Correlation between morphology and electro-optical properties of nanostructured CdO thin films: Influence of Al doping

Al doped cadmium oxide thin films have been deposited on glass substrates by sol–gel dip coating method with precursor solutions having different Al concentrations. The content of aluminum in the sol was varied from 0 to 5at.%. X-ray diffraction, Atomic Force Microscopy (AFM), Scanning Electron Microscopy (SEM), UV–Visible spectroscopy and Hall effect analyses have been used to determine correlations between the film microstructure and the optoelectronic properties. X-ray diffraction analyses, clearly established that the crystallinity deteriorates by Al doping. Crystallite size calculations based on Debye Scherrer formula indicated that the CdO crystallite size decreases with Al content (from 37 to about 11nm). SEM and AFM were applied to study the morphology and to estimate the surface roughness of the obtained films. All films were very smooth, with a characteristic spherical grain size depending on Al content. The Root Mean Square (RMS) roughness of the films varied from 4.05 to 4.35nm with increasing Al concentration. The AFM images were also used for the analysis of the fractal behavior of the films. Doping with Al increased the films' optical transparency in the visible region and their conductivity. ► Physical properties of the CdO:Al nanostructured films at different Al% are studied. ► Maximum carrier concentration has been achieved for 1at.% Al doped film. ► The undoped sample has maximum carrier mobility. ► The direct optical band gap shifted to the higher energy. ► The samples have relatively smooth surface with RMS roughness of about 4nm.