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Two different SiO2/TiO2 distributed Bragg reflectors (DBR) with ITO ohmic contacts were investigated as p-type reflective electrodes in InGaN/GaN flip-chip light-emitting diodes (FC-LEDs). The DBR structures were designed to have reflectance over 95% at wavelengths of 400–520 nm (DBR 1) and 400–720 nm (DBR 2). These ranges are wider than those of the electroluminescence spectrum of blue FC-LEDs. The FC-LEDs with DBR 1 showed an output power of 114 mW at 200 mA, while those with DBR 2 presented higher output power of 135 mW. A ray tracing simulation showed that the anomalously low output power of the FC-LEDs with DBR 1 can be attributed to the low incidence angle to the DBR due to the diffraction of the light at the patterned sapphire substrate. A finite-difference time-domain simulation and angle-dependent reflectance measurement of the DBRs were also carried out. The results showed that DBR 2 yielded high reflectance even at low incidence angles, while DBR 1 presented low reflectance at incidence angles lower than 30°, followed by a reduction of the output power.

We fabricate nonpolar InGaN/GaN single quantum-well based a-plane nanopillar green light-emitting diode (LED). The top-down fabrication method was used for fabricating nanopillar LED from the planar LED, where self-aligned In3Sn nanodots were used as an etching mask. Fabricated nanopillars have high yield with large height-to-diameter aspect ratio found by scanning-electron-microscopy characteristics. The size of nanopillars depends on the size of In3Sn nanodots which are fabricated from the ITO (indium tin oxide) thin film by 3% HCl solution. It is systematically investigated that the size of nanodots depends on the ITO thickness rather than the etching time. In order to achieve uniform current injection into nanopillars, a p-type transparent ITO contact is selectively deposited on the top of each nanopillar. The ITO contact layer consists of a slanted oblique-angle (85○/−85○) layer followed by a thick blanket layer for uniform current distribution. The macroscopic optoelectronic characteristics show the uniform current distribution over the chip area, which is also interactively explained.

GaN-based light emitting diodes (LEDs) with a nitrogen implanted current-blocking layer (CBL) were successfully demonstrated for improving the light extraction efficiency (LEE) and radiant intensity. The LEE and radiant intensity of the LEDs with a shallow implanted CBL with nitrogen was greatly increased by more than 20% compared to that of a conventional LED without the CBL due to an increase in the effective current path, which reduces light absorption at the thick p-pad electrode. Meanwhile, deep implanted CBL with a nitrogen resulted in deterioration of the LEE and radiant intensity because of formation of crystal damage, followed by absorption of the light generated at the multi-quantum well(MQW). These results clearly suggest that ion implantation method, which is widely applied in the fabrication of Si based devices, can be successfully implemented in the fabrication of GaN based LEDs by optimization of implanted depth.

We have demonstrated that color-conversion efficiency can be enhanced through the use of non-radiative energy transfer between CdSe/ZnS core/shell colloidal quantum dots(QDs) and nitride multi-quantum well(MQW) in light emitting diodes(LEDs) having nano-patterned p-GaN. The nitride LEDs having nano-patterned p-GaN were fabricated by selective deep etching of p-GaN by using self-assembled ITO nano-dots as a etch mask. For comparison, we also fabricated the nitride LEDs having groove-etched p-GaN as well as the LEDs having a normal p-GaN layer. The results show that the LEDs having nano-patterned p-GaN showed the higher color conversion efficiency of 15.5 % and the improved effective internal quantum efficiency of 71 %. The enhanced efficiency can be attributed to sufficient close QD-MQW separation due to deep etching of p-GaN by using nano-patterning, which resulted in faster energy transfer rate of 2.47 ns−1 for non-radiative QD-MQW energy-transfer.

