Influence of processing variables on the structure and properties of ZnO films

Zinc oxide films of high optical quality have been deposited onto both silica and silicon substrates using reactive sputtering, pulsed laser deposition, and an aqueous solution based technique. Films have been characterized with respect to crystalline phase and phase stability, surface morphology, and optical response by means of X-ray diffraction, Raman spectroscopy, atomic force microscopy, optical transmission and ellipsometry measurements. All films studied were of the wurtzite phase, fine-grained, and exhibited varying degrees of c-axis orientation with respect to the substrate normal depending upon deposition conditions. Films showed some degree of residual tensile stress which was inferred from the E(2) Raman line shift relative to the single-crystal frequency. The wurtzite phase was found to be stable to temperatures near 800 degrees C, but at higher temperatures, reaction with silica led to evolution of Zn2SiO4 at the interface. Variations in Raman line intensities upon post-deposition annealing have been correlated with oxidation of excess zinc in the lattice.