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Background Aortic root rupture is a severe complication of balloon-expandable transcatheter aortic valve replacement (TAVR). Although previous studies have revealed several risk factors for this complication, predicting this complication is occasionally difficult. Case summary A 78-year-old male patient underwent TAVR via a transfemoral approach using a 29-mm balloon-expandable valve. No recognized risk factors for aortic root rupture existed in pre-procedural multi-detector computed tomography (MDCT) analysis. However, after the valve deployment, sudden haemodynamic collapse occurred. Transoesophageal echocardiography revealed pericardial effusion, which led to an immediate diagnosis of cardiac tamponade following aortic root rupture. Following pericardial drainage via a subxiphoid approach, the haemodynamics were immediately stabilized. After 10 days of close observation, the patient was discharged on Day 39 without additional problems. He was still alive at the 6-month follow-up without sequelae. Discussion Established risk factors for aortic root rupture include >20% area oversizing, bicuspid aortic valve, small annulus (

The bactericidal effects of air plasma jets produced with a twisted wire-cylindrical electrode configuration were clarified in terms of plasma-induced damage to plant nutrient solutions. The bacterial suspensions were directly irradiated with air plasma jets using a low gas flow rate, which was shown to significantly inactivate the bacteria suspended in the solutions without reducing the nutrient concentrations. However, the plasma irradiation time required for inactivation depended on the type of bacteria; Escherichia coli (E. coli) and Bacillus subtilis (B. subtilis) were inactivated in 20–30 s, while Staphylococcus aureus (S. aureus) required 7 min. The inactivation of E. coli and B. subtilis decreased with increasing air gas flow rate, whereas the inactivation of S. aureus was independent of the rate. The inactivation could be attributed to a greater number of reactive oxygen and nitrogen species (RONS) from the air plasma jet, including O2 molecules in the feeding gas attaching to the bacterial suspension surface, which do not harm the nutrient components. This can be derived from the results; the air-plasma-jet-activated nutrient solutions (RONS introduced in the solutions) and the N2 plasma jets had only a limited inactivation effect on the bacteria suspended in the solutions.

Al0.24Ga0.76N thin film surfaces were irradiated simultaneously with CF4 plasma and ultraviolet (UV) at wavelengths of 280 and 310 nm. The UV wavelength and intensity were varied without changing the plasma-generating conditions. These UV photon energies were larger than the band-gap energy of AlGaN film. A compositional change in the simultaneously-irradiated surface depended on the UV wavelength. The 280-nm UV irradiation caused a greater degree of nitrogen deficiency than that introduced by 310-nm UV irradiation, causing the Ga- and Al-rich surface. Moreover, the 280-nm UV irradiation increased the amounts of F atoms and CFx fluorocarbons incorporated into the surface, in comparison with CF4 plasma-only irradiation. In contrast, the 310-nm UV irradiation reduced the amount of the incorporated F atoms and hardly increased the amount of the incorporated CFx fluorocarbons from those caused by CF4 plasma-only irradiation. These became more prominent with increasing UV intensity. These UV wavelength-dependent results can be discussed in terms of four factors: the UV photogenerated-hole-assisted oxidation, the localized surface plasmon resonance, the UV-induced migration of gallium and aluminum vacancies forming stable complexes with F, and the sticking of F-related radicals from CF4 plasma onto the surface.

A Si infrared photodetector that operates without requiring to be cooled was fabricated, and its properties were evaluated. The function of this device is to detect, as an electrical signal, carrier density changes due to stimulated emission utilizing a phonon-assisted process via dressed photons. The photosensitivities of this device were 0.21 A W−1, 0.03 A W−1, and 0.01 A W−1 for wavelengths of 1.3 μm, 1.6 μm, and 2.0 μm, respectively, when the forward current density was 50 A cm−2, and the device exhibited a higher sensitivity for wavelengths greater than the cutoff wavelength.

