Si Impurities Research Articles

Two-inch Fe-doped β-Ga2O3 (010) substrates prepared using vertical Bridgman method

The growth of large-diameter high-resistivity β-Ga2O3 (010) substrates is important for the low-cost production of lateral Ga2O3 devices. We grew a 2 inch diameter Fe-doped high-resistivity β-Ga2O3 (010) single crystal by using the vertical Bridgman (VB) method, which is expected to grow large-diameter β-Ga2O3 crystals with various crystal orientations. Two-inch substrates were prepared from the obtained crystals, and their crystallinity, concentration of Fe dopants, and electrical properties were investigated. Consequently, a 2 inch β-Ga2O3 (010) substrate, which is comparable to the largest size of (010) substrate prepared using the Czochralski method, was successfully fabricated with the VB method. The in-plane distribution of the X-ray rocking curve from 020 diffraction of the fabricated 2 inch substrate showed that the full widths at half maximums were less than 35 arcsec at almost all measurement points, indicating high crystallinity and high in-plane uniformity. In addition, the crystals contain Fe concentrations in the range of 3.5 × 1018–1.9 × 1019 cm−3, indicating that impurity Si donors are sufficiently compensated by the Fe dopants. Therefore, substrates prepared using the VB method exhibited high resistivities of 6 × 1011–9 × 1012 Ω·cm at room temperature.

Eco-friendly and economical preparation of permanent ferrite magnet with ultrapure magnetite concentrate: Focus on the action mechanism of silicon and aluminum impurities

In this study, ultrapure magnetite concentrate (UMC) was used to replace high-quality iron oxide red (IOR) for permanent ferrite magnet (PFM) preparation. UMC needs to be pre-oxidized to eliminate FeO which easily generates nonmagnetic phases in PFM. The magnetic powder and PFM products prepared with UMC and IOR had close magnetic properties, but the calcination temperature was lower and calcination time was shorter with UMC. Si and Al impurities in UMC could not only form eutectic compounds but also dissolve into the ferrite grain by substituting Fe. Those eutectic compounds benefited uniformity of grains by inhibiting grain overgrowth but decreased the purity of PFM because they were non-magnetic substances. Mn impurity in IOR entered into the ferrite grain by replacing Fe instead of participating in the formation of eutectic mixtures, while Cl impurity was evaporated during calcination, causing equipment erosion and environment pollution. UMC has the advantages of low raw material cost, good product property and non-pollution, and thus it has a broad application prospect in PFM preparation.

Specific features of the microimpurity composition of chrome-spinel inclusions in diamonds from kimberlites of Sakha-Yakutia

Specific features of the microimpurity composition of chrome-spinel inclusions in 323 diamond crystals from eight kimberlite pipes of two diamond-bearing regions of Yakutia were revealed by microprobe analysis. Processed data on their content of the Ni, Zn, V, Mn, and Si impurities are presented. It is shown that chrome-spinels in diamonds from the kimberlite pipes of the different regions are characterized by different contents of the impurity elements. The revealed differences in the composition of chrome spinel inclusions in the diamonds, as well as in the defect-impurity composition of the hosting diamonds, from the different, including neighboring, kimberlite pipes of Yakutia, are evidence of a local heterogeneity in the mantle composition within a certain kimberlite field. These data confirm the opinion of most researchers on heterogeneity of the mantle composition in different regions of the Yakutian diamondiferous province.

