Layer-controlled and atomically thin WS2 films prepared by sulfurization of atomic-layer-deposited WO3 films

Abstract

Atomically thin Tungsten disufide (WS2) film is a promising material for flexible electronics and optoelectronics. The ability to prepare controllable and uniform WS2 films over a large area is essential for their practical application. In this work, a two-step technique has been adopted to synthesize ultrathin WS2 films by sulfurization of atomic-layer-deposited WO3 films. A novel plasma enhanced atomic layer deposition (PEALD) process was employed to prepare ultrathin WO3 films by using bis(tertbutylimido)-bis(dimethylamido)-tungsten and O2 plasma as reactants. Smooth and atomically thin WS2 films are easily prepared by sulfuring the ultrathin WO3 films. It was observed that the thickness of WS2 films can be controlled by adjusting the numbers of PEALD cycles. X-ray photo-emission spectroscopy exhibits that WS2 films have good stoichiometry, and transmission electron microscopy reveals that WS2 films are polycrystalline. The field effect transistor made on the as-grown WS2 film exhibits n-type performance with an on/off current ratio of ∼105 and field-effect electron mobility of 4.5 cm2V−1s−1. The proposed growth technique for WS2 film is attractive for its applications in next-generation flexible electronics and optoelectronics, and is useful for preparations of other transition metal dichalcogenides ultrathin films.