The crystal growth and perfection of 2,4,6-trinitrotoluene

Large crystals of TNT were grown from ethyl acetate solution by both temperature lowering and solvent evaporation. The perfection of crystals grown from seeds under carefully controlled conditions was generally higher than those prepared by uncontrolled solvent evaporation. Examination by X-ray topography revealed the crystals to have a characteristic growth induced defect structure comprising growth sectors and boundaries, growth banding, solvent inclusions and dislocations. Twins and stacking faults (SF) were also observed. Many of the defects noted in the topographs can be attributed to impurities. The influence of the highly anisotropic crystal structure on the nature of growth defects is discussed. A structural model proposed to explain twinning and SF formation is partially supported by topographic evidence.     

Concept of specific supersaturation (specific supercooling) and practical aspects of its application

It is demonstrated that the normal growth rate of crystals from solutions and melts depends on the area of the crystallization front. New growth parameters, namely, the specific supersaturation and the specific supercooling, are introduced, and the quantitative dependence of the normal growth rate on these parameters is determined. It is noted that the normal growth rate affects the formation of defects. The criteria and the range of the possible use of the specific supersaturation (specific supercooling) for optimizing the conditions of crystal growth from solutions and melts are revealed.     

Influence of <Emphasis Type="Italic">in situ</Emphasis> photoexcitation on structure of damaged layer in GaAs (001) substrates implanted with Ar<Superscript>3+</Superscript> ions

The influence of photoexcitation on the formation of the defect structure in GaAs crystals implanted with 200 keV Ar⁺ ions at doses of 1 × 10¹³, 3 × 10¹³, and 5 × 10¹³ cm^?2 has been studied by high-resolution Xray diffractometry. It was found that photoexcitation gives rise to annihilation of radiation-induced Frenkel pairs, and, thus, decreases the residual concentration of radiation-induced point defects. It is established that amorphization of the damaged layer proceeds via the formation and growth of clusters of radiation-induced point defects. The vacancy-and interstitial-type clusters are spatially separated—the former are located closer to the crystal surface than the latter. Photoexcitation hinders cluster growth and stimulates diffusion of interstitial defects into the substrate depth.     

Effect of the vacancy composition of GaAs single crystals on optical quenching of luminescence through <Emphasis Type="Italic">EL</Emphasis>2 defects

Optical quenching of luminescence through EL2 defects in single crystals of undoped semi-insulating gallium arsenide is investigated. It is shown that the minimum energy of light photons providing the transition of such defects into the metastable state depends on the vacancy composition of the crystals. It is suggested that the nature of the effect revealed is related to the existence of a set of EL2 defects with different configurations. An optical method is proposed to determine the vacancy composition of undoped semi-insulating GaAs crystals.     

Working Model for Explanation of Polytype formation Based on Superlattice Ordering of Point Defects in Close Packing Structures

The model is an attempt to give an explanation of polytype orderings in the crystals. Basic assumptions of the model are: the point defects play the important part in the polytype formation; these defects influence the configuration (hexagonal or cubic) of individual layers. The defects have a tendency to ordering themselves into superlattices. It acts selectively on particular stacking of the layer sequences. The results of model operation are shown in examples of experimental data of polytypic materials; they are SiC and A^IIB_VI compounds.     

Measurement, modelling and simulation of defects in as-grown Czochralski silicon

Defects in as-grown and heat-treated 150 and 200 mm Czochralski silicon crystals are investigated for different crystal pulling conditions and thermal treatments. First results are presented using noncontact carrier recombination imaging for detection of electrically active defects. The defect densities and sizes are compared with the results of computer modelling, suggesting that the observed defects in as-grown material are most likely large voids, possibly partially filled with silicon oxide. In contrast, the defects observed after prolonged heat treatments are silicon oxide precipitates with a density which is several orders of magnitude larger. The voids nucleate at temperatures above 1100°C by a homogeneous nucleation process and grow further to the observed size during further cooling of the crystal. They are responsible for the midfield breakdown of 10–50 nm gate oxides.     

The mechanism of formation of light-scattering centers in sapphire crystals grown in gas atmospheres

The mechanism of the formation of light-scattering centers in sapphire crystals grown by horizontal directed crystallization in gas atmospheres reducing with respect to the Al₂O₃ melt was studied. The experimental regularities here significantly differ from those observed upon formation of other conventional defects in sapphire crystals (vacancy pores, gas bubbles, and so on). It is shown that the known formation mechanisms of macroscopic ≥1 mm) inclusions in crystals are not acceptable in this case. Using the model of bulk crystallization is proposed to describe the obtained regularities.     

