H interacting with intrinsic defects in Si

The Si-H stretch modes of vacancy-hydrogen complexes are studied by infrared absorption spectroscopy, uniaxial stress measurements, and ab initio theory. Hydrogen and/or deuterium is introduced by ion implantation which facilitates studies of isotopic shifts. The Si-H mode at 2222 cm⁻¹ is identified as the T₂ mode of the fully saturated vacancy (VH₄). Modes at 2166 and 2191 cm⁻¹ are ascribed to VH₃ and modes at 2121 and 2144 cm⁻¹ to VH₂. Another mode at 2068 cm⁻¹ is tentatively assigned to VH⁰ and two modes at 1987 and 1990 cm⁻¹ are tentatively ascribed to a ⟨100⟩-split interstitial saturated by two hydrogen. The calculations show that all these complexes are stable and the calculated quasi-harmonic frequencies reproduce the trend in the observed frequencies, although the theoretical values are about 5% too high. The influence of anharmonicity upon these frequencies is also briefly discussed.