ANOMALOUS TEMPERATURE-DEPENDENCE OF POSITRON TRAPPING DUE TO DIVACANCIES IN SI

The temperature dependence of positron lifetime and trapping rate due to electrically neutral divacancies in Si has been determined for temp eratures from 5.5K to 210K. The charge state of divacancies was verifi ed through the Hall effect, electron spin resonance and infrared absor ption measurements. The positron lifetime at neutral divacancies was 2 80 ps at low temperatures and increased to 295 ps at around 30K. This is explained in terms of the lattice relaxation effect accompanying th e positron trapping. The positron trapping rate due to neutral divacan cies was found to increase upon cooling, to decrease after reaching a maximum at around 30K and to increase again below 10K. The observed te mperature dependences of the trapping rate could not be explained by e xisting models. The temperature dependence was found to be reproduced by the Breit-Wigner formula for resonance phenomena. Possible reasons were discussed.