The effects of thermally-induced biaxial stress on the structural, electrical, and optical properties of Cu2O thin films

The effects of biaxial stress in Cu2O thin films grown by rf magnetron sputtering at different growth temperatures were investigated using X-ray diffraction (XRD), atomic force microscopy (AFM), electrical transport, and ellipsometric measurements. A predominant diffraction peak in the XRD patterns corresponds to the (111) plane direction of the Cu2O phase. Biaxial tensile stress was induced by thermal mismatch between the film and substrate and increased with increasing growth temperature. As the growth temperature and biaxial stress increased, the electrical resistivity decreased, while the carrier concentration and Hall mobility both increased. The ellipsometric data were fit using an optical dispersion model, and the decrease in refractive index was attributed to contraction of the lattice parameter with increasing biaxial stress. The optical absorption peaks shifted slightly toward higher energy with increasing stress. Our experimental data suggest that the mechanisms of stress are important for understanding the properties of Cu2O thin films and for the fabrication of devices using them.ope