The similarities between amorphous silicon and germanium stretch mode dynamics

We have used a free electron laser to study the vibrational relaxation of the Ge–H symmetric stretching mode in a-Ge:H thin films. The overall dynamics of the Ge–H stretch mode are remarkably similar to those measured for the Si–H stretch mode in a-Si:H. Transient grating measurements of the vibrational population decay exhibits a non-exponential shape due to the involvement of the Ge–H bending modes in the decay processes. Photon echo experiments reveal a temperature dependent pure dephasing rate dominated by elastic scattering of TO-like Ge–Ge vibrations with an excitation dependent component due to non-equilibrium host vibrations.