Optically detected magnetic-resonance experiments on as-grown magnesium-doped GaN produced by metal-organic vapor phase epitaxy reveal the presence of a triplet state spectrum with a zero-field splitting that corresponds to a pair of centers, each with a spin of 1/2, strongly coupled by an exchange interaction and separated in the direction of the c axis by 0.26 nm. The spectra show no resolved hyperfine structure, suggesting that the centers involve elements with zero nuclear spin. The separation of 0.26 nm corresponds to the distance between two octahedral interstitial sites, suggesting that the spectrum is due to an interstitial-interstitial pair, possibly involving magnesium and oxygen.
Davies, J., Aliev, G. N., Bingham, S. J., Wolverson, D., Stepanov, S., Yavich, B., & Wang, W. N. (2003). Optically detected magnetic resonance of paired defects in as-grown magnesium-doped GaN. Physical Review B, 67(3), . https://doi.org/10.1103/PhysRevB.67.035203