bluuebunny/crossref_metadata_2025_split huggingface dataset:
Synthesis and photoluminescent and electrochromic properties of aromatic poly(amine amide)s bearing pendent N‐carbazolylphenyl moieties
Authors: Liou Guey‐Sheng , Chen Hwei‐Wen , Yen Hung‐Ju 
Published: May 2006

AbstractA series of novel poly(amine amide)s (IIa–IIl) with pendent N‐carbazolylphenyl units having inherent viscosities of 0.25–1.06 dL/g were prepared via direct phosphorylation polycondensation from various dicarboxylic acids and a carbazole‐based aromatic diamine. Except for poly(amine amide) IIc, derived from trans‐1,4‐cyclohexanedicarboxylic acid, all the other amorphous poly(amine amide)s were readily soluble in many polar solvents, such as N,N‐dimethylacetamide and N‐methyl‐2‐pyrrolidone (NMP), and could be cast into transparent and flexible films. The aromatic poly (amine amide)s had useful levels of thermal stability associated with relatively high glass‐transition temperatures (268–331 °C), 10% weight loss temperatures in excess of 540 °C, and char yields at 800 °C in nitrogen higher than 60%. These polymers exhibited maximum ultraviolet–visible absorption at 293–361 nm in NMP solutions. Their photoluminescence in NMP solutions exhibited fluorescence emission maxima around 362 and 448–499 nm for aromatic–aliphatic poly(amine amide)s IIa–IIc and aromatic poly (amine amide)s IId–IIl, respectively. The fluorescence quantum yield in NMP solutions ranged from 0.34% for IIj to 4.44% for IIa. The hole‐transporting and electrochromic properties were examined with electrochemical and spectroelectrochemical methods. Cyclic voltammograms of the poly(amine amide) films cast onto an indium tin oxide coated glass substrate exhibited reversible oxidation at 0.81 V and irreversible oxidation redox couples at 1.20 V versus Ag/AgCl in acetonitrile solutions, and they revealed excellent stability of the electrochromic characteristics, with a color change from yellow to green at applied potentials ranging from 0.00 to 1.05 V. © 2006 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 44: 4108–4121, 2006
Multistep and semibatch nitroxide‐mediated controlled free‐radical emulsion polymerization: A significant step toward conceivable industrial processes
Authors: Nicolas Julien , Charleux Bernadette , Magnet Stéphanie 
Published: May 2006

AbstractNitroxide‐mediated emulsion polymerizations of n‐butyl acrylate and styrene were performed with a monofunctional, water‐soluble alkoxyamine initiator and a difunctional one. Two different processes were applied, either in two steps or under semibatch conditions. In particular, the polymerization times were strongly reduced, while high conversions and good control over the polymer characteristics were maintained. In all cases, stable latexes were recovered; with the difunctional initiator in particular, they exhibited small particles and narrow particle size distributions. © 2006 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 44: 4142–4153, 2006
Influence of substrate treatment on the growth morphology and magnetic anisotropy of epitaxial CrO2 films
Authors: Miao Guo‐Xing , Xiao Gang , Gupta Arunava 
Published: May 2006

AbstractEpitaxial CrO2 thin films deposited on HF‐cleaned TiO2(100) substrates exhibit very strong strain anisotropy, while those grown without the HF treatment step are essentially strain‐free and display bulk‐like magnetic properties. The HF treatment enhances the surface smoothness of the TiO2(100) substrate thus leading to the growth of epitaxially strained CrO2 films. The magnetic easy axis of these films changes orientation with thickness, switching from the in‐plane c ‐axis direction for relatively thick films to the b ‐axis direction for thinner films (<50 nm). Similarly, over a thickness range, a change of the easy axis direction is also observed with lowering temperature. Ion‐beam irradiation of the substrate surface prior to growth also results in the growth of strained CrO2 films, although the amount of strain is less than that observed for HF‐treated substrates. The magnetic properties as a function of thickness have also been studied for as‐deposited ‘thick’ CrO2 films that are slowly chemically etched down in thickness. Unlike as‐grown thin films below 50 nm thickness that have the easy axis along the b ‐direction, the chemically etched down CrO2 thin films of equivalent thickness retain their easy axis alignment along the c ‐direction, but display a significantly enhanced coercivity. The observed differences in the switching behavior between the as‐deposited films and those that are chemically etched can be qualitatively attributed to changes in the strain relaxation mechanism. (© 2006 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Optical properties and carrier dynamics in differently strained GaN epilayers grown on Si by MOVPE
Authors: Lutsenko E. V. , Pavlovskii V. N. , Danilchyk A. V. , Osipov K. A. , Rzheutskii N. V. , Zubialevich V. Z. , Gurskii A. L. , Yablonskii G. P. , Malinauskas T. , Jarašiūnas K. , Kazlauskas K. , Juršėnas S. , Miasojedovas S. , Žukauskas A. , Dikme Y. , Kalisch H. , Jansen R. H. , Schineller B. , Heuken M. 
Published: May 2006

