Ge Alloys Research Articles

Thermoelectric performance enhancement in p-type Si via dilute Ge alloying and B doping

Thermoelectric performance enhancement in p-type Si via dilute Ge alloying and B doping

Grain refinement of primary Cu6Sn5 in the Sn-3wt%Ag-5wt%Cu alloy by Ge

Fine grain structure is generally favoured in the alloy system. Here, we demonstrate that the fine intermetallic compounds (IMCs) in Sn-3wt%Ag-5wt%Cu (SAC35) alloy by coupling with different amount of Ge (0–0.15wt%). The effect of Ge addition on the microstructure, elemental distribution, thermal properties, solidification, and corresponding grain refinement mechanisms were studied. The results showed that Cu6Sn5 was explicitly refined in Ge added SAC35 alloys, with a maximum 59% reduction in the size of Cu6Sn5 found in the as-cast bulk SAC35-0.1wt%Ge alloy. Also, the presence of Ge reduced the thickness and grain size at the interfacial IMC layer by 21% and 22%, respectively. Synchrotron micro-XRF results revealed that the Ge preferentially exist in matrix phase. The cooling curve analyses revealed that the solidification time of Ge-coupled is shorter than that of the SAC35 alloy. The undercooling values was found to have decreased with increased Ge addition. The growth restriction factor, Q, was calculated with the aid of Thermo-Calc software, and it was found to have increased in tandem with increasing Ge amounts. The findings suggest the suitability of Ge as a grain refiner for SAC35.

Revealing the electronic, optical, elastic, mechanical, anisotropic, and thermoelectric responses of Sc2NiZ (Z = Si, Ge, and Sn) Heusler alloys via DFT calculations

AbstractRecent spintronics, thermoelectrics, and quantum computing technologies often desire different types of Heusler alloys because of their extensive uses and versatile properties. Although diverse experiments and theoretical efforts have been dedicated to several Heusler alloys for understanding their key properties, no detailed work has yet been performed on the unclear features of Sc2NiZ (Z = Si, Ge, and Sn) Heusler alloys. So, we aimed to clarify their electronic, optical, elastic, mechanical, anisotropic, and temperature‐dependent thermoelectric characteristics via density functional theory (DFT). All investigated alloys exhibit inherent metallic character confirmed by the electronic band analysis and the calculated Poisson's ratios. According to the obtained optical data, Sc2NiZ (Z = Si, Ge, and Sn) alloys can be used as efficient ultraviolet (UV) absorbers and proper infrared (IR) refractors. Sc2NiSi, Sc2NiGe, and Sc2NiSn alloys also demonstrate mechanical stability, ductility, machinability, and elastic anisotropy validated through the calculated elastic constants and their interrelated mechanical data. Notably, Sc2NiSn alloy exhibits the highest Seebeck coefficient with 120 μV/K at 300 K, and can be considered as a potential room‐temperature thermoelectric material.

(Digital Presentation) Low Temperature Formation of Binary and Ternary Group-IV Poly-Layers Via Sn-Nanodots Nuclei

Polycrystalline group-IV alloys, such as Si1-xGex, Ge1-xSnx, and Si1-x-yGexSny, have attractive benefits for thermoelectric generators which can directly convert heat energy into electricity with less environmental impact. Grain boundaries in the polycrystalline material can successfully reduce thermal conductivity which is essential to operate the thermoelectric devices under temperature difference [1]. Besides, mass differences between component elements of the alloy contribute to modulate phonon characteristics [2].In terms of the synthesis of the polycrystalline group-IV alloys, it has been challenging to realize crystallization, which typically needs high temperature annealing, simultaneously with controlling composition, especially Sn content which is limited by low solid solubility into Ge and Si as 1 at.% and 0.1 at.%, respectively, under equilibrium condition [3].As one of the solutions to obtain the polycrystalline group-IV alloys having high Sn content, using crystalline Sn nanodots as nuclei is effective for the growth of crystalline alloys at low temperature. The low temperature growth, which is the growth far away from the equilibrium, enables introduction of Sn more than its solubility limit [4].Amorphous Sn layer deposited on SiO2 substrate can be easily transformed into crystalline Sn nanodots by just applying an annealing in vacuum. We demonstrated the formation of polycrystalline Ge1-xSnx and Si1-xSnx alloys by deposition of Ge and Si on the Sn nanodots at the substrate temperature of 150 °C and 225 °C, respectively [5,6]. Adatoms, namely Ge and Si, were alloyed with the Sn nanodots acting as crystal nuclei. However, we found that Ge preferentially reacts with Sn nanodots when Si and Ge are simultaneously deposited on the Sn nanodots. In this case, Si remains as amorphous, meaning the effect of nucleus for the low temperature crystallization is not effective for Si if Ge exists. This result suggests that Si has to be crystallized prior to Ge.One can notice that the polycrystalline Si1-xSnx can be formed by the Sn nanodots mediated formation process as mentioned above. Therefore, we have proposed the 2-step formation process consisting of poly-Si1-xSnx crystallization and Ge alloying with the poly-Si1-xSnx which can be considered as a virtual substrate [6]. Using the 2-step formation process, whole deposited region was successfully crystallized with alloying Si, Ge, and Sn. The estimated Si and Sn content in the as-grown polycrystalline Si1-x-yGexSny layer were as high as 10.8% and 3.5%, respectively. The impact of introduction of Sn on phonon characteristics will be discussed at the presentation if time allows.Acknowledgements: This work was supported by JSPS KAKENHI Grant Number JP18K13786 and 21K04137 from the Japan Society for the Promotion of Science.

