Papers by Author: Joseph L. Tedesco

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Authors: Brenda L. VanMil, Rachael L. Myers-Ward, Joseph L. Tedesco, Charles R. Eddy, Glenn G. Jernigan, James C. Culbertson, Paul M. Campbell, J.M. McCrate, S.A. Kitt, D. Kurt Gaskill
Abstract: Graphene layers were created on both C and Si faces of semi-insulating, on-axis, 4H- and 6H-SiC substrates. The process was performed under high vacuum (<10-4 mbar) in a commercial chemical vapor deposition SiC reactor. A method for H2 etching the on-axis substrates was developed to produce surface steps with heights of 0.5 nm on the Si-face and 1.0 to 1.5 nm on the C-face for each polytype. A process was developed to form graphene on the substrates immediately after H2 etching and Raman spectroscopy of these samples confirmed the formation of graphene. The morphology of the graphene is described. For both faces, the underlying substrate morphology was significantly modified during graphene formation; surface steps were up to 15 nm high and the uni-form step morphology was sometimes lost. Mobilities and sheet carrier concentrations derived from Hall Effect measurements on large area (16 mm square) and small area (2 and 10 m square) samples are presented and shown to compare favorably to recent reports.
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Authors: Charles R. Eddy, Ping Wu, Ilya Zwieback, Brenda L. VanMil, Rachael L. Myers-Ward, Joseph L. Tedesco, Andrew E. Souzis, D. Kurt Gaskill
Abstract: Knoop microhardness assessments were conducted on a variety of 6H- and 4H-SiC substrates to assess any appreciable differences that may need to be considered in wafer manufacture and general application. Nitrogen-doped, vanadium-doped and unintentionally doped (UID) substrates with both on-axis and 8° off-axis orientations were assessed. In general, the Knoop hardness values fell in the 2000 to 2500 kg/mm2 range (equivalent to approximately 20 to 25 GPa). Hardness values measured in the <1100> crystal direction were significantly higher than in the <11-20> direction. Undoped and vanadium-doped samples were harder than nitrogen-doped samples. For both 6H and 4H nitrogen-doped samples, the hardness was as much as 10% higher for 8° offcut wafers than for on-axis.
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Authors: D. Kurt Gaskill, Jennifer K. Hite, James C. Culbertson, Glenn G. Jernigan, Joseph L. Tedesco, Luke O. Nyakiti, Virginia D. Wheeler, Rachael L. Myers-Ward, N.Y. Garces, Charles R. Eddy
Abstract: The growth of epitaxial graphene on C-face 6H-SiC substrates is investigated using pro-cess conditions that can form small, local areas of graphene. The thickness of SiC lost to Si sublimation is not completely countered by the thickness of the resulting graphene and so graphene-covered basins (GCBs) are formed. The GCBs are most likely nucleated at threading dislocations from the substrate. The GCB morphology exhibits ridges, similar to those found on continuous films. The GCBs expand through erosion of the surrounding SiC substrate walls, eventually coalescing into continuous films. The ratio of the Raman D and G peaks was used to estimate the crystallite length scale and it was found to be about 200 nm for small GCBs and > 1 m for continuous films.
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Authors: Nadeemullah A. Mahadik, Robert E. Stahlbush, Syed B. Qadri, Orest J. Glembocki, Dimitri A. Alexson, Rachael L. Myers-Ward, Joseph L. Tedesco, Charles R. Eddy, D. Kurt Gaskill
Abstract: The structure of various inclusions in SiC epitaxial layers grown on 4o offcut substrates was investigated using three advanced techniques. Using micro-Raman spectroscopy, the observed inclusions exhibited a complex structure having either different SiC polytypes like 3C or 6H or they were misoriented 4H-SiC inclusions. The UVPL images showed dislocations and other extended defects around the inclusion-related defects, and strain fields were observed in the x-ray topographs near the defect sites. Spectral UVPL imaging shows features with varying luminescence inside the inclusion related defects which propagate and may cause deformation in the crystalline structure and lead to non-radiative recombination centers within the defect.
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Authors: Joshua D. Caldwell, Travis J. Anderson, Karl D. Hobart, James C. Culbertson, Glenn G. Jernigan, Fritz J. Kub, Joseph L. Tedesco, Jennifer K. Hite, Michael A. Mastro, Rachael L. Myers-Ward, Charles R. Eddy, Paul M. Campbell, D. Kurt Gaskill
Abstract: Epitaxial graphene (EG) grown on the carbon-face of SiC has been shown to exhibit high carrier mobilities, in comparison to other growth techniques amenable to wafer-scale graphene fabrication. The transfer of large area (>mm2) graphene films to substrates amenable for specific applications is desirable. We demonstrate the dry transfer of EG from the C-face of 4H-SiC onto SiO2, GaN and Al2O3 substrates via two approaches using either 1) thermal release tape or 2) a spin-on, chemically-etchable dielectric. We will report on the impact that these transfer processes has upon the electrical properties of the transferred EG films.
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