AbstractOptical properties and carrier dynamics were investigated in a set of samples grown on Si utilizing different layer combinations between the topmost GaN layer and the Si substrate, including AlN/GaN distributed Bragg reflector (DBR) superlattices as well as AlGaN/GaN strain‐reducing layers. The use of the AlN/AlGaN superlattice acting both as buffer layer and as DBR opens the way to control the strain in the upper epitaxial layer in GaN‐based heterostructures grown on Si. It also can lead to a decrease of the concentration of non‐radiative defects in the upper GaN layers, which, in turn, approximately doubles the carrier lifetime and increases the concentration of non‐equilibrium carriers. Carrier lifetimes at high excitation energy densities increased from 50–78 ps to 75–200 ps in the layers with DBR. These effects lead to improved PL efficiency and to an increase of the value of optical gain from 300 cm–1 up to 4000 cm–1. The use of DBR reduces the absorption of light in the Si substrate and may improve the properties of the laser waveguide. All these effects result in a reduction of the laser threshold from 700 to 270 kW/cm2. (© 2006 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Mg doping profile in III–N light emitting diodes in close proximity to the active region
Authors: Köhler K. , Perona A. , Maier M. , Wiegert J. , Kunzer M. , Wagner J. 
Published: May 2006

AbstractWe have investigated how in (AlGaIn)N quantum well (QW) light emitting diodes, grown by low‐pressure metal‐organic vapor phase epitaxy, the actual Mg doping profile close to the interface between AlGaN electron barrier and QW active region, known to be affected by both segregation of back diffusion of Mg, can be controlled and adjusted by the appropriate choice of growth parameters. Almost identical Mg doping profiles, and thus electroluminescence efficiencies which are strongly affected by the Mg doping profile, could be achieved for different combinations of Mg precursor flow and growth temperature. (© 2006 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Si‐doped GaN/AlN quantum dot superlattices for optoelectronics at telecommunication wavelengths
Authors: Guillot F. , Tchernycheva M. , Nevou L. , Doyennette L. , Monroy E. , Julien F. H. , Dang Le Si , Remmele T. , Albrecht M. , Shibata T. , Tanaka M. 
Published: May 2006

AbstractWe report on the controlled growth of Si doped GaN/AlN quantum dot (QD) superlattices, in order to tailor their intersubband absorption within the 1.3–1.5 µm telecommunication wavelengths. The QD size is tuned by modifying the amount of GaN in the QDs and the growth temperature. Silicon can be incorporated in the QDs to populate the first electronic level, without significant perturbation of the QD morphology. As a proof of the capability of these structures for infrared detection, a quantum‐dot intersubband photodetector at 1.38 µm with lateral carrier transport is demonstrated. (© 2006 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
LPE growth of AlN from Cu–Al–Ti solution under nitrogen atmosphere
Authors: Kamei K. , Inoue S. , Shirai Y. , Tanaka T. , Okada N. , Yauchi A. 
Published: May 2006

AbstractSynthesis of single crystalline AlN has long been the subjects of intensive studies since it has exceptional properties suitable for the substrate materials for optoelectronic and electronic devices. The solution growth technique has some advantages over the sublimation growth technique. Its growth temperature is generally much lower than that of the sublimation growth. The obtained crystal is believed to show superior crystallinity since it is grown under nearly equilibrium condition. In the present study we have developed a new solution growth technique using Cu and Ti as solvents under atmospheric pressure of nitrogen. By using this solution, we have grown AlN single crystalline layer on 6H‐SiC substrate at relatively low growth temperatures such as 1600–1800 °C. The thickness of the grown layer was larger than 30 µm. TEM observation revealed the fairly low dislocation density such as 105/cm2 in the obtained AlN layers. (© 2006 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Profiling of light emission of GaN‐based laser diodes with cathodoluminescence
Authors: Godlewski M. , Phillips M. R. , Kazlauskas K. , Czernecki R. , Targowski G. , Perlin P. , Leszczyński M. , Figge S. , Hommel D. 
Published: May 2006

