Sol-Gel Derived CdO:Al Thin Films on Various Substrates: A Comprehensive Study on Structural, Morphological, Optical, and Electrical Properties

Aluminum-doped cadmium oxide (CdO:Al) thin films were deposited onto glass and silicon substrates using the sol–gel spin-coating method, with deposition time varied as a key parameter. Cadmium acetate dihydrate served as the precursor material, while aluminum nitrate was used as the aluminum dopant source. The structural, optical, and electrical properties of the CdO:Al films were characterized using X-ray diffraction (XRD), Raman spectroscopy, Ellipsometry, Surface roughness analysis, Fourier-transform infrared spectroscopy (FTIR), Electrical resistivity, and UV-Vis spectroscopy. XRD analysis revealed characteristic peaks at 2θ values of 25.89°, 38.36°, 38.9°, and 44.49° on both substrates for deposition times of 5 and 30 seconds. An additional peak at 2θ = 33° was observed only on the silicon substrate. XRD peak intensity increased with longer deposition times on both substrates. Crystallite sizes at 30 seconds were determined to be 32.08 nm on glass and 38.29 nm on silicon. The lowest deposition rates were 273.25 nm/sec for glass and 210.11 nm/sec for silicon at 30 sec. Roughness measurements indicated that silicon substrates exhibited lower RMS roughness values compared to glass. Raman spectra confirmed the presence of the crystalline CdO:Al phase with a peak at 808 nm for both substrates, and Raman intensity increased with deposition time. At 30 seconds, the refractive index and dielectric constant were found to be 3.52 and 0.15 on silicon, and 1.52 and 0.08 on glass, respectively. FTIR analysis confirmed CdO:Al presence with absorption bands at 610.91 cm⁻¹ (silicon) and 615.71 cm⁻¹ (glass). The lowest resistivity values recorded were 1.2 X10-5 Ω·cm on silicon and 3.6 X 10-4 Ω·cm on glass. UV-Vis spectroscopy estimated the optical band gap energies to be 2.8 eV for silicon and 3.1 eV for glass. The results showed that the Al-doped CdO films made by the sol-gel method on silicon acted like highly conductive semiconductors.