Systematic study of vertically aligned ZnO nanowire arrays synthesized on p-GaN substrate by hydrothermal method

This study presents a simple and effective way to synthesize well-aligned single-crystalline ZnO nanowires (NWs) by the hydrothermal method (HTM). The influence of growth conditions on the morphology of as-grown ZnO NWs is discussed from the chemical reaction equilibrium perspective. The height and diameter of the NWs demonstrated tunability through the optimization of the growth parameters. The ZnO NWs exhibited optimal alignment along the c-axis perpendicular to the substrate, as observed through scanning electron microscopy and X-ray diffraction. The nucleation and epitaxial growth mechanism of NWs on p-GaN has also been investigated. The conditions to obtain high-density and vertically aligned NWs were optimized as 0.03 mol l(-1) concentration, 90 degrees C temperature and 3 h time. Photoluminescence measurements revealed a strong and narrow UV emission at 380 nm. The formation of a ZnO/p-GaN heterojunction through HTM provides promising optoelectronic device applications riding on the advantages of feasibility, cost-effectiveness and non-toxicity. (C) 2019 The Japan Society of Applied Physics