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

Abstract

We have used positron annihilation spectroscopy to study the introduction and recovery of point defects introduced by 0.45 and $2\phantom{\rule{0.3em}{0ex}}\mathrm{MeV}$ electron irradiation at room temperature in $n$-type GaN. Isochronal annealings were performed up to $1220\phantom{\rule{0.3em}{0ex}}\mathrm{K}$. We observe vacancy defects with specific lifetime of ${\ensuremath{\tau}}_{V}=190\ifmmode\pm\else\textpm\fi{}15\phantom{\rule{0.3em}{0ex}}\mathrm{ps}$ that we tentatively identify as N vacancies or related complexes in the neutral charge state in the samples irradiated with $0.45\phantom{\rule{0.3em}{0ex}}\mathrm{MeV}$ electrons. The N vacancies are produced at a rate ${\ensuremath{\Sigma}}_{\mathrm{N}}^{0.45}\ensuremath{\simeq}0.25\phantom{\rule{0.3em}{0ex}}{\mathrm{cm}}^{\ensuremath{-}1}$. The irradiation with $2\phantom{\rule{0.3em}{0ex}}\mathrm{MeV}$ electrons produces negatively charged Ga vacancies and negative nonopen volume defects (negative ions) originating from the Ga sublattice, at a rate ${\ensuremath{\Sigma}}_{\mathrm{Ga}}^{2.0}\ensuremath{\simeq}5\phantom{\rule{0.3em}{0ex}}{\mathrm{cm}}^{\ensuremath{-}1}$. The irradiation-induced N vacancies anneal out of the samples at around $600\phantom{\rule{0.3em}{0ex}}\mathrm{K}$, 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 $600\phantom{\rule{0.3em}{0ex}}\mathrm{K}$, and this is interpreted as the isolated Ga vacancies becoming mobile with a migration barrier of ${E}_{M}^{V,\mathrm{Ga}}=1.8\ifmmode\pm\else\textpm\fi{}0.1\phantom{\rule{0.3em}{0ex}}\mathrm{eV}$. Interestingly, we observe a change of charge state of the irradiation-induced negative ions from $2\ensuremath{-}$ to $1\ensuremath{-}$ likely due to a reconstruction of the defects in two stages at annealing temperatures of about 600 and $700\phantom{\rule{0.3em}{0ex}}\mathrm{K}$. 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 $800--1100\phantom{\rule{0.3em}{0ex}}\mathrm{K}$.