Si Sn Alloys Research Articles

Epitaxial SiGeSn grown on Si by ion implantation

We have formed SixGe1−x−ySny compounds on Si substrates by ion implantation and annealing and investigated their concentration profiles, crystallization, and optical properties. Ge and Sn ions were implanted in the range (2.5–10) × 1016 Ge/cm2 at 65 keV, and (1.0–4.0) × 1016 Sn/cm2 at 100 keV, resulting in a peak implant dose at a depth of 50 nm for both species. Epitaxially regrown SixGe1−x−ySny layers (110 nm thick) were produced with Ge and Sn contents that allowed bandgap tuning in the (0.88–1.1) eV range. Shifts in photoelectron binding energies (Si 2p, Ge 3d, and Sn 3d) were consistent with ternary compound formation. Sn segregation was observed for annealing temperatures ≥600 °C. A significant increase in the optical absorption coefficient (×104 cm−1 for λ = (800–1700) nm) was observed for SiGe, SiSn, and SiGeSn alloys, with SiGeSn having coefficients several orders of magnitude higher than for Si. Contributions of segregated Sn to these properties were observed. Metastable SixGe1−x−ySny layers were achieved, which may point to a promising route to mitigate Sn incorporation challenges for near-infrared detectors.

Solid-Liquid-Solid Growth of Doped Silicon Nanowires for High-Performance Lithium-Ion Battery Anode

Silicon nanowires (SiNWs) have great potential in electronic devices, sensors, energy storage, and conversion devices. Despite various ways to synthesize SiNWs, however, the growth of SiNWs directly from stable, abundant, sustainable silica sources has yet to be achieved. Herein, we report a modified alumino-reduction process of the silica to produce tin (Sn)-doped SiNWs that can be initiated at low temperature (250 °C) based on a solid-liquid-solid growth mechanism in analogy to the well-known vapor-liquid-solid (VLS). In this growth process, the reduced silicon atoms migrate freely in the molten salt and alloy with pre-reduced Sn. The supersaturation of silicon in the Sn-Si alloy leads to the precipitation of single-crystal SiNWs. The prepared SiNWs are of excellent crystallinity and doped with high non-equilibrium concentration (~3.0at.%) of Sn. This process with the solid-liquid-solid mechanism can also be extended to produce other group IV elements-based nanowires such as germanium. In addition, the prepared Sn-doped SiNWs as the anode material in lithium-ion batteries exhibit excellent performance with a high initial Coulombic efficiency of 85.4%, and a substantial reversible capacity of 1133 mAh g-1 even after 500 cycles at 4Ag-1. By utilizing the solid-liquid-solid mechanism, this modified alumino-reduction process offers a novel route for synthesizing doped SiNWs, holding promise for diverse applications.

Investigation of Band Structure in Strained Single Crystalline Si1-X Sn X

1. Background and purpose Silicon tin (SiSn) alloys are attractive candidate for the next-generation group-IV semiconductors. It is well known that Si and Ge change from indirect to direct transition types with the addition of Sn. Among them, SiSn alloys are expected to be applied for the near-infrared optical devices because it is predicted to become a direct band-gap appropriate for the optical communication with sufficient Sn content [1]. Although the Sn composition that changes from indirect to direct band-gap has been reported using several calculations, there are few reports of experimental results. In addition, the optical properties of single crystalline Si1-x Sn x have not been sufficiently clarified owing to the difficulty of crystal growth. In this study, we evaluated the optical properties to clarify the band structure of single crystalline Si1-x Sn x . 2. Experimental method Strained 30 nm-thick Si1-x Sn x films were grown on Si substrate by molecular beam epitaxy (MBE), and epitaxial growth was confirmed by X-ray diffraction (XRD) two-dimensional reciprocal space mapping (2DRSM) [2]. The Sn composition was determined by 2DRSM. The Sn fraction x of Si1-x Sn x samples used in this study were 0.005, 0.009, 0.018, 0.022, and 0.06. The spectroscopic ellipsometry measurements were performed with an incident angle of 70°, using a 70 W xenon lamp with a wavelength range of 200 to 1600 nm for the light source. The functions used in the analysis are the Tauc-Lorentz and Lorentz function. 3. Results and Discussion Figure 1(a) and (b) show real part and imaginary part of the complex dielectric functions for Si1-x Sn x (x=0.005 - 0.06) and pure-Si, respectively. From Fig. 1, it can be confirmed that the spectra shift with increasing Sn composition and the peaks appear around 1.8 eV and 2.8 eV for the samples with high Sn composition (2.2% and 6.0%). The peak shift characteristic with the addition of Sn is similar to the results of germanium tin (GeSn) [3].The complex dielectric functions of the semiconductor include much information about the electronic band structure. In Fig. 1, the sharp peaks that are due to direct band transitions show what is known as critical points (CPs). In the case of Si, E'0 CP (Γ) and E 1 CP (L) energy are around 3.2 eV [4]. Therefore, it can be considered that the peak at 2.8 eV indicates the separation of the E'0 and E 1 CP energies due to the change in the band gap at the Γ point with the addition of Sn. The peak at 1.8 eV is unique to Si1-x Sn x , which is not found in Si. We consider that this peak is due to the split-off valence band caused by the Sn addition. The behavior of the valence band is strongly affected by strain. These results suggest a reduction of the band gap at the Γ point and the formation of an optical transition region due to the Sn addition, and reveal important findings for the application of SiSn for the near-infrared devices. Acknowledgment This work was partly supported by the Japan Society for the Promotion of Science (JSPS) (17J08240, 19K21971, and 21H01366).

