The influence of the substrate pretreatment on crystallinity of indium nitride films grown on (111)GaAs by radio frequency sputtering were investigated. It was shown that the crystalline quality of InN layers grown on GaAs can be improved by presputtering the substrate in nitrogen plasma prior to the growth. By Auger electron spectroscopy and atomic force microscopy analysis we revealed that GaN islands form on the surface of GaAs substrate due to the presputtering. The optimum presputtering time for growing InN single crystal was assessed to be the time at which GaN islands cover the substrate surface entirely.