Morphology and growth mechanism of aligned ZnO nanorods grown by catalyst-free MOCVD

We report on ZnO nanorods grown by catalyst-free metal-organic chemical vapour deposition (MOCVD) in a commercial Epigress reactor using diethylzinc and N₂O as precursors. Well-aligned ZnO nanorods with uniform diameter, length and density have been grown perpendicularly to the sapphire (0 0 0 1) surface. Scanning electron microscopy (SEM) has been used to observe the morphology of the ZnO nanorods and X-ray diffraction and transmission electron microscopy (TEM) to investigate the crystalline structure of the nanorods. TEM observation as well as photoluminescence measurements confirm the very good crystalline quality of the nanorods. SEM observation on samples that have been prepared with various deposition times has been used in order to investigate the growth mechanism. Three types of ZnO morphologies have been identified: a thin two-dimensional ZnO layer formed at the sapphire surface, covered by three-dimensional hexagonal-shaped islands and hexagonal nanorods on top of them.