Strain-related phenomena in GaN epilayers under MeV inert-gas ion irradiation

When the ion fluence was less than ∼0.055 displacement per atom(dpa), the lattice expansions and lattice strains markedly increased linearly with increasing ion fluences, accompanied by a slow enhancement in the dislocation densities, distortion parameters, and Urbach energy for both ion irradiations. Above this fluence (∼0.055 dpa), the lattice strains presented a slight increase, whereas a remarkable increase was observed in the dislocation densities, distortion parameters, and Urbach energy with the ion fluences after both ion irradiations. ∼0.055 dpa is the threshold ion fluence for defect evolution and lattice damage related to strain.