The effects of implanted nitrogen on microstructural, magnetic, and optical properties of Mn-implanted GaN were studied. N and Mn ions were coimplanted into p-GaN and subsequently annealed at 973-1173 K. Compared with Mn-implanted samples, the Curie temperature and magnetic moment significantly increased. From high-resolution transmission electron microscopy, Mn nitrides such as Mn 6N2.58 and Mn3N2 drastically decreased, and the concentration of N vacancies was reduced by the N implantation. This led to the increase of Mn concentration occupying Ga lattice sites, evident by the shift of Raman mode (E2) at 567 cm-1 to higher energy by about 2.5 cm-1. The photoluminescence peak at 2.92 eV shifted to 2.86 eV and became strong with N implantation, indicating an increase in effective hole concentration increased due to an enhanced activation of Mn impurities in p-GaN. Consequently, the enhancement of ferromagnetic property by coimplantation of Mn and N ions originated from the increase of hole concentration via the increase of Mn concentration in GaN, due to the suppression of production of Mn-N compounds.
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