Correlating the optical properties of WS2 monolayers grown by CVD with isoelectronic Mo doping level (Conference Presentation)

Abstract

Incorporating dopants in monolayer transition metal dichalcogenides (TMD) can enable manipulations of their electrical and optical properties. Previous attempts in amphoteric doping in monolayer TMDs have proven to be challenging. Here we report the incorporation of molybdenum (Mo) atoms in monolayer WS2 during growth by chemical vapor deposition, and correlate the distribution of Mo atoms with the optical properties including photoluminescence and ultrafast transient absorption dynamics. Dark field scanning transmission electron microscopy imaging quantified the isoelectronic doping of Mo in WS2 and revealed its gradual distribution along a triangular WS2 monolayer crystal, increasing from 0% at the edge to 2% in the center of the triangular WS2 triangular crystals. This agrees well with the Raman spectra data that showed two obvious modes between 360 cm-1 and 400 cm-1 that corresponded to MoS2 in the center. This in-plane gradual distribution of Mo in WS2 was found to account for the spatial variations in photoluminescence intensity and emission energy. Transition absorption spectroscopy further indicated that the incorporation of Mo in WS2 regulate the amplitude ratio of XA and XB of WS2. The effect of Mo incorporation on the electronic structure of WS2 was further elucidated by density functional theory. Finally, we compared the electrical properties of Mo incorporated and pristine WS2 monolayers by fabricating field-effect transistors. The isoelectronic doping of Mo in WS2 provides an alternative approach to engineer the bandgap and also enriches our understanding the influence of the doping on the excitonic dynamics.