Creating a Nanoscale Lateral Junction in a Semiconductor Monolayer with a Large Built-in Potential.

The ability to engineer atomically thin nanoscale lateral junctions is critical to lay the foundation for future two-dimensional (2D) device technology. However, the traditional approach to creating a heterojunction by direct growth of a heterostructure of two different materials constrains the available band offsets, and it is still unclear if large built-in potentials are attainable for 2D materials. The electronic properties of atomically thin semiconducting transition metal dichalcogenides (TMDs) are not static, and their exciton binding energy and quasiparticle band gap depend strongly on the proximal environment. Recent studies have shown that this effect can be harnessed to engineer the lateral band profile of a monolayer TMD to create a lateral electronic junction. Here we demonstrate the synthesis of a nanoscale lateral junction in monolayer MoSe by intercalating Se at the interface of an hBN/Ru(0001) substrate. The Se intercalation creates a spatially abrupt modulation of the local hBN/Ru work function, which is imprinted directly onto an overlying MoSe monolayer to create a lateral junction with a large built-in potential of 0.83 ± 0.06 eV. We spatially resolve the MoSe band profile and work function using scanning tunneling spectroscopy to map out the nanoscale depletion region. The Se intercalation also modifies the dielectric environment, influencing the local band gap renormalization and increasing the MoSe band gap by ∼0.26 ± 0.1 eV. This work illustrates that environmental proximity engineering provides a robust method to indirectly manipulate the band profile of 2D materials outside the limits of their intrinsic properties.