The remarkable success of GaN-based devices despite comparatively large defect densities has, prompted many groups to explore polycrystalline and amorphous GaN thin films for various device applications. In this paper we present the results of a series of film, growths performed using an RF plasma assisted molecular beam epitaxy system. GaN films were grown on quartz substrates in the temperature range of 150-650 degreesC, and in all cases were found to be polycrystalline and largely c-axis oriented. Rutherford backscattering spectroscopy indicates films have gallium-rich stoichiometry, except for those grown below 200 degreesC. Bandedge photoluminescence was observed at room temperature even for the films grown at 150 degreesC, and many films exhibited a measurable change in resistivity under exposure to ultraviolet radiation. (C) 2003 Elsevier B.V. All rights reserved.