Carrier Trapping by Vacancy-Type Defects in Mg-Implanted GaN Studied Using Monoenergetic Positron Beams

Vacancy-type defects in Mg-implanted GaN are probed using monoenergetic positron beams. Mg⁺ ions are implanted to provide a 500-nm-deep box profile with Mg concentrations, [Mg], of 1 × 10¹⁷–1 × 10¹⁹ cm⁻³ at room temperature. In the as-implanted samples, the major defect species is a complex of a Ga vacancy (V_Ga) and a nitrogen vacancy (V_N). After annealing above 1000 °C, the major defect species is changed to vacancy clusters due to vacancy agglomeration. This agglomeration is suppressed, and the agglomeration onset temperature is decreased with a decreasing [Mg]. For samples with [Mg] ≥ 1 × 10¹⁸ cm⁻³, the trapping rate of positrons by vacancy-type defects decrease after annealing above 1100–1200 °C. This decreases is attributed to the change in the defect charge states from neutral to positive due to a downward shift of the Fermi level. The carrier trapping/detrapping properties of the vacancy-type defects and their time dependences are also revealed.