TiO2 thin films were treated with plasma with the assistance of external heating. This plasma was produced with an O2 dielectric barrier discharge (DBD) at atmospheric and near-atmospheric gas pressures. For comparison, the samples were annealed in O2 gas and also treated with O2 DBD plasma alone. The effects of these treatments on photocatalytic activity were compared by evaluating the photodecomposition of methylene blue dye in aqueous solution. The photocatalytic activity of the heat-assisted plasma-treated sample was the most enhanced among the treatment processes. The net photodecomposition of the heat-assisted plasma-treated sample was slightly higher than or comparable to that of TiO2 anatase-phase nanoparticle powder. The photocatalytic activity enhancement can be attributed to an increase in the effective concentration of photogenerated carriers on the surface. This increase is driven by the synergistic effect between an increase in the depletion layer width and an increase in the optical absorption due to the crystalline transition from the bronze to the anatase phases. This crystalline transition occurred at a lower temperature than the annealing transformation temperature.

Photodecomposition and photobactericidal activities of anatase/rutile-mixed phase TiO2 nanoparticles annealed with low-temperature O2 plasma were clarified by comparing them with those annealed in ambient air. The photocatalytic activities of plasma-assisted-annealed sample greatly enhanced as compared with the untreated sample, under not only ultraviolet irradiation but also visible-light irradiation. The photocatalytic activities of air-annealed samples did not enhance under ultraviolet irradiation but enhanced under visible-light irradiation. The enhanced photocatalytic activities due to the plasma-assisted annealing (PAA) originated from the increased photoexcited carrier concentration. This enhancement was discussed from PAA-induced characteristic factors. PAA facilitated the phase transformation to anatase, contributing directly to extending the photoexcited carrier lifetime. PAA introduced more oxygen vacancies, contributing to trapping more photogenerated electrons. PAA also introduced more bridging/terminal oxygen groups adsorbed on the surface, increasing the upward band-bending, the depletion layer width at the surface, and the charge transfer from rutile to anatase. These two introductions contributed to facilitating the separation of photoexcited carriers. Furthermore, PAA reduced the aggregate size of TiO2 nanoparticles formed on the surface, contributing to increasing optical absorptions. More reactive oxygen species produced from the bridging/terminal oxygen groups by the photoexcited carriers would also enhance the photocatalytic activities.

Al0.24Ga0.76N thin film surfaces were etched with CF4 plasma, with and without the assistance of near-ultraviolet (UV) irradiation. The near-UV source was a black light lamp, which emitted wavelengths of 300–400 nm. The chemical compositions and morphologies of surfaces etched under the two plasma conditions were compared, to clarify the effect of near-UV irradiation on the properties of the AlGaN surface. Near-UV irradiation during CF4 plasma etching reduced the amounts of F atoms, AlFx fluorides, and GaFx fluorides incorporated into the surface, and enhanced the amount of CFx fluorocarbons. Near-UV irradiation did not influence the depth distribution of incorporated fluorine-related impurities, or the degree of nitrogen deficiency caused in the surface. These compositional changes in the surface occurred irrespective of the gas pressure. Near-UV irradiation caused a significant change in the morphology of surfaces etched at high gas pressure (13 Pa), as the etching time was increased to 60 and 100 min. Near-UV irradiation did not change the morphologies of surfaces etched at lower gas pressures (1.3 and 6.7 Pa), irrespective of etching time.

The thermal stability, in terms of cycle and rate performances at 80 °C, and its safety related to lithium ion batteries composed of a LiFePO 4 cathode and SiO anode are investigated. Based on an STEM-EELS analysis, the SiO powder is found to have an amorphous structure, in which nanosized Si particles (Si-rich phase) are uniformly dispersed in the SiO 2 matrix (SiO 2 -rich phase). During the charge/discharge cycling, the cell exhibits a satisfactory cycle performance with a discharge capacity retention of 93.6% and a voltage retention of 93.9% at the 1500 th cycle. Also, the charge and discharge capacity retentions at 10 C are 97.5% and 94.7%, respectively, together with a limited polarization, demonstrating its high rate performance. Furthermore, a 1.16 Ah LiFePO 4 /SiO laminated cell shows negligible voltage and temperature changes during the nail penetration test. The Li concentration in the active material (Si-rich phase) is found to be almost the same as that in the SiO 2 -rich phase after the test. This high thermal stability and safety may be due to the formed layer from the SiO 2 matrix, preventing any side reaction from occurring on the Si surface and isolating the internal current path during the nail penetration.

