Effects of surface morphology of ZnO seed layers on growth of ZnO nanostructures prepared by hydrothermal method and annealing.

ZnO nanostructures were grown on Si (111) substrates by a hydrothermal method. Prior to growing the ZnO nanostructures, ZnO seed layers with different post-heat temperatures were prepared by a spin-coating process. Then, the ZnO nanostructures were annealed at 500 degrees C for 20 min under an Ar atmosphere. Scanning electron microscopy (SEM), X-ray diffraction (XRD), and photoluminescence (PL) were carried out at room temperature (RT) to investigate the structural and optical properties of the as-grown and annealed ZnO nanostructures. The surface morphologies of the seed layers changed from a smooth surface to a mountain chain-like structure as the post-heating temperatures increased. The as-grown and annealed ZnO nanostructures exhibited a strong (002) diffraction peak. Compared to the as-grown ZnO nanostructures, the annealed ZnO nanostructures exhibited significantly strong enhancement in the PL intensity ratio by almost a factor of 2.

Effects of precursor concentrations and thermal annealing on ZnO nanorods grown by hydrothermal method.

ZnO nanorods were grown on spin-coated ZnO seed layers by hydrothermal method. The ZnO nanorods were grown with various precursor concentrations ranging from 0.01 to 0.3 M. Field-emission scanning electron microscopy (FE-SEM), X-ray diffraction (XRD), and photoluminescence (PL) were carried out to investigate the structural and optical properties of the ZnO nanorods. The average diameter and length of the ZnO nanorods is increased as the precursor concentration increased from 0.01 to 0.3 M. From XRD, the intensity of ZnO (002) peak is increased and full width at half maximum (FWHM) of ZnO (002) decreased as the precursor concentration increased. The FWHM of near-band-edge emission (NBE) decreased and intensity ratio of the NBE to the deep-level emission (DLE) increased as the precursor concentration increased which indicated the optical property is improved. The DLE is red-shifted from yellow- to red-emission and its intensity is increased as the annealing temperature increased due to thermal diffusion process.

Effects of thermal annealing in oxygen plasma for buffer layers on properties of ZnO thin films.

ZnO thin films with ZnO buffer layers were grown by plasma-assisted molecular beam epitaxy (PA-MBE) on p-type Si(100) substrates. Before the growth of the ZnO thin films, the ZnO buffer layers were deposited on the Si substrates for 20 minutes and then annealed at the different substrate temperature ranging from 600 to 800 degrees C in oxygen plasma. The structural and optical properties of the ZnO thin films have been investigated by X-ray diffraction (XRD), scanning electron microscopy (SEM), and room-temperature (RT) photoluminescence (PL). A narrower full width at half maximum (FWHM) of the XRD spectra for ZnO(002) and a larger grain are observed in the samples with the thermal annealed buffer layers in oxygen plasma, compared to those of the as-grown sample. The surface morphology of the samples is changed from rugged to flat surface. In the PL spectra, near-band edge emission (NBEE) at 3.2 eV (380 nm) and deep-level emission (DLE) around 1.77 to 2.75 eV (700 to 450 nm) are observed. By increasing the annealing temperatures up to 800 degrees C, the PL intensity of the NBEE peak is higher than that of the as-grown sample. These results imply that the structural and optical properties of ZnO thin films are improved by the annealing process.