bluuebunny/crossref_metadata_2025_split huggingface dataset:
A Clustering Approach for the Separation of Touching Edges in Particle Images
Authors: Korath Jose M. , Abbas Ali , Romagnoli Jose A. 
Published: April 2008

AbstractThe occurrence of touching objects in images of particulate systems is very common especially in the absence of dispersion methods during image acquisition. The separation of these touching particles is essential before accurate estimation of particle size and shape can be achieved from these images. In the current work, clustering approaches based on the fuzzy C‐means algorithm are employed to identify the touching particle regions. Firstly, clustering in the multidimensional space of image features, e.g., standard deviation, gradient and range calculated in a certain neighborhood of each pixel, is performed to trap the touching regions. Then, in a novel proposed method, the clustering of pixel intensity itself into two fuzzy clusters is performed and a feature, referred to as the ‘Fuzzy Range', is calculated for each pixel from its membership values in both clusters and is presented as a distinguishing feature of the touching regions. Both approaches are compared and the superiority of the latter method in terms of the non‐necessity of neighborhood based calculations and minimum disfiguration is elucidated. The separation methods presented herein do not make any assumption about the shape of the particle as is undertaken in many methods reported elsewhere. The technique is proven to minimize greatly the deleterious effects of over‐segmentation, as is the case with traditional watershed segmentation techniques, and consequently, it results in a superior performance.
High intensity red emission from Eu doped GaN powders
Authors: Shi Junxia , Chandrashekhar M. V. S. , Reiherzer Jesse , Schaff William , Lu Jie , Disalvo Francis , Spencer Michael 
Published: April 2008

AbstractEu doped GaN powders have been produced by a low‐cost and high‐yield method. The effect of temperature on the optical properties and structure was investigated by photoluminescence, X‐ray diffraction and Raman spectroscopy. The effective Eu incorporation was extracted by a non‐destructive strain analysis correlating the Raman with the XRD data. Luminescence intensity was closely related to the effective Eu incorporation. The maximum Eu incorporation was determined to be 0.5 at% for the sample grown at 1000 °C, which showed the strongest red photoluminescence with the highest crystallinity. (© 2008 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
MOVPE growth of blue InxGa1–xN/GaN LEDs on 150 mm Si(001)
Authors: Schulze F. , Dadgar A. , Krtschil A. , Hums C. , Reissmann L. , Diez A. , Christen J. , Krost A. 
Published: April 2008

AbstractWe report on the implementation of GaN‐based, blue light emitting diodes on 150 mm Si(001) substrates grown by metalorganic vapor phase epitaxy. The 2.8 µm thick samples are completely crack‐free and the optically active layers consist of fivefold InxGa1–xN/GaN multiple quantum wells. The homogeneity of the light emission across the whole sample is determined by photoluminescence wafer mapping exhibiting an averaged peak wavelength of 456 nm at room temperature and a standard deviation of less than 1%. A bright blue light emission is obtained by an electrical excitation with a turn‐on voltage of below 2.8 V. (© 2008 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Semipolar GaN grown on m‐plane sapphire using MOVPE
Authors: Wernicke Tim , Netzel Carsten , Weyers Markus , Kneissl Michael 
Published: April 2008

AbstractWe have investigated the MOVPE growth of semipolar gallium nitride (GaN) films on (10$ \bar 1 $0) m‐plane sapphire substrates. Specular GaN films with a RMS roughness (10 × 10 μm2) of 15.2 nm were obtained and an arrowhead like structure aligned along [$ \bar 2 $113] is prevailing. The orientation relationship was determined by XRD and yielded (2$ \bar 1 $$ \bar 1 $2)GaN ‖ (10$ \bar 1 $0)sapphire and [$ \bar 2 $113]GaN ‖ [0001]sapphire as well as [$ \bar 2 $113]GaN ‖ [000$ \bar 1 $]sapphire.PL spectra exhibited near band edge emission accompanied by a strong basal plane stacking fault emission. In addition lower energy peaks attributed to prismatic plane stacking faults and donor acceptor pair emission appeared in the spectrum. With similar growth conditions also (10$ \bar 1 $$ \bar 3 $) GaN films on m‐plane sapphire were obtained. In the later case we found that the layer was twinned, crystallites with different c‐axis orientation were present. (© 2008 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Low on‐resistance AlGaN/GaN HEMTs by reducing gate length and source‐gate length
Authors: Ide T. , Shimizu M. , Yagi S. , Inada M. , Piao G. , Yano Y. , Akutsu N. , Okumura H. , Arai K. 
Published: April 2008

