Electronic properties of silicon with ultrasmall germanium clusters

The electronic states of silicon with a periodic array of spherical germanium clusters are studied within the pseudopotential approach. The effects of quantum confinement in the energies and wave functions of the localized cluster states are analyzed. It is demonstrated that clusters up to 2.4 nm in size produce one localized s state whose energy monotonically shifts deep into the silicon band gap as the cluster size increases. The wave function of the cluster level corresponds to the single-valley approximation of the effective-mass method. In the approximation of an abruptly discontinuous potential at the heterointerface, the quantities calculated using the effective-mass method for clusters containing more than 200 Ge atoms are close to those obtained by the pseudopotential method. For smaller clusters, it is necessary to take into account the smooth potential at the interface.     

Ellipsometric study of tellurium implanted silicon

Abstract

Ellipsometric parameters as a function of the dose (D = 2.10¹³ ? 2.10¹⁵ ions cm^?2) and annealing temperature have been measured on the silicon implanted with 30 keV Te ions. Obtained information on lattice disorder are to a great extent comparable with those of other methods, e.g. backscattering technique. Moreover optical constants of a damage surface layer may be estimated.     

Effect of tellurium on electrical and structural properties of sintered silicon nitride ceramics

The effects of tellurium (Te) additives on electrical conductivity, dielectric constant and structural properties of sintered silicon nitride ceramics have been studied. Different amounts of Te (10% and 20%) were added as sintering additives to silicon nitride ceramic powders and sintering was performed. Microstructure and composition were investigated by scanning electron microscopy (SEM) and X-ray diffraction (XRD). The electrical conductivity and dielectric constant (ε′) increase exponentially with temperature greater than 800 K. The electrical conductivity and dielectric constant increase but activation energy decreases from 0.72 to 0.33 eV with the increase of Te concentration. However, the conductivity increases five orders of magnitude at the concentration of 10% of Te in Si₃N₄. As the Te concentration increases the sintered silicon nitride ceramics become denser. These types of samples can be used as high temperature semiconducting materials.     

Diffusion of selenium and tellurium in silicon

Diffusion of selenium and tellurium in silicon has been investigated in the temperature range 1000°C to 1310°C by sheet conductivity. For SiSeD ₀= 0.3±0.1 cm²/s andh=2.6±0.1 eV, and for SiTeD ₀=0.9±0.3 cm²/s and h=3.3±0.1eV have been obtained. The surface concentrations for both dopants were of the order of 5 × 10¹³ to 6×10¹⁶cm^–3. The Hall coefficient leads to an energy level of 300±15meV for selenium and 200±20meV for tellurium.     

Electronic and optical properties of single-layered silicon sheets

The electronic and optical properties of a number of single-layered silicon sheets are investigated using density functional calculations. The energy bands of silicon sheets are found to possess direct gaps and thus facilitate the material’s potential applications in optoelectronics. Bridging one-dimensional silicon chains and three-dimensional bulk silicon, two-dimensional single-layered silicon sheets present unique dimension and orientation dependencies of band structures and imaginary dielectric functions, which offer tunable band gaps and peaks in the dielectric functions associated with symmetry breaking and quantum confinement. Our study is expected to facilitate the understanding of general low-dimensional materials and their applications.     

Electronic properties of epitaxial 6H silicon carbide

The electrical conductivity and Hall coefficient were measured in the temperature range from 78 to 900 K for n-type epitaxially grown 6H silicon carbide. A many-valley model of the conduction band was used in the analysis of electron concentration as a function of temperature. From this analysis, the density of states mass to the free electron mass ratio per ellipsoid was calculated to be 0.45. It was estimated that the constant energy surface of the conduction band consists of three ellipsoids. The ionization energy of the shallowest nitrogen donor was found to be 105 meV, when the valley-orbit interaction was taken into account. The electron scattering mechanisms in the epitaxial layers were analyzed and it was shown that the dominant mechanism limiting electron mobility at high temperatures is inter-valley scattering and at low temperatures (200 K), impurity and space charge scattering. A value of $\text{360}\text{cm}{}^2\text{V}$ sec was calculated for the maximum room temperature Hall mobility expected for electrons in pure 6H SiC. The effect of epitaxial growth temperature on room temperature Hall mobility was also investigated.     

Electronic properties of epitaxial 6H silicon carbide

Two comments are made concerning a paper published by Wessels and Gatos with the above title. The first is to assert that weak-field Hall coefficient measurements are more useful in distinguishing singlevalley from multivalley models in a hexagonal crystal than is suggested in the earlier paper. The second is to point out that the mass value which Wessels and Gatos extracted from an analysis of their Hall data as a function of temperature is the total density-of-states effective mass, not the per valley value, as they claimed. Hence the combination of their result and other data does not provide any information concerning the number of valleys in the conduction band of 6H hexagonal SiC.     

ENDOR investigation of tellurium doped GaP

The hyperfine interactions of⁶⁹Ga,⁷¹Ga and³¹P nuclei with donor electrons in tellurium doped GaP have been measured by means of electron nuclear double resonance (ENDOR). Three groups of neighbour nuclei have been identified. Values of |(r)|², r ^–3, and the electric field gradient at the sites of the neighbour nuclei have been determined, and compared with those from ENDOR measurements on sulphur doped GaP.     

