Study of the Concentration Distribution of SiC Vapour in the Crystal Growth Zone

In the present work the gas dynamics in the growth zone of SiC crystals is investigated. It is shown that the propagation of SiC vapour from the growth cavity walls towards the lids is effected by diffusion. On this basis the calculation of the concentration distribution of SiC vapour (n), the equilibrium vapour concentration (n_s), and the supersaturation $ \left({\alpha {\rm = }\frac{{n - n_{\rm s} }}{{n_{\rm s} }} \cdot {\rm 100\%}} \right) $ in the crystal growth zone at different radial and axial temperature gradients is carried out by solving the Laplace equation in cylindrical coordinates for a stationary case corresponding to the conditions of crystal growth. The received results are compared with the available experimental data which gives a possibility for explaining some of the observed peculiarities during SiC crystal growth from the vapour phase by the sublimation method.     

Growth Rate Effects during Indium-Antimony Crystal Growth

Local interface velocities are tracked radioscopically in the III-V semiconductor compound indium-antimony grown in a vertical Bridgman-Stockbarger furnace. Comparisons are made of interface velocities from five different compositions (40, 49, 50, 55, and 60 at.% Sb). Under specific growth conditions, the growth velocity for stoichiometric melts was comparatively constant and very close to the translation velocity. Measured chemical homogeneity was excellent, though polycrystallinity could occur when concentration boundary layers formed ahead of the interface. Off-stoichiometric melts exhibited initial supercooling, resulting in transient interface velocities and polycrystallinity. The observed supercooling is governed by chemical segregation in the melt. Thus, local growth velocity fluctuations are unambiguously attributed to a coupling of ompositional effects in the melt and crystal facetting kinetics.     

Doping of PbTe with Ga during Growth from the Vapour Phase

In the present paper a method for doping of PbTe with Ga during crystal growth from the vapour phase is presented. The galvanomagnetic and photoelectric properties of the produced material are compared with results of other techniques and the equivalence of these physical properties is proved. Furthermore a defect model of the build-in mechanism of Ga in PbTe is shown.     

Algorithm for the Transitional Portions during the CZ Crystal Growth Using a Computer Control

A model is proposed for a non-stationary process of diameter variation (growing out and narrowing) of the crystal, grown by the automated Czochralski technique, with the aim of obtaining the initial and final “cones” of any desired configuration. The calculations are illustrated by the experimentally grown lithium niobate crystals.     

Interface Dynamics during Indium Antimonide Crystal Growth

Experiments with a stoichiometric InSb compound were first performed at small temperature gradient across the crystal/melt interface of 3 °C/cm and furnace translation velocity, V_frn, of 2 μ/sec. Known growth requirements for quality crystals were confirmed. They are, (1) the interface temperature must be close to the congruent melting temperature and, (2) the interface must be located within the adiabatic zone. These requirements can be obtained only through specific settings of the heater temperatures. An X-ray radioscopic system has been modified to accommodate real-time visualization of the crystal/melt interface during vertical Bridgman-Stockbarger growth of InSb. It is shown that asymmetric temperature settings of the heaters can be advantageously used to minimize defect formation. The interface temperature was assessed indirectly with calibrated outside thermocouples. Optical microscopy and electron microprobe analyses provided feedback on crystalline homogeneity.     

KDP晶体缺陷对生长应力分布的影响

本文采用有限元法分析了不同尺寸、形状的晶体缺陷对大口径KDP晶体生长应力分布的影响.结果表明,晶体中的缺陷导致了晶体内部应力集中,且应力集中程度与缺陷尺寸、晶体生长尺寸呈反向变化,而最大主应力与缺陷尺寸、晶体生长尺寸呈正向变化.当缺陷含有棱边或尖角时,应力集中程度和最大主应力值都明显增加.由于KDP晶体易脆性开裂,随着最大主应力值的增大,开裂机率也增大.     