Upcycling Construction and Demolition Waste into Calcium Carbonates: Characterization of Leaching Kinetics and Carbon Mineralization Conditions

Carbon mineralization is a technology that fixes CO2 permanently into solid carbonates via the reaction between CO2 and alkaline substances. In our studies, we used Ca-bearing industrial waste (i.e., construction and demolition waste) as the feedstock to produce high-purity calcium carbonates. We aim to integrate valorization of solid wastes and CO2 emission mitigation in our process. To achieve qualified products and fast kinetics, the reaction routes can be divided into two main processes: a dissolution process with acid followed by a two-step carbonation reaction. The advantages of this multistage process are obtaining products with high purity, tailored morphology, and narrowed particle size distribution. Conducting effective carbon mineralization requires a comprehensive understanding of the kinetics of the dissolution process, and it was found that the rate-limiting step is diffusion due to the intrinsic properties of the feedstock. In the subsequent carbonation process, impurities (Al, Fe, and Si) from the leachate were selectively removed as their oxides prior to the carbonation reaction, through pH swing, leveraging differential solubilities. Subsequent carbonation with bubbled CO2 under controlled conditions produced calcium carbonate with tunable forms between vaterite, aragonite, and calcite. The variations of the particle size distribution and the shape of the solid were monitored in real time through a Blaze900 probe from BlazeMetrics Co., which provided optical information, facilitating a better understanding of the kinetics and mechanisms of the dissolution and crystallization processes. Thus, alkaline industrial waste can be efficiently and sustainably utilized through the carbon mineralization pathway.

InGaAs/AlGaAs quantum well intermixing induced by Si impurities under multi-variable conditions

InGaAs/AlGaAs quantum well intermixing induced by Si impurities under multi-variable conditions

Pyrometallurgy treatment of electroplating sludge, emulsion mud and coal ash: ZnAlFeO4 spinel separation and stabilization in calcium metasilicate glass

Electroplating sludge was a hazardous waste comprised of heavy metals and other Fe/Al/Ca/Si impurities, and produced massively in surface treatment industry. In the past, it was commonly purified via hydrometallurgy, chlorination and reduction calcination routes, but also blended as additive in rotary kiln, to stabilize the heavy metals in geopolymer. Herein, an alternative strategy was developed to treat a real electroplating sludge for recycling magnetic Zn-rich spinel and stabilizing Zn in calcium metasilicate glass via a facile pyrometallurgy route with the blending of emulsion mud and coal ash. The sludge contained 35.6% Zn and 0.54% Cr and then was blended with 50% emulsion mud. After calcination at 1200 °C, the product was highly dispersed, whilst octahedral ZnAlFeO4 spinel with Zn content of 40.0% were formed and separated by using magnet, in accordance with the recycling efficiency of 51.2% Zn from the electroplating sludge. But after calcination at 1400 °C, the gypsum in emulsion mud was decomposed as CaO and accelerated the dissolution of Si-bearing substance as calcium metasilicate glass for covering ZnAlFeO4 spinel, resulting in the Zn leaching of 1568 mg/L. By adding 50% Si-rich coal ash in the calcination system, more calcium metasilicate glass were generated, and then the Zn concentration in the toxic leaching test was only 12.09 mg/L. During the calcination, Cr showed similar performance to Al/Fe and involved in the spinel formation. This provided a new route to recycle Zn from Zn-rich electroplating sludge and to solidify heavy metals via calcium metasilicate glass route.

Theoretical study of the non-parabolicity and size effects on the diamagnetic susceptibility of donor impurity in Si, HgS and GaAs cylindrical quantum dot and quantum disk: applied magnetic field influence is considered

ABSTRACT Through this work, we have investigated the influence of the conduction band non-parabolicity (NP) and magnetic field on the diamagnetic susceptibility for a confined shallow donor impurity in a homogeneous cylindrical quantum dot (CQD) and quantum disk (QDisk); the size effect has been considered. Our calculations have been performed using the variational method which consists of the choice of a trial wave function. The Schrodinger equation has been solved within the effective-mass approximation considering the infinite height potential barrier. The numerical calculations are performed taking into account different semiconductor materials (i.e. Si, HgS and GaAs). Our results reveal that both the size and conduction band NP have a significant impact on the behaviour of the diamagnetic susceptibility for both studied systems (i.e. CQD and QDisk). It has been also noticed that, for both CQD and QDisk, the NP increases the diamagnetic susceptibility (). Furthermore, this effect is remarkable for low band gap semiconductors, especially in large QD (weak radial confinement). However, it is much more important in HgS due to its narrow band gap compared to Si and GaAs materials.

