Fabrication of high-quality Co2FeSi0.5Al0.5/CoFe/MgO/Si spin injectors for Si-channel spin devices

摘要

In recent years, spin-MOSFETs [1] have received much attention for low-power and high-performance integrated circuits. Figure 1 shows the schematic device structure of a spin-MOSFET that employs half-metallic ferromagnet tunnel contacts for the source and drain. To realize spin-MOSFETs, highly efficient spin-injector/detector for the Si channel is required. Half-metallic full-Heusler alloy CoFeSiAl (CFSA) is promising for a ferromagnetic electrode material owing to its high Curie temperature (RT) and extremely high spin polarization. Although CFSA has the completely ordered L2, partially ordered B2, and disordered A2 structures, its half-metallicity remains even for the partially disordered B2 structure [2]. This structural robustness is beneficial for device process of spin-MOSFETs. Recently, we demonstrated spin accumulation in a Si channel using a CFSA/MgO/Si tunnel contact (Fig. 2) [3]. The Hanle-effect signal for spin accumulation in the channel was successfully observed. However, its intensity was weak, i.e., the spin injection efficiency was low. The roughening of the CFSA/MgO interface was also observed for the tunnel contact, which could be the one of the origins of the low spin injection efficiency.