Bridgman growth of Cdx Hg1-xTe using acrt

The Accelerated Crucible Rotation Technique (A.C.R.T.) has been applied to the Bridgman growth of the mixed semiconductor Cd_xHg_1-xTe. An increase in the level of melt mixing near to the interface has been achieved and this has resulted in a much greater degree of axial and radial composition homogeneity than hitherto possible. Effects of changes in A.C.R.T. rotational parameters and crystal start composition have been assessed. An improvement in crystallinity has also been obtained which is believed to be due to transient Couette flows at the crucible walls. It is shown that an empirical approach to optimising A.C.R.T. conditions in a particular system is necessary although a theoretical study can provide the starting point. Present address: Philips Research Laboratories, Redhill, Surrey, RH1 5HA, U.K.     

大尺寸碳化硅单晶生长环境研究

针对基于物理气相输运法的碳化硅(SiC)单晶生长系统,考虑对流换热的影响建立了传热与传质数学模型,并采用数值模拟的方法研究了其生长系统内的温度场与气相流场.研究表明:坩埚内温度、温度梯度以及加热效率随线圈匝间距与线圈直径的增加而逐渐降低.旋转坩埚可有效解决因线圈螺旋形状而导致的温度场不均匀性.通过不断调整线圈与坩埚之间的相对高度,可保证高品质晶体生长所需的最优温度场环境.此外,坩埚内径尺寸的增加,会加剧其内部自然对流效应.     

Investigation of Artificial Forced Cooling in the Bridgman Crystal Growth of Cadmium Zinc Telluride

The effects of artificial forced cooling on the solid–liquid interface and on solute segregation were investigated by modeling the vertical Bridgman method for the single-crystal growth of CdZnTe, taking into consideration effects such as increasing the axial outward heat flux from the crucible bottom, the radial outward heat flux from the crucible wall, and the carbon film thickness on the crucible inner wall. Axial artificially forced cooling noticeably increases convection and the temperature gradient in the melt next to the solid–liquid interface, and substantially reduces interface concavity at the initial solidification stage. Interface concavity increases a little when the solidification proceeds further, however. Axial artificially forced cooling reduces radial solute segregation of the initial segment of the grown crystal and slightly increases the solute iso-concentration segment. Radial artificially forced cooling enhances melt convection substantially, affects solid–liquid interface concavity only slightly, and hardly affects solute segregation in the grown crystal. Doubling the carbon film thickness weakens convection of the melt in front of the interface, substantially increases interface concavity, and hardly affects solute segregation in the grown crystal.     

自动加料单晶炉的设计与研究

由于传统的晶体生长设备不具备加料功能,在晶体生长过程中无法进行原料补充,所以最终的晶体尺寸通常受制于坩埚和设备大小。而更大尺寸的坩埚和设备成本高,这制约了大尺寸晶体的研究和发展。该文设计了一种自动加料系统,可根据已生长的晶体质量向坩埚内补充同等质量的原料,确保坩埚内固 液界面保持不变,从而实现小坩埚生长大尺寸晶体的目标,提高了设备利用率,节约了能源,降低了生产成本,促进了大尺寸晶体的发展。     

Reduction of dislocation densities in InP single crystals by the LEC method using thermal baffles

We have developed a modified liquid encapsulated Czochralski (LEC) method with thermal baffles, by which low dislocation density InP crystals can be grown. In this method, thermal baffles are set on top of the crucible in order to suppress the gas convection and thus to improve the temperature gradient in the LEC furnace. However, the dislocation densities depend not only on the temperature gradient but also on other growth conditions, such as crystal/crucible rotation rates, cooling rates, and the thickness of the pBN crucible. Since the rotation rate affects the solid/liquid interface shape, it is an important factor for the reduction of dislocation densities. By optimizing these conditions, for Sn and Fe doped InP crystals, average dislocation densities less than 5 x 10³ cm⁻² can be achieved. Dislocation free (DF) S and Zn doped InP crystals can also be grown if the carrier concentration is more than 3 x 1018 cm⁻³. The DF crystals become rectangular in shape.     

A Macro Model of Frequently Changing Mobile Networks to Perform Flow and Access Control

The area covered by a mobile ad hoc network consists of obstacles that inhibit transmission and areas where communications can take place. Physical structures, such as buildings, that block transmission, or lakes, where forwarding nodes cannot be located, are permanent obstacles. Temporary obstacles are created as mobile nodes enter or leave an area. Our hypothesis is that the spaces between nearby obstacles are bottlenecks that inhibit the flows in the network. We partition the network into areas that are encompassed by obstacles and bottlenecks. All of the nodes in an area are treated as a single super node, and the bottlenecks between areas are the links between the super nodes. As individual nodes move, the flows and paths in the model change more slowly than the paths and flows between the individual nodes. We apply flow control algorithms to the model and perform admission control within a super node based on the flows that are assigned by the flow control algorithm. We apply the model to the Columbia University campus, and use max–min, fair bottleneck flow control to assign the flows. Our hypothesis is verified for this example.     

