Cd0.96Zn0.04Te单晶生长及晶体成分偏析

采用常规Ｂｒｉｄｇｍａｎ法和ＡＣＲＴ－Ｂ法进行Ｃｄ０．９６Ｚｎ０．０４Ｔｅ晶体生长实验。结果表明：ＡＣＲＴ产生的强迫对流在很大程度上消除了侧壁形核，有利于获得大的晶体；ＡＣＲＴ的加入提高了有效分凝系数ｋｅｆｆ，使其向平衡分凝系数ｋｅｑ趋近，导致轴向的偏析增大。     

HgCdTe晶体ACRT-B法生长过程的分凝特性研究

在定量估算的基础上，明确了Ｈｇ１－ｘＣｄｘＴｅ晶体ＡＣ－ＲＴ－Ｂ法生长过程轴向溶质再分配的 经条件，导出了计算公式。以ＨｇＴｅ－ＣｄＴｅ伪二元相图为基础进行了计算表明，按照远红外控制器要求的成分配料（ｘ０＝０．２２），仅在晶锭的某一部分可获得符合成分容差的晶体，而采用其它相近的成分配比也能获得符合成分要求的晶体，采用ｘ０值更小的槽糕成分获得的满足成分要求的晶段更长，并且位于结晶质量较高的晶锭前段‘     

ACRT过程中的温度变化与测量

ＡＣＲＴ是一种新型的晶体生长技术，已成功地制备了一些优良的功能材料。作者利用自制的测温装置，测量了ＡＣＲＴ过程中的温度变化。结果表明：ＡＣＲＴ过程中液相保持时间明显延长，生长界面前沿的温度梯度极大提高。本文从流体力学传输过程研究了产生这些变化的原因。     

Hg1—xCdxTel生长中的溶质再分配及其对生长条件的限制

本文以ＨｇＴｅ－ＣｄＴｅ伪二元相图为基础，分析了Ｈｇ１－ｘＣｄｘＴｅ单晶生长过程中分凝特性及扩散规律。从维持平面生长界面的角度出发，确定了不同温度梯度下生长速度选择的上限，并从获得成分均匀晶体的角度出发讨论了晶体生长速度下限的选择条件。     

Hg1-xMnxTe晶体的生长及电学性能

利用ＡＣＲＴ－ＶＢＭ法生长Ｈｇ１－ｘＭｎｘＴｅ晶体，并对所得晶体作出宏观和微观质量评价，为改善晶体的电学性质，将生长态的晶体在低温下长时间退火。实现了晶片的反型，Ｈａｌｌ电测量的结果表明位错的数量、分布及富Ｔｅ相、晶界、杂质等的存在都对晶体的电学性质有显著的影响。     

Hg_（1－x）CdxTe生长中的溶质再分配及其对生长条件的限制

本文以ＨｇＴｅ－ＣｄＴｅ伪二元相图为基础，分析了Ｈｇ＿（１－ｘ）Ｃｄ＿ｘＴｅ单晶生长过程中分凝特性及扩散规律。从维持平面生长界面的角度出发，确定了不同温度梯度下生长速度选择的上限，并从获得成分均匀晶体的角度出发讨论了晶体生长速度下限的选择条件。     

ACRT技术对大尺寸ZnTe晶体溶液法制备及其性能影响

太赫兹(Terahertz,THz)技术在工业无损检测、科学研究和军事领域发挥着越来越重要的作用。作为太赫兹产生和探测最常用的电光晶体材料,ZnTe晶体在生长中依然面临众多挑战。为了制备大尺寸、均匀性好、高性能的ZnTe单晶,本研究在温度梯度溶液法生长ZnTe晶体过程中引入坩埚旋转加速技术,制备具有高结晶质量的ZnTe晶体。模拟计算得到不同坩埚旋转速度下生长界面处对流场和溶质分布,研究了坩埚旋转对晶体生长过程中的固液界面稳定性和晶体内Te夹杂分布的影响规律,证明坩埚旋转加速技术可以有效地促进熔体流动,改善溶质传质能力,稳定溶液法晶体生长的固液界面,不仅避免出现尾部混合相区,也减少了ZnTe晶体内Te夹杂相的数量并减小其尺寸。通过进一步优化坩埚旋转参数,制备出具有较高结晶质量的大尺寸ZnTe晶体(?60 mm)。同时,得益于晶体良好的均匀性,晶体对太赫兹的高响应区域超过90%,边缘效应小,满足太赫兹成像要求。研究表明,引入坩埚旋转加速技术为制备大尺寸ZnTe基电光晶体提供了新的思路。     

