Self-interstitial–hydrogen complexes in silicon

The vibrational properties of interstitial silane $({\mathrm{SiH}}_4{)}_i$ and silyl $({\mathrm{SiH}}_3{)}_i$ molecules in crystalline silicon are calculated using a first-principle, cluster-based, spin-polarized local-density method. The Si-H stretch modes are found to be redshifted by $\sim 300\hspace{0.5em}{\mathrm{cm}}^{-1}$ from those of the isolated molecule, which lie around $2200\hspace{0.5em}{\mathrm{cm}}^{-1}$. These results refute recent suggestions that modes observed around $2200\hspace{0.5em}{\mathrm{cm}}^{-1}$, and previously assigned to hydrogenated vacancy defects, are due to these interstitial molecules.