CaO buffer layer for the growth of ZnO thin film

We report the effect of CaO buffer layers on the structural properties of sputter-grown ZnO thin films. X-ray diffraction patterns indicated that enhanced crystallinity and alleviated compressive strain in the ZnO thin film were achieved by inserting a very thin CaO buffer layer between ZnO and the sapphire substrate. The interface was investigated by high-resolution transmission electron microscopy, and the result showed that the growth of CaO on the sapphire substrate follows the Stranski–Kristanov mode. The mechanism for the control of crystallinity and strain in the ZnO thin film was discussed, and was found to be strongly related to the growth mode of the CaO buffer layer.