Frenkel Pairs and Recombination Barriers in GaN

Frenkel-pair (FP) defects, created when an atom leaves its lattice site and forms an interstitial and a vacancy, can be introduced by radiation damage. Using first-principles calculations, we determine the recombination barriers of nitrogen-type and gallium-type FPs at various separations between their constituent defects. By comparing the Kohn–Sham states of FP defects with those of the corresponding isolated native defects, we identify the charge states of the vacancy and interstitial in the pair. The binding energy of FP defects is dominated by Coulombic interactions and follows a point-charge model at distances beyond 6 Å. Finally, we examine the FP recombination barriers at both short and long distances. At short distances, the small barrier leads to rapid recombination at room temperature, while at longer distances, the migration barrier approaches that of an isolated defect but is still affected by the Coulombic interactions. These results provide information about the timescale governing recombination at a given temperature, thereby shedding light on degradation processes resulting from radiation damage.