Positron annihilation spectroscopy was used to study the introduction and recovery of point defects introduced by 0.45 and 2MeV electron irradiation, at room temperature, of n-type GaN. Isochronal annealings were performed up to 1220K. Vacancy defects with a specific lifetime of τV=190ps were observed that were tentatively identified as being N vacancies or related complexes in the neutral charge state in the samples irradiated with 0.45MeV electrons. The N vacancies were produced at a rate ΣN0.45 ≈ 0.25/cm. The irradiation with 2MeV electrons produces negatively charged Ga vacancies and negative non-open volume defects (negative ions) originating from the Ga sub-lattice, at a rate ΣGa2.0 ≈ 5/cm. The irradiation-induced N vacancies anneal out of the samples at around 600K, possibly due to the motion of the irradiation-induced N interstitials. Half of the irradiation-induced Ga vacancies anneal out of the samples also around 600K, and this was interpreted as the isolated Ga vacancies becoming mobile with a migration barrier of EMV,Ga = 1.8eV. A change in charge state of the irradiation-induced negative ions from 2− to 1− was observed and was probably due to a reconstruction of the defects in 2 stages; at annealing temperatures of about 600 and 700K. The negative ions annealed out, together with the other half of the Ga vacancies (stabilized by, e.g., N vacancies and/or hydrogen), upon annealing at 800 to 1100K.

Introduction and Recovery of Ga and N Sublattice Defects in Electron-Irradiated GaN. F.Tuomisto, V.Ranki, D.C.Look, G.C.Farlow: Physical Review B, 2007, 76[16], 165207