Automated pulling of large-diameter alkali halide scintillation single crystals from the melt

Principles of a new high-productivity automated method for pulling large-diameter alkali halide crystals are described. On the stage of radial growth, the melt geometry is varied continuously by its level elevation in the conical crucible due to feeding by the melted raw material controlled by a lifting electrocontact probe. The melt level is stable when the crystal is grown in height. An automated system to control the crystal diameter has been developed using time intervals between feeding operations as the controlling parameter. This system allows control over the crystal diameter to an accuracy better than 1% over the range from 400 to 450 mm at the pulling rate from 6 to 6.5 mm/h. The method is used to produce scintillation alkali halide single crystals on an industrial scale.     

Hybrid technique for growing homogeneous single crystals of semiconductor solid solutions from melt

A concept and fundamentals of a hybrid technique for growing homogeneous single crystals of semiconductor solid solutions (SSs) from melt are presented. The growth consists of two stages. In the first stage, a single crystal with a specified concentration of the more refractory component is grown by an innovative method of directional constitutional supercooling of a melt in the steady-state mode. In the second stage, the melt is fed with the second component. Using an example of the classical Ge-Si system, the concentration profiles of the components along the crystal axis are calculated and the SS growth dynamics ensuring single crystallinity over the entire ingot length is determined. An analysis of the results yields the optimal technological parameters and conditions for growing homogeneous single crystals of SSs of a specified composition and size.     

The melt growth of oxide and related single crystals

This article reviews the principle changes which have occured during the last three years in the techniques used to produce single crystals of oxide and similar single crystals from the melt. The technological demands created by device applications are emphasized and the current state of knowledge upon the major crystalline defects is discussed. The role of accurate phase diagram analysis, the importance now attached to the atmosphere in which a crystal grows and the relevance of looking at crystals with greater resolution are stressed particularly.     

Growth of single crystals of semiconductor solid solutions by double feeding of the melt method

Crystallography Reports - The problem of component distribution in solid solution crystals grown from a melt fed by rods made of the components of the system, with allowance for the dependence of...     

The growing of β-copper phthalocyanine single crystals by evaporation

Purification of copper phthalocyanine and purity tests are described. An apparatus for growing of β-copper phthalocyanine single crystals and growing procedures are given.     

Pulling CsI(Na) single crystals from melt by continuous method without plastic deformation

It is established that bromine impurity in CsI(Na) crystals not only facilitates the homogeneous incorporation of an activator into the lattice and prevents complex activator clusters from forming, but it also significantly hinders (at certain concentrations) the action of the primary and secondary dislocation slip systems. It is shown that the automatic pulling of large CsI-based crystals can be provided by the introduction of a single Br impurity into the charge; this impurity, to a large extent, strengthens only the top part of the crystal. The absence of plastic deformation in CsI-CsBr(Na) crystals with a diameter Ø300 mm and height h = 600 mm (grown by the continuous method) and Ø500 mm and h = 200 mm (grown by the automatic Kiropulos method) has been experimentally confirmed.     

Studies on large uniaxially grown benzophenone single crystals

〈110〉, 〈010〉 and 〈100〉 oriented uniaxial benzophenone crystals were grown by uniaxially solution‐crystallization method of Sankaranarayanan ‐ Ramasamy (SR). The experimental parameters involved in the present study were investigated in detail and a constant growth rate was achieved by compensating the loss of growth units in the solution. A transparent uniaxial benzophenone crystal having dimension of 500 mm length and 55 mm diameter was grown at room temperature for the first time in the literature. In contrast to the conventional solution growth method, the growth rate along each direction was measured at ease during the respective growth experiment by monitoring the elevation of the solid‐liquid interface and found to be 2, 4 and 6 mm/day along the 〈110〉, 〈010〉 and 〈100〉 directions respectively for a chosen supersaturation. (© 2007 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Defects of different sizes in large paratellurite single crystals

Paratellurite single crystals have good acoustooptical properties that are important for various devices, such as deflectors, modulators, and tunable noncollinear filters. Paratellurite single crystals of up to 80 mm in diameter and 100 mm in height were grown using the Czochralski method from ultrapure melts. Optical anomalies in the grown crystals—gas bubbles, striations, impurity inclusions with nearby stresses, and regions with high dislocation densities—were studied with chemical, X-ray, and optical methods.     

Impurity induced structural phase transformations in melt grown single crystals of lead iodide

Lead iodide is a wide‐band gap and highly resistive semiconductor considered to be a promising room temperature nuclear detector. The phenomenon of polytypism is posing interesting problems of phase transformations among its polytypic modifications and formation of polytypic admixture during growth due to native impurities. Transformations have also been observed even when the material is stored for few months that causes deterioration in functioning of the PbI₂ devices. Lead iodide has been purified and single crystals were grown using zone‐refining system. The observed phase transformations during growth and storage have been explained in the light of distortion of [PbI₆]^4‐ octahedron due to impurities present in the material and the known crystal structures of PbI₂. (© 2011 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Pyroelectric properties of real LiNbO3 single crystals grown from a congruent melt

The temperature dependences of the pyroelectric coefficient of lithium niobate single crystals grown from a congruent melt have been investigated in the range of 4.2–300 K. No anomalies were found at low temperatures, and the experimental dependence is described well by the Debye-Einstein model, with T _D = 357 K and two pyroactive frequencies of 692 and 869 cm^?1. Specific features of lithium niobate have been analyzed. Two sublattices, formed by two pairs of mesotetrahedra with (according to the symmetry conditions) dipole and octupole moments, were selected in the structure. Their contributions to the total polarization differ by an order of magnitude. Vacuum annealing of the samples leads to the occurrence of anomalies only at temperatures over 280 K; these anomalities are interpreted as a manifestation of superionic conductivity.     

