Si Impurities Research Articles

Etched-And-Regrown GaN P-N Diodes with Low-Defect Interfaces Prepared by In Situ TBCl Etching.

The ability to form pristine interfaces after etching and regrowth of GaN is a prerequisite for epitaxial selective area doping, which in turn is needed for the formation of lateral PN junctions and advanced device architectures. In this work, we report the electrical properties of etched-and-regrown GaN PN diodes using an in situ Cl-based precursor, tertiary butylchloride (TBCl). We demonstrated a regrowth diode with I-V characteristics approaching that from a continuously grown reference diode. The sources of unintentional contamination from the silicon (Si) impurity and the mediating effect of Si during the TBCl etching are also investigated in this study. This work points to the potential of in situ TBCl etching toward the realization of GaN lateral PN junctions.

Tuning band alignment at a semiconductor-crystalline oxide heterojunction via electrostatic modulation of the interfacial dipole

We demonstrate that the interfacial dipole associated with bonding across the SrTiO3/Si heterojunction can be tuned through space charge, thereby enabling the band alignment to be altered via doping. Oxygen impurities in Si act as donors that create space charge by transferring electrons across the interface into SrTiO3. The space charge induces an electric field that modifies the interfacial dipole, thereby tuning the band alignment from type-II to type-III. The transferred charge, resulting in built-in electric fields, and change in band alignment are manifested in electrical transport and hard x-ray photoelectron spectroscopy measurements. Ab initio models reveal the interplay between polarization and band offsets. We find that band offsets can be tuned by modulating the density of space charge across the interface. Functionalizing the interface dipole to enable electrostatic altering of band alignment opens new pathways to realize novel behavior in semiconducting heterojunctions.

Facile and reproducible method of stabilizing hbox {Bi}_2hbox {O}_3 phases confined in nanocrystallites embedded in amorphous matrix

Bismuth sesquioxide (hbox {Bi}_2hbox {O}_3) draws much attention due to wide variety of phases in which it exists depending on the temperature. Among them, delta phase is specially interesting because of its high oxide ion conductivity and prospects of applications as an electrolyte in fuel cells. Unfortunately, it is stable only in a narrow temperature range ca. 730–830 ^{circ }C. Our group has developed a facile and reproducible two-stage method of stabilizing hbox {Bi}_2hbox {O}_3 crystalline phases confined in nanocrystallites embedded in amorphous matrix. In the first stage, glassy materials were obtained by a routine melt-quenching method: pure hbox {Bi}_2hbox {O}_3 powders were melted in porcelain crucibles and fast-cooled down to room temperature. In the second step, the materials were appropriately heat-treated to induce formation of crystallites of beta, delta or gammahbox {Bi}_2hbox {O}_3 phases confined in a glassy matrix, depending on the process conditions. It was found out that the vitrification of the initial hbox {Bi}_2hbox {O}_3 and the subsequent nanocrystallization were unexpectedly possible due to the presence of some Al, and Si impurities from the crucibles. Systematic DTA, XRD, optical, Raman and SEM/EDS studies were carried out to investigate the influence of the syntheses processes and allowed us to determine conditions under which the particular phases appear and remain stable down to room temperature.

First-principle study on the influence of common impurities in diamond on the electronic structure of Ce-related defects

This paper determines the stable configuration and electronic structure of Ce-related defects (CeV) in diamonds doped with N, B, and Si impurities using the first-principle method based on density functional theory (DFT) and the Vienna ab-initio simulation package VASP software package. To this end, the zero-phonon line size of the color center of the doped diamond CeV is calculated and the corresponding fluorescence wavelength is measured. The results provide a theoretical explanation of the influence of various impurities on the fluorescence of the CeV color center in diamonds and provides a reference for their fabrication and application.

Single Indium Atoms and Few-Atom Indium Clusters Anchored onto Graphene via Silicon Heteroatoms.

