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Now showing items 1 - 16 of 114

  • Study of spiral growth on 4H-silicon carbide on-axis substrates

    Masumoto, Keiko   Kojima, Kazutoshi   Okumura, Hajime  

    We grew epitaxial layers on on-axis carbon-face 4H-silicon carbide substrates and investigated the growth conditions for the generation of spiral growth. We discovered that spiral growth occurs in regions where the local off-angle is less than 0.05 degrees and when the spiral hillocks have a tilt angle of 0.06 degrees. Moreover, we found that each spiral hillock coalesced without causing dislocation in the areas where the spiral growth occurred. Our results indicate that spiral growth is dominant when the spiral hillocks have a tilt angle greater than the off-angle of the substrate. Step-flow growth is overcome by spiral growth because the rate of spiral growth is greater than that of step-flow growth. (C) 2017 Elsevier B.V. All rights reserved.
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  • Investigation of V-shaped extended defects in a 4H-SiC epitaxial film

    Tochigi, Eita   Matsuhata, Hirofumi   Yamaguchi, Hirotaka   Sekiguchi, Takashi   Okumura, Hajime   Ikuhara, Yuichi  

    We investigated two types of V-shaped extended defects on the basal plane in epitaxial 4H-SiC by synchrotron X-ray topography, photoluminescence imaging/spectroscopy and transmission electron microscopy (TEM). One is the (2, 5) stacking fault (in Zhdanov notation) bounded by two partial dislocations with the Burgers vector b +/- 1/4[0001]; the other is the (2, 3, 3, 5) stacking fault bounded by partial dislocations with b =3D+/- 1/4[0001]. The core of the partial dislocations associated with the (2, 3, 3, 5) fault has an out-of-plane component (Frank component) and three in-plane components (Shockley components); the three Shockley components are cancelled out in total. The electronic structures of the (2, 5) and (2, 3, 3, 5) stacking faults were further examined by photoluminescence spectroscopy and first-principles calculations. It is suggested that the (2, 5) and (2, 3, 3, 5) stacking faults both have an interband state at a similar energy level, although they differ structurally.
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  • Modeling of Al Doping During 4H-SiC Chemical-Vapor-Deposition Trench Filling

    Mochizuki, Kazuhiro   Kosugi, Ryoji   Yonezawa, Yoshiyuki   Okumura, Hajime  

    Aluminum doping during 4H-SiC chemical-vapor-deposition (CVD) trench filling was numerically modeled toward precise design of high-voltage superjunction devices. As a first-order approximation, growth-rate- and surface-normal-scaling functions were determined based on the reported experimental results. Simulated isoconcentration contours of aluminum were confirmed to qualitatively agree with the reported imaging of doping in SiC by scanning spreading resistance microscopy. Improvement of the proposed models based on additional experiments should contribute to reducing the development time for 4H-SiC superjunction devices fabricated using CVD trench filling.
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  • Raman characterization of damaged layers of 4H-SiC induced by scratching

    Nakashima, Shin-ichi   Mitani, Takeshi   Tomobe, Masaru   Kato, Tomohisa   Okumura, Hajime  

    Recent development of device fabrication of SiC is awaiting detailed study of the machining of the surfaces. We scratched 4H-SiC surfaces with a sliding microindenter made of a SiC chip, and characterized machining affected layers by micro-Raman spectroscopy. The results of the Raman measurement of the scratching grooves revealed that there were residual stress, defects, and stacking faults. Furthermore, with heavy scratching load, we found clusters of amorphous SiC, Si, amorphous carbon, and graphite in the scratching grooves. Analysis of the Raman spectra showed that SiC amorphization occurs first and surface graphitization (carbonization) is subsequently generated through the phase transformation of SiC. We expect that the Raman characterization of machined surfaces provides information on the machining mechanism for compound semiconductors. (C) 2016 Author(s). All article content, except where otherwise noted, is licensed under a Creative Commons Attribution (CC BY) license (
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  • 3.3-kV-Class 4H-SiC MeV-Implanted UMOSFET With Reduced Gate Oxide Field

    Harada, Shinsuke   Kobayashi, Yusuke   Ariyoshi, Keiko   Kojima, Takahito   Senzaki, Junji   Tanaka, Yasunori   Okumura, Hajime  

    A critical issue for SiC trench gate metal-oxide-semiconductor field-effect transistors (UMOSFETs) is gate oxide shielding from the electric field at the trench bottom. In this letter, low ON-resistance with low gate electric field was achieved in a 3.3-kV-class UMOSFET with a unique hexagonal buried p-base region formed by MeV ion implantation. The shielding effect was further enhanced by a self-aligned trench bottom shielding region. The specific ON-resistance, with and without the trench bottom shielding region, was 8.3 and 9.4 m Omega cm(2), respectively. The blocking voltage in each case was similar to 3800 V. The electric field in the gate oxide with the trench bottom shielding region was reduced to 2.5 MV/cm at 3300 V.
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    Provided is an electronic apparatus whereby it is possible to differentiate between a state of emitting a vibrating sound such as is communicated via a portion of a person's body and a state of not emitting the vibrating sound. An electronic apparatus (1) comprises: a vibration element (30) which deforms when a voltage is imparted; and a first vibration part (90) which can operate in a first state wherein the vibrating sound which is communicated via the portion of the person's body is not emitted even if the vibration element (30) deforms, and a second state wherein the vibrating sound which is communicated via the portion of the person's body is emitted by the deformation of the vibration element (30).
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  • Development of Ultrahigh-Voltage SiC Devices

