Vibrational relaxation pathways in porous silicon: A time-resolved infrared spectroscopic study

We have used a free electron laser to measure the picosecond vibrational dynamics of the SiH, Si H2, and O3 SiH stretching modes in porous silicon. A three beam pump-probe technique has been employed to make temperature dependent measurements of the population relaxation times. We demonstrate that both bending modes and scissors modes play important roles as does the vibrational bath provided by the pore walls themselves. Using a forward box, two beam photon echo technique we have measured the homogeneous dephasing times of all modes which have dynamic linewidths in the range 0.6-1.2 cm-1. The inferred pure dephasing rates are dominated by the elastic scattering of acousticlike Si-Si vibrations. © 2006 The American Physical Society.