The generation and manipulation of carrier spin polarization in semiconductors solely by electric fields has garnered significant attention as both an interesting manifestation of spin-orbit physics as well as a valuable capability for potential spin
tronics devices. One realization of these spin-orbit phenomena, the spin Hall effect (SHE), has been studied as a means of all-electrical spin current generation and spin separation in both semiconductor and metallic systems. Previous measurements of the spin Hall effect have focused on steady-state generation and time-averaged detection, without directly addressing the accumulation dynamics on the timescale of the spin coherence time. Here, we demonstrate time-resolved measurement of the dynamics of spin accumulation generated by the extrinsic spin Hall effect in a doped GaAs semiconductor channel. Using electrically-pumped time-resolved Kerr rotation, we image the accumulation, precession, and decay dynamics near the channel boundary with spatial and temporal resolution and identify multiple evolution time constants. We model these processes using time-dependent diffusion analysis utilizing both exact and numerical solution techniques and find that the underlying physical spin coherence time differs from the dynamical rates of spin accumulation and decay observed near the sample edges.
Electric field enhanced electron spin coherence is characterized using time-resolved Faraday rotation spectroscopy in n-type ZnO epilayers grown by molecular beam epitaxy. An in-plane dc electric field E almost doubles the transverse spin lifetime at
20 K, without affecting the effective g-factor. This effect persists till high temperatures, but decreases with increasing carrier concentration. Comparisons of the variations in the spin lifetime, the carrier recombination lifetime and photoluminescence lifetimes indicate that the applied E enhances the radiative recombination rate. All observed effects are independent of crystal directionality and are performed at low magnetic fields (B < 0.2 T).
Electrically generated spin accumulation due to the spin Hall effect is imaged in n-GaAs channels using Kerr rotation microscopy, focusing on its spatial distribution and time-averaged behavior in a magnetic field. Spatially-resolved imaging reveals
that spin accumulation observed in transverse arms develops due to longitudinal drift of spin polarization produced at the sample boundaries. One- and two-dimensional drift-diffusion modeling is used to explain these features, providing a more complete understanding of observations of spin accumulation and the spin Hall effect.
