Electronic structure of the (111) ideal and relaxed surface of silicon by the chemical pseudopotential method

The electronic energy structure for the (111)ideal and relaxed surfaces of silicon is calculated by the chemical pseudopotential method. We use a minimal basis set of localized orbitals and an atomic-like crystal potential to compute the interaction parameters and include self-consistency. Results are compared with other more involved theoretical calculations with satisfactory agreement.     

Electronic structure of the isolated vacancy in silicon

The many-electron molecular orbital method predicts a ground state for the various charged vacancy centres in silicon which has a spin multiplicity in agreement with the electron spin resonance results. Symmetric relaxation and Jahn-Teller contributions have been included in first order. The quantitative features of the model are very different to those implied by the one-electron model.     

Electronic structure of the ideal silicon vacancy by the muffin-tin green's function method

The muffin-tin Green's function method is applied to the ideal vacancy in silicon in the extended-charge single site approximation. The characteristics of the partially occupied gap state are found to be strongly dependent on the extent of the charge perturbation outside of the vacancy muffin-tin.     

Electronic states of silicon in Ni-silicides by nuclear magnetic resonance

Spin-lattice relaxation time (T₁) of ²⁹Si nuclei in several Ni-silicides (Ni_1?xSi_x:0.25?x?0.67) were studied at low temperature (1.4?T?4.2 K) by spin-echo technique. The relation of T₁T = const. and also very short T₁ were observed indicating that the silicides studied were metallic with enough densities of state of 3s-electrons at the Fermi energy (E_F). Another feature of the results was that T₁ decreased with the increment of silicon concentration. This effect was discussed in connection with the soft X-ray spectroscopy (SXS) data on Ni-silicides and Ni—Al compounds.     

An open-shell method for neutral vacancy in silicon and diamond

The restricted Hartree-Fock-Roothaan method with closed and open electronic shells projected by electron density matrices and the quasi-molecular large-unit-cell (LUC) model have been applied to calculate the electronic structure of monovacancy and semivacancy in the neutral charge state in the totally symmetric atomic configuration with relaxation and symmetry-lowering distortions. The difference in the energies of states with total spins of 1 and 3/2 for a neutral monovacancy is determined within the ΔSCF approximation.     

The silicon vacancy in SiC

The isolated silicon vacancy is one of the basic intrinsic defects in SiC. We present new experimental data as well as new calculations on the silicon vacancy defect levels and a new model that explains the optical transitions and the magnetic resonance signals observed as occurring in the singly negative charge state of the silicon vacancy in 4H and 6H SiC.     

Electronic states and shapes of silicon quantum dots

A curviform surface breaks the symmetrical shape of silicon quantum dots on which some bonds can produce localized electronic states in the bandgap. The calculation results show that the bonding energy and electronic states of silicon quantum dots are different on various curved surfaces, for example, a Si-O-Si bridge bond on curved surface provides localized levels in bandgap and its bonding energy is shallower than that on the facet. The red-shifting ofthe photoluminescence spectrum on smaller silicon quantum dots can be explained by the curved surface effect. Experiments demonstrate that silicon quantum dots are activated for emission due to the localized levels provided by the curved surface effect.     

Growth of precursors in silicon using pseudopotential calculations

Based on the results of pseudopotential calculations, the progression of a single interstitial into small compact clusters and ultimately into chain-like defects is examined. For clusters that consist of more than eight interstitials, the capture of bond-centered interstitials reveals a change in the growth mechanism leading to enhanced stability of clusters. The five-interstitial model is proposed to be a plausible candidate for optically active W centers, observed in ion irradiated silicon.     

Electronic properties of MgIn2S4 and CdIn2S4 by the self-consistent pseudopotential method

Summary The electronic properties of CdIn₂S₄ and MgIn₂S₄ are studied in the self-consistent local-density pseudopotential scheme based on hard-core atomic potentials. Our self-consistent calculation confirms the assumptions of previous empirical studies and provides for the lowestenergy gap values which agree with experimental data. The electron charge densities indicate that both sulphospinels are highly ionic. The two compounds have similar ground-state properties but different conduction bands. Paper presented at the ?V International Conference on Ternary and Multinary Compounds?, held in Cagliari, September 14–16, 1982.     

Charge states of the sulphur vacancy in ZnS

We study the various charge states of the undistorted sulphur vacancy in cubic ZnS crystals in the tight-binding approximation. Using Slater transition state theory, we obtain its various excitation energies which are in good agreement with correlated EPR and optical experimental results.     

Evidence for vacancy percolation in highly-doped silicon

The extreme dopant diffusivities observed in silicon for donor concentrations in excess of 2×10²⁰cm^–3 have recently been explained by a vacancy percolation model proposing that a network of fast diffusion paths is formed when the average distance of the donors becomes equal to or less than the fifth nearest-neighbour distance. Here, we report on evidence by means of¹¹⁹Sn Mössbauer spectroscopy for the postulated high vacancy concentration in the percolation cluster.     

Radiation enhanced silicon self-diffusion and the silicon vacancy at high temperatures

We report proton radiation enhanced self-diffusion (RESD) studies on Si-isotope heterostructures. Self-diffusion experiments under irradiation were performed at temperatures between 780 degrees C and 872 degrees C for various times and proton fluxes. Detailed modeling of RESD provides direct evidence that vacancies at high temperatures diffuse with a migration enthalpy of H(m)(V)=(1.8+/-0.5) eV significantly more slowly than expected from their diffusion at low temperatures, which is described by H(m)(V)<0.5 eV. We conclude that this diffusion behavior is a consequence of the microscopic configuration of the vacancy whose entropy and enthalpy of migration increase with increasing temperature.     

An ab initio analysis of electronic states associated with a silicon vacancy in cubic symmetry

The electronic orbitals localized in the vicinity of a vacancy in a silicon crystal are calculated by an ab initio method based on the density functional theory and analyzed in association with the elastic softening observed by the recent ultrasonic experiments, especially focused on an estimate of the electric quadrupole moments. The localized orbitals due to the existence of a vacancy show largely extended properties and the quadrupole moments calculated from the orbitals indicate the strong dependence on cell sizes up to 511 atoms in the basic cell. Asymptotic values of the quadrupole moments in the limit of large size are obtained by an extrapolating method. It is shown that the quadrupole moments are enhanced due to the extension of the orbitals and the ratio of the quadrupole moments of Γ₅ and Γ₃ symmetries agrees well with the value deduced from the experimental results.     

Supercell calculation on the ideal silicon single vacancy

Supercell calculations on a Si diamond lattice with 16, 54 and 128 sites containing one ideal vacancy are performed using a semi-ab-initio method. The electronic density of defect states shows an approximate linear relationship to the size of the supercell. Extrapolation of the result indicates that for a supercell of about 222 sites, the defect interaction between the adjacent cells will be negligible and the T₂ defect state is estimated to be at about 0.85 eV above the valence band edge.     

Localized states in the presence of a phosphorus vacancy in GaP

Pseudopotential calculations are reported concerning defect states introduced into the forbidden gap of GaP by an isolated phosphorus vacancy. Localized states are found with energies in the lower part of the gap. Approximate analytic wave functions belonging to these states are also presented.