POSITRON-LIFETIME STUDY ON POROUS SILICON WITH A MONOENERGETIC PULSED POSITRON BEAM

Positron-lifetime measurements have been performed on anodized porous silicon as a function of temperature by using a monoenergetic pulsed positron beam. In the lifetime spectra, a long-lived component, which can be attributed to orthopositronium formed at the surface of pores, has been observed. The intensity and the lifetime of the orthopositronium component were found to be strongly influenced by the sample temperature and the annealing temperature. A dramatic increase in the orthopositronium intensity after annealing at 300-400-degrees-C suggests a reduction of positron traps near the surface due to a microstructural change. A temperature-reversible change of the orthopositronium lifetime after annealing at 400-degrees-C suggests that there exist thermally activated dangling bonds at the pore surface at high temperatures. The present study revealed that positron lifetime is highly sensitive to changes in microstructure and pore surface conditions in porous Si.