Conclusion These findings suggest that low dose irradiation with 310 nm NB-UVB specifically suppressed the up-regulation of H1R gene expression without inducing apoptosis and that UVB of shorter or longer wavelength than 310 nm NB-UVB had no such effects. Objective To develop a narrowband-ultraviolet B(NB-UVB) phototherapy for allergic rhinitis, this study investigated the effects of irradiation with NB-UVB at wavelength of 310 nm on phorbol-12-myristate-13-acetate (PMA)-induced up-regulation of histamine H1 receptor (H1R) mRNA in HeLa cells. Methods The mRNA levels of H1R in HeLa cells were measured using real-time RT-PCR. Apoptosis were evaluated with DNA fragmentation assay. Results PMA induced a significant increase in H1R mRNA expression in HeLa cells. Irradiation with 305 nm UVB and 310 nm NB-UVB, but not with 315 nm UVB at doses of 200 and 300 mJ/cm(2) significantly suppressed PMA-induced up-regulation of H1R mRNA. At a dose of 200 mJ/cm(2), irradiation with 305 nm UVB, but not with 310 nm NB-UVB, induced apoptosis, although exposure of the cells to both 305 and 310 nm UVB induced apoptosis at a dose of 300 mJ/cm(2) after PMA treatment in HeLa cells. Conversely, irradiation with 315 nm UVB at doses of 200 and 300 mJ/cm(2) did not induce apoptosis.

Compositional and morphological changes in Al 0.24 Ga 0.76 N surfaces etched by CF 4 and Ar plasmas were investigated in order to clarify the effect of fluorine impurities incorporated in the surface by the CF 4 plasma. The CF 4 plasma effectively incorporated the fluorine impurities in the surface even at a short etching time. A small number of the incorporated fluorine impurities only contributed to the formations of Al(OH) x F y and GaF x on the surface even as the etching time increased. Although the CF 4 and Ar plasma etchings preferentially remove nitrogen atoms from the surfaces, the preferential removal induced by the CF 4 plasma etching was suppressed compared with the case of the Ar plasma etching. The CF 4 plasma etching caused a smooth surface regardless of the gas pressure and the etching time, whereas the Ar plasma etching changed the surface morphology depending on the gas pressure and the etching time. The incorporation of the fluorine impurities, which bonded with the cation vacancies such as gallium and aluminum vacancies introduced in the surface by the plasma etching, was considered to concern the suppression of the preferential removal and the formation of the smooth surface.

Damage characteristics of n-GaN thin film surfaces etched by ultraviolet (UV) light-assisted He plasmas at various gas pressures have been investigated from the viewpoint of the UV light irradiation effect. During the plasma etching, the surface is additionally irradiated with UV light emitted from a black light lamp. The peak wavelength of the emitted UV light corresponds to that of the GaN band-gap energy. The result is compared with that obtained only by use of He plasma. A morphological change in the surface etched by the UV light-assisted He plasma depends on gas pressure, whereas the He plasma only does not cause the morphological change in the surface regardless of gas pressure. The additional UV light irradiation causes a morphological change in the surface etched for a long time of more than 60 min at high gas pressures between 6.7 and 13 Pa. The morphology of the surface etched at a low gas pressure of 1.3 Pa does not change from that of the as-grown surface even with increasing etching time. The additional UV light irradiation also enhances the etch depth and suppresses a decrease in N/Ga ratio at the surface compared with that obtained only by use of the He plasma.

A face centered cubic (FCC) type Mg–Sc hydride (Mg0.8Sc0.2Hx phase) was prepared by an ultra-high pressure (UHP) technique generating an 8 GPa hydrogen pressure. Reversible hydrogen releasing and restoring behaviors have been observed by a differential scanning calorimeter (DSC) measurement at a 0.5 MPa hydrogen pressure. The hydrogen releasing temperature was lower by around 70 K than that of MgH2. The structural analysis using a Rietveld refinement of the synchrotron X-ray diffraction patterns indicated that the FCC phase was preserved without decomposition after the reproducible hydrogen releasing and restoring reactions.

