Defect production in neutron irradiated GaN

Rutherford backscattering in the channelling mode (RBS/C) and high resolution X-ray diffraction (XRD) were used to characterize GaN films after irradiation with fast and thermal neutrons to fluences of 1.0 × 1019 n/cm2 and 4.8 × 1019 n/cm2, respectively. RBS/C experiments indicate that Ga atoms are preferentially displaced along the c-axis. In good agreement, XRD shows an expansion of the lattice along the c-axis after irradiation, while no change of the in-plane lattice parameter was observed. Both fast and thermal neutrons contribute to the lattice damage and to the introduction of perpendicular elastic strain; the former due to direct knock-on atoms, the latter due to recoil processes during the neutron activation of Ga and N atoms.