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.