Effect of grain size on structural and optical properties of CdO thin films obtained by PLD

Cadmium oxide (CdO) thin films were deposited on quartz glass substrates by pulsed laser deposition from ablating Cd metallic targets. The effect of grain size on structural and optical properties of CdO thin films was studied in detail. The structural properties were determined by XRD and a cubic phase was present in all of the as-grown samples. The morphology of CdO films has been investigated by atomic force microscopy. Grain sizes between 156 and 300 nm were determined from the AFM images and increased with laser energy density. The optical properties were studied measuring the transmittance spectra. The room-temperature bandgap energies for each sample were determined from the transmittance by extrapolating absorption coefficient. The bandgap energy varies from 2.31 to 2.55 eV following closely the quantum confinement dependence of energy against crystallite radius. This shows that the absorption edges of these samples are determined primarily by the grain sizes.