Growth of Na modified potassium lithium niobate crystal by the Czochralski method

Transparent Na modified potassium lithium niobate (Na_0.23K_2.60Li_1.82Nb_5.35O_15.70; NKLN) crystal was successively grown by the Czochralski method using RF induction heating from melt composition Na₂O:K₂O : Li₂O:Nb₂O₅=2:30:25:43 mol%. NKLN crystal showed a tetragonal tungsten bronze structure with lattice constants a=12.5446±0.0010 Å and c=4.0129±0.0005 Å at room temperature. The dielectric constant along the c-axis ε₃₃ showed a sharp maximum around 480 °C. Optical transmission edge was 370 nm and optical transmission spectra showed no absorption at wavelengths ranging from 380 to 800 nm. The structural and optical properties of NKLN were similar to those of the near stoichiometric KLN crystals. We believe that the growth of NKLN by the Czochralski method has an advantage for a large size and high-quality crystal.     

Growth and characterization of ferromagnetic shape memory alloy Co50Ni20FeGa29 single crystals

Single crystals of Co₅₀Ni₂₀FeGa₂₉ with B2 phase have been obtained in a deep supercooling condition. The interface-facets and the segregation effect lead to the formation of ordered defects that store a directional internal stress. These defects give to a large energy barrier that leads to a very sharp martensitic transformation within a temperature window of only 2 K. The single crystals show good shape memory effect and superelasticity, which are anisotropic between the growth direction [0 0 1] and its equivalent direction [0 1 0]. The anisotropic behaviors are attributed to the directional internal stress caused by the ordered defects.     

CZ法生长参数对TeO2晶体质量的影响

本文主要讨论CZ法生长TeO2晶体中温度梯度、拉速、转速等工艺参数对晶体质量的影响,分析了晶体开裂、包裹物等宏观缺陷以及位错等微观缺陷的形成机理.从晶体形态、包裹体和位错密度变化等方面探讨了晶体生长参数与晶体缺陷之间的内在关系.     

Modeling analysis of liquid encapsulated Czochralski growth of GaAs and InP crystals

The results of three‐dimensional unsteady modeling of melt turbulent convection with prediction of the crystallization front geometry in liquid encapsulated Czochralski growth of InP bulk crystals and vapor pressure controlled Czochralski growth of GaAs bulk crystals are presented. The three‐dimensional model is combined with axisymmetric calculations of heat and mass transfer in the entire furnace. A comprehensive numerical analysis using various two‐dimensional steady and three‐dimensional unsteady models is also performed to explore their possibilities in predicting the melt/crystal interface geometry. The results obtained with different numerical approaches are analyzed and compared with available experimental data. It has been found that three‐dimensional unsteady consideration of heat and mass transfer in the crystallization zone provides a good reproduction of the solidification front geometry for both GaAs and InP crystal growth.     

Analysis of InP LEC metl flows using a parallel adaptive finite element scheme

A single-phase model for Liquid Encapsulated Czochralski (LEC) melt flows of InP is used in conjunction with a new three-dimensional parallel adaptive finite element scheme. Buoyancy, crystal rotation and crucible rotation are accounted for. The effect of the encapsulant rotation on the flow in the melt is accounted for by using a special boundary condition on the melt surface. The results of some quasi-steady simulations are presented.     

Scintillation properties of Zr co-doped Ce:(Gd,La)2Si2O7 grown by the Czochralski process

(Gd_0.75,Ce_0.015,La_0.235)₂Si₂O₇ (Ce:La-GPS) single crystals co-doped with 0, 100, 200, 500 and 1000 ppm Zr were grown by the Czochralski process, and their scintillation properties were investigated. We investigated the co-doping effect of a stable tetravalent ion in Ce:La-GPS for the first time. The scintillation decay times in the faster component were shortened with increasing the Zr concentration. While the non-co-doped sample showed ∼63 ns day time, the Zr 100, 200, 500 and 1000 ppm co-doped samples showed ∼61, ∼59, ∼57, ∼54 ns, respectively. Additionally, light output, photon nonproportional response (PNR) and other optical properties were investigated.     

