直拉法LiNbO_3单晶体中的旋转生长条纹

使晶体转轴与温场对称轴不一致,则在晶体弯月面内会产生随时间变化的正弦波式的温度分布。建立了晶体转速、温度起伏、表面生长条纹和内部生长条纹间的一一对应关系,从而在晶体中有意识地引入了其周期可以任意调节的旋转生长条纹。     

提拉生长铌酸锶钠锂晶体的组分过冷及提高晶体品质的研究

本文采用厚晶体抛光、腐蚀、显微观察的方法研究提拉法生长晶体的组分过冷。在高温偏光下研究了铌酸锶钠锂晶体的结构转变温度。采用最佳的生长和工艺条件克服了铌酸锶钠锂晶体的组分过冷和内部生长条纹,提高了晶体的光学均匀性。 关键词：     

钇铝石榴石单晶的生长及光学不均匀性

用提拉法生长了掺釹钇铝石榴石晶体．比较了从不同釹离子液度的熔体 中生长的晶体的光学不均匀性及其激光性能．在我们实验的釹浓度范围内,当 生长条件大致相同时,釹离子浓度愈高,晶体的光学均匀性愈差．改变生长条 件,使晶体的均匀性相近时,其脉冲激光效率随釹的浓度的提高而有所改善．此 外,还研究了晶体的光学不均匀性对晶体的激光性能的影响． 研究了影响晶体光学质量的两种重要缺陷,即核心和生长条纹．在倒圆锥 形固液界面的顶端,（２１１）小面的出现,形成了核心．核心处具有较高的釹浓度、较高的位错密度和较大的应力,并使激光束产生严重的畸变．由于温度起 伏形成的生长条纹对激光束产生衍射和散射作用．核心的出现与掺釹关系不大（主要取决于界面形状）;而条纹的加剧则与熔体中的釹浓度有着明显的关系．     

ZnTe/GaSb结构的X射线三轴晶散射和晶体截断杆研究

用X射线三轴晶散射和晶体截断杆扫描研究了不同工艺条件下分子束外延生长的ZnTe/GaSb结构．X射线晶体截断扫描显示，从衬底表面清洁温度到生长温度退火过程中采用Zn气氛的样品具有清晰的干涉条纹，而在Te气氛下退火则晶体截断扫描没有干涉条纹．在倒易点004，115附近X射线散射的二维强度分布图显示，两种条件下生长样品的晶格失配应力都没有弛豫．二维等强度分布图和沿［110］方向的扫描，都显示在Te气氛下生长的膜具有较强的漫散射，并且分布较宽．这种漫散射来源于界面相Ga₂Te_{3< 关键词：}     

高掺镁铌酸锂晶体的生长和倍频性能

我们通过测定MgO在同成分LiNbO₃中的有效分凝系数、相位匹配温度与MgO浓度之间的关系,找到了使Mg:LiNbO₃晶体的相位匹配温度达到最高的掺MgO配方,并克服了Mg:LiNbO₃晶体在高掺杂生长时易出现生长条纹和脱溶等问题,从而生长出了抗光折变能力强,光学均匀性良好的Mg:LiNbO₃晶体。用于连续泵浦Nd:YAG声-光调Q腔内倍频时,获得了平均功率最高达2瓦的二次谐波输出。 关键词：     

电子称重直径自控生长的LiNbO_3单晶体中功率条纹的研究

近年来,直拉法生长单晶体普遍地采用了电子称重直径自控技术[1,2].然而,在直径控制良好的晶体中仍然存在一种因功率起伏而产生的生长条纹(即功率条纹)[3],这种条纹影响了晶体质量.在我们实验室中,已用电子称重法生长了LiNbO3单晶体,并利用引入时标(timemarker)的方法[4]研究了功率条纹的成因,下面简要地报道所取得的主要结果. 电子称重直径自控系统的装置如图1所示.其特点是,置于电子秤上的坩埚及其托杆都不与炉内任何物体接触,处于自由状态;托杆上装有油封减震器,除可通过阻尼作用消除因晶体旋转而产生的噪音外,还可防止冷空气进入炉膛,…     