First-Principles Study of Silicon-Tin Alloys as a High-Temperature Thermoelectric Material.

Silicon–germanium (SiGe) alloys have sparked a great deal of attention due to their exceptional high-temperature thermoelectric properties. Significant effort has been expended in the quest for high-temperature thermoelectric materials. Combining density functional theory and electron–phonon coupling theory, it was discovered that silicon–tin (SiSn) alloys have remarkable high-temperature thermoelectric performance. SiSn alloys have a figure of merit above 2.0 at 800 K, resulting from their high conduction band convergence and low lattice thermal conductivity. Further evaluations reveal that Si0.75Sn0.25 is the best choice for developing the optimum ratio as a thermoelectric material. These findings will provide a basis for further studies on SiSn alloys as a potential new class of high-performance thermoelectric materials.

4D microstructural evolution in a heavily deformed ferritic alloy: A new perspective in recrystallisation studies

We present a multiscale study on the recovery and recrystallisation of a heavily deformed (85% reduction in size) Fe–Si–Sn alloy using a combination of dark field X-ray microscopy (DFXM), synchrotron X-ray diffraction (SXRD) and electron backscatter diffraction (EBSD). By utilizing DFXM, we focus on a grain within the high stored energy (HSE) regions, and track it through consecutive isothermal annealing steps. The intra-granular structure of the as-deformed grain reveals deformation bands separated by ≈3–5∘ misorientation. During the early stages of annealing, cells with 2–5∘ misorientation form while new nuclei appear. The recrystallized grains nucleate near prior grain boundaries, having a typical internal angular spread of <0.05∘. The SXRD results suggest no significant macroscopic texture change after annealing for 1400s at 610∘C in the HSE regions. All results indicate that higher misorientation zones such as grain boundaries or junction points of deformation bands are preferential nucleation regions.

Study on the microstructure and wear behavior of Mg-containing Al–12Sn–4Si alloys

Al–Sn–Si alloys have been widely used as bearing alloys in automotive engines. In those alloys, β(Sn) phase serves as the solid lubricant and Si particles are used to improve the hardness, fatigue resistance as well as seizure resistance. With the development of machinery, bearing alloys with higher load-carrying capacity and better tribological properties are demanded to meet the application under severe conditions. Adding appropriate Mg to the Al–Sn–Si alloy can effectively optimize the tribological properties. In this paper, the microstructure, mechanical properties and tribological properties of the Al–12Sn–4Si-xMg (x = 0, 0.5, 1, 1.5, all in wt.%) alloys were studied. The Al–12Sn–4Si-1.5 Mg alloy had the smallest grain size and more uniform microstructure than other specimens. The Al–12Sn–4Si-1.5 Mg alloy showed significantly better wear resistance than the Al–12Sn–4Si alloy at 2 N–70 N. The volume wear rates and friction coefficients at 15 N–70 N were lower than those at 2 N–8 N. The evolution of volume wear rate and friction coefficient with load was related to the evolution of tribolayer with load. The wear mechanism of the alloys was mainly oxidation wear, adhesive wear and fatigue wear, accompanied with abrasive wear.

