THE MICROSTRUCTURE AND ELECTRICAL-PROPERTIES OF NONALLOYED EPITAXIAL AU-GE OHMIC CONTACTS TO N-GAAS

The microstructure and electrical properties of nonalloyed epitaxial Au-Ge contacts were studied. Ohmic behavior was obtained after a 3 h anneal at 320-degrees-C with the lowest average contact resistance and specific contact resistivity found to be approximately 0.28 OMEGA mm and approximately 7 X 10(-6) OMEGA cm2, respectively. Localized reactions in the form of islands were observed across the surface of the contact after annealing and were composed of Au, Ge, and As, as determined by secondary ion mass spectroscopy (SIMS) imaging and Auger depth profiling. Back side SIMS profiles indicate deep Ge and Au diffusion into the GaAs substrate in the island regions. Ohmic contact behavior was found to depend upon both the kinetics of the reactions (localized reactions and island growth) and the thermodynamics (substantial diffusion of both Au and Ge) of the system. A model describing the coupled Au and Ge in-diffusion with respect to the GaAs substrate is presented.