Electron paramagnetic resonance of new defects in heavily phosphorus-doped silicon after electron irradiation

Seven new EPR spectra are reported for heavily phosphorus-doped silicon (7 x 1017 phosphorus atoms/cm3) irradiated at room temperature with 1.5 MeV electrons. Three of these spectra show a hyperfine structure which reveals the formation of defect complexes with electron spin S = 1/2 in which two atoms with nuclear spin I = 1/2 and 100% isotopic abundance are involved. They are identified as two-phosphorus defect complexes. One of them is tentatively ascribed to the phosphorus-vacancy-phosphorus complex in its positive charge state. Simple LCAO calculations on this model are in agreement with the observed hyperfine interactions. Another spectrum appears to arise from two next-nearest phosphorus neighbours and may be described in terms of a He+ or H+2-like effective-mass approximation. The formation by electron irradiation at room temperature of two-phosphorus centres, at a rate higher than can be accounted for by a random distribution of phosphorus, is explained in terms of the slow diffusion of phosphorus-vacancy pairs (E-centres) during irradiation at 600C and their subsequent trapping by other phosphorus centres. For this process an ionization-enhanced mechanism is essential. Calculations of the diffusion process, based on results of a computer simulation, agree with the observed production rate. (author)