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Abstract: Ion assisted molecular beam epitaxy bears the potential to tune morphological and structural parameters of semiconductor heterolayers for opto- and nanoelectronic applications. The morphology evolution and the degree of relaxation are influenced by the ion beam parameters and the strain of the heteroepitaxial film. In this work, the morphology of silicon germanium (SiGe) layers due to Si+-ion beam treatment during growth is investigated by atomic force microscopy (AFM) as a function of ion energy and ion flux density. Ion energies range from 100eV to 1000eV. The AFM measurements are used to determine the roughness distribution across the wafers. A regular pattern of SiGe crystallites is found, where the damage due to low ion energy Si+-ion bombardment is medium and the degree of relaxation, determined by Raman spectroscopy, is below 25%. [Copyright &y& Elsevier]

Abstract: Polycrystalline samples of ternary rare-earth germanides R2Co3Ge5 (R=La, Ce and Pr) have been prepared and investigated by means of magnetic susceptibility, isothermal magnetization, electrical resistivity and specific heat measurements. All these compounds crystallize in orthorhombic U2Co3Si5 structure (space group Ibam). No evidence of magnetic or superconducting transition is observed in any of these compounds down to 2K. The unit cell volume of Ce2Co3Ge5 deviates from the expected lanthanide contraction, indicating non trivalent state of Ce ions in this compound. The reduced value of effective moment (μeff ≈0.95μ B ) compared to that expected for trivalent Ce ions further supports valence-fluctuating nature of Ce in Ce2Co3Ge5. The observed temperature dependence of magnetic susceptibility is consistent with the ionic interconfiguration fluctuation (ICF) model. Although no sharp anomaly due to a phase transition is seen, a broad Schottky-type anomaly is observed in the magnetic part of specific heat of Pr2Co3Ge5. An analysis of C mag data suggests a singlet ground state in Pr2Co3Ge5 separated from the singlet first excited state by 22K and a doublet second excited state at 73K. [Copyright &y& Elsevier]

Abstract: A series of lanthanide penta-germanides LnGe5 (Ln=Ce, Pr, Nd and Sm) has been prepared by high-pressure (5–13GPa) and high-temperature (500–1200°C) reaction. CeGe5 crystallizes in an orthorhombic unit cell (S.G. Immm (71)) with a=4.000(5)Å, b=6.192(5)Å, c=9.86(1)Å, and V=244.1(5)Å3. The new germanides are isotypic with LaGe5 consisting of a Ge covalent network with tunnels where guest ions Ln 3+ are situated. The network is composed of sublayers with edge-sharing Ge six-membered rings with only boat conformation. The sublayers are connected by rare eight-coordinated Ge atoms. The cell volume of the compounds systematically decreases from La to Sm compounds, except for CeGe5, owing to the lanthanide contraction. The lattice constants of CeGe5 are smaller than those of the Pr compound because it contains Ce4+ ions. CeGe5 is paramagnetic above 2K, but does not obey the Curie–Weiss law. PrGe5 and NdGe5 are Curie–Weiss type paramagnets with Weiss temperatures of –3.3 and –18.4K. SmGe5 shows an antiferromagnetic transition at 10.4K. [Copyright &y& Elsevier]

Abstract: The V–Zr–Ge system was studied for two isothermal sections at 900 and 1200°C. Three ternary compounds VZrGe (tI12, I4/mmm, CeScSi-type), V x Zr5−x Ge4 (oP36, Pnma, Sm5Ge4-type) and V4+x Zr2−x Ge5 (oI44, Ibam, Si5V6-type) were structurally characterized. Optical microscopy and powder X-ray diffraction (XRD) were used for initial sample characterization and electron probe microanalysis (EPMA) of the annealed samples was used to determine the exact phase compositions. The variation of the cell parameters of the various ternary solid solutions with the composition was determined. The three ternary phases were structurally characterized by means of single crystal and powder XRD. While VZrGe is almost a line compound, V x Zr5−x Ge4 (0.2≤ x ≤3.0) and V4+x Zr2−x Ge5 (0.06≤ x ≤1.2) are forming extended solid solution ranges stabilized by differential fractional site occupancy of V and Zr on the metal sites. [Copyright &y& Elsevier]

A series of magnesium-substituted rare-earth metal germanides with a general formula RE5−xMgxGe4 (x ≈ 1.0−2.3; RE = Gd−Tm, Lu, Y) have been synthesized by high-temperature reactions and structurally characterized by single-crystal X-ray diffraction. These compounds crystallize with the common Gd5Si4 type structure in the orthorhombic space group Pnma (No. 62; Z = 4; Pearson's code oP36) and do not appear to undergo temperature-induced crystallographic phase transitions down to 120 K. Replacing rare-earth metal atoms with Mg, up to nearly 45% at., reduces the valence electron count and is clearly expressed in the subtle changes of the Ge−Ge and metal−metal bonding. Magnetization measurements as a function of the temperature and the applied field reveal complex magnetic structures at cryogenic temperatures and Curie−Weiss paramagnetic behavior at higher temperatures. The observed local moment magnetism is consistent with RE3+ ground states in all cases. In the magnetically ordered phases, the magnetization cannot reach saturation in fields up to 50 kOe. The structural trends across the series and the variations of the magnetic properties as a function of the Mg content are also discussed. The unique ability of the Gd5Si4 type-structure to adapt to a varied electron count has been exploited through the substitution of a trivalent rare-earth metal with the divalent Mg. As a result, a new family of rare-earth metal magnesium germanides, RE5−xMgxGe4 (RE = Gd−Tm, Lu, Y; x ≈ 1.0-2.3), have been synthesized from the corresponding elements and structurally characterized. Temperature- and field-dependent magnetization measurements show how the spontaneous magnetic order is influenced by the amount of Mg. [ABSTRACT FROM AUTHOR]

