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

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.

Efficient Photocarrier Transfer and Effective Photoluminescence Enhancement in Type I Monolayer MoTe2/WSe2 Heterostructure

“…A similar peak at 1.07 eV is observed in the 1L‐MoTe 2 /1L‐WSe 2 heterostructure, suggesting that PL from the MoTe 2 layer occurs in the heterostructure. Noticeable increase in the PL intensity is detected in the heterostructure in comparison with that in isolated MoTe 2 , which is different from those observed in various combinations of Type II TMD heterostructures where the PL intensities of both constituent layers are drastically quenched . Moreover, no additional peaks are detected below the low‐energy side of 1.07 eV, which is also different from the Type II heterostructures where additional PL peaks arising from the interlayer electron–hole pairs (interlayer exciton) obviously emerge .…”

Efficient strain modulation of 2D materials via polymer encapsulation

“…The difference between exfoliated WSe 2 and CVD grown WSe 2 could be attributed to the inferior quality of CVD grown samples, with possible dopants, defects, or pre-strains. Nevertheless, the observed ΔE g values are much higher than previous reports 10,16,18,21,22,25,[39][40][41][42][43][44] , indicating our method is a general approach for effective strain transfer with negligible slippage.…”

Strain tuning of excitons in monolayer WSe2

“…Spin and valley lifetime of excitons and electrons are expected to be longer in strained 1L WSe 2 and WS 2 since intervalley scattering is strongly suppressed. Due to the increased coherence lifetime of excitons and other tunable characteristics, strained 1Ls yield heterostructures with superior optoelectronic properties [45][46][47][48][49] . Moreover, higher mobility is expected from the devices made from strained 1L TMDCs due to decreased carrier-phonon intervalley scattering 20,24 , as in the case of strained silicon 50 .…”