Abstract
A new metastable complex in monocrystalline silicon irradiated at with protons has been studied. Electron paramagnetic resonance (EPR) Si-AA13 ( symmetry) and Si-AA14 ( symmetry) spectra as well as the known Si-A18 spectrum originate from different molecular configurations of the complex. A complete conversion between the metastable configurations is achieved by thermal annealing at K and by prolonged illumination with bandgap light at 77 K ). Deep electron levels of the complex have been established. Preferential stress-induced alignment of the interstitial oxygen at in as-grown samples (before irradiation) as well as the AA13 defect alignment at (after irradiation) have unambiguously indicated that interstitial oxygen is involved in the structure of the centre. A tentative model of the defect is a self-interstitial - oxygen-interstitial complex. A new self-interstitial-related centre (labelled AA12) was also observed after annealing of the oxygen-related metastable complex.