Abstract: We demonstrate for the first time 70nm gate length TiN/HfO2 pMOSFETs on 200mm GeOI wafers, with excellent performance: I ON =260μA/μm and I OFF =500nA/μm @ V d =−1.0V (without germanide). These performance are obtained using adapted counterdoping and pocket implants. We report the best CV/I vs. I OFF trade-off for Ge or GeOI devices: CV/I =4.4ps, I OFF =500nA/μm @ V d =−1V. Moreover, based on fine electrical characterizations (μ, D it, R access, etc.) at T =77–300K, in-depth analysis of both ON and OFF states were carried out. Besides, calibrated TCAD simulations were performed to predict the performance enhancements which can be theoretically reached after further device optimization. By using germanide and reducing both interface state density and diode leakage we expect I ON =450μA/μm, I OFF =100nA/μm @ V d =−1V for L g =70nm. [Copyright &y& Elsevier]

Contact resistivity is a key contributor to the parasitic series resistance of nanoscale MOSFETs. Since the contact resistivity is an exponential function of the Schottky barrier height, new contact materials that can provide smaller barrier heights to source-drain junctions are needed. Platinum germanosilicide (PtSi1-xGex,) is of interest as a contact material to the recessed Si1-xGex, junctions of p-channel MOSFETs due to the large work function of platinum silicide (PtSi). In this paper, we explore the impact of in-plane biaxial compressive strain in Si1-xGex layers on PtSi1-xGex formation and the impact of the PtSi1-xGex on the strain in Si1-xGex. The parameters considered in this paper include the Ge content, the thickness of the Si1-xGex epitaxial layer, and the PtSi1-xGex thickness. The results show that the resistance, surface morphology, and the crystalline structure of the PtSi1-xGex films are independent of the strain in the original Si1-xGex layer. The results also indicate that PtSi1-xGex does not influence the strain in the Si1-xGex layer. The barrier-height measurements suggest the presence of Fermi-level pinning, and the pinning position is independent of the strain in the alloy, and it is primarily determined by the Ge concentration. As a result of Fermi-level pinning, hole Schottky barrier height of PtSi1-xGex-Si1-xGex contacts is 0.1-0.2 eV higher than that of the PtSi-Si contacts. [ABSTRACT FROM AUTHOR]

Abstract: We have performed first principles total energy calculations to investigate the deposit of yttrium digermanide on the Si(111) surface. We have used the periodic density functional theory as implemented in the Quantum-ESPRESSO package. For the adsorption of a monolayer of yttrium digermanide on the Si(111)-(1×1) surface, we have found that the most stable geometry corresponds to a configuration with Y atoms occupying the T4 site above a second layer Si atom, and with a Ge bilayer on top of the structure. The atomic structure of the Ge bilayer is similar to that of Si (Ge) in the bulk but rotated 180° with respect to the crystal. For the three dimensional growth of a few layers of yttrium digermanide on Si(111) we have considered a hexagonal structure with (√3×√3) periodicity, similar to the one found in the growth of few layers of YSi2 on Si(111): graphite-like Ge planes (with vacancies) intercalated with yttrium planes. As in the case of a single layer of YGe2, there is a formation of a Ge bilayer on top of the structure. In this case, the Gedown atoms of the bilayer, which are on top the vacancies, move down towards the vacancy, while Ge atoms in the graphitic layer, which are below the Geup atoms of the bilayer, are displaced towards the vacancy. [Copyright &y& Elsevier]

The microstructural evolution and corresponding electrical contact properties of Co-germanide systems were investigated. The Co-germanide formation process underwent several intermediate, high-resistive phases (CoGe and Co[sub5]Ge[sub7]), while low-resistive CoGe[sub2] was formed over 650°C in a narrow process window of <100°C. Because of the strong Fermi level pinning effect, Co, CoGe, and Co[sub5]Ge[sub7] phases exhibited Schottky contact behaviors with similar Schottky barrier heights on n-type Ge and ohmic contact behavior on p-type Ge, respectively. However, for the CoGe[sub2]/n-type Ge contact formed at 700°C, a nearly ohmic contact behavior started to appear, which was attributed to the possible diffusion of Co atoms into the Ge substrate due to the high-temperature germanidation process. [ABSTRACT FROM AUTHOR]

Cover Feature: Experimental and Theoretical Study on the Substitution Patterns in Lithium Germanides: The Case of Li15Ge4 vs Li14ZnGe4 (Eur. J. Inorg. Germanides, Lithium, Solid-state synthesis, Structure elucidation, Zintl phases Keywords: Germanides; Lithium; Solid-state synthesis; Structure elucidation; Zintl phases EN Germanides Lithium Solid-state synthesis Structure elucidation Zintl phases 1 1 1 02/07/22 20220208 NES 220208 B The Cover Feature b shows the synthesis of Li SB 14 sb ZnGe SB 4 sb by substitution of Li by Zn within the parent Li SB 15 sb Ge SB 4 sb binary phase. [Extracted from the article]

