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ABSTRACT: Export Date: 22 April 2013, Source: Scopus, Art. No.: 826215, References: Schoedl, T., Schwarz, U.T., Kummler, V., Furitsch, M., Leber, A., Miller, A., Lell, A., Härle, V., Facet degradation of GaN heterostructure laser diodes (2005) J. Appl. Phys., 97, p. 123102;
Proceedings of SPIE - The International Society for Optical Engineering; 01/2012
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ABSTRACT: Cited By (since 1996):1, Export Date: 22 April 2013, Source: Scopus, Art. No.: 79390W, References: Ohta, M., Ohizumi, Y., Hoshina, Y., Tanaka, T., Yabuki, Y., Funato, K., Tomiya, S., Ikeda, M., High-power pure blue laser diodes (2007) Physica Status Solidi (A) Applications and Materials, 204 (6), pp. 2068-2072. , DOI 10.1002/pssa.200674748;
Proceedings of SPIE - The International Society for Optical Engineering; 01/2011
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ABSTRACT: GaN is very promising for power switching transistors taking advantages of the high breakdown strength with high saturation electron velocity. The lateral and compact device configuration enables high speed switching with reduced on-state resistance and parasitic capacitance. In this paper, state-of-the-art device technologies of GaN transistor and its monolithic integration for switching applications are reviewed. The topics include a novel normally-off transistor called Gate Injection Transistor (GIT) fabricated on a cost-effective Si substrate, and thermally stable isolation by Fe ion implantation. These are applied for the world first monolithic GaN inverter IC for motor drive with high efficiency. The presented technologies are indispensable for wide-spread use of GaN power switching transistors in the future.
Solid-State and Integrated Circuit Technology (ICSICT), 2010 10th IEEE International Conference on; 12/2010
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ABSTRACT: State-of-the-art device technologies of GaN power switching transistors are reviewed. The presented technologies solve the technical issues on GaN transistors for practical use replacing currently used Si-based power devices. Thick epitaxial growth over 6-inch Si substrates enables low cost fabrication of GaN devices with high breakdown voltages. A new operating principle for the normally-off GaN transistor called Gate Injection Transistor (GIT) is proposed in which hole injection from the p-type AlGaN gate increases the drain current by conductivity modulation. Six GITs are integrated onto a single chip on silicon as the world first GaN-based monolithic inverter IC. The inverter IC successfully drives a motor with low operating loss which is 42% reduced from that of the conventional IGBT (Insulated Gate Bipolar Transistor)-based one. These technologies are indispensable for wide-spread use of GaN power switching transistors in the future.
Power Electronics Conference (IPEC), 2010 International; 07/2010
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ABSTRACT: University of Padova in collaboration with Panasonic Corp. has developed in the recent years an in depth reliability analysis of Blu-Ray InGaN Laser Diodes (LD) submitted to CW stress at different driving conditions. The reliability analysis has been focused towards a) the identification of the effects of current, temperature and optical field and b) the identification of the physical mechanism related to degradation. Results show that LD devices exhibit a gradual threshold current increase, while slope efficiency is almost not affected by the ageing treatment. Degradation rate is found to depend on stress temperature and on current level, while it does not significantly depend on the optical field in the cavity. Within this paper we demonstrate that: (i) the degradation rate shows a linear correlation with stress current level; (ii) the Ith increase is correlated to the decrease in non-radiative lifetime (τ<sub>nr</sub>); (iii) stress temperature acts as an accelerating factor for LD degradation; (iv) pure thermal storage does not significantly degrade LDs characteristics.
Reliability Physics Symposium (IRPS), 2010 IEEE International; 06/2010
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Y. Uemoto,
T. Morita,
A. Ikoshi,
H. Umeda,
H. Matsuo,
J. Shimizu,
M. Hikita,
M. Yanagihara,
T. Ueda,
T. Tanaka, D. Ueda
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ABSTRACT: We present a GaN monolithic inverter IC on Si substrate and successful motor-drive by it for the first time. Taking advantages of the bi-directional operation free from the forward voltage off-set, the inverter can be operated just by the integrated six GaN-based normally-off gate injection transistors (GITs) without any external fast recovery diodes (FRDs) to flow the fly-wheel current. The IC enables the efficiency as high as 93% at low power operation where so far that of conventional Si-based inverters has remained lower value owing to the forward voltage off-set. The key processing technology is the newly introduced planar isolation using Fe ion implantation which fully isolates the GaN-based lateral devices each other.
Electron Devices Meeting (IEDM), 2009 IEEE International; 01/2010
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ABSTRACT: We present a detailed study of the degradation of InGaN-based laser diodes submitted to electrical stress tests, which is aimed at understanding the role of nonradiative recombination in determining the worsening of the properties of the devices. The analysis, which is carried out by means of optical techniques, indicates that stress determines an increase in the threshold current of the devices without strong modifications in the slope efficiency. For the first time, we give an experimental demonstration of the fact that the threshold current increase is correlated to the increase in the nonradiative recombination rate of the carriers in the active layer. This result has been verified in a wide range of operating current levels; furthermore, the results of stress tests carried out at different current levels support the hypothesis that current is a significant driving force for the analyzed degradation process.
