Impurities In Silicon Research Articles

The influence of impurity silicon on the adsorption of beryllium cluster toward carbon monoxide molecule

The influence of impurity silicon on the adsorption of beryllium cluster toward carbon monoxide molecule

Simultaneous removal of silicon impurities and hardness from high-temperature heavy-oil-produced-water by chemical coagulation-assisted electrocoagulation: Performance, kinetics, optimization and operational costs

To illustrate the effectiveness and optimize the simultaneous removal of silicon impurities (SiI) and hardness from high-temperature heavy-oil-produced-water (HPW) by chemical coagulation-assisted electrocoagulation (CC-EC) process, the laboratory test was employed for revealing the performance, fitting the kinetics, analysis of the reaction process and optimization of reaction conditions, while a well operation pilot-scale test was evaluated for operational costs. As the result, after optimization the removal rate of SiI and hardness was 97.3% and 98.4% in laboratory test, respectively, which was better than 84.0% and 96.0% by traditional treatment method, respectively. The power consumption of CC-EC was not significantly increased, while the coagulant consumption was reduced by 78% compared to the traditional treatment method. By reaction kinetics fitting with kinetic constant analysis, the synergy effect existed between CC and EC. The total operational costs of CC-EC process were 0.41 USD/m3 in the pilot-scale test, with a reduction of 34.86% compared to the traditional treatment method. CC-EC is a reliable treatment method for HPW reclaimed, so it has strong application potential in the treatment and reclaim of oilfield produced water and similar wastewater.

Carbon and Silicon Impurity Defects in GaN: Simulating Single-Photon Emitters by First Principles.

Defect single-photon emitters (SPE) in gallium nitride (GaN) have garnered great attentions in recent years due to the advantages they offer, including the ability to operate at room temperature, narrow emission linewidths, and high brightness. Nevertheless, the precise nature of the single-photon emission mechanism remains uncertain due to the multitude of potential defects that can form in GaN. In this work, our systematical investigation with the ab initio calculation indicates that carbon and silicon, as common dopants in gallium nitride, can interact with intrinsic defects in GaN and form new high-speed defect single-photon sources. Our findings identify a ternary defect NGaVNCN that possesses a short lifetime of less than 1 ns and a small zero-photon line (ZPL) of 864 nm. In other words, this defect can serve as a high-speed single photon source in the short wavelength window for fiber communication. In sharp contrast, the Si-supported defect NGaVNSiN has a higher unoccupied defect energy level which enters the conduction band and is therefore unsuitable for single photon emission. A systematic investigation has been conducted into the potential defects, thermal stability, and single-photon emission properties. The relaxation calculation and self-consistent calculations employed the Perdew-Burke-Ernzerhof exchange-correlation functional and Heyd-Scuseria-Ernzerhof exchange-correlation functional, respectively. These findings indicate the potential for high-performance single-photon sources through carbon or silicon doping of GaN.

Provably Trainable Rotationally Equivariant Quantum Machine Learning

Exploiting the power of quantum computation to realize superior machine learning algorithms has been a major research focus of recent years, but the prospects of quantum machine learning (QML) remain dampened by considerable technical challenges. A particularly significant issue is that generic QML models suffer from so-called barren plateaus in their training landscapes—large regions where cost function gradients vanish exponentially in the number of qubits employed, rendering large models effectively untrainable. A leading strategy for combating this effect is to build problem-specific models that take into account the symmetries of their data in order to focus on a smaller, relevant subset of Hilbert space. In this work, we introduce a family of rotationally equivariant QML models built upon the quantum Fourier transform, and leverage recent insights from the Lie-algebraic study of QML models to prove that (a subset of) our models do not exhibit barren plateaus. In addition to our analytical results we numerically test our rotationally equivariant models on a dataset of simulated scanning tunneling microscope images of phosphorus impurities in silicon, where rotational symmetry naturally arises, and find that they dramatically outperform their generic counterparts in practice. Published by the American Physical Society 2024

Deciphering the Polymorphism of CaSi2: The Influence of Heat and Composition.