The study of the interaction of indium with tellurium in silicon

The perturbed γ–γ angular correlation method has been employed to study indium-impurity pairs in silicon, consisting of the probe atom (¹¹¹In/¹¹¹Cd) and several group-VI donors. Such pairs can be identified via the interaction between the quadrupole moments of the probe nucleus and the electric field gradient (EFG) associated with the formed defect complex. A new quadrupole interaction frequency (QIF) of ν_Q=444(1) MHz (η=0) is measured at T=293 K in Te implanted silicon after annealing the sample above 700 K. The complex is attributed to the In-Te pair along 〈100〉-crystal axis in silicon. In addition, the temperature dependence of the QIF characterizing the pair has also been studied. The implantations of S and Se could not lead to the formation of observable complexes despite similar treatment of all samples. PACS 61.72.-y; 76.80.+y; 61.72.Cc     

Electronic and magnetic properties of silicon adsorption on graphene

Graphene has proved to be extremely sensitive to its surrounding environment, such as the supporting substrate and guest adatoms. In this work, the structural stabilities, and electronic and magnetic properties of graphene with low-coverage adsorption of Si atoms and dimers are studied using a first-principles method. Our results show that graphene with Si adatoms is metallic and magnetic with a tiny structural change in the graphene, while graphene with Si addimers is semi-metallic and nonmagnetic with a visible deformation of the graphene. The spin-polarized density of states is calculated in order to identify the electronic origin of the magnetic and nonmagnetic states. The present results suggest that the electronic and magnetic behaviors of graphene can be tuned simply via Si adsorptions.     

Magnetic resonance force microscopy quantum computer with tellurium donors in silicon

We propose a magnetic resonance force microscopy (MRFM)-based nuclear spin quantum computer using tellurium impurities in silicon. This approach to quantum computing combines well-developed silicon technology and expected advances in MRFM. Our proposal does not use electrostatic gates to realize quantum logic operations.     

Ferromagnetism in epitaxial germanium and silicon layers supersaturated with managanese and iron impurities

The possibility of laser synthesis of diluted magnetic semiconductors based on germanium and silicon doped with manganese or iron up to 10–15 at % has been shown. According to data on the electronic levels of 3d atoms in semiconductors, Mn and Fe impurities are most preferable for realizing ferromagnetism in Ge and Si through the Ruderman-Kittel-Kasuya-Yosida mechanism. Epitaxial Ge and Si layers 50–110 nm in thickness were grown on gallium arsenide or sapphire single crystal substrates heated to 200–480°C. The content of a 3d impurity has been measured by x-ray spectroscopy. The ferromagnetism of layers and high magnetic and acceptor activities of Mn in Ge, as well as of Mn and Fe in Si, are manifested in the observation of the Kerr effect, anomalous Hall effect, high hole conductivity, and anisotropic ferromagnetic resonance at 77–500 K. According to the ferromagnetic resonance data, the Curie point of Ge:Mn and Si:Mn on a GaAs substrate and of Si:Fe on an Al₂O₃ substrate is no lower than 420, 500, and 77 K, respectively.     

Electronic band structure and optical properties of silicon nanoporous pillar array

Silicon nanoporous pillar array (Si-NPA) is fabricated by hydrothermally etching single crystal silicon (c-Si) wafers in hydrofluoric acid containing ferric nitrate. Microstructure studies disclosed that it is a typical micron/nanometer structural composite system with clear hierarchical structures. The optical parameters of Si-NPA were calculated by general light-absorption theory and Kramers–Kronig relations based on the experimental data of reflectance and the variations compared with the counterparts of c-Si were analyzed. The features of the electronic band structure deduced from the optical measurements strongly indicate that Si-NPA material is a direct-band-gap semiconductor and possesses separated conduction sub-bands which accords with conduction band splitting caused by silicon nanocrystallites several nanometers in size. All these electronic and optical results are due to the quantum confinement effect of the carriers in silicon nanocrystallites.     

Electronic structure and optical properties of silicon nanocrystals along their aggregation stages

The structural control of silicon nanocrystals is an important technological problem. Typically, a distribution of nanocrystal sizes and shapes emerges under the uncontrolled aggregation of smaller clusters. The aim of this computational study is to investigate the evolution of the nanocrystal electronic states and their optical properties throughout their aggregation stages. To realistically tackle such systems, an atomistic electronic structure tool is required that can accommodate about tens of thousand nanocrystal and embedding lattice atoms with very irregular shapes. For this purpose, a computationally efficient pseudopotential-based electronic structure tool is developed that can handle realistic nanostructures based on the expansion of the wavefunction of the aggregate in terms of bulk Bloch bands of the constituent semiconductors. With this tool, the evolution of the electronic states as well as the polarization-dependent absorption spectra correlated with the oscillator strengths over their aggregation stages is traced. The low-lying aggregate nanocrystal states develop binding and anti-binding counterparts of the isolated states. Such information may become instrumental with the maturity of the controlled aggregation of these nanocrystals.     

Electronic properties of alkali metal/silicon interfaces: A new picture

Adsorption of Na and Cs on the Si(100)2 × 1 surface in the monolayer range is investigated by core level and valence band photoemission spectroscopy using synchrotron radiation. The alkali metals are found to induce an electronic interface state near the Fermi level while hybridization between alkali adsorbate “s” and silicon substrate “3p” valence electrons occurs. These results provide evidence that the alkali metal/silicon bonding is covalent. This covalent bond is weak and polarized while plasmon at the alkali metal core level indicates adsorbate rather than substrate metallization.