Diffusion Of Impurity Atoms Research Articles

Low-temperature strain aging in In–Pb alloys under conditions of stress relaxation

In the stress-relaxation regime the dynamic strain aging (DSA) in single crystals of the substitutional solid solutions of substitution In–Pb with 6 and 8 at. % Pb is investigated at temperatures of 77–205 K. It is determined how the DSA-related post-relaxation hardening depends on the duration of the stress relaxation, the rate of change of the stress at the end of the relaxation, the temperature, the concentration of the alloy, the flow stress, and the degree of deformation. It is shown that the DSA kinetics is described by an equation of the Harper type with an exponent of 1/3 and a low value of the activation energy for the process (0.3–0.34 eV), which makes for a low temperature for the onset of DSA (∼0.17 Tm, where Tm is the melting temperature) and is indicative of a pipe character of the diffusion. It is assumed that the obstacles to the motion of dislocations in these crystals are impurity complexes, the strength of which increases during DSA as a result of the pipe diffusion of impurity atoms al...

Changes in lithium isotopic composition in hydrogen-enriched Ti/Al systems

Changes in the isotopic composition of electrolyte lithium are studied experimentally when thin-film titanium-aluminum systems are enriched in hydrogen. Strong deviations of the lithium isotope concentration from their natural abundances are observed both in the surface titanium layer and at the titanium-aluminum interface. Analysis of the experimental results permits us to conclude that isotope-induced transformations occur in materials enriched in hydrogen due to cold diffusion of impurity atoms stimulated by hydrogen migration and non-equilibrium chemical reactions.

Atomistic analysis of the vacancy mechanism of impurity diffusion in silicon

The complete set of the four macroscopic transport coefficients describing the coupled diffusion of impurity atoms and vacancies in silicon is calculated from the atomistic mechanism by accurately taking into account the effects of the microscopic forces between dopants and vacancies. The aim of these simulations is to come to a decision concerning the validity of models like the pair diffusion model [e.g., M. Yoshida, J. Appl. Phys. 48, 2169 (1977); R. B. Fair and J. C. C. Tsai, J. Electrochem. Soc. 124, 1107 (1977); F. F. Morehead and R. F. Lever, Appl. Phys. Lett. 48, 151 (1986); B. J. Mulvaney and W. B. Richardson, Appl. Phys. Lett. 51, 1439 (1987)] or the “non-Fickian diffusion” model [M. Kurata, Y. Morikawa, K. Nagami, and H. Kuroda, Jpn. J. Appl. Phys. 12, 472 (1973); Y. Morikawa, K. Yamamoto, and K. Nagami, Appl. Phys. Lett. 36, 997 (1980); V. V. Kozlovski, V. N. Lomasov, and L. S. Vlasenko, Radiat. Eff. 106, 37 (1988); O. V. Aleksandrov, V. V. Kozlovski, V. V. Popov, and B. E. Samorukov, Phys. Status Solidi 110, K61 (1988), K. Maser, Exp. Tech. Phys. (Berlin) 34, 213 (1986), K. Maser, Ann. Phys. (Leipzig) 45, 81 (1988), K. Maser, Exp. Tech. Phys. (Berlin) 39, 169 (1991)] that make contradicting predictions for very fundamental properties like the relative direction of the fluxes of dopants and vacancies driven by a vacancy gradient and for the relation α=Td0/Dd0 between two of the four transport coefficients. Simulation results are shown for a variety of assumed interaction potentials that establish a functional dependence between α and measurable quantities, like the factor Dd/Dtracer of enhancement of dopant diffusivity over tracer diffusion, that holds for an arbitrary interaction. The comparison with experimental values for Dd/Dtracer leads to confirmation of the pair diffusion model for boron and phosphorous. For arsenic and antimony, the large scatter of the experimental data prohibits an equally definite conclusion, but at least a qualitative confirmation of pair diffusion theory (i.e., α>0 which means that dopant and vacancy fluxes have the same direction if caused by a vacancy gradient) is possible.

