Impurities In Silicon Research Articles

Impurity control in high performance multicrystalline silicon

We report results from a national project about impurities in high performance multicrystalline silicon: Contamination sources, transport routes, interaction with crystal defects and impact on solar cell efficiency parameters. Several ingots were produced in a lab scale furnace. Growth parameters and crucible types were varied, and high purity quartz crucibles were compared to novel silicon nitride crucibles. The material was characterized by a range of methods including FTIR, GDMS, NAA, EBSD, dislocation etching, lifetime analysis. Wafers were processed, and lifetime was measured during the cell processing to analyse the effect of separate processing steps. Models were constructed to simulate the impurity transport during the crystallization. The diffusivity in quartz and silicon nitride crucibles required in the modelling is not generally known, and experiments were performed to evaluate them. Variations in dislocation density have the strongest impact on lifetime, even for this high quality material. The quartz crucible has the highest contamination potential, but the uncertainty in diffusion parameters makes it difficult to conclude if this potential is reached, and for which elements. We therefore make an overview showing which value of the diffusion coefficient shift the contamination dominance between feedstock/crucible/coating. The use of high purity crucibles enables comparable or even higher lifetime material to be made in lab scale compared to industrial settings. Our results indicate that a thin layer of higher purity, lower porosity quartz on the inside of the crucible can be an effective method to transfer this improvement to industrial conditions. The cell processing indicates that the diffusion/gettering sequence profoundly decreases the lifetime by rendering the random high angle grain boundaries electrically active. However, this effect is reversed after firing of the anti‐reflective coating, when the remaining active defects are dislocation clusters and CSL boundaries. Silicon nitride crucibles appear to be a promising low oxygen alternative to traditional quartz crucibles in terms of purity.

Binary Phase Diagrams and Thermodynamic Properties of Silicon and Essential Doping Elements (Al, As, B, Bi, Ga, In, N, P, Sb and Tl).

Fabrication of solar and electronic silicon wafers involves direct contact between solid, liquid and gas phases at near equilibrium conditions. Understanding of the phase diagrams and thermochemical properties of the Si-dopant binary systems is essential for providing processing conditions and for understanding the phase formation and transformation. In this work, ten Si-based binary phase diagrams, including Si with group IIIA elements (Al, B, Ga, In and Tl) and with group VA elements (As, Bi, N, P and Sb), have been reviewed. Each of these systems has been critically discussed on both aspects of phase diagram and thermodynamic properties. The available experimental data and thermodynamic parameters in the literature have been summarized and assessed thoroughly to provide consistent understanding of each system. Some systems were re-calculated to obtain a combination of the best evaluated phase diagram and a set of optimized thermodynamic parameters. As doping levels of solar and electronic silicon are of high technological importance, diffusion data has been presented to serve as a useful reference on the properties, behavior and quantities of metal impurities in silicon. This paper is meant to bridge the theoretical understanding of phase diagrams with the research and development of solar-grade silicon production, relying on the available information in the literature and our own analysis.

Impurity gettering effect of atomic layer deposited aluminium oxide films on silicon wafers

We present experimental evidence for the impurity gettering effect of atomic layer deposited aluminium oxide (Al2O3) films on silicon wafers, during typical surface passivation activation at 425 °C. Iron was used as a model impurity in silicon to study the gettering effects. Dissolved iron concentrations were determined by carrier lifetime measurements, allowing the iron loss kinetics in silicon wafers with Al2O3 coatings to be monitored during annealing. The redistribution of iron to the surface layers and the sub-surface regions was examined by secondary ion mass spectrometry depth profiling. The results show that the atomic layer deposited Al2O3 films generate a strong gettering effect, removing 50% of the iron after 30 min at 425 °C for a 160-μm thick silicon wafer. The iron reduction process is largely diffusion-limited in the initial stages. The gettering effect is caused by the accumulation of iron at the Al2O3/Si interface.

