bluuebunny/crossref_metadata_2025 huggingface dataset:
Temperature Dependence of Linear Thermal Expansion of CuGaSe2 Crystals
Authors: Nagaoka Akira , Yoshino Kenji , Taniyama Tomoyasu , Miyake Hideto
Published: July 2012

CuGaSe2 single crystals were grown by a traveling heater method, which is one of the solution growth techniques. The temperature dependence of the X-ray diffraction of CuGaSe2 was determined between 10 and 300 K. The room temeprature XRD pattern of CuGaSe2 corresponds to the ICDD data. No secondary phases are observed in the spectrum. The lattice constant of the a-axis increases and that of the c-axis decreases with increasing temperature. The linear thermal expansion of the c-axis calculated from the lattice constants indicates a negative value from 10 to 100 K.
Reduction of Crack Formation in Transcription of Cu(In,Ga)Se2 Thin Film Solar Cell Structure
Authors: Abe Yasuhiro , Minemoto Takashi , Takakura Hideyuki
Published: July 2012

We focused on the reduction of the crack formation in the transfer of the Cu(In,Ga)Se2 (CIGS) thin film solar cell structure. We found that the crack formation was reduced by increasing the In2O3:Sn thickness. We concluded that the whole thickness of the transferred layers is an important roll in the reduction of the crack formation. Moreover, we proposed the crack occupancy as a quantitative evaluation method of the crack inside the CIGS layer.
Evaluation of Organic Thin Film Solar Cells Using 3-Diode Equivalent Circuit Model with Inverted Diode
Authors: Sakurada Yuya , Ota Yasuyuki , Watanabe Hiroki , Murata Hideyuki , Nishioka Kensuke
Published: July 2012

We proposed a modified 3-diode equivalent circuit model with an inverted diode for the analysis of the characteristics of bulk hetero junction organic solar cells before and after heat treatment with the reverse bias of -8 V. The dark current density-voltage (J-V) characteristics of the bulk hetero junction organic solar cells before and after heat treatment were measured. From dark J-V characteristics of each organic solar cell, fitting of J-V curve between measured and calculated date was carried out using a modified 3-diode equivalent circuit model with an inverted diode. Using extracted diode parameters, the performances of the bulk hetero junction organic solar cells were compared and evaluated. The measured and calculated J-V characteristics of the bulk hetero junction organic solar cell agreed well, and the organic solar cells were able to be evaluated using the proposed method.
2-Dimensional Mapping of Power Consumption Due to Electrode Resistance Using Simulator for Concentrator Photovoltaic Module
Authors: Ota Yasuyuki , Sakurada Yuya , Nishioka Kensuke
Published: July 2012

Under the concentration conditions, it is important to optimize the design of electrodes and cell structures, because the high density energy is emitted to the cell and photocurrent with high density is generated by each subcell of multi-junction solar cell. The in-plane distributions of power consumption due to the each resistance component were calculated by using total 3D simulator. In the case of optical design without homogenizer, local power consumptions due to the electrode resistance were observed at a part of cell. On the other hand, in the case of optical design with homogenizer, the power consumption was considerably reduced. This technique can be applied to the structural optimization of solar cells for concentration.
Two-Dimensional Mapping of Localized Characteristics of Concentrator Photovoltaic Module
Authors: Yano Hiroto , Nagai Hirokazu , Tamura Kazuyuki , Araki Kenji , Nishioka Kensuke
Published: July 2012

For the development of concentrator photovoltaic (CPV) module realizing high efficiency, it is necessary to achieve the high efficiency optical system including Fresnel lens and homogenizer. For the improvement of optical systems, it is very important to understand the contribution of the light irradiated to a localized position on the Fresnel lens. The light beam induced current (LBIC) system was constructed to evaluate the focusing characteristic of the CPV module. We locally irradiated a light from solar simulator to the CPV mini-module and measured the generation current, and the localized characteristics were represented by two-dimensional mappings. Moreover, we evaluated the influence of tracking error by changing the irradiation angle. In the case of tracking errors, the peak of generated current was shifted and the current was decreased. In the case of tracking error of 1.0 o, the total generated current was reduced 12%, in comparison with the normal irradiance.
Formation of Nanovoids in Femtosecond Laser-Irradiated Single Crystals of Silicon Carbide
Authors: Okada Tatsuya , Tomita Takuro , Matsuo Shigeki , Hashimoto Shuichi , Kashino Ryota , Ito Takuto
Published: July 2012

Scanning transmission electron microscopy was carried out to study the three-dimensional microstructures of periodic strained layers induced by the irradiation of femtosecond laser pulses inside a silicon carbide single crystal. The cross section of laser-irradiated line consisted of a shell-shaped modified region surrounding a core region with no modification. The laser-modified region was composed of strained layers with a typical spacing of 200 nm. Nanovoids from 10 nm to 20 nm in diameter were observed. Three-dimensional tomographic images clearly show the plate-like shape of strained layers extending parallel to the electric field of the laser light and the random distribution of nanovoids in the strained layers. The three-dimensional observation provides insight into the formation mechanisms of periodic microstructures.
Mono Vacancy Generation by Short Annealing in Nitrogen Doped FZ Silicon Wafers
Authors: Abe Takao
Published: July 2012

Using the peculiar behavior of nitrogen molecules in FZ silicon crystals contained with a high concentration of vacancies, this paper describes the following four important values: the estimated vacancy concentrations, the deep levels at 0.44 eV under the conduction band for n-type and at 0.66 eV over the valence band for p-type for mono vacancies and the diffusion coefficient of the silicon interstitials DI-FZ = 1.3×exp(-4.5 eV/kT).
Vibrational Dynamics of Impurities in Semiconductors: Phonon Trapping and Isotope Effects
Authors: Estreicher Stefan K.
Published: July 2012

