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Lattice-matched Al1−xInxN / GaN heterostructures with InN mole fraction (x) of 0.18 have attracted considerable interest for use in GaN-based optoelectronic devices. Because the light emission efficiency (η emission ) of Al1−xInxN alloys is far less than that of InxGa1−xN, understanding its causes is essential. For this purpose, room-temperature photoluminescence lifetime (τ PL RT ), which almost represents the nonradiative recombination lifetime that limits the internal quantum efficiency in low η emission semiconductors, of c-plane Al1−xInxN epilayers nearly and modestly lattice-matched to GaN (0.11 ≤ x ≤ 0.21) was examined. For the epilayers grown on low threading dislocation density (TDD) GaN substrates (≪ 10 7 c m − 2 ), τ PL RT principally decreased with increasing x, indicating a progressive increase in the concentration of nonradiative recombination centers (NRCs), N NRC . One of the probable causes is the growth temperature (T g ) reduction that is indispensable to incorporate more In, because in insufficient T g regime higher T g is preferred for enhancing the surface migration of adatoms to decrease the concentrations of vacancies that compose NRCs. The Al1−xInxN epilayers of the same x but grown on high TDD (> --> 10 8 c m − 2 ) GaN-on-sapphire templates exhibited shorter τ PL RT . Because the diffusion length of minority carriers was nearly zero in the Al1−xInxN epilayers, the shorter τ PL RT indicates higher bulk N NRC in high TDD epilayers. The Al1−xInxN epilayers of considerably rough surface morphologies exhibited spatially inhomogeneous τ PL RT , implying that excited carriers recombined everywhere at InN-rich to InN-poor portions, where N NRC were likely lower to higher, respectively, than the average due to the deviations in the surface stoichiometry at various non-c-plane surfaces at a given T g . [ABSTRACT FROM AUTHOR]

Ai Takemura,1 Tatsuro Egawa,2 Takuji Tanaka,3 Takashi Kuramoto,4 Tatsuya Hayashi,2 Akihiko Ishihara1 1Laboratory of Cell Biology and Life Science, Graduate School of Human and Environmental Studies, Kyoto University, Kyoto 606-8501, Japan; 2Laboratory of Sports and Exercise Medicine, Graduate School of Human and Environmental Studies, Kyoto University, Kyoto 606-8501, Japan; 3Department of Diagnostic Pathology, Gifu Municipal Hospital, Gifu 500-8513, Japan; 4Department of Animal Science, Faculty of Agriculture, Tokyo University of Agriculture, Atsugi 243-0034, JapanCorrespondence: Ai TakemuraDepartment of Sports Research, Japan Institute of Sport Sciences, Tokyo 115-0056, JapanTel +81-75-753-2996Fax +81-75-753-6771Email takemura.ai.46c@kyoto-u.jpPurpose: In rodents, dextran sulfate sodium (DSS)-induced diarrhea and colonic inflammation have similar symptoms to those of ulcerative colitis in humans. We examined the effects of exposure to mild hyperbaric oxygen (MHO) at an atmospheric pressure of 1317 hPa with 40% oxygen on DSS-induced diarrhea and colonic inflammation in rats.Methods: Five-week-old male Kyoto Apc Delta (KAD) rats (n = 12) were administered 2% DSS through drinking water for 1 week. Subsequently, DSS-treated male rats were not subjected to any further treatment (n = 6) or exposed to MHO (n = 6) for 2 weeks. Age-matched KAD rats not subjected to DSS treatment or exposed to MHO were used as the control group (n = 6).Results: Control rats did not exhibit diarrhea and colonic inflammation. However, DSS-treated rats exhibited diarrhea and colonic inflammation, regardless of exposure to MHO. Exposure to MHO for 2 weeks led to decreased incidence of diarrhea in DSS-treated rats (p < 0.05). Exposure to MHO had no effect on colonic inflammation in DSS-treated rats (p = 0.12).Conclusion: Exposure to MHO for 2 weeks can improve diarrhea but cannot attenuate colonic inflammation, possibly due to the short exposure duration (2 weeks) used in this study.Keywords: colonic inflammation, dextran sulfate sodium, Kyoto Apc Delta rats, mild hyperbaric oxygen, oxidative metabolism

