Thickness-Dependent Structural and Optical Properties of WS₂ Thin Films Prepared by RF Magnetron Sputtering

In this study, the thickness-dependent structural, vibrational, optical, and electrical properties of sputter-deposited WS₂ thin films were systematically investigated. Two film thicknesses, 10 nm and 100 nm, were deposited and subsequently annealed to evaluate the influence of thickness and post-deposition thermal treatment on material performance. X-ray diffraction analysis revealed thickness-dependent variations in interlayer ordering and crystallographic coherence. Raman spectroscopy confirmed the characteristic vibrational modes of WS₂ along with defect-related features, indicating the polycrystalline nature of the films. Photoluminescence spectroscopy showed that the optical response of the films is dominated by excitonic recombination. A thickness-dependent red-shift of the A-excitonic emission was observed, while the appearance of the B-excitonic transition in the annealed 100 nm film indicated improved electronic homogeneity after annealing. Diffuse reflectance spectroscopy further supported these findings, revealing a gradual decrease in the effective optical bandgap with increasing film thickness due to reduced confinement effects and enhanced interlayer electronic coupling. Hall effect measurements demonstrated n-type conductivity for both samples, attributed to intrinsic donor-like defects such as sulfur vacancies. The 10 nm film exhibited lower resistivity, higher conductivity, and slightly higher carrier mobility compared to the 100 nm film, highlighting the importance of thickness control for optimizing charge transport in WS₂ thin films. Overall, this work provides a comprehensive understanding of how thickness and thermal treatment govern the excitonic behavior, band structure, and electronic transport properties of sputter-deposited WS₂ thin films. The results offer valuable insights for the design and optimization of WS₂-based electronic and optoelectronic devices.