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We analyze the efficiency as thermoelectric energy converter of a silicon–germanium alloy with composition and temperature dependent heat conductivity. The dependency on composition is determined by a non-linear regression method (NLRM), while the dependency on temperature is approximated by a first-order expansion in the neighborhood of three reference temperatures. The differences with respect to the case of thermal conductivity depending on composition only are pointed out. The efficiency of the system is analyzed under the assumption that the optimal energy conversion corresponds to the minimum rate of energy dissipated. The values of composition and temperature which minimize such a rate are calculated as well. [ABSTRACT FROM AUTHOR]

By means of ab initio calculations we demonstrate that perturbed hexagonal germanium is a superior material for active optoelectronic devices in the infrared spectral region. Perfect lonsdaleite germanium is a pseudodirect semiconductor, with a direct fundamental band gap but almost vanishing optical transitions. Perturbing the system by replacing a germanium atom with a silicon atom in the primitive cell increases the oscillator strength at the onset gap by orders of magnitude, with a concurrent blue shift of the transition energies. This effect is mainly due to the increased s character of the lowest conduction band because of the perturbation‐induced wave function mixing. A structural distortion of pure lonsdaleite Ge can enhance as well optical oscillator strengths, but their magnitude significantly depends on the specific details of the resulting atomic geometry. In particular, moderate tensile uniaxial strain can induce an order inversion of the two lowest conduction bands, leading to an extremely efficient enhancement of the dipole matrix elements at the minimum gap. In general, chemical and/or structural perturbations are shown to make lonsdaleite germanium a suitable material for light emitting devices. [ABSTRACT FROM AUTHOR]

We analyze the efficiency as thermoelectric energy converter of a silicon–germanium alloy with composition and temperature dependent heat conductivity. The dependency on composition is determined by a non-linear regression method (NLRM), while the dependency on temperature is approximated by a first-order expansion in the neighborhood of three reference temperatures. The differences with respect to the case of thermal conductivity depending on composition only are pointed out. The efficiency of the system is analyzed under the assumption that the optimal energy conversion corresponds to the minimum rate of energy dissipated. The values of composition and temperature which minimize such a rate are calculated as well.

Environmental stability of material properties is an important factor for its utilization for electronic devices. Gases in air such as oxygen can react chemically with material and cause degradation of its properties. This work reports on effect of air on thermoelectric properties of nanostructured n-type silicon-germanium (SiGe) alloy: a well-known high temperature thermoelectric material with superior properties. Phosphorous doped SiGe alloy was synthesized via mechanical alloying followed by hot-press and characterized by powder X-ray diffraction, scanning electron microscopy, and thermoelectric measurements. The average grain size of alloyed powder was in the range 50 - 400 nm. The reduction in grain size caused decrease in thermal conductivity of SiGe alloy (2.044 W/mK at ~ 900K). To study the effect of air on the transport properties of alloy measurements were carried out in presence of air and in inert (argon) atmosphere. Interesting results have been obtained and discussed with the available literature. [ABSTRACT FROM AUTHOR]

We analyze the efficiency in terms of a thermoelectric system of a one-dimensional Silicon–Germanium alloy. The dependency of thermal conductivity on the stoichiometry is pointed out, and the best fit of the experimental data is determined by a nonlinear regression method (NLRM). The thermoelectric efficiency of that system as function of the composition and of the effective temperature gradient is calculated as well. For three different temperatures (T=300 K, T=400 K, T=500 K), we determine the values of composition and thermal conductivity corresponding to the optimal thermoelectric energy conversion. The relationship of our approach with Finite-Time Thermodynamics is pointed out.

