Vertically aligned ZnO nanorods of high crystalline and optical quality grown by dc reactive sputtering

ZnO nanorods were grown on Si and quartz substrates by direct current reactive magnetron sputtering of metallic zinc target in argon–oxygen ambient, without the use of any seed layer or catalyst. A combination of top-down and cross-sectional scanning electron microscopy studies have shown that the substrate temperature critically controls the growth behavior and morphology of ZnO films, eventually resulting in the growth of well aligned and separated ZnO nanorods at substrate temperature of ~750 °C. High resolution x-ray diffraction studies of ZnO nanorods grown at 750 °C have shown that the nanorods are highly c-axis oriented and vertically aligned perpendicular to both Si and quartz substrates, and display small values of tilt and micro-strain, particularly in the case of Si substrate (1.26° and 4 × 10−4, respectively). Cross-sectional transmission electron microscopy of ZnO nanorods demonstrates their single-crystalline nature and growth along [0002] direction. Room temperature photoluminescence spectra of ZnO nanorods display extremely high near-band-edge emission and weak defect emission due to point defects, compared to that of the ZnO films grown at lower substrate temperatures. The drastic enhancement of near-band-edge emission of ZnO nanorods (over two orders of magnitude) and strong suppression of defect emission are attributed to their high crystalline quality and absence of interface defects due to lateral coalescence.