Search

Positron annihilation measurements show that negative Ga vacancies are the dominant acceptors in n-type gallium nitride grown by hydride vapor phase epitaxy. The concentration of Ga vacancies decreases, from more than 1019 to below 1016 cm−3, as the distance from the interface region increases from 1 to 300 μm. These concentrations are the same as the total acceptor densities determined in Hall experiments. The depth profile of O is similar to that of VGa, suggesting that the Ga vacancies are complexed with the oxygen impurities.

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 $800--1100\phantom{\rule{0.3em}{0ex}}\mathrm{K}$.

Positron annihilation spectroscopy, supported by ab initio theory, has been applied to verify the decoration of Ga vacancies in $\mathrm{GaN}$ by oxygen and hydrogen. Our results indicate that the Doppler broadening measurement of electron momentum distribution is sensitive enough to distinguish even between N and O atoms neighboring the Ga vacancy. We identify isolated ${V}_{\mathrm{Ga}}$ in electron irradiated $\mathrm{GaN}$ and ${V}_{\mathrm{Ga}}\text{\ensuremath{-}}{\mathrm{O}}_{\mathrm{N}}$ complexes in highly O-doped high-purity $\mathrm{GaN}$. Evidence of H decoration of Ga vacancies is obtained in epitaxial $\mathrm{GaN}$ grown by metalorganic chemical-vapor deposition.

We have used positron annihilation spectroscopy to determine the nature and the concentrations of the open volume defects in as-grown and electron irradiated (${E}_{\mathrm{e}\mathrm{l}}=2\text{ }\mathrm{M}\mathrm{e}\mathrm{V}$, fluence $6\ifmmode\times\else\texttimes\fi{}{10}^{17}\text{ }{\mathrm{c}\mathrm{m}}^{\ensuremath{-}2}$) ZnO samples. The Zn vacancies are identified at concentrations of $[{V}_{\mathrm{Z}\mathrm{n}}]\ensuremath{\simeq}2\ifmmode\times\else\texttimes\fi{}{10}^{15}\text{ }{\mathrm{c}\mathrm{m}}^{\ensuremath{-}3}$ in the as-grown material and $[{V}_{\mathrm{Z}\mathrm{n}}]\ensuremath{\simeq}2\ifmmode\times\else\texttimes\fi{}{10}^{16}\text{ }{\mathrm{c}\mathrm{m}}^{\ensuremath{-}3}$ in the irradiated ZnO. These concentrations are in very good agreement with the total acceptor density determined by temperature dependent Hall experiments. Thus, the Zn vacancies are dominant acceptors in both as-grown and irradiated ZnO.