在惰性基板上磊晶成長之大面積二硫化鉬/石墨烯異質結構及其光偵測器之運用

Abstract

本論文一開始利用乙烷以化學氣相沉積技術在藍寶石基板上成長大面積的石墨烯薄膜，我們運用乙烷解離能小於甲烷的特性，使得碳源的裂解比起常見的甲烷能更有效率，而藉由調變成長壓力與時間，我們成功的優化以乙烷在惰性的藍寶石基板上成長出大面積石墨烯薄膜。接著我們也嘗試在運用原子層沉積系統沉積出的氧化鋁薄膜上直接成長石墨烯薄膜。最後我們利用石墨烯/藍寶石樣品作為新的基板，將不同層數的二硫化鉬薄膜直接成長在該基板上，我們成功運用此成長方式製備出大面積且可控層數的二硫化鉬/石墨烯異質結構。將該薄膜轉印至預先鍍好汲/源電極的二氧化矽/矽基板後，我們可將製作出具背電極之二硫化鉬/石墨烯異質結構光電晶體，當光由二硫化鉬所吸收後，光電子會注入石墨烯並形成類似於n型摻雜的現象而造成狄拉克點的位移。此外我們在該元件也觀察到預期之外的光伏現象。

In this thesis, we directly grow the large-area graphene on the sapphire substrate by chemical vapor deposition with ethane as the precursor. Because the dissociation energy of ethane is smaller than methane, ethane molecules can dissociate more efficiently into carbon atoms such that reduced growth time can be obtained for direct graphene growth on sapphire substrates. With the optimization of growth pressures and time durations, we have demonstrated scalable graphene film growth on the inert sapphire substrate. We have also tried similar graphene growth directly on aluminum oxide prepared by a atomic layer deposition system on Si substrates. Using the graphene/sapphire sample as the new substrate, scalable MoS2 films with good layer number controllability can be grown directly on the substrate. After transferring the MoS2/graphene films to SiO2/Si substrates with pre-patterned source/drain electrodes, bottom-gate photo-transistors with MoS2/graphene hetero-structures are fabricated. The photo-excited electrons in the MoS2 layer would be attracted by the positive drain voltage and drift to the graphene channel. Therefore, an n-type optical doping to the graphene channel is obtained, which will results in Dirac point shift for the transistors. An unexpected photo-voltaic phenomenon is also observed for the device.