AbstractCathodoluminescence is applied for evaluation of in‐plane variations of light emission from GaN‐based laser diode structures. We demonstrate that potential fluctuations affect significantly emission of laser diodes for e‐beam currents above thresholds for a stimulated emission. (© 2006 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Characterization of free standing GaN grown by HVPE on a LiAlO2 substrate
Authors: Wang Lijun , Zeimer U. , Richter E. , Hennig Ch. , Herms M. , Weyers M. 
Published: May 2006

AbstractA 230 µm thick free standing GaN layer has been grown on a LiAlO2 substrate by hydride vapor phase epitaxy, with the separation of the layer from the substrate occuring spontaneously during cooling down after growth. A strong green luminescence band is observed from the top surface, while from the bottom surface, strong blue and red bands are seen in photoluminescence (PL). The evolution of these luminescence bands with layer thickness was monitored by cross‐sectional cathodoluminescence (CL). PL and CL measurements indicate that the defect structure changes with growing layer thickness. (© 2006 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
In‐situ and real‐time monitoring of MOCVD growth of III‐nitrides by simultaneous multi‐wavelength‐ellipsometry and X‐ray‐diffraction
Authors: Simbrunner C. , Schmidegg K. , Bonanni A. , Kharchenko A. , Bethke J. , Woitok J. , Lischka K. , Sitter H. 
Published: May 2006

AbstractMetal Organic Chemical Vapor Deposition (MOCVD) is nowadays the most frequently used industrial method for growing III‐nitrides. The possible spectrum of in‐situ diagnostic tools is quite narrow because the MOCVD growth process excludes all techniques based on ultra high vacuum conditions. Therefore, only optical methods like spectroscopic ellipsometry and X‐ray diffraction give the possibility to observe and analyse the growing surface in‐situ. We attached simultaneously a multi wavelength spectroscopic ellipsometer and a X‐ray diffraction system to our reactor and could determine parameters like growth rate and layer composition from both techniques. On the one hand the optical measurement gives surface sensitive information about the sample. On the other hand the measurement of the diffraction peak of hexagonal GaN and related alloys during growth gives additional information about the entire structure and the crystal quality. (© 2006 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Large signal analysis of AlGaN/GaN‐HEMT amplifier by coupled physical device‐circuit simulation
Authors: Fujishiro H. I. , Narita S. , Tomita Y. 
Published: May 2006

AbstractThe large signal time domain simulation of the 40 GHz one‐stage amplifier with the AlGaN/GaN‐HEMT is performed by means of the coupled physical device‐circuit simulation, in which the Monte Carlo (MC) device simulator is incorporated into the embedding circuit as a realistic physics‐based device model. The forward and the backward travelling waves are extracted from the current and the voltage signal waveforms at the input and the output terminals, and then the power performances of the amplifier are evaluated using them. The amplifier exhibits the linear power gain (G a) of 12.9 dB and the saturation output power (P o,sat) of 25.7 dBm at 40 GHz. The influence of the impact ionization on the power performances is also investigated. (© 2006 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
RF and DC characteristics in Al2O3/Si3N4 insulated‐gate AlGaN/GaN heterostructure field‐effect transistors with regrown ohmic structure
Authors: Maeda Narihiko , Makimura Takashi , Maruyama Takashi , Wang Chengxin , Hiroki Masanobu , Yokoyama Haruki , Makimoto Toshiki , Kobayashi Takashi , Enoki Takatomo 
Published: May 2006

AbstractAl2O3/Si3N4 insulated‐gate AlGaN/GaN heterostructure field‐effect transistors (HFETs) have been fabricated, where the regrown ohmic structure was incorporated to reduce the contact resistance. Excellent DC and RF characteristics have been obtained together with the low gate leakage current as the result of employing the metal–insulator–semiconductor (MIS) structure. An HFET with a gate length (L g) of 0.1 μm has exhibited a drain current density (I d) and a transconductance (g m) of 1.30 A/mm and 293 mS/mm, respectively, with a reduced contact resistance of 0.3 Ω mm. The gate leakage current (I g) was as low as 1 × 10–8 A/mm in the reverse vias region, and only 4 × 10–5 A/mm even at a forward bias voltage of +3 V. In this device, the cutoff frequency (f T) and maximum oscillation frequency (f max) were estimated to be 70 and 90 GHz, respectively. In the HFETs with longer L g of 0.7 and 1.0 μm, f T and f max were 20 and 48 GHz (L g = 0.7 μm), respectively; and 14 and 35 GHz (L g = 1.0 μm), respectively. Thus, the Al2O3/Si3N4 MIS HFETs have proved to also exhibit excellent RF characteristics. (© 2006 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Electrical characterization of Si‐ion implanted AlxGa1–xN annealed at lower temperatures
Authors: Ryu Mee‐Yi , Yeo Y. K. , Zens T. W. , Marciniak M. A. , Hengehold R. L. , Steiner T. 
Published: May 2006

