Infrared transient grating measurements of the dynamics of hydrogen local mode vibrations in amorphous silicon-germanium

We report on picosecond, time-resolved measurements of the vibrational relaxation and decay pathways of the Si-H and Ge-H stretching modes in hydrogenated amorphous silicon-germanium thin films (a-SiGe: H). It is demonstrated that the decay of both modes has a nonexponential shape, attributable to the local environment of the Si-H and Ge-H bonds. Temperature dependent measurements of the ensemble averaged population decay time < T-1 > are used to demonstrate that the stretch modes relax to Si(Ge)-H bending modes and that the excess energy is dissipated,into a combination of bulk vibrations. The influence of the mixed character Si-Ge bulk vibrations upon the relaxation dynamics is discussed. (c) 2008 American Institute of Physics.