Nondestructive and local mapping photoresponse of WSe₂ by electrostatic force microscopy

We report a local mapping photoresponse of WSe₂ using a second-harmonic (2w) channel based on nondestructive electrostatic force microscopy (EFM). The 2w signals resulting from interaction between WSe₂ and EFM tip are intrinsically related to the electrical conductivity of WSe₂. The photoresponse images and rise/decay time constants of WSe₂ are obtained by local mapping 2w signals under illumination. We observe that the local photoresponse signals of WSe₂ increase with the positive tip gate voltage while the WSe₂ shows a p-type behavior in dark conditions We find that the reduced mobility of the photogenerated charge carriers resulting from the enhanced carrier scattering in the accumulation regime of WSe₂ is responsible for the gate-dependent photoresponse behavior. Our results provide a deep understanding the intrinsic optoelectrical properties of WSe₂ and contribute to the developments in the optoelectronic devices based on van der Waals layered materials.