bluuebunny/crossref_metadata_2025_split huggingface dataset:
Reliability Assurance for Thermo-Optic Solid State Optical Switches
Authors: Dobbelaere P. M. C. De , Van Der Wel P. J. , Hendriksen B. , Flipse M. C. , Thackara J. , Zhu N. , Freeman J. 
Published: April 2011

AbstractThe reliability assurance program for the BeamBoxTM thermo-optic solid state optical switches is presented. The different phases of the program are discussed, and some of the results are described.
Strength and Fatigue of Modified Sol-Gel Clad Optical Fibers
Authors: Skutnik Bolesh J. , Trumbull M. R 
Published: April 2011

AbstractDynamic and static fatigue results are presented for the first time for a new type of optical fiber, whose modified sol-gel cladding is a fenestrated (micro porous) form of silica. Unjacketed fibers have mean Weibull strengths in bending of 6.5 to 7.6 GPa with Weibull slopes in the 40 to 60 range. The strength decrease with decreasing strain rate is similar for both jacketed and unjacketed fibers. Even the unjacketed fibers tested in ambient water or in boiling water retain a majority of their mean strength, 7.6 GPa (ambient air) versus 6.5 GPa (ambient water) versus 5.5 GPa (boiling water). Exposure to boiling water for 1 hour has no measurable affect on the strength of these fibers. Exposure to boiling water for 8 hours, however, does significantly broaden the low strength end for the unjacketed fiber. The dynamic fatigue and static fatigue parameters in ambient water are substantially the same, ND = 22±2 and Ns 21±4, for the jacketed and unjacketed fibers. Possible mechanisms are discussed to explain the strength and fatigue behavior of these fibers in light of their unique structure.
Optical-Fiber and Entry-Cone Contact Stresses
Authors: Anderson J. M. , Malluck J. F. , Tabaddo M. M. , Sidbury C. K. , McNeil T. E. 
Published: April 2011

AbstractMany of the broken fibers in optical connectors, especially those that seem to occur over time without apparent provocation are found in the ferrule at the transition from entry cone to alignment capillary. This paper contends that many such breaks are due to local stresses caused by debris or some other relatively rigid imperfection in the transition neighborhood. Stress estimates from beam theory and from a finite-element model are presented along with some indirect experimental observations supporting the contention.
The Dimensional Stability of Adhesives, Zirconia, and Silica in Optical Connector Ferrules and their Impact on Optical Performance
Authors: Reith L.A. , Ebizlioglu O.S. , Koza M. , Mann J. , Ozgur M. , Bowmer T. 
Published: April 2011

AbstractIn order to achieve the optimum optical performance of fiber optic connectors, it is critical that there be good physical contact at the fiber-to-fiber interface. Loss of physical contact results in increased insertion loss and reflectance. Today's connectors are designed to have mating surfaces with tightly controlled endface geometries to ensure physical contact during temperature variations and repeated matings. However, material degradation of the fiber, ferrule, or the adhesive which holds the fiber into the ferrule, can change the endface geometry and cause eventual failure of the connector. Tests have been developed or are under development to quantify mechanical changes in these materials, including adhesive creep, fiber pistoning, ferrule deformation and roughening, and fiber deterioration. This paper will describe the latest test results acquired from applying these procedures.
Damage-Free Photo-Assisted Cryogenic Etching of GaN as Evidenced by Reduction of Yellow Luminescence
Authors: Hsieh J. T. , Hwang J. M. , Hwang H. L. , Hung W. H. 
Published: April 2011

AbstractDamage-free etching of GaN by Cl2, assisted by an ArF (193 nrm) excimer laser, is demonstrated. At low temperatures, photo-assisted etching can provide a better etch rate and largely improve the surface morphology and quality. AFM results show that the etched GaN surface is obtained with a root-mean-square roughness of 1.7 nm. As compared with the photoluminescence spectra of photoelectrochemical wet etched GaN, the photo-assisted cryogenic etching is proved to be a damage-free dry etching technique.
Mechanism for Radiative Recombination in In0.15Ga0.85N/GaN Multiple Quantum Well Structures
Authors: Monemar B , Bergman J P , Dalfors J , Pozina G , Sernelius B E , Holtz P O , Amano H , Akasaki I 
Published: April 2011

