Abstract
The adoption of 2D transition metal dichalcogenide (TMD) based optoelectronic devices is limited by Fermi level pinning effects and consequent large contact resistances upon contacting TMDs with bulk metal electrodes. A potential solution for near-ideal Schottky-Mott behavior and concomitant Schottky barrier height control is proposed by contacting TMDs and (semi-)metals in van der Waals heterostructures. However, measurement approaches to directly assess interface parameters relevant to the Schottky-Mott rule on a local scale are still lacking. In the present work, a heterostructure of monolayer tungsten diselenide (WSe2) with monolayer graphene (1LG) and bilayer graphene (2LG) is investigated on a bottom-gate substrate. Kelvin probe force microscopy and tip-enhanced photoluminescence measurements at different electrostatic doping induced Fermi levels in graphene enable decoupling and quantification of contributions from the interface dipole and electrode work function. These are used to locally probe Schottky barrier characteristics with below 32 nm lateral resolution, demonstrating that the WSe2/1LG junction operates at the Schottky-Mott limit (S approximate to 1). At the WSe2/2LG junction, a reduction of the interface dipole is directly related to changes in excitonic emission properties. These are attributed to charge transfer modulation across the interface, critical for obtaining high-performance transfer characteristics in transistors and related devices.