Optical tools such as infra-red absorption, photoluminescence, or Raman spectroscopy have been used for decades to observe the localized vibrational modes associated with impurities in semiconductors. The frequencies of these modes slightly shift with the isotope of the impurity while host-atom isotopes often show up as shoulders in the spectra. These shifts and shoulders are precious indicators of the nature of the defect. But sometimes, very small isotope-related frequency shifts cause very large changes in vibrational lifetimes. Impurity-isotope effects have now been predicted to impact the thermal conductivity of semiconductors containing a few atomic percent of impurities. Impurity isotope effects can be surprisingly large.
Formation and Annealing Behavior of Copper Centers in Silicon Crystal Measured by Photoluminescence and Deep-Level Transient Spectroscopy
Authors: Nakamura Minoru , Murakami Susumu
Published: July 2012

Formation and annealing behavior of the 1.014-eV copper center and its dissociation product (center) in silicon are characterized by photoluminescence (PL) and deep-level transient spectroscopy (DLTS) measurements. On the basis of the findings reported in this study, the structures of the centers are discussed.
Effect of Nitrogen Doping on Vacancy State in Silicon Crystals Observed by Low-Temperature Ultrasonic Measurements
Authors: Yamada-Kaneta Hiroshi , Komatsu Satoru , Baba Shotaro , Nagai Yuta , Akatsu Mitsuhiro , Nemoto Yuichi , Goto Terutaka
Published: July 2012

For the B-doped silicon crystals grown with and without N-doping, we measured the temperature dependence of the elastic constant in low-temperature region, to examine whether the N-doping annihilates the elastic softening caused by the gap-states of the isolated single vacancy. We have found that the elastic softening clearly observed for the N-free crystals is not observed for the N-doped ones, suggesting that the gap-states of the vacancies causing the elastic softening are destroyed by the N-doping. This is consistent with the model of Abe [T. Abe, J. Crystal Growth, 327 (2011) 1] in which the nitrogen molecule (N-N pair) occupies the vacancy to destroy its original gap-states. We have further observed that the N-doped silicon, which exhibits no softening in its as-grown state, exhibits the softening after the short-time annealing. This suggests that during the annealing the N-N pair is thermally activated to jump off the lattice site leaving the vacancy.
Nitrogen Doped 300 mm Czochralski Silicon Wafers Optimized with Respect to Voids with Laterally Homogeneous Internal Getter Capabilities
Authors: Kissinger Gudrun , Raming Georg , Wahlich Reinhold , Müller Timo
Published: July 2012

An internally gettering bulk defect zone and a defect denuded zone of at least 5 µm below the wafer surface were generated by out-diffusion of interstitial oxygen during annealing at temperatures in the range 1075-1100 °C in argon atmosphere. The CZ silicon material used was optimized with respect to voids and contained a central OSF region and an outer Pv region. Due to co-doping of at least 3×1013cm-3nitrogen, a laterally homogeneous bulk microdefect density was obtained which is independent of the temperature of the out-diffusion anneal. The internal getter created in this way efficiently getters nickel impurities as demonstrated in a getter test with 6.6×1011cm-3of intentional Ni contamination. In the central OSF region of the as-grown nitrogen co-doped wafers, the nuclei capable of generating OSFs also degrade the gate oxide integrity. Out-diffusion annealing at 1075-1100°C dissolves most of the defects capable of generating OSFs and it strongly improves the integrity of 5 nm gate oxides.
Electron Beam Induced Current Observation of Dislocations in 4H-SiC Introduced by Mechanical Polishing
Authors: Yao Yong Zhao , Sato Koji , Sugawara Yoshihiro , Ishikawa Yukari , Okamoto Yoshihiro , Hayashi Noritaka
Published: July 2012

Electron beam induced current (EBIC) observations have been carried out to investigate the influence of mechanical polishing (MP) direction on the dislocations formation at the Si-face c(0001) of 4H-SiC epitaxial layers. Two opposite MP directions (defined by polish pad moving direction) have been compared, which are [11-20] off-cut directions along step-up and step-down, respectively. It has been found that high density of dislocations have been formed along the polish paths for the 8o off samples with polishing pad moved in step-up direction. By contrast, step-down polishing samples have shown no significant dislocation increase although shallow polish scratches were observed. Similar experiments have also been carried out for 4o off samples, showing step-up MPs introduced more dislocations than step-down ones. The results are discussed in terms of forces along the slip plane [11-20](0001) effectively exerted by the abrasive particles on the steps.
Reliability Improvement in Silicon Dioxide
Authors: Minami Masashi , Kamiura Yoichi
Published: July 2012

There are two typical methods for silicon oxidation. One is pyrogenic oxidation using oxygen and hydrogen, the other is dry oxidation using oxygen. In this study various properties of these oxidation films were compared. The pyrogenic oxidation in turn could show better characteristic values in the all experiments. Furthermore, once dry oxidation was used even before gate oxidation, we found that dry oxidation made a source of defects generation at surface of the Si substrate.
Gate-Length Dependent Radiation Damage in 2-MeV Electron-Irradiated Si1-xGex S/D p-MOSFETs
Authors: Nakashima Toshiyuki , Idemoto Tatsuya , Tsunoda Isao , Takakura Kenichiro , Yoneoka Masashi , Ohyama Hidenori , Yoshino Kenji , Simoen Eddy , Claeys Cor
Published: July 2012

