Polarity control of zno films grown on ferroelectric (0001) linbo₃ substrates without buffer layers by pulsed-laser deposition

For this study, polarity-controlled ZnO films were grown on lithium niobate (LiNbO₃) substrates without buffer layers using the pulsed-laser deposition technique. The interfacial structure between the ZnO films and the LiNbO₃ was inspected using high-resolution transmission electron microscopy (HR-TEM) measurements, and X-ray diffraction (XRD) measurements were performed to support these HR-TEM results. The polarity determination of the ZnO films was investigated using piezoresponse force microscopy (PFM) and a chemical-etching analysis. It was verified from the PFM and chemical-etching analyses that the ZnO film grown on the (+z) LiNbO₃ was Zn-polar ZnO, while the O-polar ZnO occurred on the (-z) LiNbO₃ . Further, a possible mechanism of the interfacial atomic configuration between the ZnO on the (+z) LiNbO₃ and that on the (-z) LiNbO₃ was suggested. It appears that the electrostatic stability at the substrate surface determines the initial nucleation of the ZnO films, leading to the different polarities in the ZnO systems.