Formation of doped Al2O3 tunnel barriers by plasma oxidation of δ-doped Al

The formation of doped Al2O3 tunnel barriers, by plasma oxidation of doped Al, has been studied by in situ Auger electron spectroscopy (AES) and X-ray photoelectron spectroscopy (XPS). Ultrathin layers (<1 ML) of Ni or Si dopants were incorporated into an Al film at different depths, and subsequently plasma oxidized. Comparison of AES peak heights reveals two different types of oxidation behavior of the dopants. In the case where Ni or Si are initially present on top of the Al, they completely disappear from the immediate surface region after oxidation. Thus, Al from underneath the dopants goes through the dopant layer during oxidation, thereby burying the dopants in the Al-oxide. In contrast, for dopants sandwiched between two 7 إ Al films no significant vertical redistribution occurs, while XPS spectra show that dopants are completely oxidized. The data is used to support previous magnetoresistance measurements on magnetic tunnel junctions with doped barriers.