Exploring low, moderate and heavy Al doping impacts on microstructure and optical attributes of nanostructured cadmium oxide thin films

Bandgap tuning of semiconductors can often lead to significant performance increases and new applications for electronic, optoelectronic, and photocatalytic devices. In this study, we investigate the bandgaps of pure and aluminum doped cadmium oxide thin films synthesized using the low-cost sol-gel dip-coating method. Aluminum concentration is varied from 0 to 15 at.%, and the effects that this doping has on the microstructure, electronic and optical properties are analyzed. Using X-ray diffraction, X-ray photoelectron spectroscopy, scanning electron microscopy, atomic force microscopy, d.c. electrical measurements and Uv-vis spectrophotometery a comprehensive study was carried out on the prepared samples. Adding Al deteriorates the crystallinity and electrical traits of the films. Taken micrographs indicate an anomalous roughness increase for 10 at.% Al and emersion of bright agglomerations on the surface. Three regimes of bandgap variation via Al doping are uncovered. For doping up to 1% Al, there is a strong increase in the gap and continued doping up to 5 at.% reduces the gap, while adding 10% and 15% Al causes bandgap enhancement. By evaluating dielectric constant of the samples, the interband transition strength of the films was calculated and grew abruptly beyond 3.25 eV.