Abstract: Two new isostructural intermetallic germanides, LiSrGe2 and LiBaGe2, were synthesized as single crystals from constituent elements in molten Na. They both crystallize in the space group Pnma (no. 62) with a =7.142(1), b =4.459(1), c =11.550(2)Å, Z=4, and a =7.381(1), b =4.617(1), c =11.837(1)Å, Z =4, for LiSrGe2 and LiBaGe2, respectively. They contain one-dimensional anionic germanide chains, , running along the a-axis. The chains are in an unusual zigzag-like conformation, with weakly alternating Ge–Ge bond lengths of 2.475(1) and 2.498(1)Å, and 2.473(1) and 2.525(1)Å, for LiSrGe2 and LiBaGe2, respectively. Extended Hückel calculations suggest that LiSrGe2 is metallic: the Fermi level lies within bands having anti-bonding character. [Copyright &y& Elsevier]

We present a “nanoparticle-in-alloy” material approach with silicide and germanide fillers leading to a potential 5-fold increase in the thermoelectric figure of merit of SiGe alloys at room temperature and 2.5 times increase at 900 K. Strong reductions in computed thermal conductivity are obtained for 17 different types of silicide nanoparticles. We predict the existence of an optimal nanoparticle size that minimizes the nanocomposite’s thermal conductivity. This thermal conductivity reduction is much stronger and strikingly less sensitive to nanoparticle size for an alloy matrix than for a single crystal one. At the same time, nanoparticles do not negatively affect the electronic conduction properties of the alloy. The proposed material can be monolithically integrated into Si technology, enabling an unprecedented potential for micro refrigeration on a chip. High figure-of-merit at high temperatures (ZT ∼ 1.7 at 900 K) opens up new opportunities for thermoelectric power generation and waste heat recovery at large scale. [ABSTRACT FROM AUTHOR]

Abstract: The section Hf5Ge4–Zr5Ge4 shows the existence of extended ternary solid solutions based on the binary compounds Hf5Ge4 (Pearson symbol: oP36) and Zr5Ge4 (Pearson symbol: tP36). The corresponding homogeneity ranges have been determined experimentally at 1350°C. Partial ordering of the metal atoms at the three crystallographically independent metal sites of the structures was investigated by means of powder X-ray diffraction (XRD) followed by Rietveld refinement as well as by single crystal XRD. The two metals Hf and Zr exhibit site preferences throughout their respective homogeneity ranges. Using a simple thermodynamic model (“compound energy model”) and employing ground state energies of hypothetical ordered compounds calculated from ab initio density functional theory, the experimentally observed site fraction data were reproduced with high accuracy. The obtained Gibbs energies were furthermore used to calculate the stability ranges of the two different phases at 1350°C. The possible benefit of this approach for the prediction of phase stability and for the Calphad-type modeling of higher-order systems is discussed. [Copyright &y& Elsevier]

Abstract: The ternary rare-earth chromium germanides RECr x Ge2 (RE=Sm, Gd–Er) have been obtained by reactions of the elements, either in the presence of tin or indium flux, or through arc-melting followed by annealing at 800°C. The homogeneity range is limited to 0.25⩽x⩽0.50 for DyCr x Ge2. Single-crystal and powder X-ray diffraction studies on the RECr0.3Ge2 members revealed that they adopt the CeNiSi2-type structure (space group Cmcm, Z=4, a=4.1939(5)–4.016(2)Å, b=16.291(2)–15.6579(6)Å, c=4.0598(5)–3.9876(2)Å in the progression for RE=Sm to Er), which can be considered to be built up by stuffing transition-metal atoms into the square pyramidal sites of a “REGe2” host with the ZrSi2-type structure. (The existence of YbCr0.3Ge2 is also implicated.) Only the average structure was determined here, because unusually short Cr–Ge distances imply the development of a superstructure involving distortions of the square Ge net. Magnetic measurements on RECr0.3Ge2 (RE=Gd–Er) indicated that antiferromagnetic ordering sets in below T N (ranging from 3 to 17K), with additional transitions observed at lower temperatures for the Tb and Dy members. [Copyright &y& Elsevier]

Abstract: We have performed first principles total energy calculations to investigate the structural and electronic properties of bulk YGe2, in AlB2 type configurations. Although the experimental stoichiometry is Y2Ge3, we have also considered the ideal YGe2, and the Y3Ge5 configuration found for rare earth disilicides. Our studies using a unit cell with the ideal AlB2 structure result in a lattice parameter a larger and a c/a ratio smaller than the experimental values. On the other hand, the calculated structural parameters for the configurations with vacancies in the graphitic-like Ge planes are in excellent agreement with experimental values. The introduction of vacancies results in more favorable Y–Y and Ge–Y distances. The densities of states display p (of Ge) and d (of Y) orbital hybridizations, and they show that vacancies play an important role in the stability of the compound. [Copyright &y& Elsevier]

