Polycrystalline ß-FeSi2 layers prepared by codeposition of Si and Fe on cold and hot Si substrates and ß-FeSi2 crystals grown by chemical vapor transport were investigated. Resistivity and Hall effect measurements revealed the p-type conductivity of undoped material and the influence of some dopants of the iron group. The activation energy of a Cr-related acceptor was determined to about 85 meV. The mobility data were found to depend significantly on the purity of the preparation process.

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.

A detailed study of the electronic and optical properties of recently discovered ruthenium disilicide (RuSi2) has been performed by means of ultrasoft pseudopotential and full-potential linearized augmented plane wave methods. Three phases were considered as in FeSi2, and like that compound only the orthorhombic structure (beta-phase) was found to be an indirect bandgap semiconductor. The remaining two (alpha- and gamma-) phases, which show metallic behavior, are studied by density of states (DOS) and compared with those of FeSi2. Optical properties are discussed by analyzing the imaginary part of the dielectric function and the dipole matrix elements corresponding to different interband transitions.

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.

In the title of this paper (and also in several places in the text), the chemical notation for the orthorhombic semiconducting iron disilicide is given incorrectly. In the whole paper, the chemical formula “β-FeSi2.5” should be replaced by the formula “β-FeSi2”.

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.

This review emphasizes progress in theoretical simulation and experiments that have been performed in the past years for semiconducting silicides. New fundamental electronic and optical properties of Ca2Si and BaSi2, recently found RuSi2 phase, ternaries in Fe–Os–Si and Ru–Os–Si systems, β-FeSi2, Mg2Si and CrSi2 with stretched and compressed lattices as well as transport properties of β-FeSi2, ReSi1.75, Ru2Si3 are presented. Prospects for practical applications of semiconducting silicides are discussed.

Pure and Mn-doped single crystals of ruthenium silicide (Ru/sub 2/Si/sub 3/) have been grown by floating zone technique with radiation heating in order to investigate the thermoelectric efficiency of this compound. Electrical resistivity, Hall effect, Seebeck coefficient and thermal conductivity of the crystals were measured at 100 - 900 K. Undoped crystals show in the thermoelectric power both types of conductivity. The Seebeck coefficient of Ru/sub 1-x/Mn/sub x/Si/sub 1.5/ is positive in the whole temperature range studied and reaches the maximum value of 450 /spl mu/V/K at about 500 K. The room temperature value of 300 /spl mu/V/K is twice higher in magnitude than the corresponding value for the undoped Ru/sub 2/Si/sub 3/. The charge carrier concentration in the 1% Mn-doped samples is about 10/sup 18/cm/sup -3/ at room temperature and the Hall mobility is about 20 cm/sup 2//V/spl middot/s. The comparison with the undoped Ru/sub 2/Si/sub 3/ shows a twofold increase of the carrier mobility as the result of doping. The performed theoretical calculation of the carrier mobility is based on the effective masses, which are estimated from the ab initio electronic band structure and classical scattering mechanisms. The mobility as well as thermoelectric properties show a reasonable agreement with the experimental data for both Mn-doped and undoped Ru/sub 2/Si/sub 3/ crystals.

Transport properties of Mn-doped ruthenium silicide Ru2Si3 were studied both experimentally and theoretically. The precipitation-free Ru2Si3 single crystals were grown by the zone melting technique with radiation heating. The temperature dependence of the electrical resistivity and Hall coefficients of the crystals were measured. The electrical resistivity of 1% Mn-doped Ru2Si3 was lower than that of undoped crystals. The carrier concentration in the doped samples is about 1018 cm−3 at room temperature. Mn-doped Ru2Si3 has a twice higher carrier mobility compared to the undoped one. Theoretical calculation of the charge carrier mobility is based on the effective masses which are estimated from the ab initio electronic band structure and classical scattering mechanisms.

