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Vacancy clusters introduced by CF4-based plasma treatment in GaN probed with a monoenergetic positron beam

Vacancy-type defects introduced by CF4-plasma treatment in GaN grown on Si substrates have been studied using a monoenergetic positron beam. By positron annihilation spectroscopy, it was found that vacancies were introduced below the surface (≤30 nm), and this region expanded to a depth of 50 nm after 400 °C annealing. The major species of such defects were identified as vacancy clusters coupled with fluorine. The charge transition between these defects and optically active native defects was studied. The defects introduced by plasma treatment were found to introduce deep levels into the bandgap of GaN and act as nonradiative recombination centers.