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 1x10(17)-1x10(19)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 degrees 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]1x10(18)cm(-3), the trapping rate of positrons by vacancy-type defects decrease after annealing above 1100-1200 degrees 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.