Germanium Alloys Research Articles

Genetic-algorithm-combined density functional theory calculations for investigating atomic properties of Si−Ge alloys

Compound semiconductors are expected to expand the possibilities of semiconductor applications. In particular, Ⅳ−Ⅳ compound semiconductors, such as silicon−germanium (Si−Ge) alloys, have received much attention over the past several decades. Although many scholars have conducted experiments on Si−Ge alloys, few scholars have conducted theoretical simulations on them. Thus, fundamental understanding of nanoscale phenomena in the Si−Ge alloys is still insufficient. To address this problem, we identified energetically stable structures of the Si−Ge alloys using density-functional-theory (DFT) first-principles calculations and genetic algorithm (GA) and evaluated various properties of the Si−Ge alloys. We confirmed that the formation energies of the stable structures identified by GA-combined DFT calculations were lower than those of other Si−Ge alloys registered in an existing crystal structure database. The lattice constants and electronic band gaps of these stable structures were evaluated using DFT calculations, and trends in their properties similar to those reported in previous experimental studies were verified. From the evaluation of coordination number according to the Boltzmann distribution, we found that homoelement bonds (Si–Si and Ge−Ge) are easier to form than heteroelement bonds (Si−Ge) in the stable structures of Si−Ge alloys at any composition.

Photothermal Conversion and Laser-Induced Transformations in Silicon–Germanium Alloy Nanoparticles

Photothermal Conversion and Laser-Induced Transformations in Silicon–Germanium Alloy Nanoparticles

Laser‐Annealed SiO2/Si1−xGex Scaffolds for Nanoscaled Devices, Synergy of Experiment, and Computation

Laser‐Annealed SiO₂/Si_1−<i>x</i>Ge_<i>x</i> Scaffolds for Nanoscaled Devices, Synergy of Experiment, and Computation

Improving the performance of kesterite solar cells by solution germanium alloying.

Cation substitution is an effective strategy to regulate the defects/electronic properties of kesterite Cu2ZnSn(S,Se)4 (CZTSSe) absorbers and improve the device photovoltaic performance. Here, we report Ge alloying kesterite Cu2Zn(Sn,Ge)(S,Se)4 (CZTGSSe) via a solution approach. The results demonstrate that the same chemical reaction of Ge4+ to Sn4+ ensures homogeneous Ge incorporation in the whole range of concentrations (from 0 to unit). Ge alloying promotes grain growth and linearly enlarges the absorber band gap by solely raising the conduction band minimum, which maintains a "spike" conduction band offset at the heterojunction interface until 15% alloying concentration and thus facilitates effective charge carrier collection. A promising efficiency of 11.57% has been achieved at 15% Ge alloying concentration with a significant enhancement in open-circuit voltage and fill factor. By further 10% Ag alloying to improve the absorber film morphology, a champion device with an efficiency of 12.25% has been achieved without an antireflective coating. This result emphasizes the feasibility of achieving homogeneous and controllable Ge alloying of kesterite semiconductors through the solution method, paving the way for further improvement and optimization of device performance.

Improved CZTSe solar cell efficiency via silver and germanium alloying

In this study, we report systematic investigation of the effects of Ag and Ge alloying on properties of CZTSe layers, as well as, on the performance of solar cells fabricated using these films. In this context, Ag-Ge doped CZTSe layers were produced by selenization of Cu/Sn/Zn/Cu/(Ag,Ge)/Se precursor stack structures using rapid thermal processing. All precursor stacks and the Ag-Ge doped CZTSe films obtained after selenization exhibited (Cu + Ag)-poor and Zn-rich chemical composition. XRD studies demonstrated pure kesterite phase for all reacted films. Raman spectra confirmed this finding. Cross-sectional SEMs showed large grain structure, which resulted from Ag-Se and Ge-Se liquid phase formation that assisted crystal growth during high temperature annealing. While a slight Ag-front-gradient was achieved in Ag-doped CZTSe film, the Ag gradient disappeared with incorporation of Ge into the lattice. Addition of Ge formed a gradient within the material such that near-contact region was more Ge-rich. Solar cells fabricated using films with various compositions demonstrated that double doping CZTSe with both Ag and Ge improved the device efficiency from about 5 % to over 8 %.

