Ion channeling and Raman scattering studies of the lattice disorder and residual strain in neutron irradiated GaN

The lattice disorder in GaN produced by fast neutrons with a fluence of 6.7×1018 cm−2 has been investigated with 1.5 MeV 4He+ channeling. The slight increase in the 〈0001〉 aligned yield for as-irradiated crystals indicates that each primary knock-on produces approximately 1.7×103 displaced atoms. The displaced atoms recover by annealing at 700 °C but the biaxial compressive stress σxx of ∼0.19 GPa remains in the 1000 °C annealed GaN. There is no change in the lattice spacing of the (0002) plane for both irradiated and annealed samples, suggesting the existence of the strain perpendicular to the [0001] axis. The residual strain correlates with the neutron irradiation-induced complex defect consisting of the transmuted GeGa donor and Ga vacancy, acting as an attractive force in Ga planes in 〈0001〉 oriented GaN.