Papers by Author: Tangali S. Sudarshan

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Authors: Eugene Y. Tupitsyn, Arul Arjunan, Robert T. Bondokov, Robert M. Kennedy, Tangali S. Sudarshan
Abstract: 4H-SiC crystals were grown using the seeded sublimation technique (modified Lely technique) in the temperature range of 1950-2200°C. The nucleation of 4H-SiC on 6HSiC has been optimized and 4H-SiC crystals of 1cm thickness were grown using 6H-SiC seeds. a-face and c-face wafers obtained from the grown boules were characterized by KOH etching, X-ray diffraction, and Raman scattering studies. Complete polytypic homogeneity of 4H SiC was obtained during growth and it was found that the 6H to 4H transition occurs in three ways: 1) without a transition layer, 2) with thick 6H-SiC layer growth, and 3) with traces of 3C SiC inclusions. The crown regions of the grown crystals exhibit an X-ray rocking curve width of 21 arcsecs.
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Authors: D.J. Ewing, Qamar-ul Wahab, Sergey P. Tumakha, Leonard J. Brillson, X.Y. Ma, Tangali S. Sudarshan, L.M. Porter
Abstract: In this study, we performed a statistical analysis of 500 Ni Schottky diodes distributed across a 2-inch, n-type 4H-SiC wafer with an epilayer grown by chemical vapor deposition. A majority of the diodes displayed ideal thermionic emission when under forward bias, whereas some diodes showed ‘double-barrier’ characteristics with a ‘knee’ in the low-voltage log I vs. V plot. X-ray topography (XRT) and polarized light microscopy (PLM) revealed no correlations between screw dislocations and micropipes and the presence of double-barrier diodes. Depth resolved cathodoluminescence (DRCLS) indicated that certain deep-level states are associated with the observed electrical variations.
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Authors: Stanislav I. Soloviev, Ying Gao, Yuri I. Khlebnikov, I.I. Khlebnikov, Tangali S. Sudarshan
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Authors: Dimitri I. Cherednichenko, Yuri I. Khlebnikov, I.I. Khlebnikov, Stanislav I. Soloviev, Tangali S. Sudarshan
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Authors: Ya Ming Fan, Li Guo Zhang, Jie Wang, Xue Min Zhang, Ze Hong Zhang, Bao Shun Zhang, Tangali S. Sudarshan
Abstract: In this work, the generation of in-grown SFs, half-moon defects, and carrot defects in SiC epilayer is studied by using epitaxy-etch-epitaxy approach. It is found that under our growth conditions, most of these defects have a similar origin, and they nucleate at obstacles to step flow at the SiC substrate/epilayer interface. These obstacles may be micropipes, scratches, or foreign particles on the substrate surface.
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Authors: Tawhid Rana, Hai Zheng Song, M.V.S. Chandrashekhar, Tangali S. Sudarshan
Abstract: Formation of particles and their effect on SiC epitaxial growth in the CVD reactor is investigated. Particle induced defects in the epilayer at different gas decomposition conditions are discussed. A higher number of pits with larger diameters are observed in the epilayer for conditions where gases decompose later in the gas injector tube (i.e. nearer to the substrate). On the other hand, the number and size of these pits reduce for the condition where gas decomposes earlier in the tube. To investigate the effect of particles during the growth, various particles with different size, shape and compositions are intentionally placed on the substrate surface before epitaxial films are grown. Samples are mapped and compared at similar locations in the pre-growth, post growth and post-etch (by molten KOH) conditions. It is found that the nature of particle induced defects depends primarily on size and shape of particles.
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Authors: Eugene Y. Tupitsyn, Alexander Galyukov, Maxim V. Bogdanov, Alexey Kulik, Mark S. Ramm, Yuri N. Makarov, Tangali S. Sudarshan
Abstract: In this work the problem of growth rate decaying during growth is considered. A new design and growth profiles are suggested in order to reduce deviations of growth parameters during the process of growth.
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Authors: J.C. Burton, F.H. Long, Yuri I. Khlebnikov, I.I. Khlebnikov, Mathew Parker, Tangali S. Sudarshan
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Authors: Serguei I. Maximenko, Jaime A. Freitas, Yoosuf N. Picard, Paul B. Klein, Rachael L. Myers-Ward, Kok Keong Lew, Peter G. Muzykov, D. Kurt Gaskill, Charles R. Eddy, Tangali S. Sudarshan
Abstract: The effect of various types of in-grown stacking faults and threading screw/edge type dislocations on carrier lifetime and diffusion lengths in 4H-SiC epitaxial films was investigated through cathodoluminescence decays and charge collection efficiencies of electron beam induced current signals at specific defects sites. Most stacking faults yielded ~40% reduction in the carrier lifetime. Moreover, drastic lifetime reductions were observed in regions containing surface triangular defects and bulk 3C polytype inclusions. Dislocations of both types serve as efficient recombination centers, though stronger reduction in diffusion lengths was observed in the vicinity of screw type dislocations.
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