Modulation of trion and exciton formation in monolayer WS2 by dielectric and substrate engineering

TL;DR

This study demonstrates how substrate engineering and dielectric environment control can precisely modulate exciton and trion formation in monolayer WS2, advancing the development of optoelectronic devices.

Contribution

It provides a systematic approach to tune PL spectra in WS2 monolayers by controlling substrate defect states and dielectric separation, offering new pathways for device fabrication.

Findings

PL spectra are modulated by substrate defect states and dielectric separation.

Exciton and trion contributions can be precisely controlled through substrate engineering.

Charge nature of substrate defects influences PL behavior.

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 subtract 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 WS2 monolayer and substrate. Hence, we could precisely modulate the exciton and trion contribution in the PL spectra of WS2. The excitation power dependant measurements on dielectric engineered and patterned substrates helped us to shed light on the mechanism of PL modulation in monolayer WS2. 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.