Defect induced photoluminescence of tungsten di-sulfide monolayers

The intriguing electronic properties of graphene have renewed the interest in other 2D materials such as transition metal di-chalcogenides (TMDCs) monolayers. TMDCs, similar to graphite, have a layered structure with an indirect bandgap which becomes direct when only a monolayer is present. This leads to strongly enhanced photoluminescence (PL). However, unavoidable defects affect the opto-electronic properties of TMDC monolayers drastically, which makes it necessary to study and characterize their optical related properties. In this contribution, we present highly sensitive, non-destructive, temperature and power dependent PL measurements to study the defects present in tungsten di-sulfide (WS₂) monolayers. For this purpose, pristine samples of WS₂ were irradiated with Xe³⁰⁺ ions to additionally create defects in the monolayers. Low temperature spectra of pristine samples show two different peaks associated with free and defect-bound excitons recombinations. For higher temperature or power, only the free exciton recombinations dominate the spectrum. For the different defect densities created in the monolayers, we observed changes in the PL spectrum with regard to intensity and FWHM, which will be discussed and compared to data published in literature.