Impurity Striations During Bridgman Growth of InSb

InSb single crystals have been grown by the gradient freeze method. Striations close to the seeding interface have been evidenced by X-ray topography and correlated to temperature and growth rate oscillations. It is shown that these striations are related to light impurity segregations and that a non-linear process should be taken into account to explain the phenomena.     

Optimization of the Growth Technology for Crystals with Garnet Structure Based on X-Ray Diffraction Data

High efficiency of the methods of double-crystal X-ray diffractometry (DCXRD) and topography for improving the growth technology of highly homogeneous crystals has been demonstrated on the example of gadolinium gallium garnet (GGG) single crystals. The main types of structural defects observed in Czochralski-grown GGG crystals are found to be macroscopic inhomogeneity of composition distribution, caused by the facet effect manifestation; microinhomogeneous distribution of impurity and main components of the composition in striations; dislocations; and second-phase inclusions. The relationship between the type and density of newly formed defects and the technological conditions for crystal growth are considered. Optimization of the composition of crystals and their growth technology made it possible to obtain high-quality dislocation-free crystals of GGG and complex-substituted garnets on its basis for magneto-optical and microwave devices, elements of solid-state lasers, and other applications.     

Induced growth striations in Quartz Crystals

Due to periodical modulation of the temperature difference between the solution and growing rooms growth striations in quartz crystals have been induced. These induced striations have been found as smoky quartz coloration striations as Al containing material has been used. X-ray topographic investigations found these growth striations even in the unirradiated quartz crystal.     

X-ray topography of a crystal of tetragonal lysozyme

A crystal of the tetragonal modification of lysozyme grown under controlled conditions with in situ monitoring of the growth kinetics and morphology of the (110) face is studied by X-ray topography using synchrotron radiation. The choice of a diffraction reflection with optimal dispersion allows us to obtain an informative X-ray topographic image of the sample. It is found that the striations that are formed under changing supersaturation correspond to the type of zonality characteristic of crystals growing by the normal mechanism and differ from those observed in inorganic crystals growing by the layer-by-layer mechanism.     

Real structure investigations of LiNbO3 single crystals grown by the flux method

The real structure of flux grown LiNbO₃ crystals is investigated by etching technique, X-ray topography, and optical polariscopic method. The main defects are microdomains, dislocations and minor impurities of V³⁺−ions. The crystals do not contain growth striations. The mean dislocation density is in the order of 10³ cm⁻². The main origin of the defects seems to be post-growth mechanical stress. The results are discussed in comparison to the real structure typically found in the case of Czochralski crystals.     

Analysis of synthetic diamond single crystals by X-ray topography and double-crystal diffractometry

Structural features of diamond single crystals synthesized under high pressure and homoepitaxial films grown by chemical vapor deposition (CVD) have been analyzed by double-crystal X-ray diffractometry and topography. The conditions of a diffraction analysis of diamond crystals using Ge monochromators have been optimized. The main structural defects (dislocations, stacking faults, growth striations, second-phase inclusions, etc.) formed during crystal growth have been revealed. The nitrogen concentration in high-pressure/high-temperature (HPHT) diamond substrates is estimated based on X-ray diffraction data. The formation of dislocation bundles at the film-substrate interface in the epitaxial structures has been revealed by plane-wave topography; these dislocations are likely due to the relaxation of elastic macroscopic stresses caused by the lattice mismatch between the substrate and film. The critical thicknesses of plastic relaxation onset in CVD diamond films are calculated. The experimental techniques for studying the real diamond structure in optimizing crystal-growth technology are proven to be highly efficient.     

Melt nonstoichiometry and defect structure of ZnGeP<Subscript>2</Subscript> crystals

The defect structure of ZnGeP₂ crystals grown from a melt by the vertical Bridgman method has been investigated. A deviation of the melt composition from stoichiometric leads to the formation of striations and the inclusions of other phases which are observed as structures (chains) oriented parallel to the growth axis. According to the microanalysis data, the inclusion composition corresponds to a mixture of ZnGeP₂, Zn₃P₂, and Ge. Nanoinclusions of germanium phosphide are detected by transmission electron microscopy. X-ray topography reveals defects of four types. The main defects in the central part of an ingot are related to the composition fluctuations, and the newly formed dislocations are basically single ones. Most dislocations are formed at the crystal periphery.     