Effect of Field Annealing on Magnetic Properties of Magnetic Soft Iron–Germanium Alloys

Abstract—The concentration dependence of the magnetic properties of iron–germanium alloys before and after thermomagnetic treatment, which represents an annealing of alloy samples in the ferromagnetic state in a permanent or alternating magnetic field (magnetic field annealing – MFA), has been investigated. It is shown that before MFA, with an increase in the germanium content in the range of 3–30 at % Ge, the coercive force increases and the residual induction decreases. As a result of thermomagnetic treatment, in the alloy samples magnetic anisotropy is induced: the magnetic hysteresis loops become narrower, the residual induction increases, and the coercive force decreases. Thermomagnetic treatment is effective for Fe–Ge alloys with a germanium content from 6 to 18 at %, and its highest efficiency is observed at 12 at % Ge. Features of the structural state of iron–germanium alloys and their role in the formation of magnetic properties during annealing in a magnetic field are discussed.

Minimum entropy production in inhomogeneous thermoelectric materials

Due to their potential applications in energy production based on waste heat, direct solar radiation or other energy sources, semiconductor materials have for years attracted the attention of theoretical and experimental researchers. The focus has been on improving the performance of thermoelectric devices through several strategies and special interest has been placed on materials with spatially inhomogeneous transport properties. Inhomogeneity can be achieved in various ways, all of them leading, to a greater or lesser extent, to an improvement of the thermoelectric performance. In this paper, general linear heat and electric charge transport processes in inhomogeneous materials are addressed. The guiding idea followed here is that there exists a relationship between inhomogeneity (structuring), minimum entropy production and performance which may be fruitfully exploited for designing more efficient thermoelectric semiconductor devices. We first show that the stationary states of such materials are minimum global entropy production states. This constitutes an extension of the validity of Prigogine’s minimum entropy principle. The heat and charge transport equations obtained within the framework of classical irreversible thermodynamics are solved to find the stationary profiles of temperature and self-consistent electric potential in a one-dimensional model of a silicon–germanium alloy subjected to an external temperature difference. This allows us to assess the effect of the spatial inhomogeneity on the thermoelectric performance. We find that, regardless of the value of the applied temperature difference, the system may efficiently operate in a regime of minimum entropy production and high efficiency.

Effect of Magnetic Field Annealing on the Magnetic Properties of Soft-Magnetic Iron–Germanium Alloys

Effect of Magnetic Field Annealing on the Magnetic Properties of Soft-Magnetic Iron–Germanium Alloys

3D printing of bulk thermoelectric materials: Laser powder bed fusion of N-type silicon germanium

Among Additive Manufacturing (AM) methods, Laser Powder Bed Fusion (L-PBF), also called Selective Laser Melting (SLM), is prevalent to printing complex metal parts in small and medium series. Recent studies in L-PBF processing develops the manufacturing of new materials, including thermoelectric (TE) materials. This study presents manufacturing of an N type Si80Ge20 powder by L-PBF. Silicon germanium alloy is a TE material intended for high temperature applications. It is the first time that this semiconductor material is studied by AM technology. Dense samples of various shapes and sizes were produced, and a first process window was identified. Structural analyses have been performed, highlighting good densification. Unfortunately, mechanical cracking occurs in all samples. TE properties were investigated on as built samples, displaying low values (ZT = 0.11 at 600 °C), due to poor electrical conductivity. Overall, these results show that L-PBF of silicon germanium is possible, which could open up its scope of applications.© 2023 Published by Elsevier Ltd. Selection and/or peer-review under responsibility of Materials science in semiconductor processing.

Impact of Sn incorporation on sputter epitaxy of GeSn

Epitaxial growth of high-quality low tin content germanium (GeSn) alloy is demonstrated by sputter deposition. Adding several percent of Sn during simultaneous sputter deposition significantly improved the crystallographic structure of the GeSn alloy, leading to intense photoluminescence even at room temperature. Dislocation-free single-crystal GeSn films were formed on a Ge(100) substrate under tuned growth conditions, that is, an Sn/Ge flux ratio of 6.2% and deposition temperature of 500 °C, in which compositional gradation of the Sn content in the film thickness direction spontaneously formed. The growth mechanisms are discussed based on growth kinetics and Sn diffusion on the growing surface.

