薄層硒化銦與二硫化鉬場效電晶體之電制光學特性

Abstract

調控半導體元件的光學特性可以應用在光電子學。二維材料的能帶結構決定了光的躍遷。由於二維材料有獨特的物理特性,可以透過不同的方法來調控它們的能帶結構,包含了張力、溫度和電場等。在這篇論文中,我們將致力於薄層硒化銦與二硫化鉬場效電晶體之光學特性。在第一個部分,我們研究以薄層氮化硼覆蓋的雙層二硫化鉬在二氧化矽上的場效。我們在雙層二硫化鉬上外加垂直電場。基於理論,外加電場可以調控雙層二硫化鉬的光學性質。我們使用二硫化鉬的光致螢光光譜並分析其場效的峰值。二硫化鉬的兩個直接能隙躍遷,A 和B 激子可以透過垂直電場來調控。由於斯塔克效應,我們觀察到外加的閘極電壓降低了光致螢光放射光能量。在第二個部分,我們研究薄層硒化銦在二氧化矽上的場效。因為硒化銦容易在大氣的環境下變質,我們發展了一項非常有效的技術,用聚甲基丙烯酸甲酯立刻覆蓋在薄層硒化銦上面。我們比較了不同層數的硒化銦場效電晶體的光致螢光光譜。然後我們使用石墨烯當作上層閘極去製造雙閘極為了外加垂直電場到薄層硒化銦。硒化銦從厚層數到薄層數的能帶是由直接到非直接。我們觀察到薄層硒化銦具有顯卓的光致螢光光譜峰值能量轉移。

Tunable optical properties of semiconductor devices can have useful applications in optoelectronics. The optical transitions of 2D materials are determined by their band structures. Due to the unique physical properties of the 2D materials, there are various methods to modify their band structures, including application of strain, temperature and electric field. In this thesis, we dedicate to the optical properties of field-effect devices based on few-layer InSe and MoS2. In the first part, we study the electric field-effect of bilayer MoS2 on silicon dioxide (SiO2) cover with few-layer boron nitride. We fabricate field-effect device structure to apply vertical electric field on the bilayer MoS2. Based on the theory, electric field can tune the bandgap and optical properties of bilayer MoS2. We perform photoluminescence (PL) spectroscopy of the MoS2 devices and analyze the field-effect of the PL peaks. The peaks energy of the two direct optical transitions of MoS2, known as the A and B excitons, is tunable as the vertical electric field is applied. We observe that PL emission energy can be reduced by increasing external gate voltage at given temperature, which may be due to Stark effect. In the second part, we study the electric field-effect of few-layer InSe on silicon dioxide. Because InSe is easily degraded in ambient condition, we develop a technique to cover the few-layer InSe with polymethylmethacrylate immediately which is very effective. We compare the thickness dependence of photoluminescence of the InSe field-effect devices with different temperature. We then fabricate graphene top gate to create a duel-gate structure for applying vertical electric field on few-layer InSe. For InSe, the bandgap are direct and indirect for bulk and few-layer InSe, respectively. We observe pronounced shift of the peak energy of photoluminescence in few-layer InSe.