AbstractTo reduce the on‐resistance of AlGaN/GaN HEMTs, the gate length (LG) and gate‐source (LSG) length were reduced to submicron order. The reduction of LG and LSG effectively decreased the drain‐source spacing (LSD), which led to the reduction of the on‐resistance without degrading the breakdown voltage. Moreover, the reduction of LG and LSG enhanced the drain current and transconductance. The specific on‐resistance of 0.1 mΩ‐cm2 was achieved at a LG of 0.10 μm and a LSG of 0.5 μm. The breakdown voltage of 56 V was obtained at a specific on‐resistance of 0.12 mΩ‐cm2. This high breakdown voltage was achieved by extending the drain‐gate spacing due to the short LG and LSG. These characteristics of the fabricated device are equivalent to the trade‐off characteristics of the numerical calculation. (© 2008 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
New results on HVPE growth of AlN, GaN, InN and their alloys
Authors: Usikov A. , Soukhoveev V. , Shapovalova L. , Syrkin A. , Kovalenkov O. , Volkova A. , Sizov V. , Ivantsov V. , Dmitriev V. 
Published: April 2008

AbstractA variety of new results on HVPE growth of group III nitride layers and heterostructures are described. Crack free from 10 to 30 μm thick AlN layers were grown on 100‐mm SiC substrates. Bowing of the AlN/SiC wafers was controlled below 10 microns. Low growth rate HVPE with deposition rate below 10 nm/min was demonstrated for GaN, AlN, and AlGaN. This process resulted in the first HVPE grown multi‐quantum wells (MQWs) and superlattices. P‐type as‐grown GaN<Mg> layers with acceptor concentrations up to 3×1019 cm–3 were demonstrated. InGaN layers from 0.002 to 2 μm thick were grown by HVPE for the whole composition range using c‐plane GaN/sapphire template substrates. Non‐polar InGaN layers were grown on a‐GaN/r‐sapphire templates and m‐plane GaN bulk substrates. Blue and green all‐HVPE LEDs were made utilizing InGaN MQWs grown on p‐GaN/sapphire templates. (© 2008 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Effects of sapphire substrate misorientation on the GaN‐based light emitting diode grown by metalorganic vapour phase epitaxy
Authors: Nakamura A. , Yanagita N. , Murata T. , Hoshino K. , Tadatomo K. 
Published: April 2008

AbstractWe have systematically investigated the influence of sapphire substrate misorientation on the structural and optical properties of GaN‐based LEDs grown by MOVPE. The LED properties were found to be very sensitive to the misorientation. We grew five samples of LEDs on sapphire substrates with various misorientation angles (0.02∼1.0°). The EL intensity increased when misorientation angles increased to 0.25°. The intensity, however, decreased dramatically when misorientation angles exceeded 0.25°. We also grew the samples of each layer of the LEDs, viz., GaN, InGaN, InGaN/GaN MQWs, and p‐GaN layer. CL and PL analyses showed that the crystalline quality of InGaN (MQWs) layer became lower while that of GaN layer improved as misorientation angles increased. In addition, the increased misorientation caused the decreased indium composition and the indium compositional fluctuation. Moreover, the hole (carriers) concentration of p‐GaN layer decreased with increasing misorientation angles. As these results, the misorientation angle of around 0.25° is suitable for the LEDs. (© 2008 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Effects of resonant LO phonon assisted excitation on the photoluminescence spectra of InGaN/GaN quantum wells
Authors: Dawson P. , Hylton N. P. , Kappers M. J. , McAleese C. , Humphreys C. J. 
Published: April 2008

AbstractWe have observed oscillations in the low temperature (T < 50 K) photoluminescence excitation spectra of an InGaN/GaN single quantum well at photon energies above the GaN bandgap. We attribute the features in the spectra to excitation of electrons at multiples of the LO phonon energy above the GaN conduction band edge. The rapid cooling of these electrons to the GaN conduction band edge and their subsequent capture leads to a shift, in the photoluminescence spectrum and hence the oscillations in photoluminescence. We interpret the shift in the spectrum as being due to a modification of the occupation of the distribution of localization centres by electrons. (© 2008 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Comparison of GaInN laser structures grown on different substrates
Authors: Dräger A. , Fuhrmann D. , Netzel C. , Rossow U. , Schenk H. P. D. , Hangleiter A. 
Published: April 2008