Interaction between solute atoms and vacancies in Al-Mg-X (X＝Si, Ge) alloys

Interaction between solute atoms and vacancies in Al-Mg-X (X＝Si, Ge) alloys

Diffusion coefficients and atomic mobilities in fcc Ag–Ge and Cu–Ge alloys: Experiment and modeling

The comprehensive investigations regarding the diffusion behaviors for Ag–Ge and Cu–Ge solders play key roles in their design and application. However, the diffusion behaviors in fcc Ag–Ge and Cu–Ge binary systems have not been carried out. To fill this gap, their diffusion characteristics were studied in this work based on the measured composition profiles of diffusion couples prepared for fcc Ag/Ag–Ge diffusion couples annealed at 873, 923 and 973 K as well as fcc Cu/Cu–Ge diffusion couples annealed at 1023, 1073 and 1123 K. On the basis of measured composition profiles, the composition-dependent interdiffusivities were calculated by the numerical inverse method incorporated in CALTPP (CALculation of ThermoPhysical Properties) program, which agree well with the ones calculated by the classic Sauer-Freise method. Besides, the atomic mobilities in fcc Ag–Ge and Cu–Ge alloys were assessed based on the diffusivities obtained from the literature and this work. Comparisons between model-predicted diffusion characteristics (viz. composition profiles and interdiffusivities) and experimental ones further validate the reliability of the presently obtained atomic mobilities. Insights gained in this work are of scientific significance and practical benefit for designing new Ge-bearing Ag and Cu solers.

(Digital Presentation) 2D Silicon–Germanium-Layered Materials As Anodes for Li-Ion Batteries

To address the volume changes of Si-based and Ge-based anode materials during lithiation and delithiation, two-dimensional (2D) composites like siloxene and germanane have recently been developed. These 2D materials can insert alkali cations without an alloying reaction, thereby limiting the associated volume expansion. While Si has a high theoretical capacity and low cost, its electrical conductivity is low; on the other hand, Ge provides a higher electronic conductivity but at a higher cost. Therefore, we propose a series of 2D Si–Ge alloys, that is, Si1–x Ge x with 0.1 < x < 0.9, referred to as siliganes, with reasonable cost and encouraging electrochemical performance. The layered siliganes were obtained by fully deintercalating Ca cations from the Ca(Si1–x Ge x )2 parent phases and used as Li-ion battery (LIB) anodes. XRD, SEM, Raman spectroscopy, and infrared spectroscopy were used to characterize the materials and identify the mechanisms occurring during cycling in LIBs. Siligane_Si0.9Ge0.1 was identified as the best candidate; at a current density of 0.05 A g–1, after 10 cycles, it showed a reversible capacity of 1325 mA h g–1, with high capacity retention and coulombic efficiency.

