Defect Structure in Te-doped GaAs Single Crystals after Plastic Deformation (II). Dislocation Slip and Cell Formation

At temperatures above the brittle-to-ductile transition (490 °C) in Te-doped GaAs three types of predominant defect configurations have been observed after uniaxial compression along a [001] direction: (i) twins and stacking faults (500 … 520 °C), (ii) slip zones of dislocations (≈550 °C) and (iii) dislocation cells (580 … 590 °C). In Part II quantitative details of the appearance of slip and cell formation are given. Leading segments of gliding half loops are mainly of 60° type. Cell walls were formed by multiple slip of perfect dislocations.     

In-situ Observations on Dynamic Processes Associated with Stacking Faults and Deformation Twins in Silicon Crystals

Stacking faults and thin deformation twins are observed to develop during the in-situ deformation of silicon crystals at elevated temperatures in a HVEM. Both the nucleation and the motion of partial dislocations take place under the applied stress in the regions of the stress concentration. Twinning dislocations moving on twin boundaries are extremely flexible. The spontaneous nucleation of loops of twinning dislocation on twin boundaries is observed rather frequently. No pole mechanism is observed to be operating. Stacking faults and deformation twins interact with glide dislocations moving along the intersecting planes by various ways.     

X-ray Characterization of Defect Structure in LEC Annealed GaAs Crystals

Wafers of commercially available semi-insulating (SI) Czochralski-grown GaAs crystals have been annealed at temperatures near the melting point (> 1100 °C) both for relatively short and long time and then rapidly quenched into cold water. Heat-treated crystals have been investigated by X-ray transmission diffraction topography. Cellular structure pattern of the as-grown sample is replaced by images of precipitates spread out over whole sample. This suggests that the excess arsenic condenses as As precipitates with nucleation sites not correlated with cell walls.     

Comparison of Experiments and Theories for Plastic Deformation in thermally processed GaAs Wafers

Different types of dislocation bundles were identified in thermally processed (001) GaAs wafers. Synchrotron based single crystal X‐ray transmission topography, scanning infrared polariscopy, visible light interferometry, standard Nomarski microscopy, and Makyoh topography had been applied for this purpose and allowed for a classification of the dislocation bundles into one distinct majority and a generic minority type. The currently accepted theories are briefly discussed and it is shown that their disagreement with the core of the experimental observations is due to oversimplifications. A new theory is finally presented in a concise manner and its excellent agreement with all of the available experimental evidence is demonstrated.     

Investigation of One‐Dimensionally Disordered Structures of AIIBVI Crystals by Monte Carlo Technique. I. The 3C Disordered Structure and the 3C Structure with Different Kinds of Stacking Faults

The Monte Carlo computer simulation technique is applied to investigate one‐dimensionally disordered (ODD) structures in A^IIB^VI compounds. Computed diffracted intensities for 3C disordered structure (3C/DS) with various frequency functions of fault to fault distances have shown a strong intensity distribution dependence upon the frequency function. Distinctive features of the diffraction patterns along the 10.L reciprocal lattice row corresponding to different kinds of faults in 3C structure are discussed. In particular, both random as well as non‐random distribution of stacking faults (SFs) are considered.     

Native Point Defects and Nonstoichiometry in GaAs (I). Homogeneity Region of Gallium Arsenide

Homogeneity region and the concentration of dominant native point defects along its boundary are calculated by the method of quasichemical reactions with the use of experimental data on the structure type of solid solutions formed by the components in GaAs. The entropy and enthalpy of the formation of dominant native point defects in GaAs are obtained. Temperature ranges of the formation of microdefects-finely dispersed Ga and As precipitates are considered.     