AbstractWe present a study of the radiative recombination in In0.15Ga0.85N/GaN multiple quantum well samples, where the conditions of growth of the InGaN quantum layers were varied. The piezoelectric field as well as short range potential fluctuations are screened via different mechanisms by donor electrons and excited electron-hole pairs. These effects account for a large part of the spectral shift with donor doping (an upward shift of the photoluminescence (PL) peak up to 0.2 eV is observed for a Si donor density of 2 × 1018 cm-3 in the well), with excitation intensity and with delay time after pulsed excitation (also shifts up to 0.2 eV). It appears like 2-dimensional screening of short range potential fluctuations is needed to fully explain the data. We suggest that excitons as well as shallow donors are at least partly impact ionized by electrons in the rather strong lateral potential fluctuations.
Optical Absorption, Raman, and Photoluminescence Excitation Spectroscopy of Inhomogeneous InGaN Films
Authors: Robins L.H. , Paul A.J. , Parker C.A. , Roberts J.C. , Bedair S.M. , Piner E.L. , El-Masry N.A. 
Published: April 2011

AbstractInGal-xN films with x=0.06 to x=0.49 were characterized by optical transmittance, Raman, and photoluminescence excitation spectroscopies. Previous microstructural characterizations detected phase separation only in films with x>0.2. The transmittance data suggest that compositional inhomogeneity is also present in the lower-x films (x<0.2). Both Raman and photoluminescence excitation spectra show features that correlate with compositional inhomogeneity and phase separation in the films with x>0.2. The composition dependence of the Raman spectra, from x=0.28 to x=0.49, is consistent with an increase in the size of the phase-separated regions with increasing x.
Synthesis of Nitrogen-Rich GaNAs Semiconductor Alloys and Arsenic-Doped GaN by Metalorganic Chemical Vapor Deposition
Authors: Gherasimova M. , Gaffey B. , Mitev P. , Guido L. J. , Chang K. L. , Hsieh K. C. , Mitha S. , Spear J. 
Published: April 2011

AbstractArsenic-doped GaN films and GaNAs films have been synthesized by MOCVD. Samples were grown on sapphire, GaN-coated sapphire, and GaAs substrates. Composition, structure, and phase distribution were characterized by EPMA, SIMS, XRD, and TEM. The arsenic content increases demonstrably as the growth temperature descreases from 1030 to 700°C. In the high temperature limit, high quality arsenic-doped GaN forms on GaN-coated sapphire. In the low temperature regime, nitrogen-rich GaNAs forms under some growth conditions, with a maximum arsenic mole fraction of 3%, and phase segregation in the form of GaAs precipitates occurs with an increase in arsine pressure, Preferential formation of the nitrogen-rich phase on GaN-coated sapphire suggests the presence of substrate-induced “composition pulling”.
Defect States in SiC/GaN-and SiC/AlGaN/GaN-Heterostructures Characterized by Admittance and Photocurrent Spectroscopy
Authors: Witte H. , Krtschil A. , Lisker M. , Christen J. , Scholz F. , Off J. 
Published: April 2011

AbstractDeep defect levels in n-type GaN/AlN/6H-SiC- and GaN/AlGaN/6H-SiC- heterostructures grown by Metallorganic Vapor Phase Epitaxy were analyzed by Thermal and Optical Admittance and Photocurrent Spectroscopy. The various thermal and optical transitions in the spectra originating from both the Schottky contact as well as the GaN/SiC- and AlGaN/GaNheterojunctions were separated. This was achieved by variation of the modulation frequency, the use of different contact arrangements and by comparison with reference spectra from GaN/Sapphir samples and SiC substrates. In the GaN/AlGaN/SiC structures a bias voltage dependent peak shift was found which is correlated to an interface related defect distribution. In additionally to, SIC related defects, defect-band-transitions involving defects with transition energies at 2.2eV, 1.85eV, EG-(470±40) meV and EG-(65-95) meV were found for the GaN layer.
Microstructure of GaN Grown on (111) Si by MOCVD
Authors: Follstaedt D. M. , Han J. , Provencio P. , Fleming J. G. 
Published: April 2011

AbstractGallium nitride was grown on (111) Si by MOCVD by depositing an AlN buffer at 1080°C followed by GaN at 1060°C. The 2.2 μm layer cracked along {1-100} planes upon cooling to room temperature, but remained adherent. We were nonetheless able to examine the material between cracks with TEM. The character and arrangement of dislocations are much like those of GaN grown on Al2O3: ∼2/3 pure edge and ∼1/3 mixed (edge + screw), arranged in boundaries around domains of GaN that are slightly misoriented with respect to neighboring material. The 30 nm AlN buffer is continuous, indicating that AIN wets the Si, in contrast to GaN on Al2O3.
Epitaxial Growth of III-Nitride Layers on Aluminum Nitride Substrates
Authors: Schowalter L.J. , Shusterman Y. , Wang R. , Bhat I. , Arunmozhi G. , Slack G.A. 
Published: April 2011

