Heavily donor or acceptor doped metallurgical silicon is a promising candidate as a high-temperature thermoelectric energy converter due to the extremely low cost of its fabrication. The problem of silicon-based thermoelectric materials is the high value of the thermal conductivity; however, modern technologies offer several options for solving this problem at once. In the present work, silicon ingots heavily doped using Si:P compound were grown by the Bridgman directional crystallization method with a small (up to 5 at. %) germanium impurity fraction. The main thermoelectric parameters of the material were measured in a wide temperature range (50 – 800 °C). These are Seebeck coefficient, electrical conductivity and thermal conductivity. Based on the measurement results, the value of the thermoelectric figure of merit was calculated. The latter determines the value of the thermoelectric conversion efficiency. The study of electrical properties shows that phosphorus from the SiP compound is introduced into the lattice as a dopant and creates a high concentration of conduction electrons. The chemical analysis of the ingots showed the presence of additional background impurities, the concentration and composition of these impurities vary over the bulk of the sample. Despite the presence of impurities, the material demonstrates relatively high thermoelectric characteristics, and the efficiency is at the level of the best world results. A further potential for optimizing thermoelectric characteristics due to the possibility of a fine-grained polycrystalline structure formation is discussed.

In this paper, we analyze the contrast of images obtained by scanning electron microscopy (SEM) in the backscattered electron mode, which shows that the contrast on the polished surface of multicrystalline silicon (multisilicon) is due to the parameters of misorientation between grains. The contrast values corresponding to special oblique boundaries with various inverse density values of the coinciding nodes of the crystal lattices of neighboring grains forming these boundaries are established. Since the SEM method allows relatively large surface areas of the samples (~1 cm2) to be studied, on account of the method proposed here for identifying special oblique boundaries, it is possible to analyze the nature of the interaction of boundaries and their distribution density in the structure, depending on certain crystallization conditions. In SEM studies of multisilicon, this can be important for initial analysis of the structure and further formulation of research problems without the use of special selective etchants that destroy the surface of the studied samples.

This article investigates the relationship between the chemical composition and electrophysical properties of p- and n-type multicrystalline silicon ingots based on metallurgical silicon with a purity of 99.99 at.%. In particular, the role of impurity-impurity interactions in the production of multisilicon by the Bridgman vertical method is evaluated in order to identify approaches to controlling this process effectively. The phase equilibrium calculations in the “silicon–all impurities” and “silicon-impurity-oxygen” systems were carried out based on the Gibbs energy minimization in the Selector software package. The study investigates the rank correlations of the concentrations of various impurities with each other, as well as with the specified electrical resistivity (SER) and the lifetime of nonequilibrium charge carriers (NCC) in the direction of crystal growth. Pair correlations of the element distribution profiles were considered based on the role of the main factor represented by the ratio of individual impurity solubilities in solid or liquid silicon (k0), as well as from the standpoint of direct interaction between two elements. It was found that the k0 value for two individual impurities in silicon does not automatically lead to the pair correlation of their distribution profiles in the ingot. A significant effect on the distribution profiles of impurities in multisilicon with k0→0 has the factor of binding some part of the impurity into such a form that this impurity can be incorporated easily into a growing crystal. Binding may be induced by the interaction of the impurity in the melt with the oxygen background, its segregation at the grain boundaries, and its capture by the crystallization front in the composition of the liquid inclusion. Significant correlations of impurity distribution profiles in the ingot were demonstrated by the pairs whose elements interact without the formation of chemical compounds in the 25–1413 °C temperature range. The conducted phase equilibrium calculations for the “silicon–all impurities” system revealed the possibility of forming the VB2, TiB2, ZrB2, and MgTiO4 solid phases in the melt.

The orientation of grains and the special boundaries formed by them in multicrystalline silicon has been studied by electron backscattered diffraction. It is found that the crystallographic parameters of special boundaries (misorientation angle and rotation axis) obtained using the Tango HKL Channel 5 software module may differ from the results of their direct computation by calculating the rotation matrix in the Spyder integrated development environment, using identical formulas based on Euler angles. In particular, special boundaries ∑3, ∑9, and ∑27a with misorientation angles of 180°, 120°, and 165°, respectively, are found in multicrystalline silicon. These versions of special grain boundaries are theoretically possible for the crystals of cubic system; however, they have not been investigated experimentally in multicrystalline silicon.