AbstractIn order to get a better understanding of the influence of different substrates on GaInN laser structures we performed optical gain spectroscopy using the Variable Stripe Length Technique on laser samples grown by MOVPE. These samples were grown on SiC, GaN template on sapphire and on freestanding GaN substrates. Using the measurements on these samples the influence of the substrate on the gain performance and on the recombination processes in the samples is determined. The main focus of the studies are the measurements made on samples grown on different substrates during the same growth‐process and in addition to reach an emitting wavelength longer than 450 nm. (© 2008 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Electrical and optical properties of thick highly doped p‐type GaN layers grown by HVPE
Authors: Usikov A. , Kovalenkov O. , Soukhoveev V. , Ivantsov V. , Syrkin A. , Dmitriev V. , Nikiforov A. Yu. , Sundaresan S. G. , Jeliazkov S. J. , Davydov A. V. 
Published: April 2008

AbstractIn this paper we report 3‐7 μm thick p‐GaN growth by hydride vapor phase epitaxy (HVPE) on sapphire substrates. Mg impurity was used for doping. As‐grown GaN layers had p‐type conductivity with concentration NA‐ND up to 3×1019 cm–3. Mg atom concentration was varied from 1017 to 1020 cm–3. Hydrogen concentration was about 10 times less than that for Mg, which may explain effective p‐type doping for as‐grown GaN layers. Micro‐cathodoluminescence revealed a columnar‐like structure of the GaN layers with a non‐uniform distribution of material regions having dominant 362 nm or 430 nm luminescence. Use of these thick p‐GaN layers to grow InGaN‐based blue and green LEDs by the HVPE is demonstrated. (© 2008 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
In‐situ passivation combined with GaN buffer optimization for extremely low current dispersion and low gate leakage in Si3N4/AlGaN/GaN HEMT devices on Si (111)
Authors: Germain M. , Cheng K. , Derluyn J. , Degroote S. , Das J. , Lorenz A. , Marcon D. , Hove M. Van , Leys M. , Borghs G. 
Published: April 2008

AbstractUsing Si substrates is the sole route towards III‐nitrides process on large wafer diameter: flat, crack‐free HEMT epiwafers have been grown by MOVPE with diameter up to 150 mm, exhibiting very low sheet resistivity (260 Ω/sq.) and high uniformity (<2%), thanks to in‐situ Si3N4 capping (<5 nm). We show here that simultaneous optimization of GaN growth and of device passivation results in a drastic reduction of buffer and surface traps. This has impact onto device performance, assessed by pulse IV measurements. Drain lag is correlated with the appearance of deep defect‐related peaks in photoluminescence spectra (6 K), and completely eliminated by tuning growth temperature. Gate formation (Ni/Au) onto MOVPE‐grown Si3N4, followed by cleaning and PECVD ex‐situ passivation, leads to very low gate current dispersion, associated to gate leakage current in μA/mm range. Both dc and pulsed characteristics show a current density in the order of 0.8‐1 A/mm, whereas maximal transconductance is 250 mS/mm (Lg = 1 μm). (© 2008 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Influence of the Mn compositional distribution on the magnetic order in diluted GaMnN layers
Authors: Mai D. , Niermann T. , Zenneck J. , Roever M. , Pinto A. Bedoya , Malindretos J. , Seibt M. , Rizzi A. 
Published: April 2008

AbstractGaMnN is a prototypical GaN‐based dilute magnetic semiconductor (DMS) and its potential as a room temperature ferromagnetic material is still a controversial question to be answered. Diluted GaMnN layers with Mn concentrations up to several percent have been grown by plasma‐assisted MBE on MOVPE‐GaN templates either on p‐Si(111) or on Al2O3(0001) substrates. None of the samples reported here shows second phase precipitates in XRD or in the TEM analysis. However different composition distributions have been evidenced by EDX during the scanning TEM analysis.GaMnN grown at a substrate temperature of TS = 650 °C exhibits extended structural defects and strong compositional inhomogeneity. This could be indicative of decomposition due to local strain. Samples grown at TS = 775 °C with a Mn concentration of about 3% show a homogeneous Mn distribution in the layer. The magnetic properties are found to vary from spin glass to ferromagnetic behaviour at room temperature among different samples. (© 2008 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
High breakdown voltage AlGaN/GaN heterojunction field effect transistors on sapphire
Authors: Shi Junxia , Choi Y. C. , Pophristic M. , Spencer M. G. , Eastman L. F. 
Published: April 2008

