On the problem of the consistency of the high-temperature precipitation model with the classical nucleation theory

The adequacy of the model of high-temperature precipitation in dislocation-free silicon single crystals to the classical theory of nucleation and growth of second-phase particles in solids has been considered. It has been shown that the introduction and consideration of thermal conditions of crystal growth in the initial equations of the classical nucleation theory make it possible to explain the precipitation processes occurring in the high-temperature range and thus extend the theoretical basis of the application of the classical nucleation theory. According to the model of high-temperature precipitation, the smallest critical radius of oxygen and carbon precipitates is observed in the vicinity of the crystallization front. Cooling of the crystal is accompanied by the growth and coalescence of precipitates. During heat treatments, the nucleation of precipitates starts at low temperatures, whereas the growth and coalescence of precipitates occur with an increase in the temperature. It has been assumed that the high-temperature precipitation of impurities can determine the overall kinetics of defect formation in other dislocation-free single crystals of semiconductors and metals.     

Kinetics of high-temperature precipitation in dislocation-free silicon single crystals

The defect structure of dislocation-free silicon single crystals has been calculated using the approximate solution of the Fokker-Planck partial differential equations. It has been demonstrated that the precipitation starts to occur near the crystallization front due to the disappearance of excess intrinsic point defects on sinks whose role is played by oxygen and carbon impurities.     

Transformation of point defects in silicon dioxide during annealing

In our previous studies, we have demonstrated that annealing of silicon dioxide in the absence of oxygen leads to the formation of silicon clusters near the surface. The mechanism of the formation of silicon clusters by this technique has not been sufficiently investigated. However, it has been found that the rate of the formation of nanoclusters and their sizes depend on the concentration of point defects in the silicon dioxide and on the concentration of impurities, for example, hydroxyl groups. As a continuation of these studies, in the present work we have investigated changes in the concentration of point defects in silicon dioxide films during high-temperature annealing. A new method has been proposed for the evaluation of changes in the concentration of point defects in silicon dioxide films before and after annealing. A model of the transformation of point defects in silicon dioxide into silicon nanoclusters due to the high-temperature annealing has been developed.     

Optical properties of the surface transition-metal structures in fluoride ionic crystals and peculiarities of their formation during thermal diffusion

The possibility of forming surface films with an elevated concentration of an impurity metal during high-temperature diffusion has been analyzed for a wide series of ionic crystals: LiF with Co, Ni, Mg, Ca, Ba, and Sr impurities; NaF with Co, Mn, Mg, Ca, and Sr; MgF₂ with Co and Ni; and CaF₂ with Co. It is established that films are formed only on alkali halide crystals with impurities of transition metals and are not formed on alkaline earth fluorides with transition metals, as well as on alkali halide crystals activated with other divalent cationic impurities. The dynamics of the increase and decrease in the intensity of centers related to impurity-vacancy dipoles during thermal diffusion is shown. The mechanisms of film formation are explained in terms of the features of growth and structure of ionic crystals with cationic impurities and on the basis of isomorphism rules.     

Characterizations and formation mechanism of a new type of defect related to nitrogen doping in SiC crystals

Here, we report a commonly occurring defect related to nitrogen doping in silicon carbide crystals grown by physical vapor transport method while its formation mechanism has remained unclear. It is often mislabeled as planar hexagonal void defect (PHVD) owing to their similar in shape and size on wafer surface. Our results indicate that this is a new type of defect and differs from PHVD with respect to their nitrogen concentrations, void shapes and the connections to micropipe. We found that the carbon-rich vapor during the crystal growth is responsible for the formation of this type of defect. A possible three-stage defect developing mechanism and measures to avoid the defects are proposed.     

Kinetics of formation of vacancy microvoids and interstitial dislocation loops in dislocation-free silicon single crystals

The formation of vacancy microvoids and A-microdefects has been calculated according to the model of point defect dynamics in the absence of recombination of intrinsic point defects at high temperatures. It has been assumed that this solution is possible in the case where the precipitation of impurities begins in the vicinity of the crystallization front. It has been demonstrated that the formation of vacancy microvoids has a homogeneous nature and that the interstitial dislocation loops are predominantly formed through the deformation mechanism.     

On the formation of defect clusters in neutron-irradiated Si

The formation of radiation-induced defect clusters in neutron-irradiated silicon have been studied by solving the semilinear parabolic reaction-diffusion coupled equations. It is found that most of primary displacement defects (interstitial and vacancy) would be annihilated by direct I–V recombination in an extremely short time, and a lot of divacancies would be formed meantime. In particular, the production of 4-vacancy defects is independent of the concentration of sinks and impurities in the sample, and of the energy of recoil particles. The threshold energy of vacancy cluster formation has also been investigated. The results are discussed and compared with experiment observations.     

