A. B. Filonov

Theoretical and experimental study of interband optical transitions in semiconducting iron disilicide

The interband optical spectra of the semiconducting β phase of iron disilicide (β-FeSi2) were investigated in the energy range from 0.5 to 5.0 eV. The dielectric function and other optical functions were deduced from ellipsometric experiments and calculated within the local-density approximation by using the semirelativistic linear muffin-tin orbital method. Reasonable agreement between the calculated and measured data has been obtained.

Grain interaction effect in electronic properties of silicon nanosize films

Electronic properties of both nanometer thickness (111) monocrystalline and nanocrystalline free standing silicon films were calculated within a self-consistent linear combination of atomic orbitals method. Grained nature of the nanocrystalline films is found to induce both a direct band gap and its reduction (down to about 2 eV) with respect to an isolated grain of same size.

Ab initio modeling of the electronic and spin properties of the [NV] centers in diamond nanocrystals

The electronic and spin properties of different nanocrystals of carbon are studied. The properties of these cluster systems are modeled in terms of the ab initio (Hartree-Fock) and semiempirical (PM3, AM1) quantum-chemical methods. The calculations are performed for different carbon nanocluster systems: defect-free and with [NV]− centers, hydrogen passivated (C38H42, C71H84, C86H78), and with a free (unpassivated) surface (C38, C71, C86). The spin properties of unhydrated nanoclusters were studied for the first time. The structure of all the clusters under study was optimized using the total energy minimization principle. It is shown that, in the case of hydrated carbon nanocrystals passivated by hydrogen atoms, diamond-like clusters are formed. The atomic structure of an unpassivated nanocrystal depends on the number of atoms in the cluster, as well as on its initial geometrical parameters. In some cases, clusters with a fullerene-like surface are formed. In hydrogenpassivated diamond nanocrystals with [NV]− centers, the spin density is localized at the nuclei of C atoms nearest to the center vacancies. For the unpassivated counterparts, the spin density is localized at the nuclei of C atoms forming the surface of the corresponding nanocrystal.

Transport properties of semiconducting Rhenium silicide

Transport properties of semiconducting rhenium silicide ReSi1.75 were studied both experimentally and theoretically. For this high quality ReSi1.75 single crystals were grown by the zone melting technique with radiation heating and their resistivity and Hall coefficient were investigated. The room temperature carrier concentration in undoped material is appreciably high, about 1019 cm-3. The Hall mobility at room temperature is 30 cm2/V.s, that is considerably lower than previously reported values for single crystals. P-type conductivity persists across the entire interval investigated. Calculation of the charge carrier mobility involved the carrier effective masses, which were obtained from the ab initio electronic band structure and classical scattering mechanisms. A reasonable explanation of the hole mobility behavior is proposed and a strong anisotropy in hole effective masses and mobilities is predicted.

Electronic properties of osmium disilicide

Electronic property calculation of OsSi2 performed by the linear muffin-tin orbital method within the local density approximation scheme has shown the material to be an indirect gap semiconductor with a gap value of 0.95 eV. A direct transition with appreciable oscillator strength at 1.14 eV is predicted.

Thermoelectric efficiency of single crystal semiconducting ruthenium silicide

Thermoelectric efficiency of semiconducting ruthenium silicide Ru2Si3 has been systematically studied both experimentally and theoretically. Pure and Mn-doped Ru2Si3 single crystals were grown by zone melting with optical heating. Temperature dependences of the resistivity, Hall factor, Seebeck coefficient, and thermal conductivity were studied in the range of 100–900 K. For Mn-doped Ru2Si3 crystals, the Seebeck coefficient is positive in the whole temperature range under study, it reaches its maximum value of 400 μV/K at about 500 K. At room temperature, the Seebeck coefficient of these crystals is about 300 μV/K, which is twice as high as in the undoped material. The theoretical study of transport and thermoelectric properties includes the ab initio calculation of band structure, estimation of the carrier effective masses, modeling of the electron and hole mobilities in terms of classical scattering mechanisms, and calculation of the Seebeck coefficient and thermoelectric figure of merit, ZT. The results of theoretical modeling show a good qualitative and quantitative agreement with the experimental data.

Structural, electronic and optical properties of semiconducting rhenium silicide

Structural, electronic and optical properties of semiconducting rhenium silicide (ReSi1.75) with various distributions of the silicon vacancies have been theoretically studied by means of ultrasoft pseudopotential and full-potential linearized augmented plane wave methods. We have found that the band dispersion is affected by vacancy positions, while the dielectric function and reflectivity display similar shapes for all considered variants, that can explain the rather scattered available experimental data on the gap value. Comparison between the calculated and ellipsometrically measured dielectric function and reflectivity on ReSi1.8 polycrystals grown by the Czochralski technique shows a good agreement.

The transport and thermoelectric properties of semiconducting rhenium silicide

The transport and thermoelectric properties of semiconducting rhenium silicide ReSi1.75 are comprehensively studied both experimentally and theoretically. Single-crystal samples of undoped and aluminumdoped ReSi1.75 are grown by floating-zone melting using optical heating. The temperature dependences of the resistivity, Hall coefficient, and Seebeck coefficient (thermoelectric power) are measured in the range 77–800 K. At room temperature, the charge-carrier concentration for the undoped rhenium silicide is 1019 cm−3 and the carrier mobility is 30 cm2/(V s). The theoretical study of the transport and thermoelectric properties includes ab initio calculation of the band structure; estimation of the carrier effective masses; simulation of the electron and hole mobility, taking into account classical scattering mechanisms; and calculation of the Seebeck coefficient. The results of the simulation and the experimental data are in good agreement.

Transport Property Simulation of p-Type β-FeSi2

Estimations of mobility versus temperature for semiconducting iron disilicide in relaxation time approximation have been performed. The results obtained have shown the influence of polar optical phonon scattering to be negligible. A power-law temperature dependence T -β with β > 3/2 in the high-temperature region can be obtained due to acoustic and nonpolar phonon scatterings. The power of the exponent is strictly affected by neutral inipurity scattering as well which, in our opinion, may be connected with the crystalline purity.

Effect of stresses in electronic properties of chromium disilicide

A detailed theoretical study of electronic properties of chromium disilicide CrSi2 under isotropic and anisotropic pressure has been performed by means of linearized augmented plane wave method. It has been found that in case of isotropic deformation the indirect and first direct gaps decrease linearly with the rise of the pressure but with different rates. A similar behavior was observed for uniaxial stress, while this dependence is more complicated and not linear. When the crystal structure is being 106% stretched, chromium disilicide becomes a direct-gap semiconductor with energy gap of about 0.31 eV.