Jute-Fiber Precursor-Derived Low-Cost Sustainable Hard Carbon with Varying Micro/Mesoporosity and Distinct Storage Mechanisms for Sodium-Ion and Potassium-Ion Batteries.

Hard carbon (HC) remains the most viable choice as a negative electrode for sodium-ion batteries (SIBs) and potassium-ion batteries (PIBs) owing to its higher energy density (discharge up to zero volts), higher capacity (distinct storage mechanisms), and cycling stability. Herein, a biomass jute fiber precursor HC anode (JPC) with varying porosity is reported for the first time as a low-cost and sustainable high-performance HC anode for SIBs and PIBs. Direct carbonization results in micro-meso porous HC (JPC-D), and micro-wave pretreated jute fiber results in ultramicroporous HC (JPC-M). The mesoporosity generated in JPC-D during synthesis outperforms the ultramicroporous JPC-M with a high reversible capacity of 328 mAh g-1 (iCE = 66%) at a current density of 30 mA g-1 (0.1C) with superior capacity retention of 84% after 100 cycles in SIBs. The Na+ ion and K+ ion storage in HCs, especially at lower voltages, shows distinct storage mechanisms that depend on the morphology and porosity of the material. JPC-D contributed 39% of its total capacity through the plateau region capacity (PRC), suggesting more pore filling from hierarchical porosity in SIBs. JPC-D and JPC-M exhibit more insertion-based capacity than pore-filling processes in PIBs. The presence of inorganic impurities (Ca, Si, Al, and Fe) encapsulated in the carbon structure plays a critical role in developing mesopores. The yield (%) of HC from direct carbonization per kilogram of jute is ∼34%, which makes it cheaper than HC from sugar-based precursors and 1.5 times more affordable than other biomass-derived HC. The jute-based micro-mesoporous HC is a novel, cost-effective, sustainable approach to designing HC for a PRC-based battery-type anode in SIBs and PIBs.

First-principle study on the effect of point defects on the mechanical properties, thermal conductivity, and optical properties of wurtzite AlN

Defects (VAl/VN) and unintentional impurities (C/O/Si/Hi) will inevitably exist during the preparation of AlN by metal-organic chemical vapor deposition and physical vapor transport. In particular, Hi is very difficult to remove in a vacuum environment. First-principle calculations were used to research the mechanical properties, thermal conductivity, and optical properties of AlN and its defect-containing systems. Results showed that the deformation resistance of Al36SiN35 and Al35ON36 systems was relatively poor, and the hardness was relatively small. When the impurity C or O located in the N position, the effect on the anisotropy of AlN was relatively large. O impurities and Al vacancies had relatively large effects on the thermal conductivity of AlN lattice. When the O impurity was located at the N position and the Si impurity was located at the Al position, the influence on the optical properties of AlN was relatively large, which would help improve the polarization ability, refractive index, reflectivity, and absorption of the visible light of AlN.

Study on Purification Technology of Silicon Carbide Crystal Growth Powder.

Silicon carbide (SiC) is a wide-bandgap (WBG) semiconductor material, and its preparation process has strict requirements on the purity of raw materials. A self-developed medium-frequency induction heating furnace was used to carry out powder heat treatment and purification experiments on SiC powder to improve the purity of the powder. Samples with 3.5N purity were analyzed using XRD and GDMS characterization methods. It was found that under conditions of high-temperature (2200 °C) and long-time (50 h) processing, the impurity removal effect was quite good, but the powder loss was as high as 53.42%. The powder loss during the low-temperature (less than 2050 °C) and short-time process was less than 1.5%, but the purification effect was not substantial. After a prolonged processing time, the purification effect of low-temperature heat treatment conditions was improved, but the powder loss was also increased to 30%. In contrast, segmented purification processing at a low temperature in the early stage and a high temperature in the later stage achieved a good purification effect. On the premise of maintaining the utilization rate of raw materials, a 5N-purity SiC source was successfully prepared. The test results show that the contents of free Si, free C and free oxygen impurities were reduced to less than 0.01%, and the contents of Al, B, Fe, Mg, Na, Ti and other impurities were less than 1.15 ppm, which is close to the ppb level.

