Design and control of Ge-based metal-oxide-semiconductor interfaces for high-mobility field-effect transistors with ultrathin oxynitride gate dielectrics

High-quality Ge-based metal-oxide-semiconductor (MOS) stacks were achieved with ultrathin oxynitride (GeON) gate dielectrics. An in situ process based on plasma nitridation of the base germanium oxide (GeO₂) surface and subsequent metal electrode deposition was proven to be effective for suppressing electrical deterioration induced by the reaction at the metal/insulator interface. The electrical properties of the bottom GeON/Ge interface were further improved by both low-temperature oxidation for base GeO₂ formation and high-temperature in situ vacuum annealing after plasma nitridation of the base oxide. Based on the optimized in situ gate stack fabrication process, very high inversion carrier mobility (μ_hole: 445 cm²/Vs, μ_electron: 1114 cm²/Vs) was demonstrated for p- and n-channel Ge MOSFETs with Al/GeON/Ge gate stacks at scaled equivalent oxide thickness down to 1.4 nm.