| We have developed efficient theoretical methods to study nanoscale silicon-based semiconductor materials. The Si surface, delta-doped Si semiconductors and Si clusters are studied by Density Functional Theory with Local Density Approximation (DFT-LDA) with plane-wave, DFT-LDA with Wannier orbitals and GW approximation. First, on the Hydrogen-passivated Si surface, the migration of Si atoms is studied with FHIMD package. The result shows a special migration path along the surface dimer row. And further calculation shows that clustering is a possible mechanism for the interruption of the homoepitaxial growth of Si in low temperatures. Second, a planar Wannier orbital scheme is formulated to study phosphorus delta-doped Si. The delta-doped Si is studied at various high doping densities, ranging 1/1024 ML ∼ 1/4 ML, which is 6.6 x 1011cm-2∼1.7 x 10 14cm-2. Our result on the experimental 1/4ML doping shows that the Fermi level is 100meV below conduction band minimum, and the short range interaction effect is small. Last, an efficient GWA method is developed to study Hydrogen passivated Si clusters. The method, using basic group theory and the symmetry of the clusters, makes the GW study of nanoclusters possible. The study shows that the bright light emitted from 1-nm SiH clusters comes from the two excitations in the Si29 H24 cluster.;In this work, we have successfully studied silicon surface, phosphorus delta-doped silicon, and Hydrogen passivated silicon clusters. To study the systems efficiently, we have developed planar Wannier formula with envelope functions, and GWA formula in symmetrized plane-wave basis. The formulas are successfully applied to the studied materials. Moreover, the methods can be used to study other nano-materials. |