Abstract: The mechanisms of the platinum germanide formation by RTA processes in the Ge/Pt/Ge/SiO2/Si structure in the temperature range from 200°C to 600°C were investigated by means of transmission electron microscopy (TEM) techniques. The studies were focused on the observations of the layer microstructure and of Ge/Pt/Ge interfaces at an atomic scale by high resolution TEM (HRTEM), as well as on the identification of formed phases using analytical TEM and diffraction techniques. The formation of platinum germanides in the Ge/Pt/Ge/SiO2/Si structure is visible at 200°C. However, at this temperature only a part of Ge reacted with the whole Pt during annealing. The whole Ge layer reacted with the Pt layer at 300°C. The formed Pt–Ge layer is not a mono-layer but consists of two platinum germanides layers. The results of the annealing of Ge/Pt/Ge/SiO2/Si structure at higher temperatures are very similar to the results obtained at 300°C. Various Pt–Ge phases have been found in the samples studied. The PtGe phase in the germanide layer of the sample annealed at 200°C was found by means of TEM diffraction analysis and the energy-dispersive X-ray spectroscopy (EDXS) in scanning TEM. At 300°C the diffraction pattern reveals the reflections corresponding to PtGe and Pt2Ge3 phases. Analytical TEM studies showed that the phase composition depends on annealing temperature and that the Ge content in the Pt–Ge phases increases with temperature. [Copyright &y& Elsevier]

Abstract: We present a systematic study of the Schottky barrier lowering induced by dopant segregation during nickel germanidation at NiGe/n-Ge(100) contacts. We used two different doping ions (As/P) and prepared two different NiGe layer thicknesses (30nm/60nm) at 400°C. NiGe was found to exhibit a smooth interface to the Ge substrate and a very low specific resistance of 15.1μΩcm. Both doping species, As and P, segregated at the NiGe/Ge interface during germanidation due to the snowplow effect. We found the concentration of dopants at the NiGe/Ge interface increases with increasing implantation dose. From low-temperature measurements, significant lowering of the effective Schottky-barrier height from 0.72eV at 0K for diodes without ion implantation to 0.38eV by P segregration was determined. With a value of only 0.19eV, arsenic was found to be superior to P for Schottky barrier lowering. [Copyright &y& Elsevier]

Abstract: Thin film germanide reactions are often declared to be the same as silicides reactions which were far more studied. In this paper, we present a comparative study of the phase formation and kinetics of nickel silicides and nickel germanides by several experimental techniques. The samples, composed of a nanometric nickel film (50nm) deposited on silicon or germanium substrates, have been examined by several “in situ” real time measurements: X-ray diffraction (XRD), and differential scanning calorimetry (DSC). These original DSC and “in situ” XRD measurements have allowed us to determine the interfacial reaction rate for Ni2Si using a linear-parabolic law. During the relatively fast DSC ramp, the growth is mainly controlled by the interface while isothermal heat treatments lead to a mainly diffusion control. In contrary to what is usually found for nickel silicide and germanides, a simultaneous growth of Ni5Ge3 and NiGe has been found during “in situ” XRD measurements. The different behavior between the Ni–Si system (sequential formation) and the Ni–Ge system (simultaneous formation) is interpreted in term of diffusion and interface controlled growth. In addition, in devices, the film stability and the stress of the silicides or the germanides can be affected by an important physical characteristic that is the anisotropy of dilatation coefficient. In this work, the lattice parameters and linear thermal expansion coefficients (γ a , γ b and γ c ) of the orthorhombic Ni(Si1− X Ge X ) compounds with 0≤ X ≤1 were determined from high temperature X-ray diffraction data (298–1073K). A negative thermal expansion coefficient of the b lattice parameter of Ni(Si1− X Ge X ) for all the studied Ge concentration was observed: the magnitude of this negative thermal expansion coefficient is decreasing with increasing Ge concentration. [Copyright &y& Elsevier]

Abstract: An overview of silicides and germanides for nano-CMOS applications is presented. The historical evolution describing the migration from the use of Ti silicide to Co silicide to Ni silicide as contacting material is first discussed. These changes in silicide material were mainly motivated by the inability to form the target low resistivity silicide phase in small structures due to low nucleation density. This issue was found first for the low resistivity C54 TiSi2 at linewidths below 200nm and later for the low resistivity CoSi2, at linewidths below 40nm. A detailed description of scalability and thermal stability issues for NiSi is then presented. No nucleation issues were found in small structures for NiSi, which grows by diffusion or interface limited kinetics with Ni as main moving species. However, silicidation can be excessive in small structures due to Ni diffusion from surrounding areas, resulting in thicker films than targeted in small devices. This can be controlled by using a silicidation process with two rapid thermal processing steps, the first one to control the amount of Ni reacted and the second one to convert the silicide to the target low resistivity monosilicide phase. One of the main issues for applications of NiSi is its low thermal stability: thin NiSi films agglomerate at relatively low temperatures. The process window and thermal stability of Ni and Pt-based films reacted with Si, Si:Ge and Si:C substrates is reviewed. Addition of Ge is shown to degrade thermal stability while addition of C or Pt improves it. Contact resistivity considerations and implementation of dual band-edge silicides are discussed, as well as promising results for the extension of Ni-based silicides to future nodes. Finally a brief overview of germanides is presented discussing NiGe and PdGe as main candidates. [Copyright &y& Elsevier]

Abstract: The magnetic behavior of the R2CuGe6 ternaries (R=Gd, Tb, Dy and Er) was investigated in the temperature interval 1.72–300K and in magnetic fields up to 5T. All the compounds order antiferomagnetically with Néel temperatures of 20.6, 33.1, 22.0 and 5.6K for R=Gd, Tb, Dy and Er, respectively. Above the respective T N the reciprocal magnetic susceptibility obeys the Curie–Weiss law with the paramagnetic Curie temperature being negative for R=Gd, Tb and Dy and positive for R=Er. [Copyright &y& Elsevier]

