二維晶體異質結構在光偵測器與電晶體之應用

Abstract

本論文以化學氣相沉積法在藍寶石基板成長石墨烯與二硫化鉬薄膜，利用溫度750 oC、800 oC、850 oC、900 oC，且同時放入足量的硫粉將二硫化鉬薄膜再硫化，提升二硫化鉬薄膜品質，透過材料分析儀器檢測再硫化後的薄膜，得出溫度850 oC再硫化為最理想條件，進一步的製備出二硫化鉬/石墨烯異質結構電晶體，發現再硫化異質結構元件隨照光有巨大的狄拉克點位移，相比未再硫化的異質結構元件，其位移有大幅的提升，說明再硫化的步驟，使二硫化鉬薄膜在照光的狀況下有更多的光電子產生，並轉移至低電阻性的石墨烯，造成類似於N型參雜的現象。另外，將石墨烯薄膜作為電極與鈦/金作為電極做比較，先利用TLM模型得到石墨烯相較於鈦/金具有較小的接觸電阻，進而製作出二硫化鉬電晶體，首先在背閘極電晶體製程中，由於轉印過程較為繁雜，不可避免會出現製程汙染和光阻殘留，無法突顯出以石墨烯作為電極之優點，改善製程進一步製備出上閘極電晶體，發現石墨烯作為電極其載子遷移率高達0.251 cm2/V-1s-1，而元件電流開關比為2371.98，以金屬作為電極其載子遷移率達0.0074 cm2/V-1s-1，而元件電流開關比為113.05，說明較小的接觸電阻確實可提升元件特性，未來若發展其它二維材料可與石墨烯電極做結合，將有助於提升二維材料電晶體特性。

Enhanced photoluminescence intensities are observed for the MoS2 film prepared by chemical vapor deposition (CVD) with an additional 850 oC post-growth annealing procedure under sulfur-rich environment. The enlarged Dirac point shift of the MoS2/graphene hetero-structure photodetectors with the post-growth annealing procedure suggests that more photo-excited electrons will transport to the graphene and effectively higher n-type doped the channel. The direct 2-D crystal hetero-structure growth by using CVD has avoided the complicated procedure of sequential attachment of different 2-D crystals, which is advantageous for practical applications. For electronic device applications, we have compared graphene and Ti/Au as electrodes for MoS2 transistors. TLM model has been used to obtain the contact resistance for the two electrodes. The resistance value of graphene is much less than Ti/Au. In order to compare the impact from the two electrodes, we used them to do S/D contact to fabricate MoS2 top-gated transistor. The carrier mobility values for transistors with graphene and Ti/Au as electrodes are 0.251 cm2/V-1s-1 and 0.0074 cm2/V-1s-1, respectively. A lower contact resistance is helpful for current flows in transistors. The technique of using graphene as the electrode will help to improve the device performances for devices based on 2-D materials.