Segregation Coefficients Of Impurities Research Articles

Numerical Simulation of Flow Field Optimizing the Rotating Segregation Purification of Silicon for SoG-Si

In order to improve the preparation efficiency of high-purity silicon, a new method of rotary segregation purification has been developed to prepare polysilicon. Numerical simulation based on ANSYS19.0 software and water model experiments were used to study the distribution of flow field and optimize the impurity removal process. A numerical simulation model suitable for rotating interface is established. The simulation result is in good agreement with the water model experiment. A vortex flow is found in the middle of the mold when the mold insertion depth is 90 mm. The vortex is conducive to the thinning of the impurity enrichment layer at the solid–liquid interface. With the mold insertion depth increases from 90 to 170 mm, two vortex flows appear in the middle and bottom of the mold, respectively. Moreover, setting the mold rotation rate at 100 rpm can contribute to a more stable flow field and a higher melt flow velocity. When the diffusion layer thickness is less than 0.1 mm, the impurity segregation coefficient can approach close to its equilibrium segregation coefficient, indicating that impurity segregation be effectively enhanced by increasing the rotation rate of mold, strengthening the effect of solidification rate and increasing the rotational speed. Industrial tests were carried out at the 100 kg level. The result shows that the rotary segregation method and equipment can achieve the removal of very low impurity in silicon (99.999 pct), and SoG-Si (99.9999 pct) was obtained. This method provides a new way for silicon purification, and it is believed that better results can be obtained through continuous improvement.

INFLUENCE OF PHOSPHORUS IMPURITY ON THE STRUCTURE AND NATURE OF THE DESTRUCTION OF THE GENUINE DAMASCUS STEEL

It is established that the ancient knife blade belongs to the Eastern group of Indo-Persian steel type genuine Damascus steel with a pattern of "Kara-Taban", which literally means blackshiny. The methods of spectral, x-ray phase and optical analysis show that the genuine Damascus steel is a high-purity non-alloy high-carbon steel with a high content of phosphorus. It is revealed that phosphorus, having a high segregation coefficient of impurity contributes to the process of segregation of carbon in the process of crystallization of crucible ingots. The main physical and chemical factors influencing morphology of structure formation of genuine Damascus steel are revealed. It is established the relationship between the structure and the nature of the destruction of the genuine Damascus steel under impact load.

Influence of Impurities on the Radiation Response of the TlBr Semiconductor Crystal

Two commercially available TlBr salts were used as the raw material for crystal growths to be used as radiation detectors. Previously, TlBr salts were purified once, twice, and three times by the repeated Bridgman method. The purification efficiency was evaluated by inductively coupled plasma mass spectroscopy (ICP-MS), after each purification process. A compartmental model was proposed to fit the impurity concentration as a function of the repetition number of the Bridgman growths, as well as determine the segregation coefficients of impurities in the crystals. The crystalline structure, the stoichiometry, and the surface morphology of the crystals were evaluated, systematically, for the crystals grown with different purification numbers. To evaluate the crystal as a radiation semiconductor detector, measurements of its resistivity and gamma-ray spectroscopy were carried out, using 241Am and 133Ba sources. A significant improvement of the radiation response was observed in function of the crystal purity.

Effect of Temperature on Segregation Coefficients of Impurities in Phosphorus

The present work is focused on the relationship between effective segregation coefficient keff and temperature of melting zone for purification of phosphorus by zone melting method. Values of keff at four temperatures of melting zone are obtained for zone pass n=1 at travel velocity of molten zone v=5×10−3 m·h−1 and initial impurity concentration C0≤10 μg·g−1. lnkeff is a linear function of 1/T. The keff values of Al, Ca, Cr, Fe, Cd and Sb increase with temperatures while that of Mg is almost constant. The purification is acceptable at lower temperature of melting zone such as 323 K. The variations of enthalpy and entropy between impurities and phosphorus in the liquid and solid phases are also presented.

Study of the initial transient in the one-dimensional analytical models of impurity segregation during melt crystallization in the presence of convection

The well-known one-dimensional Burton-Prim-Slichter and Ostrogorsky-Muller analytical models obtained for the stationary mass transfer regime describe in a simple form the dependence of the effective impurity segregation coefficient on the ratio of the crystal growth and convective flow rates. Solutions for the initial transient regime are found in both models. It is shown that the formulas obtained make it possible to determine both the crystal growth rate and the convective mixing intensity on the basis of the analysis of impurity segregation in crystal.

