S. Komatsuda

Formation energy of oxygen vacancies in ZnO determined by investigating thermal behavior of Al and In impurities

Thermal behavior and interacting nature of 100-ppm Al and ∼100-ppt In impurities doped in zinc oxide (ZnO) were investigated by means of the time-differential perturbed angular correlation method with the 111In(→111Cd) probe. Contrasting interactions between Al and In impurities were observed depending on different atmospheric conditions: (1) in air, Al and In impurities irreversibly associate with each other in the process of their thermal diffusion, but (2) in vacuum, their bound state formed in air dissociates by heat treatment at temperatures higher than 873 K, and this process is enhanced with increasing temperature. Detailed investigation of the thermal behavior of the impurities has revealed that the dissociation reaction is triggered by the formation of oxygen vacancies in the vicinity of the locally associated In-Al structure. A unique method to determine the activation energy of the oxygen-vacancy formation is presented with the estimated experimental value of Ea = 0.72(6) eV.

Nuclear spin relaxation of 111Cd at the A site in spinel oxides, CdFe2O4 and CdIn2O4

Local fields in normal spinel oxides, CdFe2O4 and CdIn2O4, were measured by means of time-differential perturbed angular correlation spectroscopy with the 111In(→111Cd) and 111mCd(→111Cd) probes. The spectra obtained with the different probes show contrastive patterns in spite of the same daughter nuclei: the former shows static perturbations with explicit oscillatory structures, whereas for the latter, the angular correlations become gradually isotropic. The exponential-like relaxation patterns of the spectra observed for the 111mCd(→111Cd) probe suggest that the probes occupying the Cd A site experience time-dependent perturbation causing nuclear spin relaxation.

Thermal behavior of In impurities in ZnO

Thermally activated association and dissociation behaviors of indium impurities in Zinc oxide (ZnO) were observed on an atomic scale by means of time-differential perturbed angular correlation spectroscopy with the radioactive 111In(→111Cd) probe. We found that In impurities associate in the process of thermal diffusion to form nanoscale clusters in the ZnO matrix under thermal treatment in air, and their structures depend on the concentration of In ions introduced. Heat treatment under vacuum, however, causes dissociation of part of the clusters, suggesting that In ions leave the clusters and migrate into the ZnO matrix. Positron annihilation lifetime spectroscopy performed for the In-doped ZnO also suggests that In ions as impurities migrate into the ZnO matrix by thermal diffusion to settle themselves in Zn vacancies. Dependences of thermal behavior of In impurities on their concentration, treatment temperature, and atmospheric condition are discussed based on the results observed by the nuclear spectroscopic techniques.Thermally activated association and dissociation behaviors of indium impurities in Zinc oxide (ZnO) were observed on an atomic scale by means of time-differential perturbed angular correlation spectroscopy with the radioactive 111In(→111Cd) probe. We found that In impurities associate in the process of thermal diffusion to form nanoscale clusters in the ZnO matrix under thermal treatment in air, and their structures depend on the concentration of In ions introduced. Heat treatment under vacuum, however, causes dissociation of part of the clusters, suggesting that In ions leave the clusters and migrate into the ZnO matrix. Positron annihilation lifetime spectroscopy performed for the In-doped ZnO also suggests that In ions as impurities migrate into the ZnO matrix by thermal diffusion to settle themselves in Zn vacancies. Dependences of thermal behavior of In impurities on their concentration, treatment temperature, and atmospheric condition are discussed based on the results observed by the nuclear spectr...