溶液连续过滤快速生长KDP晶体及其品质分析

设计溶液实时连续过滤装置用于降温法快速生长KDP晶体.采用高亮度激光照射分析对比晶体内部的散射点密度,以同步辐射为光源的X射线形貌成像技术探测晶体内部的生长缺陷,并测定晶体三倍频激光(355 nm)的损伤阈值.实验结果显示,溶液连续过滤法生长的KDP晶体中包裹体和位错的密度明显降低,晶体的激光损伤阈值提高了30%.     

Heterometry-induced defects and stresses in isomorphously mixed crystals of varying composition

The comparative study of the distribution and density of dislocations and cracks in isomorphously mixed potassium-rubidium biphthalate crystals grown under the conditions of discrete and continuous changes of the solution composition with time. The method is developed for calculating the heterometry-induced internal stresses and the character of their variation in a crystal during its growth. It is established that formation of dislocations, cracks, and interzonal inclusions is associated with the effect of the heterometry-induced stresses, whereas the number of defects depends on the values of these stresses varying during crystal growth.     

Finite element analysis of dislocation density during bulk single crystal growth (effect of doping atoms in InP single crystal)

A computer code for simulation of dislocation density in a bulk single crystal during liquid encapsulated Czochralski (LEC) or Czochralski (CZ) growth process. In this computer code, the shape of crystal–melt interface and the temperature in a crystal at an arbitrary time were determined by linear interpolation of the results that were discretely obtained by heat conduction analysis of a CZ single crystal growth system. A dislocation kinetics model called Haasen–Sumino model was used as a constitutive equation. In this model, creep strain rate is related to dislocation density, and this model extended to multiaxial stress state was incorporated into a finite element elastic creep analysis program for axisymmetric bodies. Dislocation density simulations were performed using this computer code for InP bulk single crystals with about 8″ in diameter. In the analysis, the effect of dopant atoms on the dislocation density was examined. In the case of a low doped InP single crystal, dislocations are distributed in the whole of the crystal. On the other hand, in the case of a highly doped InP single crystal, dislocations are localized at both the central and peripheral regions of the crystal.     

Dislocations and dislocation reduction in space grown GaSb

The behaviour of dislocations in GaSb crystals grown in space both from a stoichiometric melt (floating zone method, FZ) and a Bi solution (floating solution zone, FSZ) respectively, is studied. Predominantly straight 60° dislocations with Burgers vectors of the type b = a/2 <110> in (111) glide planes are identified. In the 20 mm long FZ single crystal the linear growing out of the dislocations is observed which reduces the dislocation density in the centre of the crystal to values below 300 cm^–2. The Bi incorporation in the FSZ crystal results in a misfit between seed and grown crystal and in a network of misfit dislocations at the interface. Thermocapillary convection during growth as well as the surface tension may be the reasons for the presence of curved dislocations and the higher dislocation density within a 1 – 2 mm border region at the edges of both of the crystals. (© 2009 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

The role of dislocations in the formation of mechanical stresses during annealing of gallium arsenide single crystals

The effect of dislocations on the change of mechanical stresses in undoped semi-insulating gallium arsenide single crystals has been studied during their annealing in vacuum and in the arsenic atmosphere. The phenomena observed are explained by the effect of dislocations playing the role of channels for arsenic diffusion on the concentration of intrinsic point defects in the crystal regions surrounding dislocations. The mechanism of arsenic diffusion over dislocations allows one to consider dislocations as sources and sinks of arsenic without the translational and twinning processes and, thus, makes the well-known data on the reactions of dislocation interaction with point defects and the experimental structural data for single crystals more consistent.     

Propagation behavior of threading dislocations during physical vapor transport growth of silicon carbide (SiC) single crystals

The dislocation formation and propagation processes in physical vapor transport (PVT) grown 4H silicon carbide (4H–SiC) single crystals have been investigated using defect selective etching and transmission electron microscopy (TEM). It was found that while the growth initiation process generally increased the density of threading dislocations in the grown crystal, for certain areas of the crystal, threading dislocations were terminated at the growth initiation. Foreign polytype inclusions also introduced a high density of dislocations at the polytype boundary. In the polytype-transformed areas of the crystal, almost no medium size hexagonal etch pits due to threading screw dislocations were observed, indicating that the foreign polytype inclusions had ceased the propagation of threading screw dislocations. Based on these results, we argued the formation and propagation of the threading dislocations in PVT grown SiC crystals, and proposed the dislocation conversion process as a plausible cause of the density reduction of threading dislocations during the PVT growth of SiC single crystals.     

Topological classification of defects in crystals

Here we review the topological approach to the classification of defects in crystals, which are deviations from crystallinity. First, we illustrate this approach using the simpler case of dislocations. We show how the fact that dislocations are completely characterized by their Burgers vectors only, is related via topological considerations to the fact that a perfect crystal is exactly reproduced by translations through a lattice vector. Later, we present the developments of the French school and that of Rogula, comparing and contrasting them. These are attempts to generalize the above idea to include consideration of other transformations that leave a perfect crystal invariant. Finally, we discuss briefly some of the problems that still remain with this approach.     

