Visualizing Band Profiles of Gate-Tunable Junctions in MoS/WSe Heterostructure Transistors.

Heterostructure devices based on two-dimensional materials have been under intensive study due to their intriguing electrical and optical properties. One key factor in understanding these devices is their nanometer-scale band profiles, which is challenging to obtain in devices. Here, we use a technique named contact-mode scanning tunneling spectroscopy to directly visualize the band profiles of MoS/WSe heterostructure devices at different gate voltages with nanometer resolution. The long-held view of a conventional p-n junction in the MoS/WSe heterostructure is reexamined. Due to strong inter- and intralayer charge transfer, the MoS layer in contact with WSe is found to convert from n-type to p-type, and a series of gate-tunable p-n and p-p junctions are developed in the devices. Highly conductive edges are also discovered which could strongly affect the device properties.