Preparation and Characterization of Nickel and Aluminum-Codoped SnO2 Thin Films for Optoelectronic Applications

Abstract

In this study, the coating technique was used to prepare thin layers of nickel and aluminum-codoped tin oxide (SnO2: Ni; Al). This study is aimed at exploring the influence of aluminum (Al) dopant on the structural, optical, and electrical properties of the elaborated films. X-ray diffraction (XRD) studies discovered that all deposited films (Ni-doped and Al-Ni-codoped SnO2) were polycrystalline with tetragonal (quadratic) structure and exhibited [110] preferential orientation. The optical measurements exposed that all prepared films have presented good transparency. The transmittance of Ni-Al-codoped SnO2 thin films in the visible and near-infrared regions varied between 80% and 90%; this was dependent on the concentration of dopant. The band gap was determined via the equation related to the absorption coefficient. It was deduced that the optical band gap values of thin films gradually decreased from 4.084 eV to 3.991 eV, as an effect of Al content. In addition, it was concluded that the thickness values of the films pass from 571.374 nm to 694.036 nm as an effect of Al content. Moreover, the extinction coefficient decreases with the wavelength in the UV region and then varies slightly towards longer wavelengths. Moreover, the electrical resistivity was determined using the four-point probe; it was determined that the electrical resistivity decreases from $1.35\times {10}^3\left(\Omega ·\text{cm}\right)$ to $0.14\times {10}^3\left(\Omega ·\text{cm}\right)$ with aluminum concentration increasing from 0 at. % to 7 at. %. The elaborated films of SnO2 codoped with Ni and Al present were highly transparent; therefore, these thin layers look promising in the use of the window layer in PV solar cells.