Metal-doped ZnS(O) thin films on glass substrates using chemical bath deposition

Zinc sulfide (ZnS(O)) thin films doped with Mn, Ni, and Co ions are synthesized by chemical bath deposition technique onto glass substrates. X-ray diffraction study reveals that the undoped and metal-doped ZnS(O) films possess a hexagonal wurtzite crystal structure. The morphological change, upon metal-ions doping, from nanorod structures to cluster (Mn doping), compact (Ni doping), and granular shapes (Co doping) is observed. X-ray photoelectron spectroscopy reveals the presence and incorporation of metal ions into ZnS(O) lattice sites and the formation of a metal-ZnS combined structure. The band gap energy of the undoped ZnS(O) film is found to be larger than 4.0 eV, while it is 3.8, 3.7, and 3.6 eV for the Mn-ZnS(O), Ni-ZnS(O), and Co-ZnS(O) films, respectively. All the undoped and metal-doped ZnS(O) samples exhibit blue luminescence, which originates from the surface defects and trap centers. Thus, the photoluminescence (PL) (blue light emission) is due to the radiative recombination from various trap levels (shallow donor levels) to the valence band. The decrease in the PL peak intensity for the doped samples indicates the reduction of surface defects suggesting the incorporation of metal ions into the host lattice of ZnS(O). Based on the PL results, the PL energy-level diagram for the undoped and metal-doped ZnS(O) samples is proposed.