Ge incorporation in kesterite thin films by solution processing route: An in-depth study of structural and optoelectronic properties

Herein, we report a promising solution-processing method for the controlled incorporation of germanium (Ge) into Cu2ZnSnS4 (CZTS) films using a nontoxic molecular ink. The effect of Ge concentration on structural, optical, electrical and electronic properties of the films were systematically investigated. The successful Ge alloying in CZTS was confirmed by XRD analysis and exploring the sensitivity of Raman scattering. The as-synthesized Cu2ZnSn1-xGexS4 (CZTGS; x = 0, 0.1, 0.15, 0.2 and 0.25) films exhibit strong absorption in the visible region with the gradual increment in the band gap energy from 1.46 to 1.61 eV by increasing x from 0 to 0.25. A decrease in Urbach energy at higher [Ge]/[Sn + Ge] ratio supports the reduction of overall disorder into the system. The information about the correct oxidation states of the constituent elements and optimal chemical composition of the CZTGS films was obtained from X-ray photoelectron spectroscopy (XPS). The decrease in SnII/SnIV signal ratio with the increase in Ge further supports the suppression of deep-trap SnZn antisite defects. The XPS valence band spectra reveal that the position of valence band maximum ascended from 0.09 to 0.15 eV with increasing Ge content in the films. Several relevant optical constants were determined of the CZTGS films which are important for applications in solar cell devices as well as for simulation purpose.

Low-thermal-budget n-type ohmic contacts for ultrathin Si/Ge superlattice materials

Thermal budget is a vital element of Si-based superlattice material processing. In this work, a novel n-type ohmic contact scheme with a low thermal budget process is developed by combining high-dose ion implantation and low-temperature alloying techniques. The optimized specific contact resistivity (ρ c) is reduced to 6.18 × 10−3 Ω cm2 at a low thermal budget of 400 °C, and this is a result of the efficient low-temperature electrical activation of amorphous substances. It is indicated that both the high doping concentration and the formation of a NiSi(Ge) alloy phase contribute to the linear ohmic contact behavior. The ohmic contact resistance dependence on processing temperature is further revealed by a detailed Ni/Si(Ge)alloying model. A minimum ρ c of 2.51 × 10−4 Ω cm2 is achieved at a thermal budget of 450 °C, which is related to the high bonding intensity at the metal–semiconductor interface. Note that this technique is compatible with standard Si-based CMOS process flows and can be applied in high-performance insulated-gate field-effect transistor (IGFET) fabrication. Furthermore, it is verified that the Si/Ge superlattice structures in our IGFETs can serve as an efficient potential barrier to constrain electrons.

Crystallography of the martensitic transformation between Ni2In-type hexagonal and TiNiSi-type orthorhombic phases

• A bulk sample with small amounts of orthorhombic phases distributed in hexagonal matrix is obtained. • The orientation relationship between hexagonal and orthorhombic structures is [ 4 2 ¯ 2 ¯ 3 ] h / / [ 120 ] o & ( 01 1 ¯ 0 ) h / / ( 001 ) o . • The habit plane of the hexagonal-orthorhombic transformation is { 2 ¯ 1 1 3.26 } h . • The strain that induce the transformation from hexagonal to orthorhombic structures is revealed. MnMX (M = Co or Ni, X = Si or Ge) alloys, experiencing structural transformation between Ni 2 In-type hexagonal and TiNiSi-type orthorhombic phases, attract considerable attention due to their potential applications as room-temperature solid refrigerants. Although lots of studies have been carried out on how to tune this transformation and obtain large entropy change in a wide temperature region, the crystallography of this martensitic transformation is still unknown. The biggest obstacle for crystallography investigation is to obtain a bulk sample, in which hexagonal and orthorhombic phases coexist, because the MnMX alloys will fragment into powders after experiencing the transformation. For this reason, we carefully tune the transformation temperature to be slightly below 300 K. In that case, a bulk sample with small amounts of orthorhombic phases distributed in hexagonal matrix is obtained. Most importantly, there are no cracks between the two phases. It facilities us to investigate the microstructure using electron microscope. The obtained results indicate that the orientation relationship between hexagonal and orthorhombic structures is [ 4 2 ¯ 2 ¯ 3 ] h / / [ 120 ] o & ( 01 1 ¯ 0 ) h / / ( 001 ) o and the habit plane is { 2 ¯ 1 1 3.26 } h . WLR theory is also adopted to calculate the habit plane. The calculated result agrees well with the measured one. Our work reveals the crystallography of hexagonal-orthorhombic transformation for the first time and is helpful for understanding the transformation-associated physical effects in MnMX alloys.

Tuning the giant magnetocaloric effect in MnCoGe alloy with external pressure

We report the effect of hydrostatic pressure on the magnetocaloric effect across the magneto-structural transition in an off-stoichiometric Mn34.5Co33.1Ge32.4 alloy. A very large isothermal entropy change of 38.95 J kg−1 K−1 is observed at nearly 303 K for a magnetic field excursion of 7 T at ambient pressure. The temperature of the peak entropy change and, thus, the working temperature range of the alloy drastically decrease by about 45 K with the application of a moderate hydrostatic pressure of 297 MPa. This shift is explained by correlating the results of x-ray diffraction measurements performed under high pressure for studying the structural aspect of the transition. Our results highlight the potential of the Mn–Co–Ge alloy system for multi-caloric applications in which the temperature change can be achieved by more than one external stimulus. The present work may also lead to future experiments, which study the response of multi-calorics driven by many external stimuli within the same experimental environment.

