Characteristics of AuGeNi ohmic contacts to GaAs

We have studied AuGeNi ohmic contacts to n-type MBE grown GaAs epitaxial-layer with doping in the (1016-1019) cm-3 range, and found several new effects: (a) Contact resistivity exhibit a weak dependence on carrier concentration (much weaker than 1/ND depencence); (b) We find evidence for a high resistivity layer under the contact at least several thousands angstroms deep, which dominate the contact resistance in most cases; (c) We find a peripheral zone around the contact, about 1 μm wide which differs chemically from the GaAs epi-layer; (d) SIMS analysis reveals a deep diffusion into the GaAs of Ni and Ge; (e) Correlation between density of GeNi clusters in the contact and the contact resistivity are found; (f) Temperature measurements justify that tunneling is responsible for the ohmic contact. We discuss also the validity of the transmission line method and the commonly accepted model of the contact. © 1982.