IEEE Electron Device Letters 05/2009; · 2.85 Impact Factor
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ABSTRACT: This paper reports on the degradation of InGaN-based laser diodes for Blu-ray technology. The devices have been submitted to stress under: 1) constant current, different temperatures; 2) high temperature, no bias; and 3) constant temperature, several current levels. The tests carried out within this paper demonstrate that stress determines the increase in the threshold current, according to the square root of stress time. The degradation rate has been found to be strongly determined by the stress current level, while the optical field had only a limited role in determining the degradation kinetics. The impact of temperature on device degradation is also limited, as confirmed by the activation energy value of 250 meV extrapolated by measurements carried out at different temperatures. On the basis of the evidence collected within this paper, we attribute the degradation of the lasers to an electrothermally activated process that induces an increase in the nonradiative recombination rate with subsequent decrease in the optical efficiency of the active layer.
IEEE Transactions on Electron Devices 03/2009; · 2.32 Impact Factor
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ABSTRACT: We propose a new breakdown mechanism of GaN-based electron devices called ldquonatural super junctionrdquo. The junction model is supported by device simulations and experiments for newly developed multi-channel diodes with a dual-recessed structure. Based on the model, the on-resistance of the diodes can be reduced keeping high breakdown voltages. The fabricated diode achieves extremely high breakdown voltage of 9300 V with low on-state resistance RonA of 176 mOmegacm<sup>2</sup>, which is the record low value for GaN-based SBDs with the breakdown voltage over 9000 V.
Electron Devices Meeting, 2008. IEDM 2008. IEEE International; 01/2009
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ABSTRACT: This paper reports an analysis of the degradation of laser diodes for Blu-Ray technology. The study has been carried out by means of optical and electrical characterization techniques. We demonstrate that: (i) stress at constant current level determines the increase of the threshold current of the devices, and the decrease of the sub-threshold emission signal; (ii) degradation rate has an almost linear dependence on the stress current level, thus suggesting that current is a significant driving force for devices degradation. Furthermore, thanks to an accurate study of the optical parameters of the devices, we demonstrate that the degradation of the samples is due to the decrease of the non-radiative recombination lifetime of the carriers in the active layer, with subsequent decrease of the optical efficiency of the devices. Degradation can be attributed to the generation/propagation of defects in the active layer of the devices, that can be also responsible for the modification of the electrical parameters of the laser diodes.
Electron Devices Meeting, 2008. IEDM 2008. IEEE International; 01/2009
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D. Ueda,
M. Hikita,
S. Nakazawa,
K. Nakazawa,
H. Ishida,
M. Yanagihara,
K. Inoue,
T. Ueda,
Y. Uemoto,
T. Tanaka,
T. Egawa
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ABSTRACT: GaN/AlGaN device technologies are reviewed aiming at the applications to power switching systems. SL (Super Lattice) capping and QA (Quaternary Alloy) over-layer techniques have been developed to reduce the on-resistance of GaN/ AlGaN HFET. Further, we achieved GaN on Silicon epitaxial growth technology with almost the same mobility keeping the same 2DEG density, which will make the cost comparable to conventional Si one. The experimentally obtained R<sub>on</sub>A of the FET is 1.9 m¿cm<sup>2</sup>, which is 14 times lower than that of Si ones. Additionally, a novel approach to realize enhancement mode operation of GaN/AlGaN FET is proposed using minority carrier injection by the gate.
Solid-State and Integrated-Circuit Technology, 2008. ICSICT 2008. 9th International Conference on; 11/2008
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ABSTRACT: 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 2D 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.
IEEE Journal of Quantum Electronics 11/2008; · 1.88 Impact Factor
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ABSTRACT: We report a normally-off GaN-based monolithic bidirectional switch for the first time. The switch consists of a double-gate AlGaN/GaN gate injection transistor (GIT) which serves normally-off operation with high drain current utilizing the hole injection from the p-type gate. The fabricated bidirectional switch exhibits high breakdown voltage of 650 V for both polarities and low on-state resistance (R<sub>on</sub> <sup>.</sup>A) of 3.1 mΩcm<sup>2</sup> . The GaN-based bidirectional switch can be applied to AC-AC matrix converters with high efficiency.
Electron Devices Meeting, 2007. IEDM 2007. IEEE International; 01/2008
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Y. Uemoto,
D. Shibata,
M. Yanagihara,
H. Ishida,
H. Matsuo,
S. Nagai,
N. Batta,
Ming Li,
T. Ueda,
T. Tanaka, D. Ueda
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ABSTRACT: We report ultra high voltage AlGaN/GaN heterojunction transistors (HFETs) on sapphire with thick poly-AlN passivation. Extremely high blocking voltage of 8300 V is achieved while maintaining relative low specific on-state resistance (Ron*A) of 186 mOmegaldrcm<sup>2</sup>. Via-holes through sapphire at the drain electrodes enable very efficient layout of the lateral HFET array as well as better heat dissipation.