Herein, Li-ion battery using carbon fibers instead of conventional aluminum/copper foils as the current collectors is assembled. To achieve the binder-free environment, LiMn0.97Al0.03O2-based fiber type cathode is prepared directly via a two-step strategy involving electroplating and hydrothermal method by forming active materials on the individual carbon fiber. Cu6Sn5-based fiber type anode is prepared directly via electroplating and subsequent heat treatment. The resulting LiMn0.97Al0.03O2|Cu6Sn5 Li-ion battery using carbon fiber as the current collector functions at about 3 V, with an initial capacity of 180 mAh g−1 (based on the cathode). The capacity retention is 90 % after 150 cycles. In particular, the battery using phosphate-modified LiMn0.97Al0.03O2-based fiber type electrode demonstrates a better cycling and high rate performance compared to the unmodified counterpart.

Using a written questionnaire we surveyed a sample population of 155 female students, and investigated the associations between mobile phone dependence and perceived parental rearing attitudes. Participants completed the Mobile Phone Dependence Questionnaire (MPDQ; Toda, Monden, Kubo, & Morimoto, 2004) and the Parental Bonding Instrument (PBI; Parker, Tupling, & Brown, 1979). In relation to maternal rearing attitudes, analysis of responses revealed a statistically significant difference in MPDQ scores between respondents who fell in the categories for high care/high protection and low care/low protection. In relation to paternal rearing attitudes, no such difference was apparent. These findings suggest that the childhood relationship with the mother may be associated with mobile phone dependence. Furthermore, loneliness may contribute to this association.

BACKGROUND Radiofrequency ablation (RFA) has become an accepted alternative for treating intrathoracic malignancies; however, the incidence and characteristics of peri- and postprocedural complications are not well described. The purpose of the study was to assess the safety and technical feasibility of percutaneous RFA in unresectable intrathoracic malignancies. METHODS Percutaneous RFA was performed in patients with intrathoracic malignancies between June 2001 and December 2004. In total, 366 tumors were treated in 137 patients in 211 sessions. All patients were nonsurgical candidates or had refused surgery. Three hundred and thirty-six lesions were subjected to RFA for the treatment of metastases and 30 lesions for primary lung carcinoma. RESULTS Although no procedural mortality occurred, 2 patients died during the course of the study because of intractable pneumothorax and massive hemoptysis (0.9%). The overall major complication rate was 17.1% (pneumothoraces requiring tube drainage in 25, pleuritis in 6, pleural effusion requiring tube drainage in 4, lung abscess in 1, and intrapulmonary hemorrhage with hemothorax in 1). Minor complications included pneumothoraces not requiring tube drainage in 108 sessions, pleural effusion without drainage in 34, hemosputum in 9, nausea and/or vomiting in 3, subcutaneous emphysema in 3, cough in 2, skin burn in 2, atelectasis in 1, and subileus in 1. High fever and/or chest pain were seen in 33.8% and 39.3% of patients, respectively. CONCLUSIONS With over 200 procedures, RFA appears to be a safe and minimally invasive option with negligible mortality and little morbidity in selected patients with unresectable intrathoracic malignancies. Cancer 2007. © 2007 American Cancer Society.

We describe two cases of intractable pneumothorax that were attributed to a bronchopleural fistula (BPF) after radiofrequency ablation of lung tumors. In both cases, radiofrequency ablation induced necrosis of the lung tissue between the pleural space and the bronchus. The bronchopleural fistula formed after sloughing of the necrotic tissue. Management of the bronchopleural fistula was quite challenging, requiring frequent treatments, including pleurodesis, endobronchial management, and/or surgical repair. In one of the patients, air leakage persisted despite these efforts, and the patient died of acute pneumonia 52 days after the procedure. Although it is rare, with an incidence of 0.6% (2/334) at our institution, intractable pneumothorax due to bronchopleural fistula should be recognized as a risk associated with radiofrequency ablation of lung tumors.

