Carrier Type Control of WSe2 Field-Effect Transistors by Thickness Modulation and MoO3 Layer Doping

Control of the carrier type in 2D materials is critical for realizing complementary logic computation. Carrier type control in WSe2 field-effect transistors (FETs) is presented via thickness engineering and solid-state oxide doping, which are compatible with state-of-the-art integrated circuit (IC) processing. It is found that the carrier type of WSe2 FETs evolves with its thickness, namely, p-type (<4 nm), ambipolar (approximate to 6 nm), and n-type (> 15 nm). This layer-dependent carrier type can be understood as a result of drastic change of the band edge of WSe2 as a function of the thickness and their band offsets to the metal contacts. The strong carrier type tuning by solid-state oxide doping is also demonstrated, in which ambipolar characteristics of WSe 2 FETs are converted into pure p-type, and the field-effect hole mobility is enhanced by two orders of magnitude. The studies not only provide IC-compatible processing method to control the carrier type in 2D semiconductor, but also enable to build functional devices, such as, a tunable diode formed with an asymmetrical-thick WSe2 flake for fast photodetectors.