100 Jahre Einkristallzucht aus der Schmelze

Cars, television, mobile phones, digital cameras, cash machines: Daily life is strongly affected by microchips produced from high purity silicon single crystals via thin wafers. Most of these single crystals are prepared by a process invented by the German‐Polish scientist Jan Czochralski in 1916 in the “Kabelwerk Oberspree (KWO)” of the “Allgemeine Elektricitätsgesellschaft (AEG)” in Berlin‐Oberschöneweide. Czochralski discovered the famous method to pull single crystals by accident: Deep in thought, he dipped his pen not into an ink pot but into a crucible with liquid tin, both standing next to one another on his desk. Quickly he pulled his pen out and observed a thin thread of tin emerging from the tip. After etching, the thread was identified as a single crystal of tin. This observation is probably one of the most important technical inventions of the first half of the 20^th century. In 1917, he left the AEG in Berlin and worked in the metal research laboratory, later belonging to the “Metallgesellschaft”, in Frankfurt/Main. Until today, wafers of high‐purity silicon are prepared by the Czochralski method. Silicon wafers with 200 mm diameter were produced in 1990, 300 mm wafers in 2001. The production of wafers with 450 mm diameter was expected for 2016. Siltronic produced in 2009 the first dislocation‐free silicon single crystal with 450 mm diameter, and other companies followed. However, until now, the 450 mm technology is not standard. This is due to a combination of very high investment costs needed to establish the 450 mm technology and very low prices of microchips.     

Large eddy simulation of Marangoni convection in Czochralski crystal growth

Large eddy simulation model is used to simulate the fluid flow and heat transfer in an industrial Czochralski crystal growth system. The influence of Marangoni convection on the growth process is discussed. The simulation results agree well with experiment, which indicates that large eddy simulation is capable of capturing the temperature fluctuations in the melt. As the Marangoni number increases, the radial velocity along the free surface is strengthened, which makes the flow pattern shift from circumferential to spiral. At the same time, the surface tension reinforces the natural convection and forces the isotherms to curve downwards. It can also be seen from the simulation that a secondary vortex and the Ekman layer are generated. All these physical phenomena induced by Marangoni convection have great impacts on the shape of the growth interface and thus the quality of the crystal. (© 2011 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

The color of langatate crystals and its relationship with composition and optical properties

Langatate crystals grown by the Czochralski method in 〈0001〉 and 〈01 1〉 directions both without subsequent annealing (from colorless to orange crystals) and with vacuum (colorless and pale‐green crystals) and air (orange crystal) annealing have been investigated by neutron diffraction, X‐ray diffraction and optical spectroscopy. The main types of point defects were compared with absorption bands: oxygen vacancies ‐ V_O^•• (0.35‐0.36 µm), the vacancies in the lanthanum position ‐ V_La‴ (0.29‐0.30 µm); the absorption band at 0.48‐0.49 µm is typical for the colored samples. The relationship between the X color coordinate (red component) and the oxygen contents has been obtained. The green color of the sample annealed in vacuum is due to the presence of Ta⁺³ ions in the La(Ta³⁺,Ga)O₃ phase that has the structural and geometric agreement with langatate structure. (© 2012 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

直拉单晶硅生长时空洞演化的相场模拟

为研究大直径直拉硅生长时空洞的演化规律,建立了与有限元模型所模拟的晶体生长温度场相结合的空洞演化相场模型,并应用该模型模拟研究了空洞形貌及其分布状态的变化过程以及不同初始点缺陷浓度对空洞演化的影响规律.结果表明:直拉硅单晶生长过程中,空洞的演化经历了孕育-形核-长大-稳定四个阶段,其形貌和分布状态亦由孤立的球形向偏聚的串珠形转变;与较低的点缺陷浓度相比,初始点缺陷浓度较高时,空洞的数目、平均尺寸、面积分数普遍较大,孕育阶段缩短、形核和长大阶段延长;空洞的偏聚及合并、长大的现象显著;当温度低于980 K时,大直径的空洞数目不再增加.