The growth mechanisms during metalorganic vapor phase epitaxy of InGaN quantum wells (QWs) on three-dimensional GaN microfacet structures composed of (0001) and {11-22} planes were investigated. The cross section of the microfacet structures formed by regrowth was changed from triangle to trapezoid, depending on the mask geometries for the regrowth. The emission peak wavelength of the (0001) microfacet QWs was always longer than that of the {11-22} microfacet QWs, and the difference is smaller than in planar (0001) and {11-22} QWs. To clarify this observation, the local thicknesses of constituent InN and GaN on the GaN microfacets were estimated. Using a formula derived from the diffusion equation, the distribution of the local thickness is fitted to estimate the apparent diffusion lengths, λ. For Ga, λ was fitted to be 5.2 μm on (0001) and 3.1 μm on {11-22}, while for In, λ was 2.7 μm on (0001) and 1.6 μm on {11-22}. This suggests that the degree of migration of adatoms depends on both facets and atoms, which may cause the facet-dependent In compositions and lead to multiwavelength emission from microfacet InGaN QWs. (© 2007 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)

We performed near-field photoluminescence (PL) mapping and atomic force microscopy at the same scanning area to clarify relationship between luminescence dynamics and threading dislocations in violet and blue light emitting InGaN single-quantum-well structures on epitaxially laterally overgrown GaN templates at room temperature. Clear correlation has been found between the distribution of dark area in PL mapping data and threading dislocations with screw and mixed types in the violet sample. On the other hand, such correlation has not been found in the blue sample. These results indicated that the carriers/excitons are captured easily in nonradiative recombination centers (NRCs) originating from the threading dislocations in the violet sample, because the lateral diffusion length of carriers/excitons is large due to a small potential fluctuation induced by compositional fluctuation of In comparing to those in the blue sample. However, the capture to such NRCs is hindered effectively in the blue one because of the localization to potential minima. (© 2006 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)

The dependence of UV-LED lifetime on threading dislocation density(TDD) was examined. UV-LED structures were grown on standard GaN template(TDD: 1x108/cm2) and ELO-GaN(TDD: 1x107/cm2), and lifetime testing was performed under a forward current of 500 mA at junction temperature(Tj) of 75 oC. Lifetime of both LEDs were estimated as 17,600 h (standard GaN template) and 166,000 h (ELO-GaN), respectively. It was found that GaN underlying layer with TD-density of 1x107/cm2 is superior to that of 1x108/cm2 in terms of LED lifetime, despite no output power difference. Junction temperature (Tj) dependence of LED lifetime was investigated in use of standard GaN template(1x108/cm2). Tj was varied from 311 K to 422 K. The activation energy was determined to be 0.36 eV. (© 2006 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)

We have carried out time-integrated and spectrally-resolved four-wave mixing (FWM) measurements to study the effects of built-in strain within GaN films on their exciton structures and on their coherent dynamics. Precise values for exciton energies, linewidths, and oscillation periods of quantum beats were presented. Remarkable phase shifts of the quantum beats were observed in the GaN films on a-sapphire, suggesting the exciton-exciton interaction caused by the reduction of the crystal symmetry.

We use surface plasmons to increase the light emission efficiency from InGaN/GaN quantum wells by covering these with thin metallic films. Large luminescence enhancements were measured when silver or aluminum layers are deposited 10 nm above an InGaN light emitting layer, whereas no such enhancements are obtained from gold coated samples. The internal quantum efficiencies of quantum wells before and after metallization were determined from the temperature dependence of the photoluminescence intensity. Our results indicate that the use of surface plasmons will lead to a new class of very bright light emitting diodes, and highly efficient solid-state light sources. (© 2005 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)

