Crystal orientation effect on spin injection/detection efficiency in Si lateral spin-valve devices

We show evident crystal orientation effect on pure spin current transport in Si-based lateral spin-valve (LSV) devices with epitaxially grown CoFe/MgO tunnel contacts. When we compare nonlocal spin signals between LSV devices along < 1 0 0 > (Si < 1 0 0 >) and < 1 1 0 > (Si < 1 1 0 >), we find that the magnitude of the spin signals for Si < 100 > LSV devices is always larger than that for Si < 1 1 0 > LSV devices. The analyses based on the one-dimensional spin diffusion model reveal that the spin diffusion length and spin lifetime between Si < 1 0 0 > and Si < 1 1 0 > LSV devices are comparable, while the spin injection/detection efficiency in Si < 1 0 0 > LSV devices is evidently larger than that in Si < 1 1 0 > ones. Possible origins of the difference in the spin injection/detection efficiency between Si < 1 0 0 > and Si < 1 1 0 > LSV devices are discussed.