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 T1 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.