The Zintl phase CaSi2 is a layered compound with stacking variants known as 1P, 3R, and 6R. We extend the series by the 21R polytype formed by rapid cooling of the melt. The crystal structure of 21R-CaSi2 (space group R3̅m) was derived from HRTEM images, and the atomic positions were optimized by using the FPLO code (a = 3.868 Å, c = 107.276 Å). We explore polytype transformations by powder X-ray diffraction (PXRD), transmission electron microscopy (TEM), scanning electron microscopy (SEM), electron backscattering diffraction (EBSD), and thermal analysis. While 6R-CaSi2 is thermodynamically stable at ambient conditions, nanosized impurities of silicon stabilize 3R-CaSi2 as a bulk phase.

Effect of growth rate on the incorporation of silicon impurity in single crystal diamond

In this paper, we systematically investigate the influence of growth rate on the incorporation of silicon in single crystal diamond. The intensity of SiV− center is significantly enhanced with the increase of methane flow rate. By analyzing the optical emission spectrum and photoluminescence spectrum of samples grown with different methane concentrations, the enhancement of SiV− intensity is not associated with the Si–C concentration in the precursor but with the higher growth rate. In addition, an increased oxygen flow rate significantly decreases the intensity of SiV− center, which is attributed to the formation of insoluble silicon oxide as well as the relatively lower growth rate. Finally, we propose a growth model to explain the effect of growth rate on the incorporation of silicon impurity.

Carbon-Isovalent Dopant Pairs in Silicon: A Density Functional Theory Study

Carbon (C) is an important isovalent impurity in silicon (Si) that is inadvertently added in the lattice during growth. Germanium (Ge), tin (Sn), and lead (Pb) are isovalent atoms that are added in Si to improve its radiation hardness, which is important for microelectronics in space or radiation environments and near reactors or medical devices. In this work, we have employed density functional theory (DFT) calculations to study the structure and energetics of carbon substitutional-isovalent dopant substitutional CsDs (i.e., CsGes, CsSns and CsPbs) and carbon interstitial-isovalent dopant substitutional CiDs (i.e., CiGes, CiSns and CiPbs) defect pairs in Si. All these defect pairs are predicted to be bound with the larger isovalent atoms, forming stronger pairs with the carbon atoms. It is calculated that the larger the dopant, the more stable the defect pair, whereas the CsDs defects are more bound than the CiDs defects.

Evaluation of defect density in bulk gallium nitrides by photothermal deflection spectroscopy and steady-state photocapacitance methods

Bulk GaN samples were characterized by both photothermal deflection spectroscopy (PDS) and steady-state photocapacitance (SSPC) methods. The PDS signal intensity in the bandgap was found to correlate quantitatively with the defect density estimated by the SSPC method. The defect density of GaN bulks fabricated by hydride vapor phase epitaxy (HVPE) was decreased by controlling the incorporation of carbon and silicon impurities. Differences in the reciprocal of the slope near the valence band maximum and the signal intensity in the bandgap among HVPE GaN bulks could be detected by PDS, although they had the same crystalline quality. PDS can be used to evaluate the GaN bulks that have been improved with a highly insulative property caused by Fe- doping or low carbon incorporation.

Industrial aluminum hydroxides: Part 1. Phase composition and textural characteristics of industrial aluminum hydroxides/oxides

The most common component in the design of heterogeneous catalysts for oil refining and petrochemistry are aluminum oxides. Each type of hydrocarbon raw materials and technological process corresponds to the optimal characteristics of aluminum oxide supports and catalysts: specific surface area, pore size, phase and impurity compositions. Due to the trend towards import substitution, the research of domestic producers of aluminum hydroxide used for the synthesis of aluminum oxides is becoming more relevant. In this work, domestic industrial samples of aluminum hydroxides were studied by methods of X-ray phase analysis, thermogravimetry combined with differential scanning calorimetry, low-temperature nitrogen adsorption and elemental analysis. It is established that the objects of research are most often phase-inhomogeneous, in which impurities of iron, silicon and calcium are present. The influence of the degree of crystallization and the size of the coherent scattering regions of aluminum hydroxides, mainly with the structure of boehmite and, in some cases, containing bayerite, on the textural characteristics of the resulting aluminum oxides is shown.

