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

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Journal Title
Journal ISSN
Volume Title
School of Science | A1 Alkuperäisartikkeli tieteellisessä aikakauslehdessä
Date
2007
Major/Subject
Mcode
Degree programme
Language
en
Pages
165207/1-10
Series
Physical Review B, Volume 76, Issue 16
Abstract
We have used positron annihilation spectroscopy to study the introduction and recovery of point defects introduced by 0.45 and 2 MeV electron irradiation at room temperature in n-type GaN. Isochronal annealings were performed up to 1220 K. We observe vacancy defects with specific lifetime of τV=190±15ps that we tentatively identify as N vacancies or related complexes in the neutral charge state in the samples irradiated with 0.45MeV electrons. The N vacancies are produced at a rate Σ0.45N≃0.25 cm exp −1. The irradiation with 2 MeV electrons produces negatively charged Ga vacancies and negative nonopen volume defects (negative ions) originating from the Ga sublattice, at a rate Σ2.0Ga≃5cm exp −1. The irradiation-induced N vacancies anneal out of the samples at around 600 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 K, and this is interpreted as the isolated Ga vacancies becoming mobile with a migration barrier of EV,GaM=1.8±0.1eV. 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 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 800–1100K.
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Keywords
GaN, Ga vacancy, N vacancy, positron annihilation
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Citation
Tuomisto, Filip & Ranki, V. & Look, D. C. & Farlow, G. C. 2007. Introduction and recovery of Ga and N sublattice defects in electron-irradiated GaN. Physical Review B. Volume 76, Issue 16. 165207/1-10. ISSN 1098-0121 (printed). DOI: 10.1103/physrevb.76.165207.