Vacancy-type defects introduced by mechanical polishing in ammonothermal GaN studied by a monoenergetic positron beam

Vacancy-type defects introduced by mechanical polishing in basic ammonothermal GaN and their annealing behavior were studied using a monoenergetic positron beam. The major vacancy-type defect in the sample was identified as a Ga-vacancy (V Ga ) coupled with hydrogen atoms. After mechanical polishing, high-density dislocations and stacking faults were introduced in the subsurface region (<240 nm). In this region, the vacancy-type defects detected by positron annihilation were divacancies (V Ga V N ) and their complexes with hydrogen atoms. After ultra-high-pressure annealing at 1400°C, {0001} basal slip bands were the predominant defects observed using a transmission electron microscope. The major vacancy-type defects for the annealed samples were identified as V Ga coupled with multiple V N [ex V Ga (V N ) 3 ] and their complexes with hydrogen atoms. The observed annealing behavior of vacancies agreed with that estimated using photoluminescence spectroscopy.