碲锌镉垂直布里奇曼法晶体生长过程固液界面的演化

计算模拟了半导体材料碲锌镉垂直布里奇曼法单晶体生长过程,以等温线图展示了固液界面形状的演化,分析了温度梯度和坩埚移动速率对固液界面形状以及晶体内组分偏析的影响.计算结果表明在凝固的初始段,固液界面的凹陷深度较大,随后有较大幅度的减小.整个凝固过程中固液界面的凹陷深度值有一定的波动性.提高温度梯度、降低坩埚移动速率均能有效地减小固液界面的凹陷,改善晶体的径向组分偏析.     

碲镉汞晶体组分及其均匀性控制研究

本文利用碲镉汞膺二元固液T-X相图对碲镉汞晶体生长方法进行了分类研究;分析了影响碲镉汞晶体组分及其均匀性的因素,提出了存在的问题和改善的措施;认为在特定组分的固相线温度(相图中的B点)生长碲镉汞晶体是一种比较有效的方法,并报道了采用双相复合维持液相成份生长大直径40mm碲镉汞晶体组分控制研究的结果(在S≈12cm2的晶片面积上,x＝0.218±0.003).     

大尺寸碳化硅晶体生长热-质输运过程建模及数值仿真

碳化硅(SiC)电子器件的性能和成本受衬底质量影响，因此生长大直径高品质SiC单晶意义重大。物理气相传输(PVT)法是一种常用的生长方法，但其主要面临热场设计与气流控制问题。本工作对电阻加热PVT法生长150 mm SiC单晶完整过程开展数值仿真研究，建立描述SiC原料热解和再结晶及其多孔结构演变、热-质输运、晶体形貌变化的数理模型，用数值模拟手段研究晶体生长、原料演变与热场变化等过程间的耦合关系。结果显示：原料区侧面高温导致气流不均匀，晶面呈“W”形，原料区底部高温得到均匀气流和微凸晶面；长晶界面通过径向温度变化调节气相组分平衡压力，使晶面生长成等温线形状；晶体生长速率与原料温度、剩余原料量呈正相关。模拟结果与已报道实验结果吻合，对优化生长SiC单晶有指导意义。     

溶剂熔区移动法制备Cd0.9Zn0.1Te晶体及性能研究

用溶剂熔区移动法制备了掺In的Cd0.9Zn01Te晶体,晶体生长温度800℃,温度梯度为20℃/cm,生长速度0.4 mm/h.测试了晶体的Te夹杂情况、红外透过率图谱、Ⅰ～Ⅴ特性曲线和PICTS特性,并以1115℃下用VB法生长的掺In的Cd0.9Zn0.1Te晶体做为参照,对比了两者性能.结果表明,溶剂熔区移动法制备的晶体Te夹杂的密度和体积百分比比VB法晶片低,但是Te夹杂的尺寸要比VB法晶体大;溶剂熔区移动法晶体的红外透过率比VB法晶体高;溶剂熔区移动法晶体电阻率比VB法晶体高了一个数量级;PICTS测试发现,溶剂熔区移动法晶体内主要的缺陷密度低于VB法晶体.     

大尺寸电阻加热式碳化硅晶体生长热场设计与优化

大尺寸低缺陷碳化硅(SiC)单晶体是功率器件和射频(RF)器件的重要基础材料,物理气相传输(physical vapor transport, PVT)法是目前生长大尺寸SiC单晶体的主要方法。获得大尺寸高品质晶体的核心是通过调节组分、温度、压力实现气相组分在晶体生长界面均匀定向结晶,同时尽可能减小晶体的热应力。本文对电阻加热式8英寸(1英寸=2.54 cm)碳化硅大尺寸晶体生长系统展开热场设计研究。首先建立描述碳化硅原料受热分解热质输运及其多孔结构演变、系统热输运的物理和数学模型,进而使用数值模拟方法研究加热器位置、加热器功率和辐射孔径对温度分布的影响及其规律,并优化热场结构。数值模拟结果显示,通过优化散热孔形状、保温棉的结构等设计参数,电阻加热式大尺寸晶体生长系统在晶锭厚度变化、多孔介质原料消耗的情况下均能达到较低的晶体横向温度梯度和较高的纵向温度梯度。     

提拉法晶体生长数值模拟研究进展

数值模拟方法是了解晶体生长过程中各种物理现象和问题的重要手段,可以为晶体生长工艺参数的设定、温场设计等提供参考.本文介绍了最近几十年来数值模拟技术对提拉法生长晶体过程中物理问题的研究进展,同时对晶体生长过程中界面形状、液流、速度场、温度场、各种输运过程以及工艺条件和参数对晶体生长的影响等的数值模拟进行了介绍.     

