以覆蓋氣-液-固相方法合成釩摻雜之二硫化鉬薄膜

Abstract

二維材料近年來被視為下一世代的半導體材料，有別於三維材料，二維材料能以單原子層結構穩定存在，並且具備良好的物性與電性，可縮小現有的場效電晶體體積，提高晶片效能；除此之外，二維材料也能做為新穎的替代能源材料，將二氧化碳轉化成碳氫化合物，並且可透過釩摻雜來提高催化效率，期望改善全球暖化問題。本實驗研究的二維材料為屬於過渡金屬二硫族化合物(TMDCs)中的二硫化鉬，並著重於合成釩摻雜之二硫化鉬的方法，二硫化鉬不僅可應用於光電元件，亦可做為觸媒材料，若想將二硫化鉬應用於工業上，則需要合成大面積且連續均勻的薄膜，故此研究使用創新的合成方法: 覆蓋氣-液-固態方法來製備釩參雜之二硫化鉬薄膜，首先在矽基板上沉積四層前驅物薄膜，依序為:三氧化鉬、五氧化二釩、氟化鈉、二氧化矽薄膜，二氧化矽薄膜做為覆蓋層及擴散膜，防止氧化釩蒸發消失跟控制氣體硫的擴散，對於釩摻雜是重要的一環，若沒有二氧化矽覆蓋層，釩將無法成功的摻雜進二硫化鉬中；在硫化過程中氧化鉬、氧化釩與氟化鈉先反應形成鹽類液體後，氣態硫再穿過二氧化矽覆蓋層來與鹽類液體反應，最後過飽和析出釩摻雜二硫化鉬薄膜；此方法因牽涉到鹽類液態反應，因此能合成高摻雜濃度的二硫化鉬薄膜。Transition metal dichalcogenides (TMDs) have attracted people’sattention due to their outstanding physical properties. Molybdenumdisulfide (MoS 2 ) thin film has been particularly found unique applicationsin catalysis, optoelectronics, transistors, and energy storage. Theseapplications demand a large-scale synthesis of MoS 2 thin film with uniformthickness and high crystallinity. Besides, dopants in two-dimensionaldichalcogenides have a significant role in affecting electronic, mechanical,and interfacial properties. Controllable doping is desired for the intentionalmodification of such properties to enhance performance. Vanadium-doingcould enhance MoS 2 conductivity and carrier concentration so that it canimprove catalytic activity. In this report, a new capping vapor-liquid-solid(VLS) synthesis has been developed. Depositing MoO 3 , V 2 O 5 , NaF andSiO 2 on SiO 2 /Si wafer sequentially as a 4-layer precursor. Herein, SiO 2 actsas capping layer and diffusion membrane, which is critical for V-doping.During sulfurization, MoO 3 , V 2 O 5 and NaF will form Mo/V/Na salt liquidfirst. Then sulfur will diffuse through capping SiO 2 layer and dissolve inNa salt liquid. Finally, V-MoS 2 will oversaturated on the substrate. Afterthat, HF etching process is used to remove capping SiO 2 layer and V-MoS 2will show on the centimeter-scale wafer.