Structural and optical properties of Cu2O crystalline electrodeposited films

Abstract

Cuprous oxide (Cu2O) films were electrodeposited on Ni/Si(100), Au/Si(100), and Si(100) substrates from aqueous solution at room temperature. The thicknesses of the films were varied in the range of 250 to 1250 nm. It was shown that at pH 10.00, an increase of just 1% can change the Cu2O texture from [100] to [111]. Atomic force microscopy reveals that Cu2O(100) and Cu2O(111) films present rounded and faceted grains, respectively. For the thinner films, it was also observed that the substrate has a strong influence on the Cu2O orientation. The Cu2O refraction index (n) and band gap energy (E-g) were obtained from reflectance measurements. The Wemple and DiDomenico single oscillator model was applied to n data, and the dispersion energy E-d of this model was addressed to describe the density of Cu vacancies in the Cu2O lattice. It was found out that the density of this kind of defect is higher for [111] oriented Cu2O films and decreases as a function of the film thickness. This analysis also indicated that the dynamics of formation of the Cu vacancy depends on the Cu2O lattice parameter. This parameter showed that Cu2O films are initially under compressive misfit stress, but at a critical thickness, the lattice parameter abruptly increases in order to relax the Cu2O lattice structure. This sudden transition is also observed in the E-g data and is attributed to the enhancement of Cu-Cu internetwork interaction that is inversely proportional to E-g. (C) 2014 Elsevier B.V. All rights reserved.