Rietveld refinement combined with first-principles study of Zn and Al–Zn doped CdO thin films and their structural, optical and electrical characterisations

Un-doped, Zn-doped, and Al–Zn co-doped CdO thin films were deposited onto glass substrates at 350 °C by spray pyrolysis. X-ray diffraction (XRD) analysis was conducted to investigate the structural properties of the films. The XRD patterns confirmed that all the films crystallize in a cubic structure and that the addition of Zn and Al did not alter the CdO crystal structure. Energy-dispersive X-ray spectroscopy analysis further confirmed the successful incorporation of Zn and Al into the CdO films. Theoretical calculations based on first-principles were performed, and crystallographic information files (CIF) were obtained for optimized theoretical supercells in space group Pm3-m. The CIF files were used as input for experimental XRD spectra Rietveld refinement, to determine the Wyckoff positions of the dopants and their occupation rates. The optical properties of the films were characterized using transmittance measurements in the wavelength range of 300–1700 nm. The optical data indicated an increase in the average transmittance from 60 to 70% within the wavelength range of 600–1700 nm upon Al–Zn co-doping. The estimated direct optical band gap of the un-doped, doped, and co-doped CdO thin films is varied between 2.41 and 2.50 eV. All the samples exhibited n-type conductivity with low electrical resistivity of about 1.32 × 10^–4 Ω⋅cm. Co-doped CdO thin films with 1% Al and 3% Zn exhibited higher carrier concentration (4.39 × 10⁺²⁰ cm⁻³) than the other samples.