Microstructural evolution and electrical characteristics of Co-germanide contacts on Ge

The microstructural evolution and corresponding electrical contact properties of Co-germanide systems were investigated. The Co-germanide formation process underwent several intermediate, high-resistive phases (CoGe and Co ₅Ge₇), while low-resistive CoGe₂ was formed over 650°C in a narrow process window of <100°C. Because of the strong Fermi level pinning effect, Co, CoGe, and Co₅ Ge₇ phases exhibited Schottky contact behaviors with similar Schottky barrier heights on n-type Ge and ohmic contact behavior on p-type Ge, respectively. However, for the CoGe₂ n -type Ge contact formed at 700°C, a nearly ohmic contact behavior started to appear, which was attributed to the possible diffusion of Co atoms into the Ge substrate due to the high-temperature germanidation process.