Investigation of Low Angle Grain Boundaries in Hexagonal Silicon Carbide
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Investigation of Low Angle Grain Boundaries in Hexagonal Silicon Carbide Yi Chen1, Hui Chen1, Ning Zhang1, Michael Dudley1, and Ronghui Ma2 1 Materials Science and Engineering, Stony Brook University, Stony Brook, NY, 11794-2275 2 Mechanical Engineering, University of Maryland Baltimore County, Baltimore, MD, 21250
ABSTRACT Interaction between basal plane dislocations and single or well-spaced threading dislocations is discussed based on synchrotron white beam X-ray topographic studies carried out on physical vapor transport grown hexagonal silicon carbide single crystals. The basal plane dislocations are able to cut through single or well-spaced threading edge dislocations even if the formation of kinks/jogs is energetically unfavorable while threading screw dislocations were mostly observed to act as effective pinning points. However, basal plane dislocations can sometimes cut through a threading screw dislocation, forming a superjog and which subsequently migrates on the prismatic plane via a cross-slip process. Threading edge dislocation walls act as obstacles for the glide of basal plane dislocations and the mechanism by which this occurs is discussed. The character of low angle grain boundaries and their dislocation content are discussed. INTRODUCTION The group-III nitrides are of great interest due to their promising application in the fabrication of blue light emitting diodes. Silicon carbide (SiC) is widely used as a substrate for III-Nitride epitaxy due to its relatively small lattice mismatch (~3.4%). The threading dislocations (TDs) existing in the SiC substrates, e.g., threading screw dislocations (TSDs) and threading edge dislocations (TEDs), will undoubtedly affect the quality of the III-Nitride epilayers. The use of vicinal SiC rather than c-cut substrates has been reported to lead to reduced TD density1 and improved strain relaxation in gallium nitride (GaN) epilayers2. The low angle grain boundaries (LAGBs) widely present in SiC substrates, which are composed of aggregated BPDs and TDs, are known to influence the microstructure in GaN epilayers3. Therefore, studying the properties and behavior of LAGBs and associated dislocations in SiC can play a critical role in understanding their influence on GaN epitaxy and may lead to insights into strategies aimed at mitigating their negative effects. Experiment The samples used in this study were commercially available 4H-SiC substrates grown by the physical vapor transport (PVT) technique. Transmission and grazing incidence synchrotron white beam X-ray topography (SWBXT) images were recorded at the Stony Brook Synchrotron Topography Station, Beamline X-19C, at the National Synchrotron Light Source at Brookhaven National Laboratory, using Agfa Structurix D3-SC film at specimen-to-film distances between 10 and 15 cm. The Si-face was always the X-ray exit surface.
RESULTS AND DISCUSSION Interaction between a BPD and a single/well-spaced TD BPDs are mostly nucleated at the outer region of the as-grown SiC boules which contain polytype inclusion
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