Marangoni Convective Effect during Crystal Growth in Space

GaSb:Te and GaInSb samples have been solidified under microgravity conditions during the D2 Spacelab mission. Experimental design and parameters are described. Analysis of the thermal data taken during the flight, associated to numerical simulations of heat transfer in the experiment, with the help of FIDAP, gave the experimental conditions (thermal gradients and growth rate). Quantitative chemical analyses of the samples show a chemical segregation characteristic of strong mixing in the melt during crystal growth. Silica crucibles with an internal screw thread groove on the inner wall were used in order to get dewetting of samples from the crucible. It was therefore supposed that Marangoni convection on the free surface associated to the groove might have been the source of convection. This hypothesis has been studied by numerical simulation using FIDAP and the velocity field obtained is in agreement with a strong perturbation of the solutal boundary layer ahead the solid-liquid interface. This can explain the observed chemical segregation.     

晶体生长过程建模及解耦控制

晶体生长过程中其直径的控制是通过调节生长速度和热场温度而实现的.控制系统是一个双入双出系统,输入输出之间存在耦合关系.本文采用前馈补偿解耦的方法,实现了单晶炉生长控制中的解耦控制,并通过仿真及实验证明了方法的有效性.     

KDP晶体杂质对生长及出槽应力分布的影响

KDP晶体中的杂质易导致其开裂.本文采用有限元法分析了不同属性、尺寸、形状的晶体杂质对大尺寸KDP晶体生长及出槽应力分布的影响.结果表明,不同属性的杂质对晶体生长应力和出槽应力分布具有不同程度的影响.杂质附近的生长应力与杂质的弹性模量呈正向变化;杂质附近的出槽应力与杂质和晶体的热膨胀系数之差呈正向变化;杂质的尺寸越大,形状越尖锐,杂质附近的生长应力和出槽应力均增大.     

Semiopen Physical Vapour Transport Growth of Urotropine Crystals

It is reported for the first time the growth of urotropine (HMT) crystals by a semiopen physical vapour transport (SOPVT) technique. HMT crystals, approximately 1 cm³ in volume, are grown on a glass pedestal from solution-grown seeds. The final habit of the crystals is limited by rhomboedrical {110} faces which develop on an otherwise hemispherical shape. Preliminary X-ray diffraction investigations (rocking curves and topographs) point to a still non-homogeneous crystal structure, which very likely originates at the seed-crystal interface. However, in comparison with solution-grown samples, the best structural quality was observed in a SOPVT-grown sample.     

晶体生长时的固液相结构变化分析

晶体的溶解、熔化以及结晶成核生长时的固液相原子结构是怎样变化的,晶体生长时的生长基元是原子还是原子团.本文根据各种材料液相结构的最新研究结果,提出不饱和配位结构转换模式,并以此模式对各种常见晶体材料从溶解、熔化到结晶生长时的液态母相结构变化以及晶体成核过程进行了描述和分析,认为晶体生长时的界面结构和液相结构十分接近,溶解、熔化主要是晶体表面的不饱和配位原子(离子)转换到液相结构的过程,晶体生长主要是液相中的不饱和配位原子(离子)转换到固液生长界面的位错位置,使配位结构更饱和的过程.随着液相过饱和度的增大,液相结构单元的原子数越来越多,吸附到晶体生长界面若来不及转换回液相,就形成新的位错生长中心,形成晶体生长缺陷.     

直拉硅单晶中双空洞长大动力学的相场模拟

为了研究硅单晶直拉法生长过程中双空洞的长大动力学以及空洞间的相互作用机理,采用已建立的空洞演化的相场模型及其应用程序,模拟研究了直拉硅单晶生长过程中双空洞演化和相关因素的影响规律.结果表明:所建相场模型能够有效地模拟基体中空位扩散和双空洞长大的过程;双空洞长大趋势随着模拟时间和初始空位浓度的增强而加强;随着空洞初始中心间距的增加和初始空位浓度的减小,双空洞长大由相互融合模式转变为独立长大模式.     

