Effect of pH on structural and morphological properties of spray deposited p-type transparent conducting oxide CuAlO2 thin films

CuAlO2 due to its delafossite structure is known to exhibit p-type conductivity. p-CuAlO2 thin films have been prepared using spray pyrolysis technique. The films prepared using precursor solutions with different pH values have been characterized for optical, structural and morphological properties. The X-ray diffractograms of the films deposited using precursor solution with pH 3.7 do not show any peaks, these suggest the amorphous nature of the films. On the other hand, the films deposited with pH 1.5 show the peaks of CuAlO2 with delafossite crystal structure. Thus the pH of the solution is playing a crucial role in giving the crystalline product of the material of interest. Tauc's plot of the film deposited using precursor solution of pH 3.7 shows the absorption edge at 3.71 eV and the film deposited with solution pH 1.5 shows the absorption edge at 3.64 eV, corresponding to the direct band gap of CuAlO2. This confirms the formation of CuAlO2. The surface morphology of the films shows the novel networking structure. Compositional analysis done using Energy dispersive X-ray spectrum shows an excess of oxygen that should be favorable for giving the p-characteristics.