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.