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 in n-type GaN. Isochronal annealing was performed at up to 1220K. Vacancy defects with a specific lifetime of 190ps were observed and were tentatively identified as being N vacancies or related complexes in the neutral charge state in samples irradiated with 0.45MeV electrons. The N vacancies were produced at a rate ΣN0.45 of about 0.25/cm. Irradiation with 2MeV electrons produced negatively charged Ga vacancies and negative non open-volume defects (negative ions) originating from the Ga sub-lattice, at a rate ΣGa2.0 of about 5/cm. The irradiation-induced N vacancies annealed out of the samples at around 600K; due possibly to motion of the irradiation-induced N interstitials. Half of the irradiation-induced Ga vacancies also annealed out of the samples at around 600K, and this was attributed to the isolated Ga vacancies becoming mobile, with a migration barrier of EMV,Ga =1.8eV. Interestingly, a change in charge state of the irradiation-induced negative ions, from 2- to 1- was observed and was thought to be due to a reconstruction of the defects in 2 stages at annealing temperatures of about 600 and 700K. The negative ions annealed out of the samples, together with the other half of the Ga vacancies (stabilized by, e.g., N vacancies and/or H), upon thermal 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 (10pp)