Relationship between the density of states effective mass and carrier concentration of thermoelectric phosphide Ag6Ge10P12 with strong mechanical robustness

A ternary phosphide Ag6Ge10P12 containing no toxic elements has attracted much attention as an eco-friendly thermoelectric material. This study reveals the relationship between the density of states effective mass mDOS∗ and carrier concentration n for achieving higher thermoelectric performance in Ag6Ge10P12. The Seebeck coefficient S of Ag6Ge10−xGaxP12 (0.0 ≤ x ≤ 0.25) with various carrier concentrations is unexpectedly improved by increasing n. Scrutinizing electrical transport properties, including the S and electrical conductivity σ, and electronic structure indicated that the improved S is owing to the enhanced mDOS∗, which originated from tuning the Fermi level in a valence band with multi-valley and pudding-mold bands. The power factor S2σ is enhanced by both improved S and σ. The total thermal conductivity κtot monotonically decreases with increasing x because of the decrease in the lattice thermal conductivity κL. Combining the improved S2σ and reduced κtot, the maximum ZT value of Ag6Ge9.875Ga0.125P12 at 390 K reaches ∼0.33 with the optimal carrier concentration n ∼7.0 × 1020 cm−3. The present results demonstrate a guideline for enhancing the thermoelectric performance of Ag6Ge10P12 by breaking the trade-off relationship between the S and σ through n. Moreover, Young's modulus E and nanoindentation hardness H of Ag6Ge10-xGaxP12 are greater than 125 GPa and 9 GPa, respectively, comparable to those of thermoelectric Si–Ge alloy. These findings and insights in the present study will serve as a basis for enhancing the thermoelectric performance and fabricating the thermoelectric module for eco-friendly phosphide Ag6Ge10P12.

A novel technique for measuring diffusivities of short-lived radioisotopes in solids

Abstract After reminding the reader of the major techniques for measuring diffusion coefficients in solids, a detailed description of the conventional radiotracer techniques is presented. These allow to measure solid-state diffusivities in the regime 10– 8–10– 24 m2s– 1 and therefore, and for other reasons to be discussed, are superior to all competing methods. However, the conventional radiotracer techniques suffer from the restriction that they are not applicable to radio-tracer atoms with half-lives t 1/2 ≲ 1 d. The main objective of this paper is to introduce a novel experimental set-up which enables us to perform radiotracer-type diffusivity measurements with short-lived radioisotopes (1 d ≳ t ≳ 10 min). First results on the diffusion of 31Si (t 1/2 = 2.6 h) and 11C (t 1/2 = 20.38 min) in Si–Ge alloys and Si –C–N-based ceramics measured in this set-up are presented.

SiSn mediated formation of polycrystalline SiGeSn

Si1–x Sn x and Si1–x– y Ge x Sn y polycrystalline thin layers were grown using Sn nanodots as crystal nuclei. Si1–x Sn x crystallization occurred around Sn nanodots, and the substitutional Sn content was estimated as high as 1.5%. In the case of the poly-Si1–x– y Ge x Sn y , Ge and Si were deposited simultaneously on the Sn nanodots, however, Ge was preferentially incorporated into the Sn nanodots, resulting in the formation of the poly-Si1–x– y Ge x Sn y with amorphous Si residue. It was found that the poly-Si1–x Sn x formed by the Sn nanodots mediated formation can be used as the new virtual substrate to be alloyed with Ge, namely the 2-step formation process consisting of poly-Si1–x Sn x crystallization and Ge alloying with the poly-Si1–x Sn x is the effective process for the poly-Si1–x– y Ge x Sn y formation. This non-equilibrium process with achieving crystallization resulted in the substitutional Si and Sn content in the as-grown poly-Si1–x– y Ge x Sn y as high as 10.8% and 3.5%, respectively.

EMF study of liquid Al–Fe–Ge alloys

Abstract The thermodynamic properties of ternary liquid Al–Fe–Ge alloys have been studied in the temperature range of 1050 – 1250 K by the electromotive force (EMF) technique with a liquid electrolyte. The ternary alloys are characterized by negative deviations from Raoult’s law.

