Diffusion Coefficient Of Silicon Research Articles

Assessing the EDIP potential for atomic simulation of carbon diffusion, segregation and solubility in silicon melt

Molecular simulation based on empirical interatomic potential is an important tool in the study of impurity thermophysical properties, e.g. carbon diffusion, segregation and solubility in liquid silicon, which are key factors determining the carbon concentration and distribution during silicon crystal growth. The Tersoff potentials, although being very successful in describing many silicon and carbon properties, overestimate the silicon crystal melting temperature severely which incurs many criticism and restrictions when comparing the simulation results with experiments. In this study, the EDIP potential, which predicts an experimental comparable silicon melting temperature, was assessed whether it can reasonably capture the carbon diffusivity, segregation and solubility properties in silicon melt while avoiding the well-known temperature issue. We found that the EDIP potential, without requiring scaling the temperature, predicts consistent carbon and silicon diffusion coefficients with other potentials. The segregation coefficient estimated by EDIP is slightly higher than the experimental results. It fails in capturing the carbon solubility property by overestimating nearly two orders of magnitude higher than the experimental values. Based on potential energy and entropy calculation, we suggest that the problem of the EDIP potential is caused by the high entropy of the silicon melt phase. Overall, the research will provide useful information for other thermophysical studies based on EDIP potential and also be benefit to empirical potential optimization.

Characteristic properties of macroporous silicon sintering in an argon atmosphere

The temperature and time dependences of the sintering of macroporous silicon in Ar or Ar + 3% H2 are studied. The contribution of various mechanisms governing this process is determined. The specific features of the sintering of macroporous silicon are examined by means of isochronous and isothermal annealing of the samples with ordered and random macropores in the temperature range 1000–1225°C. It is found that the sintering of macroporous silicon under atmospheric pressure in an inert gas flow containing 2 × 10–4% O2 is greatly affected by thermal etching. Thermal etching competes with the substance-transfer processes characteristic of sintering and hinders the formation of a defect-free surface crust. The reason for etching consists in that gaseous silicon monoxide is generated and then carried away by the gas flow. The etching effect is dominant in the low-temperature range and is independent of whether H2 is added. The values obtained for the activation energy of the silicon diffusion coefficient, E a = 2.57 eV, and for the exponent n = 3.31–3.74 in the time dependence of the pore radius, r ~ t 1/n are indicative of a mixed substance-transfer mechanism via the surface and volume diffusion of silicon atoms.

Growth Kinetics and Microstructure Evolution of Intermediate Phases in MoSi2-Si3N4-WSi2/Mo Diffusion Couples

The growth kinetics and silicon diffusion coefficients of intermediate silicide phases in MoSi2-3.5 vol.% Si3N4-5.0 vol.% WSi2/Mo diffusion couple prepared by spark plasma sintering were investigated in temperatures ranging from 1200 to 1500 °C. The intermediate silicide phases were characterized by x-ray diffraction. The microstructures and components of the MoSi2-Si3N4-WSi2/Mo composites were investigated using scanning electron microscope with energy-dispersive spectroscopy. A special microstructure with MoSi2 core surrounded by a thin layer of (Mo,W)Si2 ring was found in the MoSi2-Si3N4-WSi2 composites. The intermediate layers of Mo5Si3 and (Mo,W)5Si3 in the MoSi2-Si3N4-WSi2/Mo diffusion couples were formed at different diffusion stages, which grew parabolically. Activation energy of the growth of intermediate layers in MoSi2-3.5 vol.% Si3N4-5.0 vol.% WSi2/Mo diffusion couple was calculated to be 316 ± 23 kJ/mol. Besides, the hindering effect of WSi2 addition on the growth of intermediate layers was illustrated by comparing the silicon diffusion coefficients in MoSi2-3.5 vol.% Si3N4-5.0 vol.% WSi2/Mo and MoSi2-3.5 vol.% Si3N4/Mo diffusion couples. MoSi2-3.5 vol.% Si3N4-5.0 vol.% WSi2 coating on Mo substrate exhibited a better high-temperature oxidation resistance in air than that of MoSi2-3.5 vol.% Si3N4 coating.

Investigation on Structures of Aluminum Melts Containing Small Amount of Silicon Element

Aluminum melt structures play significant roles in process of impurity element eliminations. In order to investigate the aluminum melt structures containing small amount of silicon element, several compositions of aluminum melts were simulated. Molecular dynamics simulation method was employed to investigate the melt structures, concentration profiles and diffusion properties. For purpose of studying structure stability, related calculations were performed by first principles molecular dynamics method. The calculated results suggest that silicon concentration has obvious influence on silicon-silicon radial distribution function; silicon element segregates in local zone in each concentration of aluminum; there is no obvious relationship between silicon concentration and silicon diffusion coefficient; the stable Al-Si phase is formed by substitution lattice point or interstitial space; and position of Fermi energy of the stable structure corresponds to the valley of density of states.

