Introduction and recovery of Ga and N sublattice defects in electron-irradiated GaN

We have used positron annihilation spectroscopy to study the introduction and recovery of point defects introduced by 0.45 and 20.3em0exMeV electron irradiation at room temperature in n-type GaN. Isochronal annealings were performed up to 12200.3em0exK. We observe vacancy defects with specific lifetime of τV=190±150.3em0exps that we tentatively identify as N vacancies or related complexes in the neutral charge state in the samples irradiated with 0.450.3em0exMeV electrons. The N vacancies are produced at a rate ΣN0.450.250.3em0excm^-1. The irradiation with 20.3em0exMeV electrons produces negatively charged Ga vacancies and negative nonopen volume defects (negative ions) originating from the Ga sublattice, at a rate ΣGa2.050.3em0excm^-1. The irradiation-induced N vacancies anneal out of the samples at around 6000.3em0exK, 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 6000.3em0exK, and this is interpreted as the isolated Ga vacancies becoming mobile with a migration barrier of EMV,Ga=1.8±0.10.3em0exeV. Interestingly, we observe a change of charge state of the irradiation-induced negative ions from 2- to 1- likely due to a reconstruction of the defects in two stages at annealing temperatures of about 600 and 7000.3em0exK. The negative ions anneal out of the samples together with the other half of the Ga vacancies (stabilized by, e.g., N vacancies and/or hydrogen) in thermal annealings at 800--11000.3em0exK.