Verifying 2D device potentials and conduction with Kelvin Probe Force Microscopy*

In a 2D field effect transistor (FET), the electrical properties of the channel are modulated using a gate voltage. The electrostatic doping of the channel and the contact resistance of the interacting layers both contribute to the overall device conductivity, which plateaus above a certain gate voltage. Other factors, such as surface cleanliness and microscopic details of the films also influence the conductivity as can be deduced from variations between multiple devices. In this study, we explore the ability of Kelvin probe force microscopy (KPFM) to separate out the different factors influencing overall device conductivity. By applying a potential bias to a simple device, we build confidence in the linear response and reproducibility of the KPFM technique. We then directly visualize the uniformity of the surfaces, the potential barriers between layers, and the characteristics of the WSe₂ film as a function of the applied voltage. These data deepen our understanding of device potentials and conduction in 2D FETs.