空间微重力汽相生长CdZnTe的研究进展

微重力条件下汽相生长CdZnTe晶体可以克服浮力对流,实现“无接触”生长,获得厚度均匀、结构完整、纯度高的材料.本文综述了国内外空间汽相生长CdZnTe晶体的研究进展.  

Effect of constrained growth on defect structures in microgravity grown CdZnTe boules

In a microgravity environment obtainable in an orbiting space shuttle, it is possible to virtually eliminate gravity related effects such as buoyancy driven convection and hydrostatic forces thus providing an ideal environment for diffusion-controlled, containerless crystal growth processes. Under such conditions, it is possible to investigate the effects of gravity independent growth parameters on crystal growth. Studies of CdZnTe boules grown on space shuttle mission USML-1 revealed that regions of the boules grown with wall contact were associated with a higher defect density than regions grown with partial or no wall contact. Defect densities in certain regions grown without wall contact were as low as 5 × 10²/cm² to 1.2 × 10³/cm². More detailed studies on the effects of wall contact were sought in the USML-2 mission. Two CdZnTe boules (GCRC-1 and GCRC-2) were grown by the seeded Bridgman-Stockbarger method. Boule GCRC-1 was grown under constrained conditions to force full wall contact while boule GCRC-2 had a tapered geometry designed to minimize wall contact. Defect distributions in the boules were investigated by synchrotron white beam x-ray topography. The sample GCRC-1 was characterized by the presence of large inhomogeneous strains, numerous grains and twins, all of which are caused by effects related to wall contact. On the other hand, a part of the boule GCRC-2 that grew free from wall contact revealed minimum surface strains, the absence of twins and a very high structural uniformity. Results clearly verify that ampoule wall contact plays an important role in determining the incidence of crystal imperfections.  

微重力条件下开口矩形容器的小Pr热毛细对流

采用数值方法研究了微重力条件下开口矩形容器内小 Prandtl数镓 (Ga)熔体生长过程中定常热毛细对流 ,讨论了 Re数、几何纵横比 A和侧壁外加温差的相对高度 H对熔体内温度场和流场分布的影响 .计算结果表明 ,热毛细对流对熔体温度分布有明显的影响 ,从而影响着晶体生长过程 .自由面两侧温度差很小 (如 0 .1K)时 ,熔体内温度场将发生变化 ;当温度差增加即 Re数增加时 ,热毛细对流加强 ,对流和扩散相互作用导致温度场分布更加不均匀 .无论多小的 H值 ,若自由面存在温差 ,都会驱动热毛细对流 ;随着 H值增加 ,热毛细对流会扩展到整个熔区 .几何纵横比 A对熔  

微重力条件下生长GaAs单晶的电学和光学性质研究

用多种实验手段分别对地面和太空生长的掺Te砷化镓单晶的电学、光学均匀性和深能级行为进行了实验研究.初步结果表明:在太空进行再生长的GaAs单晶电子浓度比原地面生长的籽晶小一个数量级,电子浓度由地面晶体到太空晶体的过渡是陡变的;DLTS测量发现太空单晶中存在两个电子陷阱,分别位于导带下0.27eV和0.60eV处,深能级密度为浅施主N_D的10~(-3)-10~(-4);少子注入未观察到空穴陷阱;用太空GaAs单晶为衬底制备的25个单异质结(SH)二极管,具有一致的I-V和发光特性,这反映了太空晶体的均匀性优于地面晶体.此外,还对太空生长GaAs单晶电子浓度降低的可能原因、深能级行为以及太空生长高质量晶体的前景作讨论.  

空间烟幕的扩散机理及衰减性能研究

烟幕干扰是针对红外探测器的一种无源干扰手段,在战场环境中,可以在目标与探测器之间释放烟幕形成屏障,降低探测器对目标的能见度,达到对目标的有效遮蔽。首先研究了在微重力高真空环境中,采用气固两相流喷射方法形成烟幕云的机理,并进行了数值模拟。然后,基于烟幕的扩散规律、材料特性及其吸收、散射和反射能力,建立了空间烟幕对红外信号的衰减性能模型。最后,基于实例仿真验证了利用空间烟幕衰减目标红外信号的可行性。  

航天器中性浮力变质心实验体六自由度动力学建模研究

实验体的动力学建模研究是航天器地面中性浮力实验的关键技术。针对实现实验体精确配平,解决水动力建模中的粘性力和惯性力不便分割等问题,采用矩阵运算形式代替矢量叉乘形式,通过应用忽略一些不易分割的次要粘性水动力项的方法,最终将实验体的质心变量和发动机推力作为控制量,建立了实验体动力学状态方程,为地面中性浮力实验环境中航天器六自由度运动控制与仿真提供了重要的理论基础。  

（英）天宫二号ZnTe：Cu晶体生长及能谱分析

在微重力条件下生长了ZnTe：Cu晶体，对其进行了光学和能谱分析，在晶锭尾部最大结晶区对其进行了组分分析。对于尾部的轴向分量，在空间样品中Cu的成分均匀性优于地面样品，并且Te/Zn比的样品高于空间样品。尾部空间样品中Cu的径向成分均匀性优于地面样品，且Te偏析更为严重。  

Strength of Soldered Joints Formed under Microgravity Conditions

Experiments have been carried out to compare the mechanical strength of joints soldered with Sn-Ag-Cu under different gravitational conditions. Joints soldered under microgravity (produced during a parabolic flight) have lower strength (by 32% in this case) than similar joints formed under normal gravity. Electron microscopy has shown that this is due to a larger volume of residual porosity (14%) in the joints formed in microgravity compared with <1% for joints formed in normal gravity. The residual porosity in joints formed in microgravity is mainly within the bulk of the solder, with some microporosity in the Cu₆Sn₅ intermetallic layer near the copper interfaces. The porosity not only weakens the joint, but also biases the failure path away from the intermetallic layer and into the bulk of the solder. These observations show that gravitational buoyancy is important for the expulsion of flux and flux residues from soldered joints.