The effect of 2-MeV electron irradiation of Si1-xGexS/D p-MOSFETs with different gate length and Ge concentration is studied. After electron irradiation, the maximum hole mobility decreases with increasing electron fluence for all gate lengths. In particular, after 5 x 1017e/cm2irradiation, the maximum hole mobility drastically decreases at short channel region for x = 0.3. Furthermore, a negative shift of the threshold voltage is clearly observed. These degradations can be explained both by the lattice defects and the stress relaxation in the Si channel created by atomic displacements.
Impact of RTA on the Morphology of Oxygen Precipitates and on the Getter Efficiency for Cu and Ni in Si Wafers
Authors: Kot Dawid , Kissinger Gudrun , Schubert Markus Andreas , Müller Timo , Sattler Andreas
Published: July 2012

The influence of RTA pre-treatments on the morphology of oxygen precipitates in silicon wafers as deduced from haze getter tests was confirmed by FTIR and TEM investigations. Based on the results of the getter tests, the ratio between the density of plate-like and octahedral precipitates was calculated for RTA pre-treated silicon samples.
Density Functional Theory Analysis on Behavior of Metal Impurities in Ge (100) / Si (100)
Authors: Maeta Takahiro , Sueoka Koji
Published: July 2012

Ge (100) thin film on Si (100) substrate is one of the new material technologies in the post scaling. In this study, we analyzed the stability of metal impurities of 4th row element around the interface of Ge (100) / Si (100) structure by using first-principles calculation. Considering the actual structure of the Ge thin film on Si (100) substrate, six calculation models were prepared. The calculated results showed that (1) Sc and Zn atoms are most stable at Ge surface, (2) Ti - Cr atoms are most stable in tensile plane-strained Si layer, (3) Mn - Cu atoms are most stable in compressive plane-strained Ge layer. These results indicate that the metal impurities concentrate on the strained region around the interface and/or Ge surface.
Evaluation of Optical Properties for Nanocrystal Si Dot Layers Fabricated by CVD as a Function of Size Reduction
Authors: Mizukami Yuki , Kosemura D. , Takei M. , Numasawa Y. , Ohshita Y. , Ogura A.
Published: July 2012

Raman spectroscopy and photoluminescence were performed in order to understand the optical properties of nanocrystal Si in relation to quantum confinement effects. The nanocrystal Si (nc-Si) dots in the SiO2 layer were fabricated by the H2 plasma treatment and chemical vapour deposition followed by the oxidation of the nc-Si dots surface. The post-annealing was also performed to improve the crystalline quality of nc-Si at 1050 °C for 5 and 10 min. There is a good correlation of the quantum confinement effects between the results of Raman spectroscopy and photoluminescence. The Raman spectra from nc-Si were analysed using the model of Richter et al. As a result, the sizes of the nc-Si dots were consistent with those obtained by transmission electron microscopy and X-ray diffraction. Moreover, the compressive stress in the nc-Si dots were evaluated which was induced by the SiO2 surroundings.
MicroRaman Spectroscopy of Si Nanowires: Influence of Size
Authors: Anaya Julián , Prieto Carmelo , Torres Alfredo , Martín-Martín Alonso , Souto Jorge , Jiménez Juan , Rodríguez Andres , Rodríguez Tomás
Published: July 2012

Si Nanowires (NWs) were studied by Raman microspectroscopy. The Raman spectrum of the NWs reveals important thermal effects, which broaden and shift the one phonon Raman bands. The low thermal conductivity of the NWs and the low thermal dissipation are responsible for the temperature enhancement in the NW under the excitation with the laser beam. We have modeled, using finite element methods, the interaction between the laser beam and the NWs. The Raman spectrum of Si NWs is interpreted in terms of the temperature induced by the laser beam excitation, in correlation with finite element methods (fem) for studying the interaction between the laser beam and the NWs.
Electron-Beam-Induced Current Study of Electronic Property Change at SrTiO3 Bicrystal Interface Induced by Forming Process
Authors: Kato Tetsuji , Nakamura Yoshiaki , Son P.P.T. , Kikkawa Jun , Sakai Akira
Published: July 2012

We investigated the spatial variation of energy band structure in a SrTiO3 (001) bicrystal with the (100) 10° tilt boundary before and after the annealing process at 973 K under a vacuum of ~10-7 Torr and after the subsequent forming process with electrical dielectric breakdown, using electron beam induced current (EBIC) method in the temperature range between 200 and 300K. Although the EBIC contrast at the tilt boundary was weak before and after the annealing, it became visible after the forming process and stronger as the observation temperature decreased to less than 260 K. It was found that the EBIC direction at the tilt boundary is opposite to that in the matrix, i.e. the single crystalline regions of both sides of the tilt boundary. In the matrix, the EBIC increased after the annealing and decreased again after the forming process. We propose energy band structures of the bicrystalline SrTiO3 after the annealing and after the forming process.
Structural and Electronic Structure of SnO2 by the First-Principle Study
Authors: Oshima Minoru , Yoshino Kenji
Published: July 2012

We performed first-principle calculations to investigate the effects of F, Cl and Sb impurities on the electronic properties of SnO2. We obtained, firstly, the electronic structure of SnO2, a valence band maximum of SnO2is an O 2p orbital and a conduction band minimum was an antibonding Sn 5s and O 2p orbitals dominantly. Secondly, those impurites doped SnO2was obtained the electronic structure. The F, Cl and Sb impurities as n-type dopants exhibited shallow donors. This calculation results were in good agreement with our prvious experiment that we obtained the low resistivity SnO2.
Basal Plane Dislocations in 4H-SiC Epilayers with Different Dopings
Authors: Zhang Xuan , Nagano Masahiro , Tsuchida Hidekazu
Published: July 2012

