Enhancement of the surface and structural properties of ZnO epitaxial films grown on Al2O3 substrates utilizing annealed ZnO buffer layers

ZnO films were grown on Al2O3 (1000) substrates without and with ZnO buffer layers by using radio-frequency magnetron sputtering. Atomic force microscopy images showed that the surface roughness of the ZnO films grown on ZnO buffer layers annealed in a vacuum was decreased, indicative of an improvement in the ZnO surfaces. X-ray diffraction patterns showed that the crystallinity of the ZnO thin films was enhanced by using the annealed ZnO buffer layer in comparison with the film grown on without a buffer layer. The improvement of the surface and structural properties of the ZnO films might be attributed to the formation of the Zn-face ZnO buffers due to annealing in a vacuum. These results indicate that the surface and structural properties of ZnO films grown on Al2O3 substrates are improved by using ZnO buffer layers annealed in a vacuum.