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

Electron paramagnetic resonance measurements on float-zone silicon implanted with protons at similar to 50 K followed by heating to room temperature have revealed two signals S1(a) and S1(b), belonging to the S1 group of signals. S1(a) and S1(b) both originate from defects with spin S = 1/2 and monoclinic-I symmetry. The near-trigonal g tensors and several sets of Si-29 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 S1(a) 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, S1(a), and S1(b) signals and of infrared-absorption lines associated with Si-H stretch modes indicate that VH0 possesses a stretch mode at 2038.5 cm(-1), whereas modes at 2068.1 and 2073.2 cm(-1) originate from the S1(a) and S1(b) defects. On the basis of theoretical results, we argue that the 2068.1-cm(-1) mode arises from V2H0 (the S1(a) defect) whereas the 2073.2-cm(-1) mode probably belongs to VnH0, n = 3 and 4 (the S1(b) defect).