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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]

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]

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]

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]