X. Lou

Electrical Detection of Spin Accumulation at a Ferromagnet-Semiconductor Interface

We show that the accumulation of spin-polarized electrons at a forward-biased Schottky tunnel barrier between Fe and -GaAs can be detected electrically. The spin accumulation leads to an additional voltage drop across the barrier that is suppressed by a small transverse magnetic field, which depolarizes the spins in the semiconductor. The dependence of the electrical accumulation signal on magnetic field, bias current, and temperature is in good agreement with the predictions of a drift-diffusion model for spin-polarized transport.

Spin injection from the Heusler alloy Co2MnGe into Al0.1Ga0.9As∕GaAs heterostructures

Electrical spin injection from the Heusler alloy Co2MnGe into a p-i-nAl0.1Ga0.9As∕GaAs light emitting diode is demonstrated. A maximum steady-state spin polarization of approximately 13% at 2 K is measured in two types of heterostructures. The injected spin polarization at 2 K is calculated to be 27% based on a calibration of the spin detector using Hanle effect measurements. Although the dependence on electrical bias conditions is qualitatively similar to Fe-based spin injection devices of the same design, the spin polarization injected from Co2MnGe decays more rapidly with increasing temperature.

Spin Injection and Relaxation in Ferromagnet-Semiconductor Heterostructures

We present a detailed description of spin injection and detection in

Spin injection from perpendicular magnetized ferromagnetic δ-MnGa into (Al,Ga)As heterostructures

\mathrm{Fe}∕{\mathrm{Al}}_{x}{\mathrm{Ga}}_{1\ensuremath{-}x}\mathrm{As}∕\mathrm{GaAs}

Electron spin dynamics and hyperfine interactions in Fe Al0.1Ga0.9As GaAs spin injection heterostructures

heterostructures for temperatures from 2 to 295 K. Measurements of the steady-state spin polarization in the semiconductor indicate three temperature regimes for spin transport and relaxation. At temperatures below 70 K, spin-polarized electrons injected into quantum well structures form excitons, and the spin polarization in the quantum well depends strongly on the electrical bias conditions. At intermediate temperatures, the spin polarization is determined primarily by the spin-relaxation rate for free electrons in the quantum well. This process is slow relative to the excitonic spin-relaxation rate at lower temperatures and is responsible for a broad maximum in the spin polarization between 100 and 200 K. The spin injection efficiency of the

Effects of doping profile and post-growth annealing on spin injection from Fe into (Al,Ga)As heterostructures

\mathrm{Fe}∕{\mathrm{Al}}_{x}{\mathrm{Ga}}_{1\ensuremath{-}x}\mathrm{As}

Optical and electrical spin injection and spin transport in hybrid Fe/GaAs devices

Schottky barrier decreases at higher temperatures, although a steady-state spin polarization of at least 6% is observed at 295 K.

Nuclear magnetic resonance in a ferromagnet–semiconductor heterostructure

Electrical spin injection from ferromagnetic δ-MnGa into an (Al,Ga)As p-i-n light-emitting diode (LED) is demonstrated. The δ-MnGa layers show strong perpendicular magnetocrystalline anisotropy, enabling detection of spin injection at remanence, without an applied magnetic field. The bias and temperature dependence of the spin injection are found to be qualitatively similar to Fe-based spin LED devices. A Hanle effect is observed and demonstrates complete depolarization of spins in the semiconductor in a transverse magnetic field.

Spin injection from the Heusler alloy Co/sub 2/MnGe into Al/sub 0.1/Ga/sub 0.9/As/GaAs heterostructures

We have studied hyperfine interactions between spin-polarized electrons and lattice nuclei in Al_0.1Ga_0.9As/GaAs quantum well (QW) heterostructures. The spin-polarized electrons are electrically injected into the semiconductor heterostructure from a metallic ferromagnet across a Schottky tunnel barrier. The spin-polarized electron current dynamically polarizes the nuclei in the QW, and the polarized nuclei in turn alter the electron spin dynamics. The steady-state electron spin is detected via the circular polarization of the emitted electroluminescence. The nuclear polarization and electron spin dynamics are accurately modeled using the formalism of optical orientation in GaAs. The nuclear spin polarization in the QW is found to depend strongly on the electron spin polarization in the QW, but only weakly on the electron density in the QW. We are able to observe nuclear magnetic resonance (NMR) at low applied magnetic fields on the order of a few hundred Oe by electrically modulating the spin injected into the QW. The electrically driven NMR demonstrates explicitly the existence of a Knight field felt by the nuclei due to the electron spin.

Spin injection into semiconductors: the role of the Fe/Al/sub x/Ga/sub 1-x/As interface

The influence of the Fe∕Ga0.9Al0.1As interface on spin injection into a spin light-emitting diode is studied. Spin injection is found to depend strongly on the interfacial doping profile demonstrating the importance of band bending in the semiconductor near the interface. The effect of post-growth annealing on spin injection from Fe contacts into GaAs-based spin light-emitting diodes is also examined. Post-growth annealing up to 250 °C is found to increase the spin injection efficiency. It is demonstrated that the annealing modifies electronic properties of the Fe∕Ga0.9Al0.1As interface, as evidenced by an increase of the Schottky barrier height.