High Performance Field-Effect Transistors Based On High-Quality WSe₂ By Chemical Vapor Deposition

In recent years,two-dimensional materials have become a central issue in the field of semiconductor research due to their excellent properties.As an intrinsic bipolar material,monolayer tungsten selenide(WSe₂)had a thickness of 0.7 nm and a direct band gap of 1.65e V,which provided a great application potential in low power,high performance digital logic circuit.How to synthesize large-area and high-quality monolayer WSe₂ film have become the key issue of current research field,which was the prerequisite for industrial application.In this paper,toward high-quality,large single-crystal monolayer WSe₂ films,controllable growth,material characteristics and electrical properties of monolayer WSe₂ were systematically researched.The research content included the following aspects:(1)From the view of the growth,two different methods including chemical vapor transport(CVT)and chemical vapor deposition(CVD)were used to synthesize monolayer tungsten selenide films.The effects of different growth parameters of synthesis monolayer WSe₂ films,including temperature,precursors weight and carrier gas,were explored.The appropriate growth parameters were finally determined.The CVD WSe₂ single-crystal size up to 140?m have been obtained.(2)Through the materials characterization by optical microscope,atomic force microscope,Raman spectrum and photoluminescence spectrum,it was shown that the monolayer WSe₂ films could be successfully grown by two different methods,and the WSe₂films grown by chemical vapor deposition method had better quality and larger size.(3)The single-layer tungsten selenide grown by chemical vapor deposition was transferred to high-?substrate,and the back gate field-effect transistor(FET)was fabricated by spin-coating,electron beam lithography(EBL),electron beam evaporation(EBE),reactive ion etching(RIE)and lift-off,respectively.The electrical properties of the back gate FET were characterized with different source/drain contact were used,including platinum(Pt),titanium(Ti)and gold(Au).These results showed that the back-gate devices with Au as source/drain contact had better performance,and the electron mobility up to 4.16 cm²/V·s.It was shown that monolayer WSe₂ back-gate FET film with Au source/drain contact had an obvious advantage on electrical performances.