Europium doping of gallium nitride using a novel ultra-high pressure annealing method was investigated. Ammonothermal gallium nitride substrates (n-type) were used as europium ion implantation targets using beam energy of 490 keV and ion fluences ranging from 1 x 1015 to 1 x 1016 Eu/cm2. The implanted samples were annealed at temperatures between 1473 K and 1753 K in high nitrogen pressure. Europium concentration profiles were analyzed along the [0001] crystallographic direction. The morphology and structural quality of implanted and annealed samples were examined. The "out-diffusion" phenomenon was noted. The presence of optically active EuGa-X defect complexes was suggested based on the analysis of photoluminescence spectra measured at low temperature (20 K). Limitations of diffusion-based europium doping of ammonothermal gallium nitride are discussed.

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