High-quality ferromagnetic CoFe/Si contacts for Si spin-transistor applications

To establish fundamental technologies for silicon(Si)-based spin transistors, we explore epitaxial growth of a ferromagnetic Co₆₀Fe₄₀ alloy on a Si substrate by using low-temperature molecular beam epitaxy for the growth temperature (T_G) below 300°C. With decreasing T_G, the quality of CoFe/Si interfaces is dramatically improved. In paticular, at T_G = 60°C, we realize high-quality Co₆₀Fe₄₀/Si(111) contacts without interfacial reaction layers and defects. This work can open up a road to operation of Si-based spin transistors with a CoFe spin injector and detector.