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

Electron paramagnetic resonance measurements on proton- and deuteron-implanted silicon crystals reveal a new signal from a vacancy-type defect with spin 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 located similar to 2.5 Angstrom from the silicon atom carrying the dangling bond. The observed properties, including the change of symmetry, allow an unambiguous identification of the signal with VOH0, the neutral charge state of the monovacancy-oxygen complex (known as the A center) binding one hydrogen atom. The hydrogen atom is observed to jump readily between two equivalent sites in the (1 1 0) mirror plane of the defect. (C) 1999 Elsevier Science B.V. All rights reserved.