A significant improvement of output power and external quantum efficiency (EQE) for nonpolar a-plane (11-20) GaN light-emitting diodes (LEDs) on r-plane sapphire substrates has been demonstrated by using embedded pyramid-shape air-gap arrays on hexagonally patterned SiO $_{2}$ layer. The air-gap structure was realized based on asymmetrical growth behavior of a-plane epitaxial lateral overgrowth (ELO) GaN along ${+}{\rm c}$ -axis and ${-}{\rm c}$ -axis. The output power and EQE of the a-plane LEDs with the air-gaps on patterned SiO $_{2}$ have increased by more than 50% when compared to those of the conventional a-plane LEDs. Theoretical fit to the measured EQE suggested that the significant improvement of EQE was mainly attributed to the increase in light extraction efficiency (EXE). Light emission pattern analysis and ray-tracing simulation revealed that the air-gap arrays on top of patterned SiO $_{2}$ enlarged the guided-light scattering at the air-gap surface due to the significant refractive index contrast with the GaN layer, followed by the improvement of EXE of nonpolar a-plane LEDs.

We report on the results of low resistance ohmic contacts to amorphous IGZO films treated with hydrogen plasma. Amorphous IGZO films with a thickness of 200 nm were deposited on glass substrates by radio frequency magnetron sputtering and exposed to inductively coupled hydrogen plasma. Using Ti, the specific contact resistivity of the ohmic contact was decreased considerably from 7.06 × 10 2 to 9.94 × 10 − 5 Ω cm 2 by a hydrogen plasma treatment without the need for a thermal treatment. The improved specific contact resistivity of ohmic contact was attributed to an increase in carrier concentration on the amorphous IGZO surface, due to the formation of high density of oxygen vacancies and O H bonds. Although the transmittance of the hydrogen plasma treated sample was decreased drastically by the formation of In clusters, the improved transmittance result without deteriorating the electrical properties was obtained effectively by removing the In clusters using a HCl solution.

InGaN/GaN based nano-pillar light emitting diodes (LEDs) with a diameter of 200-300 nm and a height of 500 nm are fabricated by inductively coupled plasma etching using self-assembled ITO nano-dots as etching mask, which were produced by wet etching of the as-deposited ITO films. The peak PL intensity of the nano-pillar LEDs was significantly higher than that of the as-grown planar LEDs, which can be attributed to the improvement of external quantum efficiency of the nano-pillar LEDs due to the large sidewall of the nano-pillars. We have also demonstrated electrical pumping of the InGaN/GaN based nano-pillar LEDs with a self-aligned TiO2 layer as a passivation of sidewall of the nano-pillars.

We investigated the In-based ohmic contacts on Nitrogen-face (N-face) n-type GaN, as well as Gaface n-type GaN, for InGaN-based vertical Light Emitting Diodes (LEDs). For this purpose, we fabricated Circular Transfer Length Method (CTLM) patterns on the N-face n-GaN that were prepared by using a laserlift off method, as well as on the Ga-face n-GaN that were prepared by using a dry etching method. Then, In/transparent conducting oxide (TCO) and In/TiW schemes were deposited on the CTLM in order for low resistance ohmic contacts to form. The In/TCO scheme on the Ga-face n-GaN showed high specific contact resistance, while the minimum specific contact resistance was only 3×10 Ω-cm after annealing at 300°C, which can be attributed to the high sheet resistance of the TCO layer. In contrast, the In/TiW scheme on the Ga-face n-GaN produced low specific contact resistance of 2.1×10 Ω-cm after annealing at 500°C for 1 min. In addition, the In/TiW scheme on the N-face n-GaN also resulted in a low specific contact resistance of 2.2×10 Ω-cm after annealing at 300°C. These results suggest that both the Ga-face n-GaN and N-face nGaN. (Received January 26, 2010)

Interfacial microstructure and elemental diffusion of Cu-doped indium oxide (CIO)/indium tin oxide (ITO) ohmic contacts to p-type GaN for light-emitting diodes (LEDs) were investigated using cross-sectional transmission electron microscopy (XTEM), X-ray photoelectron spectroscopy (XPS), and X-ray diffraction. The CIO/ITO contacts gave specific contact resistances of approximately 10(-4) omegacm2 and transmittance greater than 95% at a wavelength of 405 nm when annealed at 630 degrees C for 1 min in air. After annealing at 630 degrees C, multi-component oxides composed of Ga2O3-In2O3, Ga2O3-CuO, and In2O3-CuO formed at the interface between p-GaN and ITO. Formation of multi-component oxides reduced the barrier height between p-GaN and ITO due to their higher work functions than that of ITO, and caused Ga in the GaN to diffuse into the CIO/ITO layer, followed by generation of acceptor-like Ga vacancies near the GaN surface, which lowered contact resistivity of the CIO/ITO contacts to p-GaN after the annealing.

