Synchrotron radiation which is emitted into a narrow cone and which has a continuous spectrum was succesfully used in X‐ray topography. The exposure time to take a set of topographs (a transmission Laue pattern) from a silicon crystal on a fine grain film with a geometric resolution of a few microns turned out to be as short as some seconds. As an example for the use of the new method the contrast formation of a defect in the Laue pattern of topographs was analysed in detail. For this purpose the relative integrated intensities of different orders of reflections were calculated. They and the calculated values of extinction distances were used to estimate the image width of a dislocation whose Burgers vector could be determined.

The electrical degradation of 4H–SiC PiN diodes has recently attracted much interest and is a critical material problem for high power applications. The degradation is caused by stacking faults observed as an increased forward voltage drop after forward injection operation. In this article we have combined electrical, optical, and structural techniques to study the formation and growth of the stacking faults causing degradation. We will show three different sources causing two different types of stacking fault properties.

4H-SiC commercial wafers and sublimation grown epitaxial layers with a thickness of 100 μm have been studied concerning crystalline structure. The substrates and the epitaxial layers have been separately investigated by high-resolution x-ray diffraction and synchrotron white beam x-ray topography. The results show that the structural quality was improved in the epitaxial layers in the [112̄0] and [1̄100] directions, concerning domain distribution, lattice plane misorientation, mosaicity, and strain, compared with the substrates. Misoriented domains have merged together to form larger domains while the tilt between the domains was reduced, which resulted in nonsplitting in diffraction curves. If the misorientation in the substrate is large, we can only see a slight decrease in the misorientation in the epilayer. At some positions on the substrates block structures (mosaicity) were observed. ω-rocking curves showed smaller full width at half maximum values and more uniform and narrow peaks, while the curvature was almost the same in grown epilayers compared with the corresponding substrates. We show that threading edge dislocations along the c axis in silicon carbide grown crystals transform to deflected dislocations in the epilayer. A formation mechanism for deflected dislocations and supporting facts are presented. We further show that these deflected dislocations are one possible source for the creation of stacking faults that recently has been reported to cause degradation in processed SiC bipolar diodes.

Triangular structural defects are occasionally generated during the long-term operation of 4H-SiC pin diodes and degrade the forward characteristics of the diode. We have used synchrotron white beam x-ray topography, scanning electron microscopy, in situ cathodo luminescence, and transmission electron microscopy to characterize the structure and formation of these defects. It is shown that the defects are stacking faults on the (0001) basal planes, bound by partial dislocations with Burgers vectors 1/3〈101̄0〉 and 1/3〈011̄0〉. These partials are suggested to form by the dissociation of existing dislocations.

and Deutsches Elektronen-Synchrotron DES Y, Hamburg ( b )The reflectivity of Se and Te single crystals has been measured a t near normal incidence for photon energies between 3 and 30 eV with the electric field vector lying parallel and perpendicular t o the c-axis of the crystals. The measurements were made using the polarized continuum of the synchrotron radiation of DESY. A Kramers-Kronig analysis gave the optical constants for both directions of polarization. For both substances electron energy loss measurements are reported. Comparison with optical data gives satisfactory agreement. Even at high energies considerable anisotropic behaviour and several new spectral features are observed. They are discussed i n terms of recent. band structure calculations.Die Reflektivitat von Se-und Te-Einkristallen wurde fur Photonenenergien zwischen 3 und 30 eV bei nahezu senkrechtem Einfall mit dem elektrischen Feldvektor parallel und senkrecht zur c-Achse der Kristalle gemessen. Fiir diese Experimente wurde das polarisierte Kontinuum der Synchrotronstrahlung von DESY benutzt. Eine Kramers-Kronig Analyse lieferte die optischen Konstanten fur beide Polarisationsrichtungen. Fur beide Substanzen wird iiber Elektronenenergieverlustmessungen berichtet. Der Vergleich mit den optischen Daten ergibt eine befriedigende Ubereinstimmung. Auch bei hohen Energien werden fiir beide Substanzen ein betriichtliches anisotropes Verhalten und niehrere neue Strukturen beobachtet. Sie werden a n Hand von neuen Bandstruktur-Rechnungen diskutiert.