Short-range order in SiSn alloy enriched by second-nearest-neighbor repulsion

Although often conceived as random solid solutions, alloys may exhibit a local short-range order (SRO) where the distribution of atoms deviates from a perfect randomness, owing to complex interactions among alloying elements. SRO can affect various properties of alloys, but understanding their exact forms, roles, and origins remains challenging from experiment alone. Here we show, through combining statistical sampling and ab initio calculations, that a strong and special SRO dominates the structure of SiSn alloy, which is a key subset of group IV alloys for mid-infrared technology. Remarkably, the SRO in SiSn is found to be reflected primarily by a strong depletion in the second Sn-Sn coordination shell. This is distinguished from the main character of the SRO in the closely related GeSn alloy, which is reflected by the depletion within the first Sn-Sn coordination shell. The unique nature of SRO in SiSn alloy is further attributed to the competition between the two unfavorable local configurations in SiSn: A Sn-Sn first-nearest neighbor through a direct bond and a Sn-Sn second-nearest neighbor through a Sn-Si-Sn motif. The large energy penalty induced by Sn-Si-Sn local structural motif is found to be responsible for the difference between SiSn and GeSn in their forms of SRO. The SRO in SiSn alloy is further demonstrated to substantially raise the direct band gap. Our finding thus constitutes a new knowledge of the origin and form of SRO and lays the foundation for understanding the complex structure of SiGeSn ternary alloy.

Porous Si-Sn alloys produced by mechanical alloying and subsequent consolidation by sintering and hot-pressing

ABSTRACT Porous Si100-xSnx samples with x = 15, 30 and 40 at.% were produced from Si and Sn elemental powders by mechanical alloying followed by two different compaction and sintering processes: cold uniaxial pressure and subsequent sintering at 220°C, and hot pressing at 240°C. The results showed that it is possible to produce samples with a major porosity of close to 0.1 μm. The porosity of the Si70Sn30 sample that was mechanically alloyed for 12 h and synthesized by the former process is in the mesoporous region. The structure of all the final samples is composed of the Si, Sn and SnO phases.

Study on the mechanical and optical properties of SiSn alloy by first principles

Group-IV semiconductor alloys are important materials for in-chip and inter-chip optoelectronic applications in silicon-based high-performance large-scale integrated circuits. As photovoltaic materials, silicon–tin alloys can improve the performance of solar cells by expanding the spectral range and increasing absorption. Silicon–tin alloys have broad application prospects within the communication wavelength range of 1.0–1.6 µm. In this work, the lattice constants, mechanical and optical properties of Si32−xSnx alloy are calculated. Generalized gradient approximation with Hubbard correction parameter U was used for exchange-correlation potential. The calculation results demonstrate that the lattice constant and formation energy increase with increasing number of tin atoms. In terms of mechanical properties, Si32−xSnx alloy shows mechanical stability and strong resistance to resist external forces, and it is not prone to volume deformation. It shows metallicity and tends to be ductile. In terms of optical properties, the width of the bandgap of Si32−xSnx alloy decreases with increasing tin concentration. The absorption of visible and infrared lights of Si32−xSnx alloy increases with increasing tin concentration. The dielectric properties of Si32−xSnx alloy are significantly changed by the addition of tin atoms. Doping prolongs the carrier lifetime of Si32−xSnx alloy, and its lifetime reaches maximum when x equals 6.