On the impact of stress on intrinsic defect formation during single crystal silicon growth

The incorporation of intrinsic point defects during silicon crystal growth from the melt is discussed using most recent data for intrinsic point defect thermal equilibrium concentration and diffusivity. It is shown that by taking into account the impact of stress on the thermal equilibrium concentration of vacancies and self-interstitials, the intrinsic point defect properties derived from self- and metal-diffusion experiments can be used to model point defect incorporation and clustering during silicon crystal growth from the melt. The solution is however not unique and a large uncertainty still remains on the real thermodynamic parameters of both intrinsic point defects. Only comparison with a wide range of experimental data from crystal pulling experiments—taking into account also the stress effects—will allow to further narrow down the uncertainty ranges on the intrinsic point defect properties in silicon.     

Influence of Ring Oxidation-Induced Stack Faults on Efficiency in Silicon Solar Cells

We observe a strong correlation between the ring oxidation-induced stack faults (OISF) formed in the course of phosphor diffusion and the efficiency of Czochralski-grown silicon solar cells. The main reason for ring-OISF formation and growth in substrate is the silicon oxidation and phosphorus diffusion process induced silicon self-interstitial point defect during POCl₃ diffusion. The decreasing of minority carrier diffusion length in crystal silicon solar cell induced by ring-OISF defects is identified to be one of the major causes of efficiency loss.     

He离子注入单晶Si纳米气泡形成生长及其应用探讨

首先简述了He离子注入单晶Si引起的气泡形成、生长以及其它缺陷对其生长的影响,介绍了Si中He气泡生长的可能微观机制以及它们在现代半导体技术中潜在的应用前景,提出了该领域研究有待解决的关键问题.He ion implantation induced bubbles or cavities in silicon have been paid more and more attentions due to their potential applications in modern semiconductor technology. In this paper, He ion implantation induced formation and growth of bubbles in silicon together with their interactions with other defects were first briefly reviewed. Then the possible growth mechanisms of He bubbles in silicon and their potential applications in modern semiconductor technology were described. Finally, we presented the ke...     

Simulation of porous silicon formation and silicon epitaxy on its surface

Processes of porous silicon formation and silicon epitaxy on its surface are studied using the Monte Carlo method. The model for porous silicon formation under anode etching allows for non-uniformity of charge distribution over the silicon-electrolyte interface. Processes of diffusion, generation and recombination of holes, as well as dimensional quantization, are also considered. Gilmer's model, extended to the case of a rough surface, is used to study epitaxy. The structures obtained by simulations at different levels of doping of the crystal substrate and for various parameters (temperature, HF concentration, and anode current density) are presented. Analysis of nanoporous structures showed that the porosity changes with depth, and fractal dimensionality exists below 10 nm. It has been shown that epitaxy, developing by formation of metastable nuclei at the edges of pores, by their subsequent growth along the perimenter and by formation of a thin continuous overhanging layer, may be described within the framework of this model. Three-dimensional images of near-surface layers formed at different stages of epitaxy have been obtained. The dependence of the epitaxy kinetics on the amount of deposited silicon for different structure porosities has been revealed. Institute of Physics of Semiconductors, Siberian Branch, Russian Academy of Science. Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 3, pp. 49–56, March, 1999.     

Effect of radiation-induced emission of schottky defects on the formation of colloids in alkali halides

Formation of vacancy clusters in irradiated crystals is considered taking into account radiation-induced Schottky defect emission (RSDE) from extended defects. RSDE acts in the opposite direction compared with Frenkel pair production, and it results in the radiation-induced recovery processes. In the case of alkali halides, Schottky defects can be produced as a result of the interaction of extended defects with excitons, as has been suggested by Seitz in 1954. We consider a model that takes into account excitonic mechanisms for the creation of both Frenkel and Schottky defects, and which shows that although the contribution of the latter mechanism to the production of primary defects may be small, its role in the radiation-induced evolution of microstructure can be very significant. The model is applied to describe the evolution of sodium colloids and the formation of voids in NaCl, which is followed by a sudden fracture of the material, presenting a potential problem in rock salt-based nuclear waste repositories. The temperature, dose rate and dose dependence of colloid growth in NaCl doped with different types of impurities is analyzed. We have found that colloid growth may become negative below a threshold temperature (or above a threshold dose rate), or below a certain impurity concentration, which is determined by the RSDE, that depends strongly on the type and concentration of the impurities. The results obtained with the model are compared with experimental observations.     

Simulation of the structure of oxygen hole centers in Mg2SiO4 and Mg2SiO4: Cr forsterite crystals by the interatomic potential method

The structure of oxygen hole centers in forsterite crystals has been simulated using the interatomic potential method. The energies of isolated oxygen hole centers, as well as the energies of their clusters with intrinsic and extrinsic defects of the crystal, have been estimated for different arrangements of point defects in the structure. It has been shown that the most energetically favorable position for isolated oxygen hole centers is the O3 position, in which the gain in the formation energy is equal to 0.17 eV as compared to the O2 position and 1.66 eV as compared to the O1 position. The maximum energy gain due to the association energy can be achieved when the oxygen hole centers are located at the vertices of the tetrahedron with a silicon vacancy. The presence of chromium in the forsterite crystal can increase the probability of the formation of silicon vacancies. The obtained results have been discussed in terms of the experimental investigations of the color centers generated in the Mg₂SiO₄ and Mg₂SiO₄: Cr crystals under ionizing radiation.     

