bluuebunny/crossref_metadata_2025_split huggingface dataset:
On the Capability of the Generalized Gamma Function to Represent Spray Drop‐Size Distribution
Authors: Lecompte Matthieu , Dumouchel Christophe 
Published: April 2008

AbstractThe three‐parameter, Generalized Gamma function solution of a recent MEF formulation used to derive liquid spray drop‐size distribution, is applied to sprays resulting from three different atomization processes. The objectives of these applications are to determine the sign of the parameters for which this function reports a more reliable fit and to further understand the parameter stability problem reported elsewhere. It is found that the lack of stability of the parameters is related to a characteristic feature of the mathematical function and appears for a series of spray drop‐size distributions with constant shape. For each situation analyzed in the present study, the Generalized Gamma function provides a very good fit with parameters that are either constant or correlated to the working conditions. As far as the sign of the parameters is concerned, the results show that the best formulation is a function of the spray and that it is impossible to know, a priori, which parameter sign will report the best fit. Finally, for one situation, it is found that the Generalized Gamma function allows extrapolation of drop sizes outside the measured values. All of the results converge to conclude that the three‐parameter Generalized Gamma function, which is identical to the well‐known Nukiyama‐Tanasawa distribution, accumulates valuable attributes to represent liquid spray drop‐size distributions.
Growth and magnetization study of transition metal doped GaN nanostructures
Authors: Gupta Shalini , Kang Hun , Kane Matthew H. , Park Eun‐Hyun , Ferguson Ian T. 
Published: April 2008

AbstractThis work presents the MOCVD growth and characterization of optically active GaN nanostructures which have been doped with the transition metals manganese and iron for potential spintronic applications. Introduction of both these transition metals in GaN nanostructures enhanced the nucleation of the nanostructures resulting in reduced lateral dimensions and increased nanostructure density. Both Ga1–xMnxN and Ga1–xFexN nanostructures showed hysteresis behaviour at 5 K. Further VSM measurements on Ga1–xFexN nanostructures at 300 K showed a hysteresis curve with a reduced coercive filed and displayed superparamagnetic behaviour. These magnetically active nanostructures are promising and provide an incentive to further study them with the aim of eventually utilizing them in spintronic applications and improving device efficiency. (© 2008 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Laser threshold and optical gain of blue optically pumped InGaN/GaN multiple quantum wells (MQW) grown on Si
Authors: Lutsenko E. V. , Danilchyk A. V. , Tarasuk N. P. , Andryieuski A. V. , Pavlovskii V. N. , Gurskii A. L. , Yablonskii G. P. , Kalisch H. , Jansen R. H. , Dikme Y. , Schineller B. , Heuken M. 
Published: April 2008

AbstractOptical and laser properties of a series of MQW heterostructures with varying geometry grown on silicon with Al predeposition were investigated. Photoluminescence (PL) band positions covered a spectral range of 430 – 460 nm under Iexc=1 MW/cm2 and 445‐505 nm under Iexc=0.15 W/cm2. Laser action was achieved under transversal optical pumping at room temperature using only cleaved lateral facets of the samples as laser mirrors. The laser threshold rose from 137 kW/cm2 to 300 kW/cm2 with laser wavelength increase from 440 nm to 465 nm. Numerical simulation of the laser conditions shows that the minimal threshold is realized on the fifth order mode. However, the calculated value of material optical gain of InGaN at the laser threshold increases only from 750 cm–1 to 1020 cm–1, mainly due to absorption rise in the substrate with increasing wavelength. Correlation was observed between PL characteristics and laser threshold. (© 2008 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Effects of surface passivation films on AlGaN/GaN HEMT with MIS gate structure
Authors: Yagi S. , Shimizu M. , Ide T. , Yano Y. , Akutsu N. 
Published: April 2008

AbstractWe investigated the effect of ebeam‐deposited SiNx, SiO2, and TiO2 passivation films on the AlGaN/GaN HEMT structure. The AlGaN/GaN heterojunction structure was grown on a sapphire substrate by metal organic chemical vapor deposition. The sheet resistance of the AlGaN/GaN HEMT structure was 420‐510 Ω/□. TiO2, SiNx and SiO2 passivation films were employed as the insulator in MIS gate structure. All passivation films were deposited by electron beam evaporation at 200 °C. The thickness of SiNx, SiO2 and TiO2 passivation films were 15, 10 and 15 nm, respectively. The relative dielectric constants of the deposited SiNx, SiO2 and TiO2 were measured to be 4, 7 and 80, respectively by fabricating the capacitance structures. The sheet resistance was changed after the deposition of the insulator films. We found to be 512, 628 and 992 Ω/□ for the SiNx, SiO2 and TiO2 films, respectively. We considered that the surface passivation using the TiO2 and SiO2 films reduces the carrier density in the AlGaN/GaN channel. (© 2008 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Recombination dynamics of localized excitons in AlGaN‐based quantum wells
Authors: Murotani Hideaki , Saito Takuya , Kato Nobuo , Yamada Yoichi , Taguchi Tsunemasa 
Published: April 2008