IR studies of the oxygen and carbon precipitation processes in electron irradiated tin-doped silicon

Oxygen (O) and carbon (C) are key impurities in silicon (Si) and the control of their properties and behavior is an important issue for the microelectronic industry. A number of these properties can be manipulated by isovalent doping. Here we employ Fourier transform infrared (FTIR) spectroscopy to study the evolution of O and C concentration as well as the evolution of the oxygen precipitate bands in electron- irradiated tin (Sn) doped Si, subjected to isochronal anneals up to 950 °C. Special attention was given in connecting infrared absorption bands with certain precipitation morphologies. In this study, bands at 1040, 1060, 1080 and 1170 cm−1 generally attributed to precipitate morphologies were detected. Using arguments from classical theoretical mechanics we have attributed the 1040 cm−1 band to a structure more close to a spherical morphology, although the 1060 and 1080 cm−1 bands were attributed to structures more close to octahedral and polyhedral morphologies, respectively. Additionally the band at 1170 cm−1 was attributed to platelet precipitates. The effect of C and (C, Sn) co-doping Si in the morphologies of the precipitates bands was investigated in detail. It was found that in the irradiated material C suppresses the formation of spheroidal precipitates although it enhances the platelet precipitates, whereas in Si containing C and Sn the opposite behavior was detected. The presence of the two impurities modifies the number of the O precipitates and affects the relative density among the formed morphologies in Si, determining whether the spheroidal or platelet precipitates will prevail. The phenomenon was discussed taking into consideration the effect of the density of the nucleation sites on the interfacial energy of the precipitates. Furthermore, an inverse annealing stage in the evolution curve of C, namely an increase of C concentration prior to its complete disappearance was studied. This recovery stage was determined to be enhanced in (C, Sn) co-doping Si with relatively low Sn content although in Si with high Sn content the increase of C is substantially lower. An explanation was suggested based on the ability of the Sn to temporarily trap vacancies, thus affecting the restoration of the C substitutional atoms in the Si lattice.

РАФИНИРОВАНИЕ МОНОКРИСТАЛЛИЧЕСКИХ ЖАРОПРОЧНЫХ НИКЕЛЕВЫХ СПЛАВОВ ОТ ПРИМЕСЕЙ СЕРЫ И КРЕМНИЯ И НЕЙТРАЛИЗАЦИЯ ВРЕДНОГО ВЛИЯНИЯ ФОСФОРА

РАФИНИРОВАНИЕ МОНОКРИСТАЛЛИЧЕСКИХ ЖАРОПРОЧНЫХ НИКЕЛЕВЫХ СПЛАВОВ ОТ ПРИМЕСЕЙ СЕРЫ И КРЕМНИЯ И НЕЙТРАЛИЗАЦИЯ ВРЕДНОГО ВЛИЯНИЯ ФОСФОРА

Effect of acetic acid on the leaching behavior of impurities in metallurgical grade silicon

ABSTRACTTo explore the potential of acid leaching in purification metallurgical grade silicon (MG-Si) for solar cells, the effect of acetic acid on the leaching behavior was investigated in the present work by focusing on the behavior of impurities affected by the addition of acetic acid to a conventional acid mixture composed of hydrochloric acid and hydrofluoric acid. The etching results reveal that the HCl–HF–CH3COOH mixture is a better lixiviant for dissolving impurity inclusions in MG-Si. The extraction yield of impurities in HCl–HF–CH3COOH leaching was found to increase by 7% compared to conventional HCl–HF leaching.

Leaching behaviors of impurities in metallurgical-grade silicon with hafnium addition

