The off-lattice displacement of electrically active, substitutional B in presence of Si interstitials generated by light ion irradiation has been studied by channeling along the< 100> and< 110> axes. The channeling yield χ of B increases with the ion fluence until it saturates at χ 0.5 suggesting a non-random B displacement. At the saturation B is not electrically active and accurate angular scans indicates the formation of BB couples aligned along the< 100> direction in agreement with first principle calculations. The same kind of defect is formed upon B implantation at room temperature as demonstrated also by angular scans with χ B 0.5. A peculiar behavior is observed upon annealing: at 800 C a significant increase of randomly located B occurs and χ B 1, at higher temperatures B recovers progressively into substitional site. The χ B reaches 0.1 at 950 C and the carrier concentration coincides with the amount of …