J. Strand

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

Dynamic nuclear polarization by electrical spin injection in ferromagnet-semiconductor heterostructures.

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

Optical pumping in ferromagnet-semiconductor heterostructures: Magneto-optics and spin transport

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

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

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

Optically pumped transport in ferromagnet-semiconductor Schottky diodes (invited)

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

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

Electrical spin injection from Fe into AlxGa1-xAs quantum well heterostructures is demonstrated in small (<500 Oe) in-plane magnetic fields. The measurement is sensitive only to the component of the spin that precesses about the internal magnetic field in the semiconductor. This field is much larger than the applied field and depends strongly on the injection current density. Details of the observed hysteresis in the spin injection signal are reproduced in a model that incorporates the magnetocrystalline anisotropy of the epitaxial Fe film, spin relaxation in the semiconductor, and the dynamic polarization of nuclei by the injected spins.

Nuclear magnetic resonance in a ferromagnet–semiconductor heterostructure

Epitaxial ferromagnetic metal-semiconductor heterostructures are investigated using polarization-dependent electroabsorption measurements on GaAs p-type and n-type Schottky diodes with embedded In12xGaxAs quantum wells. We have conducted studies as a function of photon energy, bias voltage, magnetic field, and excitation geometry. For optical pumping with circularly polarized light at energies above the band edge of GaAs, photocurrents with spin polarizations on the order of 1% flow from the semiconductor to the ferromagnet under reverse-bias. For optical pumping at normal incidence, this polarization may be enhanced significantly by resonant excitation at the quantum well ground state. Measurements in a side-pumping geometry, in which the ferromagnet can be saturated in very low magnetic fields, show hysteresis that is also consistent with spin-dependent transport. Magneto-optical effects that influence these measurements are discussed.

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

Optical pumping is used to generate spin-polarized carriers in epitaxial ferromagnet-GaAs Schottky diodes with InyGa1−yAs quantum wells placed in the depletion region. A strong dependence of the photocurrent on the polarization state of the incident light is observed, and a series of measurements as a function of excitation energy, bias voltage, magnetic field, and excitation geometry are used to distinguish spin-dependent transport from a variety of background effects. The spin polarization of the photocurrent for pumping energies at and above the band gap of GaAs is of order 0.5% or less. Much larger polarization dependence is observed for excitation energies near the quantum well ground state. Although background effects are very large in this regime, the field dependence of the polarization signal for several samples is suggestive of spin-dependent transport.