Without using any interfacial passivation layers, high-kappa dielectric Y2O3, HfO2, and Ga2O3(Gd2O3) by electron beam evaporation in ultra-high-vacuum (UHV), have been directly deposited on Ge substrate. Comprehensive investigations have been carried out to study the oxide/Ge interfaces chemically, structurally, and electronically: hetero-structures of all the studied oxides on Ge are highly thermally stable with annealing to 500 degrees C, and their interfaces remain atomically sharp. The electrical analyses have been conducted on metal-oxide-semiconductor (MOS) devices, i.e. MOS capacitors (MOSCAPs) and MOS field-effect-transistors (MOSFETs). Dielectrics constants of the Y2O3, HfO2, and GGO have been extracted to be similar to 17,20, and 13-15, respectively, indicating no interfacial layer formation with 500 degrees C annealing. A low interfacial density of states (D(it)s), as low as 3 x 10(11) cm(-2) eV(-1), has been achieved for GGO/Ge near midgap along with a high Fermi-level movement efficiency as high as 80%. The GGO/Ge pMOSFETs with TiN as the metal gate have yielded very high-performances, in terms of 496 mu A/mu m, 178 mu S/mu m, and 389 cm(2)/V s in saturation drain current density, maximum transconductance, and effective hole mobility, respectively. The gate width and gate length of the MOSFET are 10 mu m and 1 mu m. (C) 2010 Elsevier Ltd. All rights reserved.