Фазообразование и время жизни неравновесных носителей заряда в мультикристаллическом кремнии на основе UMG-Si

The recombination activity of intragrain defects in multicrystalline silicon is investigated by the electron or laser beam induced current methods. The interrelation of the grain orientation with the character of the distribution of intragrain defects (dislocations and impurity inclusions) and their recombination activity is revealed. The defect grain structure is investigated using various etching procedures to reveal the defects. It is shown that the defect density and distribution in the grains depend on their orientation relative the growth axis. Therefore, it is intragrain defects and impurities that are to a large degree responsible for degradation of the nonequilibrium carrier lifetime when compared with grain boundaries.

AbstractThe recombination activity of intragrain defects in multicrystalline silicon is investigated by the electron or laser beam induced current methods. The interrelation of the grain orientation with the character of the distribution of intragrain defects (dislocations and impurity inclusions) and their recombination activity is revealed. The defect grain structure is investigated using various etching procedures to reveal the defects. It is shown that the defect density and distribution in the grains depend on their orientation relative the growth axis. Therefore, it is intragrain defects and impurities that are to a large degree responsible for degradation of the nonequilibrium carrier lifetime when compared with grain boundaries.

AbstractThe excess carrier lifetime (τ) distribution in multicrystalline silicon grown by the Bridgman technique from high-purity metallurgical silicon (HPMG-Si) is studied. The features of the variation in τ, caused by the grain-boundary structure of ingots, are revealed. The grain boundaries, dislocations, and impurity microinclusions are studied by electron probe microanalysis (EPMA) and scanning electron microscopy (SEM) using selective acid etching. The electrical activity of extended defects is measured by the electronbeam- induced-current (EBIC) method.

The electrical activity of grain boundaries in multicrystalline silicon grown from metallurgical silicon by the Bridgman method is investigated by the method of electron-beam induced current. The main tendencies of atypical manifestation of the local electrical activity of Σ3{111} and Σ9{110} special boundaries are revealed. The structural features of the grain boundaries after selective etching and the impurity-distribution characteristics in multicrystalline silicon are determined by the methods of electron backscattering diffraction and electron-probe microanalysis.

The grain structure of multisilicon crystals are investigated by scanning electron microscopy and electron backscatter diffraction. It is found that the contrast of an image obtained by scanning polished multisilicon surfaces in the mode of backscattered electrons by electron-probe microanalysis is caused by the fact that the contrasting grains on the test site of the surface belong to different crystallographic orientations. It is revealed that high-angle grain boundaries are areas where the contrast varies, whereas small-angle boundaries are not observed on the polished surfaces. Consequently, the degree of contrast of the image obtained in this scan mode can be used to qualitatively assess the degree of misorientation of neighboring grains.

The properties of special grain boundaries in multicrystalline silicon (mc-Si) grown from metallurgical refined silicon by the Bridgman-Stockbarger method have been studied. The electric activity of grain boundaries was characterized by measuring the electron-beam-induced current. Structural features of the mc-Si samples were studied by scanning electron microscopy, electron-probe microanalysis, and atomic force microscopy techniques.

Distribution of impurities in multisilicon, grown from metallurgical silicon by the Bridgmen-Stockbarger method has been studied using electron probe microanalysis. It has been found that most of the impurities occur as primary and secondary microinclusions. Primary microinclusions are large (1-100 micron) intermetallic agglomerates formed in the melt from primary microinclusions of metallurgical grade silicon. Secondary microinclusions are smaller (to 1 micron) and contain not more than three metal elements.

Multisilicon crystals grown from refined metallurgical silicon are studied by scanning electron microscopy (SEM) and electron probe microanalysis (EPMA). The varieties of intergranular boundaries are revealed. Impurities are found to be contained in inclusions in multisilicon. The intergranular boundaries contain no impurities, and they do not concentrate the elements present in multisilicon. It is proved experimentally that, in the homogeneous areas of the crystal the lifetime of minor charge carriers is maximum, whereas its minimum value corresponds to the areas with numerous intergranular boundaries.