Atomic layer-by-layer oxidation of Ge (100) and (111) surfaces by plasma post oxidation of Al2O3/Ge structures

The ultrathin GeOx/Ge interfaces formed on Ge (100) and (111) surfaces by applying plasma post oxidation to thin Al2O3/Ge structures are characterized in detail using X-ray photoelectron spectroscopy (XPS) and transmission electron microscopy. It is found that the XPS signals assigned to Ge 1+ and the 2+ states in the GeOx layers by post plasma oxidation have oscillating behaviors on Ge (100) surfaces in a period of ∼0.3 nm with an increase in the GeOx thickness. Additionally, the oscillations of the signals assigned to Ge 1+ and 2+ states show opposite phase to each other. The similar oscillation behaviors are also confirmed on Ge (111) surfaces for Ge 1+ and 3+ states in a period of ∼0.5 nm. These phenomena can be strongly regarded as an evidence of the atomic layer-by-layer oxidation of GeOx/Ge interfaces on Ge (100) and (111) surfaces.