Single atoms and few-atom nanoclusters are of high interest in catalysis and plasmonics, but pathways for their fabrication and placement remain scarce. We report here the self-assembly of room-temperature-stable single indium (In) atoms and few-atom In clusters (2–6 atoms) that are anchored to substitutional silicon (Si) impurity atoms in suspended monolayer graphene membranes. Using atomically resolved scanning transmission electron microscopy (STEM), we find that the symmetry of the In structures is critically determined by the three- or fourfold coordination of the Si “anchors”. All structures are produced without electron-beam induced materials modification. In turn, when activated by electron beam irradiation in the STEM, we observe in situ the formation, restructuring, and translation of the Si-anchored In structures. Our results on In–Si-graphene provide a materials system for controlled self-assembly and heteroatomic anchoring of single atoms and few-atom nanoclusters on graphene.

Single indium atoms and few-atom indium clusters anchored onto graphene via silicon heteroatoms

Single atoms and few-atom nanoclusters are of high interest in catalysis and plasmonics, but pathways for their fabrication and stable placement remain scarce. We report here the self-assembly of room-temperature-stable single indium (In) atoms and few-atom In clusters (2-6 atoms) that are anchored to substitutional silicon (Si) impurity atoms in suspended monolayer graphene membranes. Using atomically resolved scanning transmission electron microscopy (STEM), we find that the exact atomic arrangements of the In atoms depend strongly on the original coordination of the Si anchors in the graphene lattice: Single In atoms and In clusters with 3-fold symmetry readily form on 3-fold coordinated Si atoms, whereas 4-fold symmetric clusters are found attached to 4-fold coordinated Si atoms. All structures are produced by our fabrication route without the requirement for electron-beam induced materials modification. In turn, when activated by electron beam irradiation in the STEM, we observe in situ the formation, restructuring and translation dynamics of the Si-anchored In structures: Hexagon-centered 4-fold symmetric In clusters can (reversibly) transform into In chains or In dimers, whereas C-centered 3-fold symmetric In clusters can move along the zig-zag direction of the graphene lattice due to the migration of Si atoms during electron-beam irradiation, or transform to Si-anchored single In atoms. Our results provide a novel framework for the controlled self-assembly and heteroatomic anchoring of single atoms and few-atom clusters on graphene.

Al/SiC nanocomposites with enhanced thermomechanical properties obtained from microwave plasma-treated nanopowders

Al-based composites with enhanced thermomechanical properties are in high demand. However, obtaining a uniform distribution of the strengthening phase in the metal matrix and achieving a strong metal/ceramic interface is still a great challenge. In this work, nanoAl/nanoSiC powder mixtures after high-energy ball milling were treated with Ar microwave plasma. Plasma processing was designed to remove the initial oxide film covering Al nanoparticles (NPs) and adsorbed impurities from the surface of SiC NPs, improve the wetting of SiC with Al melt, prevent SiC nanoparticle agglomeration, and ensure their uniform distribution in the metal matrix. During plasma treatment, Al/SiC composite particles were obtained, which were subsequently utilized as ready-made structural blocks with uniformly distributed reinforcing SiC NPs to obtain Al/SiC composites with 5, 10, and 30 wt% of SiC. Spark plasma sintered Al/SiC composites using plasma-treated powder mixtures showed approximately 20% higher tensile strength. The addition of 10% SiC led to an increase in hardness by 480% (145 HV), tensile strength by 70% (317 MPa) and 95% (238 MPa) at 25 °C and 500 °C, respectively, compressive strength by 135% (578 MPa), and wear resistance by 35–50%. The effect of point defects at the Al/SiC interface, such as impurity oxygen atoms and Si monovacancies, on the binding energy and temperature-dependent critical shear stress at the interface was assessed using molecular dynamics simulations with machine learning interatomic potentials. Our study demonstrated that the plasma-chemical treatment of Al/SiC powder mixtures is a promising approach for improving the thermomechanical properties of the Al/SiC composites.

