Evidence of Pure Spin-Current Generated by Spin Pumping in Interface Localized States in Hybrid Metal-Silicon-Metal Vertical Structures

TL;DR

This study demonstrates the generation and transport of pure spin-current in vertical metal-semiconductor-metal structures with Si, using spin pumping and inverse spin-Hall effect, highlighting the role of interface localized states.

Contribution

First demonstration of pure spin-current injection and transport in vertical structures with Si, emphasizing the importance of interface localized states for spin pumping.

Findings

Pure spin-current transported over >2μm in Si at room temperature.

Localized states at MgO/Si interface are crucial for spin-current generation.

Proximity effects facilitate out-of-equilibrium spin populations in Si.

Abstract

Due to the difficulty to grow high quality semiconductors on ferromagnetic metals, the study of spin diffusion transport in Si was only limited to lateral geometry devices. In this work, by using ultra-high vacuum wafer-bonding technique, we have successfully fabricated metal semiconductor metal CoFeB/MgO/Si/Pt vertical structures. We hereby demonstrate pure spin-current injection and transport in the perpendicular current flow geometry over a distance larger than 2\mu m in n-type Si at room temperature. In those experiments, a pure propagating spin-current is generated via ferromagnetic resonance spin-pumping and converted into a measurable voltage by using the inverse spin-Hall effect occurring in the top Pt layer. A systematic study by varying both Si and MgO thicknesses reveals the important role played by the localized states at the MgO/Si interface for the spin-current generation. Proximity effects involving indirect exchange interactions between the ferromagnet and the MgO/Si interface states appears to be a prerequisite to establish the necessary out-of-equilibrium spin-population in Si under the spin-pumping action.