Infrared studies of the rotational motion of interstitial hydrogen and the vibrational lifetimes of hydrogen-decorated lattice defects in silicon

This dissertation describes new studies of interstitial H₂ in Si by vibrational spectroscopy and uniaxial stress methods. A new vibrational line for the HD molecule in Si was observed at elevated temperature (T > 20K). The interpretation of this new line leads to the conclusion that the H ₂ molecule is a nearly free rotor. The 3618.4 and 2642.6 cm−1 lines that are seen in Si that contains H and D, are assigned to interstitial ortho-H₂ and para-D₂. This conclusion was confirmed by uniaxial stress experiments performed for H₂ and D ₂ in Si. The small isotope dependence of the stress induced line splittings is also explained naturally by our model for interstitial H₂. Furthermore, our results also provide a new explanation for the behavior of complexes with the H₂, HD, or D₂ molecules bound to interstitial oxygen in Si.; In another project, the lifetimes of the vibrational modes of H- and D-decorated lattice defects were studied by measuring the vibrational line widths using high-resolution spectroscopy. The experimental results provide lower limits for the vibrational lifetimes of Si-H and Si-D stretching modes for several defects with different structures. The lifetimes are found to be strongly dependent on the defect structure. A comparison of the lifetimes of corresponding D- and H-decorated lattice defects shows that the lifetime of a D-containing defect is typically longer than that of the corresponding H-containing defect, contrary to conventional wisdom, but also that interesting exceptions to this rule are possible.