The present study investigates a suitable material, which is expected to have biocompatibility and to promote tissue regeneration. For this purpose, we have chosen chitin that was chemically modified by phosphorylation with high degree of substitution. The phosphorylated chitin (P-chitin) was synthesized using the [H.sub.3][PO.sub.4]/[P.sub.2] [O.sub.5] / [ET.sub.3] [PO.sub.4] / hexanol method. The structure of P-chitin was analyzed by FTIR, [.sup.31]P- and [.sup.13]C-NMR spectroscopic studies, scanning electron microscopy, and X-ray diffraction. The thermal properties of the P-chitin were also characterized by thermogravimetric analyses. The highly phosphorylated chitin derivatives prepared by this method were soluble in water and amorphous in nature. Thus, [H.sub.3][PO.sub.4]/[P.sub.2][O.sub.5]/[ET.sub.3][PO.sub.4]/hexanol method provides a versatile and alternative route for synthesis of P-chitin, which would be useful for biomedical applications. POLYM. ENG. SCI., 49:844-849, 2009.©2009 Society of Plastics Engineers, INTRODUCTION Chitin, a natural polymer, is the second most abundant organic resource on the earth next to cellulose. It is an exoskeleton of crustacean, cuticle of insects, and the cell [...]

A new study investigates the annealing effect of Schottky contacts on Pd, Ti and Ni/n-Al0.11Ga0.89 diodes.

A record-long room-temperature photoluminescence (PL) lifetime ( τ PL RT ) of approximately 70 ps was obtained for the sub-bandgap 3.7 eV emission band of a 300-nm-thick c-plane Al0.83In0.17N epilayer for the use in cladding layers of an edge laser structure, which were grown by metalorganic vapor phase epitaxy on a low threading dislocation density nearly lattice-matched GaN substrate. The recorded τ PL RT value was twice as long as previously reported ones, indicating half concentration of nonradiative recombination centers. Room-temperature spatially resolved cathodoluminescence intensity images for the 3.7 eV band revealed nearly zero carrier diffusion length, which is consistent with the fact that τ PL RT of 70 ps is 1/35 of the near-band-edge emission of the GaN substrate (2.4 ns). As the PL decay curves for the 3.7 eV band were sufficiently fitted by the stretched exponential function, the emission likely originates from extended states such as impurities, point defects, and their complexes, as well as localized states of uneven potential profile. [ABSTRACT FROM AUTHOR]

A study was conducted on the characteristics and degradation of an InGaN/AlGaN double-heterostructure light-emitting diode (LED) grown by metalorganic chemical vapor deposition on a sapphire substrate. The results indicate that the growth of dark regions was responsible for the degradation of electrical and optical characteristics. Moreover, GaN-based LEDs on sapphire substrates exhibit longer lifetime than the ZnSe-based LEDs.

The crystal qualities of InAlN nearly lattice-matched (LM) to GaN with different thicknesses have been investigated by X-ray diffraction (XRD) and transmission electron microscopy (TEM). It was found that the crystal quality of InAlN starts to degrade when the InAlN thickness exceeds several hundred nanometers, forming a structure consisting of two sub-layers with one sub-layer coherent to GaN and the other being degraded. Moreover, the degradation was found to be governed by the threading dislocations (TDs) propagation from the underlying GaN layer, rather than by the misfit strain between InAlN and GaN. Based on TEM observations, the growth evolution of the two-sub-layer structure is proposed, which is different from those conventional mechanisms of crystal-quality degradation in heteroepitaxial material. The results of InAlN nearly LM to GaN are suggested to be helpful in understanding the growths of lattice-mismatched systems of other In-contained III-nitrides, including InGaN/GaN. [ABSTRACT FROM AUTHOR]

