Engineering and spectroscopic characterization of defect centers in gallium nitride for quantum photonics

We report a reproducible strategy for engineering localized deep-level defect centers in free-standing gallium nitride (GaN) using magnesium-ion implantation followed by thermal annealing under nitrogen overpressure. Systematic optimization of processing conditions produces a distinct zero-phonon line (ZPL) at accompanied by well-resolved phonon replicas, with a Huang-Rhys factor of characteristic of a strongly localized defect center. Temperature-dependent photoluminescence reveals a second optical transition at that becomes thermally activated above . The energy separation and comparable linewidths of the two emissions are consistent with a thermally populated split excited-state manifold within a single defect center rather than spatially co-located independent emitters. Their distinct phonon-coupling behavior further indicate different dynamic interactions between the excited-state sublevels and the host lattice. These observations demonstrate that magnesium implantation and high-temperature annealing offer a promising route for engineering optical centers emitting near 698 nm in GaN for potential quantum photonic applications.