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 x 10(18) cm(-2) has been investigated with 1.5 MeV He-4(+) channeling. The slight increase in the <0001> aligned yield for as-irradiated crystals indicates that each primary knock-on produces approximately 1.7 x 10(3) displaced atoms. The displaced atoms recover by annealing at 700 T but the biaxial compressive stress sigma(xx) of similar to0. 19 GPa remains in the 1000 degreesC 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 Ge-Ga donor and Ga vacancy, acting as an attractive force in Ga planes in <0001> oriented GaN. (C) 2004 Elsevier Ltd. All rights reserved.