Space charge region recombination in highly efficient silicon solar cells

The recombination rate in the space charge region (SCR) of a silicon-based barrier structure with a long Shockley–Reed–Hall lifetime is calculated theoretically by taking into account the concentration gradient of excess electron-hole pairs in the base region. Effects of the SCR lifetime and applied voltage on the structure ideality factor have been analyzed. The ideality factor is significantly reduced by the concentration gradient of electron-hole pairs. This mechanism provides an increase of the effective lifetime compared to the case when it is insignificant, which is realized at sufficiently low pair concentrations. The theoretical results have been shown to be in agreement with experimental data. A method of finding the experimental recombination rate in SCR in highly efficient silicon solar cells (SCs) has been proposed and implemented. It has been shown that at the high excess carrier concentration exceeding 1015 cm–3 the contribution to the SCR recombination velocity from the initial region of SCR that became neutral is significant. From a comparison of theory with experiment, the SCR lifetime and the ratio of the hole to the electron capture cross sections are determined for a number of silicon SCs. The effect of SCR recombination on the key characteristics of highly efficient silicon SCs, such as photoconversion efficiency and open-circuit voltage, has been evaluated. It has been shown that they depend not only on the charge carrier lifetime in SCR, but also on the ratio of hole to electron capture cross sections σp /σn. When σp /σn < 1, this effect is significantly strengthened, while in the opposite case σp /σn > 1 it is weakened. It has been ascertained that in a number of highly efficient silicon SCs, the distribution of the inverse lifetime in SCR is described by the Gaussian one. The effect described in the paper is also significant for silicon diodes with a thin base, p-i-n structures, and for silicon transistors with p-n junctions. In Appendix 2, the need to take into account the lifetime of non-radiative excitonic Auger recombination with participation of deep impurities in silicon is analyzed in detail. It has been shown, in particular, that considering it enables to reconcile the theoretical and experimental dependences for the effective lifetime in the silicon bulk.

Central-cell corrections for hydrogenic, silicon (Si), selenium (Se), sulfur (S), and germanium (Ge) donor impurities and pressure–temperature effects on the optical properties of the GaAs/GaAlAs multi-layer quantum disk

GaAs/GaAlAs quantum dots can be doped with various impurities to modify their optoelectronic properties. Common impurities used for doping include: Hydrogenic impurity (HI), Silicon (Si), Selenium (Se), Germanium (Ge), and Sulfur (S) are common n-type dopant in GaAs-based materials. This work has investigated the effects of temperature and pressure on the refractive index changes (RICs) and optical absorption coefficients (OACs) in the multi-layer quantum disk, accounting for central cell correction. We have used the finite element method to calculate the eigenvalues and their corresponding wave-functions. These values are utilized in the computation of the OACs and RICs. Our outcomes can be summarized as follows: (i) The applied pressure induces a red-shift of the OACs peaks, and their magnitude is reduced. Similarly, temperature causes a blue-shift of the OACs peaks, and their magnitude is enhanced. (ii) The presence and type of impurity lead to significant changes in both OACs and RICs.

PBr3 adsorption on a chlorinated Si(100) surface with mono- and bivacancies.

For the most precise incorporation of single impurities in silicon, which is utilized to create quantum devices, a monolayer of adatoms on the Si(100) surface and a dopant-containing molecule are used. Here, we studied the interaction of phosphorus tribromide with a chlorine monolayer with mono- and bivacancies using a scanning tunneling microscope (STM) at 77K. The combination of different halogens in the molecule and the adsorbate layer enabled unambiguous identification of the structures after PBr3 dissociation on Si(100)-Cl. A Cl monolayer was exposed to PBr3 in the STM chamber, which allows us to compare the same surface areas before and after PBr3 adsorption. As a result of this comparison, we detected small changes in the chlorine layer and unraveled the molecular fragments filling mono- and bivacancies. Using density functional theory, we found that the phosphorus atom occupies a bridge position after dissociation of the PBr3 molecule, which primarily bonds with silicon in Cl bivacancies. These findings provide insight into the interaction of a dopant-containing molecule with an adsorbate monolayer on Si(100) and can be applied to improve the process of single impurity incorporation into silicon.

