Computational study of positron annihilation parameters for cation mono-vacancies and vacancy complexes in nitride semiconductor alloys

Dopant activation process in Mg-implanted GaN studied by monoenergetic positron beam

A process for activating Mg and its relationship with vacancy-type defects in Mg-implanted GaN were studied by positron annihilation spectroscopy. Mg⁺ ions were implanted with an energy of 10 keV, and the Mg concentration in the subsurface region (≤ 50 nm) was on the order of 10¹⁹ cm⁻³. After the Mg-implantation, N⁺ ions were implanted to provide a 300-nm-deep box profile with a N concentration of 6 × 10¹⁸ cm⁻³. From capacitance–voltage measurements, the sequential implantation of N was found to enhance the activation of Mg. For N-implanted GaN before annealing, the major defect species were determined to Ga-vacancy related defects such as divacancy. After annealing below 1000 °C, the clustering of vacancies was observed. Above 1200 °C annealing, however, the size of the vacancies started to decrease, which was due to recombinations of vacancy clusters and excess N atoms in the damaged region. The suppression of vacancy clustering by sequential N-implantation in Mg-implanted GaN was attributed to the origin of the enhancement of the Mg activation.

Effects of ultra-high-pressure annealing on characteristics of vacancies in Mg-implanted GaN studied using a monoenergetic positron beam

Vacancy-type defects in Mg-implanted GaN were probed by using a monoenergetic positron beam. Mg ions were implanted into GaN to obtain 0.3-μm-deep box profiles with Mg concentrations of 1 × 10¹⁹ cm⁻³. The major defect species in an as-implanted sample was determined to be Ga-vacancy related defects such as a complex between Ga and N vacancies. The sample was annealed under a nitrogen pressure of 1 GPa in a temperature range of 1000–1480 °C without a protective capping layer. Compared with the results for Mg-implanted GaN annealed with an AlN capping layer, the defect concentration was decreased by the cap-less annealing, suggesting that the surface of the sample was an effective sink for vacancies migrating toward the surface. Depth distributions of Mg after annealing above 1300 °C were influenced by the presence of residual vacancies at this temperature. Hydrogen atoms were unintentionally incorporated into the sample during annealing, and their diffusion properties were also affected by both vacancies and Mg.