Electrochemical deposition of copper(I) oxide films

Films of copper(I) oxide can be electrodeposited by reduction of copper(II) lactate in alkaline solution. Rietveld analysis of electrochemically grown films reveals pure copper(I) oxide with no copper(II) oxide or copper metal present in the films and a lattice parameter of a = 0.4266 nm. The cathodic deposition current is limited by a Schottky-like barrier that forms between the Cu2O and the deposition solution. A barrier height of 0.6 eV was determined from the exponential dependence of the deposition current on the solution temperature. At a solution pH of 9 the orientation of the film is [100], while at a solution pH of 12 the orientation changes to [111]. Atomic force images of the [100] oriented films have crystals shaped as four-sided pyramids, while the [111] films have triangular crystals. The grain size for films grown at 65 degrees C ranges from 2 to 5 mu m. A refractive index of 2.6 was measured from the transmission spectrum for wavelengths between 1350 and 2800 nm. The p-type semiconductor has a direct bandgap of 2.1 eV.