Papers by Author: S.A. Kitt

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Authors: Brenda L. VanMil, Robert E. Stahlbush, Rachael L. Myers-Ward, Yoosuf N. Picard, S.A. Kitt, J.M. McCrate, S.L. Katz, D. Kurt Gaskill, Charles R. Eddy
Abstract: Conversion of basal plane dislocations (BPD) to threading edge dislocations (TED) in 8° off-cut 4H-SiC within an n+ buffer layer would eliminate the nucleation site for Shockley-type stacking faults in active device regions grown on such buffer layers. To that end, the propagation and conversion of BPDs through in situ growth interrupts is monitored using ultraviolet photoluminescence (UVPL) wafer mapping. The optimized growth interrupt scheme lasts for 45 minutes with a propane mass flow of 10 sccm at growth temperature. This scheme has shown a conversion efficiency of up to 99% for samples with electron (hole) concentrations < 5x1014 cm-3 (8x1015 cm-3). Samples subjected to a 45 or 90 minute interrupt under 10 sccm of propane, regardless of conversion efficiency, exhibit a “slit” in the surface morphology associated with each BPD and oriented perpendicular to the off-cut and BPD propagation direction. Repetition of the optimal interrupt sequence with a 5 μm epilayer spacer grown between the two interrupts resulted in the same conversion efficiency as a single optimal growth interrupt. Incorporation of the optimal interrupt into an n+ layer is more complicated as attempts to do so in layers doped with nitrogen to 2x1018, 2x1017 and 2x1016 cm-3 resulted in conversion efficiencies of ~6%.
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.
Authors: Rachael L. Myers-Ward, Brenda L. VanMil, Robert E. Stahlbush, S.L. Katz, J.M. McCrate, S.A. Kitt, Charles R. Eddy, D. Kurt Gaskill
Abstract: Epitaxial layers were grown on 4° off-axis 4H-SiC substrates by hot-wall chemical vapor deposition. The reduced off-cut angle resulted in lower basal plane dislocation (BPD) densities. The dependence of BPD reduction on growth conditions was investigated using ultraviolet photoluminescence (UVPL) imaging. With this method, it was found that the dislocations were converting to threading edge dislocations throughout the thickness of the film. A high (≥ 97%) conversion efficiency was found for all films grown with this orientation. A conversion of 100% was achieved for several films without pre-growth treatments or growth interrupts.
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