    Fukuda, Kenji   Okamoto, Dai   Okamoto, Mitsuo   Deguchi, Tadayoshi   Mizushima, Tomonori   Takenaka, Kensuke   Fujisawa, Hiroyuki   Harada, Shinsuke   Tanaka, Yasunori   Yonezawa, Yoshiyuki   Kato, Tomohisa   Katakami, Shuji   Arai, Manabu   Takei, Manabu   Matsunaga, Shinichiro   Takao, Kazuto   Shinohe, Takashi   Izumi, Toru   Hayashi, Toshihiko   Ogata, Syuuji   Asano, Katsunori   Okumura, Hajime   Kimoto, Tsunenobu  

    Ultrahigh-voltage silicon carbide (SiC) devices [p-i-n diodes and insulated-gate bipolar transistors (IGBTs)] and switching test have been investigated. As a result, we have succeeded in developing a 13-kV p-i-n diode, 15-kV p-channel IGBT, and 16-kV flip-type n-channel implantation and epitaxial IGBT with a low differential specific on-resistance (R-diff,R-on). It was revealed that a power module fabricated using a nanotech resin, Si3N4 ceramic substrate, and W base plate was suitable for ultrahigh voltage and high temperature. A switching test was carried out using a clamped inductive load circuit, which indicated that the energy loss of a circuit with ultrahigh-voltage SiC devices is lower than that of Si devices.
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  • A roadmap for future wide bandgap semiconductor power electronics

    Okumura, Hajime  

    Energy savings and efficient usage of electric power are some of the most urgent issues for future sustainable development of human society. Power electronics is recognized as a key technology in this regard, and the innovation of power electronics is increasingly required. The important role of power electronics innovations in the future human society and a technology roadmap of power electronics utilizing wide bandgap semiconductors, which are typically represented by silicon carbide, are presented. This roadmap consists of several different domains in technology, from the materials side to the applications side. On this roadmap, three generations are defined as technological streams. Based on this roadmap, recent progress in silicon carbide power electronics is reviewed, and future prospects are discussed.
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    In this electronic apparatus, which is provided with a panel that constitutes external appearance, and which oscillates the panel, the oscillation of the panel is not easily disturbed, and dust resistance and water resistance are improved. An electronic apparatus (1) is provided with: a rectangular touch panel (20); an oscillating unit (50), which oscillates the touch panel (20); and supporting members (10a, 10b), which have the touch panel (20) disposed therein, and cover the front surface circumferential end portions of the touch panel (20). The electronic apparatus is characterized in that elastic members (70) are provided between two end side portions facing each other and the supporting members (10a, 10b), said elastic members being on the front surface of the touch panel (20), and that a flexible seal members (40) are press-fitted between the rest of the two end side portions facing each other and the supporting members (10a, 10b), said seal members being on the rear surface of the touch panel (20).
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  • Characterization of scraper-shaped defects on 4H-SiC epitaxial film surfaces

    Sako, Hideki   Yamashita, Tamotsu   Sugiyama, Naoyuki   Sameshima, Junichiro   Ishiyama, Osamu   Tamura, Kentaro   Senzaki, Junji   Matsuhata, Hirofumi   Kitabatake, Makoto   Okumura, Hajime  

    We have found undiscovered defects on a 4H-SiC epitaxial layer, the shape of which resembles a scraper in images taken by confocal differential interference contrast optical microscopy. The surface morphological structure and formation mechanism of the scraper-shaped defects were investigated by atomic force microscopy and grazing incidence monochromatic synchrotron X-ray topography, respectively. The scraper-shaped defects were surface morphological defects consisting of surface asperity and were caused by the migration of interfacial dislocations. The evaluation of the thermal oxide reliability of metal oxide semiconductor capacitors fabricated on these defects was performed by time-dependent dielectric breakdown measurement. The degradation of thermal oxide occurred only on the downstream line of the scraper-shaped defects. The thickness of the oxide layer on these defects was also investigated using cross-sectional transmission electron microscopy. (C) 2014 The Japan Society of Applied Physics
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  • Effects of interface state density on 4H-SiC n-channel field-effect mobility

    Yoshioka, Hironori   Senzaki, Junji   Shimozato, Atsushi   Tanaka, Yasunori   Okumura, Hajime  

