Surface morphology and optoelectronic studies of sol–gel derived nanostructured CdO thin films: heat treatment effect

Morphological dependence of the optoelectronic properties of sol–gel derived CdO thin films annealed at different temperatures in air has been studied. After preparing, the films were investigated by studying their structural, morphological, d.c. electrical and optical properties. X-ray diffraction results suggest that the samples are polycrystalline and the crystallinity of them enhanced with annealing temperature. The average grain size is in the range of 12–34 nm. The root mean square roughness of the films was increased from 3.09 to 6.43 nm with annealing temperature. It was observed that the electro-optical characteristics of the films were strongly affected by surface roughness. As morphology and structure changed due to heat treatment, the carrier concentration was varied from 1.13 × 10¹⁹ to 3.10 × 10¹⁹ cm⁻³ with annealing temperature and the mobility increased from less than 7 to 44.8 cm² V⁻¹ s⁻¹. It was found that the transmittance and the band gap decreased as annealing temperature increased. The optical constants of the film were studied and the dispersion of the refractive index was discussed in terms of the Wemple–DiDomenico single oscillator model. The real and imaginary parts of the dielectric constant of the films were also determined. The volume energy loss increases more than the surface energy loss at their particular peaks.