Optical Properties of Ge and Si Embedded Structure from Ab Initio Calculation

To investigate the relation between optical property and size of the nano structure, the band structures, density of states, and optical properties of series nano structures embedded in SiO₂ were calculated using the density functional theory-plane waves(DFT-PW) of first-principles method. The results show, the intermediate levels of Ge and Si nanostructure are at about 3.3 eV and 4.3 eV above Fermi level respectively, with the dimension of nanocrystal embedded in SiO₂ increasing, the absorption edge firstly move to the red side, then move to the blue side. It is indicate that the visible luminescence of nanometer-sized Si and Ge structures mostly come from the defect of its interface, the minimum size of Ge and Si nanocrystal embedded in SiO₂ that can use quantum-confined model does exist. These conclusions provide proof of improving optical properties of materials and researching luminescence mechanism deeply.