Dependence of structural and optoelectronic properties on thickness of γ-cui thin films deposited by vacuum thermal evaporation

We report on the formation of gamma phase cuprous iodide (CuI) thin films of various film thickness with high (111) orientation deposited by vacuum thermal evaporation of powders attained through a cost-saving extraction method. The study investigated the dependence of structural and optoelectronic properties of the thin films on film thickness. Structural characterisation of the films revealed an increase in crystallite size and a decrease in dislocation density with film thickness which indicated an improvement in the crystallographic microstructure. There was a strong orientation towards (111) growth. The Scanning Electron Microscope images of the CuI thin films showed a compact morphology with an increase in larger grains as film thickness increased. The thin films showed a mean optical transmittance of around 70 % in the visible region with a decreasing trend as thickness increased. There was an observed red shift of the transmittance spectra with film thickness. All thin films also showed good electrical conductivity. However, the figure of merit improved with decreasing thickness. The good optical transmittance and relatively low resistivity qualify the CuI thin films as candidates for electro-optical device applications.