Modulation of trion and exciton formation in monolayer WS <sub>2</sub> by dielectric and substrate engineering
Tamaghna Chowdhury, Diptabrata Paul, Divya Nechiyil, M. A. Gokul, Kenji Watanabe, Takashi Taniguchi, G. V. Pavan Kumar, Atikur Rahman
Abstract
Abstract Photoluminescence (PL) of transition metal dichalcogenide (TMD) monolayers is strongly influenced by the dielectric environment. The defect states present in the substrate induces uncontrollable doping in the TMD monolayer and thereby modifies the PL spectra. There have been enormous efforts to tune and overcome the effect of inevitable substrate defects in PL spectra, but a proper understanding and a convenient way are still lacking. Here, we systematically studied the effect of surface defects by gradually increasing the separation between WS 2 monolayer and substrate. Hence, we could precisely modulate the exciton and trion contribution in the PL spectra of WS 2 . The excitation power dependant measurements on dielectric engineered and patterned substrates helped us to shed light on the mechanism of PL modulation in monolayer WS 2 . We have also studied the influence of the nature of the charge carried by substrate defects on the PL spectra. These results open a new pathway to modulate and obtain the desired PL spectra of TMDs by engineering the substrates. Our findings will be useful for fabricating excitonic interconnects, valleytronic, and single-photon devices.