Hf was employed as an impurity getter to enhance the removal of impurities from metallurgical-grade Si (MG-Si) via the solidification of Si or a Si-33wt% Al solvent. The leaching behaviors of the impurities (B, Fe, Al, Ca, P, Zr, Ti, V, Mn, Hf, and Ni) within MG-Si, in the presence of 5wt% Hf, were investigated using various leaching approaches. Compared with aqua regia and HF, HCl+HF was determined to be the optimal lixiviant for the elimination of impurities from Hf-containing MG-Si. The use of a combination of HCl+HF and aqua regia reduced the quantity of impurities from 6126ppmw to 94ppmw. Eh-pH diagrams were calculated to discuss the leaching of HfSi2 in aqua regia and HF solutions. The presence of Hf in the MG-Si enhanced the removal of impurities, especially P, which cannot be efficiently removed via solidification refining and hydrometallurgical treatments. Hf-containing Si-Al solvent refining is considered the most efficient approach for the elimination of impurities (except Al). The removal fractions of B and P were 94.2% and 86.2%, respectively, achieved via the solidification of the Si-33wt% Al solvent. Moreover, 99.94% and 99.9996% of the Hf, used as an impurity getter, could be eliminated through the solidification of the Si and Si-33wt% Al solvent, respectively, decreasing from 50,000ppmw, to 28ppmw and 0.2ppmw, respectively.

Design Considerations Influencing Optical Response in Gold Spherical Nanoparticles

In this article, the relations between extinction cross section and Gold nanoparticle's parameters such as dimensions have been investigated. In this work, the extinction cross section of the core-shell nanoparticles is analyzed by changing the shell material and its thickness. By this, the interesting results such as shifting resonant peak in optical response are obtained. Moreover, a new model of nanostructure is proposed in which the resonant peak of extinction cross section can be controlled by adding silicon nanoparticles and impurity in the shell. This method can be used for tuning of the scattering properties of the core-shell nanoparticle. In the following, we demonstrate that the effective epsilon properties can be used for tuning of the desired optical response in the combinational structure of the spherical nanoparticles. At the end, the effective relative epsilon is also calculated for the selected structures. The operational frequency band is selected from 300 (THz) to 900 (THz).

РАФИНИРОВАНИЕ МОНОКРИСТАЛЛИЧЕСКИХ НИКЕЛЕВЫХ ЖАРОПРОЧНЫХ СПЛАВОВ ОТ ПРИМЕСЕЙ КРЕМНИЯ, ФОСФОРА И СЕРЫ МЕТОДОМ НАПРАВЛЕННОЙ КРИСТАЛЛИЗАЦИИ РАСПЛАВА С ВЕСЬМА НИЗКОЙ СКОРОСТЬЮ ПЕРЕМЕЩЕНИЯ ФРОНТА

РАФИНИРОВАНИЕ МОНОКРИСТАЛЛИЧЕСКИХ НИКЕЛЕВЫХ ЖАРОПРОЧНЫХ СПЛАВОВ ОТ ПРИМЕСЕЙ КРЕМНИЯ, ФОСФОРА И СЕРЫ МЕТОДОМ НАПРАВЛЕННОЙ КРИСТАЛЛИЗАЦИИ РАСПЛАВА С ВЕСЬМА НИЗКОЙ СКОРОСТЬЮ ПЕРЕМЕЩЕНИЯ ФРОНТА

Effect of electron beam injection on boron redistribution in silicon and oxide layer

Abstract The behavior of boron redistribution in silicon with and without oxide layer after electron beam injection (EBI) was investigated. Special defect shapes were generated on the surface of bare and oxidized silicon wafers. Secondary ion mass spectrometer was used to measure the boron profile. The results showed that after long EBI time, boron tended to be induced from both sides of the transition region between the oxide layer and silicon. For the sample without oxide layer after EBI, boron tended to diffuse towards the surface and its concentration obviously reduced inside the silicon. The results of the study show the potential use of the process in removing boron impurity in silicon.

Solvent Extraction of Molybdenum (VI) from Hydrochloric Acid Leach Solutions Using P507. Part I: Extraction and Mechanism

