Epitaxial growth of magnetron sputtered NiAl on Ge mediated by native GeOx

Abstract

In this work, the growth of a magnetron sputtered NiAl film on Ge was investigated. Two growth parameters were varied: the deposition temperature and the presence of native GeOx. An epitaxial layer was obtained at a deposition temperature of 400 circle C and without removal of the native GeOx prior to deposition. At this growth condition, Ni and Al diffused into the Ge forming an epitaxial germanide. This germanide is most likely the tau 3 phase of the Ni-Al-Ge ternary system. The growth of the tau 3 phase is enabled by the GeOx acting as a diffusion barrier for Al. The native GeOx was found to be amorphous and to contain holes through which the NiAl can directly contact the tau 3 germanide and grow epitaxially. These holes are likely formed by thermal degradation when the substrate is heated for deposition. The electrical resistivity for epitaxial NiAl was found to be 13 mu omega .cm at a thickness of 30 nm which was the lowest value of the tested conditions. Epitaxial NiAl can be used as a seed layer to grow other layers epitaxially in a CMOS-compatible process, e.g. Fe(Co), Cr, MgO, and Heusler alloys.