Effect of ZnO buffer layer prepared by rf sputtering on heteroepitaxial growth of high-quality ZnO films

Abstract

High-quality ZnO epitaxial films without rotation domain structure were successfully prepared on sapphire (0 0 0 1) substrates using metal organic chemical vapor deposition method. The ZnO films deposited by rf sputtering at the substrate temperature of 300°C with (0 0 0 1) preferred orientation were used as a very thin intermediate buffer layer with the thickness of 5–40 nm. In the X-ray diffraction (XRD) φ-scan pattern of the ZnO epitaxial films, only the primary domain was observed at 60° intervals. The full-width at half-maximum of the XRD rocking curve of the ZnO (0 0 0 2) diffraction was 0.64°. The electron mobility evaluated from Hall measurement using van der Pauw method was 43.4 cm2/V s, which was about 4 times larger than that of the directly grown ZnO film on the sapphire (0 0 0 1) substrate. A broad emission line is observed in the low-temperature (4.2 K) photoluminescence spectrum. This emission comes from excitons bound to neutral donors and ionized donor, and bound to ionized doners.