A study was made of the evolution of lattice defects in single-crystal ZnO bombarded with 60keV 28Si and 300keV 197Au ions at 77 and 300K. To characterize ion-beam-produced structural defects, a combination of Rutherford back-scattering/channeling spectrometry, cross-sectional transmission electron microscopy, X-ray photoelectron spectroscopy, and atomic force microscopy was used. Results showed that ZnO exhibited strong dynamic annealing, and even high-dose bombardment with heavy (197Au) ions at 77K does not render ZnO amorphous. However, a crystalline-to-amorphous phase transition could be induced by irradiation with relatively light 28Si ions. In this latter case, amorphization was attributed to strong chemical effects of Si atoms implanted into the ZnO lattice, resulting in the stabilization of an amorphous phase. High-dose heavy-ion bombardment also results in a strong stoichiometric imbalance (loss of O) in the near-surface region. A variation in irradiation temperature from 77 to 300K had a minor effect on the damage buildup behavior in ZnO bombarded with Au ions. Data analysis also showed that a variation in the density of collision cascades by increasing ion mass from 28Si up to 197Au had a negligible effect on the damage buildup behavior. For both light- (28Si) and heavy- (197Au) ion bombardment regimes, cross-sectional transmission electron microscopy reveals that ion irradiation produced energetically favorable planar defects which were parallel to the basal plane of the wurtzite structure of ZnO. The Rutherford back-scattering/channeling study also revealed the formation of a middle defect peak between the surface and bulk peaks of disorder in Au-implanted ZnO, but not in Si-bombarded samples. The formation of this middle peak, most likely to be related to complex defect agglomeration processes, was rather unexpected and had apparently not been observed in any other material. Physical mechanisms of defect formation in ZnO under ion bombardment were proposed based on these experimental findings.

Ion-Beam-Produced Structural Defects in ZnO. S.O.Kucheyev, J.S.Williams, C.Jagadish, J.Zou, C.Evans, A.J.Nelson, A.V.Hamza: Physical Review B, 2003, 67[9], 094115 (11pp)