Optically-detected magnetic resonance of spin-paired complexes emitting in the 2.3 eV spectral region in Mg-doped GaN

Optically-detected magnetic resonance (ODMR) experiments on magnesium-doped GaN produced by metal-organic vapor phase epitaxy show a group of strong signals with large linewidths (in excess of 0.15 Tesla) obtained when monitoring photoluminescence in the region between 5000 and 6200 (2.5 eV to 2.0 eV). The signals depend upon the magnesium concentration and are particularly strong in as-grown material. The behavior of the spectrum for different directions of the applied magnetic field and for three well separated microwave frequencies is well described by the spin Hamiltonian for a coupled pair of centers, each with spins of S=1 2. The large ODMR linewidths are ascribed to hyperfine interactions with gallium nuclei, leading to a model in which this broad green-yellow photoluminescence band is due to a recombination process that involves magnesium acceptors closely paired with donor centers which contain interstitial gallium ions. Annealing is presumed to dissociate these pairs and thus to provide an activation process for the magnesium acceptors.