Theory of ice premelting in porous media

Premelting describes the confluence of phenomena that are responsible for the stable existence of the liquid phase of matter in the solid region of its bulk phase diagram. Here we develop a theoretical description of the premelting of water ice contained in a porous matrix, made of a material with a melting temperature substantially larger than ice itself, to predict the amount of liquid water in the matrix at temperatures below its bulk freezing point. Our theory combines the interfacial premelting of ice in contact with the matrix, grain-boundary melting in the ice, and impurity and curvature induced premelting, with the latter occurring in regions which force the ice-liquid interface into a high curvature configuration. These regions are typically found at points where the matrix surface is concave, along contact lines of a grain boundary with the matrix, and in liquid veins. Both interfacial premelting and curvature induced premelting depend on the concentration of impurities in the liquid, which, due to the small segregation coefficient of impurities in ice are treated as homogeneously distributed in the premelted liquid. Our principal result is an equation for the fraction of liquid in the porous medium as a function of the undercooling, which embodies the combined effects of interfacial premelting, curvature induced premelting, and impurities. The result is analyzed in detail and applied to a range of experimentally relevant settings.

The distribution of Ga and Sb impurities in Ge-Si crystals grown by the Bridgman method using a feeding rod

Gallium- and antimony-doped Ge1 − xSix crystals (0 ≤ x ≤ 0.25) have been grown by the improved Bridgman method using a silicon seed and a macrohomogeneous feeding Ge-Si rod of the corresponding composition. The impurity concentration profiles along the grown crystals were determined from Hall measurements. The mathematical problem of impurity distribution along two-component mixed crystals grown from a melt with uniform and graded composition is solved in the Pfann approximation and within the virtual-crystal model for the solid solution. It is shown that the experimental impurity distributions in Ge1 − xSix crystals are described well by the data calculated on the assumption of linear change in the impurity segregation coefficient with the crystal composition.

Distribution of aluminum and indium impurities in crystals of Ge-Si solid solutions grown from the melt

The problem regarding the distribution of aluminum and indium impurities in bulk crystals of solid solutions with a variable composition Ge1−x Si x (0 ≤ x ≤ 0.3) is solved in order to establish regularities of the changes in the segregation coefficients of impurities with variations in the composition of the host lattice in the germanium-silicon system. Aluminum-and indium-doped crystals of Ge1−x Si x (0 ≤ x ≤ 0.3) solid solutions with a silicon content decreasing along the crystallization axis are grown by a modified Bridgman method with the use of a silicon seed. The concentration distribution of impurities over the length of the crystals is determined from Hall measurements. It is demonstrated that the experimental data on the concentration distribution of impurities in the crystals are in good agreement with the results obtained from the theory according to which the equilibrium segregation coefficients of impurities vary linearly with a change in the composition of Ge-Si solid solution crystals.

Segregation coefficient of impurities at polycrystalline Si/HfO 2 interfaces

We evaluated the segregation coefficient m of B, P, and As at the polycrystalline Si/HfO 2 interface. The m values of B, P, and As are between 0.3 and 1 and are similar to that of B at the polycrystalline Si/SiO 2 interface. The m value of P at the polycrystalline Si/SiO 2 interface is around 1000, and this high value largely keeps P from penetrating the thin gate SiO 2. Therefore, the penetration of B, P and As through a poly-Si/HfO 2 layer is expected to be significant since the diffusion coefficients of P and As in HfO 2 are also high, making the use of a cover layer indispensable for p + and n + polycrystalline silicon gate devices.

Effect of Temperature on Segregation Coefficients of Impurities in Tellurium

The lowest values of effective segregation coefficients Keff of impurities in tellurium are the main parameters required to obtain an optimal purification ( ≥ 6N). A series of (13 × 4) values of Keff were determined at the same starting concentration C0 and velocity of interface v. Four different temperatures of the molten zone were used. The effect of some of these values was investigated for the first time. The influence of temperature in zone refining was analyzed through the relation of ln Keff versus 1/T. Experimental study showed two kinds of impurities. The first one was easily removed despite the variation of T while the other was strongly affected by T and trapped in the molten zone. The activation energies of 13 impurities in tellurium were also determined. The values of Keff seems to be acceptable about 773°K. For the molten zone, we proposed an adequate temperature range which was about 50°K higher than the melting temperature of tellurium. This was necessary to achieve an electronic grade purification of tellurium with a good efficiency by zone melting process.