Capacitance transient spectra of processing- and radiation-induced defects in silicon solar cells

Capacitance transient spectroscopy is used to study defects in chips of fully fabricated silicon solar cells. Characteristic differences are observed as a function of the crystal growth type (crucible grown or float zoned) and dopant (boron or aluminum) of the starting material, processing variables (diffused or implanted junctions, electron beam or furnace annealing) and radiation environment (1 MeV electron irradiation).     

高纯SiC粉料中杂质浓度的控制和测试

采用燃烧合成法制备碳化硅(SiC)粉料,调整氢气和氩气体积流量比以及高纯氯化氢气体体积流量,使氮、铝和钒浓度低于二次离子质谱仪的检测下限,硼和钛浓度接近检测下限。使用制备的高纯SiC粉料生长单晶,获得电阻率大于1×10^9Ω·cm的衬底,粉料达到高纯半绝缘水平。通过研究发现,增加氢气体积流量可以降低粉料中的氮浓度,并使氮浓度低于检测限1×10^16 cm^-3,但是氢气体积流量过高会加重坩埚损耗,影响坩埚寿命和工艺稳定性;高纯氯化氢气体可以降低粉料中硼、铝、钒和钛的浓度,但其体积流量不宜过大,否则会引入新的氮杂质;粉料的色度a^*值与氮浓度呈反比关系,利用分光色差仪测试色度a^*值判断粉料氮浓度高低。     

直拉单晶硅中埚跟比的精确计算研究

在直拉单晶硅生长过程中,埚跟比（即坩埚上升速度与晶体提拉速度的比值）的设置非常重要,它直接决定了液面位置的稳定性。其不但影响单晶硅成品的质量,而且不合理的埚跟比设置可能会在直拉单晶硅生长过程中出现变晶断苞,导致单晶生长失败。目前国内大多数光伏单晶硅生产商仅仅依靠人工经验来设置埚跟比,其准确性很难保证。采用体积元积分的方...     

提拉法生长钆镓石榴石(GGG)晶体

用提拉法生长出了优质的钆镓石榴石(Gd3Ga5O12)晶体,晶体尺寸达φ35 × 70mm。详细描述 了晶体生长工艺过程,讨论了生长气氛对及坩埚形状对晶体生长的影响。     

Resource allocation between persistent and transient flows

The flow control algorithms currently used in the Internet have been tailored to share available capacity between users on the basis of the physical characteristics of the network links they use rather than the characteristics of their applications. However, real-time applications typically have very different requirements from file transfer or Web browsing, and treating them identically can result in a perception of poor quality of service even when adequate bandwidth is available. This is the motivation for differentiated services. In this paper, we explore service differentiation between persistent (fixed duration) and transient (fixed volume) flows, and also between transient flows of markedly different sizes; the latter is stimulated by current discussion on Web mice and elephants. We propose decentralized bandwidth allocation algorithms that can be implemented by end-systems without requiring the support of a complex network architecture, and show that they achieve performance very close to what is achievable by the optimal centralized scheme.     

垂直布里奇曼法生长CdZnTe晶体时固液界面形状的控制

采用有限元法对探测器材料 Cd Zn Te的晶体生长过程进行了热分析 ,研究了不同因素对生长过程中固液界面形状的影响 .模拟结果表明 ,当坩埚下降速度约为 1m m/ h时 ,可获得接近水平的固 -液界面 .晶体生长实验结果与计算机模拟的结论基本一致 .因此 ,通过适当选择和调节坩埚下降速度可获得高质量晶体 .     

Application of dynamic and combined magnetic fields in the 300 mm silicon single-crystal growth

The increase of diameter in the silicon single crystal growth from 200 to 300 mm for industrial application, and to 400 or 450 mm for research, respectively, has triggered off the development of numerous new technologies like crystal-growth-supporting systems, low-power hot zones, high strength of static magnetic fields and new quartzglas qualities. At Wacker Siltronic, new kinds of magnetic fields have been developed for 300 mm CZ growth. In this paper, the results of dynamic and combined (static and alternating) magnetic fields are discussed. Instead of buoyancy-driven convection, a magnetic-field-controlled melt flow has been obtained in large melt volumes. The crucible wall temperature and, in turn, the quartzglas corrosion has been reduced. Furthermore, the application of the magnetic fields allows the control of oxygen in a wide range.     

