The defect structure of gadolinium–calcium oxoborate single crystals highly doped with 22% Y, Gd0.78Y0.22Ca4O(BO3)3, is studied using X-ray transmission topography both with the conventional source and synchrotron radiation. Straight dislocation diffraction contrasts, white or black, depending on absorption and on its changing while the diffraction vector is reversed, are observed. A model of formation of dislocation contrast is proposed in the case of intermediate absorption.

New results on ternary InGaAs crystals grown using liquid encapsulated Czochralski technique with constant liquid composition are reported.X-ray high-resolution diffractometry (rocking curves and reciprocal space maps) as well as X-ray topography using the transmission Lang setup were used.Growth history of the bulk ingots was revealed.

We report results of X-ray investigations of tellurium-doped GaAs1-xPx (with 0.07 <= x <= 0.20) single crystals, conducted in order to support finding proper growth parameters which would yield a material of sufficient homogeneity of the lattice parameter for prospective applications. Our samples were studied using high-resolution diffractometry which allowed to obtain both rocking curves and reciprocal space maps of the diffracted intensity, as well as using plane-wave topography in the reflection mode. Weak reflections were also used to study the influence of Te atoms on the compound lattice. (c) 2007 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

Mathematica was employed to simulate X-ray rocking curves measured in many-crystal arrangements taking into account the divergence and the spectral distribution of the incident beam. The influence of the curvature of the sample on its intrinsic diffraction profile was considered. Although the effect of the monochromator is to smear out the oscillations considerably, it is shown that the radius of curvature can still be determined from the FWHM of the rocking curve.

The effect of Si doping (NSi∼3×1018 cm−3) on crystalline quality of GaN epitaxial layers grown on sapphire c face was studied by high resolution X-ray diffraction including several Bragg reflections in different scan directions, reciprocal space maps, radial scans, and measurements of radii of curvature. Elastic and hydrostatic strain components were derived taking into account strains introduced in the sapphire substrate by the highly mismatched GaN layer. Si-doped and undoped GaN layers were grown by atmospheric pressure MOCVD technique using the same growth conditions. All the layers were under compression but with slightly higher stress in the undoped layer, while the hydrostatic strain component remained unchanged. It was found that doping of GaN by Si decreased edge dislocation density and increased screw dislocation density. It could be concluded that edge-type threading dislocation arrangement, piled up in small-angle columnar grain boundaries, dominated in both samples.

Charge density of [Cu(bite)](BF4) [1] (bite = biphenyldiimino dithioether) have been studied to understand the redox process in 'blue-protein' model compounds (so called gated electron transfer) [2].Our studies were based on data collected at 20K at the SUNY X3 beamline at NSLS (λ = 0.6430 Ǻ) and at 100K at beamline F1 at HASYLAB/DESY (λ = 0.5604 Ǻ).Two crystals of different size were used to avoid absorption and to obtain high-angle reflection intensities.109 890 reflections (17619 unique) were collected with the smaller crystal at 20 K. Starting parameters for XD [3] refinement were taken from SHELXL97 results (R1 = 0.0241).The density maps indicate significant nonequivalence of the two Cu-S interactions.DFT quantum-chemical calculations [4] on the geometry optimization of the quasi-tetrahedral and quasi-squareplanar [Cu(bite)]+/2+ complexes were done.

In the present paper the orthorhombic microdefects detected in a Si single-crystal sample are analysed on the basis of theoretical simulations exactly matching the experimental x-ray diffuse scattering map. The mean radius of microdefects is estimated to be smaller than 0.1 µm.

The aim of this work is to study to what extent a typical section-topography setup can supply information about the degree of coherence of the incident x-ray beam. In real experiments, the incident beam is partially coherent, with the degree of coherence described by the shape of the correlation function. In this paper the correlation functions for the outgoing beam are calculated by solving the Takagi-Taupin equations, assuming a truncated Gauss correlation function for the incident beam with the correlation length determined by the van Cittert-Zernike theorem. Its influence on the measured intensity of the diffracted beam in section topography is investigated.

Older and newest articles on X-ray diffuse scattering are reviewed and the perspectives of further high-resolution diffractometry studies for specific semiconductor materials are demonstrated. The importance of correlations of spatial distributions of microdefects as well as correlation functions of the incident beam partial-coherence phenomena) is stressed. Other problems include the cluster expansion and Fourier transforms of these correlation functions which should improve the agreement between the simulated and experimental results.

