Fundamentals and practice of metal contacts to wide band gap semiconductor devices

AIXTRON SE, Kaiserstr. 98, 52134 Herzogenrath, Germany Received 17 October 2011, revised 22 November 2011, accepted 25 November 2011 Published online 16 December 2011 Key words wide bandgap semiconductors, SiC, GaN, ohmic contacts, diffusion barriers. Presented are the theoretical and experimental fundamentals of the fabrication of ohmic contacts to n- and p-type wide band gap semiconductors such as SiC and GaN. In particular, the Ni-Si/n-SiC, Al-Ti/p-SiC, Ti-Al/n-GaN and Ni-Au/p-GaN systems are discussed with the focus on the thermally activated chemical reactions taking place at the metal-semiconductor interface, that lead to the appearance of ohmic behaviour in the contact. Examples of reactions at very intimate interfaces are shown, which are irresolvable using even such sophisticated characterisation methods as high-resolution transmission electron microscopy and can only be explained using modelling. The issue of thermal stability of the contacts is discussed and the introduction of specifically designed diffusion barriers (eg. Ta-Si-N) into the contact metallisation stack is presented as a solution improving drastically the thermal stability of the contacts without degrading their electrical properties.

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