Zinc sulfide thin films were synthesized using the chemical bath deposition method with deposition durations ranging from 1 to 7 hours to examine the influence of deposition time and post-deposition annealing (60 °C to 100 °C) on their structural, optical, and electrical properties. X-ray diffraction confirmed the formation of the cubic zinc blende phase, with enhanced crystallinity and increased grain size at longer deposition times. Ultraviolet-visible spectroscopy revealed a tunable optical bandgap between ~3.5 and 3.8 eV, depending on deposition duration. Surface morphology and elemental composition were analyzed using scanning electron microscopy and energy-dispersive X-ray analysis. Energy-dispersive X-ray analysis results indicated that the 3-hour annealed film had a near-stoichiometric Zn:S ratio (41.1% Zn and 58.9% S), while the 1-hour annealed film exhibited a high oxygen content (70.31%) due to oxidation. Films annealed for 5 and 7 hours showed sulfur loss, resulting in zinc-rich compositions. Fourier-transform infrared spectroscopy confirmed improved Zn–S bonding over time, with sharper vibrational peaks in the 600–700 cm⁻¹ range and a marked reduction in organic and hydroxyl impurities. Among all samples, the 5-hour film showed the most favorable combination of crystallinity, purity, and low contamination, indicating its potential for optoelectronic applications. Electrical properties, evaluated using the two-probe method, demonstrated thermally activated conductivity in the 1-hour film annealed at 100°C, with an activation energy of 0.2857 eV, suggesting semiconducting behavior and applicability in thermoelectric and biosensing devices. However, electrical measurements for films deposited for 3, 5, and 7 hours were unfeasible due to extremely high resistivity and limited charge transport.

Keywords: Zinc Sulfide; Thin Films; Chemical Bath Deposition; Annealing; Optical Bandgap;