Micromorphology of as-grown surfaces of crystals

This paper describes and discusses the micromorphology of as-grown surfaces of single crystals. After a brief introduction to the methods of observation of surfaces, the mechanism of growth and development of crystals is first outlined. Here the formation of bunches and macrosteps, the relationship between the growth mechanism and the surface entropy factor, and the effect of impurities on the surface morphology are described. Common structures observed on the as-grown surfaces are then explained in relation to growth conditions of the crystals. The following growth structures are described: elementary spirals, macrospirals, hillocks of dislocation and nondislocation origin, interlacing and slip patterns, macrosteps, inclusions, block structures, growth striations and impurity striations.     

Investigations of impurity striations in potassium bichromate crystals

Impurity striations in potassium bichromate crystals (KBC, lopezite) formed during crystal growth from aqueous solution were revealed by chemical etching and analyzed. Striations were revealed as etch grooves, as rows of dislocation etch pits and as rows of flat‐bottomed etch pits. Various types and groups of striations have been visualized. Some striations were due to lateral segregation of impurities caused by convection flow of the mother solution, other were formed during growth stoppages whereas induced striations were generated by changes in hydrodynamical conditions. Growth rates changes resulted in zonal distribution of impurities, formation of planar lattice strain, rows of clusters of point defects and rows of dislocations. Generation of striations with different intensities in various sectors is a proof of the selective capture of impurities. Ratios of growth rates of various faces of KBC crystals growing in forced and free convection regimes were determined by induced striations. (© 2010 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Growth imperfections in oriented grown KDP crystals by X‐ray topographic analysis

Potassium dihydrogen phosphate (KDP) crystals were restrained to grow in two dimensions only, using a specially designed platform. This enables us to grow the blanks of frequency conversion elements that satisfy type‐II phase matching direction out of a type‐II phase‐matched seed crystal. Synchrotron radiation topography was used to study the growth mechanism of these profiling grown KDP crystals. It is found that both dislocation growth mechanism and layer growth mechanism were involved in the growing process. Inclusions, growth striations and dislocations were the main defects that influenced the crystalline quality of these crystals. High‐resolution X‐ray diffraction was employed to study the lattice integrality of the crystal.     

X-ray characterization of detached-grown germanium crystals

Germanium (1 1 1)-oriented crystals have been grown by the vertical Bridgman technique, in both detached and attached configurations. Microstructural characterization of these crystals has been performed using synchrotron white beam X-ray topography (SWBXT) and double axis X-ray diffraction. Dislocation densities were measured from X-ray topographs obtained using the reflection geometry. For detached-grown crystals, the dislocation density is on the order of 10⁴ cm⁻² in the seed region, and decreases in the direction of growth to less than 10³ cm⁻², and in some crystals reaches less than 10² cm⁻². For crystals grown in the attached configuration, dislocation densities were on the order of 10⁴ cm⁻² in the middle of the crystals, increasing to greater than 10⁵ cm⁻² near the edge. The measured dislocation densities are in excellent agreement with etch pit density (EPD) results. Broadening and splitting of the rocking curve linewidths was observed in the vicinity of subgrain boundaries identified by X-ray topography in some of the attached-grown crystal wafers. The spatial distribution of rocking curve linewidths across the wafers corresponds to the spatial distribution of defect densities measured in the X-ray topographs and EPD micrographs.     

Microstructures of Tin Iodide Single Crystals Grown in Silica Gels

Single crystals of tin iodide (SnI₂) have been grown in silica gels. A detailed microtopographical study of {100} faces have been described. Horizontal striations are predominant on these faces for most of the crystals, while few of them show vertical striations. The horizontal striations are associated with the two-dimensional nucleation theory whereas the vertical striations relate to the growth fronts. Growth layers modified by the presence of misaligned microcystals have been illustrated. The natural etch pits on {100} faces of the crystal are attributed to the dissolution of crystals in the acid set gel. In the light of these observations, the mechanism of the development and growth of these faces have been assessed and the implications are discussed.     

X-Ray study of the defect structure of PbTe single crystals

PbTe single crystals grown by different methods were thinned electrolytically and examined by X-ray transmission topography. The transmission topographs, first obtained of this material, reveal substructure, slip lines and single dislocations. The samples exhibit different structural perfection in dependence on the growth method. In crystals of relatively high perfection, slip lines are the striking feature of defect structure, caused by surface damage during mechanical preparation. The most perfect sample has a dislocation density of 10² to 2 ṁ 10³ cm⁻². No slip occurs, probably due to small dopant contents.     

