Boosting and Balancing Electron and Hole Mobility in Single- and Bilayer WSe2 Devices via Tailored Molecular Functionalization

WSe 2 is a layered ambipolar semiconductor enabling hole and electron transport, which renders it a suitable active component for logic circuitry. However, solid-state devices based on single- and bilayer WSe 2 ypically exhibit unipolar transport and poor electrical performance when conventional SiO 2 dielectric and Au electrodes are used. Here, we show that silane-containing functional molecules form ordered monolayers on the top of the WSe 2 surface, thereby boosting its electrical performance in single- and bilayer field-effect transistors. In particular, by employing SiO 2 dielectric substrates and top Au electrodes, we measure unipolar mobility as high as μ h = 150 cm 2 V -1 s -1 and μ e = 17.9 cm 2 V -1 s -1 in WSe 2 single-layer devices when ad hoc molecular monolayers are chosen. Additionally, by asymmetric double-side functionalization with two different molecules, we provide opposite polarity to the top and bottom layer of bilayer WSe 2 , demonstrating nearly balanced ambipolarity at the bilayer limit. Our results indicate that the controlled functionalization of the two sides of the WSe 2 mono- and bilayer flakes with highly ordered molecular monolayers offers the possibility to simultaneously achieve energy level engineering and defect functionalization, representing a path toward deterministic control over charge transport in 2D materials.