Strain-Mediated Interlayer Coupling Effects on the Excitonic Behaviors in an Epitaxially Grown MoS₂/WS₂ van der Waals Heterobilayer

TLDR

Van der Waals heterostructures of two different monolayer crystals are a versatile platform for studying fundamental physics and future devices, yet the underlying physics of interlayer coupling on electron–photon–phonon interactions remains poorly understood. The study analyzes how uniaxial tensile and compressive strain modulates excitonic behavior in an epitaxially grown MoS₂/WS₂ heterobilayer. The authors modulate interlayer interactions by applying uniaxial strain, thereby altering each monolayer’s band‑gap transitions and band structure. Strain‑modulated interlayer coupling changes the vibrational and excitonic properties, with the WS₂/MoS₂ photoluminescence ratio rising under tensile strain and falling under compression, highlighting a route for designing flexible heterostructure devices.

Abstract

van der Waals heterostructures composed of two different monolayer crystals have recently attracted attention as a powerful and versatile platform for studying fundamental physics, as well as having great potential in future functional devices because of the diversity in the band alignments and the unique interlayer coupling that occurs at the heterojunction interface. However, despite these attractive features, a fundamental understanding of the underlying physics accounting for the effect of interlayer coupling on the interactions between electrons, photons, and phonons in the stacked heterobilayer is still lacking. Here, we demonstrate a detailed analysis of the strain-dependent excitonic behavior of an epitaxially grown MoS2/WS2 vertical heterostructure under uniaxial tensile and compressive strain that enables the interlayer interactions to be modulated along with the electronic band structure. We find that the strain-modulated interlayer coupling directly affects the characteristic combined vibrational and excitonic properties of each monolayer in the heterobilayer. It is further revealed that the relative photoluminescence intensity ratio of WS2 to MoS2 in our heterobilayer increases monotonically with tensile strain and decreases with compressive strain. We attribute the strain-dependent emission behavior of the heterobilayer to the modulation of the band structure for each monolayer, which is dictated by the alterations in the band gap transitions. These findings present an important pathway toward designing heterostructures and flexible devices.