AbstractAlGaN/GaN heterojunction field effect transistors (HFETs) on sapphire substrates for high‐power switching applications were fabricated using a self‐align process. Without any additional field plate design, the fabricated devices with gate‐drain spacing (Lgd) of 16 µm exhibited a high breakdown voltage (BV) of 1580 V with a specific on‐resistance (ARon) of 4.0 mΩ‐cm2. This result approaches the SiC theoretical limit. The BV‐ARon performance showed a linear trend with variations of Lgd, indicating a predictable performance. In addition, the effects of the source and drain contact lengths Ls and Ld on ARon have also been investigated and optimized. (© 2008 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Intensity‐dependent photoluminescence studies of the electric field in N‐face and In‐face InN/InGaN multiple quantum wells
Authors: Chern‐Metcalfe G. D. , Readinger E. D. , Shen H. , Wraback M. , Koblmüller G. , Gallinat C. S. , Speck J. S. 
Published: April 2008

AbstractWe probe the electric field in In‐face and N‐face InN/InGaN multiple quantum wells (MQWs) using low temperature intensity‐dependent photoluminescence (PL) under continuous‐wave laser excitation at 900 nm. The In‐face structure consists of 30 periods of 2.5 nm thick InN wells and 24 nm thick In0.92Ga0.08N barriers. The N‐face sample consists of 25 periods of 1.5 nm InN wells and 15 nm thick In0.88Ga0.12N barriers. At low excitation power, the PL peak energy from both In‐face and N‐face MQWs is redshifted relative to that from bulk InN. As excitation power increases, we observe a 50 and 44 meV blueshift of the PL peak energy from the In‐face and N‐face MQWs, respectively. The blueshift is a result of the optically induced screening of the built‐in electric field. From the measured blueshift, we calculate a minimum change of the electric field to be ∼0.4 MV/cm and ∼0.6 MV/cm in the In‐face and N‐face well regions, respectively. (© 2008 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Fabrication and characterization of m‐plane (1‐100) GaN based metal‐oxide‐semiconductor capacitors
Authors: Tilak V. , Matocha K. , Dunne G. 
Published: April 2008

AbstractM‐plane non‐polar, Gallium Nitride(GaN) based metal‐oxide‐semiconductor (MOS) capacitors were fabricated by depositing 150 nm thick low‐pressure chemical vapor deposition silicon dioxide at 900 °C. No positive shift in the flat band voltage of m‐plane GaN MOS capacitors was observed versus temperature, confirming the absence of pyroelectric effects. In contrast, c‐plane (0001) polar, GaN MOS capacitors, show a positive flat band voltage shift versus temperature and the pyroelectric coefficient of –3×109 q/cm2‐K was measured. A small negative shift in flat band voltage was observed in m‐plane GaN consistent with changes in the bulk potential and corresponding decrease in the occupancy of interface traps. Time dependent dielectric(TDDB) measurements were performed at 200 °C and a mean time to failure (MTTF) of 40 hours was measured at an electric field of 5 MV/cm. (© 2008 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Strain and compositional analyses of Al‐rich Al1–xInxN films grown by MOVPE: impact on the applicability of Vegard's rule
Authors: Darakchieva V. , Beckers M. , Hultman L. , Xie M. , Monemar B. , Carlin J.‐F. , Grandjean N. 
Published: April 2008

AbstractWe have studied composition and strain in Al1–x Inx N films with 0.128≤ x≤ 0.22 grown on GaN‐buffered sapphire substrates by metalorganic vapor phase epitaxy. A good agreement between the In contents determined by Rutherford backscattering spectrometry (RBS) and Xray diffraction (XRD) is found for x≤ 18, suggesting applicability of Vegard's rule in the narrow compositional range around the lattice matching to GaN. The increase of the In content up to x = 0.22 leads to a formation of sub‐layers with a higher composition, accompanied by deviations from Vegard's rule. (© 2008 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Double heterostructure ultraviolet light emitting diodes with nanometer scale compositionally inhomogeneous active regions
Authors: Sampath A. V. , Reed M. L , Chua C. , Garrett G. A. , Dang G. , Readinger E. D. , Shen H. , Usikov A. , Kovalenkov O. , Shapovalova L. , Dmitriev V. A. , Johnson N. M. , Wraback M. 
Published: April 2008