Study on the behavior of impurities in zone melting of aluminum

In this study, the migration and distribution behaviors of Cu, Si, Fe, and Ti impurities in the process of preparing high-purity Al by zone melting under an argon atmosphere were investigated. The width of the molten zone during the experiment was determined as 40 mm, based on simulation calculation results. The influences of the travel speed of the molten area and number of zone melting times on the migration and distribution of the Cu, Si, Fe, and Ti impurities in the Al were experimentally demonstrated. The contents of the impurities Cu, Si, Fe, and Ti in the middle of the sample (i.e., 140 mm from the head end) were 0.9057, 0.8116, 0.1202, and 0.4237 ppm, respectively, when the travel speed of the molten area was 1.0 mm/min and with 15 times of zone melting. The contents of all the above impurities were reduced to the requirements of Chinese national standard and 99.9995% (i.e., 5N5) high-purity Al was obtained from 4 N Al by the zone melting method under the above optimal experimental conditions. The experimental results show that the effect of the number of zone melting times on the removal of the Cu, Si, and Fe impurities is more evident, and that these impurities are easier to separate than Ti. Therefore, high-purity Al with lower Cu, Si, and Fe contents can be obtained by optimizing the travel speed of the molten area and number of zone melting times.

Machine-learning-assisted multi-objective optimization in vertical zone refining of ultra-high purity indium

Optimization of processing parameters cannot rely on the trial-and-error method for the production of ultra-high purity metals owing to the complexity of indium raw material and multi-pass processing procedure. A multi-objective optimization strategy was proposed to optimize the process parameters for vertical zone refining of 7N-grade ultra-high purity indium (In) by using machine learning (ML). Firstly, classification models were established for certain impurities (Si, S, Fe, Zn, Ni, Cu and As). In these models, the Synthetic Minority Over-sampling Technique (SMOTE) was introduced to overcome the sample imbalance problem of the experimental dataset. The accuracy of these classification models reached above 0.9. Secondly, a ridge regression model was built to predict the total impurity content in the product. The root mean square error (RMSE) was 0.023, the Pearson correlation coefficient (r) was 0.91, and R-squared (R2) value was 0.79. Using these models, high-throughput virtual screening was performed to conduct vertical zone-refining experiments, which in turn validated the reliability of the models. Feature analysis by Shapley additive explanations (SHAP) revealed that the total impurity content in the final product strongly depended on the content of Ni and Sn impurities in the 6N-grade indium raw material and on the velocity parameter of the 2rd through 4th zone passes (V2). A lower V2 is favorable for eliminating impurities from indium raw material with total impurity content ranging from 0.2 ppm to 0.4 ppm.

Influence of growth rate on homoepitaxial growth of AlN at 1450 °C by hydride vapor phase epitaxy

The influence of growth rate on the homoepitaxial growth of AlN at 1450 °C by hydride vapor phase epitaxy on bulk AlN(0001) substrates was studied. X-ray diffraction and Raman spectroscopy revealed that high structural quality comparable to that of the initial substrate can be achieved even when the growth rate is increased to over 150 μm h−1. Although the concentration of Si impurities increased with increasing growth rate, a freestanding AlN substrate prepared from a homoepitaxial layer grown at 155.6 μm h−1 showed a steep optical absorption edge at 207 nm and high optical transmittance at longer wavelengths.

