Effects of surface treatments with (NH4)(2)S-x, HCl, and Ar+ bombardment on InN have been investigated using x-ray photoelectron spectroscopy and Auger electron spectroscopy. There was no evident influence on InN with only HCl treatment. The treatment with (NH4)(2)S-x, effectively eliminated the oxygen on the InN surface and prevented the surface oxidation due to passivation [the sulfur from (NH4)(2)S-x probably bonded with In atoms]. Ar+ treatment effectively removed the oxygen and carbon contaminations, but resulted in a large amount of N vacancies. The concentration of N vacancies of InN is closely related to the Ar+ beam current density afforded by an InN film, and a model was introduced to give an explanation. (c) 2007 American Vacuum Society.