High-Performance Thin-Film Transistors Based on Highly Crystalline CVD-Grown Multilayer MoSe2 Films

Abstract

Layered semiconductors based on transition metal dichalcogenides (TMDs) (MX2, M = Mo, W; X = S, Se, Te) exhibit many distinctive characteristics, including wide band gap (Eg > 1 eV), high carrier mobility (>100 cm2/VS), large photoresponsivity (~500 A/W), and an outstanding mechanical flexibility. Thus, the TMD materials can serve as high-performance flexible/stretchable multifunctional electronics such as field-effect transistors (FETs), photodetectors, sensors and integrated circuitries. For realizing such electronic devices, reproducible large-area production of two-dimensional TMD materials becomes a key issue. It has been reported that MoSe2 shows a higher photoresponsivity compared to MoS2 because of the quantum confinement effect during the bad gap transition. On the other hand, multilayer TMDs provide a wider spectral response and higher photoresponsivity than monolayer TMDs. Additionally, FETs based on multilayer TMDs offer a relatively high performance, which are expected to be more suitable for commercial fabrication process than monolayer TMDs. Several groups have successfully synthesized monolayer MoSe2. However, there is hardly to find any research in chemical vapor deposition (CVD)-grown multilayer MoSe2 and its applications. In this study, a highly crystalline multilayer MoSe2 film was grown by CVD method directly onto SiO2 substrates. Firstly, we used a relatively high pressure (>760 Torr) to form multiple nuclei during the CVD growth, resulting in multilayer MoSe2 film. The fabricated multilayer MoSe2 thin-film transistors (TFTs) exhibit ambipolar behaviors with reasonably large field-effect mobility (~10 cm2/Vs) and high photoresponsivity (93.7 A/W). Secondly, large-grain multilayer MoSe2 was synthesized using a modified CVD method. Polycrystalline compounds of MoSe2 as precursor were directly vaporized onto Mo-coated SiO2 substrates. The multilayer MoSe2 has a relatively large grain size of several hundred micrometers. Transistors based on such MoSe2 single grains show n-type characteristics with field-effect mobility up to 121 cm2/Vs and on/off current ratio higher than 104 on Si wafers or plastic polyimide films. The MoSe2 transistor on polyimide substrate even shows good mechanical flexibility while bending down to a radius of curvature as small as 5 mm. The overall results of CVD-grown multilayer MoSe2 offers high speed, highly photoresponsive transistor for high-performance flexible/stretchable electronics.