The Schottky barrier height of Ni on n-GaN has been measured to be 0.56 and 0.66 eV by capacitance–voltage (C–V) and current–density–temperature (J–T) methods, respectively. Gallium nickel (Ga4Ni3) is formed as Ni is deposited on the GaN film, which affects the barrier height markedly. The thermal stability of Ni on GaN is also investigated by annealing these specimens at various temperatures. Specimen annealing at temperatures above 200 °C leads to the formation of nickel nitrides Ni3N and Ni4N at the interface of Ni and GaN. These interfacial compounds change the measured barrier height to 1.0 and 0.8 eV by C–V and J–T methods, respectively. Comparisons of Schottky characteristics of Ni with those of Pt, Pd, Au, and Ti are also discussed.

Two different kinds of n-type GaN films were prepared by organometallic vapor phase epitaxy, one by using trimethylgallium (TMGa) and another by using triethylgallium (TEGa) as the alkyl source. Schottky diodes with well-behaved current–voltage and capacitance–voltage characteristics were fabricated. Deep-level transient spectroscopy studies were performed on these samples. Three distinct deep levels, labeled E1, E2, and E3, were measured in the film grown with TMGa, with an activation energy of 0.14, 0.49, and 1.63±0.3 eV, respectively. Only one level, E3, was observed in the film prepared with TEGa.

Ohmic contacts with low resistance are fabricated on n-type GaN films using Ti/Ag bilayer metallization. The GaN films are grown by low pressure metalorganic chemical vapor deposition (LP-MOCVD) with Si as the dopant. Ohmic characteristics are studied for films with carrier concentration range from 1.5×1017 to 1.7×1019 cm−3. The lowest value for the specific contact resistivity of 6.5×10−5 Ω cm2 is obtained without annealing. The barrier height of Ti on GaN is calculated to be 0.067 eV.

The GaN buffer layer was grown on the sapphire substrate by low-pressure metalorganic chemical vapor deposition (LP-MOCVD) at 525 °C. The following 1.3 μm epitaxial GaN growth was carried out at 1025 °C. We varied the ramping rate from 12.5 to 100 °C/min to study the quality of the epitaxial GaN. It has been found that the x-ray peak width, photoluminescence (PL) linewidth, Hall mobilities, and carrier concentrations of GaN epitaxial layer strongly depend on the in situ thermal ramping rate. An optimum thermal ramping rate was found to be of 20 °C/min. The maximum mobility is 435 cm2/V s at carrier concentration of 1.7×1017 cm−3. The minimum full width at half maximum (FWHM) of x ray and PL were 5.5 min and 12 meV occur at a ramping rate of 20 °C/min. The decrease of the mobility at high and low ramping rate can be attributed to the thermal stress and the reevaporation of the GaN buffer layer.

In this paper, an electrically tunable metasuface is designed for visible regime. The device mainly consists of a V-shaped metallic metasurface, an ITO film, an electro-optic (EO) dielectric and a metal layer fabricated on a silica substrate. A continuous electrical modulation of resonant wavelength has been theoretically demonstrated in the visible range from 555 nm to 640 nm by changing the voltage applied on the EO dielectric from −20 V to 20 V. During the modulation, the steering angle also changes with the selective color. The peak cross-polarized reflectivity is higher than 48% and the bandwidth is narrower than 60 nm. The resonant wavelength shift can be explained by that the refractive index variation of the EO material induces resonance condition changes of the gap surface plasmon (GSP). The results provide a novel design solution for active plasmonic devices, especially for dynamic metadevices.

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