Untersuchungen zur Neubildung von Versetzungen bei der tiegelfreien Züchtung von Silizium-Einkristallen

During the crucible free growing of dislocation free silicon monocrystals frequently spontaneous generations of new dislocations are observed which cannot be attributed to perceptible reasons. By means of X-ray topographic and metallographic methods it is tried to localize the origin of these dislocation generations in the crystal. Their generation in areas of the crystal surface permits to suppose the existence of a temperature stress mechanism, which releases the generation of new dislocations in the plastic regions of the just formed crystal in consequence of high shocks of stress.     

Effects of doping of Ca and Ba on the dislocation distribution in melt grown KCl crystals

The effects of doping of Ca and Ba (∼ 0.02 at %) upon the dislocation distribution in melt grown KCl crystals without cellular segregation were studied by an etch pit method in connection with the dispersion state of the dopants, which was examined by the dark field illumination. – (1) In the Ca-doped crystal, in which the dopants were distributed uniformly, the formation of subboundaries was completely suppressed and dislocations were distributed at random. (2) In the Ba-doped crystal, however, the dopants were non-uniformly distributed and the dislocations tended to form subboundaries. The dislocations within the subgrains were distributed in a non-uniform manner. (3) The dislocation density in the Ba doped crystal was higher than that of undoped or Ca-doped crystal. This was explained by the mechanism similar to the Tiller's prediction. – Finally, the stress distribution due to the concentration fluctuation was examined by the birefringence patterns.     

Solid mechanics and material strength studies on the melt growth of bulk single crystals

Microdefects such as dislocations and macrocracking should be controlled during the crystal growth process to obtain high-quality bulk single crystals. Solid mechanics and material strength studies on the single crystals are of importance to solve the problems related to the generation and multiplication of dislocations and the cracking of single crystals. The present paper reviews such research activities that comprise the thermal stress analysis during crystal growth process, the dislocation density estimation during crystal growth process, and the cracking of single crystal due to thermal stress.     

Synchrotron White Beam X-Ray Topography Characterization of Defect Structures in 2,10-Undecanedione/Urea Inclusion Compounds

Abstract

The defect structure of a crystal of the urea inclusion compound (UIC) of 2,10-undecanedione was investigated using Synchrotron White Beam X-ray Topography. X-ray transmission topographs recorded from different regions show that the crystal is divided into several twin domains. Each region in the crystal is revealed on the topographs by orientation contrast arising from the mutual misorientation of adjacent regions. Using a combination of pinhole Laue pattern analysis and topographic orientation contrast analysis, the twin operation was determined to be consistent with an approximately 60° rotation about the orthorhombic c-axis. Possible twin boundary structures are also presented. Other defects such as dislocations and inclusions are also characterized.     

Etch Pattern of Gel-grown Single Crystal of Ammonium Tartrate

Using optical techniques, a study was carried out of the etch patterns produced, by diluted oxalic acid and sodium hydroxide solution, at 30°C. Point bottomed and flat bottomed rectangular etch pits nucleated at the sites of dislocations parallel to ‘C’ axis of the crystal are observed. Mostly they are isolated, and randomly distributed. Further, on prolonged etching they penetrate deeper and their eccentricity can be attributed to the inclined nature of dislocations.     

Misfit Strain Relaxation by Dislocations in InAs Islands and Layers Epitaxially Grown on (001)GaAs Substrates by MOVPE

The misfit dislocation configurations in InAs islands as well as in more or less continuous layers grown on (001) oriented GaAs substrates were studied by weak-beam and high-resolution electron microscopy. The islands are confined by {101} and {111} facets where the aspect ratio (height/lateral extension) can be affected by the growth conditions. It is possible to grow well-defined islands as well as relatively continuous layers by MOVPE under As-stabilized conditions. At constant deposition parameters the growth is characterized by islands of different sizes (but with constant aspect ratio) in various strain states depending on their dislocation content. Coherently strained islands without any dislocation can be observed for heights up to 23 ML InAs, or otherwise, up to a maximal island extension of about 12 nm (for the particular aspect ratio ≈︂0.585). With further increase of island height and lateral extension, the introduction of dislocations becomes favourable. Independent of the island size, the layer thickness and the dislocation density, a residual elastic strain of about ε^r = —0.8% remains after relaxation. This means, about 88% of the total misfit strain of ε = —6.686 × 10^—2 were compensated by Lomer dislocations. These sessile Lomer dislocations lie in the island interior only, where single 60° dislocations were observed exclusively in their near-edge regions. With increasing island size and/or layer thickness some close-spaced 60° dislocations occur additionally within the interfacial region. The Lomer dislocations that are always located 4 monolayers (ML) above the InAs/GaAs interfacial plane result from the well-known fusion of two 60° slip dislocations. These 60° dislocations have been nucleated 7 … 8 ML above the interface at surface steps on the {111} facets confining the islands. Based on our experimental observations a new mechanism is proposed that explains the origin of these 60° dislocations. Their further fusion to sessile Lomer dislocations that compensate the misfit strain most efficiently occurs in the way as commonly accepted.     

