At-temperature annealing of near-surface vacancy-type defects observed by positronium formation spectroscopy

The in situ, at-temperature, real-time monitoring of open-volume defect formation, migration, coalescence and annealing has long been possible in bulk solids by measuring the Doppler broadening of annihilation radiation arising from the implantation of energetic positrons from a radioactive source. However, equivalent measurements on vacancy-type defects in thin films or within ∼ 102 nm of a solid surface have not been made, principally because of the distorting influence on the data of surface annihilations. This paper describes the first measurements known to the authors of in situ, at-temperature annealing studies of near-surface open-volume defects, using as an example a silicon sample implanted with 50 keV Si+ ions. The technique involves the measurement of the fraction of controllable-energy positrons which diffuse back to the surface and there form positronium. The applicability and limitations of this method are discussed. (author)