Effect of Sn doping on low-temperature growth of Ge epilayers on half-metallic Co2FeSi

In this study, we demonstrate the low-temperature growth of a Ge layer via Sn doping in a ferromagnet/Ge/Co-based Heusler alloy multilayer on a Si(111) substrate having a vertically stacked structure. The continuous doping of 5% Sn into the Ge interlayer enables the epitaxial growth of the Ge layer on the Co-based Heusler alloy, even at ∼110 °C, and reduces the surface roughness. Elemental mapping shows that low-temperature growth via Sn doping suppresses interdiffusion at the Ge/Co-based Heusler alloy interface. The magnetic properties of the all-epitaxial CoFe/Ge/Co-based Heusler alloy structure are improved. For vertical spin-valve devices with Sn doping, the room-temperature spin signal is enhanced. These results indicate that the chemically abrupt Ge/Co-based Heusler alloy interface enhances the magnitude of the room-temperature spin signal owing to Sn-induced low-temperature growth.