Effects of the Crystal Diameter on the Dislocation Density in KCl Crystals Grown by the Czochralski Method

The dependence of dislocation density on the crystal diameter of the Czochralski grown KCl crystals (both pure and Sr doped) was investigated by the method of the etch pit and X-ray topograph. (1) The dislocation density drastically decreased with the decrease in diameter (D) for small D (D < 2 mm, Fig. 2). (2) The dislocation density in the Sr doped crystal was lower than that of pure component in the diameter examined. (3) Many helical dislocations and dislocation loops were observed in the thin crystals (D ∼ 0.5 mm) of the pure KCl and Sr doped one, respectively, by X-ray projection topography. These results were discussed in connection with the dislocation generation mechanisms due to thermal stresses or supersaturated point defects.     

On the growth mechanism of polycrystalline snow crystals with a specific grain boundary

Observed frequently in a natural snowfall at temperatures lower than -20°C, the crossed-plate crystal is an assemblage of two to four thin basal plates, each plate extending along a CSL grain boundary with a relation of 70.3°/[11$\text{2}$0]. A possible growth mechanism is proposed to account for the characteristics growth in the direction of the axis [11$\text{2}$0]. If two or more grain boundary dislocation (GBD) structures are contained at a CSL grain boundary, growth layers will overflow alternately on the (10$\text{1}$0) planes of each component crystal at the intersection of these planes. Thus, the distinctive structure of the CSL grain boundary, like the feature of a screw dislocation step, will induce the preferential growth in this direction.     

Growth and morphology of 6H-SiC epitaxial layers by CVD

Single crystals of 6H-SiC were epitaxially grown on 6H-SiC substrates in the temperature range of 1500 to 1750°C with gas composition: H₂ ≈ 1 l/min, SiCl₄ ≈ 1 ml/min, C₃H₈ ≈ 0.05 ml/min. The grown layers were transparent and mirror-like. The morphology of the grown layer was strongly influenced by the polarity of the substrate surface. Aggregates of trapezoidal crystals were observed on the (000$\text{1}$)C surface and a mosaic pattern was observed on the (0001)Si surface. By observing the initial stage of the crystal growth, the growth mechanism of 6H-SiC is discussed. On (000$\text{1}$)C surfaces the vertical growth dominates, while on (0001)Si surfaces the lateral growth dominates.     

Growth of Inclusion Free KTP Crystals by Top Seeded Solution Growth and their Characterization

KTiOPO₄ single crystals of dimensions 34 × 15 × 15 mm³ have successfully been grown by Top Seeded Solution Growth (TSSG), using phosphate flux (K₆P₄O₁₃), employing a home made vertical cylindrical three zone resistive heated furnace. Growth experiments were carried out with <001> seed orientation. A method to grow inclusion free crystal with less dislocation density is proposed, by employing cooling rate of 0.5‐2 K/day and rotation rate of 60‐30 rpm. UV‐VIS transmission studies were performed and the dependence of absorption coefficient with wavelength is discussed. SHG elements of dimension 8 × 7.5 × 7.5 mm³ were fabricated and conversion efficiency of 58 % was achieved without antireflection coating. Nature of ionic conductivity and ferroelectric phase transition behavior of KTP crystals along the crystallographic polar axis in the frequency range of 100 Hz – 10 MHz are discussed.     

Growth of dysprosium garnet single crystals with spiral shape using Czochralski technique

The growth conditions of dysprosium garnets single crystals, to obtain a long and good spiral shape crystal, have been investigated using the conventional Czochralski technique along the [111] pulling direction. The good spiral shape of Dy₃Ga₅O₁₂ single crystal with 40 mm in length is grown with its spiral pitch and spiral diameter of 20 mm and 15 mm, respectively.     

IR-spannungsoptische Ermittlung züchtungsbedingter Eigenspannungen in Silizium

The growth conditions and the resultant defect structure are the cause of residual stresses in silicon single crystals. The field of residual stress is nearly axial symmetrically; tensile stresses are in the centre and compressive stresses are at the periphery. The field of residual stress adapts itself to crystal symmetry by plastic deformation during the growth or annealing processes. The tangential compressive stresses at the periphery are 25 kp/cm² for Czochralski-grown crystals (diameter 36 mm, etch-pit density 5 · 10³ cm⁻²) and about 70 kp/cm² for crystals grown by the floating zone technique (diameter 28 mm, etch-pit density 3 · 10⁴ cm⁻²). Dislocation free crystals are almost free of residual stresses.     

