Effective passivation and high-performance metal–oxide–semiconductor devices using ultra-high-vacuum deposited high-κ dielectrics on Ge without interfacial layers

Without using any interfacial passivation layers, high-κ dielectric Y2O3, HfO2, and Ga2O3(Gd2O3) [GGO], 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 °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 ∼17, 20, and 13–15, respectively, indicating no interfacial layer formation with 500 °C annealing. A low interfacial density of states (Dits), as low as 3 × 1011 cm−2 eV−1, has been achieved for GGO/Ge near mid-gap 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 μA/μm, 178 μS/μm, and 389 cm2/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 μm and 1 μm.