ABSTRACTThe extractant 2-ethylhexyl phosphonic acid mono-2-ethylhexyl ester (P507) was used to selectively extract molybdenum (VI) from the hydrochloric acid leach solution of molybdenite after roasting with lime. The effects of solution acidity, organic composition, extractant concentration, impurity concentration, temperature and phase volume ratio on the separation of molybdenum (VI) over impurities of iron (III), aluminum, silicon and phosphorus were investigated. The increase in solution acidity resulted in the depolymerization of molybdenum heteropolyanions and , and the formation of molybdenum cations of . The saturated loading capacity of molybdenum (VI) with 30% (v/v) P507 in sulfonated kerosene reached 44.5 g/L. More than 99.8% of the molybdenum (VI) was extracted in a four-stage counter current extraction using an organic system consisting of 30% (v/v) P507 and 70% (v/v) sulfonated kerosene and a hydrochloric acid leach solution containing 14.8 g/L Mo(VI) and 1.73 mol/L H+ with an A/O ratio of 2.86/1 at room temperature for 7 min, while the extraction of iron(III) and phosphorus was only 1.02% and 2.96%, respectively. The separation factor of molybdenum and impurities was in the range of 104.31 ~ 105.89. The extracted molybdenum (VI) species of Mo2O5A2·2HA in the loaded organic solution was identified by the combination of the slope and saturation methods, and further proved by the FTIR spectral analysis.

Development and validation of a new method for the precise and accurate determination of trace elements in silicon by ICP-OES in high silicon matrices

A ready-to-use method for the precise and fast determination of impurities in silicon is presented.

Silicon impact on carbon ordering at the martensite lattice: molecular dynamics simulations

Despite their widespread use in the industry, silicon-alloyed bainitic steels remain understudied in many respects. There is no available in-formation on the impact of silicon impurities on the properties of martensitic structure; this article deals with this issue. We present the results of computer simulation of the impact of silicon impurities on tetragonal distortion of martensite lattice and the interaction of carbon atoms in the body-centered cubic (bcc) lattice of iron using the molecular dynamics method. We developed interatomic potentials that make it possible to describe the interactions of Fe-Si-C in martensite within the framework of the embedded atom model (EAM). It has been established that when silicon is added to steel, the lattice constant c decreases noticeably and the constant a increases slightly. The tetragonality expressed by c/a ratio decreases with respect to the results of the G.V. Kurdumov experiment for any carbon concentrations. The impact of silicon on the formation of martensite was studied through calculation by minimizing the energy of the strain-induced interaction parameter from the order-disorder transition theory in Zener-Khachaturyan interstitial solutions, which determines the critical temperature of the bcc-bct (body-centered tetragonal) transition. We have not confirmed the direct proportional dependence of the change in the tetragonality of martensite and the nature of carbon activity variation during alloying with silicon, which increases activity but decreases tetragonality.

Reduction of reverse‐leakage current in selective‐area‐grown GaN‐based core–shell nanostructure LEDs using AlGaN layers

We report a simple method to improve the p‐type doping efficiency and eliminate the diode leakage current in selective‐area‐grown GaN‐based core–shell nanostructure LEDs by growing an n‐type AlGaN layer underneath the InGaN/GaN active region. A significant reduction in reverse‐leakage current density is correlated with longer AlGaN layer growth time and higher flow rate of the aluminum precursor. A comparison of the SIMS profiles with and without the underlayer indicates a high concentration of donor‐type impurities (e.g., silicon and oxygen) in the p‐GaN layer in the structure with no AlGaN underlayer. Conversely, LEDs with an AlGaN underlayer exhibit enhanced magnesium incorporation and much lower silicon and oxygen impurity concentrations within the p‐GaN layer. The reverse current density was also reduced by the addition of a p‐type AlGaN electron blocking layer above the active region.

Weak probe readout of coherent impurity orbital superpositions in silicon

Pump-probe spectroscopy is the most common time-resolved technique for investigation of electronic dynamics, and the results provide the incoherent population decay time T1. Here we use a modified pump-probe experiment to investigate coherent dynamics, and we demonstrate this with a measurement of the inhomogeneous dephasing time T2* for phosphorus impurities in silicon. The pulse sequence produces the same information as previous coherent all-optical (photon-echo-based) techniques but is simpler. The probe signal strength is first order in pulse area but its effect on the target state is only second order, meaning that it does not demolish the quantum information. We propose simple extensions to the technique to measure the homogeneous dephasing time T2, or to perform tomography of the target qubit.

