Optical Characteristics of La-Doped ZnS Thin Films Prepared by Chemical Bath Deposition

Undoped and La-doped ZnS thin films are prepared by chemical bath deposition (CBD) process through the co-precipitation reaction of inorganic precursors zinc sulfate, thiosulfate ammonia and La₂O₃. Composition of the films is analyzed using an energy-dispersive x-ray spectroscopy (EDS). Absorption spectra and spectral transmittances of the films are measured using a double beam UV-VIS spectrophotometer (TU-1901). It is found that significant red shifts in absorption spectra and decrease in absorptivity are obtained with increasing lanthanum. Moreover, optical transmittance is increased as La is doped, with a transmittance of more than 80% for wavelength above 360 nm in La-doped ZnS thin films. Compared to pure ZnS, the band gap decreases and flat-band potential positively shifts to quasi-metal for the La-doped ZnS. These results indicate that La-doped ZnS thin films could be valuably adopted as transparent electrodes.