Vacancy-Type Defects in GaN for Power Devices Probed by Positron Annihilation

Abstract

Native defects and ion-implantation induced defects in GaN were studied by means of positron annihilation. Measurements of Doppler broadening spectra of the annihilation radiation for GaN layers grown on Si substrates showed that optically active vacancy-type defects were formed in the layers. Charge transition of the defects due to electron capture occurred when the layers were irradiated by photons with energy above 2.7 eV. It was found that Ti deposition and subsequent annealing introduced vacancy clusters. We also characterized vacancy-type defects in Mg-implanted GaN. The major defect species of vacancies introduced by Mg-implantation was a complex between Ga-vacancy (VGa) and nitrogen vacancies (VNs). After annealing above 1000C, these defects started to agglomerate, and the major defect species became (VGa)2 coupled with VNs. Through this work, we have demonstrated that positron annihilation spectroscopy is a powerful tool for characterizing vacancy-type defects in GaN for power devices applications.