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 (Si1 0 0) and 1 1 0 (Si1 1 0), we find that the magnitude of the spin signals for Si1 0 0 LSV devices is always larger than that for Si1 1 0 LSV devices. The analyses based on the one-dimensional spin diffusion model reveal that the spin diffusion length and spin lifetime between Si1 0 0 and Si1 1 0 LSV devices are comparable, while the spin injection/detection efficiency in Si1 0 0 LSV devices is evidently larger than that in Si1 1 0 ones. Possible origins of the difference in the spin injection/detection efficiency between Si1 0 0 and Si1 1 0 LSV devices are discussed.