中国庚型肝炎病毒NS3区部分基因的克隆与基因特点的分析

利用逆转录多聚酶链式反应（ＲＴ－ＰＣＲ），从我国一输血后丙型肝炎病人血清中克隆到了庚型肝炎病毒ＮＳ３区的部分基因。经序列分析表明：我国庚型肝炎病毒ＮＳ３区与已知的ＧＢＶ－Ｃ及ＨＧＶ的核苷酸同源性在８１．７—８８．０％之间，而氨基酸同源性均大于９６％，氨基酸序列与ＨＣＶ、ＧＢＶ－Ａ、ＢＧＶ－Ｂ具有一定的结构相似性及数个共有的保守位点。     

大尺寸Y:PbWO4晶体的坩埚下降法生长与光学均匀性研究

报道了大尺寸Ｙ：ＰｂＷＯ４晶体的坩埚下降法生长工艺，讨论了影响晶体生长的主要 因素．探讨了消除晶体开裂、抑制晶体组分过冷的工艺措施，成功地生长出无宏观缺陷的大尺 寸Ｙ：ＰｂＷＯ４晶体，尺寸达５２ｍｉｎ×５２ｍｍ×２５０ｍｍ．同时，对实验样品沿晶体生长方向不同部 位的横向透过率及发射光谱进行了测试，结果表明，坩埚下降法生长的大尺寸Ｙ：ＰｂＷＯ４晶体 具有较好的光学均匀性．     

ACRT过程流场影响因素的数值研究

将相对体积算法扩展到三维圆柱坐标系，求解了多种条件下坩埚加速旋转过程中的流场，分析了坩埚转加速度，坩埚半径及最大转速等因素对流场的影响，计算结果与模拟实验的结论一致，各种条件下，ＡＣＲＴ过程的流场具有相同的变化趋势，逆时针流动与顺时针流动交替增强和减弱。     

在横向磁场中用Bridgman法生长HgCdTe晶体

在横向磁场中用Ｂｒｉｄｇｍａｎ法生长的晶锭其轴向组分分布在中部和尾部具有相同的趋势,在头部有三种类型的分布。磁场通过对固液混合区对流的作用影响溶质的再分布和轴向组分分布。突然施加磁场和中断磁场都引起轴向组分分布的突变。当安瓿绕生长轴匀速旋转时,晶锭的径向组分分布既没有安瓿不旋转时的偏心特征,也没有常规Ｂｒｉｄｇｍａｎ法生长晶体的径向对称性,尾部呈现圆锥状的凸起,可能是旋转生长抑制胞状结构的证据。     

Composition Distribution in the MnxCd1-xIn2Te4 Ingot Grown by ACRT-B Method

MnxCd1-xIn2Te4 (x=0.1) ingot was successfully grown by the modified Bridgman technique, which applied the accelerated crucible rotation technique (ACRT) in Bridgman process, or briefly ACRT-B. The growth interface profile shape and the composition distribution in the MnxCd1-xIn2Te4 (x=0.1) ingot were analyzed. Even though the stoichiometric composition was synthesized in the original ingot, the composition has been redistributed during the ACRT-B growth process. Mn and Cd contents decrease while In increases along the longitudinal axis. The partition ratios of solutes Mn, Cd and In at the growth interface are evaluated by a mathematical method based on the experimental data, which are found to be 1.286, 1.926 and 0.729 in α phase growth process, and 1.120, 1.055 and 0.985 in β phase growth process, respectively. In the radial direction,Mn and Cd contents increase while In decreases with the distance from the centerline of the ingot.     

