Characteristics of polarity-controlled ZnO films fabricated using the homoepitaxy technique

Hydrothermal ZnO(0001) substrates with high crystalline quality were employed in the fabrication of polarity-controlled ZnO films using laser molecular beam epitaxy. The repolished Zn- and O-polar surfaces of ZnO substrates displayed atomically flat surfaces and high crystalline quality even after annealing at high temperatures, as evidenced from high-resolution x-ray diffraction and atomic force microscopy analyses. The electrical and optical properties of Zn-polar ZnO films were significantly improved when annealed, as opposed to polished, substrates were used. This reduced the diffusion of impurities and suppressed the formation of a disordered degenerate layer that might have formed at the interface regions between the substrate and the film. On the other hand, the characteristics of O-polar ZnO films were almost independent of the ZnO substrate pretreatment. In particular, heat-treatment of the substrate for Zn-polar rather than O-polar growth played an important role in minimizing the surface damage generated during mechanical and mechano-chemical polishing. This study paid attention to the influence of heat-treatment on Zn-polar surfaces of high crystallinity ZnO substrates, providing information toward the fabrication of homoepitaxial growth in Zn-polarity. (C) 2004 American Vacuum Society.