Effect of Aluminum Doping in Cadmium Oxide Thin Films which present Nanostructure in terms of Structure, Optical and Gas Sensing

Pure and Aluminum doped CdO nanostructured thin films (1% and 3% Al) were grown on glass substrates via chemical spray pyrolysis. We looked at the effect of Aluminum doping on structural, morphological, optical, and gas sensing properties. XRD analysis reported a polycrystalline cubic structure with preferential (111) orientation. We saw that crystallite size increased from 18.37 nm (pure) to 27.63 nm (3% Al) and that dislocation density went down from 49.38×〖10〗^14 to 30.56×〖10〗^14 lines/m^2. AFM study showed that surface roughness and average particle size went down upon Aluminum inclusion. We noted that optical transmittance went down with Aluminum concentration and that the absorption coefficient went up. Also, the bandgap narrowed from 2.78 eV to 2.66 eV. NO₂ gas-sensing at 175°C showed sensitivity decreasing from 54.1% (pure) to 14.2% (3% Al) at 225 ppm, suggesting that higher Aluminum doping reduces sensor response due to structural modifications.