Influence of Ge substrate crystallinity on Co germanide formation in solid-state reactions

A strong influence of substrate crystallinity is observed for thin-film CoGe reactions. For the detected phases (CoGe, Co5 Ge7, and Co Ge2), the formation temperatures on amorphous Ge (a- Ge) are found to be the lowest, while the highest are on single-crystalline Ge(100). Moreover, while the phase sequence on Ge(100) and polycrystalline Ge (poly-Ge) was unaltered, the formation of intermediate Co5 Ge7 was not observed on a-Ge. It is likely that this is due to a promoted Co Ge2 formation on a-Ge, resulting in a ∼200 °C decrease in formation temperature (depending on the ramp rate). These observations suggest a strong competition among the formation of these Ge-rich phases. © 2007 American Institute of Physics.