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.

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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 6.10 TM cm -~ (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. Ah analysis of the reciprocal-space maps is presented. Several types of defects should be considered in order to describe isointensity contours. PACS 61.10 -X-ray diffraction and scattering. PACS 61.72. -Defects and impurities in crystals; microstructure. PACS 01.30.Cc -Conference proceedings.

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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 singledefect components are presented.