.ge / Sio <sub> 2 </ Sub> Thin Film Optical And Electrical Properties Of Nano Mosaic Simulation Analysis

The research in this dissertation is based on the density functional theory in first-principle calculation. The software we used is CASTEP module in Materals Studio. The electronic structure, geometric structure and optic properties of Ge, SiO₂ with Ge impurity defect and Ge nanocrystals embedded in SiO₂ were discussed.The electron property,geometric property and optic property of Ge crystal and matrix SiO₂ were calculated and analyzed. The results show that the absorption peak of porous germanium is at about 5.0eV, uitraviolet area. It's visible light absorption is very weak at room temperature. The Ge crystal is indirect gap semiconductor and it's band gap is about 0.677eV. The band gap of SiO₂ is 6.06eV , there is almost no absorption in 0eV⁶.5eV region. The matrix SiO₂ has two absorption peak, which are at about 12.5eV and 16.5eV respectively. The results of Ge and SiO₂ , especially the parameters of opetimized lattice are accord with experiment result. This indicate that the calculation method and parameter of software set is credible to research the photoelectric properties of Ge, Ge-doped SiO₂ and Ge/SiO₂ nano embedded materials.The model of SiO₂ with Ge impurity defect in which one silicon atom is replaced by germanium atom is fabricated and calculated. The proportion of impurity is about 2.08%. The result show that the absorption spectrum of Ge-doped SiO₂ move to red side and the absorption desity is lower than matrix SiO₂ ,but the change is not very remarkable.The refractive index is lower than pure SiO₂ . In this structure, the impurity levels are brought in the band gap of SiO₂ ,but these levels are very near to the condution level. The S orbit of O atoms in Ge-O bond mostly contribute to these impurity level.The properties of germanium nanocrystals Ge3 and Ge5 in different dimensions embedded in SiO₂ were calculated. The band gap of Ge3 and Ge5 embedded structure are 4.1eV and 2.7eV. The results show, the absorption of visible light of Ge3 structure is better than that of Ge5 structure. The intermediate level of Ge3 and Ge5 embedded structure are all at about 3.2eV above Fermi level, which are at about 1.9eV below conduction level. The results indicate that the optic properties of mini Ge nano structure are mostly contingent on the Ge-O bond in the interface of nanocrystals. This may also caused the 2.1eV PL peak observed in experiment.The Si nanocrystals in different dimension embedded in SiO₂ were calculated, the difference between Ge and Si nano structure were discussed. The results show, quantum confinement mostly decide the optic properties of Si nano structure, but in Ge nano structure, the optic properties are not only determined by the effect of quantum confinement, but also by other factors.In conclusion, the optic properties of Ge/SiO₂ mostly decided by the bond of nanocrystals interface than by quantum confinement or disperse impurity Ge atoms.