Zinc oxide (ZnO) heteroepitaxial thin films were successfully grown on p-GaN/sapphire (0001) by single-step hydrothermal route at a low temperature of 90 degrees C. Continuous ZnO thin films with c-axis orientation were grown in aqueous solution of zinc acetate di-hydrate and ammonium hydroxide. X-ray diffraction, scanning electron microscopy and room temperature photoluminescence were carried out for structural, morphological and optical property analysis. The as-grown ZnO films showed preferential growth along (0001) direction. The in-plane orientation between ZnO thin film and p-GaN buffer layer was found to be [11 (2) over bar0](ZnO)parallel to[11 (2) over bar0](GaN). Sharp luminescence peak centered at 377nm due to excitonic recombination from ZnO thin film was observed. (C) 2007 Elsevier B.V. All rights reserved.