Abstract: The ternary germanide GdRuGe was synthesized from the elements by arc-melting and its structure was refined from single crystal X-ray diffractometer data: TiNiSi type, space group Pnma, , ,  pm, , 547 values, 20 variables. The ruthenium and germanium atoms build up a three-dimensional [RuGe] polyanionic network with strongly distorted, corner-sharing tetrahedra with Ru–Ge distances ranging from 252 to 260 pm. The gadolinium atoms fill voids with coordination number 16 within the [RuGe] network. GdRuGe orders ferromagnetically around 70 K and exhibits complete saturation of the Gd moments at 5 K in the isothermal magnetization measurements. The compound also exhibits a moderate magnetocaloric effect, (for and ). [Copyright &y& Elsevier]

Abstract: We report silicide and germanide technology for ohmic contacts and metal gates of MOSFETs in this paper. We have investigated the control technology of NiSi/Si contact properties by incorporating third elements such as Ge and C for future ULSI applications. The work function and resistivity of various Ni and Pt germanides have been also examined as metal gate materials. The low resistivity and tunable work function of these silicides and germanides are desirable for future CMOS devices. [Copyright &y& Elsevier]

Abstract: A thin cobalt layer is deposited by electron beam evaporation onto a germanium substrate after an in situ cleaning annealing at 400 or 700°C. The effect of these pre-treatments on the Co/Ge Schottky barrier properties and on the germanide formation is investigated by using different techniques. A strong influence of the pre-treatment is observed. The pre-treatment at 700°C removes the native oxide but enhances the diffusion of contaminants. After post-metal deposition annealing, the sample pre-treated at 700°C shows a double layer structure due to interdiffusion, whereas some large isolated islands are present in the sample pre-treated at 400°C. [Copyright &y& Elsevier]

Abstract: Polycrystalline samples of the intermetallic compounds La2MnGe6, Ce2MnGe6, La2CuGe6, Ce2CuGe6, and R2NiGe6 (R=Gd, Tb, Dy, Ho), which belong to the Ce2CuGe6 type of structure (Amm2 or Cm2m space group), were studied by means of the electrical resistivity and differential thermopower measurements. They exhibit the metallic-like behavior in the temperature range from 5 to 290K. The peculiarities in both resistivity and thermopower temperature dependencies correlate with corresponding magnetic transition T tr temperatures. [Copyright &y& Elsevier]

The formation and morphological evolution of the germanides formed in the Ni1-xTax/Ge (x=0 and 0.1) systems were examined using ex situ and in situ annealing experiments. It was observed that the Ni-germanide in the Ni0.9Ta0.1/Ge system remained stable at temperatures up to 550 °C whereas the Ni-germanide in the Ni/Ge system agglomerated and was unstable. Microstructural and chemical analyses of the Ni0.9Ta0.1/Ge system during and after in situ annealing in a transmission electron microscope confirmed that the Ta-rich layer was formed by the accumulation of Ta atoms on the interface between the Ni0.9Ta0.1 alloy film and the Ge substrate during the diffusion reaction, and a small amount of residual Ta was found in the Ni-germanide grains. Ultimately, the Ta-rich layer helps reduce the level of agglomeration in the Ni-germanide film and improves the thermal stability of Ni-germanide. [ABSTRACT FROM AUTHOR]

Since the introduction of SiO2/Si devices in the 1960s, the only basic change in the design of a MOSFET has been in the gate length. The channel thickness has fundamentally remained unchanged, as the inversion layer in a silicon MOSFET is still about 10 nm thick. Bipolar transistor base widths have been of sub-micron dimensions all this time. It is time for a new property to be exploited in concert with the high mobility strained-silicon channels and silicon-germanium alloys. This property is the inherently low parasitic series resistance of Schottky barrier contacts. Schottky contacts, beam leads, and microbridges, while originally developed in silicon, have been successfully integrated into compound semiconductors for optoelectronics. Reintroduction of these technologies in optoelectronics based on silicon-germanium is proposed. Several new applications using platinum and rhodium compounds of silicon and germanium are presented. [ABSTRACT FROM AUTHOR]

Seven nearly stoichiometric compounds with general formulas RESn 1+ xGe 1− x(RE = Y, Gd−Tm; x≈ ±0.15) have been synthesized from the corresponding elements using high-temperature reactions and molten Sn as a metal flux. They crystallize with the centrosymmetric space group Cmcm(No. 63) and their structures can be viewed as built up of two distinct polyanionic moieties: infinite ∞1[Ge 2] zigzag chains and square sheets of tin atoms, ∞2[Sn], with rare-earth cations enclosed between them. Within this formalism, such a bonding arrangement can also be described as a ternary derivative of the ZrSi 2structure (Pearson’s symbol oC12), obtained by “coloring” the anionic sites with two different elements, Ge and Sn in the present case. This is a unique aspect of the crystal chemistry of the intermetallic compounds in general, because elements from the same group typically do not show a tendency for site preferences. It is discussed in detail, along with an analysis of the trends across the whole series. The temperature dependence of the magnetic susceptibility, resistivity, and specific heat for all members of this family (some measured down to 400 mK and in applied fields up to 70 kOe) are reported as well. All lanthanide compounds are metallic and order antiferromagnetically at low temperatures. [ABSTRACT FROM AUTHOR]

