Point defects in group-III nitride semiconductors studied by positron annihilation

Positron annihilation is an established technique for investigating vacancy-type defects in semiconductors. When a positron is implanted into solids, it annihilates with an electron and emits two 511 keV γ quanta. From measurements of Doppler broadening spectra of the annihilation radiation and the positron lifetimes, one can detect vacancy-type defects such as monovacancies and divacancies. We used monoenergetic positron beams to study vacancies in ion-implanted and rare-earth-doped GaN. We identified the defect species and estimated their concentrations from a comparison between the Doppler broadening spectra obtained through the experiments and those calculated using first-principles calculation (projector augmented-wave method). We have thus shown that positron annihilation is a useful tool for studying relationships between vacancy-type defects and properties of group-III nitrides.