GDF15 is a transcriptional target gene for p53 and its family members, p63 and p73. Its promoter region contains two p53-type response elements, RE1 and RE2, and RE2 confers p53-specific transactivation. RE2 contains several mismatches from the canonical p53 response element (RRRCWWGYYY). Two mismatches in the RRR span and T base of the RE2 core sequence in the most 3′ quarter-site are critical for inhibiting the binding affinity to p63 and p73 and corresponding promoter activity. Our results strongly suggest that differential DNA binding affinities between p53 family member proteins act, at least in part, to confer specific target gene activation.

Efficiency droop is a major obstacle facing high-power application of InGaN/GaN quantum-well (QW) light-emitting diodes. In this letter, we report the suppression of efficiency droop induced by density-activated defect recombination in nanorod structure of a-plane InGaN/GaN QWs. In the high carrier density regime, the retained emission efficiency in a dry-etched nanorod sample is observed to be over two times higher than that in its parent QW sample. We further argue that the improvement is a combined effect of the amendment contributed by lateral carrier confinement and the deterioration made by surface trapping., 18 Pages,5 figures

We report on the observation of carrier-diffusion-induced defect emission at high excitation density in a-plane InGaN single quantum wells. When increasing excitation density in a relatively high regime, we observed the emergence of defect-related emission together with a significant reduction in bandedge emission efficiency. The experimental results can be well explained with the density-activated carrier diffusion from localized states to defect states. Such a scenario of density-activated defect recombination, as confirmed by the dependences of photoluminescence on the excitation photon energy and temperature, is a plausible origin of efficiency droop in a-plane InGaN quantum-well light-emitting diodes., Comment: 15 pages, 4 figures

Recently, 3D nanostructures have attracted much interest because of their interesting electrical/optical properties such as wave guiding modes, light scattering, antireflection effects, etc. In this work, a facile yet efficient method for the fabrication of hierarchical 3D indium tin oxide (ITO) nanotrees (NTs) and their integration in GaN-based blue-light-emitting diodes (LEDs) for efficient light-extraction are reported. The ITO NTs are fabricated by the oblique-angle (≈85°) deposition method at 240 °C using electron-beam evaporation. The ITO NTs grow via a self-catalytic vapor–liquid–solid mechanism with the branches having an epitaxial relationship with the trunks. The ITO NTs successively deposited on an ITO thin film as a p-contact layer are annealed at 600 °C for 1 min under ambient air in order to form a transparent ohmic contact. The indium gallium nitrde/gallium nitride (InGaN/GaN) LED with ITO NTs presents a 29.5% enhancement in the light output power at an injection current of 20 mA, compared to the reference LED with an ITO thin film p-contact. This enhancement is ascribed to the effective light extraction of the ITO NTs due to to the gradually decreasing profile of the refractive index from 2.08 (ITO thin film), 1.15 (dense ITO NTs), 1.06 (porous ITO NTs) to 1.0 (air). These results are in good agreement with the optical simulation by the COMSOL wave optics module.

Vertical nonpolar a-plane (11-20) InGaN/GaN light-emitting diodes (LEDs) have been demonstrated by using laser lift-off technique. The forward voltage of the a-plane vertical LEDs was 4.3 V at 350 mA, which was reduced by 0.8 V compared to that of the a-plane lateral LEDs. The vertical geometry of the a-plane LEDs produced the higher quantum efficiency with a low efficiency droop and also enhanced the output power by more than 40%, when compared to those of a-plane lateral LEDs. These results can be attributed to the high thermal dissipation as well as uniform current spreading of the vertical geometry of the a-plane LEDs. Furthermore, elimination of the highly defected GaN nucleation layer after removing the sapphire substrates during the fabrication process can also enhance current injection efficiency, followed by the increase in the output power.

