Effects of plasma treatment on surface properties of 2D tungsten diselenide

Tungsten diselenide (WSe₂) can be prepared to form atomically ultrathin film and it has been studied as a next-generation semiconductor material which shows a bandgap of ~1.3eV and non-degrading performance in the air. Plasma has been frequently used for the purpose of changing surface states of semiconductor because of the advantages enabling room temperature and large scale processes. In this study, we carried out plasma treatments using various processing gases (Ar, O₂, SF₆, N₂) and observed changes in etching rate, surface morphology and surface charge state. Atomic force microscopy (AFM) and Kelvin probe force microscopy (KPFM) were used for quantitative analysis on the effects of plasma treatment. We could observe a n-type shift by introducing fluorine ions and decreasing work function to 0.7eV upon SF₆ plasma treatment, while we could observe a p-type shift by introducing nitrogen ions and increasing work function to 0.6eV. The doping is further confirmed by electrical characteristics obtained by field effect transistor.