Formation of dislocation structure in shaped single crystals during their growth from the melt by Stepanov's Method

The paper is concerned with the formation of a dislocation structure due the thermal stresses in shaped single crystals with different degree of anisotropy grown by Stepanov's method. The calculation of root-mean-square tangential stresses allows to determine the regions in which the plastic deformation may occur. Analysis of thermal stresses in separate slip systems permits to explaine the slipe band distribution in shaped single crystals.     

Growth of large single crystals of stearic acid from solution

The growing of large single crystals of stearic acid (CH₃(CH₂)₁₆COOH), one of the saturated fatty acids, from organic solutions is reported. There are two parts in this experimental investigation; (1) to clarify the relationship between polymorphism of stearic acid having three modifications, namely, the A-form (orthorhombic), the B- and C-forms (monoclinic) and the growth conditions in the case of solution growth, because this complicated relationship has apparently made it very difficult to obtain large single crystals, (2) to produce large single crystals of stearic acid under the optimum growth conditions according to part (1). As a result large single crystals of stearic acid more than 8 × 8 mm² in area of the B- and C-modifications were successfully obtained. The values of long spacing, the crystal habit and the cleavage plane are also reported.     

Growth of large KDP single crystals for UV spectrum range

The influence of various technological parameters of crystallization (acidity of growth solutions, crystallization temperature, growth rate, degree of solution purification) on the optical absorption of large KDP single crystals has been studied in the UV range of the spectrum. It is shown that the method of solvent recirculation with the use of the starting material with the microimpurity content not exceeding 5 × 10^?5 wt % and solution ultrafiltration under the optimum crystallization conditions (t_cr = 80°C, V_cr ～ (0.8–1.6) × 10^?6 cm/s, pH 4) enables one to grow KDP single crystals with cross sections up to 300 × 300 mm² and the transmission in the vicinity of the fundamental absorption edge λ = 200 nm) equal to 86%.     

Luminescent properties of CsI single crystals grown from the melt treated with EuI2

CsI single crystals treated with EuI₂ as a scavenger are grown and their radioluminescence spectra and scintillation light decay curves are obtained. Addition of the quantities of the scavenger comparable with the total concentration of the oxygen‐containing admixtures in the melt results in complete destruction of the latter. In its turn, this causes the disappearance of the band with a maximum at 2.8 eV in the radioluminescence spectrum and decreases the fraction of the slow 2 µs‐component to 0.01. The addition of larger quantities of EuI₂ leads to the appearance of a wide band with the maximum at 2.8 eV characterized by a decay constant of 2 µs; its intensity increases with the EuI₂ concentration. The maximum ratio of two faster components with the decay constants equal to 7 and 30 ns approaches 0.58:0.41 at EuI₂ concentration in CsI melt equal to 0.01 mol·kg⁻¹.     

Luminescence of GaN single crystals prepared by heating a Ga melt in Na–N2 atmosphere

Colorless transparent prismatic crystals (0.5‐2.0 mm long) and hopper crystals (1.0‐2.5 mm long) of GaN were prepared by heating a Ga melt at 800°C in Na vapor under N₂ pressures of 7.0 MPa for 300 h. The photoluminescence (PL) spectrum of a prismatic crystal at 4 K showed the emission peaks of neutral donor‐bound exciton (D⁰‐X) and free exciton (X_A) at 3.472 eV and 3.478 eV, respectively, in the near band edge region. The full‐width at half‐maximum (FWHM) of (D⁰‐X) peak was 1.9 meV. The emission peaks of a donor–acceptor pair transition (D⁰‐A⁰) and its phonon replicas were observed in a lower energy range (2.9‐3.3 eV). The emission peaks of the D⁰‐A⁰ and phonon replicas were also observed in the cathodoluminescence (CL) spectrum at 20 K. The (D⁰‐X) PL peak of a hopper crystal at 4 K was at 3.474 eV (2.1 meV higher), having a FWHM of 6.1 meV which was over 3 times larger than that of the prismatic crystal. A strong broad band with a maximum intensity around 1.96 eV was observed for the hopper crystals in the CL spectrum at room temperature. (© 2007 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

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.     

Study of the possibility of growing germanium single crystals under low temperature gradients

The possibility of growing germanium single crystals under low temperature gradients in order to produce a dislocation-free material has been studied. Germanium crystals with a dislocation density of about 100–200 cm^?2 have been grown in a system with a weight control of crystal growth at maximum axial gradients of about 1.5 K/cm.