Nanocrystalline Si: a material constructed by Si quantum dots

Intense blue luminescence with decay lifetimes of 100–500 ps is observed from nanocrystalline silicon thin films at room temperature. The grain size reduction of the silicon crystallites to 3–5 nm leads to the generation of the luminescence. It is demonstrated that the blue emission is due to direct transitions in silicon nanocrystallites which are caused by a quantum confinement effect. The contribution of silicon dioxide to the blue emission is excluded. A model is proposed to understand the enhancement of the direct transitions in silicon nanocrystallites.