Enthalpies of mixing of liquid Al–Fe–Ge alloys

Abstract The partial and integral enthalpies of mixing of Al–Fe–Ge melts have been measured by high-temperature calorimetry at 1740 ± 5 K. The integral enthalpies of mixing at 1173 K, are about 4 to 6 kJ mol–1 less negative than determined by electromotive force measurement [9]. The integral enthalpies of mixing have been also estimated on the basis of the Bonnier geometric model. The calculated values show a reasonable agreement with experimental data for x Ge &gt; 0.3. A difference between experimental and estimated integral enthalpies of mixing (up to 2.5 kJ mol–1) is observed for ternary alloys with low germanium content.

The Effect of B, Al, N, and P Impurities on the Electronic Structure of Si0.3Sn0.7Ge alloy: A First-Principles Approach

This study examines the effect of doping Si0.3Sn0.7Ge with an impurity element X (B, Al, N, or P) on the Sn site, using first-principle calculations based on the fully self-consistent Korringa-Kohn-Rostoker method with the coherent potential approximation (KKR-CPA). To treat several forms of chemical disorders of Si0.3Sn0.7Ge, X-doping was carried out by substituting small amounts of Sn with each element X, which gives rise to the alloy Si0.3Sn0.7-yXyGe. As the X content increases from y = 0.01 to 0.06, the Fermi level maintains its position in the conduction band edge. While the number of states at the Fermi level decreases. With 1% X impurity added to the alloy Si0.3Sn0.7-yXyGe, the number of carriers (electron and hole) states was generally enhanced. For the case of X = P, when compared to the parent material Si0.3Sn0.7Ge, an enhancement of 0.04 states/eV was observed. Due to the increase in the number of states, which indicates an improvement in thermopower, these alloys Si0.3Sn0.7-yXyGe are promising for application as n-type electrodes in a thermoelectric generator (TEG).

Electronic, elastic, mechanical and anisotropic response of W3XC2 (X: Si, Ge and Al) alloys via first-principles

First-principles calculations were carried out for the electronic, elastic, mechanical and anisotropic behavior of W3XC2 (X: Si, Ge and Al) alloys. Electronic bands analyses reveal an obvious metallic character for all of the investigated alloys. In addition, the calculated magnitudes of Young's modulus of the alloys follow the range of W3SiC2> W3AlC2> W3GeC2. Similarly, the hardness values of the alloys also follow the same sequence. Amongst the surveyed alloys, W3GeC2 has the highest ductility when compared to W3SiC2 and W3AlC2 alloys. According to obtained results, the most anisotropic alloy was found to be W3SiC2. On the other hand, W3GeC2 and W3AlC2 alloys are found to be more machinable than the W3SiC2 alloy.

Diamond-germanium composite films grown by microwave plasma CVD

We report on novel microcrystalline diamond-germanium composite films grown by microwave plasma-assisted chemical vapor deposition in CH4–H2-GeH4 mixtures on Si substrate. The structure of the films, characterized with scanning electron microscopy, X-ray diffraction, Raman and photoluminescence spectroscopy, is found to strongly depend on the deposition temperature: the Ge grains compete with diamond crystallites upon growth at 750–800 °C, but vanish at higher temperatures of 850–950 °C due to enhanced growth rate of diamond matrix. The Ge grains nucleated on the (100) oriented Si wafer at 800 °C are in an epitaxial relationship with the substrate, while Si–Ge alloy forms at intermediate temperatures 850–900 °C. As both components are transparent in the infrared spectrum, the composite shows certain optical transmission for wavelengths λ > 10 μm. The films revealed a bright optical emission of GeV color centers at 601 nm wavelength due to diamond doping with Ge. From the calculation of the effective coefficient of thermal expansion for the diamond-Ge composites, we show that it can be tuned to be close to that for SiC or Si single crystals by appropriate choice of the Ge volume fraction in the composite, facilitating the integration of the semiconductor wafers with the diamond-based film.

Decoupling the metal-insulator transition temperature and hysteresis of VO2 using Ge alloying and oxygen vacancies.

The metal-to-insulator transition of VO2 underpins applications in thermochromics, neuromorphic computing, and infrared vision. Ge alloying is shown to elevate the transition temperature by promoting V-V dimerization, thereby expanding the stability of the monoclinic phase to higher temperatures. By suppressing the propensity for oxygen vacancy formation, Ge alloying renders the hysteresis of the transition exquisitely sensitive to oxygen stoichiometry.