Characterization of Vacancy-Type Defects in Mg- and N-Implanted GaN by Using a Monoenergetic Positron Beam

Annealing behaviors of vacancy-type defects in Mg and N-implanted GaN were studied by positron annihilation. The major defect species in as-implanted samples was identified as Ga-vacancy (VGa)-type defects. For Mg-implanted GaN with sequential N-implantation after annealing above 1000°C, the defect species were vacancy clusters such as (VGaVN)3. Due to the downward shift of the Fermi level position resulting from a partial activation of Mg, the charge states of defects tended to become positive. For N-implanted GaN, the size of the vacancy clusters started to decrease above 1200°C annealing, which was attributed to recombinations between N-vacancies coupled with VGas and excess N atoms. The impact of sequential N-implantations on vacancies in Mg-implanted GaN was studied, and its effect was most effective when the ratio of the concentration of N to that of Mg was three.