Rashba semiconductor as spin Hall material: Experimental demonstration of spin pumping in wurtziten-GaN:Si

Abstract

Pure spin currents in semiconductors are essential for implementation in the next generation of spintronic elements. Heterostructures of III-nitride semiconductors are currently employed as central building blocks for lighting and high-power devices. Moreover, the long relaxation times and the spin-orbit coupling (SOC) in these materials indicate them as privileged hosts for spin currents and related phenomena. Spin pumping is an efficient mechanism for the inception of spin current and its conversion into charge current in nonmagnetic metals and semiconductors with Rashba SOC. We report on the generation at room temperature (RT) of pure spin current in nonmagnetic degenerate $n$-GaN:Si from a magnetic permalloy layer driven to ferromagnetic resonance (FMR) conditions. The FMR signal and the generated Hall voltages due to spin Hall effect, inverse spin Hall effect (ISHE), and spurious mechanisms are detected simultaneously. No spin-pumping-induced voltage could be measured below RT, despite the persistence of FMR signal. After eliminating the spurious (not due to ISHE) components contributing to the generated voltage, we find for $n$-GaN:Si a spin Hall angle ${\ensuremath{\theta}}_{\mathrm{SH}}=3.03\ifmmode\times\else\texttimes\fi{}{10}^{\ensuremath{-}3}$, exceeding by one order of magnitude those reported for other semiconductors, pointing at III-nitrides as particularly efficient spin current generators.