Morphologies of basal plane dislocations (BPDs) in 4H-SiC epilayers doped with nitrogen or aluminum are explained in detail. While BPDs in low N-doped or Al-doped epilayers show the morphology of gliding dislocations responding to stresses, BPDs in highly N-doped (≥1.0×1018 cm-3) epilayers appear different. Some of them are parallel to [11-20] while others are straight and tilt from [11-20]. Tilt BPDs were also studied by TEM. Factors that relate to such morphology are discussed.
Improvement of the Crystalline Quality of β-Ga2O3 Films by High-Temperature Annealing
Authors: Takahara Motoki , Funasaki Suguru , Kudou Jyun , Tsunoda Isao , Takakura Kenichiro , Ohyama Hidenori , Nakashima Toshiyuki , Shibuya Mutsuo , Murakami Katsuya , Simoen Eddy , Claeys Cor
Published: July 2012

For the purpose of improving the crystalline quality of undoped and Si doped β-Ga2O3 films, high temperature annealing at 900°C was performed. The crystalline quality of the films investigated using scanning electron microscopy and X-ray diffraction. Also the conductivity of the films is compared before and after the annealing. After the 900°C annealing, the XRD peaks intensity corresponding to β-Ga2O3 is increased. This result indicates that the crystalline quality improves by the high temperature annealing.
Characterization of Spin Coated Nondoped and In-Doped ZnO Films Using Novel Precursor Solution
Authors: Inaba Koichiro , Takemoto Yujin , Toyota Kouji , Haga Kenichi , Tokudome Kouichi , Shinmiya Masato , Kamiya Naomi , Oshima Minoru , Yoshino Kenji
Published: July 2012

A novel precursor for ZnO film deposition with Zn-O structure was synthesized by the reaction of diethylzinc and water in some ether solvents. The novel precursor was characterized by 1H-NMR spectroscopy and differential scanning calorimetry (DSC). Nondoped and In-doped ZnO films on a glass substrate have been successfully grown by conventional spin coating using nondoped and In added novel precursor solution. The samples have an optical transmittance of more than 85%, and a smooth surface determined from optical transmittance and scanning electron microscopy, respectively. The sheet resistivity of In-doped ZnO films is lower than that of nondoped ZnO film.
Electrical Properties of Fluorine Doped Tin Dioxide Film Grown by Spray Method
Authors: Oshima Minoru , Yoshino Kenji
Published: July 2012

Low resistivity, fluorine-doped tin dioxide thin films were deposited on glass substrates by spray pyrolysis. These films were prepared with different F-doping concentrations from 0 to 33 mol%. The structure of these films was investigated by X-ray diffraction and the surface morphology by Scanning Electron Microscopy. Sample compositions were evaluated using X-ray Photoemission Spectroscopy. According to these results, the films were all polycrystalline with tetragonal crystal structures. Hall measurements were used to probe the dependence of the resistivity on temperature for un-doped SnO2 and F-doped SnO2. The resistivity of un-doped SnO2 slightly increased with increasing temperature. Conversely, the resistivity of F-doped SnO2 slightly decreased with increasing temperature.
Evaluation of GexSbyTez Film Grown by Chemical Vapor Deposition
Authors: Hamada Seiti , Horiike Takafumi , Uno Tomohiro , Ishikawa Masato , Machida Hideaki , Ohshita Yoshio , Ogura Atsushi
Published: July 2012

This paper describes structure evaluation of GexSbyTez (GST) film fabricated by chemical vapor deposition (CVD). We successfully established composition controlled GST CVD with smooth surface by applying appropriate deposition conditions. By increasing Ge flow rate or reducing substrate temperature, the average grain size was reduced and the film flatness was improved. As the results, we succeeded to obtain the extremely smooth surface, and also to fill a finite hole with conformal film deposition. All GexSbyTez films showed FCC or amorphous crystalline structures, both are utilized in the proposed phase change random access memory (PRAM), in spite of the wide range of composition control. We believe these CVD-GST films are useful for PRAM applications.
Imaging and Strain Analysis of Threading-Edge and Basal-Plane Dislocations in 4H-SiC Using X-Ray Three-Dimensional Topography
Authors: Tanuma Ryohei , Mori Daisuke , Kamata Isaho , Tsuchida Hidekazu
Published: July 2012

This paper demonstrates the X-ray three-dimensional topography of basal-plane dislocations (BPDs) and threading edge dislocations (TEDs) in 4H-SiC. Cross-sectional imaging shows the propagation of BPDs from a substrate to an epilayer and the conversion of BPDs into TEDs near the epilayer/substrate interface. The strain analysis of TEDs exhibits the image of strains in the order of ±10-5. The observed strain images correlate well to simulation results.
Different Dissociation Behavior of [11-20] and Non-[11-20] Basal Plane Dislocations in 4H-SiС under Electron Beam Irradiation
Authors: Yao Yong Zhao , Sugawara Yoshihiro , Ishikawa Yukari , Danno Katsunori , Suzuki Hiroshi , Bessho Takeshi , Kawai Yoichiro , Shibata Noriyoshi
Published: July 2012

Electron beam induced current (EBIC) and etch pit method have been used to study the dissociation behavior of basal plane dislocations (BPDs) in 4H-SiC under electron beam irradiation. When 20 kV scanning electron beam was applied for 1 h, it has been found that BPDs whose dislocation lines were along [11-20] off-cut direction dissociated into partial dislocations (PDs) forming a stacking fault (SF) between them; while no dissociation was found for BPDs extending along other directions. These results are discussed in terms of different formation energy of SFs expanding from a pure screw type and a mixed type BPD. In addition, the angle between dislocation line of a BPD and the [11-20] off-cut direction might also play a role in determining the minimum energy for SF formation.
Density of Etch Pits on C-Face 4H-SiC Surface Produced by ClF3 Gas
Authors: Habuka Hitoshi , Furukawa Kazuchika , Kanai Toshimitsu , Kato Tomohisa
Published: July 2012

