Dislocation densities in copper single crystals after thermal treatment

Copper crystals of high purity and doped with nickel were subjected to a long time thermal treatment at 1050°C, in order to reduce the as-grown dislocation density of about 10⁷ cm⁻². A dissolution of the dislocations during their motion to the crystal surface was observed. Regions of different dislocation densities arose. Finally the crystals exhibited constant dislocation densities of 10² cm⁻². Such a perfection or a better one of the crystals is reached only by a long time treatment, since the dislocation velocity without external stresses cannot exceed 1 · 10⁻⁷ cm · s⁻¹ in copper single crystals of high purity.     

Chemical dissolution of calcite cleavages in aqueous solutions of sodium hydroxide

Optical study of isotropic and anisotropic etch rates by controlled chemical dissolution of calcite cleavage surfaces employing aqueous solution of sodium hydroxide at various etching temperatures is presented. The etch rates are found to be independent of etching time. The isotropic etch rates are found to be smaller than anisotropic etch rates, whereas Arrhenius plots yield activation energy for anisotropic dissolution greater than that for isotropic etching. It is also shown from a comparative study of chemical effect of various etchants on calctie cleavages that for a given plane shape of dislocation etch pits the activation energy is constant and independent of etching temperature and etchant concentration and that it is a characteristic of the etchant and not of the crystal.     

半导体单晶生长过程中的位错研究

阐述了现有的半导体单晶位错模型,即临界切应力模型和粘塑性模型的基本理论及应用状况.分析了熔体法单晶生长过程中影响位错产生、增殖的各种因素,以及抑制位错增殖的措施.与熔体不润湿、与晶体热膨胀系数相近的坩埚材料,低位错密度的籽晶可有效地抑制生长晶体的位错密度;固液界面的形状及晶体内的温度梯度是降低位错密度的关键控制因素,而两因素又受到炉膛温度梯度、长晶速率、气体和熔体对流等晶体生长工艺参数的影响.最后,对熔体单晶生长过程的位错研究进行了展望.     

pH值对KDP晶体位错结构的影响

在一定的过饱和度下,分别用点状和片状籽晶在不同pH值溶液中生长出了KDP晶体.利用化学腐蚀法对KDP晶体的不同晶面进行了腐蚀,得到了清晰的位错蚀坑.应用光学显微镜对位错蚀坑的分布特点和密度做了观察分析,发现很多位错蚀坑成线状排布.pH值对KDP晶体位错密度有较大影响,低pH值条件下生长出的晶体位错密度较大.测试了KDP晶体样本的透过率,结果表明位错密度对KDP晶体的透过率没有明显的影响.     

Estimation of Core Energy of Dislocations from Etching Data

From data on the activation energy of dissolution at a surface and at a dislocation for the {100} planes of MgO crystals the dislocation core energy is estimated employing Schaarwächter's theory of etch pit formation.     

Finite element analysis of dislocation density during bulk single crystal growth (effect of doping atoms in InP single crystal)

A computer code for simulation of dislocation density in a bulk single crystal during liquid encapsulated Czochralski (LEC) or Czochralski (CZ) growth process. In this computer code, the shape of crystal–melt interface and the temperature in a crystal at an arbitrary time were determined by linear interpolation of the results that were discretely obtained by heat conduction analysis of a CZ single crystal growth system. A dislocation kinetics model called Haasen–Sumino model was used as a constitutive equation. In this model, creep strain rate is related to dislocation density, and this model extended to multiaxial stress state was incorporated into a finite element elastic creep analysis program for axisymmetric bodies. Dislocation density simulations were performed using this computer code for InP bulk single crystals with about 8″ in diameter. In the analysis, the effect of dopant atoms on the dislocation density was examined. In the case of a low doped InP single crystal, dislocations are distributed in the whole of the crystal. On the other hand, in the case of a highly doped InP single crystal, dislocations are localized at both the central and peripheral regions of the crystal.     

Über das elektrolytische Wachstum und die Auflösung von Silbereinkristallen unter potentiostatischen Bedingungen. Einfluß der Zwillingsgrenzen

The rates of growth and dissolution of silver single crystals have been investigated under potentiostatic conditions. The results show that dissolution is more rapid than growth. That is explained with the effect of additional active centres in case of dissolution which have no noticeable influence on crystal growth rate. It is shown that twin boundaries have great influence on crystal growth rate. In the case of dissolution their effect is negligible and cannot be noticed. The asymmetry of the processes of growth and dissolution is stronger expressed in case of low values of potential, especially when crystals are of the normal type. The influence of twin boundaries on crystal growth rate increases with overvoltage.     

