Pd substitution at orthorhombic-NiSi/Si (010) epitaxial interface studied by density functional theory

摘要

NiSi is less stable than the previously-used CoSi2 at high temperatures. Some noble metals, such as Pd and Pt, have been added to NiSi to improve its thermal stability. We employed a first principles calculation to understand Pd atomic substitution at the interface. The orthorhombic structure of NiSi was used to construct an orthorhombic-NiSi/Si (010). Lattice parameters along the α- and c-axes in orthorhombic-NiSi were matched with those of Si for epitaxy contact. The 1×4×1 orthorhombic-NiSi (010) and 1 × 2 × 1 Si (010) superstructures were combined to construct the orthorhombic-NiSi/Si (010), and the superstructure was relieved in calculation to minimize its total free energy. The 1×4×1 term indicates four unit cells along the b-axis, and the same rule applies to 1 × 2 × 1. The superstructure's optimized interface thickness was 1.59 A. A Pd atom substituted for Ni and Si atoms located near the interface. Both Ni and Si atoms located at the interface were favorable for Pd atomic substitution.