Atomic simulation of crystal orientation and workpiece composition effect on nano-scratching of SiGe alloy

Silicon–germanium (SiGe) alloy is a new semiconductor material of great interest in thermoelectric devices, optoelectronic devices, infrared detectors, and semiconductor industry. In the present work, molecular dynamics simulation was conducted to investigate the deformation behavior in nano-scratching of SiGe alloy. The effect of scratching direction and Ge composition on material removal mechanism was discussed, aiming to understand the nanoscale deformation mechanism of SiGe alloy. The simulation results indicate that the machining direction and Ge composition have significant influences on the atomic flow and chip formation during nano-scratching. Besides, less subsurface damage and elastic recovery are observed when scratching along the (011)[100] direction with higher Ge composition. The highest crystal purity of the machined surface is achieved when scratching on the Si60Ge40 workpiece. Furthermore, the Ge composition has a significant influence on the workpiece temperature due to the variation of the thermal conductivity of the workpiece. This work could enrich the understanding of the deformation mechanism of SiGe alloy during nanoscale machining and open a potential to improve the machining performance of multicomponent semiconductor materials.

Enhancement of thermoelectric performance in n-type Si90Ge10-based alloy by metallic Zn doping

Silicon–germanium (SiGe) alloy has become one of the representative high-temperature thermoelectric (TE) materials due to its advantages of stability, non-toxicity, oxidation resistance, and high mechanical strength. However, the high thermal conductivity and expensive Ge greatly limit the enhancement of zT value and its application. In this paper, n-type Si90Ge10P2Znx nanocomposites were prepared by ball milling and spark plasma sintering. By adjusting the Zn content and sintering time, multiple phonon-scattering centers, such as Zn precipitates, nano-pores, and layered structures, have been introduced into the SiGe matrix. The thermal conductivity was significantly reduced to 2.59 W m−1 K−1 without deteriorate power factor (PF), thus leading to a high zT value of 1.23 at 873 K. At 323–873 K, the average zT value (zTavg) also reached 0.6, increased by approximately 25% in comparison to the reported value using the same ratio of Si90Ge10. Compared with the conventional radioisotope TE generator with Si80Ge20 composition, the zTavg value increased by nearly 30% with only half of Ge, giving strong impetus to the application of SiGe-based TE materials.

Recent Progress of Supercontinuum Generation in Nanophotonic Waveguides

AbstractSupercontinuum (SC) has opened up possibilities for numerous applications in optical communications, signal processing, metrology, and spectroscopy. Supercontinuum generation (SCG) in the integrated nonlinear platforms has attracted much interest recently, due to its fundamental advantages in terms of complementary metal oxide semiconductor compatibility, low power consumption, compact size, and cost‐effectiveness. In this paper, the latest progress on various types of nanophotonic waveguides for SCG is reviewed. The material properties of silicon, germanium, silicon–germanium alloy, silicon nitride, silica, chalcogenide, III–V materials, lithium niobate, and other materials, which are used as nonlinear media for SCG are discussed. The wavelength‐dependent nonlinear Kerr index, material, and nonlinear loss of the waveguides are taken into account. This review mainly focuses on the SCG resulting from the cubic χ(3) nonlinearity processes pumped by the femtosecond pulse. The recent representative SCG works based on the integrated optical waveguides are summarized, and further classified according to the dispersion characteristics. Furthermore, different types of spectra broadening mechanisms in details according to the classifications are analyzed. Perspectives on the SC spectral coverage, the realization of various dispersion curves, and the novel materials, which are the key aspects of the SCG in nanophotonic waveguides are provided.

Lithiophilic Nanowire Guided Li Deposition in Li Metal Batteries.

Lithium (Li) metal batteries (LMBs) provide superior energy densities far beyond current Li-ion batteries (LIBs) but practical applications are hindered by uncontrolled dendrite formation and the build-up of dead Li in "hostless" Li metal anodes. To circumvent these issues, wecreated a 3D framework of a carbon paper (CP) substrate decorated with lithiophilic nanowires (silicon (Si), germanium (Ge), and SiGe alloy NWs) that provides a robust host for efficient stripping/plating of Li metal. The lithiophilic Li22 Si5 , Li22 (Si0.5 Ge0.5 )5, and Li22 Ge5 formed during rapid Li melt infiltration prevented the formation of dead Li and dendrites. Li22 Ge5 /Li covered CP hosts delivered the best performance, with the lowest overpotentials of 40mV (three times lower than pristine Li) when cycled at 1mA cm-2 /1 mAh cm-2 for 1000h and at 3mA cm-2 /3 mAh cm-2 for 500h. Exsitu analysis confirmed the ability of the lithiophilic Li22 Ge5 decorated samples to facilitate uniform Li deposition. When paired with sulfur, LiFePO4, and NMC811 cathodes, the CP-LiGe/Li anodes delivered 200 cycles with 82%, 93%, and 90% capacity retention, respectively. The discovery of the highly stable, lithiophilic NW decorated CP hosts is a promising route toward stable cycling LMBs and provides a new design motif for hosted Li metal anodes.

