This study elucidates the thermal stability and quasi ohmic contact characteristics of Cu(RuTaNx) fabricated on a barrierless GaAs substrate. Cu(RuTaNx) was prepared by cosputtering Cu, Ta, Ru, and N. The resistivity of the Cu(RuTaNx)/GaAs structure annealed at 500 degrees C for 30 min was lower than that of the as-deposited structure, and the former was thermally stable up to 500 degrees C after 30 min of annealing. Further, the Cu(RuTaNx)/GaAs structure exhibited electrical rectifying properties upon annealing at 550 degrees C for 10 min and revealed a quasi ohmic contact, as determined by the circular transmission line model (CTLM). The formation of quasi ohmic contact is further confirmed by transmission electron microscopy and energy dispersive X-ray spectroscopy. (C) 2011 Elsevier B.V. All rights reserved.