Relation between the Activation Parameters of the Plastic Deformation in MgO Crystals Determined by Macroscopic and by In-situ HVEM Experiments

The results of macroscopic strain rate and temperature cycling tests on MgO single crystals are compared with the results of in-situ deformation tests in a HVEM on the basis of the basis of the thermally activated dislocation glide model. The activation volume estimated by strain rate cycling tests is compatible with the mean obstacle distance of the screw dislocations. However, the local stress estimated by in-situ deformation tests was found to be larger than the macroscopic yield stress.     

Defect generation on mechanically surface defects before and after the oxidation (II). Dislocation generation at cracks

The generation of crystal defects at residual cracks due to a wet oxidation of chemically mechanically polished silicon wafers at 1100 °C was investigated. It was found that the nucleation of oxidation stacking faults at these elastic cracks is impeded as compared to the regions between the cracks. However, extended dislocations, dislocation dipoles, certain stacking faults, and precipitates are generated at such cracks. These crystal defects and the crack itself impede the nucleation of oxidation stacking faults at the crack, as they locally reduce the excess interstitials at the oxidation front.     

Defect Investigations in CdTe Crystals by RXT,SCL, and EBIC(V) Techniques

The paper covers results of investigations on the defect structure of CdTe crystals. Several techniques have been involved, namely RXT supplied with CL-IR, EBIC(V), and SACP using Electron Probe Micro-Analyzer (EPMA): EBIC(V) measurements were performed on Schottky diodes with CdTe-Au contacts. It has to be emphasized that microscopic images at small magnification (45 ×) had successfully been obtained which were next correlated with X-ray topographs. The observed due to grain boundaries, twins, “as grown” dislocations as well as those introduced either during high-temperature plastic deformation or by pyramidal diamond indenter are discussed.     

Deformation Modes and Structure Evolution in Laser‐Shock‐Loaded Molybdenum Single Crystals of High Purity

This paper reports on the microstructural changes occurring within molybdenum single crystals after shock treatment with an excimer laser‐system in a confined ablation mode with different number of impacts. Using different complementary investigation methods (optical microscopy, scanning electron microscopy and transmission electron microscopy) it is found that slip and twinning are active modes of deformation during the shock‐induced plastic deformation. After laser treatment with a single laser pulse slip bands on {112} planes containing several microscopic twins are the dominating microstructural feature, whereas further laser‐shock‐processing leads to the formation of a homogeneous arrangement of screw dislocations, tangles and loops. Deformation modes and microstructure in laser shocked samples prove to be quite similar to those of explosive shocked specimens although the laser‐induced peak pressure is about an order of magnitude lower than that during explosive loading.It is shown that the laser shock‐induced hardening increases with increasing number of impacts in the range from 1 to 6 impacts. This shock‐induced strengthening is correlated with the overall dislocation density.     

EBIC/TEM Studies on the Relation between Electrical Properties,Crystallographic Structure,and Interaction with Point Defects of Epitaxial Stacking Faults in Silicon

Only after annealing, EBIC investigations on epitaxial layer defects partly gave contrasts. More information on the crystallographic structure of these defects was obtained in subsequent HVEM investigations. Experimental results confirmed the supposition that only the decoration of the crystallographic defects with additional recombination centres (impurity atoms), and not existence of the defects themselves, results in a detectable EBIC contrast. The observed getter efficiency of the various defect types is discussed. This efficiency is growing with increasing lattice distortion.     

Defect generation on mechanical surface defects before and after the oxidation (I). TEM investigations on the nucleation of oxidation stacking faults at mechanically induced weak surface defects

In order to obtain information on the nucleation mechanism of oxidation stacking faults, mechanically induced weak surface defects as simulated by low-load scratches were investigated with TEM before and after a short-time wet oxidation at 1050 °C. The experimental results could not confirm the existing models which explain stacking fault nucleation by the splitting of complete dislocations. Rather it was found that clusters of silicon interstitials are generated due to strong local compression during scratching, which then act as nuclei for stacking faults in the subsequent oxydation process.     