Physics, Chemistry and Application of Nanostructures, pp. 306-309 (2003) No AccessLATTICE MATCHING BETWEEN BULK Ru2Si3 AND NANOCRYSTALLINE RuSi2L. I. IVANENKO, V. L. SHAPOSHNIKOV, and E. A. KRUSHEVSKIL. I. IVANENKOBelarusian State University of Informatics s and Radioelectronics, P. Browka 6, 220013 Minsk, Belarus, V. L. SHAPOSHNIKOVBelarusian State University of Informatics s and Radioelectronics, P. Browka 6, 220013 Minsk, Belarus, and E. A. KRUSHEVSKIBelarusian National Technical University, F. Skaryna Ave. 65, 220013 Minsk, Belarushttps://doi.org/10.1142/9789812796738_0072Cited by:0 PreviousNext AboutSectionsPDF/EPUB ToolsAdd to favoritesDownload CitationsTrack CitationsRecommend to Library ShareShare onFacebookTwitterLinked InRedditEmail Abstract: An analysis of geometrical matching between bulk Ru2Si3 and nanocrystalline RuSi2 has been performed for three types of its lattice, namely for α-, β-, and γ-phase. The best matching has been found for α-RuSi2. This is characterized by the common unit cell area of 1.86 nm2 and 0.04 % diagonal lattice mismatch. FiguresReferencesRelatedDetails Physics, Chemistry and Application of NanostructuresMetrics History PDF download

Pure and Mn-doped single crystals of ruthenium silicide (Ru2Si3) have been grown by floating zone technique with radiation heating in order to investigate the thermoelectric efficiency of this compound. Electrical resistivity, Hall effect, Seebeck coefficient and thermal conductivity of the crystals were measured at 100 - 900 K. Undoped crystals show in the thermoelectric power both types of conductivity. The Seebeck coefficient of Ru1-xMnxSi1.5 is positive in the whole temperature range studied and reaches the maximum value of 450 muV/K at about 500 K. The room temperature value of 300 muV/K is twice higher in magnitude than the corresponding value for the undoped Ru2Si3. The charge carrier concentration in the 1% Mn-doped samples is about 10(18)cm(-3) at room temperature and the Hall mobility is about 20 cm(2)/V(.)s. The comparison with the undoped Ru2Si3 shows a twofold increase of the carrier mobility as the result of doping. The performed theoretical calculation of the carrier mobility is based on the effective masses, which are estimated from the ab initio electronic band structure and classical scattering mechanisms. The mobility as well as thermoelectric properties show a reasonable agreement with the experimental data for both Mn-doped and undoped Ru2Si3 crystals.

We investigated the temperature and magnetic field dependence of the Hall effect, the magnetization and the resistivity of Mn-doped β-FeSi2 single crystals in the temperature range of 4–300 K in magnetic fields up to 5 T. A negative magnetoresistance as well as strong nonlinear magnetic field dependence of the Hall resistivity and magnetization were observed. The anomalous contribution to the Hall resistivity is found to be important. We also observed the value of the anomalous Hall coefficient to increase with decreasing temperature as the square of the resistivity. It was shown that the magnetization of Mn-doped samples cooled in zero-external field and in a field are different. This resembles the properties of spin glasses. The dominant scattering mechanisms are determined by analyzing the Hall mobility data. The value of the valence band deformation potential is estimated. A particularly important role is played by the anomalous Hall effect which is the microscopic mechanism involving the spin dependent scattering on Mn ions and spin–orbit coupling in the Mn-doped β-FeSi2 single crystals.