Effect of Impurities on the Decarbonization of Calcium Carbonate Using Aqueous Sodium Hydroxide

Decarbonizing calcium carbonate (CaCO3) is a crucial step for a wide range of major industrial processes and materials, including Portland cement (PC) production. Apart from the carbon footprint linked to fuel combustion, the process CO2 embodied within CaCO3 represents the main concern for the sustainability of production. Our recent works demonstrated that it is possible to avoid both the fuel and process CO2 by reacting CaCO3 with aqueous NaOH and obtain Ca(OH)2 and Na2CO3·xH2O (x = 0 and 1). This present study provides a further understanding of the process by testing different raw calcareous sources. A high decarbonization (∼80%) of CaCO3 was achieved for silica-rich chalk, whereas a lower extent was obtained (∼50%) for limestone. To understand the difference in their reaction behavior, the effect of impurities was studied. The effects of the major impurities (Si, Al, and Fe) were found to be marginal, which is advantageous to process industrial grade materials, while the morphology of the raw materials presents a significant impact. The applicability of our decarbonization technology was also demonstrated on magnesite (MgCO3).

Effect of Silicate Additive on Structural and Electrical Properties of Germanium Nanowires Formed by Electrochemical Reduction from Aqueous Solutions.

Layers of germanium (Ge) nanowires (NWs) on titanium foils were grown by metal-assisted electrochemical reduction of germanium oxide in aqueous electrolytes based on germanium oxide without and with addition of sodium silicate. Structural properties and composition of Ge NWs were studied by means of the scanning and transmission electron microscopy, X-ray photoelectron spectroscopy, X-ray diffraction, and Raman spectroscopy. When sodium silicate was added to the electrolyte, Ge NWs consisted of 1–2 at.% of silicon (Si) and exhibited smaller mean diameter and improved crystallinity. Additionally, samples of Ge NW films were prepared by ultrasonic removal of Ge NWs from titanium foils followed with redeposition on corundum substrates with platinum electrodes. The electrical conductivity of Ge NW films was studied at different temperatures from 25 to 300 °C and an effect of the silicon impurity on the thermally activated electrical conductivity was revealed. Furthermore, the electrical conductivity of Ge NW films on corundum substrates exhibited a strong sensor response on the presence of saturated vapors of different liquids (water, acetone, ethanol, and isopropanol) in air and the response was dependent on the presence of Si impurities in the nanowires. The results obtained indicate the possibility of controlling the structure and electrical properties of Ge NWs by introducing silicate additives during their formation, which is of interest for applications in printed electronics and molecular sensorics.

Studies on δ-Bi2O3 Based Nanocrystalline Glass-Ceramics Stabilized at Room Temperature by Novel Methods

This study demonstrated for the first time that it is possible to prepare nanocrystalline δ-Bi2O3 that is stable at room temperature by twin-rollers and free cooling methods, using a ceramic crucible. The phase composition of prepared samples and upper limit of the thermal stability of nanograins confined in an amorphous matrix were determined by the X-ray diffraction (XRD) method. The average size of crystallites and the microstructure of studied samples was determined by SEM and XRD methods. The average grain size varied from 38 to 85 nm, depending on the preparation technique; however, it was also observed that agglomerations consisted of smaller crystallites ca. 10–30 nm. Using the EDX method, it was found that a crucial role in the preparation of nanocrystalline δ-Bi2O3 glass-ceramics was played by Si and Al impurities and their glass forming oxides from ceramic crucible. By impedance spectroscopy (IS), the temperature dependencies of electric conductivity (via oxygen ions) were studied and the activation energies of conductivity were determined.

Electronically engineering microstructural design for developing advanced steels: An exploration of high Si bainitic steel

Microstructure engineering is essential for developing advanced steels and is often carried out by thermomechanical processing. Here we report the engineering of microstructures of a high Si bainitic steel by tuning its electronic structure. It is experimentally found that the bainitic steel with Si addition processed with laser melting has a complex multiphase microstructure consisting of α-Fe, γ-Fe, ε-martensite, and nano-scale twin boundaries with significantly improved hardness. Furthermore, calculations based on density functional theory show that the observed microstructure is strongly correlated with changes in the electronic structures of Fe atoms around the Si impurities. In particular, electron localization around the Si impurities significantly alters the stacking fault energy, which promotes the formation of ε-martensite and nanoscale twin boundaries, while the Jahn-Teller splitting caused by Si dopants results in a FCC-to-BCC phase transition with a misorientation angle of 8° between the (200)γ and(1¯1¯0)α. This work suggests that controlling the microstructures by electronic structure engineering has great potential for designing new structural materials with excellent mechanical properties.

