Controllable Doping Characteristics for WSSe Monolayers Based on the Tunable S/Se Ratio.

Transition metal dichalcogenides (TMDs) have attracted much attention because of their unique characteristics and potential applications in electronic devices. Recent reports have successfully demonstrated the growth of 2-dimensional MoSSe, MoWS, MoWSe, and WSSe monolayers that exhibit tunable band gap energies. However, few works have examined the doping behavior of those 2D monolayers. This study synthesizes WSSe monolayers using the CVD process, in which different heating temperatures are applied to sulfur powders to control the ratio of S to Se in WSSe. Increasing the Se component in WSSe monolayers produced an apparent electronic state transformation from p-type to n-type, recorded through energy band diagrams. Simultaneously, p-type characteristics gradually became clear as the S component was enhanced in WSSe monolayers. In addition, Raman spectra showed a red shift of the WS-related peaks, indicating n-doping behavior in the WSSe monolayers. In contrast, with the increase of the sulfur component, the blue shift of the WSe-related peaks in the Raman spectra involved the p-doping behavior of WSSe monolayers. In addition, the optical band gap of the as-grown WSSe monolayers from 1.97 eV to 1.61 eV is precisely tunable via the different chalcogenide heating temperatures. The results regarding the doping characteristics of WSSe monolayers provide more options in electronic and optical design.