Formation and electronic states of Si nanocrystallites in amorphous Si

Si nanocrystallites formed in amorphous Si matrix emit intense blue luminescence at room temperature. A grain size reduction of Si crystallites to 3-5 nm leads to generating the luminescence. It is demonstrated that the blue luminescence from Si nanocrystallites exhibits distinct features of no intensity degradation and very fast decay lifetime (approx. 170 ps). Direct transitions in Si nanocrystallites are concluded to be the origin of the blue light emission. Furthermore, theoretical calculations of order (nanocrystalline Si phase) and disorder (amorphous Si phase) quantum dots system indicates that resonant states are generated in the nanocrystalline Si phase. The direct transitions between the resonant states should be enhanced by a modification of k-selection rules due to an interaction of the finite size crystalline region with the amorphous region, which result in the blue light emission in the nanocrystalline Si sample.