The wide band-gap nitrides are ideally suited for high-speed high-temperature applications. The field of nitride processing technology is still very much in its infancy and a large number of novel process steps are being investigated. In particular, successful development of such devices requires reliable contact technology.

The objective of this work was to develop diffusion barrier for thermally stable metallization systems to GaN. Since gold overlayer is a commonly used component of metallizations, fabrication of efficient barrier layer against Au migration/reaction was of primary concern.
High melting point, conducting thin films of of Ta-Si-N, Ti-Si-N and Ti-W-N were compared as barrier materials. They were deposited by reactive magnetron sputtering in Ar/N₂ atmosphere, from Ta₅Si₃, Ti₅Si₃ and 10%Ti-90%W targets, respectively. The effects of sputter-deposition parameters on the resistivity and the microstructure of barrier layer have been investigated. Applicability to both p-type (Au/Pd and Ni/Au) and n-type (TiAl) metallisations to GaN has been analysed. Heat treatments were performed in a rapid thermal annealer under flowing N₂. Electrical characterisation of metal/semiconductor contacts involved measurements of I-V characteristics and specific contact resistance. Reactions at metal/semiconductor interface were analysed by Rutherford backscattering method, secondary ion mass spectroscopy, x-ray diffraction and TEM.
We show that for appropriate sputter deposition conditions, amorphous Ta-Si-N, Ti-Si-N and Ti-W-N films can be obtained. Moreover, they remain in amorphous phase after annealing up to 750-900⁰C, effectively suppressing the interaction between GaN and Au.
This work was carried out with support from EC under grant G5RD-CT-2001-00566-DENIS

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