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_GaV_N) and their complexes with hydrogen atoms. After ultra-high-pressure annealing at 1400ºC, {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.