Influence of the Fourier transform of the incident beam on the measured diffracted intensity in X-ray diffraction is analysed. The theory presented is a more rigorous physical picture of X-ray diffraction in the case of a narrow incident beam than the usually assumed spherical-wave theory. The shape of diffracted beam amplitude depends on the FT of the incident beam which is fully determined by experimental conditions. The proposed methods may be used for direct calculations of the correlation function for electromagnetic fields and studies of the coherence degree of X-ray radiation.

Highly tellurium–doped GaAs samples were investigated by high–resolution X–ray diffractometry in the triple–axis mode. Different reciprocal maps, depending on the technological process, are presented and interpreted as caused by different microdefects. Computer simulations allow us to determine the type of microdefects, namely the orthorhombic defects and dislocations loops. A theoretical approach for defects composed of several atoms is proposed. Alternative descriptions of pairs of defects as uniform distributions of such paired defects or non–uniform distributions of single–defect components are presented.

The displacement field of a crystal lattice, in the continuous media approximation, caused by extended microdefects of rectangular parallelepiped shape, is considered. X-ray diffuse scattering from the defect core as well as the long-range displacement field is analyzed. A theoretical expression for the intensity of X-ray diffuse scattering resulting from randomly distributed microdefects of orthorhombic symmetry is presented using the kinematical approximation of X-ray statistical diffraction theory. The computer simulations of the isointensity contours for two sets of defect parameters are performed. A way of obtaining the defect parameters by fitting the computer simulations to the experimental data is proposed.

X–ray topography has been successfully applied to study microdefects with the sizes in the range from well below standard topographic resolution to tenths of micrometers, thus effectively widening applicability of the Lang section topography. The lower value is set by the application of high order asymmetric reflection. Disappearance of the Kato fringes on the section topography is a clear indication of the existence of defects, which are otherwise not detectable as the standard contrast features. The presence of the defects with such sizes was also confirmed by transmission electron microscopy. Microdefects in the higher end of the size spectrum are well covered by Lang traverse and section topography where detailed contrast study is possible for individual defects. Lang traverse and section topography was applied to study specific case of oxygen related defects in silicon crystals.

Diffuse scattering of x-rays is applied to studies of microdefects in annealed highly doped crystals of GaAs:Te. X-ray diffraction reciprocal space mapping was performed by high-resolution x-ray diffractometry in the triple-axis mode. The most characteristic feature of the experimental maps is the lack of the zero-intensity lines for all high-symmetry reflections. Owing to this aspect of measured maps it was possible to determine the type of microdefects. The computer simulations performed for point defects with orthorhombic symmetry in annealed crystals of GaAs fit very well to the patterns of measured iso-intensity contours. The experimental data obtained so far give the possibility of determining the displacement field outside the defect core but are not sufficient to obtain information about the interior of the defect. The mean radius of microdefects was estimated to be smaller than 0.2 m.

A numerical program written in the Mathemathica 2.1.1 package to simulate the symmetrical part of X-ray diffuse scattering is presented. This program can be used to determine the type of any point defect in any crystal by comparing X-ray triple crystal measurements with simulations. Simulations for point defects with the orthorhombic symmetry in a Si crystal, calculated for the first time to the authors knowledge, are presented.

The aim of the present work was to correlate the electric characteristics of Te-doped gallium arsenide grown by LEC technique with the defect contents of the samples. Measurements for GaAs samples, doped with Si, Ge and Ge+Te as well as undoped ones, grown by various methods (HB, VGF and LEC), were also performed. In order to characterize the defects High Resolution X-Ray Diffractometry was used. Measurements of diffuse scattering intensity maps around the reciprocal lattice points and plane wave reflection topography were employed. For most cases in the range of free-electron concentrations between 1·1017 cm−3 and 6·1018 cm−3 (as well as for SI samples) the isointensity contours in the maps exhibit generally the same character. For higher doping level the intensity of X-ray diffuse scattering increases and it can be further increased by the annealing which causes a decrease of free-electron concentration. An analysis of the reciprocal-space maps is presented. Several types of defects should be considered in order to describe isointensity contours.