Experimentally identified deep levels in type GaN at approximately 0.9–1, 1.4, and 1.8–2 eV above the valence-band maximum have been attributed to Ga vacancies. From the results of first-principles calculations, we find that from both energetic and electronic level structure standpoints it is necessary to consider the structural modification resulting from the transfer of a nearest-neighbor N atom to a Ga-vacancy site to explain the levels at 1 and 2 eV. Isolated N-antisite and nitrogen-vacancy defects are found to give rise to additional deep levels at 1.4 and 0.8 eV, respectively.
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