Spectrally narrow exciton luminescence from monolayer MoS2 exfoliated onto epitaxially grown hexagonal BN

TL;DR

This study demonstrates that monolayer MoS2 and MoSe2 exhibit spectrally narrow exciton luminescence when exfoliated onto epitaxially grown hBN, showing potential for scalable TMD heterostructure fabrication with improved optical quality.

Contribution

It shows that MBE-grown hBN can effectively enhance optical properties of TMD monolayers, offering a scalable alternative to exfoliated hBN for device applications.

Findings

MBE-grown hBN improves TMD optical quality

Encapsulated TMDs show narrower exciton linewidths

Potential for large-scale TMD heterostructure fabrication

Abstract

The strong light-matter interaction in transition Metal dichalcogenides (TMDs) monolayers (MLs) is governed by robust excitons. Important progress has been made to control the dielectric environment surrounding the MLs, especially through hexagonal boron nitride (hBN) encapsulation, which drastically reduces the inhomogeneous contribution to the exciton linewidth. Most studies use exfoliated hBN from high quality flakes grown under high pressure. In this work, we show that hBN grown by molecular beam epitaxy (MBE) over a large surface area substrate has a similarly positive impact on the optical emission from TMD MLs. We deposit MoS$_2$ and MoSe$_2$ MLs on ultrathin hBN films (few MLs thick) grown on Ni/MgO(111) by MBE. Then we cover them with exfoliated hBN to finally obtain an encapsulated sample : exfoliated hBN/TMD ML/MBE hBN. We observe an improved optical quality of our samples compared to TMD MLs exfoliated directly on SiO$_2$ substrates. Our results suggest that hBN grown by MBE could be used as a flat and charge free substrate for fabricating TMD-based heterostructures on a larger scale.