The influence of rf power and oxygen flow rate during deposition on the optical transmittance of copper oxide thin films prepared by reactive magnetron sputtering

Copper oxide films have been sputter deposited on glass substrates by reactive rf magnetron sputtering, using a solid copper target and an argon-oxygen gas atmosphere. The films were characterized by SEM/EDAX, XPS, AFM, profilometry and spectrophotometry. Optical transmission in the prepared films was measured by spectrophotometry in the 400-850 nm wavelength region. The optical transmission was found to increase from below 10% to above 80% as the rf power was reduced from 800 to 200 W at a wavelength of 550 nm. The optical bandgap value also increased from 2.05 to 2.4 eV with a reduction in rf power from 800 to 200 W. This bandgap change indicates the possibility of selectively depositing an optically transparent CU2O-rich film, an absorbing black CuO-rich film or a mixture of both phases by varying the rf power during deposition. The oxygen flow rate during deposition had a less significant effect on the optical transmittance and bandgap of the films. This dependence of the stoichiometry of the copper oxide films on the deposition conditions is explained in terms of the sticking coefficient, nucleation rates and migration of impinging copper and oxygen species on the substrate. This information is expected to underlie the successful development of copper oxide films for technological applications requiring controlled optical transmission in the visible.