Realizing Stable p-Type Transporting in Two-Dimensional WS2 Films.

Two-dimensional (2D) semiconductors have become promising candidates for nanoelectronics applications due to their unique layered structure and rich physical properties. However, the significant lack of reproducible p-type doping methods that can avoid the instability induced by the widely used charge transfer doping method greatly limits the applications of these semiconductors in complementary metal-oxide-semiconductor (CMOS) integrated digital circuits. This work presents a new scheme to realize stable p-type doping for WS2 with excellent layer controllability, wafer-level uniformity, and high reproducibility at the same time. The p-type WS2 was produced by introducing substitutional doping of sulfur with nitrogen atoms during the sulfurization of WOxNy film. Nitrogen atoms acted as acceptors moving the Fermi level of WS2 toward the valance band. Both experimental and theoretical investigations were designed to study the physical properties of the films fabricated. The WS2 based field-effect transistors exhibited a well-defined p-type behavior with a large on/off current ratio of ∼105 and a high hole mobility of ∼18.8 cm2 V-1 s-1. This opens up a promising method to realize stable p-type doping of 2D materials, which is very attractive for future large-scale 2D CMOS device applications.