Cascade phonon-assisted trapping of positrons by divacancies in n-FZ-Si(P) single crystals irradiated with 15 MeV protons

Abstract

The trapping of positrons by the radiation defects in moderately doped oxygen-lean n-FZ-Si(P) single crystal irradiated with 15 MeV protons has been investigated in a comparative way using the positron lifetime spectroscopy and Hall effect measurements. The experiments were carried out within a wide temperature interval ranging from 25 K -29 K to 300 K. The positron trapping rate for divacancies was reconstructed in the course of many-stage isochronal annealing. The concentration and the charged states of divacancies ( V 2¯ and V 2¯ ¯ ) were estimated. The temperature dependency of the trapping cross section of positrons by the negatively charged divacancies is in a good agreement with the data of calculations based on the assumptions of the cascade phonon-assisted mechanism of exchange of the energy between the positron and acoustic long-wave phonons. Obeying ~ T -3 law, the cross-section of the trapping of positrons by divacancies changes considerably ranging from ~ 1.7×10 −12 cm 2 (66 -100 K) to ~ 2×10 -14 cm 2 ( § 250 K). The characteristic length of trapping of the positron by V 2¯ ¯ divacancy was estimated to be l 0 ( V 2¯ ¯ ) § (3.4 ± 0.2)×10 −8 cm.

Similarity of Atomic Configurations of Thermally Stable Positron-Sensitive Complexes Produced with 0.9-MeV Electrons and 15-MeV Protons in <i>n–</i>FZ<i>–</i>Si:P Crystals

“…Before the annealing and at its earlier stages the average positron lifetime τ av (T) consists of several components due to the positron trapping by different defects. These are, mainly, the Ecenters, divacancies and the vacancy-impurity complexes comprising the atoms of phosphorus [2,7]. The analysis of the multi-component positron lifetime is out of the scope of this paper and will be done elsewhere.…”

“…For the proton-irradiated material this ratio is ~ 0.98 thus indicating the annealing not only of E-centers but divacancies, too. The latter were found to be the positron traps characterized by the positron lifetime τ 2 ~ 289 ps (for more detail see [7]).…”