Electron paramagnetic resonance study of hydrogen-vacancy defects in crystalline silicon

Electron paramagnetic resonance measurements on float-zone silicon implanted with protons at {~}50 K followed by heating to room temperature have revealed two signals S1ₐ and S1b belonging to the $S1$ group of signals. S1ₐ and S1b both originate from defects with spin S=1/2 and monoclinic-I symmetry. The near-trigonal g tensors and several sets of ²⁹Si hyperfine splittings all closely resemble those observed previously for VH⁰, the neutral charge state of the monovacancy binding a single hydrogen atom. Analysis of a tiny proton hyperfine splitting of S1ₐ provides strong evidence that this signal originates from V₂H⁰, the neutral charge state of the divacancy binding one hydrogen atom. Parallel studies of the thermal decays of the VH⁰, S1ₐ, and S1b signals and of infrared-absorption lines associated with Si-H stretch modes indicate that VH⁰ possesses a stretch mode at 2038.5cm^-1, whereas modes at 2068.1 and 2073.2cm^-1 originate from the S1ₐ and S1b defects. On the basis of theoretical results, we argue that the 2068.1-cm^-1 mode arises from V₂H⁰ (the S1ₐ defect) whereas the 2073.2-cm^-1 mode probably belongs to VₙH⁰, $n=3$ and 4 (the S1b defect).