Single crystals of ruthenium silicide Ru2Si3 have been grown by the floating zone technique with radiation heating in order to investigate the thermoelectric efficiency of this compound. Special attention was paid to the crystal perfection and the mechanism of defect generation, which may cause the deterioration of thermoelectric properties. Crystallographically oriented plate-like silicon inclusions in the Ru2Si3 matrix, about 1μm wide, have been detected. They are supposed to be a result of solid-state precipitation during cooling at temperatures below 1000°C. Annealing at 1000°C for 24h with subsequent freezing leads to the disappearance of these defects. The resistivity, Hall and Seebeck coefficients of single crystals have been measured across a wide temperature range. Undoped crystals show both types of conductivity in the thermoelectric power. At T=745K the Seebeck coefficient reaches its maximum value of 300μV/K. The room temperature carrier concentration in undoped material is about 1018cm−3. The Hall mobility at room temperature is 2–3cm2/Vs. The hole mobility calculated from Hall data varies with temperature as T3/2, indicating a predominant scattering of carriers at ionized impurities. The complete absence of acoustic phonon scattering allows the conclusion that point defects in the crystals dominate the intrinsic lattice properties. The intrinsic conductivity sets on at 590K, which is a relatively low value for refractory wide gap silicides. This confirms the high quality of the crystals.

Ru2Si3 single crystals have been grown by the zone melting technique with radiation heating. These crystals contain inclusions, about 500nm in size, which consist of monocrystalline ruthenium disilicide. Endothermic peaks detected at T=962°C in the DTA traces of RuSix are interpreted as decomposition of RuSi2 to Ru2Si3 and Si. This enabled us to update the Si-rich part of the Ru–Si phase diagram.

Results of magnetization and magnetic susceptibility measurements on undoped and Co-doped FeSi2.5 single crystals are presented. The temperature dependence of the magnetic susceptibility of the Co-doped sample in the range of 5–300 K can be explained by temperature-dependent contributions due to paramagnetic centers and the carriers excited thermally in the extrinsic conductivity region. The values of the paramagnetic Curie temperature and activation energy of the donor levels were estimated. It is also shown that the magnetic susceptibility of Co-doped samples cooled in zero external field and in a field are different. This resembles the properties of spin-glasses and indicates the presence of coupling between magnetic centers.

A detailed study of optical properties of ruthenium silicide (Ru 2 Si 3 ) has been performed by means of first-principle full-potential linearized-augmented-plane-wave method (FLAPW) calculations. The calculated spectral dependence of the absorption coefficient was compared with absorption measurements, indicating very good agreement. The compound is found to be a direct-gap semiconductor with low oscillator strength of the first interband transition.

High-purity single crystals are necessary to investigate the intrinsic properties of undoped β-FeSi2 which is dependent on the composition within the homogeneity range of the phase. Therefore, iron was used as the initial material for growing β-FeSi2 single crystals with a high-purity with respect to metallic as well as non-metallic impurities. Chemical vapor transport in a closed system was used for single crystal growth. By optimization of the whole preparation process a final purity of approximately 99.996% by weight could be achieved. The content of the main electrically active elements was lower than 20 ppm. By optimizing the transport process untwinned single crystals with flat surfaces could be obtained. To fix the composition of the crystals at the lower and upper phase boundary FeSi/FeSi2 and FeSi2/Si sources were used only and the crystals were heat-equilibrated at 700, 825, 925 and 975°C for different times. Only n-type single crystals were obtained even in both equilibria, with FeSi and with Si, respectively. Therefore, the p-type conductivity of undoped single crystals reported in the literature result from non-intentional doping by the impurity level of the used source material. The single crystals grown at both phase boundaries are expected to differ in the concentration of native defects and with that in the electrical properties. Four point measurements have shown a clear relation between the temperature dependence of the resistivity and the annealing temperature. However, different values of the resistivity at room temperature of crystals at the lower and upper phase boundary were only found in 975°C annealed crystals. In no case were low ohmic single crystals obtained.

The optical properties of ruthenium silicide Ru2Si3 have been studied theoretically and experimentally. The energy band spectrum and optical properties were simulated with the aid of the first‐principle self‐consistent method of linear attached plane waves. The spectral dependence of the absorption coefficient in the 0.52.2 eV energy range was measured experimentally by the photothermal refractive spectroscopy method. It is established that ruthenium silicide is a direct‐gap semiconductor having an energy gap of 0.84 eV and a low oscillator strength of the first direct transition.