Vacancy-type defects in Mg-implanted GaN probed by a monoenergetic positron beam

Positron annihilation is a non-destructive tool for investigating vacancy-type defects in materials. Detectable defects are monovacancies to vacancy clusters, and there is no restriction of sample temperature or conductivity. Using this technique, we studied defects introduced by Mg-implantation in GaN. Mg ions of multiple energies (15-180 keV) were implanted to provide a 200-nm-deep box profile with Mg concentration of 4×10¹⁹ cm^-3. The major defect species of vacancies introduced by Mg-implantation was a complex between Ga-vacancy (V_Ga) and nitrogen vacancies (V_Ns). After annealing above 1000°C, these defects started to agglomerate, and the major defect species became (V_Ga)₂ coupled with V_Ns. The depth distribution of vacancy-type defects agreed well with that of implanted Mg, and no large change in the distribution was observed up to 1300°C annealing.