Effects of La2O3 Addition into CaO-SiO2 Slag: Structural Evolution and Impurity Separation from Si-Sn Alloy

Boron (B) and phosphorus (P) are the most problematic impurities to be removed in the production of solar-grade silicon by the metallurgical process. In this work, the distribution of B and P between CaO-(La2O3)-SiO2 slags and Si-10 mass pct Sn melt was experimentally studied. B distribution coefficient increased from 2.93 in binary CaO-SiO2 slag to 3.33 and 3.65 with 2 and 10 mass pct La2O3 additions, respectively. In the followed acid-leaching experiments, the slag-treated Si-Sn alloys exhibited higher B and P removal than that of the initial alloy without slag treatment. Molecular dynamics simulations were performed to study the effect of La2O3 addition on the slag structural and transport properties. A novel oxygen classification method was proposed to distinguish the different structural roles of La and Ca in the CaO-La2O3-SiO2 system. It was found that La3+ prefers to stay in the depolymerized region, mostly connects with 6-7 non-bridging oxygen, and requires a weak charge compensation with Ca2+. Possible silicothermic reduction was evaluated to discuss the slag chemistry and the mass transfer between slag and metal phase. A thermodynamic model was derived to theoretically study the alloying effect on impurity distribution in slag refining where positive interaction coefficient and high alloying concentration were found most beneficial to improve the impurity removal.

Group 14 semiconductor alloys in the P41212 phase: A comprehensive study

This study reported the structural properties, stability, mechanical anisotropy properties (anisotropy in Poisson's ratio, shear modulus, Young's modulus, and the universal elastic anisotropy index) and electronic properties (electronic band structure) of Si20-xGex, Ge20-xSnx, and Si20-xSnx alloy (x = 0, 4, 8, 12, 16, and 20) in the P41212 phase. The lattice parameters of semiconductor alloys in the P41212 phase increased with increasing x. The dynamic and mechanical stability of the Si20-xGex, Ge20-xSnx, and Si20-xSnx alloy (x = 0, 4, 8, 12, 16, and 20) in the P41212 phase were proven by phonon spectra and elastic constants. In terms of Young's modulus, the shear modulus, Poisson's ratio, and AU, Ge12Sn8 in the P41212 phase displayed the maximum anisotropy, while Si12Sn8 in the P41212 phase exhibited the minimum anisotropy. The electronic band structures with the HSE06 hybrid functional indicated that all Si20-xGex, Ge20-xSnx, and Si20-xSnx alloy (x = 0, 4, 8, 12, 16, and 20) in the P41212 phase were indirect band gap semiconductor materials. The Si-Ge alloy band gap modulation range in the P41212 phase was small compared to that of Si-Sn and Ge-Sn alloys in the P41212 phase, while Si-Sn and Ge-Sn alloys had a better band gap modulation effect.

Optimization of Mg2(Si-Sn) based thermoelectric generators using the Taguchi method

The performance of thermoelectric generators (TEGs) besides depending on material’s figure of merit, is also a function of the module design like the heat exchanger design, thermoelectric leg size, configuration, and contact resistances. Optimizing these parameters using conventional experimental methods is quite time-consuming and inconvenient. Taguchi optimization method could be used an efficient technique to predict the performance of a TEG module with less number of experimental runs as compared to the customary techniques. The most commonly used materials in thermoelectric applications in the medium temperature range (400–900 K) are the PbTe alloys and Mg 2 (Si-Sn) based alloys. N-type Mg 2 (Si-Sn) alloys often being integrated with higher manganese silicide (HMS) for fabricating TEGs, pose problems in maintaining the long-term stability of such generators owing to the imperfectly matched thermomechanical properties between these materials. Therefore, it is required to evaluate a TEG system that is completely made out of magnesium based thermoelectric alloys (both p- and n-type). The current study examines the scope of Mg 2 (Si-Sn) thermoelectric generators based on the numerical modeling technique along with employing Taguchi and ANOVA techniques for improving the overall system output. A TEG system comprising of 36 modules is built using numerical modeling which is followed by optimization of pivotal design parameters through the Taguchi and ANOVA methods. Optimal control factor settings obtained from the Taguchi method result in output power and conversion efficiency values of 90.04 W and 9.08% respectively. The predicted optimal output Y predicted is also calculated, the respective values obtained for output power and conversion efficiency are 59.9 W and 9.12%. From ANOVA analysis, it is observed that the most significant variable for power output is the cross-sectional area with a percentage contribution of 35.22% and that for the conversion efficiency is the temperature difference between the two ends of the TEG having a percentage contribution of 97.73%.

