The A center binding a single hydrogen atom in crystalline silicon observed by EPR

Electron paramagnetic resonance measurements on proton- and deuteron-implan ted silicon crystals reveal a new signal from a vacancy-type defect with sp in S = 1/2, which is observable only in oxygen-rich material. The signal is strongly temperature-dependent, displaying monoclinic-l symmetry below 180 K and orthorhombic-l symmetry above 240 K in the proton-implanted samples. Resolved proton-hyperfine splittings show that a single hydrogen atom is l ocated similar to 2.5 Angstrom from the silicon atom carrying the dangling bond. The observed properties, including the change of symmetry, allow an u nambiguous identification of the signal with VOH0, the neutral charge state of the monovacancy-oxygen complex (known as the A center) binding one hydr ogen atom. The hydrogen atom is observed to jump readily between two equiva lent sites in the (1 1 0) mirror plane of the defect. (C) 1999 Elsevier Sci ence B.V. All rights reserved.