    We investigated the effects of D-IT at the interface between SiO2 and Si-, C-, and a-face 4H-SiC in n-channel metal-oxide-semiconductor field-effect transistors (MOSFETs) that were subjected to dry/nitridation and pyrogenic/hydrotreatment processes. D-IT at E-C - E-T = 0.2 eV was evaluated by the C - psi(S) method using MOS capacitors and was accurately reflected in the subthreshold slope of the MOSFETs. The peak field-effect mobility was inversely proportional to D-IT. The mobility for the a-face MOSFETs was 1.5 times or more higher than the other faces mobilities, indicating that mobility limiting factors other than D-IT(0.2 eV) may exist for the Si- and C-face interfaces. (C) 2014 AIP Publishing LLC.
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  • Comparison of dislocation behavior in Si- and C-face 4H-SiC

    Chen, Bin   Matsuhata, Hirofumi   Sekiguchi, Takashi   Ohyanagi, Takasumi   Kinoshita, Akimasa   Okumura, Hajime  

    The dislocation behavior in C-face 4H-SiC homoepitaxial films was studied by using electron-beam-induced current (EBIC) technique and is compared with that in Si-face ones. For the basal plane dislocations (BPDs) with the same line shape appearing in the EBIC images, the mobile partial dislocations (PDs) originated from the dissociation of such BPDs move in two opposite directions, while they move in one direction in the Si-face samples. The difference of the PD movement between two faces is discussed. (C) 2011 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim
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  • Investigation of Low Off-Angled 4H-SiC Epitaxial Wafers for Power Device Applications

    Kojima, Kazutoshi   Masumoto, Keiko   Asamizu, Hirokuni   Harada, Shinsuke   Okumura, Hajime  

    We investigated the potential of low off angled 4H-SiC epitaxial wafers for use in power device applications. To this end, we successfully grew epitaxial layers on 2 degree off-angled and vicinal 4H-SiC Si-face substrate with good surface morphology and low defects density. Schottky diodes, metal oxide semiconductor (MOS) capacitors, and trench metal oxide semiconductor field effective transistors (MOSFETs) were fabricated on these epitaxial layers, and we investigated their characteristics. The results were comparable, with respect to the Schottky diodes and trench MOSFETs and the reliability of MOS capacitors, to those for similar devices fabricated on 4 degree off-angled 4H-SiC Si-face epitaxial wafers. These results suggest that low off-angled 4H-SiC Si-face epitaxial wafers may be effectively utilized in power device applications. (C) 2017 The Electrochemical Society. All rights reserved.
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  • AlN bulk crystal growth by sublimation method

    Kato, Tomohisa   Nagai, Ichiro   Miura, Tomonori   Kamata, Hiroyuki   Naoe, Kunihiro   Sanada, Kazuo   Okumura, Hajime  

    In this study, we report the growth of aluminum nitride (AlN) bulk single crystals by the sublimation method. The crystals were grown in a newly designed TaC crucible. The crucible has a TaC guard ring around the seed crystal to protect against polycrystal deposition around the seed crystal during the initial growth stage. The ring enhances lateral enlargement growth because it protects against the polycrystal deposition. The (0001) oriented AlN crystals were grown on (0001) SiC and (0001) AlN seed crystals. The largest grown crystal was 43 mm in diameter. The best quality area on the grown AlN crystal had the lowest etch pit density of 1x10(-4)cm(-2). (C) 2010 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim
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  • Hopping conduction range of heavily Al-doped 4H-SiC thick epilayers grown by CVD

    Ji, Shiyang   Eto, Kazuma   Yoshida, Sadafumi   Kojima, Kazutoshi   Ishida, Yuuki   Saito, Shingo   Tsuchida, Hidekazu   Okumura, Hajime  

    To outline the hopping conduction range, the electrical characteristics of CVD-grown heavily Al-doped 4H-SiC thick epilayers (2.0 x 10(19)-4.0 x 10(20) cm(-3)) were investigated in a wide temperature regime (20-900 K). It is found that, below 100 K, hopping conduction dominates the carrier transport for all epilayers, and the corresponding hopping conduction activation energy shows a maximum of similar to 30 meV at around 1.1 x 10(20) cm(-3). With increasing doping level, the temperature dependence of resistivity evolves and finally obeys the similar to 1/T-1/4 law in the entire temperature regime, which gives direct evidence of variable-range hopping conduction. (C) 2015 The Japan Society of Applied Physics
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  • AlN bulk single crystal growth on 6H-SiC substrates by sublimation method

    Nagai, Ichiro   Kato, Tomohisa   Miura, Tomonori   Kamata, Hiroyuki   Naoe, Kunihiro   Sanada, Kazuo   Okumura, Hajime  

    Large and thick AlN bulk single crystals up to 43 mm in diameter and 10 mm in thickness have been successfully grown on 6H-SiC (0 0 0 1) substrates by the sublimation method using a TaC crucible. Raman spectrum indicates that the polytype of the grown AlN single crystals is a Wurtzite-2H type structure, and the crystals do not include any impurity phases. The quality at the top of the crystal improves as crystal thickness increases along the < 0 0 0 1 > direction during growth: a low etch pit density (7 x 10(4) cm(-2)) and a small full width at half maximum for a 0002 X-ray rocking curve (58 arcsec) have been achieved at a thickness of similar to 8 mm. The possible mechanism behind the improvement in the AlN crystal quality is also discussed. (C) 2010 Elsevier B.V. All rights reserved.
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