Approximation of Composition and Temperature Dependent Heat Conductivity and Optimization of Thermoelectric Energy Conversion in Silicon–Germanium Alloys

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

New and Recent Results for Thermoelectric Energy Conversion in Graded Alloys at Nanoscale.

In this article, we review the main features of nonlocal and nonlinear heat transport in nanosystems and analyze some celebrated differential equations which describe this phenomenon. Then, we present a new heat-transport equation arising within the so-called thermomass theory of heat conduction. We illustrate how such a theory can be applied to the analysis of the efficiency of a thermoelectric energy generator constituted by a Silicon–Germanium alloy, as the application and new results for a nanowire of length nm, are presented as well. The thermal conductivity of the nanowire as a function of composition and temperature is determined in light of the experimental data. Additionally, the best-fit curve is obtained. The dependency of the thermoelectric efficiency of the system on both the composition and the difference of temperature applied to its ends is investigated. For the temperatures K, K, and K, we calculate the values of the composition corresponding to the optimal efficiency, as well as the optimal values of the thermal conductivity. Finally, these new results are compared with recent ones obtained for a system of length mm, in order to point out the benefits due to the miniaturization in thermoelectric energy conversion.

Gamma, X-ray, and neutron shielding properties of silicon–germanium alloys

This work focuses on the gamma/X-ray and neutron shielding properties of silicon–germanium alloys in different compositions such as Si0.1Ge0.9 (SG1), Si0.2Ge0.8, Si0.4Ge0.6, Si0.6Ge0.4, Si0.8Ge0.2, and Si0.9Ge0.1. Among all the selected alloys, SG1 has less half-value thickness, tenth-value thickness, and penetration depth, whereas specific gamma-ray constant, Zeff, electron density, radiation protection efficiency, and kinetic energy released in matter have larger values compared to the other studied alloys. The neutron shielding parameters, such as coherent neutron scattering length, incoherent neutron scattering length, coherent neutron scattering cross-section, and incoherent neutron scattering cross-sections are smaller for the SG1 alloy than the other studied alloys. Furthermore, total neutron scattering cross-section and neutron absorption cross-section are found to be larger for SG1 than the other studied alloys. Based on gamma/X-ray and neutron shielding parameter analysis, we have suggested a shielding material consisting of ordinary concrete and SG1 alloy of particular thickness to cease X-ray/gamma-ray and neutron radiation. By analyzing all these parameters, we suggest that the SG1 alloy might be a good shielding material for X-rays/gamma-rays and for neutrons compared to other selected alloys.

Hopping charge transport in hydrogenated amorphous silicon–germanium alloy thin films

Measurements of the dark conductivity and thermoelectric power in hydrogenated amorphous silicon–germanium alloys (a-Si1-xGex:H) reveal that charge transport is not well described by an Arrhenius expression. For alloys with concentrations of Ge below 20%, anomalous hopping conductivity is observed with a power-law exponent of 3/4, while the temperature dependence of the conductivity of alloys with higher Ge concentrations is best fit by a combination of anomalous hopping and a power-law temperature dependence. The latter has been attributed to charge transport via multi-phonon hopping. Corresponding measurements of the Seebeck coefficient reveal that the thermopower is n-type for the purely a-Si:H and a-Ge:H samples but that it exhibits a transition from negative to positive values as a function of the Ge content and temperature. These findings are interpreted in terms of conduction via hopping through either exponential band tail states or dangling bond defects, suggesting that the concept of a mobility edge, accepted for over five decades, may not be necessary to account for charge transport in amorphous semiconductors.

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.

Study of machining accuracy in ultrasonic elliptical vibration cutting of alloyed iron alloy carbon with a germanium

Engineering materials refers to the group of materials that are used in the construction of manmade structures and components. The primary function of an engineering material is to withstand applied loading without breaking and without exhibiting excessive deflection. The major classifications of engineering materials include metals, polymers, ceramics, and composites. The germanium is an excellent material for infrared optical devices, whereas ultraprecision micro-machining of the germanium is difficult due to its brittleness. In Uzbekistan, alloyed engineering materials are mainly produced by the “Almalyk” plant and “Navoi” plant. Mechanical processing of these materials is one of the problems of today. The article analyzes the process of ultrasonic vibration treatment of an alloyed iron alloy carbon with a germanium alloy. Experiments were carried out in the mechanical processing departments of the plant "Almalyk". Graphs are given based on the results obtained. Based on the results of the experiment, the conclusion was given.