AbstractThe effect of internal electric field on exciton localization in AlGaN‐based quantum wells (QWs) has been studied by means of time‐resolved photoluminescence (PL) spectroscopy. The observed time‐dependent PL was analyzed using rate equations, which enabled us to obtain the PL lifetime and the localization time of excitons for three QWs with different well‐layer thickness. The localization time became longer with increasing well‐layer thickness. This result indicated that a quantum confined Stark effect caused the reduction in transition probability of excitons from extended to localized states. In addition, the localization time decreased with increasing excitation density and the three QWs indicated almost the same localization time at higher excitation density. Since the alloy composition was the same for the three QWs, the degree of localization due to alloy disorder did not change so much. Therefore, the screening of the internal electric field resulted in the same localization time. (© 2008 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
340 nm‐band high‐power InAlGaN quantum well ultraviolet light‐emitting diode using p‐type InAlGaN layers
Authors: Fujikawa Sachie , Takano Takayoshi , Kondo Yukihiro , Hirayama Hideki 
Published: April 2008

AbstractIn order to achieve high‐efficiency ultraviolet (UV) light‐emitting diodes (LEDs), p‐type layers with sufficient hole concentration is quite important to suppress the electron overflow. We introduced Mg‐doped InAlGaN for p‐type layers of the UV‐LEDs for the purpose of obtaining higher hole concentration, and achieved high power CW operations of the UV‐LEDs. 340 nm‐band InAlGaN‐based multi‐quantum‐well (MQWs) UV‐LEDs with Mg‐doped InAlGaN electron‐blocking layer (EBL) and Mg‐doped InAlGaN layers were grown on sapphire substrates by metal‐organic chemical vapor deposition (MOCVD). The output power of UV‐LED with p‐InAlGaN layers was approximately 4.7 times larger than that with p‐AlGaN layers. Maximum output power and the external quantum efficiency (EQE) of the LED with p‐InAlGaN layers were 8.4 mW and 0.9%, respectively, at emission wavelength of 346 nm under room temperature (RT) CW operation. From these results, p‐InAlGaN is shown to be useful for the realization of high‐efficiency UV‐LEDs. (© 2008 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Optimization of GaN MOS capacitors and FETs
Authors: Huang W. , Khan T. , Chow T. P. 
Published: April 2008

AbstractIn this paper, three different gate oxide processes were explored and compared. All MOS capacitors were fabricated on n‐type GaN epitaxial layers grown by MOCVD on sapphire substrates. C‐V measurements were performed on the three samples and their characteristics were compared. The very small interface‐state density makes OX3 a very good process choice for GaN MOSFETs and the trend of decreasing interface‐state density deeper into the bandgap allows the demonstration of GaN inversion‐mode MOSFET.Both accumulation and inversion‐mode MOSFETs were fabricated and characterized using OX3 process conditions. Field‐effect mobilities were extracted on both circular and linear devices with different channel lengths. Mobilities in two perpendicular directions in (0001)‐plane show similar values. Current collapse testing was also performed on our GaN MOSFETs and no current collapse was observed. In addition, an NMOS inverter stage, utilizing an enhancement‐mode MOSFET and a depletion‐mode MOSFET has also been demonstrated and characterized. (© 2008 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Surface treatment on the growth surface of semi‐insulating GaN bulk substrate for III‐nitride heterostructure field‐effect transistors
Authors: Ryou J.‐H. , Liu J. P. , Zhang Y. , Horne C. A. , Lee W. , Shen S.‐C. , Dupuis R. D. 
Published: April 2008

