Optical properties of ZnS and Cr-doped ZnS thin films prepared by chemical bath deposition method

Abstract

Thin films of ZnS and Cr-doped ZnS have been prepared on the glass substrates by chemical bath deposition (CBD) technique by using zinc acetate {Zn(CH₃COO)₂} as zinc ion source, thiourea {SC(NH₂)₂} as sulphide ion source and CrO₃ as chromium ion source under various molarities taking ammonia solution as complexing agent. pH of the solution was maintained between 9 and 10 at temperature 70 °C. Films have been characterized by using X-ray diffraction (XRD) and UV-VIS Spectra. Optical absorption, transmission and photoconductivity for both types of the films have been observed. Optical constants like refractive index, extinction coefficient, absorption coefficient and dielectric constant for both the films have been measured from transmittance spectra, and decay constant and carrier life time have been measured from photoconductivity observation. Study shows that band gap energy of the doped films decreases more as compared to the un-doped films showing more dc conductivity in doped films. Study of photoconductivity also shows that photoconductivity drop is slower with a longer life time of excess carriers, so the time lag of the radiation detector (photodetector) becomes greater and higher optical responsivity which has attributed to the Cr-doped thin film.