Lineshape characterization of excitons in monolayer WS2 by two-dimensional electronic spectroscopy.

Liang Guo,Zhuquan Zhang,Chun-An Chen,Daniele M Monahan,Graham R Fleming,Yi-Hsien Lee

doi:10.1039/d0na00240b

Abstract

The optical properties of monolayer transition metal dichalcogenides (TMDCs), an important family of two-dimensional (2D) semiconductors for optoelectronic applications, are dominated by two excitons A (XA) and B (XB) located at K/K's valleys. The lineshape of the excitons is an indicator of the interaction of the excitons with other particles and also largely determines the performance of TMDC-based optoelectronic devices. In this work, we apply 2D electronic spectroscopy (2DES), which enables separation of the intrinsic homogeneous linewidth and the extrinsic inhomogeneous linewidth, to dissect the lineshape of XA in monolayer WS2. With a home-built broadband optical parametric amplifier, the 2D spectra give the exciton linewidth values for extensive ranges of excitation densities and temperatures, reflecting inter-exciton and exciton–phonon interactions. Meanwhile, the time-domain evolution of the lineshape reveals a similar rate of spectral diffusion to that in quantum wells (QWs) based on III–V semiconductors.

Highlights

Monolayer transition metal dichalcogenides (TMDCs) have kindled a burst of research interest due to their salient optical properties such as direct bandgaps[1,2] and a valley degree of freedom tunable by optical helicity.[3,4] Quantum con nement and reduced dielectric screening in two-dimensional (2D) structures give excitons with large binding energies,[5,6] which play a key role in the interaction of light and monolayer TMDCs
The lineshape of the excitons is an indicator of the interaction of the excitons with other particles and largely determines the performance of TMDC-based optoelectronic devices
The homogeneous linewidth clearly rises with increasing exciton density due to the inter-exciton many-body interaction

Summary

Introduction

Monolayer transition metal dichalcogenides (TMDCs) have kindled a burst of research interest due to their salient optical properties such as direct bandgaps[1,2] and a valley degree of freedom tunable by optical helicity.[3,4] Quantum con nement and reduced dielectric screening in two-dimensional (2D) structures give excitons with large binding energies,[5,6] which play a key role in the interaction of light and monolayer TMDCs. The linewidth of the excitons affects the absorption and the emission spectra, which largely determine the performance of TMDC-based optoelectronic devices. The energy uctuation landscape is encoded in the exciton lineshape and its time-domain dynamics, which re ects the interaction of the excitons and the other particles such as phonons.[7,8] characterization of the exciton lineshape could provide insights for both application and fundamental research. There has recently been a growing demand for accessing the intrinsic linewidth of the excitons in monolayer TMDCs,[9,10]

Methods

Results

Conclusion