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Both high-beam-quality and high-power operation of InGaN laser array are realized by lateral-corrugated waveguides (LCWG) with reduced higher-order transverse modes. In our proposed structure, the number of higher-order modes supported by the waveguide and scattered by the LCWG is smaller than that of a conventional LCWG, which suppresses the deterioration of quantum efficiency. This contributes to high-power operation for laser processing, since the maximum output power of an array is sensitive to the efficiency. Even at 55 W from a single InGaN array chip, averaged lateral beam-quality factor of 4.9 is successfully obtained for individual emissions in the array. [ABSTRACT FROM AUTHOR]

Loss of vacuum in vacuum interrupter (VI) is becoming an interesting theme for VI used in medium voltage range beyond its lifetime of typically 20–30 years. The early detection of abnormality in the vacuum insulated equipment is important not only for the operating vacuum circuit breakers (VCBs) in medium voltage but also for the development of higher voltage VCBs, such as cubicle type gas insulated switchgear (C-GIS) with compressed gas and/or insulation gas. The purpose of present study is to estimate the vacuum degree in VI by measuring partial discharges (PDs) occurring in medium vacuum range for more than 1 Pa. As a leakage gas, atmospheric air and SF 6 gas were sealed into the VI with close-state, whose pressure was regulated through vacuum pump systems, which corresponds to the left region of its PD inception voltage (PDIV) curve. From PD current waveforms measured by detecting resistor connected to plane electrode outside the VI, PD charges, occurrence frequency and phase characteristics of PDs for each applied AC voltage and internal vacuum pressure were determined. It was concluded that, by statistical processing using PD parameters and histogram, a number of occurrence of PD and PD charges would be dominant parameter for determination of the internal pressure of VI with the leakage gas of air. [ABSTRACT FROM AUTHOR]

This paper reviews the recent activities for normally-off GaN-based gate injection transistors (GITs) on Si substrates and their application to inverters. Epitaxial growth of the AlGaN/GaN heterostructures with good crystallinity over 200-mm Si substrates with eliminated bowing enables low-cost fabrication of GaN devices with high breakdown voltages. A novel normally-off GaN transistor called as GIT is proposed in which hole injection from the p-type AlGaN gate increases the drain current with low on-state resistance by conductivity modulation. The low on-state resistance in GaN-based devices greatly helps to increase the efficiency of power switching systems. A GaN-based three-phase inverter successfully drives a motor with high efficiency of 99.3% at a high output power of 1500 W. The presented GaN-based devices are expected to greatly help saving energy in the future as an indispensable power switching system. [ABSTRACT FROM AUTHOR]

Ion implantation technique can be applied for planar isolation of AlGaN/GaN heterojunction field-effect transistors (HFETs), which enables high-density integration of the power switching transistors. So far, the reported isolation using ion implantation for GaN devices has never maintained high isolation voltages after high-temperature processing over 800 ^\circ\C which is commonly used for the fabrication. In this paper, we present detailed analysis and mechanism of thermally stable isolation of GaN devices by Fe ion implantation keeping high breakdown voltage between the devices after high-temperature annealing. Ion species forming deep levels at atomic sites in GaN are examined by using first-principle calculation prior to the experiments. The calculation indicates that the Fe ions stay at Ga sites with deep levels in GaN. The following experiments using various ion species well agree with the aforementioned predictions, where implanted regions by other ions than Fe exhibit reduction of the resistivity after high-temperature annealing to recover the processing damage by the ion implantation. As a result, it is experimentally found that Fe is the only choice to serve high resistivity after the annealing. The Fe ion implantation enables high breakdown voltage of 900 V after the annealing at 1200 ^\circ\C. This technique is indispensable to enable monolithic integration of the lateral AlGaN/GaN HFETs for high-voltage power switching systems. [ABSTRACT FROM PUBLISHER]

The switching waveforms and losses of a GaN gate injection transistor (GIT) bidirectional switch, a type of four-terminal device, were analyzed for the first time using an equivalent circuit model. By applying a three-terminal model to the equivalent circuit model of the GIT bidirectional switch and by using the waveforms of the chopper circuit, the parameters were derived with high accuracy. Furthermore, gate resistance dependence was added to the input capacitance component connected to the gate terminal in order to contain the influence of the gate structure of the GIT. It was confirmed that the calculated switching waveforms and losses agree well with those of the experimental values with over 90% accuracy, even in cases where circuit conditions for circuit voltage, load current, and gate resistance were varied. [ABSTRACT FROM PUBLISHER]

