Effects of ZnO/MgO Double Buffer Layers on Structural Quality and Electron Mobility of ZnO Epitaxial Films Grown on c-Plane Sapphire

High-electron-mobility ZnO epilayers were grown on c-plane sapphire with ZnO/MgO double-buffer layers by plasma-assisted molecular beam epitaxy. Precisely controlled low growth rate of the double-buffer layers was crucial to the improvement of electrical properties. Both X-ray diffraction ω rocking curve measurement and calculated electron mobilities revealed that the improvement of electron mobility of ZnO films is due to a decrease in dislocation density. The highest electron mobility of 137 cm2V-1 s-1 in as-grown ZnO film was achieved at room temperature.