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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.

Propagation of optical pulses in a resonantly absorbing medium is studied. Propagation time of nanosecond pulses was measured for the Rb D 1 transition. At the center of two absorption lines, delay of the pulse peak which is about ten times as large as the pulse width was observed, where zero delay is defined for the propagation with the light velocity in vacuum. On the other hand, at the peak of an absorption line, negative delay was observed for large absorption, where the advance time is as large as 25% of the pulse width. Simulation including the effect of absorption and phase shift reproduced well the experimental results.

Effects of the Ti buffer layer on crystallization processes of lead-zirconate-titanate (PZT) films by the sol-gel deposition technique were investigated. The Ti buffer layer was deposited on a Pt/TiN/SiO2/Si substrate by electron beam evaporation at the back-pressure of 1×10-11 Torr. Homogeneous crystalline PZT film of perovskite structure with fine grains were successfully obtained on the substrate with a Ti buffer layer. In contrast, a rosette-structure film which consists of large grains surrounded by a second phase was formed on a pure Pt surface. Ti existing at the interface between Pt and PZT acts as nuclei, and affects the growth of fine grains. Furthermore, leakage current density was drastically reduced from 5×10-5 A/cm2 to 6×10-9 A/cm2 at 4 V for 200-nm-thick film formed on a substrate with a buffer layer. Crystalline orientations and microstructures of PZT films were strongly dependent on the equivalent thickness of the buffer layer and there was an optimum thickness. When the equivalent thickness of the buffer layer was 2 nm, PZT showed <111>-preferred orientation and a homogeneous film structure with fine grains on the <111>-oriented Pt/SiO2/Si substrate.

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