Effects of growth conditions on the structural and the optical properties of ZnO submicron particles grown by using vapor phase transport

Zinc oxide (ZnO) submicron particles were synthesized on a Au-catalyzed Si substrate by using vapor phase transport at atmospheric pressure with a mixture of ZnO and graphite powders as the source materials. Au catalyst layers with thicknesses of 75.6 Å were deposited using a thermal evaporator. ZnO submicron particles were synthesized under various growth conditions, such as growth temperatures ranging from 700 to 1000 °C and distances between the source material and substrate ranging from 5 to 50 mm; the synthesis was carried out using argon and oxygen as the ambient gas. The structural and the optical properties of the ZnO submicron particles were investigated by using field-emission scanning electron microscopy (FE-SEM), X-ray diffraction (XRD), and photoluminescence (PL). The SEM images of the first experimental series, which were grown at various temperatures, revealed that dispersively distributed submicron particles with diameters ranging from 100 to 500 nm were formed on the substrates. The largest average diameter of the ZnO submicron particles was obtained at a growth temperature of 800 °C. In addition, the highest intensity and narrowest full width at half maximum (FWHM) of the ZnO (002) diffraction peak located at 34.4° were observed for ZnO submicron particles grown at 800 °C. In the PL spectra, the intensity of the near-band-edge emission (NBE) peak increased rapidly as the growth temperature was increased to 800 °C and then decreased as the growth temperature was increased further to 1000 °C. In the second experimental series, in which various distances between the powder source and Si substrate were used, the ZnO submicron particles exhibited different grain sizes ranging from 100 to 250 nm. As the distance from the source was increased, the grain size of the ZnO submicron particles increased because more O2 molecules remained in the small quartz tube in which the ZnO and the graphite powders were mixed. Among the various ZnO diffraction peaks, the ZnO (002) peak located at 34.4° was the most intense. In addition, the FWHM of the ZnO (002) diffraction peak was 0.062° for a source-to-substrate distance of 50 mm. In the PL spectra, all samples except the sample with a source-to-substrate distance of 5 mm showed a dominant NBE peak at about 3.28 eV.