Structure-Dependent Vibrational Lifetimes of Hydrogen in Silicon

The lifetimes of the Si-H vibrational stretch modes of the ${\mathrm{H}}_2^{*}$ ( $2062{\mathrm{cm}}^{-1\mathrm{}}$) and $\mathrm{H}V̇V{\mathrm{H}}_{\left(110\right)}$ ( $2072.5{\mathrm{cm}}^{-1\mathrm{}}$) defects in crystalline Si are measured directly by transient bleaching spectroscopy from 10 K to room temperature. The interstitial-type defect ${\mathrm{H}}_2^{*}$ has a lifetime of 4.2 ps at 10 K, whereas the lifetime of the vacancy-type complex $\mathrm{H}V̇V{\mathrm{H}}_{\left(110\right)}$ is 2 orders of magnitude longer, 295 ps. The temperature dependence of the lifetime of ${\mathrm{H}}_2^{*}$ is governed by TA phonons, while $\mathrm{H}V̇V{\mathrm{H}}_{\left(110\right)}$ is governed by LA phonons. This behavior is attributed to the distinctly different local structure of these defects and the accompanying local vibrational modes.