ZnO single crystals were implanted with He ions of energy of 20 to 100keV. The total implantation dose was 4.4 x 1015/cm2. Doppler broadening of positron annihilation spectra was measured using a slow positron beam to study the implantation-induced defects. The results suggested that after implantation, divacancies or larger vacancy clusters were produced. After annealing below 400C, He impurity begins to occupy the vacancy clusters. Upon further annealing above 400C, the vacancy clusters grew in size. At annealing temperature of above 800C, He atom was released from the vacancy clusters, and the vacancies begin to recover.

Vacancy-Type Defects Induced by He-Implantation in ZnO Studied by a Slow Positron Beam. Chen, Z.Q., Kawasuso, A.: Acta Physica Sinica, 2006, 55[8], 4353-7