We report the behavior of nitrogen implanted into GaAs wafer upon annealing in the range of 500 degrees C to 1000 degrees C. The SIMS results show out-diffusion of nitrogen and the peaks in the distribution profiles of implanted nitrogen broadening. XPS measurements indicate that the N bonding configuration before annealing is contributed by N-As, interstitial N-N and the N-As complex. However, N-As complex disappears completely upon annealing at temperature higher than 700 degrees C. The spectra and quantitative analysis reveal that a saturation of N-As happens as annealing temperature increases. Before the saturation, the substitional N-As keeps rising, which leads to the elevation of n-type doping level in host. Whereas beyond the saturation, the excess thermal energy beyond saturation triggers the kick-out mechanism and induces dramatic increase in the amount of N-N split interstitials, resulting in suppression of the nitrogen out-diffusion during annealing and pining of the Fermi level. (C) 2012 Elsevier B.V. All rights reserved.