AbstractWe report on the fabrication and evaluation of flip‐chipped double heterostructure UVLEDs operating at 320 nm that employ a bulk (80nm) AlGaN active region containing nanoscale compositional inhomogeneities (NCI), deposited by plasma‐assisted molecular beam epitaxy. The devices were deposited on AlGaN templates grown by hydride vapor phase epitaxy and contain electron and hole injection layers grown by metalorganic chemical vapor deposition. A packaged, 300 μm x 300 μm device with 3% internal quantum efficiency has a peak output power of 0.56 mW at 90 mA DC current that corresponds to an external quantum efficiency of 0.15%. Nearly constant external quantum efficiency is observed for DC current density up to 100 A/cm2, suggesting that the NCI regions effectively suppress the deleterious effects of polarization fields at low injection currents that should inhibit radiative recombination in double heterostructure devices. (© 2008 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Electron transport properties of low sheet‐resistance two‐dimensional electron gases in ultrathin AlN/GaN heterojunctions grown by MBE
Authors: Cao Yu , Wang Kejia , Jena Debdeep 
Published: April 2008

AbstractA study of the transport properties of polarizationinduced 2DEGs at MBE‐grown single AlN/GaN heterostructures with different growth rates is reported. It is observed that faster growth rates lead to high mobilities, approaching ∼ 1600 cm2/Vs at 300 K and ∼ 6000 cm2/Vs at low temperatures for ultrathin (2.3 nm AlN/GaN) heterojunctions. By using a theoretical model in conjunction with experimentally measured transport properties, it is concluded that the 300 K sheet resistances of very high density 2DEGs at AlN/GaN heterojunctions are currently limited (∼ 170 Ω /□) by interface roughness scattering, and can be further reduced by improving the growth conditions. (© 2008 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Integration of InGaN quantum dots into nitride‐based microcavities
Authors: Kruse C. , Figge S. , Dartsch H. , Tessarek C. , Hommel D. , Lohmeyer H. , Kalden J. , Sebald K. , Gutowski J. 
Published: April 2008

AbstractWe report on the successful integration of a single InGaN quantum dot sheet into a resonant half cavity structure con‐sisting of an AlGaN/GaN distributed Bragg reflector and a GaN λ‐cavity layer. For reference, small‐diameter pillar mi‐crocavites fabricated by focused‐ion beam etching from an empty planar cavity are studied. These structures exhibit discrete transversal modes and Q factors of 260. The quantum dot active region has been grown by metal‐organic vapour‐phase epitaxy using a two‐step deposition technique. Optical spectra measured by micro‐photoluminescence reveal distinct spectrally sharp emission lines around 2.73 eV which can be attributed to the emission of single InGaN quantum dots. (© 2008 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Enlargement of bulk non‐polar GaN substrates by HVPE regrowth
Authors: Lai K. Y. , Wheeler V. D. , Grenko J. A. , Johnson M. A. L. , Hanser A. D. , Preble E. A. , Liu L. , Paskova T. , Evans K. R. 
Published: April 2008

AbstractM‐plane non‐polar bulk GaN substrates were regrown by hydride vapour phase epitaxy (HVPE), aiming to enlarge their lateral size. The non‐polar GaN substrates were synthesized by growing thick GaN boules by HVPE along the c‐axis, and wafering transversely to expose non‐polar (m‐ or a‐plane) surfaces. Non‐polar GaN substrates obtained in this manner contains lower defect density comparing to those produced by heteroepitaxial growth. After the regrowth, substantial lateral expansion in [0001], [1120] and [1120] was observed. Threading dislocation densities were estimated by cathodoluminescence measured at the cross‐section areas. The dislocation densities in the substrate and the regrown areas were approximately 5×106 cm–2 and 1×106 cm–2, respectively, indicating a comparable structural quality achieved by the regrowth. Non‐polar GaN substrates prepared by this process provide a promising method to fabricate devices for next generation. (© 2008 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
GaN MMICs for RF power applications in the 50 GHz to 110 GHz frequency range
Authors: Micovic M. , Kurdoghlian A. , Hashimoto P. , Hu M. , Antcliffe M. , Willadsen P. J. , Wong W. S. , Bowen R. , Milosavljevic I. , Yoon Y. , Schmitz A. , Wetzel M. , Chow D. H. 
Published: April 2008

AbstractAt 2006 IEDM outstanding potential of GaN MMIC technology for RF power applications at frequencies exceeding 80 GHz was reported for the first time. The first reported W‐band GaN power MMIC had over 16 dB of saturated power gain in a frequency range between 78 GHz and 88 GHz and produced almost the same output power at this frequency band as the state of the art InP HEMT MMIC with 10 times larger output device periphery. In this presentation we will describe improvements in GaN MMIC process that led to these breakthrough results and discuss the impact of GaN technology on the development of high frequency millimeter‐wave power modules. (© 2008 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)