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The impact of Cubic Silicon Carbide (3C-SiC) transition layer on breakdown voltage and frequency performance of GaN high electron mobility transistors is investigated. A combination of distinct material and device characterizations techniques, including Raman spectroscopy, coplanar waveguides, electrical measurements, and Technology Computer-Aided Design (TCAD) simulations, are adopted to inspect the role of the 3C-SiC interlayer. Raman spectra reveal a good quality of the 3C-SiC layer, similar to the mono-crystalline 3C-SiC spectra. A relatively low transmission loss of ∼0.16 dB/mm at 40 GHz is measured for the device with 3C-SiC layer, rather than 2.1 dB/mm for the device without 3C-SiC. In addition, a soft breakdown voltage around 1530 V at 1 μA/mm is achieved, which is three times larger compared with that of the conventional device. The failure mechanism, related to carrier injection at the nucleation layer, is not observed in the structure with the 3C-SiC layer. Instead, TCAD simulations disclose a substantial improvement of the buffer/substrate interface through the suppression of an interface current path. [ABSTRACT FROM AUTHOR]

A cost-effective fabrication process is developed to improve the power performance of AlGaN/GaN High Electron Mobility Transistors (HEMTs). This process uses nitrogen ion (N+) implantation to form multiple parallel nanoribbons on AlGaN/GaN heterostructures, with a thin buffer layer (AlGaN/GaN NR-HEMTs). The stopping and range of ions in matter simulations of the N+ implantation combined with measured current-field characteristics reveal a good electrical isolation beneath the two-dimensional electron gas, resulting in substantial increase in the breakdown field of the NR-HEMTs, when compared to conventional AlGaN/GaN HEMTs. The fabricated AlGaN/GaN NR-HEMTs performed (i) an ON/OFF current ratio more than two orders of magnitude larger and (ii) a buffer leakage current more than one order of magnitude weaker than that of the conventional AlGaN/GaN HEMTs. The on-resistance, RON, and series resistance, RS, of AlGaN/GaN NR-HEMTs are both reduced by one order of magnitude when compared to those of the conventional AlGaN/GaN HEMTs. These have boosted the drive current density by up to 435%. Furthermore, we have found that the architecture of the AlGaN/GaN NR-HEMTs reduces the destructive impact of electron traps in the device. An optimized AlGaN/GaN NR-HEMT exhibited a better electrostatic integrity, a subthreshold slope of ∼210 mV/dec instead of 730 mV/dec for a conventional GaN HEMT. A higher linearity in the transconductance, gm, of NR-HEMTs is observed, twice of that of a conventional GaN HEMT. These results demonstrate the great interest of developed process technology of NR-HEMTs for high-power switching applications. [ABSTRACT FROM AUTHOR]

Heavily boron doped diamond epilayers with thicknesses ranging from 40 to less than 2 nm and buried between nominally undoped thicker layers have been grown in two different reactors. Two types of [100]-oriented single crystal diamond substrates were used after being characterized by X-ray white beam topography. The chemical composition and thickness of these so-called deltadoped structures have been studied by secondary ion mass spectrometry, transmission electron microscopy, and spectroscopic ellipsometry. Temperature-dependent Hall effect and four probe resistivity measurements have been performed on mesa-patterned Hall bars. The temperature dependence of the hole sheet carrier density and mobility has been investigated over a broad temperature range (6K2/Vs, independently of the layer thickness and the substrate type. Comparison with previously published data and theoretical calculations showed that scattering by ionized impurities explained only partially this low common value. None of the delta-layers showed any sign of confinement-induced mobility enhancement, even for thicknesses lower than 2 nm. [ABSTRACT FROM AUTHOR]

We study both theoretically and experimentally the interaction of surface elastic waves with 2D surface phononic crystal (PnC) on a piezoelectric substrate. A rigorous analysis based on 3D finite element method is conducted to calculate the band structure of the PnC and to analyze the transmission spectrum (module and phase). Interdigital transducers (IDTs) are considered for electrical excitation and detection, and absorbing boundary conditions are used to suppress wave's reflection from the edges. The PnCs are composed of an array of 20 Nickel cylindrical pillars arranged in a square lattice symmetry, and deposited on a LiNbO3 substrate (128°Y cut-X propagating) between two dispersive IDTs. We investigate by means of band diagrams and transmission spectrum the opening band-gaps originating from pillars resonant modes and from Bragg band-gap. The physical parameters that influence and determine their appearance are also discussed. Experimental validation is achieved through electrical measurement of the transmission characteristics, including amplitude and phase. [ABSTRACT FROM AUTHOR]

Optical waveguiding properties of a thick wurtzite aluminum nitride highly [002]-textured hetero-epitaxial film on (001) basal plane of sapphire substrate are studied. The physical properties of the film are determined by X-ray diffraction, atomic force microscopy, microRaman, and photocurrent spectroscopy. The refractive index and the thermo-optic coefficients are determined by m-lines spectroscopy using the classical prism coupling technique. The optical losses of this planar waveguide are also measured in the spectral range of 450-1553 nm. The lower value of optical losses is equal to 0.7 dB/cm at 1553 nm. The optical losses due to the surface scattering are simulated showing that the contribution is the most significant at near infrared wavelength range, whereas the optical losses are due to volume scattering and material absorption in the visible range. The good physical properties and the low optical losses obtained from this planar waveguide are encouraging to achieve a wide bandgap optical guiding platform from these aluminum nitride thin films. [ABSTRACT FROM AUTHOR]