Studying on mineralogical and petrological characteristics of Gara Djebilet oolitic iron ore, Tindouf (Algeria)

Demand for iron ore worldwide has been steadily increasing which leads to the extraction of iron ore deposits with more complex mineralogies and higher levels of silicon and phosphorus impurities. This is the case in Algeria with the iron ore deposit of Gara Djebilet, Tindouf; where it has recently been exploited to ensure the sufficiency of iron ore required to produce iron and steel products. This deposit has remained unexploited for several decades due to inadequate knowledge of its mineralogy, treatment, and economic assessments. The aim of this study is to find out the microstructure, chemical composition, and mineralogical distribution of valuable minerals and impurities, to understand the efficient processing methods for this specific iron ore. The characterization of representative ironstone samples taken from the studied area was carried out using optical microscopy, X-ray fluorescence spectrometer (XRF), petrographic microscope, X-ray diffractometer (XRD), and scanning electron microscope (SEM) coupled with energy dispersive X-ray spectroscopy (EDS). The results of the mineralogical analyses confirmed that it is an oolitic fine-grained ore consisting of gangue minerals principally composed of quartz, apatite, and iron-rich concentric cored structures. Chemical analyses of the ore indicate that it contains 56.58 wt% Fe with 7.98 wt% SiO2, 7.09 wt% Al2O3, and minor amounts of P2O5, CaO, MgO, and TiO2 compounds. The phosphorus associated was present in both ooids and groundmass, indicating that the ore has a complex texture with very rich and diverse mineralogy. For that, two potential scenarios were proposed for processing of the studied iron ore.

Removal of metal impurities from diamond wire saw silicon powder by vacuum electromagnetic directional solidification

The utilization of high-purity silicon (∼99.9999 %) is prevalent in the solar photovoltaic sector, and achieving a reduction in its cost has emerged as a pivotal engineering objective within the silicon solar industry. Recycling silicon from diamond wire saw silicon powder (DWSSP) is a promising solution to fulfill the continuously expanding of high purity silicon demand. Vacuum directional solidification technology using high-frequency electromagnetic induction heating was proposed to purify DWSSP for the first time efficiently. The silicon melt and gas interface reaction, as well as metal impurities’ microsegregation in silicon ingot were observed. The effects of vacuum level and electromagnetic force on the separation of silicon and metal impurities were investigated using thermodynamics and electromagnetic mechanics. Results indicate that the content of oxygen in the silicon reduced from 30.91 wt% to 5.08 wt%, and the actual sample composition including for uptake of residual gas contamination steadily declined as the vacuum level increased from 600 Pa to 10 Pa. Vacuum electromagnetic directional solidification reduced the content of metal impurities from 641 ppmw to 29.80 ppmw, increases the proportion of crystalline silicon area, and makes the silicon lattice arrangement more regular.

Electron Spin-Lattice Relaxation of Substitutional Nitrogen in Silicon: The Role of Disorder and Motional Effects.

In a previous investigation, the authors proposed nitrogen as a possible candidate for exploiting the donor spin in silicon quantum devices. This system is characterized by a ground state deeper than the other group V impurities in silicon, offering less stringent requirements on the device temperature necessary to access the unionized state. The nitrogen donor is slightly displaced from the substitutional site, and upon heating, the system undergoes a motional transition. In the present article, we show the results from our investigation on the spin-relaxation times in natSi and 28Si substrates and discuss the motional effects on relaxation. The stretched exponential relaxation observed is interpreted as a distribution of spin-lattice relaxation times, whose origin is also discussed. This information greatly contributes to the assessment of a nitrogen-doped silicon system as a potential candidate for quantum devices working at temperatures higher than those required for other group V donors in silicon.

Hydrogen Reactions with Dopants and Impurities in Solar Silicon from First Principles

A theoretical account of some of the most likely hydrogen‐related reactions with impurities in n‐ and p‐type solar‐grade silicon is presented. These include reactions with dopants and carbon, which are relevant in the context of lifetime degradation of silicon solar cells, most notably of light‐ and elevated temperature‐induced degradation of the cells. Among the problems addressed, a comparative study of acceptor‐enhanced dissociation of hydrogen molecules in B‐ and Ga‐doped material, their subsequent reaction steps toward formation of acceptor–hydrogen pairs, the proposal of mechanisms which explain the observed kinetics of photo‐/carrier‐induced dissociation of PH and CH pairs in n‐type Si, analysis of reactions involving direct interactions between molecules with P and C, and the assignment of several electron and hole traps with detailed atomistic‐ and wavefunction‐resolved models is highlighted.

