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

摘要

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 (～300 ps) was attributed to bulk nanocrystal states similar to those of bulk silicon, while the faster one (～3 ps) was attributed to surface states at grain boundaries, more dominant in the smaller nanocrystals due to their larger surface/volume ratio.