Infrared four-wave mixing experiments performed upon deuterated amorphous silicon layers ($a\mathrm{\text{−}}\mathrm{S}\mathrm{i}:\mathrm{D}$) reveal profound differences in the dynamics of Si-D stretch vibrations compared to those of analogous Si-H vibrational modes in hydrogenated amorphous silicon ($a\mathrm{\text{−}}\mathrm{S}\mathrm{i}:\mathrm{H}$). Remarkably, transient-grating measurements of the population decay rate of the Si-D vibrations show single-exponential decay directly into collective modes of the $a\mathrm{\text{−}}\mathrm{S}\mathrm{i}$ host, bypassing the local bending modes of the defect into which the Si-H vibrations decay. Photon-echo measurements of the vibrational dephasing suggest at low temperature contributions from TO nonequilibrium phonons and at elevated temperatures elastic phonon scattering of TA phonons.

• Received 7 March 2002

DOI:https://doi.org/10.1103/PhysRevLett.89.125504