Identification of theVAl-ONdefect complex in AlN single crystals

In this Rapid Communication, we report positron annihilation results on in-grown and proton irradiation-induced vacancies and their decoration in aluminium nitride (AlN) single crystals. By combining positron lifetime and coincidence Doppler measurements with ab initio calculations, we identify in-grown ${V}_{\mathrm{Al}}\ensuremath{-}{\mathrm{O}}_{\mathrm{N}}$ complexes in the concentration range ${10}^{18}$ cm${}^{\ensuremath{-}3}$ as the dominant form of ${V}_{\mathrm{Al}}$ in the AlN single crystals, while isolated ${V}_{\mathrm{Al}}$ were introduced by irradiation. Further, we identify the UV absorption feature at around 360 nm that involves ${V}_{\mathrm{Al}}$.