Thiourea-Assisted Deposition of Cadmium Sulfide Thin Films: Structural and Optical Analysis

Abstract

In this study, cadmium sulfide (CdS) thin films were grown on glass substrates via chemical bath deposition, with a focus on how varying thiourea doses influence film formation. Structural analysis revealed that all samples crystallized in a cubic zinc blende phase; however, increasing thiourea content led to marked reductions in grain size (55.67 nm to 11.34 nm ) and overall crystallinity. Concurrently, microstrain and dislocation density exhibited notable increases (from 0.62×10^(-3) to 3.0×10^(-3) and from 0.32×10^(-3) lines/nm² to 7.7×10^(-3) lines/nm² respectivaly) , indicating degradation in crystalline quality and the emergence of lattice imperfections. Morphological assessment revealed reduced grain connectivity and enhanced surface disorder at higher thiourea levels. Optical characterization showed a progressive blue shift in the transmission spectra, increased transmittance, and a widening of the optical band gap from 1.80 eV to 1.96 eV. The Urbach energy rose from 0.2 eV to 0.5 eV, while the refractive index decreased with increasing precursor dose. These findings demonstrate that thiourea serves as a critical parameter for modulating both structural integrity and optoelectronic performance in CdS thin films, supporting their tunability for advanced photonic and photovoltaic applications.