Complex excitonic emissions in CVD grown 1L-WS₂ on 2D and 3D interfaces

We report on the intrinsic and extrinsic effects on the excitonic properties of single-layer WS₂ synthesized by ambient pressure chemical vapor deposition (APCVD). Due to the valley-spin configuration, the excitonic species in WS₂ have a rich complexity comprising of bright and dark excitons, which can be neutral or charged, bound to defects, and multi-exciton (biexciton) species. The relative intensities and resolution of the rich excitonic emissions depend on the density of free carriers and defects, the dielectric background, the local strain, and the experimental conditions such as temperature and illumination power. We investigate single-layer WS₂ grown by APCVD on substrates which had 2D-inert (hBN) and 3D interfaces with large and small lattice mismatch (SiO₂ and c-Al₂O₃), as well as transferred onto SiO₂ with pre patterned holes providing suspended regions. To characterize the nature of excitonic emissions, we studied the effects of illumination power, temperature, valley selectivity, and carrier concentration using photoluminescence and Raman spectroscopy.