Abstract: Results are presented of a comparative study of the dependence of carrier recombination characteristics on excitation and dopant concentration in Si and Ge. The bulk lifetime observations are simulated by combining the Shockley–Read–Hall model with Auger recombination above a doping concentration threshold. It is shown that the bulk carrier lifetime behaviour in Si and Ge is very similar. The lifetime dependence on dopant concentration in germanium can be phenomenologically described by assuming a linear increase of recombination centre concentration with dopant concentration. Recombination characteristics in n-Ge implanted with Co, Fe, Ti, Ni and Cr are studied before and after annealing. [Copyright &y& Elsevier]

The ternary rare-earth chromium germanides RECrGe3(RE La−Nd, Sm) have been synthesized by direct reactions of the elements in the presence of Sn flux, or by arc-melting and annealing at 800 °C. Their structures were determined by single-crystal and powder X-ray diffraction. They adopt a hexagonal perovskite structure type (P63/mmc, Z 2; a 6.2004(1)−6.0812(3) Å, c 5.7660(6)−5.6594(3) Å for RE La−Sm), unusual for an intermetallic compound, in which chains of face-sharing Cr-centered octahedra are linked by triangular Ge3clusters. Electrical resistivity measurements show metallic behavior for all RE members, with prominent transitions that coincide closely with ferromagnetic transitions (Tcranging from 60 to 155 K) seen in the magnetic susceptibility curves. Band structure calculations on LaCrGe3show the presence of a narrow, partially filled band with high DOS at the Fermi level. [ABSTRACT FROM AUTHOR]

Among uranium transition metal germanides, UPdGe reveals fascinating magnetic and electrical properties. We have recently performed electronic band-structure calculations of this compound and its non-5f electron counterpart ThPdGe in the paramagnetic state. The obtained theoretical electron densities of states (DOS) were compared with newly measured X-ray photoemission spectra (XPS). For UPdGe some disagreement was observed probably due to the predominant localized character of 5f electron states observed in the XPS spectra. [ABSTRACT FROM AUTHOR]

The results of an experimental study concerning the thermodynamic stability of the Yb germanides, described as intermediate valence compounds, complemented by a computational investigation for the Yb3Ge5compound are reported. These compounds belong to the rare earth (RE) tetrelides (tetrel Si, Ge, i.e., group 14 elements), a class of intermetallic materials showing unusual and promising physical properties (giant magnetocaloric effect, magnetostriction, and magnetoresistence). The high-temperature decomposition reactions of the Yb−Ge intermediate phases were studied experimentally by means of the KEMS (Knudsen effusion mass spectrometry) and KEWL (Knudsen effusion weight loss) techniques. From the reaction enthalpies derived by measuring the Yb(g) decomposition pressures as a function of temperature, the heats of formation of five out of six of the intermediate phases in the Yb−Ge system were calculated. From the computational side, the stability of the Yb3Ge5(s) compound has been investigated by DFT-LCAO-B3LYP (density functional theory-linear combination of atomic orbitals-hybrid b3lyp exchange-correlation functional) first principles calculations deriving its equilibrium geometry and the enthalpy of formation at 0 K in relation to the intermediate valence state of Yb in the lattice. [ABSTRACT FROM AUTHOR]

In this work, the formation of nickel germanide is investigated by spectroscopic ellipsometry. The phase transition and thickness of nickel germanide were identified nondestructively by spectroscopic ellipsometry. The results were compared with traditional analytical tools such as four point probe, Rutherford backscattering spectrometry, and X-ray photoelectron spectroscopy, and showed good agreement. The optical properties (refractive index) of nickel germanide were obtained from spectroscopic ellipsometer measurements and applied to the thickness measurement of nickel germanide successfully. [ABSTRACT FROM AUTHOR]

Abstract: We present first results of ab initio computations within the density functional theory in order to study the differences in chemical bonding and the experimentally observed different magnetic behaviour of the orthorhombic, TiNiSi related ternary germanides CeRhGe (antiferromagnet) and CeIrGe (intermediate valence compound). The calculations reveal strong contributions of the cerium 4f states at the Fermi level. Ingoing from CeRhGe to CeIrGe stronger Ce–Ir versus Ce–Rh interactions are found. [Copyright &y& Elsevier]

Abstract: The germanide Yb2Ru3Ge4 was synthesized from the elements using the Bridgman crystal growth technique. The monoclinic Hf2Ru3Si4 type structure was investigated by X-ray powder and single crystal diffraction: C2/c, Z=8, a=1993.0(3)pm, b=550.69(8)pm, c=1388.0(2)pm, β=128.383(9)°, wR 2=0.0569, 2047 F 2 values, and 84 variables. Yb2Ru3Ge4 contains two crystallographically independent ytterbium sites with coordination numbers of 18 and 17 for Yb1 and Yb2, respectively. Each ytterbium atom has three ytterbium neighbors at Yb–Yb distances ranging from 345 to 368pm. The shortest interatomic distances occur for the Ru–Ge contacts. The three crystallographically independent ruthenium sites have between five and six germanium neighbors in distorted trigonal bipyramidal (Ru1Ge5) or octahedral (Ru2Ge6 and Ru3Ge6) coordination at Ru–Ge distances ranging from 245 to 279pm. The Ru2 atoms form zig-zag chains running parallel to the b-axis at Ru2–Ru2 of 284pm. The RuGe5 and RuGe6 units are condensed via common edges and faces leading to a complex three-dimensional [Ru3Ge4] network. [Copyright &y& Elsevier]