Evaluation of Strain-Shift Coefficients for SiSn by Raman Spectroscopy

We report on the strain-shift coefficient of silicon tin (SiSn) alloys obtained by ultraviolet (UV) Raman spectroscopy. The values of the Raman peak shift of the Si-Si mode for the SiSn (Sn fraction: 0.5, 0.9, 1.8, 2.2, and 6.0%) thin films were found to increase with Sn fraction and it indicates that compressive strain is induced in the SiSn films. The strain-shift coefficient of the Si-Si mode obtained from linear fits to the measurement data (UV Raman spectroscopy and X-ray diffraction reciprocal space mapping) has a good agreement with the values of the strain-shift coefficients about strained Si and strained silicon germanium, and commercial high-purity Si reported by previous studies. The strain-shift coefficient determined by in this work contribute to realize strain measurements for the next-generation SiSn devices such as near-infrared optical and thermoelectric devices.

Analysis of the Microstructure, Phase Composition, and Oxidation Kinetics of Heat-Resistant Titanium Alloys with Gadolinium

The structure, phase composition, and local chemical composition of half-finished products (rods) made from Ti–Al–Mo–Zr–Si- and Ti–Al–Mo–Zr–Sn–Si-based alloys additionally microalloyed with 0.4 wt % gadolinium have been studied in this work. The structure of the rod made from the Gd-alloyed Ti–Al–Mo–Zr–Si composition was found to be characterized by the presence of Gd2O3 gadolinium oxide particles. The structure of the rod made from the Gd-alloyed Ti–Al–Mo–Zr–Sn–Si composition, which contains tin as a low-melting element, is characterized by the presence of Gd–Sn–O complex oxide particles, whose cores and shells are Gd5Sn3 intermetallics and Gd2O3 gadolinium oxide, respectively. The formation of such particles in both alloys occurs at the stage of ingot solidification, and the particles remain in the materials at all stages of their subsequent treatment. The oxidation kinetics of the alloys upon isothermal holding in a temperature range of 600–800°С is studied depending on the structure of half-finished products. The oxidation processes of the Ti–Al–Mo–Zr–Sn–Si alloy are less intensive than those of the Ti–Al–Mo–Zr–Si alloy. The alloying with gadolinium up to 0.4 wt % leads to the accelerated oxidation of the tin-free alloy, which is due to the presence of Gd2O3 particles precipitated at grain boundaries and interfaces. The alloying of the tin-containing composition with gadolinium almost does not affect the oxidation kinetics at 600–700°С and slightly decelerates the oxidation at 750–800°С; this is related to the presence of the Gd–Sn–O oxide particles in the structure, which are uniformly distributed over the grain body. The laws of oxidation of both the compositions free from gadolinium and alloyed with gadolinium were determined. It was shown that the oxide film formed upon the oxidation of both alloys is multilayer and consists of alternating layers of aluminum and titanium oxides. In this case, the progressive growth of oxide film layers alters the film exfoliation owing to the high brittleness of aluminum oxides. The presence of gadolinium oxide particles in both alloys leads to the porosity of diffusion zone of the base metal upon oxidation.

Purification of metallurgical-grade silicon combining Sn–Si solvent refining with gas pressure filtration

In this study, the purification of metallurgical-grade silicon using a combination of solvent refining and gas pressure filtration was investigated in the Sn–Si alloy. After the solvent refining process, the silicon was separated from the solvent by gas pressure filtration. The effects of pressure differentials (p), separation temperatures (T), and silicon contents in the alloy (ω(a)) on the separation efficiency were evaluated. The filtration result was improved with a higher pressure differential. The separation temperature had little effect on the separation efficiency, whereas a higher silicon content in the alloy led to a decrease of the separation efficiency. The final purification result after separation was examined, and a better separation contributed to the removal of impurity. The optimal result for separation was obtained at p = 0.30 MPa, T = 250 °C, and ω(a) = 20 wt%, and 93.6% of tin was separated into the filtrate, while almost all the silicon was recovered and formed the separated silicon with a silicon content of 80.0 wt%. At the same time, most impurities were eliminated and 94.9% of B was removed after refining the sample twice.

Structure and Optical Properties of Co-Sputtered Amorphous Silicon Tin Alloy Films for NIR-II Region Sensor.