光学材料结晶化研究

本文通过分析光学材料中光谱与温度之间的关系证实了晶体生长过程中的相变团簇模型,认为晶体内部热辐射流是引起固-液界边界层温度场发生传导的可能原因.引入了前结晶的概念,并结合实际中的不同晶体生长方法讨论了包裹体及气泡的抑止机理,通过计算得到了生长理想晶体的最大生长速率并且解释了由于界面层的摆动使得晶体生长过程中产生的微气泡没有被移动的界面层所捕获.     

化学计量比LiNbO3晶体宏观生长缺陷的观察

本文对采用双坩埚提拉法(DCCZ)生长的化学计量比LiNbO3晶体中出现的机械双晶、组分过冷、包裹体等宏观生长缺陷进行了观察和分析.结果表明机械双晶通常以{102}和{104}面族为双晶面,而不是以前文献报道的{102}和{012}面族;化学计量比LiNbO3晶体双坩埚提拉法生长与同成份晶体生长不同,前者是助熔剂生长体系,生长速度稍快或温度较小的波动就会导致组分过冷,而后者属于纯熔体生长体系,不容易产生组分过冷;包裹体是由于组分过冷生长时界面失稳夹入熔体所造成的.由于这些缺陷的存在都会严重影响单晶的获得率和质量,为此,我们通过大量实验研究后提出了可以减少和避免这些生长缺陷提高晶体质量的方法.     

室温核辐射探测器用碲锌镉晶体生长研究进展

碲锌镉(CdZnTe,CZT)晶体被认为是目前最有前途的室温半导体探测器材料之一,基于该晶体的探测器件具有能量分辨率高、体积小、便携等优点.而大面积CZT像素探测器的快速发展以及对高能、大剂量X射线探测的需求,对CZT材料的质量和尺寸提出了更高的要求.本文从CZT晶体的基本物性参数入手,探讨了大尺寸CZT晶体生长的影响因素,对两种主要的CZT生长方法——布里奇曼法和移动加热器法的研究进展进行了综述.     

移动加热器法生长CdMnTe晶体的性能研究

采用垂直布里奇曼法(VB)生长CdMnTe晶体,由于生长温度高、堆垛层错能低、热应力大等因素,晶体中存在大量孪晶、杂质、夹杂相等,限制其在核辐射探测器方面的应用.为了提高晶体的质量,本文采用移动加热器法(travelling heater method,THM)生长CdMnTe晶体,对该方法生长的晶体中Mn的轴向分布、杂质浓度、Te夹杂和电学性能进行测试分析,并与VB法生长的晶体作对比.结果表明THM法生长的CdMnTe晶体中Mn的轴向分布均匀,杂质浓度低于VB法制得的晶体,Te夹杂的尺寸5～25 μm,浓度105 cm-3,电阻率为109～1010Ω·cm,导电类型为弱n型,制备的探测器在室温下对241Am放射源有能谱响应.实验表明THM法生长的CMT晶体在晶体质量和电学性能方面明显优于VB法.     

分离结晶垂直Bridgman法生长CdZnTe晶体的全局数值模拟

采用FLUENT软件对分离结晶Bridgman法生长CdZnTe晶体进行了全局数值模拟.模拟对象为:熔体上部边界条件分别为固壁和自由表面时两种晶体生长系统.重点考虑坩埚和晶体之间狭缝宽度e和重力对分离结晶过程的影响.在计算中分别取e=0 mm、0.5 mm和1 mm三种狭缝宽度,得到了在微重力和常重力条件下的温度分布、结晶界面形状以及流函数分布图.结果表明:在微重力条件下,当熔体上部为固壁时,随着狭缝宽度的增大,热毛细力作用增强,流动强度增强;当熔体上部为自由表面时,则与之相反.在常重力条件下,由于浮力-热毛细对流的共同作用,随着狭缝宽度的增加,流动强度逐渐减弱,有助于提高晶体生长质量.     