Silicon diffusion in germanium described by connecting point defect parameters with bulk properties

Silicon diffusion properties in germanium over a range of temperatures and pressures are technologically important for the formation of efficient nanoelectronic devices. Using experimental diffusivity data it is shown that elastic and expansivity data can describe the silicon diffusion coefficients in germanium in the temperature range of 827 K to 1176 K. In that respect, the applicability of the cBΩ model, which assumes that the defect Gibbs energy is proportional to the isothermal bulk modulus and the mean volume per atom, is discussed.

Effect of Liquid-phase Siliconizing Process on Silicon Diffusion Behavior in Mo Matrix

AbstractMoSi2 functionally graded coating on Mo substrate is prepared by liquid-phase siliconizing technology. The SEM, GDS and XRD analysis shows that the silicon content in gradient layer appears in three changing regularities. Along the Mo substrate to the surface of the coating, the phase composition of gradient coating changes as follows: Mo → transition layer Mo (main phase) + Mo3Si + Mo5Si3 → intermediate layer MoSi2 → surface layer MoSi2 (main phase) + Si. According to the Si-Mo diffusion couple and Arrhenius equation, the activation energy (Q) was obtained as 430 kJ·mol−1, and the Arrhenius dependence of D on temperature can be described as D = 4.9 × 10−3 exp(−430000/RT) m2/s. The diffusion temperature has an important influence on silicon diffusion coefficient. As the diffusion temperature increases, silicon diffusion coefficient is also gradually increasing.

Diffusion mechanisms in lithium disilicate melt by molecular dynamics simulation

In this work we study the diffusion mechanisms in lithium disilicate melt using molecular dynamics simulation, which has an edge over other simulation methods because it can track down actual atomic rearrangements in materials once a realistic interaction potential is applied. Our simulation results of diffusion coefficients show an excellent agreement with experiments. Using the diffusion coefficient of silicon, we are able to demonstrate that this glass-forming liquid obeys the well-known Stokes–Einstein relation at least down to 1600K. The relaxation obtained via the self-part of the intermediate scattering function decouples from viscosity measurements at temperatures below 2000K. Additionally, an analysis on the dynamical behavior of slow-diffusing atoms reveals explicitly the presence of dynamical heterogeneities.

Microstructure of MoSi<sub>2</sub> Coating with B Addition Prepared by Vacuum Cladding

The high-temperature oxidation-resistant MoSi2 coating with B addition on Mo substrate was prepared by vacuum cladding. The structure and composition of the coating were investigated by SEM and EDS. The results indicate that good metallurgical bond between all coatings and substrate has been developed. Throughout cracks were avoided by the addition of B. Three multi-layer structures as MoSi2, Mo5SiB2, and Mo3Si were formed by diffusion from outside to inside. The thickness of Mo5SiB2 layer was reduced because of the decreased diffusion coefficient of silicon in MoSi2 with the addition of boron.

Study of selective oxidation by means of glow discharge optical emission spectroscopy

In the continuous annealing process, steel sheets are annealed at 800 °C in an atmosphere of nitrogen and hydrogen (5 vol.%) containing low water partial pressure (20–50 Pa). Under these conditions, the most oxidizable alloying elements in the steel segregate towards the surface where they form oxide particles. The Mn, Al, Si and B concentration gradients resulting from this selective oxidation were measured as a function of annealing time by the glow discharge optical emission spectroscopy method. The manganese and silicon diffusion coefficients in steel were then estimated using Wagner’s diffusion model.

High-temperature and electrochemical oxidation of transition metal silicides

High-temperature and electrochemical oxidation of transition metal silicides, which are widely used in microelectronics as ohmic contacts and protective coatings for high-temperature alloys, are discussed in this review. The process of oxide film formation during annealing or anodizing is extremely important for both applications of silicides. It is discussed for three disilicides: MoSi2, WSi2, and TiSi2. It has been shown that different types of oxide films may form on the disilicide surface depending on the thermodynamic (formation enthalpies of silicides and associated oxides) and kinetic (diffusion coefficients of silicon in silicide and oxygen diffusivity in oxide) factors: onephase (MoSi2), mixed (WSi2), and multilayer (TiSi2) films. The “silicide pest” phenomenon is discussed in terms of thermodynamic, kinetic, and structural factors influencing the pesting. Analysis of electrochemical oxidation mechanisms for silicides in various electrolyte media reveals numerous similarities between anodic and high-temperature oxidation mechanisms. It is shown that slow silicon transport during anodic treatment at room temperature leads to the formation of multiphase mixed oxide films under electrochemical polarization.

