Positron Probing of Vacancy Volume of Thermally Stable Deep Donors Produced with 15 MeV Protons in n-FZ-Si:P Crystals

Abstract

The free volume of the thermally stable vacancy center in n-FZ-Si:P has been probed by positrons. The defects were produced with 15 MeV protons, and then the irradiated material was subjected to the isochronal annealing. The positron lifetime has been determined over the temperature range ~ 30 K – 300 K; the samples-satellites have been characterized by Hall effect measurements. The microstructure of the center involves, at least, one atom of phosphorus and it manifests itself as a deep donor. The center is singly negatively charged and the cascade phonon-assisted trapping of positron proceeds over the length characteristic of the point defect, l0~3.62 a. u. Obeying ~ T–3law, the positron trapping cross section ranges 3∙10–12cm2(66K) to 2.5∙10–14cm2(266 K). The positron lifetimes ranging from ~240 ps to ~280 ps suggest that the atomic relaxation is directed inward towards the free volume of the deep donor involving, at least, two vacancies.