Reduced electrical resistivity of reaction-sintered SiC by nitrogen doping
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Hyunho Shina) Department of Ceramic Engineering, Kangnung National University, Kangnung, Jibyun-dong, 210-702, Republic of Korea
Young-Hyun Lee Device and Materials Laboratory, LG Electronics Institute of Technology, Woomyeon-dong, Seocho-gu, Seoul 137-724, Republic of Korea
Sang-Won Kang Department of Materials Science and Engineering, Korea Advanced Institute of Science and Technology, Yusong-gu, Daejeon 305-701, Republic of Korea (Received 19 September 2007; accepted 10 January 2008)
A post heat treatment of reaction-sintered SiC at 1700 °C in nitrogen atmosphere significantly reduced electrical resistivity. A trace of insulating Si3N4 phase was detected via nitrogen heat treatment in high-resolution transmission electron microscopy observation; however, based on x-ray photoelectron spectroscopy, the evidence of nitrogen doping into SiC lattice has been claimed as the mechanism to the decreased resistivity. The increase of the total volume of SiC was apparent in x-ray diffraction during the nitrogen heat treatment, which was interpreted to stem from the growth of the nitrogen-doped intergranular SiC particles and surface doping of the primary SiC to reduce the contact resistance between the primary SiC particles. I. INTRODUCTION
Reaction-sintered SiC (RSSC) has received much interest for use in semiconductor processing, nuclear fuel preparation, and high-temperature thermomechanical applications.1,2 SiC is usually fabricated by infiltrating silicon melt to a porous SiC–C preform,3–5 which has a benefit over the mixing of fine silicon powder with SiC in that a low-cost bulk type of silicon can be used for melt infiltration. In general, residual silicon exists after reaction sintering, which can be eliminated by a post process such as evaporation at temperatures higher than those of the reaction sintering. From the viewpoints of electromachining and electrical heater applications of the reaction-sintered SiC, decreased electrical resistivity is highly important. In this regard, Fumio6 recently reported notable progress: the introduction of nitrogen sources such as hexamethylenetetra-amine in the preform or nitrogen heat treatment yielded a significantly diminished electrical resistivity of the final product. More specifically, electrical resistivity a)
Address all correspondence to this author. e-mail: [email protected] DOI: 10.1557/JMR.2008.0144 1020 J. Mater. Res., Vol. 23, No. 4, Apr 2008 http://journals.cambridge.org Downloaded: 14 Mar 2015
of approximately 0.9 ohm⭈cm was achieved, while the resistivity was 550 ohm⭈cm for the case when no nitrogen source was used. This result is fairly interesting in that there exists a possibility of the formation of the insulating Si3N4 phase by the introduction of nitrogen source. In Ref. 6 the nitrogen doping into SiC was then deduced to be the mechanism to explain the markedly decreased electrical resistivity by the nitrogen source; however, no experimental evidence for the nitrogen doping was presented. Furthermore, the possibility of the nitrogen doping into a
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