Reaction mechanism transformation of LPCVD-grown MoS2 from isolated triangular grains to continuous films

Abstract Two-dimensional (2D) MoS2 and other transition metal dichalcogenides (TMDs) provide an unprecedented prospect of atomic-level semiconducting physics, vdW integration and novel applications. Many efforts have been devoted to chemical vapor deposition (CVD) synthesis of 2D layered MoS2 in various shapes. Here, we examine the reaction transition of 2D MoS2 from isolated triangular grains to continuous thin films by low-pressure CVD (LPCVD). Both the supply amount of MoO3 precursor and its gap height from the growing substrate play a key role to control the concentration and distribution of the active Mo species near the substrate surface. It is observed that the distinct morphology evolution of LPCVD-grown MoS2 changes from gradient-distributed triangular grains to continuous thin films with large-scale uniformity. By controlling the partial pressure of the active Mo species, the large-scale, continuous MoS2 thin films have been obtained with different thicknesses including monolayers, bilayers and trilayers. The clear understanding of the LPCVD-synthesized MoS2 reaction transition is of great significance to optimize the specific preparation of 2D TMDs with scalable and high quality for future 2D semiconductors and optoelectronic devices.