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 ${S1\mathrm{}}_a$ and ${S1\mathrm{}}_b$ belonging to the $S1\mathrm{}$ group of signals. ${S1\mathrm{}}_a$ and ${S1\mathrm{}}_b$ both originate from defects with spin $S=\frac{1}{2}$ and monoclinic-I symmetry. The near-trigonal g tensors and several sets of ${}^{29}\mathrm{Si}$ hyperfine splittings all closely resemble those observed previously for $V{\mathrm{H}}^0,$ the neutral charge state of the monovacancy binding a single hydrogen atom. Analysis of a tiny proton hyperfine splitting of ${S1\mathrm{}}_a$ provides strong evidence that this signal originates from $V_2{\mathrm{H}}^0,$ the neutral charge state of the divacancy binding one hydrogen atom. Parallel studies of the thermal decays of the $V{\mathrm{H}}^0,$ ${S1\mathrm{}}_a,$ and ${S1\mathrm{}}_b$ signals and of infrared-absorption lines associated with Si-H stretch modes indicate that $V{\mathrm{H}}^0$ possesses a stretch mode at $2038.5{\mathrm{cm}}^{\mathrm{-}1},$ whereas modes at 2068.1 and $2073.2{\mathrm{cm}}^{\mathrm{-}1}$ originate from the ${S1\mathrm{}}_a$ and ${S1\mathrm{}}_b$ defects. On the basis of theoretical results, we argue that the $2068.1-{\mathrm{cm}}^{\mathrm{-}1}$ mode arises from $V_2{\mathrm{H}}^0$ (the ${S1\mathrm{}}_a$ defect) whereas the $2073.2-{\mathrm{cm}}^{\mathrm{-}1}$ mode probably belongs to $V_n{\mathrm{H}}^0,$ $n=3\mathrm{}$ and 4 (the ${S1\mathrm{}}_b$ defect).