Comparative study of structural, optical and electrical properties of electrochemically deposited Eu, Sm and Gd doped ZnSe thin films

A facile approach involving electrochemical deposition method was utilized to coat ITO substrate with zinc selenide thin films at different rare earth metal (Eu³⁺, Sm³⁺ and Gd³⁺) ions. The characteristics of deposited films were studied in relation with the doped metal ions. The structure of the coating was confirmed to be hexagonal wurtzite in (101) plane by X-ray analysis. The new antistructural modeling shows that the doping of ZnSe lattice by rare earth cations increases the concentration of the surface active centers such as \({\text{Gd}}_{{{\text{Zn}}}}^{\cdot },\,{\text{Eu}}_{{{\text{Zn}}}}^{\cdot },\,{\text{Sm}}_{{{\text{Zn}}}}^{\cdot },\,{\text{and}}\,{\text{V}^{\prime\prime}_{{\text{Zn}}}}\), which are located in the cationic sublattice. XRD data revealed that the average crystallite size of ZnSe and ZnSe:Eu, ZnSe:Sm, and ZnSe:Gd was 63, 54, 47, and 49 nm, respectively. The morphological results by scanning electron microscopy indicate that the spherical-like structure with agglomeration of grains and a slight increase in the particle size. Energy dispersive X-ray, UV–Visible and photoluminescence spectroscopy were used to study the composition and optical properties of the films. A blue-shift was observed in ZnSe thin films. The bandgap energy of undoped ZnSe and ZnSe:Eu, ZnSe:Sm, and ZnSe:Gd were found to be 2.28, 2.44, 2.68 and 2.75 eV, respectively. Among the different coated films, the Gd³⁺ ion doped ZnSe thin film exhibited a lesser charge transfer resistance of 25.5 Ω as analyzed from the electrochemical impedance measurement. The photoelectrochemical studies reveal that the rate of photoinduced charge carriers was higher in Gd³⁺ ion doped thin film. The present studies suggested that the Gd³⁺ ion doped ZnSe thin film can be a promising material for electrochemical device applications.