Spectroscopic imaging ellipsometry is used to characterize films containing self-assembled SiGe/Si in-plane nanowires grown by molecular beam epitaxy on a Si(001) substrate. The spatial resolution of the order of ∼1 μm allows to study individual nanowires. The obtained images consist of both ψ and Δ values measured in every pixel. From them, spatially resolved contributions to the dielectric function within the films are well visible, coming for example from composition variations. In particular, a strong in-plane anisotropy of the optical response of the nanowires is evidenced. Spectroscopic measurements from different regions of the film are analyzed and compared to spectra calculated using standard ellipsometry multilayer models. The results show the potential of imaging ellipsometry to study micro- and nanostructured semiconductor samples. [ABSTRACT FROM AUTHOR]

In the course of the research, we have noted the influence of weak constant magnetic field on the structure, phase composition, and properties of silicon, namely, significant increment of microhardness and considerable degradation of electrophysical properties, forming of polycrystalline structure in silicon specimens. The qualitative explanations of magneto-stimulated phenomena in studied specimens have been suggested. In the article the influence of alloying and magnetic processing (MP) at the structure and properties of Si specimens has been studied. [ABSTRACT FROM AUTHOR]

Abstract: An N-type Si92Ge08 (7000at. ppm P doping) powder (matrix) prepared by mechanical alloying was homogeneously mixed with 1.3vol.% nanosized molybdenum. The “composite” and matrix powders were sintered by spark plasma sintering, using optimized parameters. The as-sintered “composite” material exhibits a dimensionless thermoelectrical figure of merit (ZT) of ∼1.0 at 700°C. For the same temperature, the ZT value is only 0.7 for the as-sintered matrix alone. In the composite material, transmission electron microscopy observations enable the detection of nanosized (average diameter of ∼30nm) MoSi2 inclusions that formed in situ during sintering via the reaction between the native silicon–germanium matrix and the added molybdenum particles. The presence of such nanosized inclusions reduces significantly the lattice contribution to the thermal conductivity of the sintered “composite” material, explaining the strong increase of the ZT parameter in comparison to the sintered matrix alone. [Copyright &y& Elsevier]

We applied the parametric bootstrap to the X-ray microanalysis of Si-Ge binary alloys, in order to assess the dependence of the Ge concentrations and the local film thickness, obtained by using previously described Monte Carlo methods, on the precision of the measured intensities. We show how it is possible by this method to determine the statistical errors associated with the quantitative analysis performed in sample regions of different composition and thickness, but by conducting only one measurement. We recommend the use of the bootstrap for a broad range of applications for quantitative microanalysis to estimate the precision of the final results and to compare the performances of different methods to each other. Finally, we exploited a test based on bootstrap confidence intervals to ascertain if, for given X-ray intensities, different values of the estimated composition in two points of the sample are indicative of an actual lack of homogeneity. [ABSTRACT FROM AUTHOR]

Abstract: As a fully miscible solid solution, silicon–germanium (Si1−x Ge x ) alloy has attracted significant interest in recent years owing to its manifold applications in microelectronic and optoelectronic devices raised by the possibility of tailoring the band gap and lattice parameter. These additional degrees of freedom and the random distribution of Si and Ge atoms imply new phenomena not observed in elemental group-IV semiconductors. A fundamental understanding of the microscopic properties of the alloy is therefore essential for a good control of SiGe-based device performance. As a corollary, an ultimate understanding of the electronic properties of the most abundant point defects and impurities is needed. This review aims at describing recent results obtained with metallic impurities and irradiation-induced interstitial defects in strain relaxed Si1−x Ge x alloy in which two main aspects will be highlighted. Firstly, the electronic transitions between deep levels and the allowed bands as a function of Ge composition will be discussed with a special emphasis on practical consequences of the alloy-induced energy shifts. Secondly, the role of the atomic environment on the electronic transitions and diffusion mechanism will be highlighted. [Copyright &y& Elsevier]

Abstract: In this work we have investigated the influence of the Ge composition on the minority carrier lifetime in Czochralski (Cz) grown monocrystalline Si1− x Ge x alloys in the composition range of 0

Abstract: Defect monitoring and engineering techniques were applied to multicrystalline silicon grown from electronic grade silicon scraps and strained silicon–germanium alloys to test their suitability for low-cost photovoltaics and high-speed electronics, respectively. The combination of lifetime, photoluminescence and electron beam induced current (EBIC) measurements was found a very effective practice for the analysis of the effect of impurities on the electrical activity of grain boundaries and dislocations in multicrystalline silicon. Room temperature photoluminescence has been also used to monitor the effect of various cell fabrication process steps on the local recombination activity of defects. The application of the EBIC technique was found as well a good tool for a quantitative determination of threading dislocation density in Si–Ge alloys, in view of the optimisation of the low energy plasma-enhanced chemical vapour deposition (LEPECVD) used for their growth. [Copyright &y& Elsevier]