Temperature-dependent Raman and photoluminescence of β-Ga2O3 doped with shallow donors and deep acceptors impurities

Ion doping technology with precise control of doping concentration and configuration can optimize the performance of β-phase gallium oxide (β-Ga2O3) high-power electronic and optoelectronic devices. In this work, shallow-donor Si and deep-acceptor Mg impurities are doped in β-Ga2O3 separately using edge-defined film-fed growth (EFG) method. Laser scanning confocal microscopy and X-ray diffraction analyses show that the as-grown un/Si/Mg-doped β-Ga2O3 substrates have superior qualities such as smooth surface, homogenous phase, and high crystallinity. Raman spectroscopy analysis indicate that the Raman shift and full width at half-maximum (FWHM) has a linear relationship with temperature in the range of 77–297 K. The temperature-variable photoluminescence (PL) spectroscopy suggests that the Si doping introduces less damage to the β-Ga2O3 lattice structure and the Si-doped sample has higher stability at different temperatures, however, the local atomic configurations of Mg impurities can be more easily/significantly affected by temperature. The work can offer an insightful reference to applications of ion-doped β-Ga2O3 optoelectronic devices.

The impact of interfacial Si contamination on GaN-on-GaN regrowth for high power vertical devices

The development of gallium nitride (GaN) power devices requires a reliable selective-area doping process, which is difficult to achieve because of ongoing challenges associated with the required etch-then-regrow process. The presence of silicon (Si) impurities of unclear physical origin at the GaN regrowth interface has proven to be a major bottleneck. This paper investigates the origin of Si contamination at the epitaxial GaN-on-GaN interface and demonstrates an approach that markedly reduces its impact on device performance. An optimized dry-etching approach combined with UV-ozone and chemical etching is shown to greatly reduce the Si concentration levels at the regrowth interface, and a significant improvement in a reverse leakage current in vertical GaN-based p–n diodes is achieved.

Real-time visualization of particle evolution during reactive flux-assisted processing of aluminum melts

A multi-modal, multi-scale correlative tomography investigation of Al-TiC metal matrix composites processed via flux-assisted reaction synthesis is reported. Synchrotron X-ray microradiography is utilized to visualize the reaction and particle evolution in real-time. Changes in particle diameter and areal number density suggest that the process is nucleation- rather than growth-dominated. At 950 °C, the bulk of the reaction takes place in a relatively short time span of less than 600 s. The microstructure is imaged at higher resolution in 2D (scanning electron microscopy) and 3D (synchrotron X-ray nanotomography), revealing the formation of carbide particles with a hexagonal platelet morphology. We propose that the morphology arises due to the incorporation of Si impurities during the experiment. It is expected that the correlative tomography workflow and analysis may guide future metal matrix composite (MMC) processing strategies.

Growth defects in heteroepitaxial diamond

In focus of this report are the mechanisms of formation, propagation, and interaction of growth defects in heteroepitaxial diamond films along with their impact on the optical emission properties of N- and Si-vacancy (NV and SiV) color centers. Here, we analyze and discuss the properties of incoherent grain boundaries (IGBs) and extended defects in a nitrogen- and boron-doped heterodiamond nucleated and grown on Ir(001) via bias-enhanced nucleation and chemical vapor deposition techniques. We show that the low-angle IGBs alter the structural and optical emission properties of NV and SiV complexes by subduing NV emission and supporting the formation of interstitial Si-vacancy complexes dominating in the faulted IGB regions. We also demonstrate that the IGB-confined threading dislocations are responsible for the vertical transport and incorporation of Si impurities in thick layers, leading to an enhanced SiV emission from the IGBs.

P removal from Si by Si-Ca-Al alloying-leaching refining: Effect of Al and the CaAl2Si2 phase