Influence of Chromium and Titanium Oxide Dopants on the Real Structure and the Mechanical Properties of Corundum Single Crystals

The real structure and the mechanical properties of pure and doped corundum single crystals have been investigated. The single crystals were obtained by the Verneuil-method. The results allow to propose two different models concerning the influence of the chromium and titanium oxide on the properties of corundum single crystals. Optimum concentration of the chromium oxide impurities was approximately determined, from which corundum single crystals with higher hardness can be obtained. It was stated that titanium oxide impurities with some concentrations made the crystals more fragile without plastically changes in the region of the individual mosaic blocks.     

Growth of semiconductor silicon crystals

This paper focuses on the recent developments in Czochralski (CZ) crystal growth of silicon for large-scale integrated circuits (LSIs) and multi-crystalline silicon growth using a directional solidification method for solar cells. Growth of silicon crystals by the CZ method currently allows the growth of high-quality crystals that satisfy the device requirements of LSIs or power devices for electric cars. This paper covers how to obtain high-quality crystals with low impurity content and few point defects. It also covers the directional solidification method, which yields crystals with medium conversion efficiency for photovoltaic applications. We discuss the defects and impurities that degrade the efficiency and the steps to overcome these problems.     

Photoacoustic Spectroscopy of Defect States in Etched and Air-annealed CuInSe2 Single Crystals

Photoacoustic spectra of cleaved, polished and etched, and air-annealed n-type CuInSe₂ single crystals are measured at different frequencies between 30 and 312 Hz. The spectra related to the bulk of the crystals exhibit five structures due to defects that are also present in p-type crystals. Polishing and etching as well as subsequent air annealing at 100, 200 and 300 °C reveal rather complex changes of the defect equilibrium in the near-surface region of the crystals which include both relative concentration changes of existing defects and creation of new defects. The results for polished and etched crystals correspond to trends expected from etching induced local modifications of the composition and structure as revealed by electron spectroscopies and ion channeling. Air annealing is found to affect all existing defects and to create up to five new defects which cannot be explained in terms of the related point defect model proposed by CAHEN and NOUFI.     

The melt growth of oxide and related single crystals

This article reviews the principle changes which have occured during the last three years in the techniques used to produce single crystals of oxide and similar single crystals from the melt. The technological demands created by device applications are emphasized and the current state of knowledge upon the major crystalline defects is discussed. The role of accurate phase diagram analysis, the importance now attached to the atmosphere in which a crystal grows and the relevance of looking at crystals with greater resolution are stressed particularly.     

Ion channeling study of defects in CuInTe2 single crystals

Ion channeling spectra of as-grown CuInTe₂ single crystals are measured using a 2 MeV ⁴He⁺ analysing beam. It is found that the measured minimum yields cannot be explained within a model of randomly distributed non-interacting point defects caused by deviations from ideal stoichiometry. A model with extended defects due to vacancy clustering and dislocation formation is proposed to interprete the experimental results.     

Thermochemical analysis of native point defects and substitutional carbon and boron in GaAs crystal growth

The phase extent of GaAs has been analyzed and compared with published phase diagrams as related to total and partial point defect equilibria including charged and uncharged Frenkel, Schottky, antisite defects and substitutional carbon and boron on both sublattices. The well-known transition between semiconducting and semi-insulating behaviour at 300 K as a function of melt stoichiometry in LEC crystals can be reproduced in our model in which complete equilibrium exists above, only electronic equilibrium below a freeze-in temperature of 1100 K. The corresponding model standard enthalpy of formation of neutral Schottky defects is 4.0 eV, of a pair of neutral uncorrelated antisite defects 3.8 eV, of neutral Ga Frenkel defects 4.1 eV and of neutral As Frenkel defects 3.6 eV. Defect reactions in cooling processes after crystal growth are discussed and shown to be quite different for crystals with high or low dislocation density. Semi-insulating behaviour requires the existence of carbon acceptors if dislocations provide internal sources and sinks for point defects. For ideal crystals carbon would not be necessary. The possible site distribution of C and B is analyzed in its dependence on temperature and chemical potential of As. Constitutional supercooling is negligible in LEC growth. Macrosegregation is severe if the As fraction in the melt deviates more than ±0.02 from the stoichiometric value 0.5.     

