We have found excellent electrical characteristics in germanium oxide grown by plasma oxidation for germanium metalinsulator-semiconductor gate dielectric applications. An oxygen plasma stream generated by electron cyclotron resonance was used to oxidize a germanium surface without substrate heating. A transmission electron microscope observation revealed that the obtained germanium oxide/germanium interface is atomically smooth. The energy distribution of interface trap density (D it ) in the upper half of the p-type germanium band gap was measured by the ac conductance method. It is shown that the D it at the midgap is $6 Â 10 10 cm À2 ÁeV À1 and increases exponentially as the energy increases to the conduction-band edge.

In this letter, we describe the electrical behavior of the GeO x and p-type Ge interface on the basis of capacitance and conductance measurements. The primary conclusion of this work is that when the Ge surface is biased in the depletion region, the frequency response of interface traps in the lower half of the Ge band-gap is so fast that there is no significant frequency dispersion observed in the capacitance measurements over a typical frequency range of ≤ 1 MHz. As a result, the density and energy distributions of the interface traps cannot be determined by a conventional method of combined high-frequency and low-frequency capacitance measurements. Instead, a comparison of the measured capacitance with a theoretical capacitance calculated for a system with no interface traps must be conducted to obtain information on the interface traps. Furthermore, the conductance method provides information on the interface traps in the upper half of the p-type Ge band-gap.

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