Recovery of tungsten from spent selective catalytic reduction catalyst by sulfuric acid precipitation and evaporation crystallization method

AbstractBACKGROUNDSelective catalytic reduction (SCR) can effectively handle NOx from flue gas in coal‐fired power plants. However, as the core part of the SCR method, V2O5–WO3/TiO2 catalyst has a limited operational life in the complex flue gas environment. The recovery of rare metals from spent catalyst would not only bring economic benefits but also solve environmental problems. The process of reducing acid leaching and further roasting‐water leaching could realize the efficient recycling of vanadium, tungsten and titanium.RESULTSAfter reducing acid leaching and roasting‐water leaching to treat spent SCR catalyst, the obtained solution containing tungsten was used as the raw material in this study. The optimal pH value of solution for removal of silicon and aluminum impurities was 9.2–9.5. The best tungsten precipitation conditions were shown as follows: a tungsten concentration of 30 g L−1, a sulfuric acid concentration of 8 mol L−1, reaction temperature of 70 °C and reaction time of 2 h. Under the optimal tungsten precipitation conditions, the tungsten precipitation efficiency can reach 92.53%. Finally, in order to further improve the purity of the crude H2WO4, the crude H2WO4 was fully dissolved in ammonia, followed by filtration and evaporation crystallization to obtain 5(NH4)2O.12WO3.5H2O (APT) crystals with a purity of 93.05 wt%. The crystallization efficiency of APT was 73.37% at 60 °C for 2 h with a rotor speed of 400 rpm.CONCLUSIONThese results indicated that a higher purity of APT crystals can be obtained by the steps of removing silicon and aluminum, precipitation of tungsten by sulfuric acid, ammonia dissolution and evaporation crystallization. © 2023 Society of Chemical Industry (SCI).

Electrical properties of silicon-implanted β-Ga2O3:Fe crystals

Ion implantation is a promising method for the development of β-Ga2O3-based technologies and devices. However, the physical principles of ion implantation for this particular semiconductor are still at the early stage of development. One of the primary tasks is the study of electrical properties of the ion-doped layers. In this work, we have investigated the electrical parameters of layers produced by ion implantation of a shallow donor impurity—silicon—into a semi-insulating β-Ga2O3 doped with iron and having a surface orientation of (−201). It is established that the activation efficiency of the implanted impurity significantly exceeds unity after post-implantation annealing at high temperatures. This indicates that not only silicon itself contributes to conductivity, but also defects formed with its (and, probably, iron) participation are involved. The temperature dependence of electron mobility is consistent with the theoretically calculated one under the assumption that, apart from shallow donors, there are also deep defect-associated donors and acceptors. It is assumed that the established properties are specific for the case of direct Si implantation into β-Ga2O3 doped with Fe.

Removal of impurities from Metallurgical silicon by adding ZnO and BaO to the CaO–SiO2 slag system

One of the essential techniques for eliminating metallurgical silicon impurities during a metallurgical process is slag refining. In the present investigation, BaO and ZnO were added to a binary slag system composed of CaO–SiO2 in weight percentages that varied from 5 to 20 %, and the effects of various slag system compositions, Slag-Si mass ratios (slag-silicon ratios), and refining times on the content of metallurgical silicon impurities were investigated. The mass transfer coefficients βAl and βB for Al and B were 3.01×10−6m·s−1, 6.80×10−7m·s−1, respectively, and the apparent rate constants (kB, kAl) of Al and B obtained for the refining time were 3.84×10−4s−1 and 8.67×10−5s−1, respectively, The experimental results show that in the slagging refining process, the loss rate of silicon increases slightly with the extension of the refining time and is much smaller than that of the blowing refining, so it can be considered to be a more superior method of removing impurities from industrial silicon.

Study on the characteristics of Si-doped diamond synthesized by different iron-based catalyst systems under high temperature and pressure

This article investigates the effects of different iron based catalysts on the morphology and quality characteristics of diamond single crystals synthesized in high-temperature and high-pressure environments. The results indicated that incorporating silicon impurities led to defects in diamond crystals, increased internal stress in the lattice, and decreased crystal quality. In addition, there are also differences in the synthesis of silicon doped diamonds under different iron based catalyst systems. This manuscript uses optical microscopy, scanning electron microscopy and Raman spectroscopy to characterize diamond crystals, exploring the influence of catalyst differences on the structure of silicon-doped diamonds. At the same time, simulation analysis was conducted on the convective field of the catalyst in the diamond synthesis chamber, and the convective field characteristics of silicon doped diamond growth under different iron based catalysts were established. The simulation results are consistent with the synthesis experimental work. This work provides a new approach to improve the quality of silicon doped diamond single crystals.