We report both temperature and excitation density dependent, four wave mixing measurements on Si-D stretch vibrations in deuterated amorphous silicon thin films. Utilising the infrared output of a free electron laser (FEL), we have made transient grating measurements of the temperature dependent anharmonic decay rate of Si-D stretch vibrations in deuterated amorphous silicon. Unlike Si-H vibrations, it is round that the excited deuterium mode relaxed with a single exponential decay rate into collective modes of the host, bypassing the local bending modes. Vibrational photon echo measurements suggest that phase coherence is lost via elastic phonon scattering with excitation (but not temperature) dependent contributions from non-equilibrium phonons. The degradation of p-i-n solar cells with identical intrinsic absorber layers (to those used for the time domain experiments) under prolonged light soaking treatments show that α-Si:D has a superior resistance to light induced defect creation.
