The growth of (0002) orientated polycrystalline undoped and Ga-doped ZnO films by DC sputtering under Ar is described. The (0002) peak intensity decreases with increasing substrate temperature in both doped and undoped samples. The average grain sizes are very small. This indicates that ZnO films with low crystallinity are obtained at high substrate temperatures. It is deduced that surface damage can be increased by high energy plasmas of neutral Ar particles at high substrate temperatures. The average surface roughness for both undoped and Ga-doped ZnO films decreases with increasing substrate temperatures. It is deduced that energies of sputter particles decrease with increasing substrate temperatures due to collisions with Ar particles. The surface roughness corresponds well to the structure model.