Radiofrequency (RF) nitrogen plasma sources are commonly employed in the growth of group III-nitrides by molecular beam epitaxy and reactive evaporation. These sources produce atomic nitrogen and excited molecules (W). In this work the relative flux of these two species produced by an RF source was studied by emission spectroscopy as a function of power, pressure, and argon dilution. Polycrystalline indium nitride thin films were synthesized under the same conditions. It was found that argon dilution had a strong influence on the production of active nitrogen, with maximum fluxes obtained around similar to 40% N-2. Film properties, as measured by X-ray diffraction, atomic force microscopy and Hall effect, were also optimized at this condition. It was observed that the Hall mobility scaled with the sum of N and N-2* emission, suggesting that both species may be beneficial for InN growth. (c) 2005 Elsevier B.V. All rights reserved.