Neutral and charged excitons (trions) in atomically-thin materials offer important capabilities for photonics, from ultrafast photodetectors to highly-efficient light-emitting diodes and lasers. Recent studies of van der Waals (vdW) heterostructures comprised of dissimilar monolayer materials have uncovered a wealth of optical phenomena that are predominantly governed by interlayer interactions. Here, we examine the optical properties in NbSe2 - MoSe2 vdW heterostructures, which provide an important model system to study metal-semiconductor interfaces, a common element in optoelectronics. Through low-temperature photoluminescence (PL) microscopy we discover a sharp emission feature, L1, that is localized at the NbSe2-capped regions of MoSe2. L1 is observed at energies below the commonly-studied MoSe2 excitons and trions, and exhibits temperature- and power-dependent PL consistent with exciton localization in a confining potential. Remarkably, L1 is very robust not just in different samples, but also under a variety of fabrication processes. Using first-principles calculations we reveal that the confinement potential required for exciton localization naturally arises from the in-plane band bending due to the changes in the electron affinity between pristine MoSe2 and NbSe2 - MoSe2 heterostructure. We discuss the implications of our studies for atomically-thin optoelectronics devices with atomically-sharp interfaces and tunable electronic structures.
@article{arxiv.2004.02961,
title = {Localized Excitons in NbSe$_2$-MoSe$_2$ Heterostructures},
author = {Jaydeep Joshi and Tong Zhou and Sergiy Krylyuk and Albert V. Davydov and Igor Zutic and Patrick M. Vora},
journal= {arXiv preprint arXiv:2004.02961},
year = {2020}
}