The authors report on the effect of metal-precursor gas ratios on AlInN/GaN structures for high efficiency ultraviolet photodiodes. AlInN/GaN structures with the different metal-precursor gas ratio, namely V/III ratio, were grown on AlN templates by metal organic chemical vapor deposition. Nearly lattice-matched AlInN layer is obtained at the higher temperature by decreasing the V/III ratio. AlInN layers are found to have good crystal qualities with no dependency on the V/III ratio. However, pit density depends slightly on the V/III ratio, indicating good surface morphology is obtained by decreasing the V/III ratio. The fabricated photodiodes also show good device characteristics by decreasing the V/III ratio. The spectral responsivity at the cutoff wavelength increases from 1 to 20 mA/W, indicating that the quantum efficiency is greatly improved. We believe that the further optimization of the growth parameters for AlInN/GaN structures is one of the effective approaches in realizing high efficiency ultraviolet photodiodes. [ABSTRACT FROM AUTHOR]

The mechanism of the effect of n-GaN thickness on the internal quantum efficiency (IQE) in InxGa1-xN multiple-quantum-wells (MQWs) grown on GaN/Si by means of metal organic chemical vapor deposition has been investigated by x-ray diffractometry, photoluminescence, and transmission electron microscopy. It is found that the increasing n-GaN thickness obviously improves the IQE in InxGa1-xN MQWs. It is clarified that the threading dislocation density (TDD) directly determines the V-defect density and the V-defect density is lower than the TDD. As the n-GaN thickness increases from 1.0 to 2.0 μm, the TDD significantly decreases by one order of magnitude. The V-defect density obviously reduces from 3.9 × 109 cm-2 to 8.7 × 108 cm-2, while the IQE in InxGa1-xN MQWs is improved from 28.3 to 44.6%. As the GaN thickness increases, the V-defect density in the InxGa1-xN MQW decreases due to the reduction of TDD in GaN, and subsequently the nonradiative recombination centers are effectively eliminated due to the reduction of the V-defect density in the InxGa1-xN MQWs. [ABSTRACT FROM AUTHOR]

GaN-based light-emitting diodes (LEDs) grown on template of 3C-SiC/Si(111) were demonstrated. The structural properties have been investigated systematically by means of atomic force microscopy, x-ray diffraction, and transmission electron microscopy. It is found that the intermediate layer (IL) of 3C-SiC leads to not only a significant improvement in the crystalline quality of GaN, but also better interfaces between the buffer layer and the initial layers of strained-layer superlattice. The device properties were also evaluated using the measurements of current-voltage, electroluminescence, and light output power-current. Compared to conventional LEDs that do not contain 3C-SiC IL, the device with IL exhibits enhanced output power by more than 200% at an injection current of 20 mA, and the operating voltage is slightly increased from 3.7 to 3.9 V. These results indicate that using 3C-SiC as IL is one of the promising approaches to improve the performance of LEDs on silicon. [ABSTRACT FROM AUTHOR]

Pd Schottky barrier diodes were fabricated on undoped AlxIn0.02Ga0.98-xN/GaN with x less than 20%. The material properties, which were characterized by photoluminescence, x-ray diffraction, and atomic force microscopy, indicated that the quaternary samples were coherently grown on GaN template with high crystalline quality. The flatband barrier height obtained by capacitance-voltage (C-V) measurement increased with increasing Al mole fraction (increasing the band gap of the quaternary) up to 2.06 eV, in agreement with the predictions of the Schottky-Mott theory. However, current-voltage (I-V) measurements revealed that the barrier height decreased from 1.32 to 1.12 eV, which was accompanied by an increase in ideality factor from 1.04 to 1.73. The large difference of barrier height between I-V and C-V measurements could not be quantitatively explained by the traditional electron transport mechanisms of Schottky diode, such as tunneling effect, image force effect, and barrier inhomogeneity theory. Strong polarization effect in strained AlxIn0.02Ga0.98-xN/GaN heterostructure was proposed to account for the experimental results, since similar phenomena had been observed extensively in strained AlyGa1-yN/GaN heterojunction structures. [ABSTRACT FROM AUTHOR]

Studies of AlAs/GaAs distributed Bragg reflector structure shows quasiperiodic zigzag roughness, nonuniformity of thickness and the compositional transitions. The degraded heterointerfaces lead to lower reflectivity of the AlAs/GaAs distributed Bragg reflector on the silicon substrate. The reflector was grown by metalorganic chemical vapour deposition technique. Scanning electron and transmission electron microscopy and Auger electron spectroscopy were used.