Enhanced optical properties of MoSe$_2$ grown by molecular beam epitaxy on hexagonal boron nitride

TL;DR

This study demonstrates a novel molecular beam epitaxy method to grow high-quality monolayer MoSe₂ on hBN, achieving narrow photoluminescence linewidths and room temperature optical signatures, advancing large-area TMD device fabrication.

Contribution

First successful growth of monolayer MoSe₂ on hBN via MBE with optical properties comparable to exfoliated flakes.

Findings

Narrow PL linewidth down to 5.5 meV at 13 K

Detectable PL at room temperature

Clear reflectivity signatures of excitons

Abstract

Transition metal dichalcogenides (TMD) like MoSe$_2$ exhibit remarkable optical properties such as intense photoluminescence (PL) in the monolayer form. To date, narrow-linewidth PL is only achieved in micrometer-sized exfoliated TMD flakes encapsulated in hexagonal boron nitride (hBN). In this work, we develop a growth strategy to prepare monolayer MoSe$_2$ on hBN flakes by molecular beam epitaxy in the van der Waals regime. It constitutes the first step towards the development of large area single crystalline TMDs encapsulated in hBN for potential integration in electronic or opto-electronic devices. For this purpose, we define a two-step growth strategy to achieve monolayer-thick MoSe$_2$ grains on hBN flakes. The high quality of MoSe$_2$ allows us to detect very narrow PL linewidth down to 5.5 meV at 13 K, comparable to the one of encapsulated exfoliated MoSe$_2$ flakes. Moreover, sizeable PL can be detected at room temperature as well as clear reflectivity signatures of A, B and charged excitons.