Chemical and electronic properties of Fe/MgO/Ge heterostructures for spin electronics

We report on the chemical and electronic properties of epitaxial Fe/MgO/Ge(001) heterostructures probed by X-ray Photoemission Spectroscopy. At variance with the Fe/MgO/Fe system, annealing at 570 K produces a sizable interdiffusion at the upper Fe/MgO interface, while at 470 K this process is inhibited. The XPS analysis of band alignment in heterostructures annealed at 470 K grown onto an intrinsic Ge substrate indicates that the Fermi level is placed at the center of the MgO gap and that the Schottky barrier height is 0.35 +/- 0.1 eV, thus indicating a partial depinning of the Fermi level.