Experimental and Computer Simulation Study of the Variation with Depth of the X-raySection Topograph Images of a Dislocation

International audienceA systematic study of the variations of the contrast of a dislocation in silicon on section topographs with thedepth of the line was performed both experimentally and with computer simulations. Mo Kalpha1 radiationand 33-3 and -3-33 symmetric reflections were used. The crystal thickness was 440 microns so that the value of mu*twas 0.64. The influence of the orientation of the dislocation was studied for values of the angle betweenthe line and its Burgers vector ranging between 60 and 90 ° in the glide plane. It was observed that when thedislocation lies close to the entrance surface, whatever its orientation, its image is centred around the traceof the plane of incidence passing through the intersection of the dislocation with the direct beam whilewhen the dislocation lies close to the exit surface its image is centred around the projection of the disloca-tion on the section pattern. The variation of the orientation of the image for intermediate depths of thedislocation is interpreted by means of the geometrical construction of the dynamical image. The values of theorientation of the image calculated according to this simple model are in good agreement with thosemeasured on both experimental and simulated topographs. The same geometrical model enables thedifference in the relative positions of the direct and dynamic images of stereo pairs to be explained. A newfeature was observed in the simulated images and several of the experimental ones, namely a con-centration of intensity along the projection of the dislocation in the reflected direction. Slit width wastaken into account in the simulations for a better fit with experimental topographs but not polarization,which was taken to be normal to the plane of incidence. Because of the small value of the crystalthickness and of mu*t, the variation of the contrast with the Burgers vector is very small, making itsdetermination very difficult

X-ray Diffraction Topography - Investigation of Single Crystals Grown by the Czochralski Method

X-ray diffraction topography is one of basic diagnostics tools serving for visualisation of single crystal lattice defects. Defects of various kinds can be observed. The present study is a review of topographic results obtained in the X-ray laboratory of the Institute of Experimental Physics, University of Warsaw, for three families of single crystals grown by the Czochralski method: (i) silicon (Si) and $Si_{1-x}Ge_{x}$, (ii) selected binary REVO_4 oxides and (iii) selected ternary $ABCO_4$ oxides. The effect of chemical composition, growth conditions and post growth thermal annealing on the defect appearing in crystals is discussed. Various defects are revealed: the growth dislocations (some early Si crystals), the composition-gradient-induced lattice deformation $(Si_{1-x}Ge_{x}$, solid solutions $Ca_{x}Sr_{1-x}NdAlO_4)$, defects generated in Si after the post growth thermal processes, oriented elongated rod-like macro-defects tending to form networks within the crystal core, cellular structure in the outer shell $(SrLaGaO_4)$, and variously developed block structure (in selected binary $\text{REVO}_4$ crystals)

Interference Fringes in the Plane Wave Topographic Images of Growth Bands in Si:Ge

An Si:Ge crystal with approximately 3% of germanium was studied with strongly collimated short-wavelength monochromatic synchrotron beam (beamline E2 at HASYLAB). The topographs obtained in the asymmetric 224 reflection revealed the presence of interference fringes related to growth bands caused by segregation of germanium. The fringes, observed for the first time, were strongly dependent on the angular setting and it was possible to distinguish at least three systems of fringes. A number of features of the existing strain field, which may be important for the formation of the fringes, was determined using other topographic methods, especially the Bragg-case section topography

Conventional and synchrotron X-ray topography of defects in core region of SrLaGaO4SrLaGaO_4

$SrLaGaO_4$ single crystals are perspective substrate materials for high temperature superconductors thin films, elements of thermal radiation receivers and other electronic devices. The defect structure of the Czochralski grown $SrLaGaO_4$ crystal was investigated by means of X-ray topography exploring both conventional and synchrotron sources. The crystal lattice defects in the core region of the crystal were investigated. The regular network of defects arranged in rows only in ⟨100⟩ direction was observed. Owing to high resolution of synchrotron radiation white beam back reflection topographs one can distinguish individual spots forming the lines of the rows. It can be supposed that these elongated rod-like volume defects are located in 100 lattice planes forming a kind of walls. They are built approximately of the same phase as crystal but crystallize at a different moment than a rest of the crystal due to the constitutional supercooling