我国首次空间生长GaAs单晶实验的结果分析

在空间微重力环境中,用重熔再结晶法从悬浮熔体生长了掺杂Te-GsAs单晶,晶体从中间断开表明长悬浮熔体的不稳定性,晶体中部未见杂质条纹说明浮力对流已消失,而外层有杂质条纹表明存在Marangoni对流,晶体中杂质含量减少和宏观分布不均匀,是短熔区杂质分凝机制控制和杂质Te从熔体挥发的结果,晶体中的高位错缺陷是快速生长和退火时产生的热应力以及界面籽晶侧的空位团崩塌造成的。 关键词：     

钽铌酸钾晶体二次电光效应的应用研究进展

钽铌酸钾晶体(KTN)是目前已知的具有最大二次电光系数的晶体,利用其电光效应可改变光的相位、强度和传播方向,可广泛应用于光通讯、屏幕显示和生物医疗等领域。讨论了晶体组分、温度、缺陷和生长条纹对KTN晶体二次电光系数的影响;介绍了近几年国际上报道的几种基于KTN晶体二次电光效应的器件电光调制器、光开关、光束扫描器、变焦透镜和光谱仪,阐述了它们的的基本原理、研究现状和应用前景;对国内外KTN晶体电光器件研究的发展趋势进行了展望。     

温度梯度法生长Nd:YAG激光晶体的核心分布

用温度梯度法生长了直径为75 mm大尺寸的Nd∶YAG激光晶体，通过退火排除了生长过程中进入晶体的碳原子. 用正交偏光显微镜观察了晶体的核心分布以及生长条纹. 测试了室温下的吸收谱并利用吸收谱研究了Nd离子在YAG晶体中的分布. 比较了温度梯度法与提拉法生长晶体的区别. 关键词： 材料 缺陷 温度梯度法 Nd∶YAG     

电光材料调制误差对平行光束干涉投影的影响

为研究电光材料调制误差对干涉条纹质量的影响,建立了电光晶体对干涉条纹的成像模型,分析了晶体折射率、平面度与波前调制的关系及其非理想情况下的条纹成像特征。实验表明,晶体折射率的畸变会使干涉条纹变形,折射率离散化阶数直接造成投影条纹的高次谐波成分,甚至使投影条纹严重失真;在折射率线性增长的情况下,晶体平面度在0.1 μm的范围内也会引起干涉条纹畸变。     

Liquid/solid interface profile of melt grown oxide crystals II. Crystal quality

Temperature gradients and rotation rates influence the quality of Czochralski grown oxide crystals. Decreasing the heat transfer from the melt level and increasing the rotation rate increases the optical homogeneity and structural perfection of the crystal, due to convex interface becoming flattened. Growth striations due to temperature fluctuations in the melt during growth are affected by the heat losses from the melt level but are practically unaffected by the rotation rate as long as a narrow ring of centrifugally streaming melt in the neighbourhood of the growing crystal is not formed. The parts of the crystals grown in the presence of this ring contain no striations.     

Reduced pore diameter fluctuations of macroporous silicon fabricated from neutron‐transmutation‐doped material

The precision of photo‐electrochemical etching of perfectly‐ordered macropores in single‐crystalline silicon is limited by pore diameter fluctuations due to doping variations of the starting wafer (striations). The doping variation originates from the rotation during crystal growth in the float‐zone or Czochralski process, respectively. Experimentally, variations of the pore diameter up to 7% can occur. These so‐called striations limit performance of possible applications of macroporous silicon. As doping inhomogeneities are the reason for the striations, uniformly doped silicon wafers by neutron transmutation doping were used for the first time. Photoelectrochemical etching of neutron transmutated silicon has been carried out and the pore diameter fluctuation has been reduced by about 40% compared to standard doped float‐zone wafers. (© 2010 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

A study of the contrast on growth striations in silicon by X-ray double crystal topography in the Laue case

The image of growth striations in Si formed by the double crystal X-ray topography in the Laue case (DCTL) is investigated. The results of the dynamical diffraction theory for crystals with small microdefects have been compared with the contrast behaviour determined experimentally. It has been found that the theory explains qualitatively the contrast on the striations and it has been demonstrated that the DCTL method is suitable for detection of the presence of small microdefects in growth striations. Since the paper completes a series of papers on X-ray topography of growth striations, some general conclusions are formulated concerning the applicability of the X-ray topographical methods to the investigation of the structure of the growth striations     

