Effects of 850 °C annealing on near-surface defects in Mg-ion-implanted GaN examined using MOS structures

The effects of annealing at 850 °C on the near-surface defects in Mg-ion-implanted GaN were examined using subsequently formed metal–oxide–semiconductor structures. Here, Mg ions were implanted at 50 keV at a modest dose of 1.5 × 1011 or 1.5 × 1012 cm−2 into n-type GaN so as to not compensate fully for the doping density of 3.8 × 1017 cm−3 to maintain the n-type conduction of GaN for investigating the defect states near the conduction band. In the lower-dose sample, annealing at 850 °C for 30 min was effective in improving the capacitance–voltage (C–V) characteristics compared to those of the as-implanted samples. However, in the higher-dose sample, the improvement in the C–V characteristics was limited by acceptor-type defect states even after annealing at 850 °C for 60 min. Considering the results of the analysis of the interface state density distributions and doping profiles, we found that simple native defects were annealed out at 850 °C, whereas divacancy defects were detected even after annealing at 850 °C for up to 60 min. Nevertheless, the experimental results indicated the possibility that prolonging the annealing at 850 °C or raising the annealing temperature might lead to the elimination of divacancy defects through diffusion toward the GaN surface, where the vacancy defects can be distinguished.