Growth kinetics of Mo 3Si layer in the Mo 5Si 3/Mo diffusion couple

The diffusion processes and growth kinetics of the Mo 3Si silicide layer occurring at annealing the Mo 5Si 3/Mo diffusion couple between 1180 and 1800 °C were studied by electrothermography. The experimental results are supplemented with calculations on the behaviour of the initial Mo 5Si 3/Mo diffusion couple on the basis of the reaction diffusion model describing the transformation of the Mo 5Si 3 layer into a Mo 3Si one. The values of the parabolic growth constant for Mo 3Si layer were determined and the silicon diffusion coefficient in the Mo 3Si phase was calculated: D = 0.165 exp[(− 247 ± 10) / RT], cm 2/s, where the activation energy is expressed in terms of kJ/mol.

Simulation of alloying-element diffusion during electrodiffusion heat treatment of steels

The effect of an electric current on the diffusion of alloy-forming components and vacancies in alloy steels subjected to electrodiffusion heat treatment has been studied. The diffusion coefficients of chromium, silicon, and aluminum are shown to increase by one to three orders of magnitude as compared to the reported data.

Diffusion annealing of Mo/MoSi 2 couple and silicon diffusivity in Mo 5Si 3 layer

Kinetics of molybdenum disilicide (MoSi 2) layer transformation into Mo 5Si 3 one was studied at isothermal annealing of the MoSi 2/Mo diffusion couple within the temperature interval 1200–1800 °C. It was revealed that the growth of intermediate silicide layer followed a parabolic law and did not accompanied by formation of the lowest Mo 3Si silicide. By analyzing the diffusion problem solid-phase diffusion coefficient of silicon in the Mo 5Si 3 layer was calculated.

Modeling of low temperature SiGe oxidation

A mathematical model for low temperature oxidation of strained Si 1− x Ge x alloys has been developed. Based on the growth kinetics of ultrathin (<10 nm) SiO 2/GeO 2 on strained- Si 1− x Ge x layer, the growth of oxide is simulated using analytical methods. The main feature of the model is the assumption of simultaneous oxidation of germanium and silicon when exposing the Si 1− x Ge x to an oxidizing atmosphere. It is found that the model gives a good account of the oxidation process. Kinetic parameters, i.e., interfacial reaction rate constant for oxidation of germanium and diffusion coefficient of silicon (germanium) in Si 1− x Ge x , are extracted by fitting the simulation to the experimental data. The developed model is implemented in commercial process simulator SILVACO-ATHENA for SiGe MOSFET simulation.

Si diffusion in epitaxial GaN

AbstractThe aim of this work is to determine diffusion coefficient of silicon in gallium nitride under different annealing conditions. Silicon was implanted into 3 µm thick GaN layer deposited on sapphire substrate with MOVPE (Metalorganic Vapour Phase Epitaxy) method. Implantation was performed at room temperature to a dose of 6×1015/cm2 at energy of 100 keV. The samples were annealed under 1 atm nitrogen pressure at 900–1200 °C with or without an AlN protective layer. The extent of diffusion of the implanted species was characterized using the SIMS (Secondary Ion Mass Spectrometry) technique. The resultant concentration profiles are characterized with two diffusion fronts: slow diffused Si atoms at high concentration and fast diffused Si atoms at low concentration. We ascribe the first mechanism as to originate from diffusion in the crystal bulk (substitutional migration), while the second one – from diffusion via grain boundaries/dislocations. Si diffusion coefficient in a crystal was found to be dependent on annealing conditions, in contrast to diffusion via grain boundary. Calculated diffusion coefficient parameters for annealing with and without AlN layer amount respectively to: DO = 6.5×10–11 cm2/s, Ea = 0.89 eV and DO = 9.1×10–8 cm2/s, Ea = 1.55 eV. (© 2006 WILEY‐VCH Verlag GmbH &amp; Co. KGaA, Weinheim)

Study of fast diffusion species in Sc/Si multilayers by W-based marker analysis

Interdiffusion in periodic Sc/Si multilayers with W-based diffusion markers was studied by cross-section transmission electron microscopy and small angle X-ray diffractometry (SAXD). Formation of amorphous ScSi silicide was observed as a result of solid-state amorphization taking place in the Sc/Si multilayers in the 210–250 °C temperature range. The diffusion-governed growth behavior of the amorphous silicide was revealed. The diffusion marker analysis was applied to determine a ratio of intrinsic diffusion coefficients of scandium and silicon. The diffusion-induced shift of the diffusion markers was measured by SAXD with accuracy better than 0.2 nm. It was determined that the intrinsic diffusion coefficient of Si in amorphous silicide was twenty times higher than the one of Sc.

