Positron Annihilation in Neutron-Irradiatedp-Type Silicon

Abstract

Effects of neutron irradiation and subsequent thermal annealing on positron-lifetime spectra in p-type silicon have been studied. In unirradiated samples, two annihilation rates (4.13 X 10 sec ' with an intensity of 98% and 7.14 )& 10 sec ' with an intensity of 2%) are observed. The annihilation rate of the dominant component becomes smaller upon irradiation. The effect saturates at high integrated neutron flux,~1 X 10" n/cm', and disappears completely upon thermal annealing at 400-500'C. The annealing behavior is dependent on the integrated neutron flux. These results show that some neutron-induced defects act as positron traps at room temperature. Our study also gives evidence that high-order vacancy defects are formed during annealing near 300 C, The mean electron density of the positron-sensitive defects (positron traps) is estimated from the saturation value of the annihilation rate to be about 35%%uo less than that in the perfect crystal. The diffusion coefficient and the mobility of thermalized positrons in silicon are estimated to be about 0.16 cm'/sec and 6.4 cm'/secV, respectively.

Annihilation of Positrons in Electron‐Irradiated Silicon Crystals

“…Cheng and Yeh [2] generated defects by proton bombardment and concluded from lifetime measurements that the electron density in the defects is lowered by 30% with respect to t,he perfect crystal. Irradiation with neutrons led to an increase of the mean lifetime from 241 t,o 307 ps [3]. Brandt …”