AbstractAl0.25Ga0.75N/GaN heterostructure field‐effect transistor (HFET) structures are grown on semi‐insulating GaN substrates by metalorganic chemical vapor deposition with Fe‐doped GaN buffer layer and various surface treatments prior to the epitaxial growth of the structure. The surface treatments are intended to remove suspected surface‐charge‐containing layer and they include wet chemical etching, in‐situ thermal etching, plasma dry etching, and photo‐enhanced chemical etching. Photo‐enhanced chemical (PEC) etching was effective in achieving microscopically smooth surface and in eliminating surface charge layer on the surface of semi‐insulating GaN substrates. RMS surface roughness of PEC etched surface of the semi‐insulating GaN substrate is 0.1∼0.2 nm for 1×1 μm2 scan. C ‐V measurement shows well‐defined 2‐dimensional‐gas‐related charge without any growth‐interface‐related charge for a HFET grown on a semi‐insulating GaN substrate with optimized photo‐enhanced chemical etching of the surface. (© 2008 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Luminescence properties of AlxGa1–xN(0.4 < x < 0.5)/AlyGa1–yN (0.6 < y ≤ 1) quantum structures grown by gas source molecular beam epitaxy
Authors: Nikishin S. , Borisov B. , Kuryatkov V. , Song D. , Holtz M. , Garrett G. A. , Sarney W. L. , Sampath A. V. , Shen H. , Wraback M. 
Published: April 2008

AbstractWe report structural and optical properties of AlxGa1–xN (0.4 < x < 0.5)/AlyGa1–yN (0.6 < y ≤ 1) quantum structures grown by gas source molecular beam epitaxy with ammonia on (0001) sapphire substrates. The structures are designed for light emission at ∼ 280 nm. The AlxGa1–xN (0.4 < x < 0.5) well material was grown under two dimensional (2D), three dimensional (3D), and (2D+3D) conditions by the varying group‐III/ammonia ratio. The formation of nanoscale islands, or quantum dots (QDs), in the wells grown in 3D and (2D+3D) modes was observed using transmission electron microscopy. Optical properties are investigated using room temperature cathodoluminescence and time‐resolved photoluminescence. Systematic studies allow us to obtain well growth conditions to produce ∼ 60 fold intensity enhancement over purely two‐dimensional structures. Under these conditions, corresponding to deposition ∼ 10 monolayers of well material, we obtain emission at ∼ 280 nm with narrowest line width and longest photoluminescence decay time. (© 2008 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Closed‐loop MBE growth of droplet‐free GaN with very metal rich conditions using Metal Modulated Epitaxy with Mg and In
Authors: Burnham S. D. , Henderson W. , Doolittle W. A. 
Published: April 2008

AbstractImprovements to the Metal Modulated Epitaxy (MME) technique are achieved through computer controlled shutter transitions based on feedback from RHEED transients (S. D. Burnham and W. A. Doolittle, J. Vac. Sci. Technol. B 24, 2100 (2006) [1]), thus creating a closed‐loop control system for nitride MBE, the first of its kind. A high‐sensitivity 22 bit camera is used to determine when RHEED transients have subsided, upon which a shutter transition is initiated allowing the efficient buildup and depletion of the metal bilayer, which improves surface morphology and growth rate compared to the standard MME technique. RMS surface roughness was reduced by 41% by using this “Smart Shuttering” improvement to MME. A substantially higher peak concentration of Mg, approaching 2% atomic concentration, was achieved using the MME technique. As expected, a negligible amount of In was incorporated into the very Ga‐rich films. Using the new closed loop control system developed for MBE, the surface morphology was improved for GaN films while highly repeatable holes concentrations as high as 4.7×1018 cm–3 with 1.07 cm2/V‐sec mobility was obtained. This approach offers great promise for improved reproducibility and improved material quality. (© 2008 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Integration of a matrix addressable blue/green LED array with multicore imaging fiber for spatiotemporal excitation in endoscopic biomedical applications
Authors: Xu H. , Davitt K. M. , Dong W. , Song Y.‐K. , Patterson W. R. , Nurmikko A. V. , Aizenman C. D. 
Published: April 2008

AbstractWe have developed a micro‐scale endoscopic optical image projection device, integrating an InGaN MQW blue/green two‐dimensional (2D) LED array to a multicore imaging fiber. A scalable matrix addressing scheme was used for the electrical access to individual elements in the densely packed 2D‐LED array. A prototype 10×10 element array was fabricated by specialized device process flow, using deep reactive ion etching and polyimide etch‐back processes for device isolation and planarization. Individual elements of the array have been operated under cw current injection up to 3 kA/cm2, suggesting uncompromised performance and robustness of the planarized device structure. The device was butt‐coupled to a 30,000 pixel multicore image fiber to generate a spatiotemporal pattern of light at the output end of the fiber. As application demonstration, selected illumination patterns have been projected to the eye of Xenopus laevis tadpoles in studies of their developing visual system, as well as optically excitable neural cells in the brain. (© 2008 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Low‐temperature grown compositionally graded InGaN films
Authors: Miller N. , Jones R. E. , Yu K. M. , Ager J. W. , Liliental‐Weber Z. , Haller E. E. , Walukiewicz W. , Williamson T. L. , Hoffbauer M. A. 
Published: April 2008