ICP-AES analysis of silicon, germanium, and their oxides

The techniques of atomic emission spectrometry with inductively coupled plasma (ICP-AES) for quantitative determination impurities in silicon, germanium, and their dioxides are developed. Analytical lines for silicon-matrix (29 trace elements) and germanium-matrix (42 trace elements) are selected. Matrix interferences caused by the presence of silicon and germanium in the solutions are studied. The optimal concentrations of matrix are determined. LODs for trace elements are in the range from n × 10–7 to n × 10–5 wt %; RSD < 20%. The accuracy of the results is confirmed by the method of “introduced–found.” The developed techniques are express, simple, and can determine a broad range of trace elements.

Diagnostics of impurity composition of high-purity monosilane by results of the analysis of a test silicon single crystal

Elements the 3 and 5 of groups of the Periodic System and carbon are the most important impurities in silicon. The estimation technique of carbon, boron and phosphorus impurity content in high-purity monosilane has been proposed. The technique involves the preparation of polycrystalline silicon by silane decomposition, growing a test single crystal by the floating zone melting method and analysis of single crystal samples by IR spectroscopy. Calculation of impurity concentration in polycrystalline silicon has been performed using results on their content in the test single crystal samples, data on impurity distribution in the liquid-solid system and sample coordinates along the ingot length. Effective impurity distribution coefficients in the solid-liquid system for specific growing conditions have been calculated using the Burton-Prim-Slichter equation. Results for the test silicon samples with natural isotopic composition and 28Si isotope enriched ones obtained from monosilane samples with different impurity contents have been reported. Results on IR spectroscopic studies of impurity composition for the test silicon single crystal are in agreement with the concentration data obtained by chromatography. The concentration of 3 and 5 group impurities in monosilane were in the range 4x10−9−2x10−6 at. %, and for carbon concentration was 2x10−6–6x10−4 at.%. The measurement uncertainty by IR spectroscopy does not exceed 15% for carbon impurity and 20% for boron and phosphorus. We show that the upper limit of carbon content in monosilane detected using this method is determined by its solubility in silicon, while the bottom limit depends on the detection accuracy of the IR spectroscopy technique and possible background contamination.

Luminescent properties of diamond single crystals of pyramidal shape

The luminescence properties of needle-like crystals of diamond, obtained by selective oxidation of textured polycrystalline diamond films, are studied. Diamond films were grown by chemical vapor deposition from a methane–hydrogen mixture activated by a DC discharge. The spectra of photo- and cathodoluminescence and the spatial distribution of the intensity of radiation at different wavelengths are obtained for individual needle-like crystals. Based on the spectral characteristics, conclusions are made about the presence of optically active defects containing nitrogen and silicon impurities in their structure, as well as the significant effect of structural defects on their luminescence spectra.

Removal of impurities from zirconium tetrafluoride using metallic zirconium chips

The sublimation refining of zirconium tetrafluoride (ZTF) from impurities in the presence of metallic zirconium chips is studied. It is shown that, in the presence of metallic zirconium chips, the contents of aluminum, nickel, oxygen, chromium, iron, and silicon impurities in a desublimate decrease and the rate of ZTF sublimation increases. The method of refining is tested under laboratory and pilot conditions and can be recommended for commercial application.

Porosity and insulating properties of silica-fume based foams

The synthesis of silica-fume based foams, with a multi-range macroporosity, was obtained by alkaline activation. Foams were obtained through an in situ foaming process exploiting the gaseous production of hydrogen caused by the oxidation, in alkaline medium, of metal silicon impurities contained in silica fume. Potassium or sodium alkaline solutions were selected and a temperature of 70°C was sufficient to promote the development of hydrogen bubbles, the increase of the viscosity and the consolidation of the foams. The balance of these reactions allowed to entrap hydrogen bubbles inside the structures creating highly porous foams. The foams were characterized in term of macro- and microstructure, porosity distribution, infrared spectroscopy, thermal and acoustic properties achieved. The foams showed ultra-macroporous structures, with a total porosity of ≈80%. The average values of bulk density (0.5gcm−3), thermal conductivity (0.16Wm−1K−1), and the acoustic behaviors, highlighted a use of the foams as promising insulating materials.