Conductivity type of Ni–Cu hydroxide films deposited by electrochemical deposition

Abstract Metal hydroxides are inexpensive materials. They are typically considered insulators; however, some metal hydroxides have been employed as electronic materials. Understanding the electrical properties of metal hydroxides is essential for their effective use in electronics. In this study, Ni–Cu hydroxide films with different Cu contents were electrochemically deposited on indium tin oxide (ITO)-coated glass substrates from aqueous solutions of Ni(NO 3 ) 2 ·6H 2 O and CuCl 2 ·2H 2 O, by varying the Cu/(Ni+Cu) ratio. The Ni–Cu hydroxide films were amorphous and contained water and nitrate ions. Their bandgap and resistivity decreased with increasing Cu/(Ni+Cu) ratio. Samples with Cu/(Ni+Cu) ratios of 0.5 and 0.6 exhibited p-type conductivity and had an optical bandgap of approximately 2.5 eV. In the O 1s x-ray photoelectron spectroscopy (XPS) spectra, peaks corresponding to hydroxides and H 2 O were observed, while no signals related to metal oxides were detected. In the Cu 2p 3/2 and Ni 2p 3/2 XPS spectra, the intensity of the Cu + peak increased and that of the Ni 2+ peak decreased with increasing Cu/(Ni+Cu) ratio. The observed p-type conductivity, along with the changes in resistivity and bandgap, can be attributed to the increased presence of Cu + species in the films.