Effects of ultrathin layers on the growth of vertically aligned wurtzite ZnO nanostructures on perovskite single-crystal substrates

In this study, ZnO nanostructures were grown on various ultra-thin layers coated (1 0 0)-oriented SrTiO3 (STO) single-crystal substrates using thermal evaporation of metallic zinc at 600 °C. This study used the ZnO seed layer and/or metal catalyst layer to grow high-density ZnO nanostructures on STO substrates. X-ray diffraction and scanning electron microscopy (SEM) measurements showed that the use of Au and Ag catalysts is crucial in producing ZnO nanostructures with a preferential c-axis direction. The as-grown ZnO nanostructures had a hexagonal facet. Among various STO substrates (Au/STO, Ag/STO, ZnO/STO, Au/ZnO/STO, and Ag/ZnO/STO), the ZnO nanostructures grown on the Au/STO substrate had the highest degree of vertical alignment, and the intensity ratio of the UV to visible emission band reached 55. Conversely, the ZnO nanostructures grown on the ZnO seed layer-coated STO substrate were more randomly oriented, and the intensity ratio of the UV to visible emission band was only 9.5. The cathodoluminescence (CL) results showed that higher vertically aligned ZnO nanostructures have lower-density crystal defects. The current–voltage measurements supported the structural analysis.