Versetzungsinduzierte Brechzahlinhomogenitäten

Inhomogenities of refractive index decisively influence the optical quality of elements for high precision optics. The present paper investigates the variation of refractive index induced by crystal defects, especially by dislocations. On the basis of the results for cubic crystals published by Nikitenko and Dedukh, equations were derived to calculate inhomogeneities induced by a dislocation in a generally anisotropic crystal. Numerical evaluations of the theory are performed for real dislocations in ADP, KDP and α-quartz.     

温梯法白宝石晶体的缺陷研究

采用导向温梯法(TGT)生长出[0001]方向直径为76mm的白宝石晶体.利用扫描电子显微镜(SEM)观察晶体(0001)面的腐蚀坑形态,并对晶体内部的包裹物进行了能谱(EDS)分析.白宝石晶体中的生长缺陷主要为位错和包裹体等.Al2O3晶体(0001)面的位错腐蚀坑呈六角形,并且有台阶状结构.分析了(0001)面内的位错类型.确定了TGT法生长的白宝石内部的包裹物的主要成分为碳.     

Mechanism of condensation of heteroepitaxial A3B5 layers pulse of moderate power

The mechanism of condensation of heteroepitaxial layers in laser deposition was studied on GaAs films on NaCl. Films were deposited in a superhigh vacuum using laser pulses of moderate power. Pulsed deposition proved to be more suitable for nucleation and growth than continuous deposition. However in this case it is important to compare the number of atoms deposited per pulse and the number of preferential adsorption centres in the substrate temperature of 310 °C. The density of dislocations in the films was about 10⁹ cm⁻². The main reasons for the dislocations are the excess of low volatile component and thermal stresses. Using a laser with quantum energy higher than the energy gap of the deposited semiconductor GaAs, which provides congruent evaporation, and making an additional deposition of As, we could reduce dislocations to 10⁷ cm⁻². A mechanism is proposed to explain the reduction of temperature in single crystal growth under laser deposition: high energy ion component of laser plasma gives rise to orienting defects on the substrate surface, and these defects determine epitaxial growth.     

Lattice strain and misfit dislocations in GaAs-GaAlAsP heterojunctions

The lattice strain and misfit dislocations in a GaAs-GaAlAsP heterojunction were examined. The change in lattice strain with the composition ratio or the position of the crystal was measured, and it was found that some of the misfit dislocations introduced in the heterojunction were edge-type dislocations. The critical thickness of the epitaxial layer for the generation of misfit dislocations was also measured. The critical differential strain between the atomic layers was on the order of several angstroms. The distribution of lattice strain was analyzed by a two-dimensional simple cubic lattice model, and the distribution of differential strain was examined.     

Dislocations (Solitons) in anharmonic crystals

Static dislocations (solitons) in an anharmonic lattice are studied within the framework of the Frenkel-Kontorova model. The dislocation-induced fields corresponding to the displacement vector and the stress tensor are calculated, and their properties are analyzed. The process of soliton nucleation is discussed in terms of the kinetics of the excited phonon subsystem of a loaded crystal. The expressions describing the nucleation time and the force and the energy conditions of a dislocation (soliton) nucleation are derived.     

TEM and X-ray investigations of defect structure of PbSnTe crystal

The Pb_0.8Sn_0.2Te single crystal grown by the Bridgman technique was examined by X-ray and TEM methods. The X-ray reflection topography revealed that the PbSnTe crystal consisted of monocrystallinic blocks with linear dimensions of 1–5 mm separated by low angle boundaries of tilt-twist character. “As grown” defects observed by TEM method have been identified as single perfect dislocations and dislocation pairs. A mean density of dislocations inside the crystal blocks was no more than 10³ cm⁻². Except “as grown” defects rows of mobile dislocations were observed. All of dislocations lines were characterized by the same type of Burgers vector, i.e. b = 1/2a〈110〉.     

Inclined Dislocations in Synthetic Calcite Crystals

A large number of perfect (100) cleavages were obtained by cleaving the laboratory grown synthetic calcite crystals. By etching such cleavages in 20% ammonium chloride solution, it is established that the pits indicate the sites of dislocations in the crystals. This is further confirmed by comparing the etch patterns on matched cleavage surfaces. Eccentricity of the pits has been attributed to the inclined nature of dislocations. Existence of parallel dislocations seems to be due to the purity of the crystal. These observations are verified by comparing etch patterns produced on opposite faces of a thin flake (0.048 mm thick) and also by successive etching and polishing a cleavage surface. It is conjectured that curl-bottomed pits nucleate at the sites of screw dislocations in the crystal. The implications are discussed.