Near-infrared brain imaging technology has great potential as a non-invasive, real-time inspection technique. Silicon-tin (SiSn) alloy films could be a promising material for near-infrared brain detectors. This study mainly reports on the structure of amorphous silicon tin alloy thin films by Raman spectroscopy to investigate the influence of doped-Sn on an a-Si network. The variations in TO peak caused by the increase in Sn concentration indicate a decrease in the short-range order of the a-Si network. A model has been proposed to successfully explain the non-linear variation in Raman parameters of ITA/ITO and ILA+LO/ITO. The variations of Raman parameters of the films with a higher deposition temperature indicate the presence of SiSn nanocrystals, though the SiSn nanocrystals present no Raman peaks in Raman spectra. XRD and TEM analysis further illustrate the existence of nanocrystals. The ratio of photo/dark conductivity and optical bandgap results demonstrate that the films can be selected as a sensitive layer material for NIR-II region sensors.

The Structure and Properties of Sn/SiSn-nanodisperse Alloy Thin Films

Near-infrared brain imaging technology has great advantages in brain imaging and inspection of brain disorders compared to traditional brain imaging technology. Silicon-tin (SiSn) alloys are expected to be the material for infrared brain imaging detectors. The structure and properties of the SiSn alloy thin films with relatively low Sn concentration, which are the key for it to be used in near-infrared brain imaging technology, have not been reported yet. Here, we report the deposition time, growth temperature, microstructure, resistivity, and transmittance of amorphous silicon-tin (a-Si1-xSnx) alloy thin films prepared by radio frequency (RF) magnetron sputtering. Reasonable deposition time and growth temperature for the preparation of the films are given in this paper. Sn nanocrystals are observed in the a-Si1-xSnx alloy thin films. The variations in resistivity and transmittance indicate that it has excellent electrical and optical properties so that it can be used as a near-infrared brain imaging detector material.

Microstructures and mechanical properties of ternary Ti–Si–Sn alloys

Titanium based alloys are one of the important structural materials with applications ranging from aerospace to biomedical industries. Several ternary Ti–Si–Sn alloys were explored in this study to design the microstructure comprising of binary and ternary eutectics corresponding to Ti–Si, Ti–Sn and Ti–Si–Sn system. The microstructural evolution in these alloys was studied using a combination of characterization techniques and thermodynamic calculations. The predicted solidification path from thermodynamic calculations well supported the experimental microstructural data. In addition, mechanical property and microstructure relationship were determined by performing hardness measurements and evaluating stress-strain curves under compression.

Tin-based donors in SiSn alloys

Tin-containing Group IV alloys show great promise for a number of next-generation CMOS-compatible devices. Not least of those are optoelectronic devices such as lasers and light-emitting diodes. To obtain reliable operation, a high control over the doping in such materials is needed at all stages of device processing. In this paper, we report tin-based donors in silicon, which appear after heat treatment of a silicon-tin alloy at temperatures between 650°C and 900°C. Two stages of the donor are observed, called SD I and SD II, which are formed subsequently. A broad long-lifetime infrared photoluminescence is also observed during the first stages of donor formation. We discuss evolving tin clusters as the origin of both the observed donors and the photoluminescence, in analogy to the oxygen-based thermal donors in silicon and germanium.

Effect of Zr addition on B-removal behaviour during solidification purification of Si with Si–Sn solvent

This paper details a novel attempt for B removal from Si by adding Zr as the trapping agent in solidification refining with Si–Sn solvent. The premise of the study is as follows: (i) B becomes more thermodynamically unstable in Si–Sn melt and (ii) Zr has a strong affinity for B, which is expected to enhance the formation of the B–Zr intermetallic compound. The B-removal mechanism is discussed from the aspects of theoretical analysis and experimental design. The effects of different variables, such as the moving direction, moving rate, Zr addition content, and initial Sn content in Si–Sn alloys, on the B-removal fraction are observed. Furthermore, the solubility product of the B–Zr compound in the Si–Sn melt is measured using equilibrium technology, to be ≥ 9.62 × 10−10 (1605 K, Si-50 at.% Sn) and ≥3.32 × 10−10 (1575 K, Si-65 at.% Sn). Enriched B and Zr regions are found in the mushy zone, but separated from each other. The maximum removal fraction of B is 73.6%; further, the added Zr is almost completely eliminated and does not contaminate the refined Si. This study provides an alternative perspective for B removal via Si–Sn solvent refining to produce solar-grade Si.