Reduction of thermal resistance in AlGaN/GaN heterojunction field-effect transistors (HFETs) is critical for further increase in their output power to be handled in these promising material systems. In this paper, we present a new technique to reduce it using polycrystalline AlN passivation deposited by dc sputtering as a surface heat spreader over AlGaN/GaN HFETs. The AlN is deposited by dc sputtering, and it is well oriented to the c-axis. The measured thermal resistances of AlGaN/GaN HFETs with AlN passivation are lower than those with SiN passivation, which well agree with the results of the thermal simulation. The most notable change of the characteristics by AlN passivation is that the drain current increases by 30%, and the ON-state resistance is reduced by 66% by the passivation; moreover, the current collapse suppresses successfully. As a result, the radio frequency output power is higher than that with conventional SiN passivation and is increased by increasing the thickness of AlN passivation. Thus, reduction of the thermal resistance and higher output power by AlN passivation is experimentally achieved. [ABSTRACT FROM AUTHOR]

Nonpolar AlGaN/GaN metal-insulator-semiconductor-heterojunction field-effect transistors (MIS-HFETs) with a complete normally off operation have been demonstrated for the first time. To realize the normally off operation of the MIS-HFETs, a 2-nm-thick SiN (as an insulator) and GaN-based nonpolar epitaxial layers that are free from polarization charges are employed. We have found that a thicker nonpolar AlN buffer layer achieves a GaN layer with a narrower full width at half maximum of the X-ray rocking curve and higher electron mobility. The fabricated MIS gate structure on the AlN buffer layer successfully decreases the gate leakage current and enables a more positive gate bias of up to +4 V, which is advantageous to achieve a higher drain current. Moreover, the n-GaN capping layer between gate and ohmic electrodes helps to reduce parasitic resistance and suppress current collapse. The fabricated a-plane MIS-HFET exhibits a threshold voltage of +1.3 V with a high drain current of 112 mA/mm. The presented MIS-HFETs will be desirable in next-generation radio-frequency and power switching application fields. [ABSTRACT FROM AUTHOR]

In this paper, we demonstrate a novel method to integrate photonic crystals (PhCs) on GaN-based blue light-emitting diodes (LEDs) using a silicon substrate as a mold for forming the PhCs. This method starts with fabricating a 2-D grooved Si substrate as that mold. Subsequently, GaN-based epitaxial layers are grown on the Si mold-substrate, which effectively reduces the dislocation density in GaN by enhanced lateral epitaxial growth. After the epitaxial layers are bonded onto a highly reflective substrate, the Si mold-substrate is removed. This substrate-transfer technique replicates PhC from the mold-substrate on the LED surface free from processing damages. The resultant LEDs with PhC have outperformed the LEDs without PhC in the optical output power by 80%, taking advantage of the enhanced light extraction by PhC. [ABSTRACT FROM AUTHOR]

We have developed a normally-off GaN-based transistor using conductivity modulation, which we call a gate injection transistor (GIT). This new device principle utilizes hole-injection from the p-AlGaN to the AlGaN/GaN heterojunction, which simultaneously increases the electron density in the channel, resulting in a dramatic increase of the drain current owing to the conductivity modulation. The fabricated GIT exhibits a threshold voltage of 1.0 V with a maximum drain current of 200 mA/mm, in which a forward gate voltage of up to 6 V can be applied. The obtained specific ON-state resistance (RON · A) and the OFF-state breakdown voltage (BVds) are 2.6 mΩ cm2 and 800 V, respectively. The developed GIT is advantageous for power switching applications. [ABSTRACT FROM AUTHOR]

Orientation effect on AlGaN/GaN heterojunction field-effect transistors (HFETs) has been experimentally and theoretically examined in detail. The drain-currents of the fabricated AlGaN/GaN HFETs with various gate directions do not depend on the gate orientation, whereas those of GaAs-based HFETs strongly depend on the gate direction due to the piezoelectric charges induced around the gate electrode. The piezoelectric charges induced in the vicinity of the gate electrode are simulated by using a finite-element method. This simulation solves the piezoelectric equations with piezoelectric and elastic stiffness constants, assuming that stress is applied to the gate edges in the HFET. The detailed simulation reveals that the piezoelectric charge distribution does not depend on the gate direction, although a large amount of piezoelectric charges is induced in the vicinity of the gate edges, which is consistent with the experimental result. Moreover, it is mathematically clarified that these experimental and simulated results are due to the symmetry characteristic of the piezoelectric and elastic stiffness constants for nitride semiconductor materials. [ABSTRACT FROM AUTHOR]

