Annealing properties of vacancy-type defects in ion implanted GaN during ultra-high-pressure annealing studied by using a monoenergetic positron beam

Behaviors of vacancy-type defects in ion-implanted GaN were studied by means of positron annihilation. Si or Mg ions were implanted into GaN to obtain 300-nm-deep box profiles of the impurities. The ion-implanted samples were annealed up to 1480°C under a N₂ pressure of 1 GPa (ultra-high-pressure annealing: UHPA). For as-implanted GaN, the major defect species was identified as Ga-vacancy-type defects such as a divacancy (V_GaV_N). After annealing above 1000°C, vacancy clusters, such as (V_GaV_N)₃, were introduced, and they were found to be remained even after 1480°C annealing. For Mg-implanted GaN with [Mg]=10¹⁸ cm^-3, no large change in the depth distribution of Mg was observed before and after annealing at 1400°C. For the sample with [Mg]=10¹⁹ cm^-3, however, Mg diffused into the bulk, which was attributed to the over-doping of Mg and their vacancy-assisted diffusion. The Mg diffusion was suppressed by sequential N-implantation, which was attributed to the reaction between Mg and vacancies under a N-rich condition. Interactions between vacancies, Mg, and H during UHPA were also discussed.