─ 8 ─(4) Both as-deposited Ni and Pd electrodes show poor con-ductivity.(5) Heat treatment at 673 K for 3.6 ks improves the conductiv-ity at high voltage. The conductivity is improved further by application of 30 V between the electrodes during the heat treatment. (6) Ni electrodes achieve higher conductivity than Pd elec-trodes. 4. ConclusionsThe present study proposed and demonstrated strategies for designing low-contact-resistance electrodes on two represen-tative wide bandgap compound semiconductors, SiC and GaN, both of which are required in the next generation power electronics. The strategies and methods were newly proposed, based on rm materials science. The points to control the ma-terials behavior and to lead the materials to the preferred state are presented.AcknowledgmentThe present study was nancially supported by JSPS KAK-ENHI Grant Number 26420702.References1)L. D. Madsen: Formation of Ohmic contacts to α-SiC and their impact on devices, Journal of Electronic Mate-rials, 30 (2001), 1353-1360.2)R. J. Trew, M. W. Shin and V. Gatto: High power appli-cations for GaN-based devices, Solid-State Electronics, 41 (1997), 1561-1567.3)L. M. Porter and R. F. Davis: A critical review of Ohmic and rectifying contacts for silicon carbide, Materials Sci-ence and Engineering: B, 34 (1995), 83-105.4)S.-K. Lee, C.-M. Zetterling, M. Östling, J.-P. Palmquist and U. Jansson: Low resistivity Ohmic contacts on 4H-silicon carbide for high power and high temperature device applications, Microelectronic Engineering, 60 (2001), 261-268.5)S. Tsukimoto, K. Nitta, T. Sakai, M. Moriyama and M. Murakami: Correlation between the electrical properties and the interfacial microstructures of TiAl-based Ohmic contacts to p-type 4H-SiC, Journal of Electronic Materi-als, 33 (2004), 460-466.6)A. N. Bright, D. M. Tricker, C. J. Humphreys and R. Da-vies: A transmission electron microscopy study of micro-structure evolution with increasing annealing temperature in Ti/Al Ohmic contacts to n-GaN, Journal of Electronic Materials, 30 (2001), L13-L16.7)R. Wenzel, G. G. Fischer and R. Schmid-Fetzer: Ohmic contacts on p-GaN (Part I): investigation of different contact metals and their thermal treatment, Materials Science in Semiconductor Processing, 4 (2001), 357-365.8)S. N. Mohammad: Contact mechanisms and design prin-ciples for alloyed Ohmic contacts to p-type GaN, Philo-sophical Magazine, 84 (2004), 2559-2598.9)S. Tanimoto, M. Miyabe, T. Shiiyama, T. Suzuki, H. Ya-maguchi, S. Nakashima and H. Okumura: Toward a bet-ter understanding of Ni-based ohmic contacts on SiC, Materials Science Forum, 679-680 (2011), 465-468. 10)B. Pécz: Contact formation in SiC devices, Applied Sur-face Science, 184 (2001), 287-294. 11)C. Arvieu, J. P. Manaud and J. M. Quenisset: Interaction between titanium and carbon at moderate temperatures, Journal of Alloys and Compounds, 368 (2004), 116-122. 12)S. Zaima, Y. Shibata, H. Adachi, C. Oshima, S. Otani, M. Aono and Y. Ishizawa: Atomic chemical composition and reactivity of the TiC(111) surface, Surface Scieence, 157 (1985), 380-392. 13)T. Ohyanagi, Y. Onose and A. Watanabe: Ti/Ni bilayer Ohmic contact on 4H-SiC, Journal of Vacuum Science and Technology B, 26 (2008), 1359-1362. 14)P Villars, A Prince and H Okamoto (Editors): Handbook of Ternary Alloy Phase Diagrams CD-ROM, ASM Inter-national, Materials Park, Ohio, USA, (1997). 15)M. Naka, J. C. Feng and J. C. Schuster: Phase reaction and diffusion path of the SiC/Ti system, Metallurgical and Materials Transactions A, 28 (1997), 1385-1390. 16)O. Kubaschewski, C. B. Alcock and P. J. Spencer: Mate-rials Thermochemistry 6th edition, Pergamon Press, Ox-ford, UK, (1993), ps. 265, 300, 308. 17)J. H. Gülpen, A. Kodentsov and F. J. J. van Loo: Growth of silicides in Ni-Si and Ni-SiC bulk diffusion couples, Zeitschrift für Metallkunde, 86 (1995), 530-539. 18)T. B. Massalski, H. Okamoto, P. R. Subramanian and L. Kacprzak (Editors): Binary Alloy Phase Diagrams, 2nd edition plus updates on CD-ROM, ASM International, Materials Park, Ohio, USA, (1996). 19)T. Teraoka, H. Nakane and H. Adachi: Hydrogen perme-ability of palladium needles and possibility of new eld ion source, Japanese Journal of Applied Physics, 33 (1994), L1110-L1112.
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