Growth of a-plane ZnO Thin Films on r-plane Sapphire by Plasma-assisted MBE

摘要

ZnO thin films have been epitaxially grown on r-plane sapphire by RF-plasma-assisted molecular beam epitaxy. X-ray diffraction (XRD) and transmission electron microscopy (TEM) studies indicate that the epitaxial relationship between ZnO and r-plane sapphire is (1120 )_(ZnO)∥ (1102 )_(sapphire) and [0001]_(ZnO)∥ [ 1101 ]_(sapphire). Atomic force microscopy measurements reveal islands extended along the sapphire [1101] direction. XRD omega rocking curves for the ZnO (1120) reflection measured either parallel or perpendicular to the island direction suggest the defect density anisotropy along these directions. Due to the small lattice mismatch along the ZnO [0001] direction, few misfit dislocations were observed at the ZnO/Al_2O_3 interface in the high-resolution cross-sectional TEM image with the zone axis along the ZnO [ 1100 ] direction.