AbstractElectrical activation studies of Si‐implanted Alx Ga1–x N (x = 0.1 and 0.18) grown on sapphire substrate have been made as a function of anneal time, anneal temperature, and ion dose. Silicon implantation was done at room temperature with a dose ranging from 5 × 1013 to 5 × 1015 cm–2 at 200 keV. The samples were proximity cap annealed from 1100 to 1250 °C for 5–40 min with a 500 Å‐thick AlN cap in a nitrogen environment. The electrical activation efficiencies of 84% and 75% were obtained for the Al0.1Ga0.9N after annealing at 1200 °C for 40 min for a dose of 5 × 1013 and 1 × 1014 cm–2, respectively. For the Al0.18Ga0.82N, nearly 100% activation for a dose of 5 × 1014 cm–2 and 94% for a dose of 1 × 1015 cm–2 were achieved after annealing at 1250 °C and 1200 °C for 20 min, respectively. Both the activation efficiency and mobility increase with anneal time and anneal temperature, indicating an improved implantation damage recovery. The highest mobility obtained at room temperature is 89 cm2/Vs for the Al0.1Ga0.9N samples having doses of 5 × 1013 and 1 × 1014 cm–2 and annealed at either 1200 °C for 40 min or 1250 °C for 20 min. (© 2006 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Analysis of TMGa/NH3/H2 reaction system in GaN‐MOVPE growth by computational simulation
Authors: Hirako A. , Koiso S. , Ohkawa K. 
Published: May 2006

AbstractWe report the major growth pathways of GaN metalorganic vapor‐phase epitaxial growth from a TMGa/NH3/H2 system studied by computational simulation. It has been found that the most major growth pathway is stepwise elimination of CH4 from TMGa:NH3 adducts (TMGa:NH3 → DMGaNH2 → MMGaNH → Ga–N → Growth), and the second major growth pathway is due to GaNH2 molecules sublimated from GaN layer. [Ga–N]n was generated by polymerization of Ga–N molecules around the susceptor heated. GaN layer was deposited on not only the substrate but also the heated reactor walls. (© 2006 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Deep‐UV LED controlled AlGaN‐based SAW oscillator
Authors: Ciplys D. , Shur M. S. , Sereika A. , Rimeika R. , Gaska R. , Fareed Q. , Zhang J. , Hu X. , Lunev A. , Bilenko Yu. 
Published: May 2006

AbstractWe have demonstrated the possibility of controlling the frequency of an AlGaN‐based SAW delay‐line oscillator by LEDs emitting in deep UV range. The energy bandgap of AlGaN corresponded to the cutoff wavelength of 270 nm. The deep UV LEDs used in these experiments were supplied by Sensor Electronic Technology, Inc. and had the photon energies 265 nm and 305 nm. We also used 375 nm LED from Nichia Corporation. The SAW delay‐line oscillator had the SAW delay line between the output and input of an RF wide‐band amplifier. Illumination of the SAW propagation path by a UV LED resulted in the downshift of the oscillator frequency. We attribute this shift to the interaction of the SAW with photoexcited carriers in the AlGaN layer. The responsivity of the SAW oscillator significantly varied with the LED wavelength and was slightly dependent on the incident optical power. At optical powers within 15–40 μW the responsivities were 0.5 kHz/μW at 265 nm, 0.18 kHz/μW at 305 nm, and 0.03 kHz/μW at 375 nm. No response was observed from the green (560 nm) LED with a similar optical power. The comparatively strong response at 305 nm wavelength (below the energy bandgap of AlGaN) indicated the importance of trapping effects. (© 2006 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Misfit dislocations in In‐rich InGaN/GaN quantum well structures
Authors: Costa P. M. F. J. , Datta R. , Kappers M. J. , Vickers M. E. , Humphreys C. J. , Graham D. M. , Dawson P. , Godfrey M. J. , Thrush E. J. , Mullins J. T. 
Published: May 2006