温度梯度和生长速率对CdZnTe-VBM生长晶体的影响

计算模拟了半导体材料CdZnTe垂直布里奇曼法(CdZnTe-VBM)单晶体生长过程，分析了炉膛温度梯度和坩埚移动速率对结晶界面形态和晶体内组份偏析的影响。计算结果表明炉膛温度梯度和生长速率的变化明显影响固-液界面前沿对流场的形态和强度。界面凹陷深度随着炉膛温度梯度的增加和生长速率减小而减小。炉膛温度梯度的增加和生长速率的减小虽然均能有效的减小径向偏析，但却增加轴向偏析，减小轴向等浓度区的长度。     

强化换热对CdZnTe晶体生长过程的影响

为了优化CdZnTe晶体生长过程的工艺参数,利用数值模拟方法研究了强化换热对晶体生长过程固液界面凹陷、溶质组分偏析的影响.结果表明:当坩埚轴向散热强度大幅度增加时,固液界面前沿的对流显著增强;随着凝固过程的进行,固液界面凹陷深度先是显著减小,随后显著增加;晶体起始段溶质组分的径向偏析明显减小,溶质组分轴向等浓度区增长.当坩埚侧面径向散热强度增加时,固液界面前沿的对流和界面凹陷深度先是有所减弱,随后又有较大增加.当坩埚内壁碳膜厚度增加时,界面前沿的对流强度显著减弱,而固液界面凹陷深度明显增加.径向散热和碳膜厚度的增加皆不能明显影响晶体内溶质组分分布.     

Controlling heterojunction abruptness in VLS-grown semiconductor nanowires via in situ catalyst alloying

For advanced device applications, increasing the compositional abruptness of axial heterostructured and modulation doped nanowires is critical for optimizing performance. For nanowires grown from metal catalysts, the transition region width is dictated by the solute solubility within the catalyst. For example, as a result of the relatively high solubility of Si and Ge in liquid Au for vapor-liquid-solid (VLS) grown nanowires, the transition region width between an axial Si-Ge heterojunction is typically on the order of the nanowire diameter. When the solute solubility in the catalyst is lowered, the heterojunction width can be made sharper. Here we show for the first time the systematic increase in interface sharpness between axial Ge-Si heterojunction nanowires grown by the VLS growth method using a Au-Ga alloy catalyst. Through in situ tailoring of the catalyst composition using trimethylgallium, the Ge-Si heterojunction width is systematically controlled by tuning the semiconductor solubility within a metal Au-Ga alloy catalyst. The present approach of alloying to control solute solubilities in the liquid catalyst may be extended to increasing the sharpness of axial dopant profiles, for example, in Si-Ge pn-heterojunction nanowires which is important for such applications as nanowire tunnel field effect transistors or in Si pn-junction nanowires.     

Bulk Bridgman growth of cadmium mercury telluride for IR applications

Cadmium mercury telluride (CMT, CD_xHg_1-xTe) is the pre-eminent infrared material, despite the difficulties associated with the production and subsequent processing of this ternary compound. By varying the x value the material can be made to cover all the important infrared (IR) ranges of interest. The first technique developed was the basic vertical Bridgman process with typical crystal dimensions of 13 mm diameter and 150 mm length. We found it necessary to purify both the mercury and the tellurium on-site before use to obtain the required electrical properties. There is marked segregation of the matrix elements in Bridgman growth that is both a disadvantage and an advantage. Its disadvantage is that the yield of material in terms of composition for the two most common regions required (x=0.21 and 0.3 for 8–14 and 3–5 m atmospheric transmission windows, respectively) is low. The advantage is that both regions of interest are produced in the same crystal. A further advantage is that segregation of impurities also occurs and leads to low background donor levels in Bridgman material. This Bridgman material is used exclusively for photoconductive IR detectors that require n-type material. The main disadvantages of the Bridgman technique are that material is non-uniform in composition in the radial direction, as well as in the growth direction, and there are numerous grain and sub-grain boundaries. An improved process was developed at BAE Systems based on the accelerated crucible rotation technique (ACRT). Here, growth ampoules are subjected to periodic acceleration/deceleration in their rotation, rather than constant rotation as in the Bridgman process. The major effect of this is to stir the melt during growth and produce flatter solid/liquid interfaces. This, in turn, improves the radial and axial compositional uniformity of the material, normally by a factor of at least ten-fold. The only drawback is that the material is now p-type as grown and must be annealed in mercury vapor to convert it to n-type. An additional marked advantage of ACRT is that the improved radial compositional uniformity enables larger diameter material to be considered. We are currently growing 20 mm diameter, 200 mm long crystals of 0.5 kg weight with acceptable uniformity of composition and good electrical properties for current photoconductive detector programs. © 2001 Kluwer Academic Publishers     

