雙層二硫化鉬於圖案化藍寶石基板上之光與物質作用分析

Abstract

近年來二維材料發展了許多研究與應用，而屬於過渡金屬二硫族化物中的二硫化鉬也受到了相當的重視，因為二硫化鉬在單層原子的狀態下能夠擁有直接能隙和良好的光吸收效率，這些良好了光電特性讓二硫化鉬在光電元件的應用上受到矚目，但是受到單層狀態下厚度的限制，單層二硫化鉬的整體光吸收量並不高，所以在元件應用上，提高整體二硫化鉬的光與物質作用就變成一個很重要的課題，因此我們提出一個新的方式，將二硫化鉬成長在圖案化的藍寶石基板上，借由入射光的散射來增加二硫化鉬的光與物質作用。 本論文中，我們使用化學氣相沉積的方式在週期性光子晶體陣列上長成雙層的二硫化鉬，借由熱膨脹的概念，我們發現因為藍寶石基板在不同的方向會有不同的熱膨脹系數，因此會導致二硫化鉬有能帶上的變化，這些能帶上的變化有助於驅動載子往平坦的地方流動、幫助載子收集。最後我們製作出雙層二硫化鉬的光偵測器並量測其元件特性，相較於在平坦基板上的光偵測器，我們發現圖案化基板上的光偵測器因為有較強的光與物質作用而會有較大的光電流增益而且使用不同形狀的基板會讓光偵測器在特定的入射光波段能夠擁有最佳的光電流增益。我們相信在未來，我們可以根據不同的元件應用來挑選不同的圖案化基板來達到在特定波段下光與物質作用的最佳提升。

Two-dimensional (2D) materials have attracted a great attention due to their high performance for several applications. Molybdenum disulfide (MoS2), as a transition metal dichalcogenides (TMDCs) material, has shown extraordinary properties in photoelectric and photovoltaic devices in recent years due to the direct band gap of monolayer and strong light-matter interaction with light. However, owing to the innate thinness of monolayer MoS2, such a strong interaction must be further enhanced before it can be used in practical devices. Therefore, we develop a new approach to enhance the absorption by directly grow MoS2 on patterned sapphire substrate (PSS). The integration of PSS and MoS2 can enhance the light-matter interaction by the scattering of incident light. In this thesis, we directly synthesize the bilayer MoS2 on photonic crystal structures by using chemical vapor deposition (CVD)-growth method, and we have an amazing discovery after sulfurization process. Through thermal stress concept, we utilize the natural properties of sapphire (it has two different thermal expansion coefficients) and successfully tuned the band gap of bilayer MoS2. Our approach has an extraordinary capability to drive electrons toward flat region of the substrate by the shift of the band gap, allowing the electrode collects electrons more easily. Eventually, the bilayer MoS2 photodetectors with patterned and flat sapphire substrate are produced and demonstrated the performance of each sample. Those photodetectors with patterned substrates have outstanding broadband enhancement of photocurrent since the enhancement of light-matter interaction by the integration of patterned substrates and MoS2. Interestingly, different shape of patterned substrates will have the best enhancement of photocurrent at different region of incident light. It is believed that in the future, we can design or choose different patterned substrate to strongly enhance the absorption at specific region of incident light for different applications.