Downscaling alone is not sufficient to sustain the development of CMOS devices, and further paradigm shifts are necessary. In this paper, we argue such a shift is possible and show through technology computer-aided design simulations that a symmetrically operating CMOS device pair may be built under a single gate structure by a surprisingly simple choice of device layout and channel engineering parameters. As a result, we predict that another seemingly fundamental CMOS architectural requirement, the need to build two separate MOSFETs with individual gate stacks, may be eliminated. We call this new architecture a complementary orthogonal stacked MOS (COSMOS), which places the n and p MOSFETs perpendicular to one another under a single gate, integrating them vertically, as well as laterally. We demonstrate how the device may be built, operated, and optimized for symmetric operation, as well as verifying logic NOT operation via three-dimensional device simulations. The COSMOS architecture would not only mean significant savings in the active device area of a conventional digital CMOS layout, but also reductions in RC device parasitics associated with building and wiring two sets of devices for a single Boolean output function. [ABSTRACT FROM PUBLISHER]

Time resolved photo-and thermoelectric effects (TTE) can be used to simultaneously determine, trap levels and trap state density differences in microcrystalline (μc-SiGe:H) samples. Here, in particular, the trap state density differences are obtained from the decay of the ambipolar charge distribution, i.e. stage II of the TTE transients. This type of spectroscopy has been applied for the first time to μc-SiGe:H samples and indeed trap states which seem to relate to concentration fluctuations, i.e. Si(Ge) and Ge(Si) clusters are observed. [Copyright &y& Elsevier]

Exposure of hydrogenated amorphous silicon, a-Si:H, to light produces large-scale structural changes and increases the density of dangling Si bond defects acting as efficient carrier recombination centers. The latter is the well-studied Staebler–Wronski effect (SWE). All light-induced changes are metastable and disappear after annealing to approximately 200°C. This review focuses on one of the large-scale changes, namely that of the macroscopic density of the material. In all device quality materials, the initial stress is compressive with values typically in the range of 108–109 Pa. Exposure to light produces additional compressive stress, which can exceed 2×107 Pa. The observed change of stress is due to a change of the volume of the unsupported material and not of its elastic modulus. The relative volume change, ΔV/V, at 300 K becomes detectable at values in excess of about 10−6 after only a few photons per Si atom have been absorbed. ΔV/V saturates above 10−3, under high-intensity light after an average of more than 106 photons per Si atom have been absorbed. ΔV/V initially grows with t0.50±0.04 under CW illumination producing carrier generation rate G in the range of 1021 to a few 1023 cm−3 s−1. The approach to saturation is well fitted by a stretched exponential function with stretch exponent close to 0.5. ΔV/V is approximately proportional to G. The fastest and largest photo-expansion has been observed in the so-called “edge material” between the amorphous and microcrystalline state, produced by plasma enhanced CVD from increasingly diluted silane/hydrogen gas mixtures. The quantum efficiency of volume expansion has been observed to increase with the photon energy of the light in contrast to the SWE. No volume increase is observed in Ge rich a-Si1−xGex:H alloys and in hydrogenated microcrystalline material. Photo-expansion and the SWE show marked difference in spatial extend in the network, different evolution in time and different wavelength dependence. Hence, the two effects appear to be independent even though both involve hydrogen. [Copyright &y& Elsevier]

The application of the laser-induced pyrolysis to the organogermanium nanocluster (OGE) spin-coated on a Si substrate provides a novel method to form a Si–Ge alloy. The structural and morphological changes via increasing the number of laser shots were studied by micro-Raman spectroscopy and scanning electron microscopy (SEM). [Copyright &y& Elsevier]

Polymorphous silicon–germanium (pm-SiGe:H) thin films with Ge contents varying from 1 to 35% were fabricated by plasma enhanced chemical vapour deposition in a high pressure range (1350 mtorr) and under high hydrogen dilution. The electrical and optical properties of these films were studied using a set of complementary techniques. These materials were then incorporated in the i layer of p–i–n solar cells. The performance of such solar cells and the use of these pm-SiGe alloys as the bottom cell of tandem pm-Si:H/pm-SiGe:H cells are finally discussed with the help of numerical simulations. [Copyright &y& Elsevier]

