Off-axis electron holography is utilized to identify point defect reactions and quantify their dynamics by probing the time and temperature dependence of the Fermi level upon annealing. The methodology is illustrated using implanted carbon (C) in GaN, where a site switching phenomenon of C, from substitutional to interstitial, is found to be responsible for lifting the Fermi-level pinning in the lower part of the band gap. The carbon site switching process has an activation barrier energy of 2.27±0.26eV.