Ambipolar Charge Transport in Two-Dimensional WS2 Metal-Insulator-Semiconductor and Metal-Insulator-Semiconductor Field-Effect Transistors.

Two-dimensional (2D) materials with ambipolar transport characteristics have attracted considerable attention as post-complementary metal-oxide semiconductor (CMOS) materials. These materials allow for electron- or hole-dominant conduction to be achieved in a single channel of the field-effect transistors (FETs) without an extrinsic doping. In this study, all-2D metal-insulator-semiconductor (MIS)-based devices, which were composed of all-2D graphene, hexagonal boron nitride, and WS2, exhibited ambipolar and symmetrical transport characteristics with a low surface state density (Dit, min ≈ 7 × 1011 cm-2·eV-1). Hole- or electron-dominant inversion under the influence of electrostatic doping was obtained in a WS2-based 2D capacitor up to a frequency range of 1 MHz. n- and p-channel conductions with enhancement-mode operations were selectively realized in a single MISFET, which presented a current on/off ratio of >106 and high field-effect mobility (μe = 58-67 cm2/V·s and μh = 19-30 cm2/V·s). Furthermore, a monolithic CMOS-like logic inverter, which employed a single WS2 flake, exhibited a high gain of 78. These results can be used to reduce the footprints of the device architectures and simplify the device fabrication processes of next-generation CMOS integrated circuits.