Phase formation in intermixed Ni–Ge thin films: Influence of Ge content and low-temperature nucleation of hexagonal nickel germanides

• We study phase formation in the Ni–Ge thin film system using in situ XRD and TEM.
• We deposited Ni films with different Ge concentrations using combinatorial sputtering.
• A metastable germanide was observed when adding between 36 and 48 at.‰Ge.
• When adding between 36 and 42 at.% Ge, this phase is already present as-deposited.

In this study, we focus on phase formation in intermixed Ni–Ge thin films as they represent a simplified model of the small intermixed interface layer that is believed to form upon deposition of Ni on Ge and where initial phase formation happens. A combinatorial sputter deposition technique was used to co-deposit a range of intermixed Ni–Ge thin films with Ge concentrations varying between 0 and 50 at.%Ge in a single deposition on both Ge (100) and inert SiO2 substrates. In situ X-ray diffraction and transmission electron microscopy where used to study phase formation. In almost the entire composition range under investigation, crystalline phases where found to be present in the as-deposited films. Between 36 and 48 at.%Ge, high-temperature hexagonal nickel germanides were found to occur metastabily below 300 °C, both on SiO2 and Ge (100) substrates. For Ge concentrations in the range between 36 and 42 at.%, this hexagonal germanide phase was even found to be present at room temperature in the as-deposited films. The results obtained in this work could provide more insight in the phase sequence of a pure Ni film on Ge.

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