Divacancy-tin complexes in electron-irradiated silicon studied by EPR

n- and p-type float-zone silicon containing 10¹⁸-cm^-3 tin were irradiated with 2 MeV electrons to a dose of 10¹⁸cm^-2 and subsequently examined by electron paramagnetic resonance (EPR). The p-type material yields only the well-known Si-G29 signal due to the tin-vacancy complex SnV⁰, whereas the as-irradiated n-type material in addition displays the Si-G7 signal (V₂^-), DK4, recently assigned to SnV^- in a set of slightly inequivalent configurations, and a new signal DK1, from a defects with $S=1/2$ containing one tin nucleus. DK1, which we assign to (SnV-V)^-, undergoes a reversible triclinic-monoclinic transformation at ≈15K. Annealing at 428 K removes Si-G29 and DK4 and produces a six-fold increase of Si-G7 and DK1, the kinetics indicating that about 50% of SnV is transformed into V₂ and (SnV-V). Annealing at 503 K destroys Si-G7 and DK1, the decay of DK1 being linked to the emergence of two new signals DK2 and DK3 from defects with $S=1/2,$ monoclinic-I symmetry, and two equivalent tin nuclei each, which we identify as (SnV-VSn)^- and (Sn₂V-V)^-. The structures of the tin-divacancy complexes are discussed in terms of modifications imposed on the basic divacancy structure by the larger size and lower ionization potential of the tin atom as compared to silicon. A model is proposed for the migration of (SnV-V) in the lattice at 500 K, indicated by the process (SnV-V)+Sn→(SnV-VSn).