The Influence of Interstitials and Growth Conditions on the X-Ray Colorability of Synthetic Quartz Crystals

The saturation colorability of quartz crystals depends not only on the contamination of the material but also on the regarded growth sector. But even in the same sector the colorability varies locally. Investigations of crystals with induced growth striations and defined local growth rate showed that the dependence of the colorability on the growth conditions is very complex. The growth rate to colorability characteristics may have positive or negative slopes regarding e.g. —x-or z-sections. Optical investigations of —x-sections prove that under certain circumstances light and/or dark striations may occur or even uncolorable regions may be observed, althought the contamination is sure. We explain this by the interaction of the coloration centres with interstitials. That effect might be of importance for the evaluation of the impurity by means of the coloration of natural or synthetic quartz crystals.     

The crystal growth and perfection of 2,4,6-trinitrotoluene

Large crystals of TNT were grown from ethyl acetate solution by both temperature lowering and solvent evaporation. The perfection of crystals grown from seeds under carefully controlled conditions was generally higher than those prepared by uncontrolled solvent evaporation. Examination by X-ray topography revealed the crystals to have a characteristic growth induced defect structure comprising growth sectors and boundaries, growth banding, solvent inclusions and dislocations. Twins and stacking faults (SF) were also observed. Many of the defects noted in the topographs can be attributed to impurities. The influence of the highly anisotropic crystal structure on the nature of growth defects is discussed. A structural model proposed to explain twinning and SF formation is partially supported by topographic evidence.     

Nd:LuVO4晶体缺陷的研究

采用提拉法生长的Nd:LuVO4晶体是一种适合二极管泵浦的新型激光晶体,运用化学腐蚀结合光学显微术和同步辐射白光X射线形貌术对Nd:LuVO4晶体缺陷进行观察,结果表明:晶体的主要缺陷为位错和小角晶界.利用高分辨X射线衍射仪进一步验证了这一结果.并初步讨论了缺陷形成的原因.     

Growth and some properties of TeO<Subscript>2</Subscript> single crystals with a large diameter

Large-diameter single crystals of TeO₂ are grown by the Czochralski method in specially designed setups with automatic monitoring of the crystal growth. The degree of perfection of the grown crystals is examined using selective etching and X-ray topography (the Shultz method). The temperature dependence of the microhardness of TeO₂ single crystals is investigated for different crystallographic planes, namely, (001), (100), and (110).     

Long-term Crystal Growth under Microgravity during the EURECA-1 Mission (II) THM Growth of Sulphur-doped InP

Long-term crystal growth experiments were successfully performed under microgravity conditions during the first flight of the unmanned EURECA-1 mission in the automatic mirror furnace (AMF). Two crystals of sulphur-doped InP with [001] and [111] orientation respectively were grown from indium solution by the travelling heater method (THM). The absence of time dependent buoyancy-driven convection is documented by the lack of type I striations in the space-grown crystals. The sulphur concentration is measured by spatially resolved photoluminescence. As expected, the macrosegregation can be described by a pure diffusion-controlled model which is in good agreement with the findings from the first German spacelab mission D1. Compared to the earth-grown reference samples, both of the space-grown InP crystals show strong disturbances such as inclusions and type II striations. The morphological instabilities are similar to growth disturbances already known from the space-grown MD-ELI-01 from the D1 mission.     

Crystalline quality of lysozyme crystals grown in agarose and silica gels studied by X-ray diffraction techniques

The crystalline quality of hen egg white lysozyme (HEWL) crystals grown in agarose gels and in silica gels has been characterized by measuring resolution and mosaic spread. These crystals have been compared to solution grown ones. A quasi-plane-wave X-ray topography study has also been done on some crystals. The study concerns triclinic, monoclinic, orthorhombic and tetragonal forms of HEWL. One observes that the resolution is not really changed by gelling the growth medium, even for rather high gel contents (agarose 0.5% wt/wt). On the contrary, mosaicity, characterized through reflection profile recordings allows to differentiate crystals grown by different techniques: agarose gel grown crystals are, on average, better than solution grown ones but the best crystals are obtained in silica gel. X-ray topography confirms this result.     

Preparation and Properties of YIG Single Crystals

In this paper a summary is given on the reproducible preparation of large, nearly defectless yttrium iron garnet single crystals (YIG) grown in fluxes by slowly cooling with accelerated crucible rotation (ACRT) and local bottom cooling. The surface morphology of the growth faces is discussed with regard to the growth mechanism. By different methods the crystals are characterized regarding their lattice defects (impurities, growth striations, dislocations, inclusions). Ferromagnetic resonance measurements in the X-band at polished, inclusionsfree discs show that the linewidth ΔH of any crystals from different runs are less than 0.45 Oe.