We have fabricated ferromagnet-insulator-ferromagnet tunnel junctions with Co and NiFe electrodes, where the Co electrodes are pinned with a hard magnetic Co81Pt19 alloy layer. This approach gives a coercivity of about 300 Oe for the Co layer, while that of the NiFe is about 80 Oe, so we obtain antiparallel magnetization over a wide field range. The Al2O3 tunneling barrier layers were formed by in situ plasma oxidation of elemental Al layers with thicknesses from 10 to 25 Å. For the junctions, we find room temperature magnetoresistance ratios as high as 13% and nonlinear current–voltage curves that are well fit by the Simmons tunneling theory. Depth profiling x-ray photoelectron spectroscopy of oxidized Al barrier layers on Co underlayers reveals a stoichiometry of nearly Al2O3.
High crystalline quality thick GaN films were grown by vapor phase epitaxy using GaC13 and NH 3. The growth rate was in the range of 10 ~ 15 ~m/h. GaN films grown at higher temperatures (960~ 1020 ~ were single crystalline with smooth surface morphologies. No chlorine impurity was incorporated in these films during growth. The best crystalline quality and surface morphology of grown films was achieved by sputtering a thin A1N buffer layer, prior to growth. According to reflection high energy electron diffraction and atomic force microscopy measurements, as-sputtered AlN buffer layer was amorphous with root means square roughness of 0.395 nm and then crystallized during the GaN growth. This improved the GaN growth due to more uniform distribution of GaN nucleation. Rutherford backscattering channeling experiments produced the lowest value from the GaN film grown on a-AlzO 3 with a 500/k A1N buffer layer at 1020~
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