Binding energy and recombination barriers of Frenkel pairs in gallium nitride

Frenkel pair (FP) defects, which are created when an atom leaves its lattice site, forming one interstitial and one vacancy, can be introduced as a result of radiation damage. Employing first-principles calculations, we analyze the recombination process of nitrogen-type and gallium-type FP defects with different distances between the constituent defects. By comparing Kohn-Sham states of FP defects and isolated native defects, we can identify the electronic charge states of the vacancy and interstitial within the pair. We find that the binding energy of FP defects is dominated by Coulomb interaction and can be explained with a point-charge model for distances beyond 6 . Finally, recombination barriers of FPs are examined for both short and long distances. For short distances, the single-move recombination has a small barrier, which would lead to rapid recombination at room temperature. At longer distances the value of the initial migration barrier is very close to that of an isolated defect, but still exhibits some variation that can be attributed to Coulomb interactions. Our computational results provide information about the time scale that governs recombination at a given temperature, thus shedding light on the degradation processes resulting from radiation damage.