Compositional and structural properties of nanostructured ZnO thin films grown by oblique angle reactive sputtering deposition: effect on the refractive index

Abstract

In this work, we report the successful growth of ZnO nanostructured films by oblique angle magnetron sputtering deposition (OAD) from a Zn target in a mixture gas of Ar/O2. The film microstructure and the surface morphology of the samples were explored by HRSEM. The crystalline structure and the composition were determined by XRD and RBS, respectively. The optical properties of the ZnO films (refractive index, n, and extinction coefficient, k) were also studied by spectroscopic ellipsometry. Films were found to be porous and consisting of an inclined columnar structure, with columns tilting in the direction of the incident flux. The experimental results reveal that the deposition angle, the Ar/O2 gas ratio and the distance between the target and the substrate play a significant role in the composition, crystalline structure and optical and electrical properties of the ZnO thin films. In particular, it has been found that using different deposition angles in the range 0◦–85◦ it is possible to control the refractive index varying from 1.9 to 1.5, due to the high porosity of the films as a result of the self-shadowing columnar structure produced during the process.