Crystal growth from solution: Development in computer simulation

It is shown in this paper that progress has been made in the understanding of crystal growth mechanisms of organic crystals growing from organic solutions or aqueous solution.The main part of this paper is devoted to the statistical mechanical background of the simulations. It is shown that it follows from the same formalism from which the transition probabilities of the computer simulations are derived that (i) crystal growth from solution is an allowed interpretation of the simulations (ii) expressions for the surface energy factor α and the driving force for crystallization $\text{Δμ}\text{kT}$ can be derived for a real system.     

The solid state controlled growth of sulphides and selenides of Ag and Cu using crystal rotation

An improved crystal growth method for ionic-electronic mixed conductors, such as the high temperature cubic modifications of Ag₂X and Cu₂X (where X = S or Se), is presented. Ag or Cu atoms are mobile in these compounds. If the respective sulphur or selenium vapour pressure was sufficiently high at the growth surface, the growth rate was limited by the solid state chemical diffusion of Ag or Cu atoms which was controlled by the rate of the injection of the metal atoms into the compounds. The crystals were grown in a silica ampoule, held in a vertical two zone furnace and rotated at 1 rpm about the vertical axis to achieve a uniform axial temperature distribution. Nearly cylindrical single crystals of size about 3–10 mm diameter, 10–35 mm long were grown by this method.     

4 inch低位错密度InP单晶的VGF生长及性质研究

采用高压垂直温度梯度凝固法(VGF)生长了非掺、掺硫和掺铁的4 inch直径(100)InP单晶,获得的单晶的平均位错密度均小于5000 cm-2.对4 inch InP晶片上进行多点X-射线双晶衍射测试, 其(004)X-射线双晶衍射峰的半峰宽约为30弧秒且分布均匀.与液封直拉法(LEC)相比, VGF-InP单晶生长过程的温度梯度很低,导致其孪晶出现的几率显著增加.然而大量晶体生长结果表明VGF-InP晶锭上出现孪晶后,通常晶体的生长方向仍为(100)方向,这确保从生长的4 inchVGF-InP(100)晶锭上仍能获得相当数量的2~4 inch(100)晶片.由于铁在InP中的分凝系数很小,掺Fe-InP单晶VGF生长过程中容易出现组份过冷,导致多晶生长.通过控制生长温度梯度及掺铁量,可获得较高的掺铁InP单晶成晶率.对VGF-InP单晶的电学性质、位错密度及位错的分布特点、晶体完整性等进行了研究.     

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)     

Analyses of Crystal Shape Monitoring of LEC-Grown InP Crystals by using a Disc Approximation Approach

This paper analyzes crystal shape monitoring for automatic diameter control (ADC) during the liquid encapsulated Czochralski (LEC) growth of InP crystals. The crystal diameter (shape) is monitored numerically (diagrammatically) by using a disc approximation approach based on precise weight and pulling length measurements. The error in the diameter calculation based on the approximation is estimated to be sufficiently small for practical use. The monitoring accuracy was investigated for crystal bodies with nearly flat growth interfaces, and for their shoulder portions with largely convex growth interfaces. For the straight body portions, the accuracy depended on diameter, d, and improved from ±15% for d=10 mm to ±3% for d=50mm. For the shoulder portions, the diameter was monitored with nearly the same accuracy. This method has therefore made it possible to monitor the growing crystal visually in real time, and was applied to the growth of <111> InP crystals with a cone angle of less than 39° and a smooth appearance to avoid twinning.     

Long-term Crystal Growth under Microgravity during the EURECA-1 Mission (I) THM Growth of AlxGa1−xSb

Long-term crystal growth experiments were successfully performed under microgravity conditions during the first flight of the unmanned mission EURECA-1 in the automatic mirror furnace (AMF). Two crystals of Al_xGa_1−xSb with [001] and [111] orientation respectively were grown from gallium solution by the travelling heater method. The grown length of the single crystals is 4.0 mm and 4.2 mm respectively. The space-grown samples show a high microscopic homogeneity which indicates the absence of time dependent convection. From pulse markers a constant growth rate of 0.6 ± 0.1 μm/min is measured which is lower than 0.8 ± 0.1 μm/min obtained in earth grown reference samples. Details about the experiment performance and the growth results are given.     

Dislocations in magnetic garnet crystals

1. Dislocations in magnetic flux-grown garnet crystals (Y₃Fe₅O₁₂ and others) have been observed. As a rule, {110} growth pyramids have more defects than {211} ones. 2. The highest content of defects (dislocation density 10³–10⁴ cm⁻²) is observed in Y₃Fe₅O₁₂ that grows on crucible walls adjacent to the free surface of the solution where the flow of heat is not uniform to the greatest degree. Bottom grown crystals usually have less dislocations. Far fewer dislocations are in wall grown crystals, least of all dislocations are contained in crystals that grow inside the solution. The solution pouring off at the end of the crystallization period increases dislocation density by some dozens. 3. Heat treatment decreases dislocation density. The less dislocation content and the lower ordering are in the initial crystal, the higher heat treatment effectiveness.     

