Ohmic contacts for GaAs devices using epitaxial Ge films

Ohmic contacts to n-type GaAs have been developed using epitaxial Ge films on GaAs alloyed with Ni overlayers by solid state diffusion at temperatures of 450°C - 550°C. These contacts have applications to high reliability, high temperature microwave devices. The Ge films were deposited epitaxially on heated GaAs substrates. Reflection electron diffraction of the Ge layers prior to deposition of the Ni overlayers reveals the presence of high quality single-crystalline films. Interdiffusion at the Ge-GaAs and Ni/Ge-GaAs interfaces was examined by Auger Electron Spectroscopy (AES) sputter profiling techniques A very sharp profile is observed at the as deposited Ge-GaAs interface. Even after sintering, there is very little penetration of Ge into GaAs in the absence of Ni. With the presence of a Ni overlayer, significant interdiffusion between Ge and GaAs is revealed by AES profiles, thus indicating the presence of an n⁺layer at the Ni/Ge-GaAs interface. The presence of a Ge doped n⁺layer was examined by electrical measurements using n- and p-GaAs substrates.