High-pressure oxidation (HPO) of germanium (Ge) for improving electrical properties of Ge/GeO 2 stacks was investigated. The capacitance-voltage (C-V ) characteristics of metal/GeO 2 /Ge capacitors fabricated with HPO revealed improved electrical properties without any post-deposition annealing, and the interface states density (D it ) was reduced to 2 Â 10 11 eV À1 cm À2 near the midgap. Moreover, the refractive index of thermally oxidized GeO 2 was increased by HPO. It is also discussed from a thermodynamic viewpoint of the Ge/GeO 2 system that the GeO desorption from Ge/GeO 2 stacks could be efficiently suppressed by HPO.

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We have systematically investigated Ge interface passivation methods, and the highest electron (1920 cm 2 /Vs) and hole mobility (725 cm 2 /Vs) have been demonstrated by dramatic reduction of D it through the collaboration of self-passivation and valency passivation. In Si passivation, it is found that Si contributes to the upper half (worse) and lower one (better) in the bandgap differently. This study strongly suggests us that high performance Ge CMOS is really feasible.