The etch pits on the C-face 4H-SiC substrate was produced by chlorine trifluoride gas at various temperatures. The etch pit density showed the comparable value to the current dislocation density level of the Si-face 4H-SiC, when the etching was performed around 713 K. Thus, the etch pit density obtained by this technique is expected to reveal the crystal quality.
Defect Related Leakage Current Components in SiC Schottky Barrier Diode
Authors: Ohtsuka Kenichi , Nakatani T. , Nagae A. , Watanabe H. , Nakaki Y. , Fujii Y. , Fujihira K. , Nakata S. , Yutani N.
Published: July 2012

SiC Schottky barrier diodes were fabricated and measured properties were characterized by device simulation. Most of devices show low leakage current, however, a few devices show leakage current larger than the values estimated from deviation of drift layer parameters. The leakage current component remarkable in lower voltage and saturating at higher voltage is related to Schottky barrier tunneling at macroscopic defects. The component remarkable in higher voltage is considered to be due to microscopic defect related generation current, concerning with non-stoichiometry.
Rapid Terahertz Imaging of Carrier Density of 3C-SiC
Authors: Hamano Akihide , Ohno Seigo , Minamide Hiroaki , Ito Hiromasa , Usuki Yoshiyuki
Published: July 2012

The reflectance around the longitudinal optical (LO) phonon frequency in the terahertz region changes with the carrier density of silicon carbide (SiC), while the reflectance around the transverse optical (TO) phonon frequency remains constantly high. The relative reflectance obtained from the reflectance at the two frequencies related to the TO and LO phonon was evaluated as a function of the carrier density of SiC. Two waves around these phonon frequencies can be generated easily using a tunable terahertz source. Nondestructive imaging of the carrier density of cubic SiC (3C-SiC) at the rate of 1 s per point was carried out successfully using this tunable terahertz source.
Cathodoluminescence Study of Ammonothermal GaN Crystals
Authors: Hortelano Vanesa , Martínez Oscar , Jiménez Juan , Wang Bu Guo , Swider S. , Suscavage Michael , Bliss David
Published: July 2012

GaN crystals grown in supercritical ammonia by the ammonothermal method were studied by cathodoluminescence (CL), both in image and spectrally resolved modes. The main extended defects and the incorporation of point defects and impurities in different growth sectors were revealed. The influence of the seeds, the role of the growth planes and the changes in the crystal quality during the growth run are discussed.
Defect Propagation from 3C-SiC to III-Nitride
Authors: Abe Yoshihisa , Fujimori Hiroyuki , Watanabe Arata , Ohmori Noriko , Komiyama Jun , Suzuki Shunichi , Nakanishi Hideo , Egawa Takashi
Published: July 2012

Role of 3C-SiC intermediate layer (3C-SiC IL) and a propagation of crystal defects from 3C-SiC IL to III-nitride epilayers has been investigated by observing the interface between the 3C-SiC IL and III-nitride epilayers. We found that better quality epilayers were obtained by using such intermediate layers than by direct growth on Si substrates. In the case of III-nitride epilayers grown directly on Si, the layers grown at the initial stage are not flat. The 3C-SiC IL grown on Si (111) substrates has many stacking faults (SFs) that form along the 3C-SiC {111} planes. The initial III-nitride films have V-shaped trenches due to the SFs of the 3C-SiC IL. However, some SFs do not lead to the V-shaped defects.
Microscopic Degradation Analysis of RF-Stressed AlGaN/GaN HEMTs
Authors: Gütle Frank , Baeumler Martina , Dammann Michael , Cäsar Markus , Walcher Herbert , Waltereit Patrick , Bronner Wolfgang , Müller Stefan , Kiefer Rudolf , Quay Rüdiger , Mikulla Michael , Ambacher Oliver , Graff Andreas , Altmann Frank , Simon Michel
Published: July 2012

An AlGaN/GaN high electron mobility transistor (HEMT) stressed at 10 GHz and increased channel temperatures of T ≈ 260 °C has been analyzed by electroluminescence microscopy (ELM) and infrared thermography (IRT). After stress a negative threshold shift is seen in the electrical characteristics. Based on the current dependence of the electroluminescence (EL) intensity image and a local increase of T this shift can be assigned to the degradation of one of its gate fingers. Transmission electron microscopy (TEM) images of this gate finger revealed structural changes along the drain-side edge of the gate.
Distribution of Misfit Dislocations at the InGaAs/GaAs(001) Interface Observed by Monochromatic X-Ray Topography
Authors: Suzuki Hidetoshi , Sasaki Takuo , Yamamoto Susumu , Ohshita Yoshio , Fukuyama Atsuhiko , Yamaguchi Masafumi
Published: July 2012

Anisotropies in misfit dislocations (MDs) at the interface of InGaAs/GaAs (001) are investigated by monochromatic X-ray topography (XRT) technique. Single MD line or several MD lines (MD bunching) are observed as white lines in XRT. Distribution, density, and number of MDs in one MD bunching are evaluated. The density of α-MDs is larger than that of β-MDs. Number of MDs in one MD bunching distribute with two peaks in both in-plane directions. In macroscopic view, α-MD bunching lay more orderly than the other. While in microscopic view, α-MDs gather for the range narrower than β-MDs.
Effects of in Content on Anisotropies in Strain Relaxation Processes of InGaAs/GaAs (001) Measured by Real-Time Three-Dimensional Reciprocal Space Mapping
Authors: Suzuki Hidetoshi , Sasaki Takuo , Takahasi Masamitu , Ohshita Yoshio , Yamaguchi Masafumi
Published: July 2012

