Study of defects and interfaces in epitaxial ZnO films on (1 1 2̄ 0) Al₂O₃ grown by electron cyclotron resonance-assisted molecular beam epitaxy

The detailed defects and interface in the ZnO films on (1 1 2̄ 0) a-plane of sapphire have been characterized using transmission electron microscopy. The single crystal ZnO films are grown by electron cyclotron resonance-assisted molecular beam epitaxy. The orientation relationship between ZnO films and sapphire is (0 0 0 1)_ZnO∥(1 1 2̄ 0)_sapphire and [2 1̄ 1̄ 0]_ZnO∥[0 0 0 1]_sapphire. A majority of the threading dislocations was found to be screw or mixed. When the interfaces are observed in [0 0 0 1]_sapphire direction, the interfaces appear structurally semicoherent with a comparative regular array of misfit dislocations at an interface accommodating a mismatch of about 2.45%. Good matches between simulated and experimental images of the ZnO/a-plane sapphire were obtained. The structural model for the atomic arrangements of the interface was proposed.