流出口引擎的可加强及可扩展的数据结构

Flow-based measurement is a popular method for various network monitoring usages. However, many flow exporting softwares have still low performance to collect all flows. In this paper, we propose a IPFIX-based flow export engine with an enhanced and extensible data structure, called XFix, on the basis of a GPL tool, -nProbe. In the engine, we use an extensible two-dimensional hash table for flow aggregation, which is able to improve the performance of the metering process as well as support bidirectional flow. Experimental results have shown its efficiency in multi-thread processing activity.     

单晶炉坩埚旋转速度控制系统设计

在单晶硅生产过程中,对单晶硅坩埚旋转速度有十分严格的要求。针对实际情况,本文采用神经网络自适应PID控制算法,通过80C196KB单片机实现对单晶炉的坩埚旋转速度精确平稳的控制。通过与模糊PID及传统PID算法比较表明,该方法在坩埚旋转过程中控制效果及抗干扰能力优于另两种控制方法。     

Si1-xGex单晶用热系统改进

阐述了对原GaAs单晶拉制用LEC单晶炉热系统进行改造使其适于Si1-xGex单晶生长的过程。借助数值模拟的方法分析了晶体生长区域内的温度分布情况，并通过分析发现了原有热系统的不足。重新对原热系统进行了改造，添加了起到保温和氩气导流作用的热屏和上保温装置，使原来的敞开式热场变为密闭式热场，满足了SihGe；单晶拉制的要求。通过具体实验和数值模拟结合，分析了氩气流场及不同流场对晶体生长的影响，发现并改进了单晶炉的氩气供给装置存在的问题。     

垂直Bridgman法生长氟化钙晶体的数值分析

利用Fluent软件,模拟计算了垂直Bridgman法大尺寸氟化钙晶体生长的具体过程,研究了晶体生长过程中的热传递和熔体对流传热,分析了固相、液相和坩埚的热导率的差异对坩埚中心轴的轴向温度分布和轴向温度梯度以及界面处的径向温度分布和径向温度梯度的影响。分析结果表明:熔体对流传热的效果随晶体生长的不断进行逐渐减弱;固相、液相和坩埚的热导率的差异对坩埚中心轴的轴向温度分布和轴向温度梯度以及界面处的径向温度分布和径向温度梯度有重要影响;晶体的结晶速度和坩埚的下降速度存在不一致性。     

一种大象流两级识别方法

基于大象流的识别准确度高且开销低,对于解决SDN流量管理过程中控制器单点故障问题具有重要意义.针对现有大象流识别方法识别开销大的问题,提出一种大象流两级识别方法.该方法在第一阶段提出基于TCP发送队列的可疑大象流识别算法,在第二阶段提出基于流持续时间的真实大象流识别算法;第一阶段是在端系统中识别可疑大象流,用于降低第二阶段真实大象流识别过程中SDN控制器所需监测的网络流数量.实验分析表明,在保证大象流识别的高准确度前提下,大象流两级识别方法较基于采样的大象流识别方法可以降低约85％的控制器识别开销.     

Parameter Optimization of CdZnTe Crystal Growth Simulated by Finite Element Method

During the crystal grown by VBM, the solid/liquid interface configurations greatly influence the quality of as-grown crystals. In this paper, finite element method (FEM) was used to simulate the growth process of CdZnTe crystal. The effects of different crucible moving rates and temperature gradient of adiabatic zone on crystal growth rate and solid-liquid interface configuration were studied as well. Simulation results show that when crucible moves at the rate of about 1 mm/h, which is nearly equal to crystal growth rate, nearly flat solid/liquid interface and little variation of axial temperature gradient near it can be attained, which are well consistent with the results of experiments. CdZnTe crystal with low dislocation density can be obtained by employing appropriate crucible moving rate during the crystal growth process.     

Physical vapor deposition of GaAs on single crystal sapphire

The growth by physical vapor deposition of GaAs films on single crystal sapphire has been studied. A vacuum evaporation technique was used whereby Ga and As₂ vapors were supplied from a single crucible containing GaAs. In the substrate temperature range investigated, 200–600°C, only GaAs was observed; neither excess Ga nor As was detected. Reflection electron diffraction indicated the best films, grown at ~ 585°C, were single crystal with twinning. Films grown at lower temperatures were increasingly polycrystalline. Laue back-reflection x-ray diffraction generally indicated a larger degree of polycrystallinity or less well developed single crystallinity than did the reflection electron diffraction. Films grown on poorly polished substrates were consistently poorer in quality than those grown on scratch-free substrates. The films had resistivities > 1 × 10⁵ ohm-cm.