INVESTIGATION OF VOLTAGE MODULATION ON THE OPTICAL AND STRUCTURAL PROPERTIES OF ELECTRODEPOSITED ZINC SULFIDE (ZnS) THIN FILMS

Zinc sulfide thin films were successfully deposited onto a fluorine-doped tin oxide (FTO) glass substrate by employing electrodeposition method in this work.The basic materials used were; zinc acetate dihydrate which served as zinc source, thiourea (H2NCSNH2) served as sulfur source, FTO was the working electrode, silver/silver chloride served as the reference electrode, while platinum rod was used as the counter electrode.Deposition voltages of 2.0 volts, 4.0 volts and 6.0 volts from a DC supply unit (model Long Wei: PS-305D) were optimized to investigate their effects on the optical and structural properties of the thin films for applications.The films were characterized using UV-Vis spectrophotometer and X-ray diffractometry analysis to investigate the properties of the films.The results showed that the absorbance of the films is low but was influenced by the deposition voltage with the film deposited at 6.0 volts having the highest values in the range of 0.15 to 0.30 while the film deposited at 2.0 volts has the lowest value in the range of 0 to 0.10 within the visible (VIS) and near infrared (NIR) regions.The percentage reflectance of the films was also found to be low but increased with an increase deposition voltage throughout the VIS and NIR regions.The films have high percentage of transmittance with the values in the range of 80% to 100% for the film deposited at 2.0 volts but decreased to the values in the range of 50% to 70% for the film deposited at 6.0 volts within the VIS and NIR regions.The refractive index of the films was also influenced by the deposition voltage by increasing its values from 1.0 to 1.9 for the for film formed at 2.0 volts but increased to the range of 2.15 to 2.6 for the film formed at 6.0 volts.The direct bandgap energy was found to be 2.13 eV, 2.65 eV and 2.90 eV for the film deposited at 2.0 volts, 4.0 volts and 6.0 volts respectively.The X-ray diffraction analysis showed that the films have trigonal (hexagonal axes) structure and influenced by deposition voltage variations.The average crystallite size for the films formed at 2.0 volts and 6.0 volts are 29.68 nm and 20.64 nm