On the void distribution and size in shaped sapphire crystals

Ribbon and rod sapphire pulling has been performed in three different crystal growth equipments in order to study the effect of the installation, of the atmosphere, of the die shape, of the feed material and of the pulling rate on the distribution, number and diameter of the characteristic voids (micro‐bubbles) in the crystals. The location of the bubbles in the crystals depends on the die geometry; however, in most cases they are essentially located close to the crystal periphery and then can be efficiently removed by lapping. After statistical analysis of the results, it is demonstrated that the number of gas moles incorporated in the crystals, inside the voids, is totally independent of any growth parameter. It is also shown that the bubble diameter depends only on the pulling rate. Consequently, for a given pulling rate, the number of bubbles auto‐adjusts in order to satisfy the constant molar gas incorporation. (© 2005 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Simplified version of calculation of the composition distribution along a single crystal of a binary solid solution obtained by pulling from a feeding melt

The possibility of obtaining single crystals of binary solid solutions exhibiting strong segregation upon crystallization by pulling from a feeding melt with the use of a crucible shaped as a truncated cone and a feeding ingot of complex shape is shown. The composition distribution along the crystal length is found by solving the continuity equation for the second component flux under certain initial and boundary conditions. It is shown that single crystals can be obtained in which the second-component concentration in the stationary mode exceeds the corresponding value in the feeding ingot. The method developed is applied to Ge-Si solid solutions.     

Investigation of the single crystal growing process of neodymium-doped YAG garnets using radiotracers

Radioisotopic methods of investigation of Nd behaviour during pulling of single crystals of YAG-type garnets were applied. For the investigation of homogeneity of Nd distribution an autoradiographic method was used, and for the determination of Nd contents in single crystals and Nd effective partition ratios — techniques of radiotracers and gamma spectrometry. The conclusions from this work can find technological application.     

Growth of Bi–Sb Gradient Crystals for X-ray Monochromators by means of the Gradient Projection Method

Crystals with a well defined slope of composition have been grown by the Gradient Projection Method (GPM). In the system Bi–Sb gradient crystals with a lattice parameter gradient of Δa /Δa/dz = 0.835%/cm and Δc/c /dz = 0.79%/cm have been obtained. The concentration profiles of the grown crystals with large single crystalline parts exhibit a linear distribution. The adjustment of the dissolving rate allows to control the growth velocity and thus the quality of the grown crystals is increased.     

红外LED用GaAs单晶的垂直梯度凝固制备研究

GaAs单晶是当前光电子器件的主要衬底材料之一,在红外LED中有着重要应用。但杂质浓度高、迁移率低等缺点会严重影响红外LED器件性能。为生产出低杂质浓度、高迁移率、载流子分布均匀、高利用率的红外LED用掺硅垂直梯度凝固(VGF)法GaAs单晶,本文研究了热场分布、合成舟和炉膛材质、工艺参数对单晶的成晶质量、杂质浓度、迁移率、载流子分布的影响。利用CGSim软件对单晶生长热场系统进行数值模拟研究,温区一至温区六长度比例为8∶12∶9∶5∶5∶7时,恒温区达到最长,位错密度达到1 000 cm^-2以下,成晶率达到85%。采用打毛石英合成舟进行GaAs合成,用莫来石炉膛替代石英炉膛,可以获得迁移率整体高于3 000 cm²/(V·s)的GaAs单晶,满足红外LED使用要求。对单晶生长工艺参数展开研究,采用提高头部生长速度、降低尾部生长速度的方式提高单晶轴向载流子浓度均匀性,头尾部载流子浓度差降低33%,尾部迁移率从2 900 cm²/(V·s)提高到3 560 cm²/(V·s)。单晶有效利用长度提高33...     

Crystal growth of β-Phthalocyanines from the vapour phase in closed ampoules

An influence of temperature gradient, inert gas pressure and pulling rate on the growth parameters of β-phthalocyanine single crystals grown in the closed ampoules is investigated. The morphology and structure — sensitive properties of β-CuPc crystals grown under different conditions are compared.     

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.     

Controlled growth of Ti4O7 crystals by chemical transport reactions

Ti₄O₇ is a striking example of the difficulties involved in the simultaneous control of crystal growth and composition. In this respect, the usual back-transport step must be avoided because it results to the formation of mixed phases. However, an appropriate H₂ heat treatment can reduce these mixed crystals into single phase single crystals. This result is ascertained by accurate and sensitive physical methods. Finally suitable pulling transport experiments lead to the growth of centimeter long crystals.     

