Quantitative study for surface properties of AlGaN epi-layers by ARXPS Hongquan Yang, Xiong Zhang, Shuchang Wang, Min Zhu and Yiping Cui Eur. Phys. J. Appl. Phys., 72 2 (2015) 20301 Published online: 30 October 2015 DOI: 10.1051/epjap/2015150418