Optically detected magnetic resonance of epitaxial nitrogen-doped ZnO

Optically detected magnetic resonance (ODMR) experiments on epitaxial nitrogen-doped ZnO show spectra due to (i) a shallow donor with the full wurtzite symmetry, (ii) a previously unobserved spin-$1∕2$ center of axial symmetry whose principal axis is tilted slightly away from the crystal c axis, and (iii) a spin--1 triplet state of orthorhombic symmetry. The spin-$1∕2$ center has a g tensor that is of a different form from that of previously reported ODMR spectra for ZnO and is consistent with a model that contains a zinc interstitial, possibly in association with a nitrogen atom. The g values for the triplet state are the average of those for a shallow donor and the spin-$1∕2$ center, and the spectrum is thus assigned to a pair of such centers strongly coupled by a spin-exchange interaction.