Molecular Modeling of Bulk Impurity Segregation and Impurity-Mediated Crystal Habit Modification of Naphthalene and Phenanthrene in the Presence of Heteroimpurity Species

The ability to predict particle morphology (shape) in the presence of habit-modifying impurities is of great use in allowing the optimization of growth conditions to produce a required crystal habit. Previous morphological modeling techniques developed by the authors1,2 utilized the attachment energy method, which assumes knowledge of the solid-state structure, to simulate the shape of organic particulate solids while keeping the position of the impurity in the lattice fixed. These techniques are improved upon here by allowing the orientation of the adsorbing impurity molecule to be relaxed with respect to the intermolecular forces of the crystal bulk using a restricted molecular mechanics approach. This results in far more accurate attachment energiesand hence morphological simulationsthan could be achieved before. The calculations also allow improved binding energies for additives in different crystal faces to be ascertained; these can be used as a measure of the equilibrium impurity segregation coefficient for liquid/solid solidification. The method is illustrated by considering the morphological impact of a variety of host/additive systems, including naphthalene doped by biphenyl and phenanthrene crystallizing in the presence of biphenyl or anthracene. A forward look to the development of this approach for more complex systems is also provided.

Segregation Behavior of Impurities in Gallium during Directional Solidification

The effective solid–liquid segregation coefficients of impurities in Ga were measured in binary and multicomponent gallium–impurity (Sn, In, Cu, Ge, Ag) systems. The results demonstrate that the introduction of Sn into both binary and multicomponent systems notably increases the effective segregation coefficients of the other impurities. The likely reason is that the presence of Sn leads to the formation of linear and planar defects, which gives rise to nonequilibrium impurity trapping by the growing gallium crystal.

Molecular dynamics simulation of morphological instabilities in solid-fluid interfaces

We perform molecular dynamics simulations of directional growth of a binary alloy. We fix the temperature gradient, pulling speed, impurity concentration and only vary the impurity segregation coefficient. By changing the range of the Lennard Jones potential of impurity atoms as compared to the range of the potential of solvent atoms, the elastic energy cost causes a decreases of solubility of the impurity atoms into the matrix (solvent) solid phase and consequently a decrease in the impurity segregation coefficient. Within certain range of segregation coefficients, the growing interface is planar; below it, the interface becomes unstable and a cellular structure emerges.

Effect of Cu(II) ions on the growth of ammonium oxalate monohydrate crystals from aqueous solutions: growth kinetics, segregation coefficient and characterisation of incorporation sites

The experimental results of a study of the effect of concentration of Cu(II) ions and solution supersaturation on growth rates of ammonium oxalate monohydrate crystals, impurity segregation coefficient and sites of incorporation of cations in the crystal lattice are described and discussed. It is found that the effects of impurities on growth kinetics and the value of the segregation coefficient are related processes and involve adsorption of impurity particles on growing surfaces. Examination of EPR spectra shows that high incorporations of Cu(II) ions in the crystal lattice favour the substitution of ammonium sites while at low incorporations copper(II) ions enter the lattice both in interstitial and substitutional lattice positions.

Segregation coefficients of impurities in selenium by zone refining

The purification of Se by zone refining process was studied. The impurity solute levels along the length of a zone-refined Se sample were measured by spark source mass spectrographic analysis. By comparing the experimental concentration levels with theoretical curves the segregation coefficient, defined as the ratio of equilibrium concentration of a given solute in the solid to that in the liquid, k= x s/ x l , for most of the impurities in Se are found to be close to unity, i.e., between 0.85 and 1.15, with the k value for Si, Zn, Fe, Na and Al greater than 1 and that for S, Cl, Ca, P, As, Mn and Cr less than 1. This implies that a large number of passes is needed for the successful implementation of zone refining in the purification of Se.

