Probing the inter-layer exciton physics in a MoS$_2$/MoSe$_2$/MoS$_2$ van der Waals heterostructure

TL;DR

This study demonstrates long-lived inter-layer exciton emission with controllable circular polarization in a MoS₂/MoSe₂/MoS₂ heterostructure, revealing complex photoluminescence dynamics and valley polarization effects.

Contribution

It reports the first observation of long-lived inter-layer excitons in a MoS₂/MoSe₂/MoS₂ heterostructure and analyzes their polarization and dynamics.

Findings

Long-lived inter-layer exciton emission observed.

Circular polarization of emission can be controlled.

Complex photoluminescence dynamics indicating multiple bandgaps.

Abstract

Stacking atomic monolayers of semiconducting transition metal dichalcogenides (TMDs) has emerged as an effective way to engineer their properties. In principle, the staggered band alignment of TMD heterostructures should result in the formation of inter-layer excitons with long lifetimes and robust valley polarization. However, these features have been observed simultaneously only in MoSe$_2$/WSe$_2$ heterostructures. Here we report on the observation of long lived inter-layer exciton emission in a MoS$_2$/MoSe$_2$/MoS$_2$ trilayer van der Waals heterostructure. The inter-layer nature of the observed transition is confirmed by photoluminescence spectroscopy, as well as by analyzing the temporal, excitation power and temperature dependence of the inter-layer emission peak. The observed complex photoluminescence dynamics suggests the presence of quasi-degenerate momentum-direct and momentum-indirect bandgaps. We show that circularly polarized optical pumping results in long lived valley polarization of inter-layer exciton. Intriguingly, the inter-layer exciton photoluminescence has helicity opposite to the excitation. Our results show that through a careful choice of the TMDs forming the van der Waals heterostructure it is possible to control the circular polarization of the inter-layer exciton emission.