Papers by Author: Zlatko Sitar

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Authors: Balaji Raghothamachar, Rafael Dalmau, Michael Dudley, Raoul Schlesser, Dejin Zhuang, Ziad Herro, Zlatko Sitar
Abstract: Using a combination of synchrotron white beam x-ray topography (SWBXT) and high resolution x-ray diffraction (HRXRD), the structural quality of AlN crystals grown by various sublimation-based techniques have been non-destructively analyzed. Spontaneously nucleated AlN crystals are characterized by very low defect densities but their size is small. Self-seeding results in nucleation of multiple grains of different orientations, a few of which are of good quality while most are highly strained. Using readily available commercial 4H and 6H-SiC substrates, several growth runs have been carried out using different growth conditions to obtain thick AlN layers, either attached to the seed or free-standing. While attached layers are typically cracked and highly strained, crack-free free-standing layers can be obtained by delamination or SiC decomposition. X-ray characterization reveals these crystals have good purity but moderately high defect densities.
Authors: Z. Gu, J.H. Edgar, Balaji Raghothamachar, Michael Dudley, Dejin Zhuang, Zlatko Sitar
Abstract: The benefits of depositing AlN-SiC alloy transition layers on SiC substrates before the seeded growth of bulk AlN crystals were determined. The presence of the AlN-SiC alloy layer helped to suppress the SiC decomposition by providing vapor sources of silicon and carbon. It enabled a higher growth temperature, and hence a higher growth rate. In addition, cracks in the final AlN crystals can be decreased because of the intermediate lattice constants and thermal expansion coefficient of AlN-SiC alloy. AlN-SiC alloys were first grown on off-axis SiC substrates by the sublimation-recondensation method. Then pure AlN crystals were grown upon those. For comparison, AlN crystals were directly grown on SiC substrates under similar conditions. X-ray diffraction (XRD) confirmed the formation of a pure single crystalline AlN layer upon the AlN-SiC alloy on SiC substrate. The presence of an AlN-SiC transition layer effectively inhibited the appearance of cracks in the resultant AlN crystals. X-ray topography (XRT) demonstrated that the thick AlN layer effectively released the strain present.
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