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 $V_{\mathrm{Al}}-{\mathrm{O}}_{\mathrm{N}}$ complexes in the concentration range ${10}^{18}$ cm${}^{-3}$ 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 $V_{\mathrm{Al}}$.

• Received 27 June 2011

DOI:https://doi.org/10.1103/PhysRevB.84.081204