Revealing the Competition between Defect-Trapped Exciton and Band-Edge Exciton Photoluminescence in Monolayer Hexagonal WS2

Monolayer transition-metal dichalcogenides grown by chemical vapor deposition (CVD) always contain certain types of defects that dramatically affect their electronic and optical properties. For CVD-grown hexagonal WS2 monolayer, complex photoluminescence (PL) patterns are commonly observed, but the defect-related optical mechanisms are still not well understood. Here, by combining the optical and structural characterizations and ab initio calculations, the correlation between the patterned PL emission and the details of defects in CVD-grown hexagonal WS2 monolayer are revealed. The temperature-dependent PL spectra show the correlation between the defect-trapped and band-edge exciton emission. The high-resolution scanning transmission electron microscopy identifies the positive correlation between the density of WSx-vacancy and PL intensity. In the end, the ab initio calculations and molecule adsorption PL spectra show that the coexistence of p- and n-doping effects, caused by the W and S complex vacancy, weakens the modulation of molecular adsorption on PL intensity. This work gives new insights into the origin of the inhomogeneous PL distribution in WS2 monolayer, which provides important guidance in the regulation of electronic and optical properties of transition-metal dichalcogenides via defect engineering.

Automated summary

This study reveals the correlation between the patterned photoluminescence (PL) emission and the details of defects in chemical vapor deposition (CVD)-grown hexagonal WS2 monolayer through optical and structural characterizations and ab initio calculations. The temperature-dependent PL spectra show the correlation between defect-trapped and band-edge exciton emission. High-resolution scanning transmission electron microscopy identifies the positive correlation between WSx-vacancy density and PL intensity. Ab initio calculations and molecule adsorption PL spectra show that the coexistence of p- and n-doping effects weakens the modulation of molecular adsorption on PL intensity.