Research on quantum well intermixing of 680 nm AlGaInP/GaInP semiconductor lasers induced by composited Si–Si3N4 dielectric layer

The optical catastrophic damage that usually occurs at the cavity surface of semiconductor lasers has become the main bottleneck affecting the improvement of laser output power and long-term reliability. To improve the output power of 680 nm AlGaInP/GaInP quantum well red semiconductor lasers, Si–Si3N4 composited dielectric layers are used to induce its quantum wells to be intermixed at the cavity surface to make a non-absorption window. Si with a thickness of 100 nm and Si3N4 with a thickness of 100 nm were grown on the surface of the epitaxial wafer by magnetron sputtering and PECVD as diffusion source and driving source, respectively. Compared with traditional Si impurity induced quantum well intermixing, this paper realizes the blue shift of 54.8 nm in the nonabsorbent window region at a lower annealing temperature of 600 °C and annealing time of 10 min. Under this annealing condition, the wavelength of the gain luminescence region basically does not shift to short wavelength, and the surface morphology of the whole epitaxial wafer remains fine after annealing. The application of this process condition can reduce the difficulty of production and save cost, which provides an effective method for upcoming fabrication.

Indium as a surfactant: Effects on growth morphology and background impurity in GaN films grown by ammonia-assisted molecular beam epitaxy

We report on the improvement of the surface morphology of c-plane GaN films grown at high growth rates (∼1 µm/h) using ammonia molecular beam epitaxy through a series of growth optimizations as well as the introduction of indium as a surfactant. The indium surfactant was expected to help with the adatom mobility and, thus, provide smoother growth surfaces. Through a combination of varying V/III ratios, In flux, and growth temperatures, an optimal condition for surface morphology, characterized by atomic force microscopy, was achieved. At higher Ga fluxes for fast growth rates (∼1 µm/h and beam equivalent pressures of ∼5 × 10−7 Torr), higher ammonia flows were necessary to preserve the surface morphology. In addition, indium was an effective surfactant—reducing the roughness and improving the overall surface morphology. However, excessive indium causes the surface morphology to degrade, potentially due to the enhancement of the Ga desorption from the surface as a result of the reaction of indium with ammonia for high indium fluxes. The indium surfactant also resulted in a reduction of background Si impurity concentrations in the film. These effects allow for the growth of thick drift layers with low background dopant concentrations for vertical GaN power devices.

Structural and electrical characterizations of Si-implanted GaN with a high dose at elevated temperatures

Si implantation with a dose of 2×1015 cm−2 into GaN was performed at temperatures from 25 to 300°C, followed by annealing at 1200°C for 5 min. High resolution X-ray diffraction was used to monitor the implantation induced lattice strain after implantation and after annealing. The sheet concentrations and mobilities of electrons after activation annealing were measured by Hall measurement. Results show the effect of increasing implantation temperature on electrical activation of Si impurities in GaN is minor. Still, the lattice strain decreases with implantation temperature. The average electron concentration increases with implantation temperature from RT (6.26±0.76×1019 cm−3) to 250°C (8.06±0.98×1019 cm−3) and begins to show a trend of decrease as it increases to 300°C. The average electron mobility decreases with implantation temperature from RT (102.0±2.5 cm2 V−1·s−1) to 250°C (89.2±2.2 cm2 V−1·s−1) and begins to show a trend of increase as it increases to 300°C. The defects nature at elevated implantation temperatures and their correlation with electrical activation and scattering mechanism of carriers need further investigation.