Simulation of Grazing-Incidence Synchrotron X-ray Topographic Images of Threading c+a Dislocations in 4H-SiC
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Simulation of Grazing-Incidence Synchrotron X-ray Topographic Images of Threading c+a Dislocations in 4H-SiC Fangzhen Wu1, Shayan Byrappa1, Huanhuan Wang1, Yi Chen1, Balaji Raghothamachar1, Michael Dudley1,a, Edward K. Sanchez2,b, Gil Chung2, Darren Hansen2, Stephan G. Mueller2 and Mark J. Loboda2 1 Department of Materials Science and Engineering, Stony Brook University, Stony Brook, New York, 11794, USA 2 Dow Corning Compound Semiconductor Solutions, Midland, Michigan, 48686, USA a [email protected], b [email protected] ABSTRACT Synchrotron X-ray topography (SXRT) of various geometries has been successfully utilized to image c+a dislocations in 4H-SiC crystals. Although molten potassium hydroxide(KOH) can be used to reveal the location of such dislocations, it is not possible to determine their senses or their Burgers vector magnitude. A simple, non-destructive method has been proposed to determine the Burgers vector of these c+a dislocations called the ray tracing simulation, which has been successfully implemented previously in revealing the dislocation sense and magnitude of micropipes, closed-core threading screw dislocations (TSDs) and threading edge dislocations (TEDs) in 4H-SiC. In this paper, grazing incidence topography is performed using the monochromatic beam for the horizontally cut wafers to record pyramidal reflections of 11-28 type. Ray tracing simulation has been successfully implemented to correlate the simulated images with experimental images which are discussed in the paper. INTRODUCTION Recently we reported SXRT studies on axial slices cut from 4H-SiC PVT-grown boules which unambiguously proved the existence of threading dislocations with Burgers vector of c+a. [1]. However, cutting such axial slices while good for research purposes is not economical as it is destructive to the boule. Recently we also reported observations carried out on commercial offcut (0001) wafers of complex stacking faults with fault vectors such as s+c/2 and s+c/4 which was interpreted as indirect evidence for the existence of threading dislocations with Burgers vector of c+a [2,3,4]. The formation mechanism of these faults involved the deflection of threading c+a dislocations onto the basal plane. For those threading c+a dislocations that go through the wafer, interaction with the surface must exist and evidence to reveal the character must exist if suitable characterization technique can be used. Etching is widely used to characterize the defects in SiC crystals, but no evidence to date has been found to support the existence of threading c+a dislocations. This may simply be due to the fact that the stress field associated with the ccomponent of Burgers vector is much stronger than that of a-component so that the etching associated with the c-component may mask that of the a-component. On the other hand, synchrotron x-ray topography, which has much higher resolution than traditional x-ray topography, is sensitive to the detailed stress field associated with defects. Back reflection and grazing inc
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