Imaging Spatial Distribution of Photogenerated Carriers in Monolayer MoS 2 with Kelvin Probe Force Microscopy.

The spatial distribution of photogenerated carriers in atomically thin MoS 2 flakes is investigated by measuring surface potential changes under light illumination using Kelvin probe force microscopy (KPFM). It is demonstrated that the vertical redistribution of photogenerated carriers, which is responsible for photocurrent generation in MoS 2 photodetectors, can be imaged as surface potential changes with KPFM. The polarity of surface potential changes points to the trapping of photogenerated holes at the interface between MoS 2 and the substrate as a major mechanism for the photoresponse in monolayer MoS 2 . The temporal response of the surface potential changes is compatible with the time constant of MoS 2 photodetectors. The spatial inhomogeneity in the surface potential changes at the low light intensity that is related to the defect distribution in MoS 2 is also investigated.