺灣科技大學 === 應用科技研究所 === 106 === Abstract In this thesis, we have successfully grown W1-xNbxSe2 (Tungsten-doped Niobium diselenides，0 ≤ x≤ 0.2 ) series layered crystals, MoTe2 (molybdenum ditelluride) and WTe2 (Tungsten ditelluride) layer compounds by chemical vapor transport method using I2 as the transport agent. Using XRD, we find that W1-xNbxSe2 (0 ≤ x ≤ 0.2) with a Nb doping peak shifts to a high angle, resulting in a decrease in the lattice constant and a forming 2H (Two layer hexagonal) structure. Through the resistivity measurement WSe2 semiconductors become metallic and high conductivity due to Nb doping. Thermoelectric and Hall measurements, showed W1-xNbxSe2 is a degenerate P-type semiconductor, and Raman optical measurement revealed W1-xNbxSe2 with Nb impurity displayed E12g and A1g vibration modes shift to lower wave numbers. At the same time, using XRD, we can prove that WTe2 and MoTe2 are 2H (Two layer hexagonal) structures, and through the resistivity measurement, they are found to be high conductive. The characteristics of conductive N-type semiconductors and the thinning of WTe2 by Raman reveals that the vibration modes A51 = 161cm-1 and A21 = 212cm-1 have a tendency to increase intensity and have a polarization characteristic. The thickness of MoTe2 becomes thinning to make a vibration mode states E2g = 234cm-1 and B2g = 301cm-1 have a tendency to increase intensity and have polarization characteristics. Finally, through piezoelectric modulation and transmittance, we can find that MoTe2 is an indirect semiconductor which has A, B and C excitons. The indirect energy gap at room temperature is 0.91 eV and the direct energy gap is 1.06 eV. Keywords: Layered structure, Transition metal dichalcogenides , X-ray photoelectron spectrometer, X-ray lattice diffraction analyzer, Raman scattering, modulation spectroscopy, voltage-current measurement, Hall measurement, scanning electron microscope, Transmission electron microscope , an atomic force microscope.