The paper presents a polycrystalline GaN thin film with a hexagonal wurtzite structure under the optimized sputtering conditions of 40 W RF power, 5 mT working pressure, using pure nitrogen gas with a substrate temperature of 700˚C. The study examines the effects of surface disorders and incorporates it in the thin films characteristics. A radio frequency (RF) Ultra High Vacuum (UHV) Magnetron Sputtering System has been used for the deposition of Gallium Nitride (GaN) on silicon, sapphire and glass substrates with different parameters. The power is varied from 40 W to 50 W, and the pressure from 4 mT to 15 mT. The effects of the RF sputtering powers and gas pressures on the structural properties are investigated experimentally. Sputtering at a lower RF power of 15 W does increase the N atomic percentage, however the deposition rate is substantially slower and the films are amorphous. GaN deposited on both silicon and sapphire wafer resulted in thin films close to stoichiometric once the N 2 concentration is 60% or higher. It is also observed that the substrate cooling/heating effects improve the quality of the thin films with fewer defects present at the surface of the GaN epi-structure.