晶格畸变检测仪研究碳化硅晶片中位错缺陷分布

利用晶格畸变检测仪研究了SiC晶片位错分布情况,通过对熔融KOH腐蚀后的SiC晶片进行全片或局部扫描,从而得到完整SiC晶片或局部区域的位错分布.与LEXT OLS40003D激光共聚焦显微镜扫描腐蚀图进行比较,晶格畸变检测仪扫描腐蚀图可以将晶片上位错腐蚀坑信息完全呈现出来,且根据腐蚀坑呈现的颜色及尺寸大小,可以分辨出...     

Investigation of GaN crystal quality on silicon substrates using GaN/AlN superlattice structures

The crystal quality of GaN thin film on silicon using GaN/AlN superlattice structures was investigated. The growth was carried out on Si(111) for GaN(0001) in a metal‐organic vapor phase epitaxy system. Various GaN/AlN superlattice intermediate layers have been designed to decrease the dislocation density. The results showed that the etch pit density could be greatly reduced by one order of magnitude. Cross‐sectional transmission electron microscopy (XTEM) study confirmed the efficiency of GaN/AlN superlattice in blocking threading dislocation propagation in GaN crystal. The design of nine period GaN/AlN (20nm/2nm) superlattice has been evidenced to be effective in reducing the dislocation density and improving the crystal quality. In addition, the dislocation bending in GaN/AlN interface and dislocation merging is investigated. (© 2007 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Untersuchungen zur Neubildung von Versetzungen bei der tiegelfreien Züchtung von Silizium-Einkristallen

During the crucible free growing of dislocation free silicon monocrystals frequently spontaneous generations of new dislocations are observed which cannot be attributed to perceptible reasons. By means of X-ray topographic and metallographic methods it is tried to localize the origin of these dislocation generations in the crystal. Their generation in areas of the crystal surface permits to suppose the existence of a temperature stress mechanism, which releases the generation of new dislocations in the plastic regions of the just formed crystal in consequence of high shocks of stress.     

导模法生长六片片状蓝宝石晶体的研究

采用导模法生长出六片片状蓝宝石晶体,单片尺寸为350 mm×80 mm×2 mm.通过CGSim模拟软件模拟计算和实验验证,确定了合适的生长温场为横向温梯2.9~4.6 K/mm,生长速度控制在5~10 mm/h之间.对晶体进行双晶摇摆曲线测试,峰强度很高且对称性良好,摇摆曲线的半高宽FWHM=16.946″,证明晶体的结晶完整性很高.采用化学腐蚀法对六片晶体进行位错密度的检测,计算出晶体的位错密度都在103量级,中间晶体位错密度小于两边晶体的位错密度.测试了六片晶体的弯曲强度,最高强度达1583 MPa,中间晶体强度大于两边.     

Solvent mediated stabilisation of dissolution at the resorcinol‐water interface

Experimental evidence suggests dissolution along the polar c‐axis of α‐resorcinol in water preferentially occurs at the {011} surface. In an attempt to understand the mechanism by which solvent influences this process, dissolution at the resorcinol {0$ \bar 1 $ $ \bar 1 $ } and {0$ \bar 1 $ $ \bar 1 $ } surfaces has been studied using Molecular Dynamics simulations. Our computations indicate dissolution at the two faces is dependent upon solvent behaviour at the crystal surface, where strong water‐crystal interactions serve to stabilise the crystal surface and retard dissolution. (© 2010 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

CdZnTe晶体位错处的Raman光谱及PL谱研究

利用显微Raman光谱技术,对比研究了CdZnTe晶体无位错区和位锘密集区的Raman光谱.研究发现,CdZnTe晶体无位错区的Raman光谱出现了与Te有关的A1模(119 cm-1)、类CdTe的TO1模(138 cm-1)和类ZnTe 的TO2模(179 cm-1);CdZnTe晶体位错密集区的Raman光谱中仅出现了与Te有关的A1模和类CdTe的TO1模,CdZnTe晶体类ZnTe的TO2模消失.对CdZnTe试样位错密集区进行变温光致发光谱测试,结果表明,束缚在中性施主上的激子的离解为电子空穴对,电子空穴的非辐射复合过程吸收了类ZnTe的TO2模声子能量,造成Raman 光谱中类ZnTe的TO2模缺失.     

