Defects in electron-irradiated Si studied by positron-lifetime spectroscopy

Abstract

Differently doped and undoped silicon was irradiated with electrons to study the formation of nonequilibrium defects and their annealing behavior. The annealing curves, measured by positron lifetime and also partly by the shape parameters of the Doppler-broadened annihilation line, depend strongly on the doping concentration and the oxygen content. In addition, temperature-dependent positron-lifetime measurements starting at 15 K were performed after low-temperature and room-temperature irradiation with different doses and in different annealing states. Shallow positron traps were detected for all conductivity types of irradiated Si. However, the concentration of shallow traps depends on the crystal-growth procedure. Electron-irradiated Czochralski-grown samples contain a higher number of shallow traps than electron-irradiated floating-zonegrown material. Due to the different concentrations of oxygen in these differently grown Si, we conclude that the oxygen atoms are a part of these traps. A possible candidate is the irradiation-induced A center. Correlated infrared-absorption investigations were carried out to support this interpretation.

Properties of Neutron Doped Multicrystalline Silicon for Solar Cells

“…The E-type defect is a complex (V-P) of a monovacancy and an atom of phosphorus. The theoretically calculated value of the positron lifetime in this type of defect is 270 ps [14] that is very close to our experimental result. Because the trapping rate into divacancies below tm = 700…”

Stability of large vacancy clusters in silicon

“…A recent work about the defect-related positron lifetime in monovacancies gives V 1 ϭ(282Ϯ5) ps and that monovacancies become mobile at 170 K. 4 The temperature range for the dissociation of divacancies has been determined to be around 550 K. This corresponds to the SCC-DFTB result of a divacancy dissociation energy of 1.8 eV. The activation energy for the migration of monovacancies according to an empirical TB result is estimated to be 1.54 eV.…”

“…Vacancy clusters in silicon are detected by electron paramagnetic resonance ͑EPR͒, positron annihilation spectroscopy ͑PAS͒, and other methods not only after damage ͑electron [1][2][3][4] and neutron irradiation [5][6][7] or plastic deformation 8 ͒, but also in as-grown samples. 9 Due to a lack of computational data on structure and stability of vacancy clusters detected in silicon in the 1970's and 1980's, their size has been under discussion for a long time.…”

Modeling the momentum distributions of annihilating electron-positron pairs in solids

“…No experimental Doppler broadening data exists for the monovacancy in Si. Mäkinen et al 46 and Polity et al 47 obtained the positron lifetimes of 273 and 282 ps, respectively, for the monovacancy in Si created by electron irradiation. Taking into account that the calculated bulk lifetime with the LDA lattice constant used ͑208 ps͒ is lower than the experimental ones by Mäkinen et al and Polity et al ͑221 and 218 ps, respectively͒ we conclude that our result for the lifetime is in a good agreement with experiment.…”