# Direct exciton emission from atomically thin transition metal dichalcogenide heterostructures near the lifetime limit

## TL;DR

Encapsulating atomically thin TMDCs in hBN significantly narrows excitonic linewidths, approaching the homogeneous limit, and enhances optical quality by reducing inhomogeneous broadening and stabilizing exciton and trion emissions.

## Contribution

This study demonstrates that hBN encapsulation of TMDC monolayers reduces linewidths to near the lifetime limit and improves optical stability, a novel approach for high-quality 2D material optoelectronics.

## Key findings

- Linewidths reduced to ~3.5-5.0 meV with hBN encapsulation.
- Encapsulation shifts spectral weight towards neutral or charged excitons depending on doping.
- Encapsulated MoS₂ shows resolvable exciton and trion emission under high power.

## Abstract

We demonstrate the reduction of the inhomogeneous linewidth of the free excitons in atomically thin transition metal dichalcogenides (TMDCs) MoSe$_{2}$, WSe$_{2}$ and MoS$_{2}$ by encapsulation within few nanometer thick hBN. Encapsulation is shown to result in a significant reduction of the 10K excitonic linewidths down to $\sim3.5 \text{ meV}$ for n-MoSe$_{2}$, $\sim5.0 \text{ meV}$ for p-WSe$_{2}$ and $\sim4.8 \text{ meV}$ for n-MoS$_{2}$. Evidence is obtained that the hBN environment effectively lowers the Fermi level since the relative spectral weight shifts towards the neutral exciton emission in n-doped TMDCs and towards charged exciton emission in p-doped TMDCs. Moreover, we find that fully encapsulated MoS$_{2}$ shows resolvable exciton and trion emission even after high power density excitation in contrast to non-encapsulated materials. Our findings suggest that encapsulation of mechanically exfoliated few-monolayer TMDCs within nanometer thick hBN dramatically enhances optical quality, producing ultra-narrow linewidths that approach the homogeneous limit.