Growth Kinetics and Silicon Diffusivity in MoSi&lt;sub&gt;2&lt;/sub&gt; and WSi&lt;sub&gt;2&lt;/sub&gt; Disilicides

Growth kinetics and silicon diffusivities in MoSi2 and WSi2 silicide phases were studied at selected temperatures over the temperature range from 900 to 1500 o C using reaction between dense metal and silicon vapor. Experiments were carried out by electrothermography method [1] using molybdenum and tungsten wires 100 µm in diameter and 8.5 cm length as initial samples directly heated by electrical current. As a silicon source rarefied monosilane was used providing controllable conditions of the silicon supply to the metal surface. To ensure diffusive mode of interaction the partial pressure of silane was selected in the way that certain prevailing of the rate of silicon supply to the surface over the rate of its diffusion into the formed silicide layer was provided in order to hinder the formation of a redundant solid silicon layer (at T < Si melt T ). It is established that for the case of molybdenum two compact uniform layers (MoSi2 and Mo5Si3) were observed in diffusion zone, and the MoSi2 layer was by about one order of magnitude larger in thickness than the Mo5Si3 layer. In the case of tungsten a single-layered diffusive zone is formed, consisting of WSi2 compact and uniform layer; the W5Si3 silicide is not detected at all. In all cases growth kinetics of disilicide layers, up to 5-7 µm thicknesses, conforms well to the parabolic law, which testifies indirectly that the first type boundary condition is realized on the gas medium/MeSi2 boundary. The silicon diffusion coefficients in MoSi2 and WSi2 layers were calculated on the basis of measured parabolic growth constants.

Kinetics of Structural and Phase Transformations in Thin SiO[sub x] Films in the Course of a Rapid Thermal Annealing

Infrared spectroscopy and analysis of photoluminescence spectra have been used to study variations in the composition of the oxide phase in a SiOx film and the precipitation of the Si phase in the course of a rapid thermal annealing for 1–40 s at temperatures of 500–1000°C. Kinetics of phase segregation has been observed for the first time at temperatures of 600–700°C: an increase in the amount of precipitated silicon as the annealing duration increases followed by an eventual leveling off. The phase separation is brought to completion in a time as short as 1 s at temperatures higher than 900°C. The diffusion coefficient is estimated in the context of a model of the diffusion-controlled formation of Si nanoparticles. The obtained values of the diffusion coefficient exceed, by five to ten orders of magnitude, those of the silicon diffusion coefficients in SiO2 and Si and are comparable to the diffusion coefficients of the oxygen contained in these structures. It is assumed that oxygen mobility forms the basis for the mechanism of structural and phase transformations in the SiOx layers and for the formation of Si nanoparticles in the course of annealing.

Physicochemical interaction at the contact of higher manganese silicide with chromium

Diffusion processes taking place at the contact of higher manganese silicide MnSi1.71−1.75 with chromium at elevated temperatures are considered. The microstructures of cast and annealed samples show a diffusion region that evolves at the HMS/Cr interface during the HMS melt crystallization on chromium flakes. As the temperature and time of annealing of HMS/Cr samples increase, the diffusion region grows thicker and new phases appear. It is shown that the diffusion is of reaction character. The diffusion coefficients of magnesium, chromium, and silicon in the solid solution based on manganese and chromium monosilicides and in the solid solution based on the Cr3Si compound are calculated. It is also shown that, when the temperature of the HMS used as a thermoelement positive leg is optimal, the depletion time of a 10-µm-thick chromium layer exceeds 15000 h. Intermetallic phases forming in the diffusion region between the HMS and Cr are of metallic conduction and exhibit a high thermal conductivity, which minimizes energy losses in the contact layers of thermoelements.

Solid state Si diffusion and joint formation involving aluminum brazing sheet

The paper provides information about the use of in situ determined diffusion coefficients of silicon for modeling of a brazed joint formation, i.e. formation of the equilibrium surface of a molten Al+ xSi alloy at the onset of solidification in the joint. Diffusion coefficients of Si were determined (within both the joint and/or residue zone) to analyze its migration across the clad–core interface of an Al brazing sheet, including both the period prior to reaching brazing temperature range, and the peak brazing temperature range. Subsequently, diffusion coefficients were used to predict the joint formation during brazing. Migration of silicon is not uniform along the clad–core interface during brazing and depends, in addition to material characteristics and process parameters, on the vicinity of the joint zone. It is argued that, due to these alterations, the joint formation modeling must be performed by using in situ determined diffusion coefficients. The diffusion coefficients determined directly from electron probe microanalysis (EPMA) scans at different locations along the cladding sheet and within the joint zone differ between each other and when compared to the literature data. This variation influences the outcome of the residue formation modeling; hence the joint formation modeling may be affected. The relation between these phenomena is briefly discussed and quantitative data regarding diffusion coefficients, and in particular an approach to utilization of these data in modeling of joint formation, are provided.