Interfacial structure and defect analysis of nonpolar ZnO films grown on R-plane sapphire by molecular beam epitaxy

The interfacial relationship and the microstructure of nonpolar (11−20) ZnO films epitaxially grown on (1−102) R-plane sapphire by molecular beam epitaxy are investigated by transmission electron microscopy. The already-reported epitaxial relationships [1−100]ZnO∥[11−20]sapphire and ⟨0001⟩ZnO∥[−1101]sapphire are confirmed, and we have determined the orientation of the Zn–O (cation-anion) bond along [0001]ZnO in the films as being uniquely defined with respect to a reference surface Al–O bond on the sapphire substrate. The microstructure of the films is dominated by the presence of I1 basal stacking faults [density=(1–2)×105cm−1] and related partial dislocations [density=(4–7)×1010cm−2]. It is shown that I1 basal stacking faults correspond to dissociated perfect dislocations, either c or a+c type.