• Al 2 O 3 crucible led to P removal degradation for Ca-containing Si alloys. • Increasing Ca/Al ratio and total alloying amount (Ca + Al) promote P removal. • A model for P removal prediction was obtained for Si-Ca-Al alloy system. • Ca concentration in liquid phase found as the essential driving force for P segregation. • CaAl 2 Si 2 exhibits higher P solubility than CaSi 2 but not decisive for P segregation. Phosphorus (P) is a critical impurity in metallurgical-grade Si that needed to be removed for solar-grade Si production. The Si-Ca-Al-P system is one of the most crucial alloy systems for Si refining, where P can be separated by either the Si-Al solvent refining or the Si-Ca alloying-leaching process. In this work, a series of Si-Ca-Al alloys were obtained to investigate the role of alloy composition and the CaAl 2 Si 2 phase in P segregation and separation. The used alumina crucible led to heavy Al contamination and resulted in unexpected Si-Ca-Al alloy compositions. CaAl 2 Si 2 and CaSi 2 were found as the main precipitates, and relatively higher P content was detected in the CaAl 2 Si 2 phase. Leaching experiments indicate that P removal degree increases with increasing Ca/Al ratio and increasing total alloying amount (Ca + Al). Effects of alloy composition were further analyzed by statistical methods, which indicates Ca firmly plays a strong, positive, and monotonic role in P removal while no strong attraction between Al and P. Theoretical P removal model for the Si-Ca-Al system was established and in good agreement with measured results. Interaction coefficients of Ca and Al to P were fitted as ε Ca P = - 19.2 and ε Al P = - 1.8 , which further confirms Ca is the essential driving force for P segregation. Finally, the possibility of P solid solution formation was verified by first-principle simulations that both CaAl 2 Si 2 and CaSi 2 are able to dissolve P, especially through the Si site, but the CaAl 2 Si 2 phase is more favourable for P dissolution than CaSi 2 , which explains the reason of the often detected high P content in CaAl 2 Si 2 .

Impurity Migrations in Aluminum Reduction Process and Quality Improvement by Anti-oxidized Prebaked Anode

Higher quality primary aluminum is increasingly required for high-performance alloy products. The influence of the impurity contents in such raw materials as prebaked anodes, alumina, etc. and impact of the process operations on the quality of primary aluminum are discussed in detail in this paper. The results show that Fe and Si are the major impurity components migrated in primary aluminum. The impurity Fe mainly comes from the cell covering material, prebaked anode, alumina, and operation process. The impurity Si mainly comes from the same sources as well as fluoride salts. Besides, a kind of anti-oxidized prebaked anodes with excellent reactivity to CO2 and air was studied and developed to reduce obviously Si content in primary aluminum and to improve aluminum quality.

Effect of processing history on corrosion behaviours of high purity Mg

In this study, the effects of processing history on corrosion behaviours of pure Mg with controlled impurity content, were analysed systematically. Results revealed that impurity Fe and Si were precipitated into the Fe-Si phase by heat treatment prior to extrusion, leading to severe micro-galvanic corrosion of as-extruded pure Mg despite the same impurity contents with as-cast pure Mg. This result suggests that control of the actual tolerance limit, considering not only the impurity content but also the processing history, is required in designing alloys.

Local Multimodal Electro‐Chemical‐Structural Characterization of Solid‐Electrolyte Grain Boundaries

AbstractTypical models of polycrystalline ionic materials treat the grain boundary properties as single valued, without consideration of the full range of values that define the macroscopically measured average. Here a unique experimental platform suitable for local multimodal characterization of individual grain boundaries in bicrystal fibers is reported. A variation of three orders of magnitude in the grain boundary conductivity of ceria is observed, as measured across six individual bicrystals by both alternating current impedance spectroscopy and direct current (D.C.) linear sweep voltammetry. Nonlinear behavior of the D.C. measurements is consistent with resistance due to a space charge effect. Time‐of‐flight secondary ion beam spectroscopy reveals a correlation between grain boundary resistance and the concentration of impurities Si, Al, and Ca segregated at the grain boundaries, although the bulk concentrations of these impurities are negligible. Electron backscatter diffraction analysis of the crystal orientations suggests a correlation between the misorientation across the grain boundaries and grain boundary resistance. These correlations point towards a grain boundary resistance that arises from impurity‐generated space charge effects and variations in impurity concentration and hence resistivity driven by the energetics of impurity segregation to grain boundaries of differing surface energies.

A Study of Selenium and Tellurium Distribution Behavior, Taking the Copper Matte Flash Converting Process as the Background

Single particle experiments were carried out in the present study. An industrial copper matte powder, containing 68.04 wt.% Cu, 0.50 wt.% Se and 0.08 wt.% Te was taken as the starting material. Se and Te phase assemblies and distribution behaviors were systematically investigated in the air atmosphere. It was found that Se reported to blister copper, matte, and oxide phase, whilst Te will enrich in oxide phases, including phases in the Fe-Si-Te-O, Ca-Fe-Te-O, and Ca-Te-O-(S) systems. As the temperature increases, the selenium and tellurium content in the copper and matte phases decreases. The introduction of CaO flux, and typical impurities of Pb and Si, had significant influence on Se and Te distribution. The results revealed that CaO addition and Si impurity accelerated the removal of Se and Te from the copper and matte phases, but Pb impurity increased Se and Te in Cu-rich phases.

