Reduced Turn-On Voltage and Boosted Mobility in Monolayer WS₂ Transistors by Mild Ar⁺ Plasma Treatment

Monolayer two-dimensional transition-metal dichalcogenides, such as tungsten disulfide (WS₂), are regarded as promising candidates for optoelectronic and electronic applications. Although theoretical calculations have predicted outstanding electronic properties of WS₂, the performance of WS₂-based electronic devices is still limited by the relatively high Schottky barrier and low carrier mobility. In this work, low-energy argon (Ar⁺) plasma treatment was used as a nondestructive preconditioning technique to tailor the electrical properties of the WS₂ monolayer grown by chemical vapor deposition. Photoluminescence and Raman spectroscopy were used to monitor the modified optical properties of WS₂ with increasing plasma treatment time. An improved electrical conductivity was observed after a short-time plasma treatment. The physical mechanism was further revealed by a comparative study between top-electrode and bottom-electrode devices and simulation based on the density functional theory. It is concluded that mild Ar⁺ plasma treatment can effectively lower the Schottky barrier height and the effective mass of carriers, which reduces the turn-on voltage and enhances the mobility, respectively. However, if the processing time is too long, the WS₂ lattice structure will be destroyed. This work has provided an effective method for manipulating the Schottky barrier and mobility of monolayer WS₂ transistors and paves the way for developing high-performance electronic devices based on 2D semiconductors.