Thermal behavior of floating gate oxide defects (moving bits)

The defect density of the oxides used in non-volatile memories (NVM) is a key parameter to the understanding of the data loss of these structures. One of the most critical phenomena responsible for this loss (in the range of oxide thicknesses used in NVM devices) is the stress induced leakage current (SILC). The origin of SILC is generally attributed to the trap assisted tunnelling (TAT); therefore, a better understanding of the evolution of the oxide defects is necessary. It is known that the leakage through the oxide defects is temperature accelerated below 100 °C. Besides, it was observed that above 100 °C, the oxide defects are annealed. To better understand the temperature behavior of the defect population, a dedicated method has been devised and applied to several baking experiments. It leads to new observations and to the correction of some biased interpretations due to unsuitable experimental methods. Indeed, in this paper, we point out the fact that the annealing effect already occurs at 60 °C. The activation energy was calculated and found independent from both the electrical field across the oxide and the number of program/erase (P/E) cycles. The temperature behavior of the leakage is found to be more complex than what was reported in the literature: it is a balance between two opposite phenomena. Based on that, a new model describing the defect population evolution is proposed.     

Effect of magnetic field on melt flow and crystal growth of oxide crystals

The flow in an oxide melt such as LiNbO, and TiO₂ in a high magnetic field was observed by using magnetic-field-applied Czochralski equipment for oxide crystals. It was found that the flows in oxides melts were very much different from these in a semiconductor melt. The single crystals of TiO₂ were grown in a magnetic field by using this equipment.     

Studies on crystal growth,optical and electrical characterization of pure and Dy-doped bismuth silicate single crystals

(0.5 mol%) Dysprosium (Dy) doped bismuth silicon oxide (BSO) single crystals were grown by the Czochralski technique under air atmosphere. Detailed analysis of Dy-doped BSO with pure BSO has been studied through optical analysis. The absorption edges of pure and Dy-doped BSO crystals are found to be 405 nm and 415 nm, respectively. The shift in the absorption edge is contributed to the defect centers created in the crystal with Dy-doping. The shifts observed in the Raman spectra on doping Dy are found to be lower, when compared with the pure BSO crystal. This effect can be correlated to the lattice distortion induced by the Dy doping. The oxide formation and intrinsic defects in the BSO crystal have been identified by photoluminescence analysis. Dielectric measurements reveal that higher permeability value in the BSO sample is due to the presence of charged defects, which can be related to the space charge polarization. There is a slight decrease in dielectric constant on doping with Dy. The piezoelectric value explains the defects formed in the crystal. On poling, d₃₃ value of BSO and Dy-doped BSO are 32 pC/N and 40 pC/N, respectively.     

Nd:LuVO4晶体缺陷的研究

采用提拉法生长的Nd:LuVO4晶体是一种适合二极管泵浦的新型激光晶体,运用化学腐蚀结合光学显微术和同步辐射白光X射线形貌术对Nd:LuVO4晶体缺陷进行观察,结果表明:晶体的主要缺陷为位错和小角晶界.利用高分辨X射线衍射仪进一步验证了这一结果.并初步讨论了缺陷形成的原因.     

ZnO晶体的功能梯度分析

分析n-ZnO薄膜和硼掺杂p型金刚石薄膜在{111}面金刚石衬底上制作n-ZnO/p-金刚石p-n异质结的应用,ZnO体晶微观结构和缺陷分布及电阻、载流子浓度、迁移率分布特征,探讨了应用功能梯度材料理论研究ZnO晶体材料的方法.从而提出应系统地建立ZnO晶体内部组成和结构的梯度分布特性数据库,从不同的应用角度来进行ZnO晶体材料设计和研究.     

Surface structures of fluorite crystals

Optical studies have been made of the microstructures on the natural {100} and {111} faces of natural fluorite crystals. The protrudance of triangular elevations, growth pyramids, and natural etch pits have been observed on a large number of crystals. It is suggested that fluorite crystals grown by two-dimensional spreading and piling of growth layers parallel to {100} faces. The natural etch pits on {100} and {111} faces suggest that they have been produced as a result of a dissolution process in nature. The natural faces have been etched in the laboratory and it is established that the pits indicate the existence of linear defects in the crystals. The implications are discussed.     

Electron Beam Induced Changes of the Real Structure of Semiconductors

The formation of irradiation defects produced in a high voltage electron microscope (HVEM) has been studied in Ge and other semiconductor crystals in dependence on various thermal treatments and on covering of the specimen surface. It has been concluded that the defect formation depends — besides general features known for pure metals — also on the state of electrically neutral impurities. Besides, various interactions between dislocations and irradiation defects were observed.