EFFECTS OF AU ON NIGE(AU)W OHMIC CONTACTS TO N-GAAS

The contact resistance and thermal stability of NiGe(Au)W ohmic contacts are reported as a function of their Au content. The contact resistance, measured by the transmission line method, is found to decrease monotonically from a maximum of approximately 0.8-OMEGA mm for the Au-free NiGeW contacts, to less than 0.15-OMEGA mm for NiGe(Au)W containing approximately 60 angstrom of Au. The low Au content contacts are also found to be more stable than their Au-free counterparts when stressed at 400-degrees-C for a number of hours. Possible mechanisms to explain these results are proposed.