High performance titanium nitride sub-100 nm rectifying contact, deposited by sputtering on AlGaN/GaN high electron mobility transistors, shows a reverse leakage current as low as 38 pA/mm at VGS=-40V and a Schottky barrier height of 0.95 eV. Based on structural characterization and 3D simulations, it is found that the polarization gradient induced by the gate metallization forms a P-type pseudo-doping region under the gate between the tensile surface and the compressively strained bulk AlGaN barrier layer. The strain induced by the gate metallization can compensate for the piezoelectric component. As a result, the gate contact can operate at temperatures as high as 700°C and can withstand a large reverse bias of up to -100 V, which is interesting for high-performance transistors dedicated to power applications. [ABSTRACT FROM AUTHOR]

In this work, AlGaN/GaN high electron mobility transistors on (1 0 0) and (1 1 0) oriented silicon substrates are investigated in view of monolithic integration with silicon MOSFETs for making more compact microwave power electronics. Epilayers are grown by molecular beam epitaxy on highly resistive substrates. It was shown that a better crystal quality as well as higher low-field electron mobility are obtained on the (1 1 0) orientation. Sub-micron gate length devices are then processed to estimate the millimeter-wave and microwave power performances of this new generation of devices. Load-pull measurements are performed from 4 GHz up to 40 GHz. Optimizations for the best power-added efficiency or for maximum output power density show the great potential of the Si(1 1 0) substrate for GaN-based power devices. At 18 GHz, these two different optimizations lead to a saturated output power density and an associated power-added efficiency of 2.4 W mm-1-40% and 3.76 W mm-1-33%, respectively. At 40 GHz, a record saturated output power density of 3.3 W mm-1 is achieved with an associated power-added efficiency of 20.1% and a linear power gain of 10.6 dB. In comparison, devices on Si(1 0 0) show less attractive performance due to a lower material quality with an output power density of 2.9 W mm-1, an associated power-added efficiency of 20.4% and a linear power gain of 7.5 dB at 10 GHz. [ABSTRACT FROM AUTHOR]

A silicon micro-machined thermal gas flow sensor operating in anemometric mode has been designed, fabricated and investigated for continuous and pulsatile flows. The sensor is specifically designed to achieve high sensitivity, fast response time and high robustness. It is composed of four metallic resistors interconnected to form a Wheatstone bridge. Two of them act simultaneously as the heating and sensing elements and the two others are used as a temperature reference. The heating element consists of a metallic wire of platinum Pt (2 μm width, 2 mm length) maintained on each lateral side by periodic silicon oxide SiO2 micro-bridges. Finite element simulations show that this structure achieves a fast thermal response time of 200 μs in constant current operating mode and a coefficient of temperature rise close to 25 °C/120 μW based on bulk electrical resistivity and when the Pt wire and SiO2 thicknesses are close to 100 nm and 500 nm, respectively. This design allows the fabrication of a robust thermal flow sensor with heating elements as long as possible, which enables accurate measurements with high signal to noise ratio. The sensor is then characterised experimentally; its electrical and thermal properties are obtained in the absence of fluid flow. These results confirm the effectiveness of the thermal insulation as predicted by the simulations. In a second step, the fluidic characterizations are reported and discussed for both continuous and pulsatile flows. In continuous mode, the sensor response was studied for gas flow rate ranging from 0 L min-1 to 10 L min-1. In pulsatile mode, the sensor is integrated inside a channel of a micro-valve actuated at 200 Hz. The measurements are compared with those obtained by a classical commercial hot wire [ABSTRACT FROM AUTHOR]

This letter reports the first millimeter-wave power demonstration of AlGaN/GaN high-electron-mobility transistors grown on a (110) silicon substrate. Owing to an AlN/AlGaN stress-mitigating stack and in spite of the twofold surface symmetry of Si (110), it is possible to obtain crack-free GaN layers for the fabrication of millimeter-wave power devices with high performance. The device exhibits a maximum dc drain current density of 1.55 A/mm at VGS = \0\ \V with an extrinsic transconductance of 476 mS/mm. An extrinsic current gain cutoff frequency of 81 GHz and a maximum oscillation frequency of 106 GHz are deduced from Sij parameters. At 40 GHz, an output power density of 3.3 W/mm associated with a power-added efficiency of 20.1% and a linear power gain of 10.6 dB is obtained. [ABSTRACT FROM PUBLISHER]

In this reported work, the thermal resistance of AlGaN/GaN HEMTs processed on SopSiC composite substrate is determined by electrical I-V pulsed measurement. SopSiC substrate is based on an innovative structure with a thin Si single crystal layer transferred on top of a thick polycrystalline SiC wafer. For the first time, it is demonstrated that the thermal resistivity of such devices reaches 18.9 K·mm/W when 7.5 W/mm power is dissipated, while 23.5 K·mm/W are measured on silicon in the same conditions. This result shows the capabilities of composite substrates to compete with silicon for microwave power applications. [ABSTRACT FROM AUTHOR]