A Study on Carbon Incorporation in Semi‐Insulating GaAs Crystals Grown by the Vapor Pressure Controlled Czochralski Technique (VCz) Part I: Experiments and Results

In the past it has been demonstrated that the carbon concentration of large semi‐insulating (SI) GaAs single crystals grown by the conventional liquid encapsulation Czochralski (LEC) technique can be controlled by several methods including variations of growth parameters. It was the aim of the present paper to clarify which of the relationships of LEC growth could be used for a carbon control in the VCz‐method characterized by the application of an inner chamber made from graphite to avoid selective As evaporation. In detail this comprised a study of the influence of several growth parameters like the water content of the boric oxide, the composition of the working atmosphere, the gas flow, a titanium gettering and additions of gallium oxide. As a result, for the first time carbon concentrations down to ≈ 1014 cm^‐3 were obtained in 3'' (75 mm) diameter VCz crystals.     

Deformation stages in a stabilized loading cycle of fatigued FCC metals(II). Discussion and conclusions

Considering the experimental results presented in Part I of this work and taking into account the nature of the deformation mechanisms during cycling, four deformation stages are assumed to exist in a stabilized loading cycle. The mechanical behaviour in the stages is discussed on different structure levels. In particular, it is shown that the heterogeneous plastic deformation caused by different local yield stresses in the dislocation-dense and dislocation-poor regions of the material seems to be limited to a relatively small interval of plastic strain ε_p (10⁻⁴ ≦ ε_p ≦ 10⁻³).     

Native Point Defects and Nonstoichiometry in GaAs (II) Mechanism of Formation and Degradation of Semiinsulating Properties of Undoped Gallium Arsenide Crystals

The nature of the main electron trap, EL2, in undoped semiinsulating GaAs crystals have been studied both qualitatively and quantitatively. It has been shown that point defects which, most probably, are responsible for the EL2 level are antisite As_Ga defects or (As_i V_Gs) complexes which are indistinguishable from the thermodynamic standpoint. The enthalpy and entropy of As_Ga formation according to the reaction As_As + V_Ga ⇄ As_Ga + V_As are equal to 0.5 eV and −7k, respectively.     

Influence of γ-Irradiation on Some Properties of NaCl: Eu++ Crystals (I). Optical and Dielectrical Characteristics of the Dopant Ions

The present work opens a series of papers describing a variety of properties of the same material, and deals with the effect of Eu⁺⁺ ions, and y–irradiation on the optical and dielectrical characteristics of NaCl crystals. For nonirradiated crystals four types of Eu⁺⁺-related absorption spectra have been identified and correlated with I.V. dipoles and three types of precipitates stable in the well aged crystals. For the solution—treated samples the effect of irradiation was to diminish the concentration of I.V. dipoles and to change the absorption spectrum in a remarkable way. These changes are explained in terms of the formation of some dopant—related clusters different of those obtainable thermally. No spectroscopic evidences have been obtained for the radiation—induced changes of the valence state of the dopant irrespective of its dispersion degree.     

Transformation of Light Wave in Absorbing Crystals with Low Symmetry and Determination of their Own Waves Parameters (I)

The decision of the direct and reverse problems in the optics of the low symmetry absorbing crystals are obtained and graphically represented by the specific drawing on the Poincare sphere. The direct problem is connected with the transmission and reflection of the normally incident light wave and reverse problem — with the determination of the own waves parameters. Instead of the usually used boundary conditions the equations of Fresnel and Airy are applied to each of the own waves separately, as the incident, reflected and transmitted waves are represented by the vector sum of the own waves. On the basis of the comparatively simple decision of the direct problem the simpliest method of the reverse problem decision, i.e. for the determination of the own waves parameters in the crystal plate is proposed. In the capacity of the experimental data for this purpose the measured polarization parameters, the reflection- and transmission coefficients of the reflected and transmitted waves must be used as well as the right and left circular polarized incident waves and also two different, but close thicknesses of the crystal plate.