Identification of Ga interstitials in GaAlNP

New dilute nitride Ga1−xAlxNyP1−y alloys grown by gas-source molecular beam epitaxy have been studied by the optical detected magnetic resonance technique. Two paramagnetic defect centers with an effective electron spin S=12 were observed and shown to involve Ga interstitials (denoted as Gai-A and Gai-B), both exhibiting the characteristic hyperfine (HF) structure from the two Ga isotopes. The HF interaction is shown to be nearly isotropic and rather strong, providing evidence for an A1 symmetry of the electron wave function highly localized at the Ga atom. We tentatively attribute Gai-A and Gai-B to the interstitial sites surrounded by group-III and group-(V and III) atoms, respectively.