Controllable Doping Characteristics for WS(x)Se(y) 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 MoS(x)Se(y), Mo(x)W(y)S(2), Mo(x)W(y)Se(2), and WS(x)Se(y) monolayers that exhibit tunable band gap energies. However, few works have examined the doping behavior of those 2D monolayers. This study synthesizes WS(x)Se(y) monolayers using the CVD process, in which different heating temperatures are applied to sulfur powders to control the ratio of S to Se in WS(x)Se(y). Increasing the Se component in WS(x)Se(y) 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 WS(x)Se(y) monolayers. In addition, Raman spectra showed a red shift of the WS(2)-related peaks, indicating n-doping behavior in the WS(x)Se(y) monolayers. In contrast, with the increase of the sulfur component, the blue shift of the WSe(2)-related peaks in the Raman spectra involved the p-doping behavior of WS(x)Se(y) monolayers. In addition, the optical band gap of the as-grown WS(x)Se(y) 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 WS(x)Se(y) monolayers provide more options in electronic and optical design.