We have used positron annihilation spectroscopy to study the introduction and recovery of point defects introduced by 0.45 and $2\mathrm{MeV}$ electron irradiation at room temperature in $n$-type GaN. Isochronal annealings were performed up to $1220\mathrm{K}$. We observe vacancy defects with specific lifetime of ${\tau }_V=190\pm 15\mathrm{ps}$ that we tentatively identify as N vacancies or related complexes in the neutral charge state in the samples irradiated with $0.45\mathrm{MeV}$ electrons. The N vacancies are produced at a rate ${\Sigma }_{\mathrm{N}}^{0.45}\simeq 0.25{\mathrm{cm}}^{-1}$. The irradiation with $2\mathrm{MeV}$ electrons produces negatively charged Ga vacancies and negative nonopen volume defects (negative ions) originating from the Ga sublattice, at a rate ${\Sigma }_{\mathrm{Ga}}^{2.0}\simeq 5{\mathrm{cm}}^{-1}$. The irradiation-induced N vacancies anneal out of the samples at around $600\mathrm{K}$, 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 $600\mathrm{K}$, and this is interpreted as the isolated Ga vacancies becoming mobile with a migration barrier of $E_M^{V,\mathrm{Ga}}=1.8\pm 0.1\mathrm{eV}$. 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 $700\mathrm{K}$. 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 $800–1100\mathrm{K}$.

• Received 31 May 2007

DOI:https://doi.org/10.1103/PhysRevB.76.165207