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The growth of Gd2O3 on Ge(001) substrates addresses the double intent of fabricating high dielectric constant oxide stacks as a replacement of the SiO2-based technology (no longer suited to a further oxide down-scaling) and of taking advantage from the higher carrier mobility in the Ge channel. From the structural viewpoint, further reasons for the integration in advanced microelectronic devices mainly rely on the good lattice matching and on the thermodynamic stability. Indeed, crystalline Gd2O3 films was deposited both on GaAs [M. Hong, et al., Science 283, 1897 (1999)] and on Si [H. J. Osten, et al., J. Cryst. Growth 235, 229 (2002)], whereas no experimental evidence has been reported for Ge. In this work, we provide solid evidences on the growth of crystalline Gd2O3 films on Ge(001) by molecular beam epitaxy (MBE), which validates the Gd2O3 as a polyvalent gate oxide for the commensurate growth on different semiconductor substrates. We study the structural properties of Gd2O3films grown on Ge(001) by means of in situ real time electron diffraction (RHEED) and X-ray photoelectron spectroscopy (XPS) and of ex situ X-ray Diffraction (XRD), Transmission Electron Microscopy (TEM), Atomic Force Microscopy (AFM) and time of flight secondary ion mass spectroscopy (ToF-SIMS). Two oxidizing species have been utilized during growth: molecular oxygen (MO) and atomic oxygen (AO) beams. As a main result, we show that different crystalline structures and interfacial properties can be obtained depending on the oxidizing species used in the growth process. While the film crystallinity is strictly related to the MO mediation, an amorphous Gd2O3 phase and an interface layer occur when AO is used. Imparting a crystalline registry to the Gd2O3 films via the MO mediation prevents the occurrence of the interface layer thus yielding an atomically and chemically sharp interface against the Ge substrate The stabilization of this interface is rationalized with thermodynamics arguments. |