Low-temperature growth and doping of InP:S single crystals from melt-solution in microgravity

The effect of microgravity on the growth of bulk InP:S single crystals from a melt with an initial equilibrium composition (84 at % In, 16 at % P, and ～2.2 × 10¹⁸ at cm^?3 of S) on board the Foton-11 satellite was investigated. The growth of crystals on board the satellite and on Earth (a reference crystal) was carried out by the traveling heater method. The samples of the grown crystals were investigated by metallography, double-crystal X-ray diffractometry, single-and double-crystal X-ray topography, and secondary-ion mass spectrometry. It is shown that the mass transfer in the melt in microgravity is similar to the diffusion mode. Hence, the mass transfer in the melt results in the following: the formation of a nonstationary boundary layer, depleted in phosphorus; the constitutional supercooling at the crystallization front accompanied with the development of a cellular substructure in the early growth stage; and the hypothetical phase structurization of the transition layer with the formation of In-based associates (clusters), which were found in the grown crystals in the form of spherical defects 10–20 μm in diameter. The coefficients of sulfur distribution k₀ = 0.274 and k_eff = 0.43, the sulfur diffusivity in the melt D_S = 4.2 × 10^?7 cm²/s, and the effective thickness of the transition layer δ = 0.07 cm in terrestrial gravity are determined. The data obtained are necessary to develop a mathematical model of crystallization in zero gravity.     

近化学计量比铌酸锂晶体组分过冷与临界生长速率研究

本文在用双坩埚提拉法生长近化学计量比LiNbO3晶体的过程中观察到了组分过冷的实验数据,同时根据Tiller-Chalmers稳定性判据公式半定量计算了近化学计量比LiNbO3晶体临界生长速率的理论值,得到一般电阻加热双坩埚提拉法生长近化学计量比LiNbO3晶体的临界生长速率为0.1mm/h数量级.通过临界生长速率解释了一系列晶体生长的实验结果.提出了一些工艺措施来避免组分过冷,根据这些工艺获得了无包裹体的近化学计量比LiNbO3晶体.     

Growth and interface study of 2 in diameter CdZnTe by THM technique

Growth interface of large diameter CdZnTe ingots grown from Te solution by travelling heater method have been studied. Both macroscopic and microscopic investigations were carried out. The results indicated that the shape of the interface strongly governs the grain growth on the ingot, while the microscopic morphology of the growth interface is responsible for Te inclusions in the grown crystal.     

Numerical optimization of thermal field in CdTe crystal growth by travelling heater method

Cadmium telluride (CdTe) and his compounds play a leading role in X‐ray and γ‐ray detector technology. One of the most used methods for growing these crystals is the travelling heater method (THM). The ingots obtained by using this technique show excellent composition uniformity, but the structural quality is affected by the presence of large grains which appear because of large curvatures of the solid‐liquid interface during the solidification process. This numerical work investigate the thermal field and melt convection in CdTe processing by THM in order to elucidate the mechanism of growing these crystals. The influence of the furnace geometry on the interface shape and temperature gradient in liquid is analyzed for samples with small (1 cm) and large (5 cm) diameters. The computations include flow effects on thermal field in the melted zone. The thermal conditions are optimized for THM growth of CdTe crystals at high solidification temperatures. A new multi‐zone furnace configuration for growing crystals of large diameter and flattened interface is proposed in this work.     

Melt growth and post‐grown annealing of semiinsulating (CdZn)Te by vertical gradient freeze method

We present results of development of CdZnTe semi‐insulating crystals prepared by Vertical Gradient Freeze method in a 4‐zone furnace. We applied the way of growth of the crystal from the top when the first crystallization seed is created on the surface of the melt. The typical height of the crystals is 5 cm. Resistivity and photoconductivity profiles measured along the growth axis by contactless method are compared and their mutual correlation is explained based on a model of relative shift of the Fermi level and the midgap level present in the material. The influence of the Fermi level on electron trapping and recombination is summarized. We present here results of a two‐step annealing method aimed at reduction of Te inclusions while keeping the resistivity high. We employed CdTe:Cl VGF grown samples to eliminate Te inclusions observed in as grown crystals by two‐step post grown annealing in Cd and Te atmosphere and present a model of the processes leading to high resistivity material after annealing.     

