Influence of grain size on ultrafast carrier dynamics in thin nanocrystalline silicon films

The ultrafast carrier dynamics in thin nanocrystalline silicon films (10 and 20 nm thick) on quartz over a broad spectral range using optical pumping at a moderate fluence of 2.5 mJ/cm(2) were studied. The films were composed of randomly oriented silicon nanocrystals of various sizes and shapes. The authors probed a fast and a slow relaxation mechanism. The slow decay (similar to 300 ps) was attributed to bulk nanocrystal states similar to those of bulk silicon, while the faster one (similar to 3 ps) was attributed to surface states at grain boundaries, more dominant in the smaller nanocrystals due to their larger surface/volume ratio. (C) 2007 American Institute of Physics.