A comparative study on the structural and spectroscopic ellipsometry characterizations of (Co, Ni)-doped SnO2 nanostructured films spin-coated on glass substrates

The pure, Co- and Ni-doped SnO2 nanostructured films were coated on glass by spin coating method. The influence of doping Ni and Co metal ions on optoelectronic and structural properties of the pure film were analysed by X-ray diffraction (XRD) and spectroscopic ellipsometry (SE) techniques. XRD results revealed that substitution of Co2+ and Ni2+ into the tetragonal rutile structure of SnO2 changes the lattice parameters (a and c) slightly and decreases the grain size (d). The refractive index (n), the extinction coefficient (k), optical transmittance (T) and dielectric constant (ɛ) were determined for samples using SE technique. According to SE analysis, the incorporation of Ni and Co ions decreases the optical transparency (T%) and increases the ratio of charge carrier concentration to effective mass (N/m*). The results confirmed that the N/m* increases lead to decreasing of the sheet resistance (Rsh) values of doped SnO2 films compared to the pure one. The bandgap energy (Eg) of films were also calculated. According to the literature, the Eg value of the pure SnO2 thin film is 3.8 eV. This amount decreased to 3.7 and 3.55 eV for Co- and Ni-doped SnO2 films, respectively. The Eg value decrease by Co and Ni incorporation is related to the increase of carrier concentration due to the Moss-Burstein effect.