X-ray photoelectron spectroscopy analysis and band offset determination of CeO2deposited on epitaxial (100), (110), and (111)Ge

Abstract

The oxidation states, interface, and band alignment properties of physical vapor deposited CeO2 films on epitaxial (100), (110), and (111)Ge were investigated by x-ray photoelectron spectroscopy (XPS). The cross-sectional transmission electron microscopy demonstrated the polycrystalline nature of the CeO2 film. XPS analysis showed multiple Ce3d and Ce4d oxidation states with a mixture of Ce3+ and Ce4+ components existing in CeO2. Angular resolved XPS investigations indicate that the CeO2 films mostly consist of Ce4+ oxidation states while the Ce3+ oxidation states are preferentially present near the surface. The CeO2/(100)Ge, CeO2/(110)Ge, and CeO2/(111)Ge structures showed almost identical valence band offset (VBO) values of 1.6, 1.5, and 1.6 eV, respectively, using XPS measurements from Ce3d core level (CL) peaks. These (VBO) values were also supported by XPS measurements from shallow Ce4d CL binding energy peaks. The conduction band offset values between CeO2/Ge were ∼1.3 eV using the measured optical bandgap of CeO2. The XPS spectral analysis of cerium oxidation states and the measured band offset parameters for carrier confinement would offer an important path for the future design of Ge-based metal-oxide semiconductor devices.