ABSTRACT
Due to the difficulty of growing high-quality semiconductors on ferromagnetic metals, the study of spin diffusion transport in Si was limited to lateral geometry devices. In this work, by using an ultrahigh-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 µm 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 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 establishing the necessary out-of-equilibrium spin population in Si under the spin-pumping action.
ABSTRACT
A GeSi modulator based on two-mode interference is designed in this study. A GeSi layer with a height of 0.22 µm is introduced to decrease the optical power overlap of the two modes. A doping region in which the free carrier plasma dispersion effect exists to change the oscillation period for on- and off-state switching is identified. A doping concentration of 1×10¹8 cm⻳ for both n and p type is selected. The single modulation arm for 3 V operation is 1416.3 µm long. The extinction ratio and insertion loss are 15 and 5 dB, respectively. The traveling electrode design shows 3 dB bandwidth as large as 50 GHz.
