Study of spin transport and magnetoresistance effect in silicon-based lateral spin devices for spin-mosfet applications

In this paper, we introduce the current status of research and development on silicon-based spin metal-oxide-semiconductor field-effect transistors (Si spin-MOSFETs) in terms of electrical spin injection, spin transport, and spin detection in Si-based lateral spin-valve devices. First, it is important for understanding the spin transport in Si to obtain reliably large spin signals for analyses. By using n⁺-Si spin-transport layers with a small cross-sectional area of ~0.3 μm², we can observe 50-fold the magnitude of four-terminal nonlocal (NL) magnetoresistance signals and NL Hanle signals at room temperature in previous works. Next, by analyzing these spin signals, we can reliably estimate the spin diffusion length and spin relaxation time of n⁺-Si at room temperature. Also, we clarify that inter-valley spin-flip scattering is one of the dominant spin relaxation mechanisms in n⁺-Si at room temperature. Furthermore, we find the crystal orientation effect on spin injection/detection efficiency in n⁺-Si and discuss the possible origins. Finally, we demonstrate a room-temperature MR ratio of 0.06%, twice as large as that in the previous work.