In this paper, we present recessed AlGaN/GaN heterojunction field-effect transistors (HFETs) with lattice-matched InAIGaN capping layers, which reduce both ohmic contact resistance and series resistance between the AIGaN and the capping layer. The lattice-matched alloy epitaxial layer with both In and Al high compositions are successfully grown by metal-organic chemical vapor deposition. The grown lattice-matched In0.09Al0.32Ga0.59N capping layer has close total polarization and bandgap to those of the underlying Al0.26Ga0.74N layer. The balanced polarization eliminates the depletion of electrons at the In0.09 Al0.32 Ga0.59N/Al0.26 Ga0.74N interface, which can reduce the series resistance across it. It is also noted that the fabricated HFET exhibits very low ohmic contact resistance of 1.0 × 10-6 μ · cm2 or less. Detailed analysis of the source resistance reveals that the series resistance at the In0.09Al0.32Ga0.59N/Al0.26Ga0.74N interface is one fifth as low as the resistance at the conventional GaN/Al0.26 Ga0.74N interface. [ABSTRACT FROM AUTHOR]

We have developed a high-power AIGaN/GaN HFET fabricated on 4-in conductive Si substrate with a source-via grounding (SVG) structure. The SVG structure enables efficient chip layout and high packing density by the vertical configuration. By establishing a high-quality epitaxial technology on a Si substrate and by significantly reducing the parasitic resistance, a very low specific on-state resistance of 1.9 mΩ ·cm2 is achieved. The breakdown voltage is as high as 350 V, which is attributed to the Si substrate acting as a backside field plate. Because of reduction of the parasitic inductance, very high level of current (2.0 kA/cm2) transients, i.e., a turn-on time of 98 ps and a turn-off time of 96ps, are successfully measured for the first time. [ABSTRACT FROM AUTHOR]

A high-power single-pole double throw (SPDT) switch IC using AlGaN/GaN heterojunction field-effect transistors (HFETs) is demonstrated for the first time. The reduction of on-resistance (Ron) and off-capacitance (Coff) for AlGaN/GaN HFETs enables the GaN-based switch IC that can be applied for practical RF applications. A novel Si-doping technique is employed to reduce ohmic contact resistance, which successfully reduces the Ron. The Coff of the HFETs on a sapphire substrate is found to be smaller than that on a SiC substrate, together with low cost fabrication. The GaN-based SPDT switch IC with single-stage configuration is designed by using a circuit simulator based on the extracted device parameters. The fabricated SPDT switch IC achieves insertion loss of 0.26 dB and Isolation of 27 dB at 1 GHz, as well as an extremely high-power handling capability of 43 W. This value is 10 times higher than that of typical GaAs-based switch ICs. In addition, the switch IC exhibits low distortion characteristics, where the third-order intercept point of 41 dBm is achieved. The chip size is reduced to 40% as compared with conventional four stage GaAs-based switch ICs by using the single-stage circuit configuration. [ABSTRACT FROM AUTHOR]

We have developed a novel AlGaN-GaN hetero-junction field effect transistor (HFET) with an ultralow source resistance by employing the novel superlattice (SL) cap structure. The particular advantage of the SL cap, i.e., the existence of multiple layers of the polarization-induced two-dimensional electron gas (2DEG) with high mobility and high concentration at each AIGaN-GaN interface, is fully exploited for lowering the lateral resistance and the potential barrier at the interface of the SL cap and the HFET barrier layer. By designing the AlGaN-GaN thickness ratio, we have established a method to obtain the optimized SL structure and have achieved an extremely low source resistance of 0.4 Ω · mm which is lower not only than HFETs with the conventional structure but also than those with the n-GaN cap structure. The SL cap HFET fabricated on a sapphire substrate exhibited excellent dc and RF performance, i.e., maximum transconductance of over 400 mS/mm, maximum drain current of 1.2 A/mm, a cutoff frequency of 60 GHz, a maximum frequency of oscillation of 140 GHz, and a very low noise figure minimum of 0.7 dB at 12 GHz. [ABSTRACT FROM AUTHOR]