Spatial distribution of photoluminescence (PL) spectra has been assessed in violet light emitting InGaN single-quantum-well (SQW) structures by employing a scanning near-field optical microscope (SNOM) at room temperature. Clear correlation has been found between PL intensity and PL peak wavelength under illumination collection (I-C) mode, where strong PL was observed in the area emitting at lower energy bands. However, dark spots having diamter of about a few hundreds nm appeared also in lower energy region. Moreover, multi-mode SNOM-PL with a spatial resolution of 200 nm revealed that the difference of PL-intensity image between I-C mode and illumination (I) mode is not so large comparing with a blue light emitting InGaN-SQW. These findings suggest that threading dislocations act as nonradiative recombination centers in the violet sample unlike blue ones, and that the diffusion length to such centers is larger than that to localized centers leading to radiative recombination. Furthermore, nonradiative recombination centers originating from point defects have been spatially identified in the violet sample grown on epitaxially laterally overgrown (ELO) GaN template. (© 2005 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)

We fabricated GaN-based ultraviolet laser structures having air/semiconductor distributed Bragg reflectors (DBR) as a cavity mirror by focused ion beam (FIB) etching. The designed structure consisted of 5 pairs of 3λ/4 air gaps and 7λ/4 semiconductor layers. A scanning electron microscope (SEM) measurement showed that the fabricated DBR had vertical sidewalls and that the widths of air gaps and semiconductor layers were 275–305 nm and 260–290 nm, respectively. The numerical calculation taken a diffraction loss in the air gap into account demonstrated that the reflectivity of the fabricated DBR mirror should be higher than 95%. The photo-pumped lasing measurement revealed that the threshold excitation power density of the laser structure with the DBR mirror at one end of the laser cavity was reduced by 27% compared with the one without DBR mirrors. This reduction in the lasing threshold corresponds to the improvement of the reflectivity from 17% for facet mirrors to 52–74% for the DBR mirrors, suggesting that the fabricated DBR mirror has high potential for application to integrated photonic components. (© 2005 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) See erratum physica status solidi (c) Vol. 2, No. 7, 2932 (2005)

Since 1993, InGaN light-emitting diodes (LEDs) have been improved and commercialized, but these devices have not fulfilled their original promise as solid-state replacements for light bulbs as their light-emission efficiencies have been limited. Here we describe a method to enhance this efficiency through the energy transfer between quantum wells (QWs) and surface plasmons (SPs). SPs can increase the density of states and the spontaneous emission rate in the semiconductor, and lead to the enhancement of light emission by SP-QW coupling. Large enhancements of the internal quantum efficiencies (eta(int)) were measured when silver or aluminium layers were deposited 10 nm above an InGaN light-emitting layer, whereas no such enhancements were obtained from gold-coated samples. Our results indicate that the use of SPs would lead to a new class of very bright LEDs, and highly efficient solid-state light sources.

We review the recent progress of nitride-based light-emitting diodes (LEDs) and discuss the relation between dislocation density and quantum efficiency. We also discuss how to improve the external quantum efficiency of nitride-based LEDs. Secondly, the group-III nitride laser diodes (LDs), which emit from near-ultraviolet to pure-blue, are reviewed. Reducing threading dislocations can increase the lifetime of nitride LDs. Using the epitaxial lateral overgrowth technique, a dislocations density of the order of 105 cm−2 has been obtained. The relation between the lifetime of nitride LDs and the density of dislocations is discussed. Finally, near-ultraviolet LDs and pure-blue LDs are described. (© 2003 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)

We investigated the hot carrier dynamics in InGaN multi-quantum wells using photoluminescence, time-resolved photoluminescence (TRPL) and white-light pump and probe methods at room temperature. The pump and probe spectra or ΔOD spectra have not reflected the screening of electric field by photoexcited carriers but the distribution of hot carriers. It reflects the band filling of the tail state in lower energy side and Maxwell-Boltzmann-like tail of hot carriers on the higher energy side. ΔOD spectra in 1.5 ps rose in the observed spectral region, which indicates that thermalization among carriers is very fast. It is because of carrier-LO phonon and carrier-carrier interaction. After 2 ps ΔOD spectra are red shifted as increasing the time delay. At 40 ps time delay, the Maxwell-Boltzmann-like tail shows still the high temperature of carriers. This slow cooling is likely due to the hot phonon effects where the nonequilibrium phonon population may lead to a reabsorption of phonons by photoexcited carriers.

