Two-dimensional (2D) transition-metal dichalcogenide (TMD) semiconductors are promising materials for realizing band-to-band tunneling devices owing to the atomically thin layer and abrupt interface of their heterostructures. In this study, we transferred scalable few-atomic-layer thin films using metal-organic chemical vapor deposition (MOCVD)-grown molybdenum disulfide (MoS2) as an n-channel and CVD-grown molybdenum ditelluride (MoTe2) and tungsten diselenide (WSe2) as p-channels to build van der Waals vertical heterostructures. The heterostructures of intrinsic MoS2 and MoTe2 (or WSe2), each having n-type, ambipolar, or high p-type conductivity, were suitable for tunneling field-effect transistor (TFET) applications. We measured the electrical transport properties of the MoS2/MoTe2 (or WSe2) heterostructures using an ion-gel top gate. The fabricated TFET with MoS2/MoTe2 (or WSe2) heterostructures exhibits a subthreshold swing as low as 9.1 (or 7.5) mV/dec. The negative differential transconductance, negative differential resistance, and temperature-dependent I–V characteristics demonstrate the band-to-band tunneling process. The findings have significant potential for applications in the large-area production of next-generation wearable, stretchable, and flexible low-power electronic devices.

Two-dimensional transition-metal dichalcogenide (TMD) device performance is significantly affected by the contact resistance of Schottky contacts at the p-type TMD-metal-electrode interface. The contact resistance and the Schottky barrier height (SBH) of a chemical-vapor-deposition-grown multilayer WSe 2 film-based field-effect transistor with Au electrodes were investigated. The experimentally measured and calculated SBH was determined from temperature-dependent currentvoltage measurements and thermionic emission model. The transfer length method was employed to investigate the contact resistance between the WSe 2 and the Au electrode. SBH values of 56 meV for negative V ds and 55.7 meV for positive V ds and a contact resistance of 12 kΩ•μm were found. An ion-gel-gated field-effect transistor based on multilayer WSe 2 exhibited ambipolar behavior with a mobility and an on/off ratio of 1.09 × 10 −2 cm 2 /V s and 10 3 , respectively.

A top-gate field-effect transistor (FET), based on monolayer (ML) tungsten disulfide (WS2), and with an ion-gel dielectric was developed. The high electrical contact resistance of the Schottky contacts at the n-type transition metal dichalcogenides/metal electrode interfaces often adversely affects the device performance. We report the contact resistance and Schottky barrier height of an FET with Au electrodes. The FET is based on ML WS2 that was synthesised using chemical vapour deposition and was assessed using the transfer-length method and low-temperature measurements. Raman and photoluminescence spectra were recorded to determine the optical properties of the WS2 layers. The ML WS2 FET with an ion-gel top gate dielectric exhibits n-type behaviour, with a mobility, on/off ratio of 1.97 cm2/V·s, 1.51×105, respectively.

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Polymer electrolytes and ionic liquids (ILs) have attracted significant interest in applications as gate dielectrics. In this study, we fabricated top-gated molybdenum disulfide (MoS 2 ) thin-film transistors using IL and ion-gel (IG) gate dielectrics. Room-temperature Raman spectra measurements indicated a dominant peak spectral emission at 358 cm −1 (𝐸 1 2𝑔 ) and 406.44 cm −1 (𝐴 1g ) associated with bilayer MoS 2 films. The fabricated thin-film field-effect transistors (FET) with IG gate dielectric exhibited band transport with a highest mobility of 0.5 cm 2 /V⋅s, and a poor 𝐼 ON /𝐼 OFF ratio of ~10. By contrast, the FET with IL gate dielectric exhibited a 3400 % improvement in terms of the mobility (17.9 cm 2 /V⋅s), and a 1000 % improvement of the 𝐼 ON /𝐼 OFF ratio (~100).