Analysis of the dopant segregation effects at the floating zone growth of large silicon crystals

A computer simulation is carried out to study the dopant concentration fields in the molten zone and in the growing crystal for the floating zone (FZ) growth of large (> 100 mm) Si crystals with the needle-eye technique and with feed/crystal rotation. The mathematical model developed in the previous work is used to calculate the shape of the molten zone and the velocity field in the melt. The influence of melt convection on the dopant concentration field is considered. The significance of the rotation scheme of the feed rod and crystal on the dopant distribution is investigated. The calculated dopant concentration directly at the growth interface is used to determine the normalized lateral resistivity distribution in the single crystal. The calculated resistivity distributions are compared with lateral spreading resistivity measurements in the single crystal.     

Mechanism for generating interstitial atoms by thermal stress during silicon crystal growth

It has been known that, in growing silicon from melts, vacancies (Vs) predominantly exist in crystals obtained by high-rate growth, while interstitial atoms (Is) predominantly exist in crystals obtained by low-rate growth. To reveal the cause, the temperature distributions in growing crystal surfaces were measured. From this result, it was presumed that the high-rate growth causes a small temperature gradient between the growth interface and the interior of the crystal; in contrast, the low-rate growth causes a large temperature gradient between the growth interface and the interior of the crystal. However, this presumption is opposite to the commonly-accepted notion in melt growth. In order to experimentally demonstrate that the low-rate growth increases the temperature gradient and consequently generates Is, crystals were filled with vacancies by the high-rate growth, and then the pulling was stopped as the extreme condition of the low-rate growth. Nevertheless, the crystals continued to grow spontaneously after the pulling was stopped. Hence, simultaneously with the pulling-stop, the temperature of the melts was increased to melt the spontaneously grown portions, so that the diameters were restored to sizes at the moment of pulling-stop. Then, the crystals were cooled as the cooling time elapsed, and the temperature gradient in the crystals was increased. By using X-ray topographs before and after oxygen precipitation in combination with a minority carrier lifetime distribution, a time-dependent change in the defect type distribution was successfully observed in a three-dimensional manner from the growth interface to the low-temperature portion where the cooling progressed. This result revealed that Vs are uniformly introduced in a grown crystal regardless of the pulling rate as long as the growth continues, and the Vs agglomerate as a void and remain in the crystal, unless recombined with Is. On the other hand, Is are generated only in a region where the temperature gradient is large by low-rate growth. In particular, the generation starts near the peripheral portion in the vicinity of the solid–liquid interface. First, the generated Is are recombined with Vs introduced into the growth interface, so that a recombination region is always formed which is regarded as substantially defect free. Excessively generated Is after the recombination agglomerate and form a dislocation loop region. Unlike conventional Voronkov's diffusion model, Is hardly diffuse over a long distance. Is are generated by re-heating after growth.[In a steady state, the crystal growth rate is synonymous with the pulling rate. Meanwhile, when an atypical operation is performed, the pulling rate is specifically used.]This review on point defects formation intends to contribute further silicon crystals development, because electronic devices are aimed to have finer structures, and there is a demand for more perfect crystals with controlled point defects.     

Growth and Optical Properties of Doped LiTaO3 Single Crystals

Single crystals of lithium tantalate (LiTaO₃) doped with Pr, Nd + Yb and Tm were grown by the Czochralski method. A thermal system with 50 mm diameter iridium crucible and two different afterheaters (active and passive) was checked with respect to temperature distribution in a pulling region. The obtained crystals were up to 20 mm in diameter and up 50 mm in length. Crystals were poled, and the Curie temperature was determined for specimens cut of from different parts of single crystals. The polarized absorption spectra, time resolved emission spectra and emission lifetime of Pr³⁺ doped LiTaO₃ crystals were measured. An intense emission from the ³P₀ level was observed. Optical properties of the Yb³⁺ ions excited by energy transfer from Nd3+ ions have been researched for LiTaO₃:Nd, Yb crystals.     

Modeling of convection during the growth of Ga x In1 − x Sb single crystals by the Czochralski method in the presence of ultrasound

Crystallography Reports - The effect of ultrasound on convective flow in the melt at pulling of Ga0.03In0.97Sb single crystals has been modeled by the light cut method in an ebonite crucible using...     

On the Iso‐Diameter Growth of β ‐BaB2O4 (BBO) Crystals by Flux Pulling Method

The iso‐diameter growth of β ‐BaB₂O₄ (BBO) crystals by the flux pulling method have been studied based on the phase equilibrium diagram in the BaB₂O₄‐Na₂O pseudo‐binary system and from the interface stability. The mathematical expressions for the cooling rate in the growth of the crystals with constant diameter under stable growth conditions are derived, the experimental phenomena such as diameter contraction and difficulty to grow a lengthy crystal by the flux pulling method are explained, the prerequisite for iso‐diameter BBO crystal growth from the flux is suggested; a new continuous charging flux pulling method is introduced to grow large‐sized high quality crystals with a relative high growth rate.     

