Investigating the effects of varying sulfur concentration on ZnS_xSe_1-x (0 ≤ x ≤ 1.0) thin films prepared by photo-assisted chemical bath method

Zinc sulfur-selenide (ZnS_xSe_1-x) (0 ≤ x ≤ 1.0) thin films were grown on glass substrates using photo-assisted chemical bath deposition technique and the deposited samples were annealed in an open-air furnace at 250 ℃ for 3 h. X-ray diffraction analysis revealed a phase transition from hexagonal ZnSe to cubic ZnS as x changes from 0 to 1.0. Raman scattering showed two longitudinal optical modes due to ZnSe structure. The effects of S and Se ions variation is observed by the change in surface morphology from nanoflakes to spherical particles as x increased. The presence of the expected elementary composition was confirmed by the energy dispersive x-ray spectroscopy. The bandgap of the films was found to increase from 2.68 to 3.50 eV with a corresponding decrease in crystallite size (11.9 – 7.1 nm) as x varied from 0 to 1.0. Photoluminescence excitation and emission showed defect emission peaks ascribed to intrinsic and extrinsic deep level defects such as Zn²⁺ or S^2- ions vacancies and interstitials. The emission colours were tuned from red to yellowish-green with increased x values as confirmed from Commission Internationale de L'Eclairage analysis. The tunability of the ZnS_xSe_1-x structural, optical and morphological properties makes it a good candidate for optoelectronic applications.