We have investigated the high-temperature degradation of optical power as well as electrical properties of InGaN/GaN light-emitting diodes (LEDs) fabricated with ITO transparent p-electrode during accelerated electro-thermal stress. As the thermal stress increased from 150 degrees C to 250 degrees C at a electrical stress of 200 mA, the optical power of the LEDs was significantly reduced. Degradation of the optical power was thermally activated, with the activation of 0.9 eV. In addition, the activation energy of the degradation of optical power was fairly similar to that of the degradation of series resistance of the LEDs, 1.0 eV, which implies that the increase in the series resistance may result in the severe degradation of optical power. We also showed that the increase in the series resistance of the LEDs during the accelerated electro-thermal stress can be attributed to reduction of the active acceptor concentration in the p-type semiconductor layers and local joule heating due to the current crowding.

We have demonstrated that the light extraction efficiency of the InGaN based multi-quantum well light-emitting diodes (LEDs) can be improved by using a single die growth (SDG) method. The SDG was performed by patterning the n-GaN and sapphire substrate with a size of single chip (600 x 250 microm2) by using a laser scriber, followed by the regrowth of the n-GaN and LED structures on the laser patterned n-GaN. We fabricated lateral LED chips having the SDG structures (SDG-LEDs), in which the thickness of the regrown n-GaN was varied from 2 to 6 microm. For comparison, we also fabricated conventional LED chips without the SDG structures. The SDG-LEDs showed lower operating voltage when compared to the conventional LEDs. In addition, the output power of the SDG-LEDs was significantly higher than that of the conventional LEDs. From optical ray tracing simulations, the increase in the thickness and sidewall angle of the regrown n-GaN and LED structures may enhance photon escapes from the tilted facets of the regrown n-GaN, followed by the increase in light output power and extraction efficiency of the SDG-LEDs.

Interfacial microstructure and elemental diffusion of Cu-doped indium oxide (CIO)/indium tin oxide (ITO) ohmic contacts to p-type GaN for light-emitting diodes (LEDs) were investigated using cross-sectional transmission electron microscopy (XTEM), X-ray photoelectron spectroscopy (XPS), and X-ray diffraction. The CIO/ITO contacts gave specific contact resistances of approximately 10(-4) omegacm2 and transmittance greater than 95% at a wavelength of 405 nm when annealed at 630 degrees C for 1 min in air. After annealing at 630 degrees C, multi-component oxides composed of Ga2O3-In2O3, Ga2O3-CuO, and In2O3-CuO formed at the interface between p-GaN and ITO. Formation of multi-component oxides reduced the barrier height between p-GaN and ITO due to their higher work functions than that of ITO, and caused Ga in the GaN to diffuse into the CIO/ITO layer, followed by generation of acceptor-like Ga vacancies near the GaN surface, which lowered contact resistivity of the CIO/ITO contacts to p-GaN after the annealing.

Overexpression of several aquaporins has been reported in different types of human cancer but the role of AQPs in human carcinogenesis has not yet been clearly defined. Here, we demonstrate that ectopic expression of human AQP5 (hAQP5), a water channel expressed in lung, salivary glands, and kidney, induces many phenotypic changes characteristic of transformation both in vitro and in vivo. Furthermore, the cell proliferative ability of AQP5 appears to be dependent upon the phosphorylation of a cAMP-protein kinase (PKA) consensus site located in a cytoplasmic loop of AQP5. In addition, phosphorylation of the PKA consensus site was found to be phosphorylated preferentially in tumors. These findings altogether indicate that hAQP5 plays an important role in human carcinogenesis and, furthermore, provide an attractive therapeutic target.

Isoflavones are synthesized by isoflavone synthases via the phenylpropanoid pathway in legumes. We have cloned two isoflavone synthase genes, IFS1 and IFS2, from a total of 18 soybean cultivars. The amino acid residues of the proteins that differed between cultivars were dispersed over the entire coding region. However, amino acid sequence variation did not occur in conserved domains such as the ERR triad region, except that one conserved amino acid was changed in the IFS2 protein of the GS12 cultivar (R374G) and the IFS1 proteins of the 99M06 and Soja99s65 cultivars (A109T, F105I). In three cultivars (99M06, 99M116, and Simheukpi), most of amino acid changes were such that the difference between the amino acid sequences of IFS1 and IFS2 was reduced. The expression profiles of three enzymes that convert naringenin to the isoflavone, genistein, chalcone isomerase (CHI), isoflavone synthase (IFS) and flavanone 3-hydroxylase (F3H) were examined. In general, IFS mRNA was more abundant in etiolated seedlings than mature plants whereas the levels of CHI and F3H mRNAs were similar in the two stages. During seed development, IFS was expressed a little later than CHI and F3H but expression of these three genes was barely detectable, if at all, during later seed hardening. In addition, we found that the levels of CHI, F3H, and IFS mRNAs were under circadian control. We also showed that IFS was induced by wounding and by application of methyl jasmonate to etiolated soybean seedlings.