Electron Devices Meeting, 2007. IEDM 2007. IEEE International; 01/2008
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ABSTRACT: A 26 GHz short-range radar (SRR) system has been developed based on a 2.5 Gcps direct sequence spread spectrum (DSSS) technique combined with simple homodyne detection. Separate frequency-triplers have been provided with transmitter (TX) and receiver (RX) chips to cut off the carrier-leakage path from local signal. By using this configuration, carrier-leakage in TX signal can be significantly suppressed falling into the satisfactory range of the UWB regulation. The present radar system achieved the maximum detection range of 14 m with the resolution of 6 cm. TX, RX, and PN generator chipset has been developed using InGaP/GaAs HBT process, where fT/fmax of 65 GHz/ 83 GHz were attained.
Microwave Symposium, 2007. IEEE/MTT-S International; 07/2007
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ABSTRACT: We have developed a K-band AlGaN/GaN HFET MMIC amplifier by applying an AlGaN/GaN superlattice (SL) capped structure on sapphire substrate. Owing to the lowest (0.4 Ω · mm) source resistance of AlGaN/GaN HFETs, the HFETs exhibited excellent DC and RF characteristics, and sufficient ability to operate in the K-band frequency range is obtained. The fabricated MMIC with a CPW-line structure exhibited a small-signal gain higher than 10 dB with a 3-dB bandwidth of 20-24.5 GHz and that of 13 dB at 21.6GHz when biased at a supply voltage of 7 V. The 1dB compression point (P<sub>1dB</sub>) referred to output of 15.4 dBm at 21.6 GHz was obtained. This work is the first report of MMIC amplifier fabricated on sapphire successfully operating in the K band.
Microwave Symposium Digest, 2005 IEEE MTT-S International; 07/2005
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ABSTRACT: We present a high power AlGaN/GaN HFET fabricated on a conductive Si substrate with a source-via grounding (SVG) structure. The device has a very low specific on-state resistance of 1.9 mΩ·cm<sup>2</sup> and a high off-state breakdown voltage of 350 V, and a current handling capability of 150 A. In addition, a sub-nano second switching t<sub>r</sub> of 98 psec and t<sub>f</sub> of 96 psec, with a current density as high as 2.0 kA/cm<sup>2</sup> is demonstrated for the first time.
Electron Devices Meeting, 2004. IEDM Technical Digest. IEEE International; 01/2005
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Thrombosis Research 09/1995; 79(3):337-41. · 2.44 Impact Factor
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ABSTRACT: Cyclosporine A (CyA), a potent immunosuppressive drug, has been used in renal transplant recipients with increasing frequency since 1982. Despite its efficacy, CyA therapy has been associated with an increased incidence of thromboembolic complications. This has been attributed to increased thromboxane production, reduced prostacyclin synthesis and increased platelet aggregability. The coagulation system is also altered in CyA-treated patients and some of these changes would favor thrombosis. Increased fibrinogen and FVII:C levels have also been associated with an enhanced risk of thrombosis. In contrast, CyA therapy was reported to increase the levels of antithrombin III and protein C, two proteins known to protect against venous thromboembolism. However, the possible effect of CyA on the fibrinolytic system has not been thoroughly investigated and rather confusing data have been reported concerning both enhancement and suppression of fibrinolysis. Serotonin (5-hydroxytryptamine, 5-HT) may play a role in hemostasis and platelet/vessel wall interactions. It may facilitate platelet thrombus formation by potentiating the aggregatory response to other agents such as ADP, collagen or epinephrine and by causing vasoconstriction. Taking all these data into consideration we have measured some fibrinolytic parameters, whole blood and plasma serotonin concentration in cyclosporine A- and non-cyclosporine A-treated kidney transplant recipients.
Thrombosis Research 11/1994; 76(1):97-102. · 2.44 Impact Factor
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ABSTRACT: Whole blood and plasma serotonin (5-HT), its major metabolite--5-hydroxyindoleacetic acid (5-HIAA), renal cortical blood flow, serum creatinine and whole blood cyclosporine A (CyA) levels were investigated in rats administered with CyA at a dose of 5 mg/kg b.w. or 10 mg/kg b.w. for 14 consecutive days. Serum creatinine remained unaltered during CyA treatment and no apparent changes in excised kidneys were found. Dose-dependent increases in whole blood and plasma 5-HT as well as whole blood 5-HIAA levels were observed. Renal cortical blood flow declined significantly and correlated inversely with whole blood 5-HT and 5-HIAA as well as with plasma 5-HT. Whole blood 5-HT was positively related to whole blood CyA levels. Taking all these data into account and considering the fact that 5-HT is a potent vasoconstrictor, a possible role of this amine in the pathogenesis of renal ischemia during CyA administration is suggested.
Thrombosis Research 11/1994; 76(2):171-9. · 2.44 Impact Factor
