| This thesis has studied the structures of several new materials and their electronic and optic properties by using the first principles calculation on the basis of density functional theory. The content of this thesis can be divided into two sections:1. In this part, we performed study on the structure properties of bivariate and tribasic oxidizing materials belongs to IV family on the basis of the first principles. Search for oxides of higher dielectric constant is always one of the focuses of semiconductor research, such as the research on transition metal oxides TiO2, ZrO2 and HfO2, respectively. Besides, the isomers of some common oxide might have potential higher dielectric constant. According to a recent report, which point out that a kind of high-density cube poly-silicon with the structure of inversed-Ag2O shows the potential of high dielectric coefficient. In addition, it has well compatibility to the surface of monocrystalline silicon Si (100), suggesting that it is possible to form a kind of free-defect superlattice. It has a good prospect in future appliance. In this work, we introduce the two kinds of elements belongs to IV family, they are Ge and Sn. Utilizing the first principles calculation, the electronic structure and optical properties are compared among the oxides of those two elements and their ternary compounds. The objects of this study include SiO2, GeO2 and SnO2 and Si0.5Ge0.5O2, Si0.5Sn0.5O2 and Ge0.5Sn0.5O2, respectively Firstly, the geometric parameters are optimized from eternal coordinate. Band structure and density of state distribution are calculated hereafter, from which the dielectric coefficients and absorption spectrum functions were derived. By comparing their differences and interrelations, we found that ternary oxide has a higher density and static dielectric constant. As the variation of the ordinal number of elements, the higher the lattice parameters of compounds are, the smaller the bandwidth. Moreover, lattice parameters of Sio.5Geo.5O2 and SiO2 are very close to the surface of Si (100).2. First principles calculations for the structural, electronic and optical properties of the V-doped SiGe2N4 and GeSi2N4 with the cuprite structure are performed by using a plane wave pseudopotential method in the framework of density functional theory. The inter-band materials are promising to improve the conversion efficiency of solar cells by realize broad spectrum absorption of the sunlight. Recently, the study on new inter-band materials, which can meet the requirement of application in solar cells, is one of the hot topic in the scientific community. Attempts both experimentally and theoretically have been made to find the materials that can form the inter-band. It is reported that the inter-band can be formed in the doped chalcopyrite and spinel structured semiconductor materials. In this part, the wide bandgap double cubic spinel nitrides SiGe2N4 and GeSi2N4 are chosen as the hosts. By using transition metal V to replace the Ge and Si atoms located at the octahedral and tetrahedral positions respectively, we obtained four derivatives. By comparing the band structure of these compounds, it can be found that there formed a local band, which locates at the forbidden band of the hosts, made up of the t2g state of the transition metal. This local band can be regarded as the inter-band. In addition, the photoelectric conversion efficiency of these compounds is discussed. By comparing the absorption spectra between the derivatives and the hosts in the range of solar radiation spectrum, the inter-band plays an role in enhancing the absorption. The octahedrally replaced derivatives show enhancement in the VIS and IR region. |
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