Vacancies and electron trapping centers in acidic ammonothermal GaN probed by a monoenergetic positron beam

•Vacancy-type defects in ammonothermal GaN were studied by positron annihilation.•The defect species was identified as a Ga-vacancy coupled with impurities.•Electron trapping centers were studied by positron annihilation with illumination.

Defects in ammonothermal GaN have been studied using a monoenergetic positron beam. Through measurements of Doppler broadening spectra of the annihilation radiation, the major defect species was identified as a Ga vacancy coupled with impurities such as oxygen and/or hydrogen. Those defects were found to be stable even after annealing at 1000 °C. The shape parameter S for the Doppler broadening spectrum corresponding to positron annihilation at the surface was found to be decreased by illumination within energy ranges of 1.5–2.6 eV and 3.2–3.6 eV. This phenomenon is attributed to the suppression of recombinations between holes and electrons due to trapping centers, which can hold electrons for a long time, and a resultant accumulation of holes at the surface. Recovery of the S value required almost one day, but it was shortened by the annealing at 1000 °C.