Directional solidification of InxGa1−xAs

We have investigated a constitutional supercooling and segregation phenomena in In_xGa_1−xAs crystals unidirectionally solidified in a vertical system. The constitutional supercooling generates characteristic fluctuations of composition along the growth direction and this can be explained by a free nucleation ahead from the growth interface. The macroscopic compositional profiles of the grown crystals suggest that a transport of solute is mainly dominated by the diffusion. Such a growth mode is partly attributed to the difference in density between InAs and GaAs.     

Growth of cadmium zinc telluride by liquid phase electroepitaxy

This study was undertaken to examine the feasibility of growing CdZnTe by liquid phase electroepitaxy. Based on our successful LPEE system of GaInAs, a new crucible to grow CdZnTe was developed. The development presented numerous difficulties. The physical properties of CdZnTe make this material very difficult to grow. All components of the system were investigated. Electromigration of the solute across the solution carries species towards the growth interface. In liquid Cd‐Zn‐Te, the CdTe and ZnTe species remain associated, contrary to the GaInAs system. Experiments showed that LPEE growth of CdZnTe is possible and the electromigration mechanism functions well in the CdZnTe solution. Despite this, other problems remained with the new LPEE system. The preparation of the solution proved difficult without pressurizing the LPEE crucible. Control of the reaction required the use of pre‐compounded CdTe and ZnTe. Proper control of the solution saturation is imperative to ensure minimal dissolution of the seed prior to growth initiation and a reasonable growth rate during growth. The solution remained an issue during the duration of growth due to the high vapor pressures of the constituents. Tellurium evaporation during growth could lower solution volume until electrical contact across the solution is broken. Careful preparation of appropriate solution volume was imperative for successful growth. In LPEE, a uniform electric current passage across the growth interface is necessary for uniform and stable growth interface. This requires the design of a uniform contact zone between the bottom graphite electrode and the seed crystal. The contact zone issue was not adequately resolved in this study. However, a number of successful growth runs were achieved despite the electrical contact problems. Results show that the LPEE of growth CdZnTe is feasible. (© 2006 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Growth of high-purity ZnTe single crystals by the sublimation travelling heater method

A travelling heater method (THM) was developed to grow high-purity ZnTe from the vapor phase. This crystal growth method is called the “sublimation THM”. The temperature of the sublimation interface was set at 815°C and the temperature of the growth interface was varied from 785 to 800°C. The growth rate was 3 mm/day. Under these conditions, it was found that the growth process was mainly due to surface nucleation. Characteristics of the crystals were compared with those of solution-THM and vapor phase epitaxially grown crystals. The free-exciton line at 2.381 eV strongly appears and a doublet structure in neutral- acceptor bound exciton at 2.375 eV is clearly resolved with splitting energy of about 0.7 meV. We thus conclude that the THM from the vapor phase is suitable for preparing ZnTe single crystals which have excellent luminescent properties.     

1英寸Cs2LiLaBr6∶Ce闪烁晶体的生长及性能研究

Cs₂LiLaBr₆∶Ce(CLLB∶Ce)晶体n/γ双读出闪烁性能优异,其实用化瓶颈在于大尺寸、高光学质量晶体的生长。本研究采用非化学计量比配比,避开CLLB∶Ce非一致熔融组分区域,通过改进研制坩埚下降法晶体生长炉,并优化温度场和降低坩埚下降速度等晶体生长工艺,从而克服组分过冷,保持生长界面稳定,得到了直径1英寸(1英寸=2.54 cm)的CLLB∶Ce晶体毛坯,等径透明部分长度达40 mm,单晶比例由52%提高至79%,可见光区光学透过率达到70%以上。在¹³⁷Cs激发下能量分辨率达3.7%,在²⁵²Cf激发下晶体的品质因子达到1.42,可以很好地甄别中子和γ射线。