Temperature Dependent Excitonic Transition Energy of MoSxSe2-x Alloys

• Main Authors: CHEN, TZU-YU, 陳姿妤
• Other Authors: HSU, HUNG-PIN
• Format: Others
• Language: zh-TW
• Published: 2019
• Online Access: http://ndltd.ncl.edu.tw/handle/j7rh5y

碩士 === 明志科技大學 === 電子工程系碩士班 === 107 === Two-dimensional transition metal chalcogenides (TMDCs) have attracted attention because of their layer-to-layer sandwich structure. This structure can be easily fabricated in atomic scale thickness. The layer is bonded by weak Van der Waals Force (vdW). Compare to graphene, TMDCs have both semiconductor and metal properties. The band gap can be changed from an indirect energy gap to a direct energy gap by varying the thickness from bulk to monolayer. The unique optoelectronic properties have great potential for the applications in next generation semiconductor industry. In this study, the chemical vapor transport (CVT) is used to add the conductive agent iodine (I2) or bromine (Br2) to grow the MoSxSe2-x(2≤x≤0) ternary alloy. The composition and its surface morphology were confirmed by scanning electron microscope and energy dispersive X-ray spectrometer. In optical measurement, piezoreflectance (PzR) spectroscopy technology was used to measure the exciton transition energies. The PzR spectroscopy has been employed to study the temperature and compositional dependence of the excitonic transition energy of MoSxSe2-x alloys in the temperature range from 25 to 295 K. Their temperature dependences were analyzed using Varshni semi-empirical expressions. It is found that the values of Varshni coefficients obtained from MoSxSe2-x varied with bowing effects with increases sulfur composition. Based on the experimental results, the temperature and compositional dependence of excitonic transition energy of MoSxSe2-x alloys has been empirically deduced for the entire alloy range in this study.