Ultrafast infrared experiments on Si-H vibrations in a-Si:H

Ultrafast infrared experiments in a-Si:H are presented on Si-H vibrations grown by plasma enhanced chemical vapor deposition and hot-wire techniques, in the temperature regime between 10 and 300 K. Non-exponential population decay of the stretching mode is observed, with a mean time constant ranging from 30 to 100 ps. At low temperatures (~15 K) the phase relaxation is limited by the population decay, but speeds up at high temperatures and becomes a single exponential. The phase relaxation depends on the power of the laser. We discuss the results in terms of a model in which the stretching mode is localized and decays into three bending modes and one TA phonon.