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

TL;DR

This paper demonstrates a method to create a nanoscale lateral heterojunction in monolayer MoSe2 with a large built-in potential by intercalating Se, enabling environmental engineering of 2D material electronic properties for future device applications.

Contribution

It introduces a novel approach to engineer lateral heterojunctions in 2D materials through environmental proximity manipulation, surpassing traditional growth constraints.

Findings

Achieved a 0.83 eV built-in potential in MoSe2 heterojunction.

Demonstrated local band gap increase of ~0.26 eV due to dielectric environment change.

Mapped nanoscale depletion region using scanning tunneling spectroscopy.

Abstract

The ability to engineer atomically thin nanoscale lateral heterojunctions (HJs) 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 monolayer TMDs to create a heterojunction. Here we demonstrate the synthesis of a nanoscale lateral heterojunction in monolayer MoSe2 by intercalating Se at the interface of a 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 MoSe2 monolayer to create a large built-in potential of 0.83 eV. We spatially resolve the MoSe2 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 MoSe2 band gap by ~0.26 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, providing avenues for future device design.