Point defect characterization of group-III nitrides by using monoenergetic positron beams

Positron annihilation is a powerful technique for evaluating point defects in semiconductors. Using this technique, one can detect vacancy-type defects in subsurface regions with high-sensitivity. We have used monoenergetic positron beams to probe native vacancies in InxGa1-xN grown on sapphire and GaN substrates by metalorganic vapor phase epitaxy. It was found that vacancy-type defects were introduced with increasing InN composition, and the major defect species was identified as complexes between a cation vacancy and a nitrogen vacancy. The concentration of the defects was found to be suppressed by Mg doping, suggesting that Mg is an excellent suppressor of cation vacancies in InxGa1-xN. The crystal quality of the InxGa1-xN films was greatly improved using the GaN substrate, but point defects, especially vacancy-type defects were found to present in the film.