Morphology and growth mechanism of vapor grown Cd crystals as affected by Bi impurity

The effects of Bi impurity on the morphology and growth mechanism of (physical) vapor-deposited Cd crystals were investigated. Scanning electron microscopic observation revealed, for the first time, hexagonal prismatic Cd crystals which were grown on the Bi contaminated pyrex glass tube wall. This kind of morphology does not appear in the case of pure Cd without the impurity Bi. The top of the hexagonal prismatic crystal was usually rounded hemispherically. X-ray microprobe investigations showed that the tip of the crystals contained about 57 wt% Bi. It was concluded that the Cd hexagonal prismatic crystals grow by the mechanism of vapor-liquid-solid with the impurity Bi.     

声光晶体TeO2的生长及缺陷研究

本文研究了直接ＴeO２晶体中的主要晶体缺陷形成机理,讨论分析了Ｔ eO2单晶生长的工艺参数对晶体缺陷的影响,结果表明：晶体裂缝的主要与温度梯度有关,温度梯度大于２０－２５℃/cm及出现界面翻转时,易造成晶全的开裂,位错密度增加,晶体中的包裹体主要为气态包裹全,它的形成主要与籽晶的转速和晶体的提拉速率有关,转速１５－１８r/min,拉速０.55mm/h,固液界面微凹,可以减少晶体中的气态包裹体,晶体台阶由晶体生长过程中温度和生长速度的引起伏引起,当台阶间距较宽时,易形成包裹体。     

Compositional variation in Si-rich SiGe single crystals grown by multi-component zone melting method using Si seed and source crystals

The effect of the supply of depleted Si solute elements on the compositional variation in the Si-rich SiGe bulk crystals was studied using the method which was used to grow Ge-rich SiGe single crystals with a uniform composition. By selecting the proper pulling rate, we can obtain Si-rich Si_1−xGe_x bulk crystals with uniform composition of x=0.1 without using the supply mechanism of depleted Si solute elements. When the supply mechanism of Si solute elements was used, the initial composition in Si-rich SiGe crystals can be much more easily determined by controlling the growth temperature than that in Ge-rich crystals because the Si seed crystal is not melted down. The supply of Si solute elements is very effective to change the compositional variation even for Si-rich SiGe crystals.     

The twisting of LiNbO3 single crystals grown by the Czochralski method

As a result of our experimental work of mainly practical importance we established that for LiNbO₃ single crystals the Mg and Fe dopants promote spirality whereas decreasing of the pulling velocity strongly reduces the propensity of the system to produce spiralshaped crystals.     

Near‐stoichiometric LiNbO3:ZrO2 single crystal growth by micro pulling down method

Crack‐free, rod‐shaped single crystals of undoped and 0.5, 0.7 and 1.0 mol% ZrO₂‐doped LiNbO₃ with a near‐stoichiometric composition were grown by the micro‐pulling down (μ‐PD) method. The structural properties of the grown crystals were examined by powder X‐ray diffraction (XRD). Electron probe micro analysis (EPMA) of the near‐stoichiometric LiNbO₃ single crystals revealed the homogeneous incorporation of Zr ions. The change in the refractive index and IR transmission spectra of the grown crystals were examined as a function of the Zr concentration. (© 2010 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Étude expérimentale des paramètres thermiques qui conditionnent la pureté de monocristaux de gallium obtenus par tirage

Crystal shape, temperature gradient at the interface and efficiency of solute rejection are studied as a function of the initial melt temperature for gallium single crystals grown by the pulling technique. In an alloy containing about 100 ppm Ag, the critical temperature gradient where a constitutional supercooling occurs, is found to be close to 8.8°C cm⁻¹.     

System of Mathematical Models for the Analysis of Industrial FZ-Si-Crystal Growth Processes

A system of coupled mathematical models and the corresponding program package is developed to study the interface shape, heat transfer, thermal stresses, fluid flow as well as the transient dopant segregation in the floating zone (FZ) growth of large silicon crystals (diameter more than 100mm) grown by the needle-eye technique. The floating zone method with needle-eye technique is used to produce high-purity silicon single crystals for semiconductor devices to overcome the problems resulting from the use of crucibles. The high frequency electric current induced by the pancake induction coil, the temperature gradients and the feed/crystal rotation determine the free surface shape of the molten zone and cause the fluid motion. The quality of the growing crystal depends on the shape of the growth interface, the temperature gradients and corresponding thermal stresses in the single crystal, the fluid flow, and especially on the dopant segregation near the growth interface. From the calculated transient dopant concentration fields in the molten zone the macroscopic and microscopic resistivity distribution in the single crystal is derived. The numerical results of the resistivity distributions are compared with the resistivity distributions measured in the grown crystal.