Polycrystalline GaN was grown on silica glass substrates by metalorganic chemical vapor deposition using a two-step growth process. It was found that the optical and structural properties were significantly dependent on the growth conditions of GaN buffer layers. Growth parameters for the low-temperature buffer layers, such as the growth temperature, the growth time, the trimethyl gallium flow rate and the ramping time, have played important roles in improving the quality of polycrystalline GaN. This tendency is quite similar to the case of a GaN epilayer on a sapphire substrate. (C) 2002 Elsevier Science B.V. All rights reserved.