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The electrical characteristics of both n-and p-type GaN metal-oxide semiconductor (MOS) capacitors utilizing plasma-enhanced CVD-SiO 2 as the gate dielectric were measured. Both capacitance and conductance techniques were used to obtain the MOS properties (such as interface state density). Devices annealed at 1000°C/30 min. in N 2 yielded an interface state density of 3.8 3 10 10 cm ÿ2 eV ÿ1 at 0.19 eV from the conduction band edge, and it decreased to 1.1 3 10 10 cm ÿ2 eV ÿ1 deeper into the band gap. A total fixed oxide charge density of 8 3 10 12 q cm ÿ2 near the valence band was estimated. Unlike the symmetric interface state density distribution in Si, an asymmetric interface state density distribution with lower density near the conduction band and higher density near the valence band was determined.

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We report on the microwave characterization of a novel one-dimensional Josephson metamaterial composed of a chain of asymmetric superconducting quantum interference devices (SQUIDs) with nearest-neighbor coupling through common Josephson junctions. This metamaterial demonstrates a strong Kerr nonlinearity, with a Kerr constant tunable over a wide range, from positive to negative values, by a magnetic flux threading the SQUIDs. The experimental results are in good agreement with the theory of nonlinear effects in Josephson chains. The metamaterial is very promising as an active medium for Josephson traveling-wave parametric amplifiers; its use facilitates phase matching in a four-wave mixing process for efficient parametric gain.

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