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In this paper, the influence of a 10-nm-thick silicon-dioxide layer, as a passivation or as a gate insulation, on the performance of heterojunction field-effect transistors (HFETs) and metal-oxide-semiconductor HFETs (MOSHFETs), based on an undoped AlGaN/GaN heterostructure on a SiC substrate, was investigated. Channel-conductivity results yield a nearly 50% increase of mobility in the MOSHFET samples compared to the unpassivated HFETs. This increase of the transport properties of the MOSHFET channel is confirmed by a similar 45% increase of the cutoff frequency, from 16.5 to 24 GHz. Hall measurements, however, show a 10% decrease of the mobility in the heterostructure with a SiO2 top layer. In this paper, the superior performance of the MOSHFET transistor, in contradiction to the Hall results, is attributed to the screening of the Coulomb scattering of the charged surface defects by the gate-metallization layer. [ABSTRACT FROM AUTHOR]

The authors report on the fabrication and characterization of photodetectors based on nitrogen-ion-implanted GaAs and the annealing dynamics in these devices. An energy of 400 keV was used to implant N ions in a GaAs substrate at an ion concentration of ∼1×1016 cm-2. Dark current measurements as well as measurements under illumination show that the material properties rapidly change during the annealing process. Photodetectors based on nitrogen-implanted GaAs materials with annealing temperatures up to 400 °C exhibit a subpicosecond carrier lifetime up to 0.6 ps. These properties make nitrogen-ion-implanted GaAs an ideal material for ultrafast photodetectors, as alternative to low-temperature-grown GaAs. [ABSTRACT FROM AUTHOR]

In this paper, the multiphysical and frequency-dependent characterization of a microwave argon plasma jet in the GHz range is presented. Three different frequency ranges around 1.3, 2.4, and 3.5GHz are compared using electrical, geometrical, optical, and thermal analyses for different power levels between 2 and 10 W at a constant gas flow. Based on measurements using the large signal S-parameter measuring technique, the plasma base point impedance and microwave conductivity are determined via circuit and finite-element method simulations. Major changes within a small frequency interval are exhibited. Optical measurements are dependent on the geometrical dimension changes of the microwave plasma. It is shown that the geometrical dimensions are strongly dependent on frequency and applied power. These investigated dependencies of the microwave plasma on operation conditions open up new degrees of freedom to match the frequency to the application needs. A description of different applications is given based on the different areas of the measurement results. [ABSTRACT FROM PUBLISHER]

This paper describes the development of a capacitively coupled high-pressure lamp with input power between 20 and 43 W at 2.45 GHz, using a coaxial line network. Compared with other electrodeless lamp systems, no cavity has to be used and a reduction in the input power is achieved. Therefore, this lamp is an alternative to the halogen incandescent lamp for domestic lighting. To serve the demands of domestic lighting, the filling of the lamp is optimized over all other resulting requirements, such as high efficacy at low induced powers and fast startups. A workflow to develop RF-driven plasma applications is presented, which makes use of the hot S-parameter technique. Descriptions of the fitting process inside a circuit and FEM simulator are given. Results of the combined ignition and operation network from simulations and measurements are compared. An initial prototype is built and measurements of the lamp’s lighting properties are presented along with an investigation of the efficacy optimizations using large signal amplitude modulation. With this lamp, an efficacy of 135 lmW−1 is achieved. [ABSTRACT FROM PUBLISHER]

This paper outlines an efficient numerical method to design terahertz photomixers. The simulations are benchmarked using measured power levels from results published in the literature. Next, the method is applied to two new photomixer designs based on the high impedance T-match antenna with bias supply DC-blocking structures for either a uniplanar layout or a multilayer structure for improved device reliability. Manufacturability is favoured by avoiding the use of airbridges, substrate thinning or under-etching. The estimated output power of the improved design is 9.0 $$\upmu \!\text {W}$$ , which is an improvement of three times over the reference photomixer. [ABSTRACT FROM AUTHOR]

We report on the preparation and properties of GaN and AlN layers grown by molecular-beam epitaxy on silver metal substrates. X-ray diffraction rocking curves show polycrystalline character of GaN with high preferential GaN(11-22) orientation. An intermetallic phase of Ga3Ag is found at the GaN/Ag interface. On the other hand, AlN layers exhibit a monocrystalline structure with a growth direction of (0002). Schottky diodes prepared on GaN layers show good rectifying behavior and relatively low leakage current (∼10-3 A/cm2). These results indicate that the III-nitride growth on metallic substrates might be used for low-cost and large-area electronic and photonic devices. [ABSTRACT FROM AUTHOR]