Structural characterization of ZnO films grown by molecular beam epitaxy on sapphire with MgO buffer

The structural characteristics of the ZnO film grown on sapphire substrate using a thin MgO buffer layer were studied using transmission electron microscopy and high-resolution x-ray diffraction. The growth was carried out in a modified plasma-molecular beam epitaxy system. The observed misfit dislocations were well confined at the sapphire overgrown interface exhibiting domain matching epitaxy, where the integral multiples of lattice constants match across the interface. The main extended defects in the ZnO film were the threading dislocations having a mean density of 4×109cm−2. The formation of the MgO buffer layer as well as the ZnO growth were monitored in situ by reflection high-energy electron diffraction. The very thin ∼1nm, MgO buffer layer can partially interdiffuse with the ZnO as well as react with the Al2O3 substrate forming an intermediate epitaxial layer having the spinel (MgO∕Al2O3) structure.