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We demonstrated three-dimensional (3D) graphene foam-based transparent conductive electrodes in GaN-based blue light-emitting diodes (LEDs). A 3D graphene foam structure grown on 3D Cu foam using a chemical vapor deposition method was transferred onto a p-GaN layer of blue LEDs. Optical and electrical performances were greatly enhanced by employing 3D graphene foam as transparent conductive electrodes in blue LED devices, which were analyzed by electroluminescence measurements, micro-Raman spectroscopy, and light intensity-current-voltage testing. The forward operating voltage and the light output power at an injection current of 100 mA of the GaN-based blue LEDs with a graphene foam-based transparent conductive electrode were improved by ∼26% and ∼14%, respectively. The robustness, high transmittance, and outstanding conductivity of 3D graphene foam show great potentials for advanced transparent conductive electrodes in optoelectronic devices.

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In this study, we investigated the effect of dislocations on the contact resistivity of ohmic contacts on p-GaN. This was accomplished by measuring the current-voltage characteristics for nonalloyed Pd ohmic contacts on lateral epitaxial overgrowth (LEO) GaN, which has a low dislocation density, as well as on dislocated GaN. We fabricated transfer-length measurement (TLM) patterns with a very narrow mesa structure, which allowed the production of TLM patterns on the LEO GaN as well as on dislocated GaN. A comparison between the contact resistivity of the Pd contacts on LEO GaN and that of the contacts on dislocated GaN revealed that dislocations have minimal influence on the contact resistivity of the Pd contacts on p-GaN. We also demonstrated that the operating voltage of the InGaN-based laser diodes did not depend on the dislocations. However, the dislocations did have a significant influence on the threshold current of the laser diodes.

We investigate the effects of reduced exciton diffusion on the emission properties in InGaN/GaN multiple-quantum-well nanorods. Time-resolved photoluminescence spectra are recorded and compared in dry-etched InGaN/GaN nanorods and parent multiple quantum wells at various temperatures with carrier density in different regimes. Faster carrier recombination and absence of delayed rise in the emission dynamics are found in nanorods. Many effects, including surface damages and partial relaxation of the strain, may cause the faster recombination in nanorods. Together with these enhanced carrier recombination processes, the reduced exciton diffusion may induce the different temperature-dependent emission dynamics characterized by the delayed rise in time-resolved photoluminescence spectra.

We fabricated an InGaN based nanorod LED structure with colloidal quantum-dot (QD) phosphors deposited in between the nanorods, creating side-wall coupling between QD phosphors and InGaN multiple-quantum-well (MQW) emitters. Time-resolved photoluminescence measurements for nanorod structures with and without colloidal QD coating were performed to study the direct MQW-to-QD non-radiative energy transfer.

We present in this communication our study of the nonradiative energy transfer between colloidal quantum dot (QD) phosphors and nitride nanopillar light emitting diodes (LEDs). An epitaxial p-i-n InGaN/GaN multiple quantum-well (QW) heterostructure was patterned and dry-etched to form dense arrays of nanopillars using a novel etch mask consisting of self-assembled In3Sn clusters. Colloidal QD phosphors have been deposited into the gaps between the nanopillars, leading to sidewall coupling between the QDs and InGaN QW emitters. In this approach, close QW-QD contact and a low-resistance design of the LED contact layer were achieved simultaneously. Strong non-radiative energy transfer was observed from the InGaN QW to the colloidal QD phosphors, which led to a 263% enhancement in effective internal quantum efficiency for the QDs incorporated in the nanopillar LEDs, as compared to those deposited over planar LED structures. Time-resolved photoluminescence was used to characterize the energy transfer process between the QW and QDs. The measured rate of non-radiative QD-QW energy-transfer agrees well with the value calculated from the quantum efficiency data for the QDs in the nanopillar LED.