Growth of non-polar ZnO films on a-GaN/r-Al2O3 templates by radio-frequency magnetron sputtering

In this work, non-polar (1,1,−2,0) ZnO thin films have been grown on a-GaN/r-Al2O3 templates by radio-frequency magnetron sputtering. By varying the substrate temperature, the ZnO thin films were transformed from polycrystalline structure to epitaxial one on a-GaN/r-Al2O3 templates. High-quality (1,1,−2,0) ZnO epitaxial thin films were grown on the a-GaN/r-Al2O3 template at the optimized condition of 300 °C, which was confirmed by X-ray diffraction. The full width at half maximum (FWHM) of the (1,1,−2,0) ω-rocking curve of the a-plane ZnO films grown on the a-GaN/r-Al2O3 template was 0.51°, indicating a small mosaicity and a low dislocation density in the ZnO film grown on the a-GaN/r-Al2O3 template. Its surface roughness observed by atomic force microscopy was about 2.32 nm. Furthermore, the comparative investigation results show that the ZnO films grown on a-GaN/r-Al2O3 templates are more likely to form in the (1,1,−2,0)-orientation than those directly grown on r-sapphire.