We used the metalorganic vapor-phase epitaxy for the growth of ZnO nanostructures on sapphire substrate. We studied the mechanism of epitaxial nanoneedle growth and the formation of quantum dots (QDs) into amorphous ZnO. The precursor combination diethylzinc (DEZn) and N2O was used for needle growth via the vapor liquid solid mechanism with evaporated gold films and for "initiator free" needle growth without catalyst. The needle orientations, the epitaxial relationships between ZnO and Al2O3 substrate and the dependences on growth parameters were investigated using scanning electron microscopy and X-ray diffraction measurements. For the growth of ZnO QDs iso-propanol (i-PrOH) was used as oxygen source. The QDs with radius of only few nanometers were embedded into amorphous ZnO. They show blue-shifted cathodoluminescence spectra and their mean diameter depends on the supersaturation in the gas phase. (c) 2008 Elsevier B.V. All rights reserved.