Speaker：Prof. Akira Uedono,University of Tsukuba
Time：10：00a.m.Wednesday, May 11
Positron annihilation is a non-destructive tool for investigating vacancy-type defects in materials. Detectable defects are monovacancies to vacancy clusters, and there is no restriction of sample temperature or conductivity. When a positron is implanted into condensed matter, it annihilates with an electron and emits two g quanta. The energy distribution of the g rays is broadened by the momentum component of the annihilating electron-positron pair pL. A freely diffusing positron may be localized in a vacancy-type defect because of Coulomb repulsion from positively charged ion cores. Because the momentum distribution of the electrons in such defects differs from that of electrons in the bulk material, these defects can be detected by measuring the Doppler broadening spectra of the annihilation radiation. In this talk, we report studies of vacancy-type defects in Mg-implanted GaN, GaN grown on Si, and bulk GaN. These studies show that positron annihilation spectroscopy is a useful tool for a study of vacancies in GaN, and could contribute the development of GaN-based devices.
Akira Uedono is a Professor in Division of Applied Physics, Faculty of Pure and Applied Science, University of Tsukuba, Japan. He earned his Ph.D. in material sciences at the Institute of Materials Science, University of Tsukuba. He has been research associate at Yokohama City University and University of Tokyo. His research is mainly focused on defects and atomic scale disorder in solids. His work aims at the development of positron annihilation technique for material characterization and its application for semiconductor technology and other field.