Abstract: The electronic structure and optical properties of Si_3 and Si_5 nanocrystals with different sizes embedded in SiO_2 have been investigated by first-principles pseudopotential plane-wave method. The results show the bandgap of Si_3 embeded structure is wider than Si_5 embeded structure, with the sizes of silicon nanocrystals embedded in SiO_2 decreasing, while the absorption efficiency of Si_5 embeded structure for visible light is better than Si_3 embeded structure. The first absorption peak of Si_3 embeded structure is at about 3.9 eV and Si_5 embeded structure is at about 4.6 eV. Calculation shows 45.46;, the proportion of the Si atoms of silicon nanocrystals to the molecular number of substrate, is a better structure parameters, which is good for the absorption efficiency of visible light at this ratio.

Key words: The electronic structure and optical properties of Si_3 and Si_5 nanocrystals with different sizes embedded in SiO_2 have been investigated by first-principles pseudopotential plane-wave method. The results show the bandgap of Si_3 embeded structure is wider than Si_5 embeded structure, with the sizes of silicon nanocrystals embedded in SiO_2 decreasing, while the absorption efficiency of Si_5 embeded structure for visible light is better than Si_3 embeded structure. The first absorption peak of Si_3 embeded structure is at about 3.9 eV and Si_5 embeded structure is at about 4.6 eV. Calculation shows 45.46;, the proportion of the Si atoms of silicon nanocrystals to the molecular number of substrate, is a better structure parameters, which is good for the absorption efficiency of visible light at this ratio.