AbstractStrain relaxation has been studied for the 10‐period quantum well (QW) heterostructures grown by MOVPE, In0.16Ga0.84N/GaN and In0.2Ga0.8N/GaN, both emitting with high efficiency in the blue and green regions, respectively. Additionally, a set of high‐In content InGaN/GaN QW structures, where growth parameters were kept constant but QW numbers varied between 1 and 10, were also analysed by TEM, XRD and PL. For the highly‐efficient green and the set of variable QW samples, TEM structural studies identified large well‐width fluctuations and misfit dislocations that thread into the sample surface and are generated in the quantum well stack. This contrasts with similar observations of blue‐emitting MQWs where misfit dislocations are not seen. PL measurements have been carried out for the In‐rich QW series and did not reveal a greater degradation of the optical properties with increasing numbers of quantum wells in the stack. (© 2006 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Group III‐nitride and SiC based micro‐ and nanoelectromechanical resonators for sensor applications
Authors: Förster Ch. , Cimalla V. , Lebedev V. , Pezoldt J. , Brueckner K. , Stephan R. , Hein M. , Aperathitis E. , Ambacher O. 
Published: May 2006

AbstractMicro‐ and nanomechanical AlN and 3C‐SiC resonator beams with resonant frequencies between 20 kHz and 2 MHz, depending on the resonator geometry, have been realized and characterized at ambient conditions. Up to 200 nm thin epitaxial group III‐nitrides and SiC layers were grown on silicon (111) and (100) oriented substrates, respectively. The beams were dry‐etched by an electron cyclotron resonance (ECR) plasma and an inductive coupled plasma (ICP) technique. The freestanding resonator bars have dimensions in the sub‐µm to nm‐range. The operation principle based on the known magneto motive actuation and a thin conductive metal layer on top of the resonator realizes the detection. The main fabrication steps of the resonator beams are presented. The resonant frequencies, the quality factors of the MEMS and NEMS are investigated in dependence on the geometry and the residual strain in the epitaxial layers. (© 2006 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Investigation of buffer structures for the growth of a high quality AlGaN/GaN hetero‐structure with a high power operation FET on Si substrate using MOCVD
Authors: Yoshida Seikoh , Katoh Sadahiro , Takehara Hironari , Satoh Yoshihiro , Li Jiang , Ikeda Nariaki , Hataya Kohji , Sasaki Hitoshi 
Published: May 2006

AbstractIn order to obtain a high quality thick GaN layer on a 2‐inch Si substrate without any crack, we investigated three kinds of buffer layer (AlGaN graded structure, AlN/GaN super lattice (SL) structure, and AlN/thick GaN/AlN structure) using a metal‐organic chemical vapor deposition (MOCVD). As a result, we obtained a crack‐free AlGaN/GaN hetero‐structure with a smooth surface using three kinds of buffer structure. We also observed the cross‐sectional TEM image of three kinds of buffer structures. In the case of using an AlGaN graded buffer on the AlN buffer, the number of surface defect with the size of 10000 nm was comparatively larger compared with the other buffer structures. In the case of using an AlN (18 nm)/GaN (5 nm) super‐lattice (SL) buffer, a 1000 nm‐thick GaN was grown without crack. In the case of using three AlN (50 nm)/two thick GaN (200 nm) buffer structure, the threading dislocation using this buffer was 1.5 × 109 cm–2 and the value was smaller compared with the other buffer structures. This reduction effect of dislocation was larger than the other buffer structures. We also fabricated a HFET using the AlGaN/GaN heterostructure using three AlN/two thick GaN buffer. It was confirmed that the breakdown voltage of FET was over 400 V. (© 2006 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Over 1000 mW single mode operation of planar inner stripe blue‐violet laser diodes
Authors: Sasaoka C. , Fukuda K. , Ohya M. , Shiba K. , Sumino M. , Kohmoto S. , Naniwae K. , Matsudate M. , Mizuki E. , Masumoto I. , Kobayashi R. , Kudo K. , Sasaki T. , Nishi K. 
Published: May 2006

AbstractWe report the 1000 mW single mode operation of a planar blue‐violet laser diode with inner stripe waveguide. Kink‐free output surpassed 400 mW (CW) and 600 mW (50 ns pulsed, duty 50%) at temperatures up to 90 °C. Precise optical field design for narrow stripe waveguide as well as damage‐free stripe formation was a key to achieving watt class output. By utilizing buried AlN as optical and current confinement layers, a damage‐free inner stripe as narrow as 1.0 μm wide was successfully fabricated. Planar inner stripe structure also has the advantage of a small increase in the electrical resistance for such a narrow stripe, which is favorable for high power operations. The results here indicate the potential of this planar blue‐violet laser diode for high power applications as the next generation of optical disc systems. (© 2006 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)