Study on the formation mechanism of isoniazid crystal defects and defect elimination strategy based on ultrasound

In crystallization, crystal growth defects may reduce the strength and purity of crystals, which are not welcomed in the industry. Herein, isoniazid (INH) crystals were chosen as an example to investigate the formation of crystal defects at the molecular scale by combining experiments and molecular dynamics simulations. It was found that the strong interaction between the solvent and the crystal surface, high temperature, small stirring rate, and low supersaturation can lead to more pronounced crystal defects. The bulk severity of INH crystal defects was reflected by N₂ adsorption–desorption measurement. Besides, the single-crystal growth experiments manifested the rough growth mechanism for the (1 1 0) surface in the axial direction and the stepwise growth mechanism for the (0 0 2) surface in the radial direction. For the (1 1 0) surface, cavities occurred under the condition where the growth rate of the crystal edges and corners was greater than that of the surface center due to the starvation phenomenon of diffusion. While for the (0 0 2) surface, when the solvent removal rate was lower than the solute insertion rate, liquid inclusions were formed, which was verified by Raman microscopy. Furthermore, the ultrasonic strategy was successfully proposed to eliminate INH crystal defects and prepare perfect INH crystals. Moreover, the mechanism of ultrasound to reduce the crystal defect was proposed. We believe this work can provide insights into the design and preparation of defect-free crystals in crystallization.     

An electron diffraction and high-resolution transmission electron microscopy study of defect structure in silicon doped with transition metal impurities

Features of defect formation upon the decomposition of a supersaturated solid solution of a transition metal in silicon were studied. Zinc was used as the transition metal impurity. The silicon was doped with zinc by high-temperature diffusion annealing with subsequent quenching. Microstructures of this material were studied by electron diffraction and high-resolution X-ray transmission electron microscopy combined with X-ray energy-dispersion microanalysis. It was established that the studied material was a quite perfect single crystal but contained chaotically distributed dislocations.     

EPR diagnostics of laser materials based on ZnSe crystals doped with transition elements

The electron paramagnetic resonance (EPR) spectra observed in laser materials based on zinc selenide (ZnSe) crystals doped with transition elements have been analyzed and identified. It has been shown that, in addition to working impurities (Cr²⁺, Co²⁺, or Fe²⁺), the diffusion layer exhibits EPR spectra of accompanying impurities due to the diffusion of transition elements (chromium, cobalt, or iron) used in the preparation of active materials for quantum electronics (lasers, switches) operating in the mid-infrared range. EPR diagnostics of these impurities can be used in the development of appropriate regimes for minimizing concentrations of accompanying impurities that adversely affect the performance characteristics of laser materials. It has been found that, during the diffusion of transition metals, ions of the accompanying impurity Mn²⁺, which is characterized by extremely informative EPR spectra, are embedded in the crystal lattice. It has been proposed to use these ions as ideal markers to control, on the electronic level, the crystal structure of the active diffusion layer.     

Pore- and delamination-induced mismatch strain relaxation and conditions for the formation of dislocations,cracks, and buckles in the epitaxial AlN(0001)/SiC/Si(111) heterostructure

A method has been proposed using the example of an AlN/SiC/Si heterostructure according to which the strain state induced in multilayer epitaxial films by the mismatch in the lattice parameters and thermal expansion coefficients of the crystals can be calculated from the experimental temperature dependence of the curvature of the crystal plate. The method makes it possible to estimate the imperfection of the hetero-structure from defect-relieved mechanical stresses caused by mismatch strains. It has been found that there are specific features in the formation of the relief of AlN films grown on SiC/Si substrates prepared by the atomic substitution. Criteria for the formation and preferred orientations of defects (dislocations, cracks, delaminations, and buckles) in AlN films have been calculated. For this purpose, the surface energies and energies of adhesion for different twins at the semiconductor interfaces have been calculated using computational quantum chemistry methods for different crystal faces.     

Interaction of impurity and intrinsic defects in forsterite and its role in the formation of spectral and luminescence properties

This paper reports on the results of investigations of the coefficients of chromium distribution between a crystal and a melt of forsterite, the absorption and luminescence spectra, and the electron paramagnetic resonance spectra of chromium centers in Mg₂SiO₄: Cr, Mg₂SiO₄: Cr: Sc, and Mg₂SiO₄: Cr: Li crystals. It has been established that the concentration dependences of these properties vary upon changing over from the range of trace concentrations of chromium, scandium, or lithium impurities in the melt to the range of higher concentrations of these impurities. The observed phenomenon is explained by the interaction of impurities with intrinsic defects of the crystal, which is called as the microimpurity trapping effect. According to the performed estimations, the concentration of predominant intrinsic defects (magnesium Frenkel defects) in the forsterite crystals grown from the melt is equal to (7.5 ± 0.3) × 10⁻⁶ atomic fractions. The energy of the formation of magnesium Frenkel defects can be estimated as 4.2 ± 0.2 eV.