The effects of In incorporation on anisotropies in the strain relaxation mechanisms of InGaAs on GaAs systems are investigated using a three-dimensional reciprocal space mapping (3D-RSM) technique. Relaxation processes are classified as belonging to one of the following four phases: no relaxation, gradual relaxation, rapid relaxation, and relaxation saturation. Anisotropies appear in the gradual relaxation phase and almost disappear in the rapid relaxation phase. These anisotropies are enhanced by In content. When In content is low, both α- and β-misfit dislocations (MDs) are observed at the same thickness; the density of α-MDs increases more rapidly than that of β-MDs. When In content is high, only α-MDs appear in the gradual relaxation phase. These results suggest that In atoms prevent nucleation and/or gliding of β-MDs.
Nitrogen Related Deep Levels in GaAsN Films Investigated by a Temperature Dependence of Piezoelectric Photothermal Signal
Authors: Kashima Koshiro , Fukuyama Atsuhiko , Nakano Yosuke , Inagaki Makoto , Suzuki Hidetoshi , Yamaguchi Masafumi , Ikari Tetsuo
Published: July 2012

The temperature dependences of the piezoelectric photo-thermal (PPT) signals from unintentionally doped p-type GaAsN films grown on semi-insulating GaAs substrate were measured from 80 to 300 K. From the theoretical analysis based on the rate equation for the recombination of photo exited carriers to the localized levels, we identified five majority hole traps, P1-P5 in GaAsN films. Among them, estimated concentrations of the P3 and P5 traps increased with the nitrogen contents. Therefore, we concluded that these two traps were due to nitrogen-related recombination centers in GaAsN.
Intermixing in InP-Based Quantum Well Photonic Structures Induced by the Dry-Etching Process: A Spectral Imaging Cathodoluminescence Study
Authors: Hortelano Vanessa , Jiménez Juan , Landesman Jean Pierre , Rhallabi Ahmed
Published: July 2012

Ridge waveguides in InP-based heterostructures were fabricated by inductively coupled plasma (ICP) reactive ion etching using chlorine-based gases. The heterostructures included a series of 6 quantum wells (QW) made from quaternary material GaxIn1-xAsyP1-y emitting at 1.55 µm, and located very close to the surface (first QW at 250 nm). The etched structures (different widths and depths) were characterized at room and low temperature (80 K) by spectrum image cathodoluminescence (CL). The signature of the QWs was used to investigate effects induced by the dry etching process. Defects (or defect complexes) were observed, especially close to the edges of the etched structures, as well as a blue-shift of the CL lines from the nominal position. This was attributed to some intermixing of the QWs. Intermixing is induced by the defects that form during the dry etching process. The origin of these defects is discussed, taking into account previous studies performed on similar samples, except for the fact that the etched material was bulk InP instead of QW layers.
Induction of Type I IFN Is a Physiological Immune Reaction to Apoptotic Cell-Derived Membrane Microparticles
Authors: Schiller Martin , Parcina Marijo , Heyder Petra , Foermer Sandra , Ostrop Jenny , Leo Albrecht , Heeg Klaus , Herrmann Martin , Lorenz Hanns-Martin , Bekeredjian-Ding Isabelle
Published: July 2012

Membrane microparticles (MMP) released from apoptotic cells deliver signals that secure the anti-inflammatory response beyond the nearest proximity of the apoptotic cell. Plasmacytoid dendritic cells (pDC) are sentinels prepared to detect cellular processes that endanger the organism. They play a key role in the regulation of both pro- and anti-inflammatory immune responses. Based on the assumption that pDC could participate in the initiation of the anti-inflammatory response to apoptotic cells, we investigated the effects of apoptotic cell-derived MMP on human pDC. The results obtained in our experiments confirmed that MMP released from apoptotic cells trigger IFN-α secretion from human pDC. They further suggest that pDC activation results from sensing of DNA contained in MMP. MMP-DNA displays a particularly strong stimulatory activity compared with MMP-RNA and other sources of DNA. Inhibition of MMP-induced IFN-α secretion by cytochalasin D, chloroquine, and an inhibitory G-rich oligodeoxynucleotide identify TLR9 as the receptor for MMP-DNA. In marked contrast to the pDC response in autoimmune patients, in healthy subjects MMP-mediated stimulation of pDC-derived IFN-α was found to be independent of FcγRIIA (CD32A). Based on our findings, we conclude that induction of pDC-derived IFN-α by MMP is a physiological event; future investigations are necessary to elucidate whether pDC activation promotes inflammation or propagates tolerance in the context of apoptotic cell clearance.
IL-2 Receptor Signaling Is Essential for the Development of Klrg1+ Terminally Differentiated T Regulatory Cells
Authors: Cheng Guoyan , Yuan Xiaomei , Tsai Matthew S. , Podack Eckhard R. , Yu Aixin , Malek Thomas R.
Published: July 2012

Thymic-derived natural T regulatory cells (Tregs) are characterized by functional and phenotypic heterogeneity. Recently, a small fraction of peripheral Tregs has been shown to express Klrg1, but it remains unclear as to what extent Klrg1 defines a unique Treg subset. In this study, we show that Klrg1+ Tregs represent a terminally differentiated Treg subset derived from Klrg1− Tregs. This subset is a recent Ag-responsive and highly activated short-lived Treg population that expresses enhanced levels of Treg suppressive molecules and that preferentially resides within mucosal tissues. The development of Klrg1+ Tregs also requires extensive IL-2R signaling. This activity represents a distinct function for IL-2, independent from its contribution to Treg homeostasis and competitive fitness. These and other properties are analogous to terminally differentiated short-lived CD8+ T effector cells. Our findings suggest that an important pathway driving Ag-activated conventional T lymphocytes also operates for Tregs.
IL-10 Regulates Il12b Expression via Histone Deacetylation: Implications for Intestinal Macrophage Homeostasis
Authors: Kobayashi Taku , Matsuoka Katsuyoshi , Sheikh Shehzad Z. , Russo Steven M. , Mishima Yoshiyuki , Collins Colm , deZoeten Edwin F. , Karp Christopher L. , Ting Jenny P. Y. , Sartor R. Balfour , Plevy Scott E.
Published: July 2012

