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Efficient spin injection through a crystalline AlO x tunnel barrier prepared by the oxidation of an ultra-thin Al epitaxial layer on GaAs
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Image of FIG. 1.
FIG. 1.

(a) Schematic illustrations of two different oxidation reactions occurring around an Al monolayer (ML) chemisorbed on the GaAs interface. The atomic configuration of 1-ML Al on top of the As-terminated GaAs(001) surface is shown schematically in the upper panel. Blue and yellow planes are those representing the Al and As planes, respectively. The oxidation of an Al-As bond (reaction A) is shown in the lower, left panel, whereas the oxidation of an Al-Al bond (reaction B) in the lower, right panel. (b) Schematic illustration of static enthalpy diagram for reactions A and B at room temperature. The values of activation and reaction enthalpies are calculated on the basis of the bond dissociation energy listed in Table I .

Image of FIG. 2.
FIG. 2.

RHEED patterns observed along two orthogonal azimuths, GaAs [ ] and [110], after completing five different processes; (a) epitaxial growth of a top -AlGaAs layer in a DH, (b) epitaxial growth of a first Al layer, (c) post-oxidation of the first Al epilayer, (d) deposition of a second Al layer, and (e) post-oxidation of the second Al layer. The acceleration voltage of an electron beam was 15 keV. (f) A plot of spacing of lattice planes in accordance with the progress of oxidation process. (g) Schematic illustrations of atomic configurations of (left panels) an Al epilayer and (right panels) an oxidized Al epilayer from the top and side views, respectively. Atoms and bonds aligned on the paper plane are shown by larger circles and solid lines, respectively. Those on the plane a half-ML away from the paper plane are represented by smaller circles and broken lines, respectively.

Image of FIG. 3.
FIG. 3.

(a) Cross-sectional, bright-field TEM image around Fe/AlO/AlGaAs region in a spin-LED structure. Hitachi H-9000NAR was used with an acceleration voltage of 200 keV. Specimens with the cross section of the (110) plane were prepared by the micro-sampling method using a Ga focus-ion beam equipment. (b) Magnified view of the image shown in (a). Calculated lattice images (c) for the -AlO(111)/AlGaAs(110) and (d) for the fcc-Al(100)/AlGaAs(110) structures. Calculation was carried out by using simulation code QSTEM. (e) Further magnified views of (upper two panels) the oxidized Al region together with a calculated lattice image for -AlO(111), and (lower two panels) the AlGaAs epitaxial region together with a calculated lattice image for AlGaAs(110). Dotted lines are eye guides for visual inspection.

Image of FIG. 4.
FIG. 4.

(a) Spatial profiles of EELS signals for iron (Fe), aluminum (Al), oxygen (O), gallium (Ga), and arsenic (As) across a Fe/AlO/AlGaAs interface. The distance is defined as the position measured from the origin in the AlGaAs region. The corresponding TEM image is shown in the upper part of the figure, in which the position of an AlO layer, the bright region, is supposed to be at  = 17–18.2 nm. (b) EELS spectra around the Fe-L threshold energy (708 eV) obtained at different values.

Image of FIG. 5.
FIG. 5.

characteristics of diode A (red lines) and diode B (blue lines) measured at 80 K. A broken line represents the curve obtained from the model calculation based on the using Simmons′ equation.

Image of FIG. 6.
FIG. 6.

(a) σ and σ components of EL spectra obtained from (a) spin-LED C and (b) spin-LED D. No external magnetic field was applied during the measurements. Insets are schematic illustrations of experimental configurations showing EL emission from a cleaved side wall and parallel relation between a magnetization vector and an optical axis.


Generic image for table
Table I.

A list of bond dissociation energy at 298 K.


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752b84549af89a08dbdd7fdb8b9568b5 journal.articlezxybnytfddd
Scitation: Efficient spin injection through a crystalline AlOx tunnel barrier prepared by the oxidation of an ultra-thin Al epitaxial layer on GaAs