Interface and defect structures in ZnO films on m-plane sapphire substrates

Interface and defect structures in ZnO films grown on (101¯0)m-plane sapphire substrates by plasma-assisted molecular beam epitaxy were investigated by transmission electron microscopy (TEM). Distribution of misfit dislocations (MDs) at the ZnO/Al2O3 interfaces was orientation dependent and quite anisotropic. In addition, type-І1 stacking faults (SFs) bounded by the Frank dislocations with the Burgers vector of 1/6[202¯3] were observed to be predominant. Many SFs initiated from the interface to the film surface were observed in addition to the MDs at the interface. The analysis of the high-resolution TEM revealed no correlation between the SFs and the MDs. The ZnO films were not found to be pure m  -plane ZnO and (101¯3) domains were frequently observed in the film with otherwise mostly (101¯0)m  -plane in nature. These (101¯3) domains were not nucleated at the interface but initiated inside the ZnO film above the interface and reached the top surface.