XRF Analysis of Impurity Metal Elements in Iron Base Alloy

The content of Si, Mn, V, Cu and other impurity elements in tool steel samples was analyzed by wavelength dispersive X-ray fluorescence spectrometry (XRF). Using Ag target X-ray tube and the SDD detector (FWHM < 135 eV@5.9 keV). The best working conditions of the instrument are tested before measurement, including tube pressure, flow, filter used and measuring time. The repeatability of the instrument is verified to meet the standard. Finally, the detection limit of the instrument is tested. In the analysis and comparison, linear regression method is used to eliminate the matrix effect among the elements in the sample, and it is found that the multiple linear regression method has a good correction effect on the matrix effect. The results show that the average relative errors of Si, Mn, V and Cu are 3.24%, 3.05%, 0.29% and 0.59% respectively by using the optimal linear regression analysis. The method improves the control requirements of impurity elements in iron base alloy.

Ab initio моделирование энергии растворения и энергии связи водорода с 3sp-, 3d- и 4d-примесями в ОЦК-железе

A fundamental understanding of the localization of H atoms in steel is an important step towards a theoretical description of the mechanisms of hydrogen embrittlement at the atomic level. Ab initio calculations within the framework of density functional theory (DFT) is used to investigate the effect of various substitutional impurities Mg, Al, Si, Sc, Ti, V, Cr, Mn, Co, Ni, Cu, Zn, Y, Zr, Nb, Mo , Pd and Cd on the energy of hydrogen dissolution in the lattice of bcc iron. The electronic and elastic contributions of various impurities to the dissolution energy are distinguished, and their influence on the binding energy of hydrogen and impurities is analyzed. The existence of a linear dependence of the energy of hydrogen dissolution on the magnitude of the change in the electron density of the intra-tetrahedral pore after the introduction of a hydrogen atom into it is shown. The results obtained made it possible to formulate the key mechanisms for controlling the localization of hydrogen in bcc iron by substitution impurities.

Over 80% power-added-efficiency GaN high-electron-mobility transistors on free-standing GaN substrates

This paper demonstrates highly efficient GaN high-electron-mobility transistors (HEMTs) on GaN substrates with reduced interface contamination. By applying a hydrofluoric acid-based pre-growth treatment to a GaN substrate, the Si impurity concentration at the interface between the GaN substrate and the epitaxial layer can successfully be reduced. RF performance was enhanced by pre-growth treatment owing to the suppression of Si-induced parasitic loss. As a result, GaN HEMTs on GaN substrates exhibited an excellent power-added efficiency of 82.8% at a 2.45 GHz. To the best of our knowledge, this exceeds that of the previously reported discrete GaN HEMTs at around this frequency range.

To question about Fe5B3 boride formation in boron-rich Fe–В alloys

The structure of boron-rich iron alloys in the concentration range of 9.0–15.0 wt. % В, 0.01–0.17 wt. % C, Fe – the balance (with charge impurities of Si, Al, Mn) was investigated in this work. The methods of metallographic, X-ray, stop-quenching, scanning electron microscopic, energy dispersive, and fluorescent spectral analyses were applied. The FeB- and Fe2B-based solid solutions are proved to be the major constituents of the investigated alloys. No evidence is found for the possible formation of the Fe5B3 boride via peritectic reaction L+FeB→Fe5B3 at 1650 K and its further decomposition via eutectoid reaction Fe5B3→FeB+Fe2B at 1410 K. It is shown that the phase under consideration is iron hemiboride alloyed mainly by silicon which peritectically forms from primary crystals of iron monoboride and the rest of liquid at 1650 K. The thermal effect at 1410 K is assumed to be caused by a heat production connected with polymorphic transformation α-FeB→β-FeB in the presence of carbon.