An investigation of the influence of substrate temperature on optoelectronic properties and microstructure of a-SiGe:H films fabricated by low frequency 55 kHz PECVD method was carried out. It was found that the decrease of substrate temperature leads to increase of photosensitivity. The IR spectroscopy analysis and modeling of photoconductivity have shown that the clustering of SiH and SiH2 bonds on the surface of island and Si related defects determine the density of states distribution in the mobility gap. The energy band diagram was analyzed and it was shown that density of states distribution does not significantly change with the decrease of substrate temperature, which is attributed to the ion bombardment of the growth surface in low frequency discharge. Thus, 55 kHz PECVD method allows the decrease of the deposition temperature for the fabrication of low band gap a-SiGe:H films with the device quality electronic properties and at high deposition rate. [Copyright &y& Elsevier]

Solid boron and antimony doping of silicon and SiGe grown by molecular beam epitaxy using disilane and germane as sources has been studied. Elemental boron is a well behaved p-type dopant. At effusion cell temperatures of 1700-1750°C, hole carrier concentrations in the 10 cm range have been obtained. Elemental antimony doping shows surface segregation problems. For uniformly doped layers, the as-grown materials do not show n-type conductivity. Electron concentrations in the 10 cm range were obtained by post-growth conventional and rapid thermal annealing at 900 and 1000°C, respectively. The electron Hall mobility improves with optimum annealing time. Delta doping of buried layers exhibits slightly better incorporation behavior including significant surface riding effects. [ABSTRACT FROM AUTHOR]

SiGe heterostructures have been grown by molecular beam epitaxy, with nominal compositions of 10 and 15 at %. Analytical electron microscopy, Rutherford backscattering spectrometry and ion channeling have been used in order to determine film thickness, Ge molar fraction and tetragonal distortion. The actual Ge concentrations were found to be smaller than the nominal ones. For all the SiGe films a coherent growth was found, with a small deviation from the perfect tetragonal distortion. The good agreement found between the results obtained by each analytical technique demonstrate that these methods of characterization are powerful tools for the control of the epitaxial layer parameters. [ABSTRACT FROM AUTHOR]

We analyze the efficiency in terms of a thermoelectric system of a one-dimensional Silicon–Germanium alloy. The dependency of thermal conductivity on the stoichiometry is pointed out, and the best fit of the experimental data is determined by a nonlinear regression method (NLRM). The thermoelectric efficiency of that system as function of the composition and of the effective temperature gradient is calculated as well. For three different temperatures ( T = 300   K , T = 400   K , T = 500   K ), we determine the values of composition and thermal conductivity corresponding to the optimal thermoelectric energy conversion. The relationship of our approach with Finite-Time Thermodynamics is pointed out. [ABSTRACT FROM AUTHOR]

Herein, Si–Ge binary alloy films are prepared by deposition on rough copper (Cu) foil and multiwalled carbon nanotube (MWCNT) sheets using radio frequency (RF) magnetron sputtering. The as‐prepared SiGe@Cu and SiGe@MWCNT thin films are then characterized by spectroscopy and microscopy techniques. Scanning electron microscopy (SEM) shows that SiGe nanosheets are deposited on the Cu foil, whereas amorphous SiGe spherical nanoparticles are deposited on the MWCNT surface and incorporated inside its pores. Raman and X‐ray diffraction (XRD) confirm an amorphous structure for the sputtered films. SiGe film thicknesses of 201, 386, and 582 nm are measured by topography after 0.5, 1, and 2 h RF sputtering, respectively. The electrochemical performance of SiGe@Cu and SiGe@CNT is assessed by cyclic voltammetry (CV) and galvanostatic charge–discharge (GCD) in half cells using Li metal as the counter and reference electrode and 1 m LiPF6 in organic carbonates electrolyte. SiGe@Cu exhibits a very stable cyclability during the first ten cycles. The specific charge capacity retention decreases from 97.7%, 94.5%, 88.7%, and 81.2% after 20, 30, 40, and 50 cycles, respectively. A higher specific capacity of SiGe@MWCNT is measured due to deeper lithiation/delithiation reactions. Thus, more investigations are needed to improve the performance of SiGe during long cycling. [ABSTRACT FROM AUTHOR]