Numerical simulation of the LEC-growth of GaAs crystals with account of high-pressure gas convection

The influence of the inert gas pressure on the growth of 4 GaAs crystals by the liquid encapsulated Czochralski method (LEC) process is studied for a range of the Ar gas pressure up to 10 bar by using our finite-volume computer code STHAMAS. Up to the pressure of 0.6 bar we are considering laminar convection. For the pressure range from 5 to 10 bar we are using the buoyancy extended standard k-ε turbulence model with wall functions to simulate the gas flow. The numerical results show that the Argon gas pressure has a strong influence on the consumption of heater power in qualitative agreement with our experimental results. The convex curvature of the growth interface and the maximum thermal stress (von Mises criterion) are found to increase with increasing gas pressure both in the laminar and turbulent evaluations.     

Nonvolatile holographic recording in Ti, Fe Co-doped LiTaO3 crystal

Ti, Fe Co-doped LiTaO₃ (LT) crystals have been grown by the Czochralski method from the congruent melts. The absorption spectra of crystal were measured before and after ultraviolet illumination. Holograms have been recorded in doubly doped crystals with continuous-wave laser light by use of two-color method. The maximum value of refractive-index changes 7×10⁻⁵ is achieved.     

Preparation of NaCl color center laser crystals and perturbation effect of ions

NaCl:(F₂⁺)_AH-type color center laser crystals were prepared by the crystal growth, additional coloration, annealing, and by light aggregation at 290 and 77 K. The formation process of color center in NaCl crystals were investigated, the influence of doped cation and anion ions on the stability and optical properties of color centers is discussed in this paper.     

无位错Te-GaSb(100)单晶抛光衬底的晶格完整性

采用液封直拉(LEC)法批量生长的直径2英寸(1英寸=2.54 cm)n型Te-GaSb(100)单晶的位错腐蚀坑密度(EPD)通常低于300 cm^-2,达到无位错水平。本文利用X射线摇摆曲线以及倒易空间图(RSM)对这种GaSb单晶抛光衬底的晶格完整性和亚表面损伤情况进行了分析表征,结果表明经过工艺条件优化的化学机械抛光处理,GaSb单晶衬底表面达到原子级光滑,不存在亚表面损伤层。利用分子束外延在这种衬底上可稳定生长出高质量的Ⅱ类超晶格外延材料并呈现出优异的红外探测性能。在此基础上,对CaSb衬底材料的物性、生长制备和衬底加工条件之间的内在关系进行了综合分析。     

Visualization and computational steering of fluid motion in Czochralski crucibles during silicon crystal growth

This paper describes the authors' utilization of both post- and co-visualization techniques to indicate details of the fluid motion in a Czochralski crucible. Different visualization methods (particle tracing, isosurface extraction and line integral convolution) are discussed and applied to time-dependent flow in the crucible. Co-visualization is used to investigate the dynamic evolution of the flow structures at high temporal resolution. Moreover, the co-visualization approach also allows for interactive online visualization and computational steering, which strongly increases the user's ability to visualize the results and to supervise and dynamically control the entire computational process. By means of the resulting pictures and animations, the interaction of the different forces, which are responsible for the complex flow in the crucible is illuminated. In this way, the transport processes in the melt flow are characterized. Special attention is paid to the Marangoni-driven convection close to the interface between the melt and the crystal. The methodology for visualization and computational steering described in the paper can be applied to all kinds of complex three-dimensional and unsteady flow simulations. Its application is essential for handling the overwhelming amount of data produced by modern flow predictions. Consequently, it will play a decisive role in the next generation of CFD codes.     

Growth,etching morphology and spectra of LiAlO2 crystal

γ‐LiAlO₂ single crystal was successfully grown by Czochralski method. The crystal quality was characterized by X‐ray rocking curve and chemical etching. The effects of air‐annealing and vapor transport equilibration (VTE) on the crystal quality, etch pits and absorption spectra of LiAlO₂ were also investigated in detail. The results show that the as‐grown crystal has very high quality with the full width at half maximum (FWHM) of 17.7‐22.6 arcsec. Dislocation density in the middle part of the crystal is as low as about 3.0×10³ cm^–2. The VTE‐treated slice has larger FWHM value, etch pits density and absorption coefficient as compared with those of untreated and air‐annealed slices, which indicates that the crystal quality became inferior after VTE treatment. (© 2008 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

软轴型单晶炉提拉系统的振动建模与分析

当软轴型单晶炉提拉系统工作在某一转速附近时,其重锤摆动量会显著增大,严重影响单晶生长质量.为解决此问题,需要建立该系统的数学模型来研究提拉系统的动力学特性.本文在对提拉系统工作原理分析的基础上,应用Lagrange第二类方程建立了考虑该系统面内、面外振动的四自由度非线性振动微分方程.导出了该非线性模型的近似线性模型,对非线性模型响应与线性模型响应做了比较.进一步分析了系统的稳定性,应用Campbell图得到了考虑回转惯性效应后系统的临界转速.通过数值仿真定量说明了减小对中误差和增大阻尼可以减小重锤系统最大摆动幅值.     

大尺寸掺钛铝酸铍(Ti~(3+):BeAl_2O_4)激光晶体的提拉法生长

应用提拉法技术,采用BeO:Al2O3:Ti2O3摩尔比=100:99.85:0.15的化学组分配比,以及选用合适的固液界面温度梯度与生长速度等优化工艺条件,成功地生长出了T3+离子掺杂、无气泡、无云层和核心、尺寸≈Ф60mm×85mm的粉红色Ti3+:BeAl2O4大尺寸晶体。测定了Ti3+:BeAl2O4晶体的激发与荧光光谱。沿着晶体生长方向,晶体的颜色变深。在激发光谱中观测到了502 nm与567nm的激发峰,在发射光谱中观察到了发光中心为710nm的宽带荧光。两激发峰与Ti3+离子的2T2→2E能级跃迁有关,710nm的荧光峰是由振动能级2E→2T2产生的。从不同部位晶体的吸收强度和颜色变化可得到Ti3+离子在BeAl2O4晶体中的有效分凝系数小于1。     

Czochralski Growth of Potassium Lithium Niobate Single Crystals with Low Li Content and Their Characterization

Single crystalline and crack free potassium lithium niobate (KLN) single crystals with low Li content were grown by the Czochralski method. The crystal composition can be written as K_2.60Li_1.17Nb_5.44O₁₅ (=K_2.95Li_1.33Nb_6.17O₁₇) which contain relatively fewer Li ions than ferroelectric K₃Li₂Nb₅O₁₅ crystals. All experimental results show that the deficiency of the Li ions in the KLN crystals strongly influences their physical properties. Especially, the as‐grown crystals do not indicate any signature for a ferroelectric phase transition in contrast to the ferroelectric K₃Li₂Nb₅O₁₅ crystals. However, due to ionic conduction, the temperature dependence of the dielectric constant of such KLN‐2 crystals show a broad anomaly near 300°C. In addition, the existence of proton defects can be revealed by infrared absorption spectroscopy near 3500 cm^‐1 in as‐grown crystals.