The phase and texture of of Er-germanide formed on Ge(001) through a solid-state reaction between Er thin films and Ge(001) via rapid thermal annealing (300–600°C) were investigated. It was found that amorphous ErGe1.2 forms at 300°C, followed by the formation of AlB2 hexagonal ErGe1.5 at 400–500°C and then orthorhombic ErGe1.8 at 600°C. X-ray diffraction pole figure measurement revealed that the ErGe1.5 films formed at 400–500°C consist predominantly of epitaxial grains with an Orientation relationship of ErGe1.5(11¯00)[0001]//Ge(001)[011¯], although the presence of a considerable amount of epitaxial grains with an orientation relationship of ErGe1.5( 101¯2)[011¯0]//Ge(001l)[010] was also observed in the film formed at 400°C. The germanide film formed at 600°C was found to consist of randomly orientated orthorhombic ErGe1.8 grains. Among the three different germanide phases, ErGe1.5 showed minimum resistivity values as low as ∼19 μΩ cm. [ABSTRACT FROM AUTHOR]

This work is an attempt to systematize the magnetic properties of RTxX2 (R - rare earth, T - transition metal, X - Si, Ge, Sn) compounds crystallizing in the orthorhombic CeNiSi2-type structure. All silicides crystallize in the stoichiometric structure RTX2, while germanides and stannides form mainly detected RTxX2 structures (0 < x < 1). This family of compounds exhibits a complex magnetic behaviour. Two factors influencing stability of various magnetic structures are considered with the purpose of finding the magnetic ordering scheme: magnetic interactions of the RKKY type and crystal electric field effect. [ABSTRACT FROM AUTHOR]

We have investigated solid-state reactions in an equiatomic mixture of Fe and Ge powders during ball milling in a water-cooled high-energy mill under an argon atmosphere. The mechanical alloying products have been characterized by x-ray diffraction, Mössbauer spectroscopy, and calorimetry. The observed sequence of phase formation correlates with the thermodynamic properties of the iron germanides involved. The alloy prepared by ball milling for 2 h consists entirely of nanocrystallites (≃15 nm) of the low-temperature, stable, cubic ( B20) phase of FeGe. [ABSTRACT FROM AUTHOR]

Abstract: Ge-on-insulator (GOI) layer by the Ge-condensation technique is characterized from the viewpoint of the carrier transport. We fabricate GOI channel metal-oxide-semiconductor field-effect transistors (MOSFETs) featuring ultra-low Schottky barrier metal source/drain for holes using Pt germanide where a buried oxide and a silicon substrate are used as a gate dielectric and a bottom gate electrode, respectively. P-type and N-type channel MOSFET operations in the accumulation and inversion mode, respectively, are demonstrated successfully, according to Schottky barrier heights for each carrier. Hall measurement for the GOI layers indicates the existence of relatively high carrier density of holes, 1.3×1017 cm−3, which is not attributable to doped impurities. [Copyright &y& Elsevier]

Abstract: We have proposed Metal Source/Drain MOSFETs (MSD-MOSFETs) with Ge-on-Insulator (GOI) channels using germanides as source/drain metal material. Here the characterization of Schottky barrier hieght (SBH) at the germanide/Ge interfaces is a key issue for a Ge channel MSD-MOSFET. However, there are few published reports on the subject. In this paper, we present the results of the characterization of platinum germanide/Ge interfaces. SBHs of platinum germanide/n- and p-Ge(100) junctions were evaluated to examine the applicability of platinum germanide to MSD-MOSFETs. The SBH for platinum germanide/p-Ge(100) was found to be as low as 0.1 eV over a wide range of anneal temperatures. As a result, we conclude that platinum germanide is a promising S/D material for Ge channel MSD-MOSFETs. [Copyright &y& Elsevier]

Abstract: A process to stabilise the formation of NiGe using Zr alloying engineering approach was investigated. The NiGe film maintained continuity up to 600 °C with NiGe phase stable up to 700 °C. Secondary ion mass spectroscopy and transmission electron microscopy characterisations showed that a thin ZrO x layer was formed on top of NiGe. The ZrO x layer acted as a capping layer to NiGe. As a result, the morphology and phase formation of NiGe were stabilised. We propose Ni(Zr) alloy as a promising material for germanides metallisation contacts in metal-oxide-semiconductor field-effect transistors (MOSFETs). [Copyright &y& Elsevier]

Abstract: In this study, we survey Schottky diode property of both p-metal (Ni) germanide and n-metal (Zr, Er and Yb) germanide in contact with Ge (100). Our experimental results demonstrate that Φ p values obtained for NiGe/n-Ge is − 0.07 eV, and Φ n values for YbGe/p-Ge is 0.139 eV, the lowest hole barrier so far reported. In addition, NiGe Schottky source/drain p-MOSFET with HfO2/TaN gate stack and AlN/SiO2 stacked spacer were fabricated and measured. The drain current at V D = V G − V th =− 1.5 V is ∼ 4.0 μA/μm of the gate length L G =8 μm device. The I on/I off ratio is ∼ 103, and sub-threshold swing is 137 mV/dec. [Copyright &y& Elsevier]