To prevent excessive inflammatory responses to commensal microbes, intestinal macrophages, unlike their systemic counterparts, do not produce inflammatory cytokines in response to enteric bacteria. Consequently, loss of macrophage tolerance to the enteric microbiota plays a central role in the pathogenesis of inflammatory bowel diseases. Therefore, we examined whether the hyporesponsive phenotype of intestinal macrophages is programmed by prior exposure to the microbiota. IL-10, but not in vivo exposure to the microbiota, programs intestinal macrophage tolerance, because wild-type (WT) colonic macrophages from germ-free and specific pathogen-free (SPF)-derived mice produce IL-10, but not IL-12 p40, when activated with enteric bacteria. Basal and activated IL-10 expression is mediated through a MyD88-dependent pathway. Conversely, colonic macrophages from germ-free and SPF-derived colitis-prone Il10−/− mice demonstrated robust production of IL-12 p40. Next, mechanisms through which IL-10 inhibits Il12b expression were investigated. Although Il12b mRNA was transiently induced in LPS-activated WT bone marrow-derived macrophages (BMDMs), expression persisted in Il10−/− BMDMs. There were no differences in nucleosome remodeling, mRNA stability, NF-κB activation, or MAPK signaling to explain prolonged transcription of Il12b in Il10−/− BMDMs. However, acetylated histone H4 transiently associated with the Il12b promoter in WT BMDMs, whereas association of these factors was prolonged in Il10−/− BMDMs. Experiments using histone deacetylase (HDAC) inhibitors and HDAC3 short hairpin RNA indicate that HDAC3 is involved in histone deacetylation of the Il12b promoter by IL-10. These results suggest that histone deacetylation on the Il12b promoter by HDAC3 mediates homeostatic effects of IL-10 in macrophages.
Atypical Hemolytic Uremic Syndrome-Associated Variants and Autoantibodies Impair Binding of Factor H and Factor H-Related Protein 1 to Pentraxin 3
Authors: Kopp Anne , Strobel Stefanie , Tortajada Agustín , Rodríguez de Córdoba Santiago , Sánchez-Corral Pilar , Prohászka Zoltán , López-Trascasa Margarita , Józsi Mihály
Published: July 2012

Atypical hemolytic uremic syndrome (aHUS) is a renal disease associated with complement alternative pathway dysregulation and is characterized by endothelial injury. Pentraxin 3 (PTX3) is a soluble pattern recognition molecule expressed by endothelial cells and upregulated under inflammatory conditions. PTX3 activates complement, but it also binds the complement inhibitor factor H. In this study, we show that native factor H, factor H-like protein 1, and factor H-related protein 1 (CFHR1) bind to PTX3 and that PTX3-bound factor H and factor H-like protein 1 maintain their complement regulatory activities. PTX3, when bound to extracellular matrix, recruited functionally active factor H. Residues within short consensus repeat 20 of factor H that are relevant for PTX3 binding were identified using a peptide array. aHUS-associated factor H mutations within this binding site caused a reduced factor H binding to PTX3. Similarly, seven of nine analyzed anti-factor H autoantibodies isolated from aHUS patients inhibited the interaction between factor H and PTX3, and five autoantibodies also inhibited PTX3 binding to CFHR1. Moreover, the aHUS-associated CFHR1*B variant showed reduced binding to PTX3 in comparison with CFHR1*A. Thus, the interactions of PTX3 with complement regulators are impaired by certain mutations and autoantibodies affecting factor H and CFHR1, which could result in an enhanced local complement-mediated inflammation, endothelial cell activation, and damage in aHUS.
Identification of IL-7–Producing Cells in Primary and Secondary Lymphoid Organs Using IL-7–GFP Knock-In Mice
Authors: Hara Takahiro , Shitara Soichiro , Imai Kumiko , Miyachi Hitoshi , Kitano Satsuki , Yao Hisayuki , Tani-ichi Shizue , Ikuta Koichi
Published: July 2012

IL-7 is a cytokine crucial for development and maintenance of lymphocytes and other hematopoietic cells. However, how IL-7–expressing cells are distributed in lymphoid organs is not well known. To address this question, we established and analyzed IL-7–GFP knock-in mice. Thymic epithelial cells (TECs) expressed high GFP levels in the cortex and medulla, as detected with an anti-GFP Ab. Thymic mesenchymal cells also expressed GFP. Flow cytometry analysis suggested that cortical TECs expressed higher GFP levels than did medullary TECs. In bone marrow, immunohistochemistry indicated high levels of GFP in many VCAM-1+ mesenchymal stromal cells and in some VCAM-1− cells. Additionally, half of the VCAM-1+CD31− stromal cells and some platelet-derived growth factor receptor α+ stromal cells were GFP+, as detected by flow cytometry. Moreover, we detected GFP expression in fibroblastic reticular cells in the T cell zone and cortical ridge of lymph nodes. Remarkably, lymphatic endothelial cells (LECs) expressed GFP at high levels within the lymph node medulla, skin epidermis, and intestinal tissues. Additionally, we detected abundant IL-7 transcripts in isolated LECs, suggesting that LECs produce IL-7, a heretofore unknown finding. Furthermore, GFP is expressed in a subpopulation of intestinal epithelial cells, and that expression was markedly upregulated in a dextran sulfate sodium-induced acute colitis model. Overall, IL-7–GFP knock-in mice serve as a unique and powerful tool to examine the identity and distribution of IL-7–expressing cells in vivo.
Type I IFN Receptor and the B Cell Antigen Receptor Regulate TLR7 Responses via Distinct Molecular Mechanisms
Authors: Poovassery Jayakumar S. , Bishop Gail A.
Published: July 2012

