ZnO crystals were implanted with N+, O+ and Al+, and co-implanted with O+ N+ and Al+ N+ ions. Positron annihilation measurements indicate introduction of vacancy clusters upon implantation. In the N+-implanted and Al+ N+ co-implanted samples, these vacancy clusters were only partially annealed at 800C, as compared with their entire recovery in the O+- and Al+-implanted samples at 800 to 900C, suggesting a strong interaction between nitrogen and vacancy clusters. However, in the O+ N+ co-implanted sample, most vacancy clusters disappeared at 800C. Oxygen probably scavenged nitrogen to enhance the annealing of the vacancy clusters. Upon further annealing at 1000 to 1100C, nitrogen also formed stable complexes with thermally generated vacancies. These nitrogen-related vacancy complexes required high-temperature annealing at 1200 to 1250C to be fully removed.Interaction of Nitrogen with Vacancy Defects in N+-Implanted ZnO Studied using a Slow Positron Beam. Chen, Z.Q., Maekawa, M., Kawasuso, A., Suzuki, R., Ohdaira, T.: Applied Physics Letters, 2005, 87[9], 091910