Selective homoepitaxial growth and luminescent properties of ZnO nanopillars

High spatial density ZnO nanopillars (NPs) have been fabricated on catalyst- and pattern-free Si wafers using atmospheric pressure metal organic chemical vapor deposition (APMOCVD) at a moderate temperature (500 deg. C). The nanopillar diameter is ∼ 35 nm and the length is ∼ 150 nm, with a density of ∼ 2 x 109 cm-2. The growth evolution of the nanopillars, providing the (0001)NP||(0001)ZnOgrain||(100)Sisurface epitaxial relationship, is extensively studied by scanning and high resolution transmission microscopy. The approach to obtaining the ZnO 1D structures is explained in terms of selective homoepitaxial growth via the crystallographic anisotropy of the seeding layer. The advanced PL properties of ZnO NPs, e.g. indications of free excitonic and absence of defect emission, are related to their single crystalline nature within one pillar and most probably better stoichiometry and less contamination. The observed efficient monochromatic UV emission from the ZnO NPs at room temperature points toward their potential application as building blocks for nanoscale optoelectronic devices.