Crystals were implanted with 20 to 80keV H ions, up to a total dose of 4.4 x 1015/cm2. Positron lifetime and Doppler broadening of annihilation radiation measurements revealed the introduction of Zn vacancy-related defects after implantation. These vacancies were found to be filled with H atoms. After isochronal annealing (200 to 500C), the vacancies agglomerated into H bubbles. Further annealing (600 to 700C) caused the release of H from the bubbles; leaving a large number of micro-voids. These micro-voids annealed out at 1000C. Raman spectroscopy of the implanted sample revealed an enhancement of vibrational modes at about 575/cm; which indicated the introduction of O vacancies. These O vacancies disappeared at 600 to 700C, and this was supposed to contribute to H bubble formation. Cathodoluminescence measurements revealed that H ions also passivated deep level emission centers before their release from the sample, leading to an improvement of the ultra-violet emission.

Microvoid Formation in Hydrogen-Implanted ZnO Probed by a Slow Positron Beam. Chen, Z.Q., Kawasuso, A., Xu, Y., Naramoto, H., Yuan, X.L., Sekiguchi, T., Suzuki, R., Ohdaira, T.: Physical Review B, 2005, 71[11], 115213