A Model of Coupled Diffusion of Impurity Atoms and Point Defects in the Vicinity of Semiconductor Interfaces and Grain Boundaries

A Model of Coupled Diffusion of Impurity Atoms and Point Defects in the Vicinity of Semiconductor Interfaces and Grain Boundaries

Diffusion of self-interstitial atoms in silicon

Self-interstitial atoms are the principal point defects in silicon. These defects influence the diffusion of impurity atoms in silicon and their solubility. A method for the independent determination of the equilibrium concentration and of the diffusivity of these self-interstitials is suggested. In the framework of this approach some experimental results are discussed.

Enhanced Diffusion of Impurities and Defects in Crystals in Conditions of Ultrasonic and Radiative Excitation of the Crystal Lattice

AbstractOn the basis of the quantum theory of diffusion the influence of crystal lattice excitations (ultrasonic, nuclear irradiation) on the diffusion of impurity atoms is analysed. The effects considered in the paper are determined by two factors: the change of population of the impurity oscillator levels due to interaction with nonequilibrium excitations of the crystal lattice, and the changé of the probability of diffusion transitions on the given level. The effects are qualitatively different for heavy impurity atoms whose diffusion is enhanced in nonequilibrium conditions and for light impurity atoms for which the effect of additional localization is possible.

Dopant redistribution during annealing of amorphized Si〈111〉

Abstract Diffusion of impurity atoms in solid-phase epitaxially grown silicon layers was studied by back-scattering spectrometry. The samples were amorphized by ion implantation with As and Ge into 〈100〉- and 〈111〉-oriented samples. The amorphized regions were recrystallized by furnace annealing. Asymmetrically enhanced diffusion is observed for 〈111〉 samples for both As and Ge. The results are discussed qualitatively in terms of increased point-defect injection at the surface.

Stochastic modeling of cascade damage — collisional processes

A stochastic method of modeling was developed for the processes containing cascade collisions, and applied to the problems of the diffusion of impurity atoms and the evolution of precipitates under irradiation producing cascades. Calculations are presented for the first and second moments of the fluctuating loss of impurity atoms constituting precipitates which is produced by cascade sputtering and subsequent thermal migrations. These moments, together with those related to the cascade disordering of precipitates and the transport of impurity atoms to precipitates by diffusion associated with neighboring cascades, provided Fokker-Planck equations which describe the evolution of precipitates.

The effect of heat treatment on redistribution of fast diffusing impurities in polycrystalline silicon

The effect of heat treatment on minority carrier surface recombination velocity in polycrystalline silicon samples has been examined in the temperature range (600–900 °C) using the electron-beam induced-current mode of a scanning electron microscope. Minority carrier trap center density, calculated from minority carrier surface recombination velocity data, varying from 8.9×1011 to 6.37×1013 cm−2 have been measured. A finite variation in the minority carrier trap center density indicates that metallic impurities diffuse to the surface from the bulk of the sample. The activation energy of impurity atom diffusion is found to be 1.1±0.1 eV.

Strain in evaporated Nb thin films

Strain behavior of polycrystalline Nb thin films deposited onto oxidized silicon substrates using an electron gun in a high vacuum system was studied by an x-ray diffraction technique. The sign and magnitude of strain in Nb thin films were found to have a strong dependence on the film thickness. For films thinner than approximately 10 nm, the compressive strain was observed, which was considered to be due to diffusion of impurity atoms, most likely oxygen, into grain boundaries of Nb films within an extremely short distance from the film surface. For thicker films, the tensile strain was observed and a strong dependence of the strain (normal to the film surface) on crystal orientations of grains was observed. This dependence agreed very well with the one calculated using a biaxial stress model. The biaxial stress applied in the planar direction was calculated to be 1.0×1010 dyne/cm2 from the measured strain values. The present result indicates that the strain in the Nb films is not induced by temperature increase during the film preparation, but it is more likely due to grain growth during and/or immediately after the film deposition. Based on the biaxial stress model and strain distributions parallel and normal to the substrate planes and strain energies stored in grains with different crystal orientations were calculated.

Implantation of dopants in InSb with the aid of laser radiation

A study was made of the process occurring in the course of laser implantation of tellurium and selenium atoms in indium antimonide. The surface topography after irradiation, the implanted atom profiles, and electrophysical characteristics of the junctions formed in indium antimonide were investigated. Possible mechanisms of the diffusion of impurity atoms from diffusant films of different thicknesses subjected to illumination with laser radiation of different energy densities were analyzed.