Solution growth of new ferroelectric glycine phosphite unidirectional single crystals at room temperature

Glycine phosphite [NH₃CH₂COOH₃PO₃], abbreviated as GPI is the second hydrogen bonded ferroelectric crystal combination of phosphorous acid and amino acid following βnine phosphite crystals abbreviated as BPI. Sankaranarayanan and Ramasamy‐Technique was adopted to prepare the ferroelectric glycine phosphite unidirectional single crystal. The growth orientation was imposed by the pre‐grown 〈010〉 seed. As water was the solvent, transparent, colourless crystal with cylindrical shaped ingot of sized 20mm‐diameter was grown. Powder X‐ray diffraction, HRXRD, FTIR, dielectric and mechanical studies were carried out. The results are discussed in detail. (© 2007 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Growth and characterization of magneto‐optical YFeO3 crystals

The floating zone growth of magneto‐optical crystal YFeO₃ has been investigated. The polycrystalline feed rod was prepared by a pressure of 250MPa and sintering at about 1500°C. A crack‐ free YFeO₃ single crystal has been successfully grown. The crystal preferred to crystallize along <100> direction with about 10° deviation. The X‐ray rocking curve of the crystal has a FWHM of 24 arcsec, confirming the high crystal quality of the sample. The (100) plane was etched by hot phosphoric acid and the dislocation density was about 10⁴/cm². A thin outer layer with Y₂O₃‐rich composition was found at the periphery of as‐grown crystals, which was attributed to the Fe₂O₃ evaporation during growth. (© 2007 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Crystal growth and dislocation structure of gallium antimonide

Single crystals of GaSb have been grown by the Czochralski method under reducing conditions. Crystals were grown in the 〈100〉, 〈111〉, and 〈112〉 directions. The 〈111〉 growth direction was found to be the most suitable for the successful and reliable crystal growth. Dislocation densities in 〈111〉 oriented crystals were examined by chemical etching. The etch pits density in these crystals didn't exceed the value of 1 × 10² cm⁻².     

Plastic bend in a growing crystal

In case of nonlinear axial temperature distribution the relaxation of thermoelastic stresses results in the plastic bend of the growing crystal, i. e. in the generation of a residual lattice curvature equal to ϱ b . Based on results from Billig and from Indenbom the author presents estimations of dislocation densities (ϱ) (i. e. residual lattice curvature) taking into account an elastic limit differing from zero. It is shown that sign and value of the residual lattice curvature may be effectively used as criteria pointing out how thermal conditions should be changed for abtaining more perfect crystals. This approach application allowed to grow larger KCl single crystals (300 mm in diameter more than 100 kg by weight) with better structure perfection (specific subboundaries surface 2—3 cm²/cm³, mean subgrain dimension 0.6—1 cm, mean mutual disorientation of subgrains of not more than 6′).     

Bulk GaN crystals grown by HVPE

We succeeded in preparing very thick c-plane bulk gallium nitride (GaN) crystals grown by hydride vapor phase epitaxy. Growth of the bulk GaN crystals was performed on templates with 3 μm GaN layer grown by metal organic chemical vapor deposition on (0 0 0 1) sapphire substrates. Colorless freestanding bulk GaN crystals were obtained through self-separation processes. The crystal's diameter and thickness were about 52 and 5.8 mm, respectively. No surface pits were observed within an area of 46 mm diameter of the bulk GaN crystal. The dislocation density decreased with growth direction (from N-face side to Ga-face side) and ranged from 5.1×10⁶ cm⁻² near the N-face surface to 1.2×10⁶ cm⁻² near the Ga-face. A major impurity was Si, and other impurities (O, C, Cl, H, Fe, Ni and Cr) were near or below the detection limits by SIMS measurements.     

Growth and Spectrometric Tests on Bi4Ge3O12 Crystals

A resistance-heated furnace with a good control of temperature gradients is used for the Czochralski growth of precipitate and colour free Bi₄Ge₃O₁₂ (BGO) crystals up to 30 mm in diameter and 80 mm in length from a 45 mm diameter crucible. The quality of the grown crystals is discussed in connection with the growth conditions. Spectrometric tests made on scintillators obtained from BGO crystals are presented. A Monte Carlo program is used in order to compute the full energy peak efficiency of the detector for different energies and geometries. The computed values are compared to the experimental results.