工业晶体生长

本文考察了一些典型的晶体材料及其工业生长技术,如提拉法生长硅单晶,水热法生长水晶,VGF法生长GaAs,下降法生长锗酸铋,壳熔法生长锆石等,探讨了工业晶体生长的特点和发展方向.     

助熔剂法晶体生长计算机控制系统研究

根据助熔剂法晶体生长的基本要求,试制了一种基于PC总线的高精度计算机温度控制系统,系统硬件总体结构包括由温度信号采集,远程信号传输,控制命令变频传输,功率信号放大及电流反馈控制等功能模块.控制软件建立在Windows环境下,由Genie 2.0图控组件平台和利用VB 3.0开发的数据管理控制模块两个部分组成.文中讨论了主要的软硬件结构,并介绍了连续高温控温实验的结果.     

AlN晶体PVT生长装置的智能控制系统研究

AlN晶体的物理气相传输(PVT)法生长条件要求苛刻,如0.3~5 atm的高纯氮气生长气氛和2100~2400 ℃的生长温度.结合AlN晶体PVT生长工艺的特点,通过可编程逻辑控制器(PLC)进行适用于氮化铝(AlN)晶体PVT生长装置的智能控制系统的研究.首先,提出了倒置温场的生长工艺以降低AlN晶体PVT生长的成核数量,并通过自动控制程序设计满足不同生长阶段的温场要求;其次,针对设备可能存在超温、超压及冷却水断流等实验安全问题,设计并实现系统的自动化报警及自处理操作;最后,在实验操作上,实现AlN晶体生长的"一键式"全自动化工作.     

三维运动下KDP晶体生长过程中的应力分析

作为一种新型溶液晶体生长方式,“三维运动生长法”能够快速生长高质量大尺寸的KDP晶体.为了了解KDP晶体在三维运动生长过程中晶体内部的应力状态,本文采用有限元法对三维运动下KDP晶体生长过程中的应力分布进行了计算.结果表明,掣晶杆顶端附近以及晶面和掣晶杆交接处存在明显的应力集中,主应力较大,是晶体生长过程中的易开裂点.增加掣晶杆直径,使用圆头掣晶杆和降低三维运动过程中的加速度能够降低晶体内部的最大主应力,减小晶体在生长过程中开裂的机率.     

Atomic Processes during Crystal Growth Studied by Reflection High-Energy Electron Diffraction

After a short retrospect on the development of the electron diffraction techniques it is shown that the atomic-scale morphology of the crystal surface and growth processes on it can be studied in detail during molecular beam epitaxy (MBE) by reflection high-energy electron diffraction (RHEED). This is demonstrated for the evolution of the terrace-step-structure of the singular GaAs (001) surface during growth and after growth interruption and for the attachment of Si atoms at misorientation steps on vicinal GaAs (001) surfaces.     

固态材料形成过程中的晶体生长机理探讨

同样由熔体凝固、溶液沉淀或者气相沉积出来,为什么有的材料呈晶相,有的呈非晶相? 晶体生长是由自组装形成的还是由外界条件决定的?是哪项因素决定了晶体生长时原子的有序排列?本文根据实际现象,用晶体生长的热力学理论分析了逆向离子解离对晶体成核及生长的作用机理,并对固态材料的形成与晶体成核生长之间的关系也作了进一步的阐述和分析,由此得出结论认为,由化学键结合的材料在晶体生长时必须伴随着逆向离子解离平衡,正是固态材料形成过程中的逆向离子解离过程,如同时伴随着电离的溶解、熔化及升华过程,决定了晶体生长时原子的有序排列.     

Modified Growth of Mercuric Iodide Crystals from the Vapour Phase

The Hgl₂ single crystal with shiny natural crystal planes, low density of dislocation, and 350 g in weight has been grown by a new technique of modified vapoir phase located point method. The perfection and nuclear spectroscopic performance of the grown crystals are also studied.