Dielectric and substrate engineered tuning of photoluminescence in monolayer WS₂

The dielectric environment strongly influences the photoluminescence (PL) of transition metal dichalcogenide (TMD) monolayers. The PL spectra are usually modified by the defect states present in the monolayer and substrate interface. To study the effect of substrate defects on PL, we have gradually increased the separation between substrate and WS₂ by placing hBN of various thicknesses in between. Further dielectric engineering was done by patterning the substrate with holes and pillars. In this way, we were able to tune the contribution of trion and exciton in the PL of WS₂. An excitation power-dependent study was also done to understand the tuning mechanism of PL in various kinds of engineered substrates. The charge of the substrate defects is also important in determining the nature of the PL spectra in monolayer WS₂. This effect was also studied by treating the substrate with APTES which changes the nature of the charge carried by a SiO₂/Si substrate. This study will be important for the fabrication of valleytronic and excitonic interconnects.