The ambipolar transport behavior of WSe2 transistors and its analogue circuits

Tungsten diselenide (WSe2) has many excellent properties and provides superb potential in applications of valley-based electronics, spin-electronics, and optoelectronics. To facilitate the digital and analog application of WSe2 in CMOS, it is essential to understand the underlying ambipolar hole and electron transport behavior. Herein, the electric field screening of WSe2 with a thickness range of 1–40 layers is systemically studied by electrostatic force microscopy in combination with non-linear Thomas–Fermi theory to interpret the experimental results. The ambipolar transport behavior of 1–40 layers of WSe2 transistors is systematically investigated with varied temperature from 300 to 5 K. The thickness-dependent transport properties (carrier mobility and Schottky barrier) are discussed. Furthermore, the surface potential of WSe2 as a function of gate voltage is performed under Kelvin probe force microscopy to directly investigate its ambipolar behavior. The results show that the Fermi level will upshift by 100 meV when WSe2 transmits from an insulator to an n-type semiconductor and downshift by 340 meV when WSe2 transmits from an insulator to a p-type semiconductor. Finally, the ambipolar WSe2 transistor-based analog circuit exhibits phase-control by gate voltage in an analog inverter, which demonstrates practical application in 2D communication electronics. Transistors made from two-dimensional tungsten selenide (WSe2) crystals may simplify fabrication of electronic communication devices. Modern transistors amplify and manipulate current by applying electric fields to semiconductor films known as channels that are designed to transport either positive or negative charges. Mingdong Dong from Aarhus University in Denmark and colleagues have developed a new transistor that can move both types of charge. The team found that when individual flakes of WSe2 were stacked into a multi-layered channel structure, the dominant type of charge transported could be switched using an external electrode. A prototype amplifier constructed from two WSe2-based transistors showed this approach enabled fundamental control over analog signals, and could potentially be used in complex circuits that require fewer materials and smaller chip footprints than usual. Compared with unipolar transistors, ambipolar transistors, which can easily switch between n-type and p-type behavior by applying an electric field, are most promising candidates since they can effectively simplify circuit design and save the layout area in CMOS. In this study, we take a deep insight into the thickness dependent physical properties of WSe2, where the optical properties, electric field screening effect, and the ambipolar transport behavior are systematically studied. Furthermore, the investigation of ambipolar WSe2 transistors in analogue circuits exhibiting gate-controlled phase change directly explores its practical application in 2D communication electronics.