化学腐蚀法研究Nd:YAG晶体位错

采用化学腐蚀法研究Nd∶YAG晶体位错.研究发现,腐蚀剂、腐蚀温度以及腐蚀时间对位错的显示都有影响.浓磷酸腐蚀剂在220 ℃下腐蚀20 min时,显示的位错最为清晰.蚀坑形状为菱形,经过计算,位错密度大约为10~3 cm~(-2).同一种腐蚀剂在不同的腐蚀时间所形成的位错蚀坑大小和形貌是不同的.同时发现在样品的边缘有位错塞积群.     

Improvement of Initial Conditions of the Crystal Growth by Dissolution and Refaceting

The influence of significant dissolution and refaceting of KDP and Rochelle salt crystals on their further growth is studied. It is shown that the crystal growth rate ‐ initial crystal size dependence is better defined for growth after refaceting. Initial conditions for growth of individual crystals after refaceting are better defined, than in the case of classical seed nucleation. By dissolution and refaceting, it is easy to provide the same initial conditions for crystal growth in each of several experiments, preformed under the same macroscopic external conditions.     

Study of the dissolution and growth of salt single crystals in inhomogeneous acoustic fields: II. A focused acoustic field

The growth and dissolution of the isolated (100) face of a KDP crystal at exposure of the phase boundary to focused acoustic fields have been investigated. Visualization tools have been developed and the scale and dynamics of the arising acoustic flows have been established. A quadratic dependence of the dissolution rate on the sound pressure has been obtained; such a dependence is in agreement with the theoretical concepts about the dependence of the mass exchange rate in the acoustic boundary layer on the field parameters. A significant growth response of the face under study, normally exposed to ultrasound along the acoustic axis in the prefocal and postfocal planes of a spherical concentrator (f = 1.4 MHz), has been revealed. It is shown that the mechanisms of mass exchange enhancement in these acoustic modes are radically different. The results obtained show a possibility of controlling growth and dissolution of crystals by varying the parameters of an inhomogeneous acoustic field.     

碳化硅单晶位错研究进展

SiC作为代表性的第三代半导体材料,具有优异的物理化学性能。随着材料及应用的发展,SiC衬底在航天电源、电动汽车、智能电网、轨道交通、工业电机等领域的应用日益重要。相比第一代半导体材料如Si和第二代半导体材料如GaAs而言,SiC衬底质量还有很大的改善空间,是现阶段研发和产业的热点。其中SiC单晶缺陷,特别是一维位错缺陷的检测和降低,是近10年内重要的研究内容。本文重点对SiC中位错的形成原因、位错检测技术、位错密度降低方法及近年来SiC单晶中位错的优化水平进行总结归纳,并提出了SiC需要继续突破和发展的方向。     

提高(100)晶向磷化铟单晶的成晶率和质量的研究

通过对高压液封直拉法单晶生长过程的热传输和影响熔体温度起伏的几个关键因素的分析,研究适合生长(100)晶向磷化铟单晶的热场系统,有效地降低了孪晶产生的几率,重复地生长出了整锭掺硫和掺铁的、直径为50mm和76mm的(100)磷化铟单晶.测试结果表明我们生长(100)磷化铟单晶的热场在生长过程中使晶锭保持较为平坦的固液界面,可稳定地获得具有低的缺陷密度和良好的电学均匀性的高质量磷化铟单晶材料.     

Single‐crystal sapphire microstructure for high‐resolution synchrotron X‐ray monochromators

We report on the growth and characterization of sapphire single crystals for X‐ray optics applications. Structural defects were studied by means of laboratory double‐crystal X‐ray diffractometry and white‐beam synchrotron‐radiation topography. The investigations confirmed that the main defect types are dislocations. The best quality crystal was grown using the Kyropoulos technique. Therein the dislocation density was 10²–10³ cm⁻² and a small area with approximately 2*2 mm² did not show dislocation contrast in many reflections. This crystal has suitable quality for application as a backscattering monochromator. A clear correlation between growth rate and dislocation density is observed, though growth rate is not the only parameter impacting the quality.     

Fluctuations of impurity composition and their role in dislocation cross slip in crystals

The influence of impurities on the kinetics of split-dislocation cross slip caused by a change in the stacking-fault energy is studied theoretically. It is shown that the fluctuations in the impurity composition of a crystal make a considerable contribution to the kinetics of dislocation cross slip. The activation-energy spectrum and the average frequency of the processes of dislocation cross slip are calculated for a model of random impurity distribution in a crystal. The calculation shows that the fluctuations in impurity concentration, reducing the stacking-fault energy, play an important role in the low-temperature region.