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Electrical properties and microstructure of ternary Ge/Ti/Al ohmic contacts to p-type 4H–SiC

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3 Author(s)
Tsukimoto, S. ; Department of Materials Science and Engineering, Kyoto University, Kyoto 606-8501, Japan ; Sakai, T. ; Murakami, M.

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The high-power SiC devices require ohmic contact materials, which are prepared by annealing at temperatures lower than 800 °C. Recently, we demonstrated in our previous paper [J. Appl. Phys. 95, 2187 (2004)] that an addition of a small amount of Ge to the conventional binary Ti/Al contacts reduced the ohmic contact formation temperature by about 500 °C, and this ternary contacts yielded a specific contact resistance of approximately 1×10-4 Ω cm2 after annealing at a temperature as low as 600 °C. In this paper, the electrical properties and the microstructures of the Ge/Ti/Al contacts (where a slash “/” indicates the deposition sequence) were investigated by current-voltage measurements and transmission electron microscopy observations, respectively, in order to understand the ohmic contact formation mechanism. Ti3SiC2 compound layers (which were previously observed at the metal/SiC interface in the Ti/Al ohmic contacts after annealing at temperatures higher than 1000 °C) were observed to grow epitaxially on the SiC surface after annealing at temperatures as low as 600 °C. The Ti3SiC2 layers were believed to act as a p-type intermediate semiconductor layer, which played a key role to reduce the Schottky barrier height at the contacting metal/SiC interface. Further reduction of the conta- ct resistances of the Ge/Ti/Al contacts would be achieved by increasing the coverage of the Ti3SiC2 layers on the SiC surface.

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Journal of Applied Physics  (Volume:96 ,  Issue: 9 )