Dynamics of vibrations in a mixed amorphous-nanocrystalline Si system - art. no. 045203

We present results of pulsed Raman and phonon-induced luminescence experime nts on a mixed amorphous-nanocrystalline silicon system (a-nc-Si:H). With t hese experiments, the decay and transport of nonequilibrium phonons in a-nc -Si:H was examined and compared with the behavior of phonons of the same fr equencies in a-Si:H and c-Si. From the Raman measurements. we find that in the spectral region of the TO vibrations in the crystallites (505-520 cm(-1 )), phonons have shorter decay times than the TO phonons in a-Si:H, but lon ger than in c-Si. In addition. the lifetimes increase with decreasing frequ ency, from less than 10 ns at 515 cm(-1) to similar to 30 ns at 505 cm(-1). We further show that phonons with a frequency of similar to 150 cm(-1) in a-nc-Si:H have longer lifetimes than in a-Si:H (tau <10 ns). Finally, the d iffusion of 29-cm(-1) phonons through the a-nc-Si:H and a-Si:H material was examined in phonon-induced luminescence experiments. Transport through the a-nc-Si:H film appears to be much slower than through the a-Si:H layer. We explain these results as effects of phonon confinement. and relate them to the extremely long phonon lifetimes found in Raman experiments on a-Si(:H) .