Bound and unbound biexcitons in a free-standing bulk GaN are investigated by time-integrated and spectrally-resolved four-wave mixing measurements, where the formation of hetero-biexcitons that consist of A and B excitons (XX AB ) as well as A biexcitons and their unbound biexciton are clearly observed. Through the FWM spectra and delay-time dependence, it is found that the interaction between A and B excitons gives rise to the phase shifts of the quantum beating and the energy shifts of the spectra, which is considered as the effect of the unbound state of XX AB (i.e. XX * AB ). This interaction is found to play an important role in the FWM signals for all polarizations.

Optical properties induced by two major effects, potential fluctuation and piezoelectric fields, have been assessed to interpret the emission mechanism in low-dimensional nitride semiconductors because the former leads to the exciton/carrier localization, and the latter to the quantum confined Stark effect (QCSE). Degenerated white-light pump-and-probe spectroscopy has been employed to assess which factor plays an important role in the series of In x Ga 1-x N multiple quantum well (MQW) structures whose well widths are 3 nm, 5 nm and 10 nm. Moreover, photoluminescence (PL) mapping with scanning near-field optical microscopy (SNOM) has revealed the dense distribution of island-like structures, the size of which ranges from 20 nm to 70 nm in a 3 nm-thick In x Ga 1-x N single quantum well (SQW) structure emitting at blue spectral region.

We have remarkably improved the emission efficiency of 365 nm ultraviolet (UV) light emitting diode (LED). Rugged pattern is fabricated on the surface of LED chips in order to enhance the extraction efficiency. As a result, the extraction efficiency of this LED approximately increased by 50%. When this UV LED was operated at a forward-bias pulsed current of 500 mA at room temperature (RT), the peak wavelength, the output power (Po), the operating voltage (Vf) and the external quantum efficiency (ηex) were 365 nm, 240 mW, 4.5 V and 14.1%, respectively. On the other hand, at a forward-bias direct current of 500 mA at RT, Po, Vf and ηex were 210 mW, 4.3 V and 12.4%, respectively. The ηex at 365 nm increased to double that of the reported value before. (© 2003 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)

The crystal orientation of GaN films deposited on fused quartz substrates by rf planar magnetron sputtering using a mesh to guard against plasma exposure was investigated by X-ray diffraction. Sample films were deposited at constant N 2 gas pressure and input power at a range of substrate temperatures between 84°C and 600°C. It was found that GaN films with good crystal orientation can be produced by rf sputtering with the c -axis of GaN crystals oriented normal to the substrate surface in almost all films produced. The crystal 0 0·2 orientation was good at substrate temperatures exceeding 300°C, however, films deposited at 600°C peeled from the substrate. The fine mesh installed to protect the film from exposure to plasma was found to be very useful for depositing films with a good crystal orientation of 0 0·2, and the best crystal orientation was realized for a film deposited by sputtering with a target to mesh separation of 30 mm.

InGaN multiple quantum well laser diode (LD) wafer that lased at 400 nm was shown to have the InN mole fraction, x , of only 6% in the wells. Nanometer-probe compositional analysis showed that the fluctuation of x was as small as 1% or less, which is the resolution limit. However, the wells exhibited a Stokes-like shift (SS) of 49 meV and an effective localization depth E 0 was estimated by time-resolved photoluminescence (TRPL) measurement to be 35 meV at 300 K. Since the effective electric field due to polarization in the wells is estimated to be as small as 286 kV/cm, SS is considered to originate from an effective bandgap inhomogeneity. Because the well thickness fluctuation was insufficient to produce SS or E 0 , the exciton localization is considered to be an intrinsic phenomenon in InGaN material. Indeed, bulk cubic In 0.1 Ga 0.9 N, which does not suffer any polarization field or thickness fluctuation effect, exhibited an SS of 140 meV at 77 K and similar TRPL results. The origin of the localization is considered to be due to the large bandgap bowing and In clustering in InGaN material. Such shallow and low density localized states are leveled by injecting high density carriers under the lasing conditions for the 400 nm LDs.