Toll-like receptor 7 (TLR7) signals to B cells are critically involved in the innate immune response to microbes, as well as pathogenesis of autoimmune diseases, but the molecular mechanisms that normally regulate these responses are incompletely understood. We previously reported that repeated stimulation through TLR7 induces a state of hyporesponsiveness (TLR tolerance) in both human and mouse B cells, characterized by marked inhibition of particular signaling pathways. BCR signals prevent and overcome TLR7 tolerance. Because optimal responses to TLR7 in B cells require type I IFN, we investigated whether BCR-mediated effects on TLR7 tolerance are mediated by type I IFN receptor (IFNAR) signals. Surprisingly, although BCR-mediated reversal of TLR7 tolerance was IFNAR independent, IFNAR signals alone also blocked TLR7 tolerance, despite enhancing TLR7 expression. Both BCR and IFNAR signals restored the phosphorylation of the transcriptional regulator c-Jun, but only BCR signals blocked the tolerance-mediated inhibition of JNK. Both BCR and IFNAR-mediated regulation was dependent on activation of the PI3K/Akt/mammalian target of rapamycin signaling pathway, indicating a central role for this axis in integrating TLR7, BCR, and IFNAR signals in B cells. These new findings reveal distinct and overlapping signaling mechanisms used by BCR and IFNAR in the regulation of TLR7 tolerance and activation.
T Cell Responses to Known Allergen Proteins Are Differently Polarized and Account for a Variable Fraction of Total Response to Allergen Extracts
Authors: Oseroff Carla , Sidney John , Vita Randi , Tripple Victoria , McKinney Denise M. , Southwood Scott , Brodie Tess M. , Sallusto Federica , Grey Howard , Alam Rafeul , Broide David , Greenbaum Jason A. , Kolla Ravi , Peters Bjoern , Sette Alessandro
Published: July 2012

A panel of 133 allergens derived from 28 different sources, including fungi, trees, grasses, weeds, and indoor allergens, was surveyed utilizing prediction of HLA class II-binding peptides and ELISPOT assays with PBMC from allergic donors, resulting in the identification of 257 T cell epitopes. More than 90% of the epitopes were novel, and for 14 allergen sources were the first ever identified to our knowledge. The epitopes identified in the different allergen sources summed up to a variable fraction of the total extract response. In cases of allergens in which the identified T cell epitopes accounted for a minor fraction of the extract response, fewer known protein sequences were available, suggesting that for low epitope coverage allergen sources, additional allergen proteins remain to be identified. IL-5 and IFN-γ responses were measured as prototype Th2 and Th1 responses, respectively. Whereas in some cases (e.g., orchard grass, Alternaria, cypress, and Russian thistle) IL-5 production greatly exceeded IFN-γ, in others (e.g., Aspergillus, Penicillum, and alder) the production of IFN-γ exceeded IL-5. Thus, different allergen sources are associated with variable polarization of the responding T cells. The present study represents the most comprehensive survey to date of human allergen-derived T cell epitopes. These epitopes might be used to characterize T cell phenotype/T cell plasticity as a function of seasonality, or as a result of specific immunotherapy treatment or varying disease severity (asthma or rhinitis).
Lipocalin 2 Deficiency Dysregulates Iron Homeostasis and Exacerbates Endotoxin-Induced Sepsis
Authors: Srinivasan Gayathri , Aitken Jesse D. , Zhang Benyue , Carvalho Frederic A. , Chassaing Benoit , Shashidharamurthy Rangaiah , Borregaard Niels , Jones Dean P. , Gewirtz Andrew T. , Vijay-Kumar Matam
Published: July 2012

Various states of inflammation, including sepsis, are associated with hypoferremia, which limits iron availability to pathogens and reduces iron-mediated oxidative stress. Lipocalin 2 (Lcn2; siderocalin, 24p3) plays a central role in iron transport. Accordingly, Lcn2-deficient (Lcn2KO) mice exhibit elevated intracellular labile iron. In this study, we report that LPS induced systemic Lcn2 by 150-fold in wild-type mice at 24 h. Relative to wild-type littermates, Lcn2KO mice were markedly more sensitive to endotoxemia, exhibiting elevated indices of organ damage (transaminasemia, lactate dehydrogenase) and increased mortality. Such exacerbated endotoxemia was associated with substantially increased caspase-3 cleavage and concomitantly elevated immune cell apoptosis. Furthermore, cells from Lcn2KO mice were hyperresponsive to LPS ex vivo, exhibiting elevated cytokine secretion. Additionally, Lcn2KO mice exhibited delayed LPS-induced hypoferremia despite normal hepatic hepcidin expression and displayed decreased levels of the tissue redox state indicators cysteine and glutathione in liver and plasma. Desferroxamine, an iron chelator, significantly protects Lcn2KO mice from LPS-induced toxicity, including mortality, suggesting that Lcn2 may act as an antioxidant in vivo by regulating iron homeostasis. Thus, Lcn2-mediated regulation of labile iron protects the host against sepsis. Its small size and simple structure may make Lcn2 a deployable treatment for sepsis.
A Conservative Single Visit Reattachment of Fractured Crown Fragment
Authors: Shetty Prashant P. , Metgud Sandeep , Jain Ankit , Dhillon Gurbani , Astekar Madhusudan
Published: July 2012

Injury of anterior teeth is a relatively common event that mainly affects children and adolescents. Dentists are confronted with managing dental trauma and restoring fractured teeth on a regular basis. Hence the techniques that speed and simplify the treatment, restore esthetics and improve long term success rate are considered of potential value. If an intact tooth fragment is present after trauma, immediate attachment of the incisal edge is a conservative yet, simple and aesthetic alternative. Fracture reattachment possesses challenging conservative and economically viable procedure within a single visit. The authors wuld report a case of fractured maxillary central incisor using fragment reattachment.