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.

PACS. 61.10F -Experimental techniques (inc. apparatus, techniques and calculation methods PACS. 42.82 -Integrated optics. PACS. 66.30 J -Diffusion, migration, and displacement of impurities. for analysing experimental results).

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Titanium-diffused and proton-exchanged (PE) LiNbO3 single crystals of congruent composition were investigated by topographic methods in reflection mode using synchrotron radiation. The white beam topographs obtained for z-cut Ti:LiNbO3 samples revealed a characteristic distribution of defects with increasing concentration of Ti atoms in the near-surface region. For crystals with doses above 3.0*1020 cm-3 of indiffused atoms the density of introduced defects was fairly high resulting in rather homogeneous images. For white beam topographs of z-cut LiNbO3 samples with PE regions two images arising from the PE layer and from the substrate are distinguished, indicating the different lattice parameter of both parts of the crystal.