Structural and phase changes in metals and alloys crystallized in a gamma-ray flux

This review presents data on the influence of γ-irradiation (1011–1012 kW/cm2) on the process of crystallization of metals and alloys. Studies are presented of the structure, phase composition, crystallization parameters, and redistribution of impurities along single crystals. We show that the relationship between the phase and structural components changes under irradiation, while an improvement of the structure of single crystals of metals and alloys, an enhancement of the efficiency of purifying them of impurities, more intensive mixing of alloys, and a decrease in the thickness of the diffusion layer at the melt-crystal phase boundary take place. Under the action of γ-irradiation the crystallization parameters are altered: the equilibrium temperatures of the process and the segregation coefficients of impurities. This alters the crystallization mechanism. Possible mechanisms of the observed phenomena are discussed.

Silicon incorporation anomaly in LEC grown GaAs

The growth of Si doped LEC GaAs shows a significant deviation in the Si incorporation from the prediction of a classic segregation model. As a rule, it is expected that for a given impurity segregation coefficient, the dopant incorporation throughout the crystal may be calculated with fairly good accuracy. In fact, Te-doped GaAs LEC doping profiles show a close approximation to this classic model. However, in Si doped GaAs LEC growth, the doping distribution in the crystals deviates significantly from the segregation model. In some cases, this deviation is of several orders of magnitude. The degree of deviation was found to be dependent on the growth conditions. This work was performed to understand the source of the deviation from the model and to allow for an accurate account of the Si incorporation. In this work, Si doped GaAs crystals were grown by low pressure LEC. These crystals were targeted for doping in the 1016 to low 1018 cm-3 range. The actual dopant incorporation was significantly lower than the segregation model predicted, and the axial doping variation was much too flat. Moreover, in spite of an intentional Si doping, a significant number of crystals were semi-insulating. Analysis of the experimental data has shown that this doping behavior cannot be explained by the assumption of an unknown compensating impurity. A different model has been developed that is consistent with all of our observations and that provides an accurate account of the Si incorporation. Understanding the Si incorporating anomaly has allowed us to make successful process changes and improvements. This model explains the observed doping anomaly by taking account of the diffusion of Si between the GaAs melt and the B2O3 encapsulant, as well as some permanent Si trapping in the B2O3. When the interaction of the Si with B2O3 is taken into account, the Si incorporation follows the segregation model and the anomaly vanishes.

Effect of Lattice Mismatch on Electric Properties near Heterointerface of InxGa1-xAsyP1-y(y

The electrical properties near the heterointerface of InxGa1-xAsyP1-y(y<0.01) grown on (100) GaAs by liquid phase epitaxy are investigated as a function of the lattice mismatch (Δa/a)⊥. It is shown that the electron mobility is limited by the space-charge scattering which is increased with increasing (Δa/a)⊥. The space-charge scattering due to the lattice-mismatch becomes significant near the heterointerface (≃0.1 µm). The in-depth profile shows that the electron mobility is decreased and the electron concentration is increased near the heterointerface (≃0.1 µm). This is attributed to the high segregation coefficient of impurities at the initial growth step as well as the misfit dislocation.

Metastable honeycomb model of laser annealing

A model for microstructural double bifurcation following abrupt energy deposition by intense laser pulses to produce epitaxial regrowth of disordered Si surface layers can account for recent observations that indicate local heating far below the bulk melting point. The model also indentifies and explains anomalous functional behavior in k′(v), the crystal impurity segregation coefficient, as a function of regrowth front velocity v.

Pulsed Laser Annealing of Ion Implanted Si

In order to clarify an influence of initial spin density or optical absorption coefficienton the pulsed-laser annealing effect, we have performed systematically ion backscatteringand channeling (RBS) analysis and ESR measurement as a function of spindensities in ion-implanted Si samples. An effect of implanted ion species has also beeninvestigated. It was found that the initial spin density can yield a good criterion forpredicting the annealing effect below implanted doses of 1×1016 /cm2 because the spindensity is strongly correlated with the optical absorption coefficient. From spindensitymeasurement, the initial absorption coefficient of as-implanted Si layer was foundto be a very important factor which dominates the effect of laser annealing even if thereis a nonlinear absorption mechanism. As to impurity effect, it was also clarified thatlaser annealing effects are much different among ion species. This seems to be duemainly to the difference of segregation coefficient of impurity in Si.