Irradiation-induced defects in InN and GaN studied with positron annihilation

We use positron annihilation to study 2-MeV 4He+ irradiated and subsequently rapid-thermal-annealed InN grown by molecular-beam epitaxy and GaN grown by metal-organic chemical-vapour deposition. The irradiation fluences were in the range 5 × 1014–2 × 1016 cm−2. In vacancies are introduced in the irradiation at a low rate of 100 cm−1, with their concentration saturating in the mid-1017 cm−3 range at an irradiation fluence of 2 × 1015 cm−2. The annealing, performed at temperatures between 425 and 475 °C, is observed to result in an inhomogeneous redistribution of the In vacancies. The behaviour is opposite to GaN, where Ga vacancies are introduced at a much higher rate of 3600 cm−1 showing no detectable saturation. About half of the Ga vacancies are found to recover in the annealing, in agreement with previous studies, while the remaining Ga vacancies undergo no spatial redistribution.