Polycrystalline GaN films were deposited on quartz and ZnO buffer layers over quartz by reactive sputtering of a GaAs target in 100% nitrogen at 550 degrees C and 700 degrees C. Micro-structural investigations of the films were carried out using high resolution X-ray diffraction, atomic force microscopy and Raman spectroscopy. GaN films deposited on ZnO buffer layers exhibit strongly preferred (0002) orientation of crystallites. In particular, the film deposited at 700 degrees C on ZnO buffer layer over amorphous quartz substrate showed large crystallite size, both along and perpendicular to growth direction, strong and nearly complete c-axis orientation of crystallites with tilt of similar to 2.5 degrees and low value of micro-strain similar to 2x10(-3). The significant improvement in crystallinity and orientation of crystallites in the GaN film is attributed to the presence of the ZnO buffer layer on quartz substrate and its small lattice mismatch (1.8%) with GaN. (c) 2008 Elsevier B.V. All rights reserved.