Impact of deposition rate on structural, optical, and electrical properties of WS2 thin films

In this work, WS2 thin films approximately 200 nm thick were successfully synthesized on glass substrates using RF sputtering, applying deposition rates of 1 and 2 Å/s. The impact of these rates on the films’ structure, surface morphology, optical properties, and electrical characteristics was thoroughly investigated. Field emission scanning electron microscope analysis revealed a morphology transition from nanoparticles to nanosheets as the rate increased. Atomic force microscope (AFM) analysis revealed that higher deposition rates increased grain size, nanosheet formation, and surface roughness in WS2 films. X-ray diffraction and Raman results showed enhanced crystallinity and the emergence of multiple growth orientations at higher deposition rates. Optical measurements indicated reduced transmittance and bandgap in the higher-rate film, attributed to morphological and structural improvements. Hall effect results showed significantly enhanced electrical conductivity in the nanosheet-based film due to increased carrier concentration and mobility. The Urbach energy values were also extracted, showing lower disorder in the high-rate film (79 meV) compared to the low-rate sample (106 meV). These findings underscore the key role of deposition rate in tailoring WS2 thin film properties for optoelectronic applications.