新概念晶体提拉方法及其可能的应用简介

介绍了一种利用金属材料的热膨胀而产生的位移代替传统的机械电机提拉晶体的新方法,可以预见这种新型提拉方法既可以消除晶体提拉过程中由于拉速的不平滑而引进的晶体生长条纹,同时也可以作为研究晶体生长机理的有力工具,另一方面,该方法可以用来提拉这样的一灰晶体,这种晶体溶质的浓度周期地分布于其中,且其周期远小于用机械电机所提拉的晶体溶质浓度的周期,同时,另一种新颖的控温方式被首次提出,即先把金属棒加热膨胀至一定的长度再冷却使之收缩,由于这种控温方式温度波动极端微小,使得金属棒收缩所产生的位移随时间的变化率达到微观的平滑极限。     

Detection of growth striations in single crystals by digital processing of topographic images

The possibility of detecting growth striations by digital processing based on analysis of the brightness and frequency characteristics of images has been demonstrated by the example of x-ray topographic contrast of a GaSb(Si) single crystal. It has been shown that a higher efficiency of detecting growth striations in topograms is obtained by wavelet processing of the analyzed contrast.     

GGG单晶的助熔生长与成核温度的确定

我们研究了GGG单晶的助熔生长,实验证明在PbO-PbF₂系助熔剂中GGG结晶的组分范围相当宽,生长相当稳定,而且位错密度较低。用感生条纹技术确定了GGG晶体生长的成核温度。 关键词：     

A method of precise determination of the optical constants of uniaxial crystals from the compensator parameters

A method of determination of the refractive indices of uniaxial crystals from the compensator parameters is proposed. In this case, the accuracy is limited by the temperature fluctuations inside a crystal. The orientation of the optical axis with respect to the surface and the thickness and the thermal expansion coefficient of the crystal can be determined additionally. This method can be used for precise determination of the refractive indices and absorption coefficients of biaxial crystals. Experimental results of determination of the temperature coefficients of the refractive indices and of linear expansion for a plane-parallel plate cut from artificial crystalline quartz parallel to the optical axis are presented.     

Effect of gravitation vector orientation relative to the solidification front on the micro- and macrohomogeneity of semiconductor crystals grown under terrestrial and space conditions

The influence of gravitation vector orientation relative to the solidification front on the dopant distribution micro- and macrohomogeneity in vertical oriented crystallization of highly Ga-doped Ge crystals has been investigated using computer simulation. The deviation of the axis for crystal growth relative to the g ₀ vector, when a free surface of the melt is present, has been found to provide the formation of striations with a reduced dopant concentration. The influence of the solidification rate, convective and diffusion mass flows on the dopant distribution macrohomogeneity has been investigated.     

X-ray study of structural features of GaSb(Si) single crystals grown using a set of diffraction methods under various heat and mass transfer conditions

Structural features of GaSb(Si) single crystals grown under various heat and mass transfer conditions were studied by x-ray topography and by double- and triple-crystal diffractometry. It was shown that a decrease in the convective flow intensity during crystal growth by the vertical Bridgman method with axisymmetric upper heat supply in comparison with the Czochralski method eliminates growth striations (caused by microsegregation) and improves the uniformity of electrical parameters of materials. According to triple-crystal x-ray diffractometry data, the increased density of structural defects observed in some crystal regions causes significant lattice distortions, which makes an additional contribution to crystal inhomogeneity. Some specific features in x-ray topography images of growth striations, caused by a high silicon concentration and a dopant state deviation from an ideal substitutional solid solution, were revealed.     

Influence of ultrasonic vibrations on the growth of semiconductor single crystals

The influence of ultrasonic vibrations on striations in InSb, GaAs and Bi-Sb alloy single crystals grown by a modified Czochralski method was investigated. Ultrasonic vibrations at frequencies of 0.15, 0.25, 0.6, 1.2, 2.5, 5 or 10 MHz were introduced into the melt parallel to the pulling axis. The introduction of ultrasonic vibrations at a frequency up to 5 MHz eliminates the striations in GaAs and Bi-Sb alloy single crystals growing with constant diameter. It was found that for Bi-Sb alloy single crystals of constant diameter growth, after ‘processing’ of the melt with ultrasonic vibrations, the striations do not reappear until after 2 h. The effectiveness of the influence of the ultrasonic vibrations on the decrease of growth striations in InSb, GaAs and Bi-Sb alloy growing crystals was estimated with the help of the calculation of the sound absorption coefficient.