Observation of robust charge transfer under strain engineering in two-dimensional MoS₂-WSe₂ heterostructures

Strain is one of the effective ways to modulate the band structure of monolayer transition metal dichalcogenides (TMDCs), which has been reported in theoretical and steady-state spectroscopic studies. However, the strain effects on the charge transfer processes in TMDC heterostructures have not been experimentally addressed thus far. Here, we systematically investigate the strain-mediated transient spectral evolutions corresponding to excitons at band-edge and higher energy states for monolayer MoS₂ and monolayer WSe₂. It is demonstrated that Γ and K valleys in monolayer WSe₂ and monolayer MoS₂ present different strain responses, according to the broadband femtosecond pump-probe experimental results. It is further observed that the resulting band offset changes tuned by applied tensile strains in MoS₂-WSe₂ heterostructures would not affect the band-edge electron transfer profiles, where only monolayer WSe₂ is excited. From a flexible optoelectronic applications perspective, the robust charge transfer under strain engineering in TMDC heterostructures is very advantageous.