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

Abstract

The in situ, at-temperature, real-time monitoring ofopen-volume defect formation, migration, coalescence andannealing has long been possible in bulk solids by measuringthe Doppler broadening of annihilation radiation arising from the implantation of energetic positrons from a radioactivesource. However, equivalent measurements on vacancy-typedefects in thin films or within ~102 nm of a solidsurface have not been made, principally because of thedistorting influence on the data of surface annihilations. Thispaper describes the first measurements known to the authors ofin situ, at-temperature annealing studies ofnear-surface open-volume defects, using as an example a siliconsample implanted with 50 keV Si+ ions. The techniqueinvolves the measurement of the fraction of controllable-energy positrons which diffuse back to the surface and there formpositronium. The applicability and limitations of this methodare discussed.