AbstractA new thin film growth technique known as energetic neutral atomic‐beam lithography/epitaxy (ENABLE) provides a large energetic N atom flux and eliminates the need for high substrate temperatures as compared to molecular beam epitaxy, making isothermal growth over the entire InGaN alloy composition range possible without phase separation. 500–800 nm thick compositionally graded InGaN films were grown by ENABLE at ∼450 °C with the following structure types: (1) with the Ga‐rich material on the surface and (2) with the Inrich material on the surface. Rutherford backscattering spectrometry, transmission electron microscopy, X‐ray diffraction, absorption spectroscopy, photoluminescence, and Hall effect measurements were used to assess the thickness, composition, crystalline quality, and optical and electrical properties of the films. The results establish the new ENABLE method as uniquely capable of growing compositionally graded InGaN films and, in the future, InN/GaN heterostructures. (© 2008 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
High‐resolution Rutherford backscattering spectrometry for InAlGaN/AlGaN single quantum well structure
Authors: Sakuta H. , Fukui T. , Miyachi T. , Kurai S. , Taguchi T. 
Published: April 2008

AbstractInAlGaN/AlGaN single quantum well (SQW) structure has been studied by means of high‐resolution Rutherford backscattering spectrometry (HRBS). The HRBS spectrum of a SQW structure was clearly observed. The composition of each layer was estimated to be In0.02Al0.17Ga0.81N/Al0.28Ga0.72N from the HRBS measurement. The channeling measurement shows the high degree of the crystalline perfection that can be achieved in such epitaxial layers from the minimum yield of 3.2% in the direction of the <11–23> axis. The channeling measurement also shows atomic disorder differences between InAlGaN epitaxial layer and AlGaN epitaxial layer. Furthermore Al, Ga and In minimum yields in the InAlGaN layer were estimated to be χmin(Ga) = 4.9%, χmin(Al) = 9.4% and χmin(In) = 6.6%, respectively. Larger normalized yield of Al than those of Ga and In in the InAlGaN layer indicates that Al atomic disorder becomes larger to compensate the compressive stress of Ga and In. (© 2008 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
GaN HEMT thermal behavior and implications for reliability testing and analysis
Authors: Green Daniel S. , Vembu Bharath , Hepper David , Gibb Shawn R. , Jin Daniel , Vetury Rama , Shealy Jeffrey B. , Beechem L. Thomas , Graham Samuel 
Published: April 2008

AbstractGaN HEMT reliability evaluation in a typical Arrhenius manner requires establishing peak junction temperature for a particular stress condition. Several new techniques have yielded promising results toward establishing peak temperature for these devices in combination with detailed physical modeling, particularly micro‐Raman imaging. This paper compares results from finite element modeling to measurements by infrared imaging and micro‐Raman imaging. The limitations of IR imaging were confirmed similar to earlier reports. Two techniques for establishing temperature from micro‐Raman measurements were used to reveal excellent correlation to the model, and also provide insight into the relationship between temperature and structural change in the device. Temperature modeling data is reported for base plate temperature from 85°C to 250°C for practical GaN HEMT devices. Implications of the measurements for GaN HEMT reliability stress testing and analysis will be discussed. (© 2008 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Formation of ohmic contacts to ultra‐thin channel AlN/GaN HEMTs
Authors: Zimmermann Tom , Deen David , Cao Yu , Jena Debdeep , Xing Huili Grace 
Published: April 2008

AbstractAlN/GaN‐based high electron mobility transistors with ultra‐thin AlN barriers of 2.3 ‐ 5 nm are attractive candidates for very high speed applications owing to the aggressive scalability such structures afford. We report the first study on formation of ohmic contacts to these high quality ultra‐thin channel heterostructures (ns > 1x1013 cm–2 and μ > 900 cm2/Vs) with systematically varying barrier thicknesses. While the conventional ohmic contacts to AlGaN/GaN structures generally require high temperature annealing, these ohmic contacts were found to behave ohmic or near ohmic as‐deposited. Annealing (400‐860 0C) improves the contact resistance to a range of 0.8 ‐ 2 ohm‐mm but the annealing conditions strongly depend on the AlN thickness as well as the heterostructure quality (μ). All alloyed contacts show smooth morphology, making them suitable for e‐beam lithographically defined gate patterning. (© 2008 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
A novel GaN‐based multiparameter sensor system for biochemical analysis
Authors: Lübbers B. , Kittler G. , Ort P. , Linkohr S. , Wegener D. , Baur B. , Gebinoga M. , Weise F. , Eickhoff M. , Maroldt S. , Schober A. , Ambacher O. 
Published: April 2008