Comments on "Two-dimensional numerical analysis of impurity atom diffusion in semiconductors"

Comments on "Two-dimensional numerical analysis of impurity atom diffusion in semiconductors"

Kinetics of impurity particles in low-temperature matrices

The correlation between impurity atom diffusion coefficients and the parameters of interaction potentials of impurities with low-temperature matrix particles is established. The kinetics of the impurity particles in such a system is investigated and the possibility for obtaining information both on the diffusion coefficients and interatomic interaction potential parameters from the spectroscopic data is shown. The thermal conditions of the system are studied, that made it possible to determine the limits with respect to thermal instability as well as temperatures and size of the matrix. [Russian Text Ignored]

FEDSS—Finite-element diffusion-simulation system

The FEDSS program simulates semiconductor processes in two dimensions. An accurate model of the diffusion of impurity atoms into a substrate is necessary to assess the effects of process changes on impurity profiles. The process steps to be modeled include ion implantation, oxidation/drive-in, chemical predeposition through the surface, and oxide deposition. The finite-element method transforms the diffusion equation for impurity atoms to a simulation model at a discrete number of points. Direct techniques are used to solve the resulting matrix equations. The impurity distributions resulting from sequences of the process steps are shown.

FFT calculation of two-step semiconductor impurity diffusion

The fast Fourier transform (FFT) is used to efficiently calculate an approximation to the second step of the two-step semiconductor impurity atom diffusion. The linearized one-dimensional diffusion equation is assumed with zero oxide growth. The calculation is shown to be a convolution, and the criteria for minimizing aliasing and overlap are outlined. Calculations for erfc (error function) and ion-implanted profiles are shown. Computation time is about 800 ms for a 256-point profile, using APL on an IBM System/370 Model 168 computer. Less than 2-percent error occurs in curve area and surface concentration for typical profiles.

Investigation of the diffusion of impurity atoms in plasmas by laser fluorescence

A pulse of aluminum atoms was injected into hydrogen gas and plasma by focusing a TEA CO2-laser beam onto a solid target. The propagation along the axis of the target was investigated by measuring the local atomic densities using dye laser excited fluorescence. A diffusion model allowed the derivation of diffusion coefficients as well as of the rate coefficient for ionization of the Al atoms from the observations.

On internal friction due to the diffusion of impurity atoms along dislocations

A calculation of the relaxational internal friction arising as a result of the redistribution of impurity atoms in a dislocation segment under the influence of small variable external stresses is presented. The relaxation-time distribution function is determined, and the width and height of the corresponding peak are estimated.

Statistical nature of impurity-atom diffusion and its influence on the characteristics of narrow-base bipolar transistors

Statistical fluctuations inherent in any diffusion process could place fundamental limitations on the minimum basewidth obtainable in bipolar-transistor fabrication. Calculations are presented to demonstrate the probability of encountering channels of low impurity-atom density (hence reduced punch-through voltage) in a very-narrow-base transistor.

Electro-transport of hydrogen in ?-iron

The migration of hydrogen in α-iron under the influence of an electric field was studied in a wide temperature interval. In every case hydrogen migrated toward the cathode. The transport charges are positive and decrease exponentially with rising temperature. The effective charge is practically independent of the concentration of hydrogen in iron (in the concentration range studied). To explain the results obtained, a vacancy mechanism of electro-transport was postulated; it envisages the movement of vacancies as a result of their interaction with the current carrier flux in the metal and the diffusion of impurity atoms carried by the migrating vacancies.

The formation of stable austenite during heating of quenched steel 10G2S1D

1. On heating of quenched low-carbon low-alloy steel 10G2S1D at temperatures somewhat above Ac1 a finely dispersed mixture of fragmented ferrite and austenite is formed, which is resistant on cooling in air and is limited by the size of former martensite needles. 2. The formation of thermally stable austenite is due to stabilization as the result of redistribution of carbon, nitrogen, manganese, and other elements between the α- and γ-solid solutions. In this case the ferritic matrix is refined due to the diffusion of impurity atoms into local volumes of austenite. 3. The redistribution process of atoms of impurity and alloying elements controls the formation of stable austenite. The formation of austenite resistant during cooling in air requires holding at 720–740°C for at least 20 min, which excludes its formation in the heat-affected zone during welding.