The optical properties of a single-band near-perfect absorber are studied numerically by using a finite element method in conjunction with a two-fluid model. Based on a metal-superconductor-metal (MSM) scheme, the proposed structure comprises a lossless superconducting layer sandwiched by a silver square array and ground silver plane. The simulation results clearly show that near-perfect absorption band can be realized and promptly tuned from green light to red light by the temperature of the system. The designed MSM absorber also presents the characteristics of polarization insensitivity and wide-angle incidence up to 50 degree. This prompt manipulation of the near-perfect absorption band makes this MSM absorber a great potential candidate when designing an in-situ absorption band selector in the visible light wavelength regime.

The use of a Cu/Pt/Ti Schottky contact structure and Cu-based airbridges for high-frequency metamorphic high electron mobility transistor (MHEMT) is successfully developed. The material characteristics of the Cu/Pt/Ti Schottky contact on iInAlAs were studied. Judging from the results of the X-ray diffraction analysis, Auger electron spectroscopy, and transmission electron microscopy, the Cu/Pt/Ti Schottky contact structure on InAlAs was very stable after annealing at 350 C. However, after 400 C annealing, the reaction of copper with the layers underneath started to occur and formed the Cu 4 Ti phase. The Cumetallized MHEMT using the proposed Cu/Pt/Ti T-gate structure and Cu-based airbridges has a saturated drain current of 673 mA/mm and a maximum transconductance of 750 mS/mm. The gate to drain breakdown voltage measured was 14.5 V at a gate reverse current of À1 mA/mm. The device also demonstrated a cutoff frequency F t of 90 GHz and a maximum frequency of oscillation F max of 165 GHz. An MHEMT with a Au/Pt/Ti gate was fabricated and compared with an MHEMT fabricated with the proposed Cu/Pt/Ti gate. These two kinds of MHEMTs showed similar F t and F max . These results demonstrate that the Cu/Pt/Ti T-gate and Cu-based airbridges can be used for MHEMT fabrication with excellent electrical characteristics.

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