Abstract: The two families of intermetallic phases REAuAl4Ge2 (1) (RE=Ce, Pr, Nd, Sm, Eu, Gd, Tb, Dy, Er, Tm and Yb) and REAuAl4(Au x Ge1− x )2 (2) () (RE=Ce and Eu) were obtained by the reactive combination of RE, Au and Ge in liquid aluminum. The structure of (1) adopts the space group R-3m (CeAuAl4Ge2, , ; NdAuAl4Ge2, , ; GdAuAl4Ge2, , ; ErAuAl4Ge2, , ). The structure of (2) adopts the tetragonal space group P4/mmm with lattice parameters: , for EuAuAl4(Au x Ge1− x )2 (). Both structure types present slabs of “AuAl4Ge2” or “AuAl4(Au x Ge1− x )2” stacking along the c-axis with layers of RE atoms in between. Magnetic susceptibility measurements indicate that the RE atoms (except for Ce and Eu) possess magnetic moments consistent with +3 species. The Ce atoms in CeAuAl4Ge2 and CeAuAl4(Au x Ge1− x )2 () appear to be in a mixed +3/+4 valence state; DyAuAl4Ge2 undergoes an antiferromagnetic transition at 11K and below this temperature exhibits metamagnetic behavior. The Eu atoms in EuAuAl4(Au x Ge1− x )2 () appear to be in a 2+ oxidation state. [Copyright &y& Elsevier]

Polycrystalline Si0.4Ge0.6 was prepared by electron-beam float-zone melting, and its thermoelectric properties were studied in the intrinsic region. The samples were found to be p-type, with a room-temperature resistivity from 5 to 20 Ωcm. The thermoelectric figure of merit of the alloy in the intrinsic region (500–1000 K) is lower than that of heavily doped alloys. Above 1000 K, a sharp rise in its thermoelectric figure of merit would be expected. [ABSTRACT FROM AUTHOR]

Abstract: In this study, we investigated fabrication and characteristics of germanides Schottky contacts on germanium. Ti- and Ni-germanides were fabricated on n-Ge(100) substrates by sputtering metal Ti or Ni on Ge followed by a furnace annealing. The influence of annealing temperature on the electrical properties of Ti- and Ni-germanide on n-Ge(100) substrates was investigated. The low temperature ∼300°C annealing helped to obtain the optimized Schottky contact characteristics in both Ti-germanide/Ge and Ni-germanide/Ge substrates contacts. The well-behaved Ti-germanides/n-Ge Schottky contact with 0.34eV barrier height was obtained by using a 300°C annealing process. [Copyright &y& Elsevier]

Polycrystalline Si0.4Ge0.6 was prepared by electron-beam float-zone melting, and its thermoelectric properties were studied in the intrinsic region. The samples were found to be p-type, with a room-temperature resistivity from 5 to 20 Ωcm. The thermoelectric figure of merit of the alloy in the intrinsic region (500–1000 K) is lower than that of heavily doped alloys. Above 1000 K, a sharp rise in its thermoelectric figure of merit would be expected. [ABSTRACT FROM AUTHOR]

Abstract: The ternary R2NiGe6 germanides (R=Y, Ce, Pr, Nd, Gd, Tb, Dy, Ho, Er, Tm) with Ce2CuGe6 structure (space group Cm2m, Pearson symbol oS18) were prepared by arc melting. The magnetic properties were measured in fields up to 10T in the temperature range 2–300K. Except for R=Y and Ce, these ternary compounds order antiferromagnetically at low temperatures (Néel''s temperature T N) and exhibit metamagnetic behaviors. The experimental critical field of the low temperature metamagnetic process was found fairly related to the values of T N and θ p. [Copyright &y& Elsevier]

Abstract: Ce2Ge2In was synthesized by arc-melting the elements under argon. Its Mo2FeB2 type structure was refined on the basis of the single crystal data: , , pm, , 339 values and 12 variable parameters. The structure is an intergrowth of distorted AlB2 and CsCl related slabs of compositions CeGe 2 and CeIn with a Gece of 253 pm within the AlB2 slabs. The COHP analysis confirms strong covalent Ge which determines the structure more than the corresponding Ptin isostructural Ce2Pt2In. The weaker Ptg energy is compensated by stronger Cections, which results in almost identical total ICOHP bonding energies for Ce2Pt2In and Ce2Ge2In. [Copyright &y& Elsevier]

The available data are analyzed on the enthalpies of formation of intermetallic compounds in binary systems of rare-earth metals with group IV p-elements. Consideration is given to effects of metallochemical factors on these enthalpies of formation. For REM silicides and germanides, the dominant effect comes from the size factor, while for the plumbides, it comes from the electronegativity. The effects of these factors tend to balance for compounds containing tin. [ABSTRACT FROM AUTHOR]

A new germanide, SrGe6-δ(δ ≅ 0.5), was synthesized by the reaction of Sr and Ge mixtures under a pressure of 5 GPa at 1200 °C. It crystallized in the orthorhombic space group Cmcm (No. 63) with a = 4.0981(6) Å, b = 11.159(1) Å, C = 12.6825(8) Å, V = 580.0(1) Å, and Z = 4. SrGe6-δ is composed of a Ge covalent network having a cagelike structure and Sr atoms situated in the cages. Each Ge atom is coordinated by four neighboring Ge atoms. The coordination polyhedra are fairly distorted from an ideal tetrahedron, and the Ge network contains vacancies and disordering. The resistivity shows metallic behavior down to 2 K, and the positive thermoelectric power indicates the dominant carriers to be holes. [ABSTRACT FROM AUTHOR]