Papers by Author: Charles R. Eddy

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Authors: Jian Hui Zhang, Leonid Fursin, Xue Qing Li, Xiao Hui Wang, Jian Hui Zhao, Brenda L. VanMil, Rachael L. Myers-Ward, Charles R. Eddy, D. Kurt Gaskill
Abstract: This work reports 4H-SiC bipolar junction transistor (BJT) results based upon our first intentionally graded base BJT wafer with both base and emitter epi-layers continuously grown in the same reactor. The 4H-SiC BJTs were designed to improve the common emitter current gain through the built-in electrical fields originating from the grading of the base doping. Continuously-grown epi-layers are also believed to be the key to increasing carrier lifetime and high current gains. The 4H-SiC BJT wafer was grown in an Aixtron/Epigress VP508, a horizontal hot-wall chemical vapor deposition reactor using standard silane/propane chemistry and nitrogen and aluminum dopants. High performance 4H-SiC BJTs based on this initial non-optimized graded base doping have been demonstrated, including a 4H-SiC BJT with a DC current gain of ~33, specific on-resistance of 2.9 mcm2, and blocking voltage VCEO of over 1000 V.
Authors: Jun Hu, Xiao Bin Xin, Petre Alexandrov, Jian Hui Zhao, Brenda L. VanMil, D. Kurt Gaskill, Kok Keong Lew, Rachael L. Myers-Ward, Charles R. Eddy
Abstract: This paper reports a 4H-SiC single photo avalanche diode (SPAD) operating at the solar blind wavelength of 280 nm. The SPAD has an avalanche breakdown voltage of 114V. At 90% and 95% of the breakdown voltage, the SPAD shows a low dark current of 57.2fA and 159fA, respectively. The quantum efficiency of 29.8% at 280nm and <0.007% at 400nm indicates a high UV-to-visible rejection ratio of >4300. Single photon counting measurement at 280nm shows that a single photon detection efficiency of 2.83% with a low dark count rate of 22kHz is achieved at the avalanche breakdown voltage of 116.8V.
Authors: Zachary Stum, A.V. Bolotnikov, Peter A. Losee, Kevin Matocha, Steve Arthur, Jeff Nasadoski, R. Ramakrishna Rao, O.S. Saadeh, Ljubisa Stevanovic, Rachael L. Myers-Ward, Charles R. Eddy, D. Kurt Gaskill
Abstract: Doubly-implanted SiC vertical MOSFETs were fabricated displaying a blocking voltage of 4.2kV and a specific on-resistance of 23 mΩ-cm2, on a 4.5mm x 2.25mm device. Design variations on smaller (1.1mm x 1.1mm) devices showed on-resistance as low as 17 mΩ-cm2 with a blocking voltage of 3.3kV. Analysis is presented of the on-resistance and temperature dependence (up to 175°C), as well as switching performance. Switching tests taken at 1000V and 6A showed turn-on and turn-off transients of approximately 20-40ns.
Authors: Robert E. Stahlbush, Rachael L. Myers-Ward, Brenda L. VanMil, D. Kurt Gaskill, Charles R. Eddy
Abstract: The recently developed technique of UVPL imaging has been used to track the path of basal plane dislocations (BPDs) in SiC epitaxial layers. The glide of BPDs during epitaxial growth has been observed and the role of this glide in forming half-loop arrays has been examined. The ability to track the path of BPDs through the epitaxy has made it possible to develop a BPD reduction process for epitaxy grown on 8° offcut wafers, which uses an in situ growth interrupt and has achieved a BPD reduction of > 98%. The images also provide insight into the strong BPD reduction that typically occurs in epitaxy grown on 4° offcut wafers.
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: 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.
Authors: D. Kurt Gaskill, Michael A. Mastro, Kok Keong Lew, Brenda L. VanMil, Rachael L. Myers-Ward, Ronald T. Holm, Charles R. Eddy
Abstract: A set of three 4H-SiC wafers with manufacturer specified micropipe density of 0-5 cm-2 were characterized by x-ray diffraction (XRD) maps before and after final chemical-mechanical polish. After final polish, the wafers were also investigated with atomic force microscopy, radius of curvature measurements and cross-polarization (x-pol) mapping. It was found that there was largely a lack of correlation between the XRD and x-pol maps, which strongly suggests that x-pol is insensitive to crystalline imperfections to which XRD is sensitive.
Authors: Marko J. Tadjer, Karl D. Hobart, Michael A. Mastro, Travis J. Anderson, Eugene A. Imhoff, Fritz J. Kub, Jennifer K. Hite, Charles R. Eddy
Abstract: Field-effect transistors were fabricated on GaN and Al0.2Ga0.8N epitaxial layers grown by metal organic chemical vapor deposition (MOCVD) on sapphire substrates. The threshold voltage VTH was higher when AlGaN was used as an active layer. VTH also increased with temperature due to the increased positive polarization charge at the GaN/AlN buffer/sapphire interfaces. Drain current increased at high temperatures even with more positive threshold voltage, which makes GaN-based FET devices attractive for high temperature operation.
Authors: Virginia D. Wheeler, Brenda L. VanMil, Rachael L. Myers-Ward, S. Chung, Yoosuf N. Picard, Marek Skowronski, Robert E. Stahlbush, Nadeemullah A. Mahadik, Charles R. Eddy, D. Kurt Gaskill
Abstract: The effectiveness of an in-situ growth interrupt in nitrogen doped 8° off-cut epilayers was investigated using ultraviolet photoluminescence imaging. Low-doped n-type epilayers (<1016 cm-3) exhibited an abrupt increase in BPD to TED conversion at the growth interrupt and achieved 96-99% conversion overall (< 10 BPDs/cm-2), while high-doped epilayers had minimal conversion at the interrupt (< 1%) and overall (< 30%). This large discrepancy suggests nitrogen prohibits or alters the conversion mechanism at the growth interrupt. Therefore, a novel SEM technique was developed to "freeze-in" the interface morphology and help elucidate the conversion mechanism. Preliminary results suggest that preferential etching at the point of BPD intersection with the surface is greatly reduced in highly doped layers, which inhibits the conversion mechanism.
Authors: Travis J. Anderson, Karl D. Hobart, Luke O. Nyakiti, Virginia D. Wheeler, Rachael L. Myers-Ward, Joshua D. Caldwell, Francisco J. Bezares, D. Kurt Gaskill, Charles R. Eddy, Francis J. Kub, Glenn G. Jernigan, M.J. Tadjer, Eugene A. Imhoff
Abstract: Graphene, a 2D material, has motivated significant research in the study of its in-plane charge carrier transport in order to understand and exploit its unique physical and electrical properties. The vertical graphene-semiconductor system, however, also presents opportunities for unique devices, yet there have been few attempts to understand the properties of carrier transport through the graphene sheet into an underlying substrate. In this work, we investigate the epitaxial graphene/4H-SiC system, studying both p and n-type SiC substrates with varying doping levels in order to better understand this vertical heterojunction.
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