Vacancy‐Type Defects and Their Trapping/Detrapping of Charge Carriers in Ion‐Implanted GaN Studied by Positron Annihilation

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Annealing behaviors of vacancy‐type defects in ion‐implanted GaN are studied by positron annihilation. Mg+ and N+ ions are implanted to obtain 700 nm deep box profiles with Mg and N concentrations of 1 × 1018 cm−3, and the samples are annealed using an ultrahigh‐pressure annealing system. For as‐implanted samples, the major defect species is identified as Ga‐vacancy (VGa)‐type defects. For N‐implanted GaN, the size of the vacancies increases as the annealing temperature increases up to 1100 °C and then shrank above 1200 °C. This behavior is attributed to recombinations between N‐vacancy (VN)‐type defects and excess N. For Mg‐implanted GaN, the major defect species after annealing above 1000 °C is vacancy clusters such as (VGaVN)3. Some of them act as nonradiative recombination centers for blue and ultraviolet luminescence. Their energy levels corresponding to the transition from positive to neutral are located between 2.6 eV above the valence band maximum and the conduction band minimum. The thermal activation process of electron detrapping from the vacancy clusters is also studied. For Mg‐implanted GaN, one of the major secondary defects is collapsed vacancy disks forming dislocation loops. They are eliminated by additional N implantation, which is associated with vacancy agglomerations under the annealing in VGa‐rich condition.