Carrier dynamics in GaN and InGaN/GaN SQW structures were observed by using the transient grating (TG) method with sub-picosecond pulsed laser at room temperature. The diffusion coefficients (D) of photo-created carriers were estimated by the decay rate time of TG signals and the photoluminescence (PL) lifetime. It was found that D depends on the emission wavelength (In composition). The relationship between the emission efficiencies and carrier diffusion was considered in terms of the spatial inhomogeneity of In composition.

Spatial distribution of photoluminescence (PL) spectra has been assessed in an InGaN single quantum well (SQW) structure by means of fluorescence microscopy and scanning near-field optical microscopy (SNOM) under illumination-collection mode. The PL intensity of fluorescence image is uniform at 77 K, but the dark spot areas were extended with increasing temperature. The near-field PL images revealed the variation of both peak energy and intensity in PL spectra according to the probing location with the scale less than a few hundreds nm.

Defects in GaN grown using metalorganic chemical vapor deposition were studied through the use of monoenergetic positron beams. For Mg-doped GaN, no large change in the diffusion length of positrons was observed before and after activation of Mg. This was attributed to the scattering of positrons by potentials caused by electric dipoles of Mg–hydrogen pairs. For Si-doped GaN, the line-shape parameter S increased as carrier density increased, suggesting an introduction of Ga vacancy due to the Fermi level effect. Based on these results, we discuss the effects of the growth polar direction of GaN on optical properties in this article. Although the optical properties of a GaN film grown toward the Ga face direction exhibited excitonic features, a film grown toward the N face (−c) direction exhibited broadened photoluminescence and transmittance spectra, and a Stokes shift of about 20 meV was observed. This difference was attributed to extended band-tail states introduced by high concentrations of donors and ...

Optical properties of the InGaN single-quantum-well amber light-emitting-diodes were investigated to verify the importance of localized quantum well (QW) excitons in their spontaneous emission mechanisms. The internal piezoelectric field (FPZ) across the QW of the order of 1.4 MV/cm was confirmed to point from the surface to the substrate. Transmittance and photovoltaic spectra exhibited a broad band tail state, and the emission lifetime increased with decreasing detection photon energy. The electroluminescence spectra did not show remarkable energy shift between 10 and 300 K. The spectra exhibited an exponential tail and the higher energy portion increased more rapidly than that of the lower energy one, reflecting a thermal distribution of the localized carriers within the tail states. Since the well thickness is only 2.5 nm and is atomically flat, the device is considered to exhibit reasonably efficient emission with the external quantum efficiency of 5% at 20 mA in spite of the presence of FPZ and larg...

Optical gain of InGaN quantum well laser diodes and its internal field dependences are investigated. Gain spectra are experimentally measured by the Hakki-Paoli method. Inhomogeneous broadening of the gain spectra as well as of the electroluminescence spectra increases with In content of the active layers due to potential fluctuation. From measured carrier decay times and current density, we estimated the carrier density for which modal gain overcomes internal loss. We present gain calculation including quantum confined Stark effect, Coulomb screening and valence band structure simultaneously. Calculated and measured carrier densities are in good agreement. In InGaN quantum well laser diodes working at 470 nm, the quantum confined Stark effect reduces the optical transition probability down to 30% of its value without internal field. Wavelength (nm) 520 500 480 460 440 420 400 380 2.4 2.6 2.8 3.0 3.2 3.4 Photon energy (eV) Typical electroluminescence spectra of InGaN quantum well laser diodes with different peak wavelengths. Injected current is 10 mA.

3.6 lm in total flux and 54 lm/W in luminous efficacy for a white LED (CCT = 6700 K) have been achieved. These are a result of improvements in light-extracting efficiency and light conversion efficiency of phosphor. Luminous efficacy was as high as 102 lm/W at a forward current of 0.2 mA. Efficient ultraviolet LEDs with an emission wavelength of 365 nm have been developed. Light output was 1 W under DC, and was 1.5 W under pulsed operation. It was very important to use a high quality GaN template with low dislocation density. Light extraction efficiency was improved by surface patterning. (© 2005 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)