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Formation and role of graphite and nickel silicide in nickel based ohmic contacts to n -type silicon carbide

Lookup NU author(s): Irina Nikitina, Dr Konstantin Vasilevskiy, Professor Nick Wright, Dr Alton Horsfall, Professor Anthony O'Neill, Dr Christopher Johnson

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Abstract

Nickel-based contacts, deposited on 4H-SiC C-face substrates, were annealed at temperatures ranging from 800 to 1040 °C and the phase composition of the contact layers analyzed by x-ray diffraction techniques. Ni2 Si was identified as the dominant phase for annealing temperatures exceeding 925 °C, with further increases in concentration with increasing temperature. At the highest annealing temperature of 1040 °C, a 40 nm thick nanocrystalline graphite film at the Ni2 Si-SiC interface was discovered and its presence confirmed by Raman spectroscopy. The roles of the Ni2 Si and graphite films in the formation of ohmic contacts were determined by their subsequent exclusion from the contact composition. Following deposition and annealing, the Ni2 Si and graphite layers were etched away selectively and replaced with new metal films deposited at room temperature and without any annealing. Measurement of the current-voltage characteristics revealed that the ohmic nature of the contacts was preserved after removal of the Ni2 Si and the graphite layers. It is concluded that the main reason for the conversion of Schottky to ohmic contacts during high-temperature annealing is a change of the electrical properties of the underlying SiC rather than being attributable to the presence of nickel silicides or graphite. It is proposed that a solid-state reaction between nickel and silicon carbide, similar to catalytic graphitization of carbon, may take place during Ni-SiC contact annealing at the temperature of 1040 °C. This process may result in the creation of sufficient carbon vacancies in the near-interface region of the SiC to allow increased electron transport through the Schottky barrier. © 2005 American Institute of Physics.


Publication metadata

Author(s): Nikitina IP, Vassilevski KV, Wright NG, Horsfall AB, O'Neill AG, Johnson CM

Publication type: Article

Publication status: Published

Journal: Journal of Applied Physics

Year: 2005

Volume: 97

Issue: 8

Pages: 1-7

ISSN (print): 0021-8979

ISSN (electronic): 1520-8850

Publisher: American Institute of Physics

URL: http://dx.doi.org/ 1520-8850

DOI: 10.1063/1.1872200


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