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Low-resistivity p-type GaN films, which were obtained by N 2 -ambient thermal annealing or low-energy electron-beam irradiation (LEEBI) treatment, showed a resistivity as high as 1×10 6 Ω·cm after NH 3 -ambient thermal annealing at temperatures above 600°C. In the case of N 2 -ambient thermal annealing at temperatures between room temperature and 1000°C, the low-resistivity p-type GaN films showed no change in resistivity, which was almost constant between 2 Ω·cm and 8 Ω·cm. These results indicate that atomic hydrogen produced by NH 3 dissociation at temperatures above 400°C is related to the hole compensation mechanism. A hydrogenation process whereby acceptor-H neutral complexes are formed in p-type GaN films was proposed. The formation of acceptor-H neutral complexes causes hole compensation, and deep-level and weak blue emissions in photoluminescence.
Nakamura et al. (Fri,) studied this question.