SiH stretch modes of hydrogen — vacancy defects in silicon

The SiH stretch modes in proton-implanted crystalline silicon have been studied by FTIR spectroscopy. From the annealing behaviour and dose dependence of the stretch-mode intensities, it is found that one complex gives rise to modes at 2121 and 2144 cm−1, a second to modes at 2166 and 2191 cm−1, and a third to a single mode at 2222 cm−1. The isotope shifts of these centres have been obtained from measurements on samples implanted with protons and deuterons. Moreover, the symmetries of the centres have been determined from uniaxial stress measurements. We assign the 2121 and 2144 cm−1 modes to VH2, the 2166 and 2191 cm−1 modes to VH3, and the 2222 cm−1 mode to VH4. Another mode at 2068 cm−1 is tentatively ascribed to VH. The SiH and SiD stretch modes of VHnDm (n + m ≤ 4) have been calculated with a simple model which has been used to fit all the experimental frequencies. The agreement between fitted and observed frequcies is excellent.