Coupled transport of multi-component solutes in porous media

Coupled convective-diffusive transport of multicomponent solutes in spatially-periodic models of porous media is considered. Species coupling at the micro- or interstitial scale results from a first-order irreversible surface reaction on the bed elements, composing the porous medium, and from the off-diagonal terms of the microscale matrix transport coefficients.The coarse-scale long-time solute matrix properties are calculated, namely, mean effective reactivity, velocity and dispersivity. These coefficients are analyzed in several important particular cases, pertaining to reactive and nonreactive constituents. The solution scheme is illustrated by an example of two reactive solute components with diffusional coupling, flowing in a bundle of tubes model porous medium. The effective matrix axial transport coefficients are analyzed for various values of the dimensionless Damkohler number, Da, associated with the surface-reaction constant. Analytical expressions for the effective axial transport properties are obtained in cases of extreme (small and large) values of the dimensionless Damkohler numbers.The microscale molecular diffusive coupling provides for each solute constituent two diffusive pathways to the reactive tube wall: one – via the direct diffusivity component, another – via the coupling diffusivity. The macroscopic manifestation of this microscale coupling is to give rise to coupling off-diagonal terms in the effective matrix transport coefficients: positive off-diagonal terms in the reactivity matrix and negative off-diagonal terms in velocity and dispersivity matrices. From a physical viewpoint microscale coupling brings about a more uniform solute distribution within the tube cross section, which reduces the effective axial transport.     

A numerical investigation of dopant segregation by modified vertical gradient freezing with moderate magnetic and weak electric fields

The paper numerically investigates melt growth of doped gallium-antimonide (GaSb) semiconductor crystals by the vertical gradient freeze (VGF) method utilizing a submerged heater. Electromagnetic (EM) stirring can be induced in the gallium-antimonide melt just above the crystal growth interface by applying a small radial electric current in the melt together with an axial magnetic field. The transport of any dopant by the stirring can promote better compositional homogeneity. This investigation presents a numerical model for the unsteady transport of a dopant during the VGF process by submerged heater growth with a moderate axial magnetic field and a weak electric field. Numerical predictions of the dopant distributions in the crystal and in the melt at several different stages during growth are presented.     

垂直布里奇曼法CdZnTe晶体生长过程的数值分析

模拟计算了半导体材料CdZnTe布里奇曼法单晶体生长过程，分析了熔体的过热温度、坩埚侧面强化换热以及坩埚加速旋转(ACRT)等因素对结晶界面的形态和晶体组分偏析的影响。结果表明：当熔体的过热温度减小时，熔体中自然对流的强度显著降低，固液界面的凹陷深度有所增加，晶体的轴向等浓度区显著加长，而晶体组分的径向偏析明显增大，坩埚的侧面强化换热增加了自然对流强度，也增大了固液界面的凹陷，但是对溶质成分的偏析影响较小，坩埚加速旋转引起的强迫对流强度远大于自然对流，显著增大了固液界面的凹陷，使熔体中的溶质分布成为均一的浓度场，显著减小了晶体组分的径向偏析，增加了晶体组分的轴向偏析。