Effects of CVD growth parameters on global and local optical properties of MoS2 monolayers

Semiconducting transition metal dichalcogenides (TMDs) attract significant attention owing to their unique properties originating from their atomically thin layered structure. Chemical vapor deposition (CVD) has shown great promise to fabricate large-scale and high-quality TMDC films with exceptional electronic and optical properties. Controllable fabrication of high-quality TMD monolayers with low defect content is still challenging and hinders their adoption for technological application. The optical properties of CVD grown monolayer MoS2 are largely influenced by the stoichiometry during CVD by controlled sulfurization of molybdenum (Mo) precursors. Here, we investigate how the sulfur concentration influences the sample morphology and, both globally and locally, their optical response. We confirm that samples grown under a Mo:S > 1:2 stoichiometric ratio have regular morphology facilitated by a moderate coverage of triangular monocrystals with excellent optical response. However, if the sulfur concentration is increased compared to the ideal stoichiometric ratio, the samples' growth is polycrystalline with dendritic morphology and poor optical response. Our data-driven approach correlates resulting optical spectra analysis and crystal morphology with the growth conditions immediately upon the sample growth cycle, providing a crucial link to determine the next optimal CVD growth conditions. Optical micrographs and spectra acquisition together with the subsequent data analysis have proved to be a practical and necessary pathway to address the challenges towards the controlled synthesis of 2D TMDs and their alloys with desired optical and electronic properties.