AbstractGaN and its ternary alloys offer several advantages for the fabrication of biochemical sensors systems due to their chemical stability and optical transparency. We employ ion‐sensitive field effect transistors (ISFET) based on a surface sensitive AlGaN/GaN heterostructure. Combined with a picoliter dosing system, an integrated micro reference electrode and an optical spectroscopy system a novel multi‐parameter analysis system for aqueous solutions in the micro‐ to nanoliter range was constructed. Application examples are presented to illustrate the application potential of the sensor system e.g. in the high‐throughput screening of cancer drugs. Simultaneous opto‐electrochemical monitoring of enzyme reaction kinetics by pH and absorption measurements in 700 nl and parallel automated measurements with functionalized enzyme‐modified FETs (EnFET) and a reference ISFET in 3 µl are demonstrated. The experimental data obtained agree well with published values for the reaction kinetic and with reference measurements performed with a state‐of‐the‐art pH‐meter and spectrophotometer which require 1000‐fold larger volumes. (© 2008 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
InGaN‐based LEDs grown by plasma‐assisted MBE on (0001) sapphire with GaN QDs in the nucleation layer
Authors: Thomidis C. , Nikiforov A. Yu. , Xu Tao , Moustakas Theodore D. 
Published: April 2008

AbstractBlue‐violet LEDs based on InGaN MQWs were grown by RF‐plasma MBE on (0001) sapphire with GaN QDs incorporated in the nucleation layer as a mechanism of dislocation filtering. Devices with dimensions 800 μm x 800 μm were fabricated and evaluated at a bare die configuration by measuring their EL spectra and power output. At low injection current, the EL spectra peak at 440 nm. At high injection current a second peak at 385 nm becomes the dominant one and it is attributed to tunneling of injected electrons through the electron blocking layer. The dependence of the power output as a function of the injection current was studied systematically in order to evaluate the effects of heating. Power outputs up to 9 mW were measured at injection current of 1 A. (© 2008 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Optical properties of single and multi‐layer InGaN quantum dots
Authors: Sebald K. , Lohmeyer H. , Herlufsen S. , Kalden J. , Gutowski J. , Tessarek C. , Yamaguchi T. , Hommel D. 
Published: April 2008

AbstractWe discuss the optical properties of single InGaN QDs grown by MOVPE. The samples were structured into mesas by focused‐ion‐beam etching and investigated by micro‐photoluminescence measurements. The QDs are characterized by a high temperature stability of their emission up to 150 K and strong localization of the carriers within the quantum dots, indicated by the observation of antibinding biexcitonic complexes. The influences of piezoelectric fields and spectral diffusion effects were investigated. Furthermore, the polarization of individual QD emission lines was analyzed giving an insight into their geometrical shape. The quantum dots were used for the realization of quantum dot stacks. The photoluminescence of these samples can be traced up to room temperature. (© 2008 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Synthesis of rare‐earth activated AlN and GaN powders via a three‐step conversion process
Authors: Tao Jonathan H. , Perea‐Lopez Nestor , McKittrick Joanna , Talbot Jan B. , Klinedinst Keith , Raukas Madis , Laski Joseph , Mishra Kailash C. , Hirata Gustavo 
Published: April 2008

AbstractUsing a three‐step solution method, we have successfully synthesized rare‐earth (RE) activated AlN, GaN, and pure GaAlN powders. Aluminium and/or gallium nitrates are first dissolved in water. For AlN:RE, rare‐earth nitrates converted from their corresponding oxides of Dy3+ and Tm3+ are then added to the precursor nitrate solution. The mixture is subsequently converted into Al(OH)3:RE by combining with aqueous NH4OH at room temperature. The product is then mixed with aqueous NH4F to form (NH4)3AlF6:RE. The conversion process is complete when the hexafluoride compound is flushed with anhydrous ammonia to produce the final nitride product AlN:Dy3+,Tm3+. GaN, GaN:Tb3+ and GaAlN are synthesized similarly. Single phase, pure GaN and GaAlN formation has been confirmed. Dysprosium oxide has been observed in AlN:Dy3+, Tm3+. Oxygen concentration of approximately 4 at% has been measured in GaN powders, and is slightly higher in AlN powders. Spectroscopic measurements show clearly observable emission from Dy3+ and Tm3+ co‐activated AlN samples. In activated GaN samples, Tb3+ emission has been observed. (© 2008 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)