Ar+ sputtering was applied for exploring the graded band gap profile and the effectiveness of surface contaminations removal, especially the oxide, of the AlGaN material for preparing high performance photocathodes. The X-ray photoelectron spectroscopy scan(XPS) and spectral curves fitting indicated that after conventional chemical cleaning, there were still large amount of carbon and oxygen on surface, where the oxide mainly included gallium oxide and aluminum oxide. After Ar+ sputtering for 0.5 min and 1 min, these carbon and oxygen were both completely removed from surface and the proportion of Al changed from original 29.8% to 36.7% and 37.8%, respectively, more suitable to the solar blind detection. The variation trend of Al and Ga from surface to bulk confirmed the graded band gap profile of this AlGaN material, which would introduce built-in electric field for preparing high performance photocathode. (C) 2017 Elsevier B.V. All rights reserved.