Investigation Of The Chemical Vapor Deposition And Properties Of The Two-Dimensional Tungsten Sulfide Films

The electrical structure of hexagonal tungsten disulfide?WS₂?is dependent on the thickness of the film.Unlike bulk materials,monolayer WS₂ is a direct band gap semiconductor with a band gap of ca.1.9 eV.The high quantum efficiency(ca.106 cm^-1)and carrier mobility(1000 cm²v^-1s^-1)make monolayer WS₂ a wide potential application in the field of nano optoelectron devices.However,the controllable growth of the two-dimensional WS₂ films is currently difficult to achieve,which limits its use in optoelectronic devices.In view of the current problems in the fabrication of the monolayer WS₂ film,we investigated a novel chemical vapor deposition?CVD?method to grow continuous monolayer/multilayers WS₂ with large-area.In this thesis,we deposited WS₂ film on the silicon oxide/silicon substrate using water vapor as a transport agent and zinc oxide?ZnO?as a heterogeneous nucleating agent.The effects of the growth time,the amount of transport agent,and the carrier gas flow rate,cooling rate and growth atmosphere on the growth behavior of WS₂ were studied.Based on the successful synthesis of two-dimensional WS₂ thin films,the stability and electrical properties of tungsten sulfide were also studied.The results show that the WS₂ film is unstable in air and decomposes when the temperature is higher than the room temperature.The higher the temperature,the poorer the stability.When the temperature increases to 400 ?,it will completely decompose.In addition,the plasma discharge in the air will also cause the decomposition of the monolayer WS₂.In order to improve the stability of tungsten sulfide,PMMA film was used.It is found that the PMMA film which covered on the surface of the WS₂ film can effectively protect the WS₂ from oxidation in air.In the last part of this thesis,the photo-detector based on the organic/inorganic heterojunction structure was prepared and studied.The results show the detector with a response of 0.1 A/W is very sensitive to light,indicating monolayer/multilayer WS₂ film has potential application in the field of photodetectors.