Spin MOSFET has drawn much attention as an attractive candidate for future semiconductor devices because of its nonvolatility and reconfigurability. For realization of the spin MOSFET, highly efficient spin injection from ferromagnets to semiconductors with low parasitic resistance is one of the most important key technologies. Recently, we demonstrated room-temperature spin transport in germanium (Ge) based lateral spin valve devices with Schottky-tunnel contact, where the interface resistance at the ferromagnet/Ge is much smaller than that with conventional insulating tunnel barriers. However, when the thermal annealing was conducted to fabricate gate-stack structures for the spin MOSFET, the spin injection/detection efficiency was degraded due to the formation of reaction layers at the ferromagnetic alloys/Ge interface. In this study, we explore the enhancement in the thermal stability of the ferromagnet/Ge interface and demonstrate room-temperature spin signals even for the lateral spin device annealed at 250°C by an insertion of five Fe atomic layers between the ferromagnetic alloys and Ge.
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