Modulated wafer-scale WS2 films based on atomic-layer-deposition for various device applications

Abstract

Tungsten disulfide (WS₂) is promising for potential applications in transistors and gas sensors due to its high mobility and high adsorption of gas molecules onto edge sites. This work comprehensively studied the deposition temperature, growth mechanism, annealing conditions, and Nb doping of WS₂ to prepare high-quality wafer-scale N- and P-type WS₂ films by atomic layer deposition (ALD). It shows that the deposition and annealing temperature greatly influence the electronic properties and crystallinity of WS₂, and insufficient annealing will seriously reduce the switch ratio and on-state current of the field effect transistors (FETs). Besides, the morphologies and carrier types of WS₂ films can be controlled by adjusting the processes of ALD. The obtained WS₂ films and the films with vertical structures were used to fabricate FETs and gas sensors, respectively. Among them, the I_on/I_off ratio of N- and P-type WS₂ FETs is 10⁵ and 10², respectively, and the response of N- and P-type gas sensors is 14% and 42% under 50 ppm NH₃ at room temperature, respectively. We have successfully demonstrated a controllable ALD process to modify the morphology and doping behavior of WS₂ films with various device functionalities based on acquisitive characteristics.