AbstractHigh quality, epitaxial growth of AlN and AlxGal-xN by OMVPE has been demonstrated on single-crystal AIN substrates. Here we report characterization of epitaxial layers on an a-face AlN substrate using Rutherford Backscattering/ion channeling, atomic force microscopy (AFM), x-ray rocking curves, and preliminary electrical characterization. Ion channeling along the [1010] axis gives a channeling minimum yield of 1.5% indicating a very high quality epitaxial layer.
Growth and Characterization of BxGal-xN on 6H-SiC (0001) by MOVPE
Authors: Wei C. H. , Xie Z. Y. , Edgar J. H. , Zeng K. C. , Lin J. Y. , Jiang H. X. , Ignatiev C. , Chaudhuri J. , Braski D. N. 
Published: April 2011

AbstractBoron was incorporated into GaN in order to determine its limits of solubility, its ability of reducing the lattice constant mismatch with 6H-SiC, as well as its effects on the structural and optical properties of GaN epilayers. BxGal-xN films were deposited on 6H-SiC (0001) substrates at 950 °C by low pressure MOVPE using diborane, trimethylgallium, and ammonia as precursors. A single phase alloy with x=0.015 was successfully produced at a gas reactant B/Ga ratio of 0.005. Phase separation into pure GaN and BxGal-xN alloy with x=0.30 was deposited for a B/Ga reactant ratio of 0.01. This is the highest B fraction of the wurtzite structure alloy ever reported. For B/Ga ratio ≥ 0.02, no BxGal-xN was formed, and the solid solution contained two phases: wurtzite GaN and BN based on the results of Auger and x-ray diffraction. The band edge emission of BxGal-xN varied from 3.451 eV for x=0 with FWHM of 39.2 meV to 3.465 eV for x=0.015 with FWHM of 35.1 meV. The narrower FWHM indicated that the quality of GaN epilayer was improved with small amount of boron incorporation.
GaN: From Selective Area to Epitaxial Lateral Overgrowth
Authors: Li X. , Bishop S. G. , Coleman J. J. 
Published: April 2011

AbstractThe evolution of the topography of GaN stripes as a function of stripe width (2 - 120 μm), fill factor and substrate smoothness has been explored. The spatially resolved optical properties of these structures have been characterized by cathodoluminescence imaging and line scans. Implications from the optical study have been discussed.
A Critical Comparison Between Movpe and MBE Growth of III-V Nitride Semiconductor Materials for Opto-Electronic Device Applications
Authors: Johnson M.A.L. , Yu Zhonghai , Brown J.D. , Koeck F.A. , El-Masry N.A. , Kong H.S. , Edmond J.A. , Cook J.W. , Schetzina J.F. 
Published: April 2011

AbstractA systematic study of the growth and doping of GaN, AlGaN, and InGaN by both molecular beam epitaxy (MBE) and metal-organic vapor phase epitaxy (MOVPE) has been performed. Critical differences between the resulting epitaxy are observed in the p-type doping using magnesium as the acceptor species. MBE growth, using rf-plasma sources to generate the active nitrogen species for growth, has been used for III-Nitride compounds doped either n-type with silicon or p-type with magnesium. Blue and violet light emitting diode (LED) test structures were fabricated. These vertical devices required a relatively high forward current and exhibited high leakage currents. This behavior was attributed to parallel shorting mechanisms along the dislocations in MBE grown layers. For comparison, similar devices were fabricated using a single wafer vertical flow MOVPE reactor and ammonia as the active nitrogen species. MOVPE grown blue LEDs exhibited excellent forward device characteristics and a high reverse breakdown voltage. We feel that the excess hydrogen, which is present on the GaN surface due to the dissociation of ammonia in MOVPE, acts to passivate the dislocations and eliminate parallel shorting for vertical device structures. These findings support the widespread acceptance of MOVPE, rather than MBE, as the epitaxial growth technique of choice for III-V nitride materials used in vertical transport bipolar devices for optoelectronic applications.
Gan Nanotubes
Authors: Lee Seung Mi , Lee Young Hee , Hwang Yong Gyoo , Eisner J. , Porezag Dirk , Frauenheim Thomas 
Published: April 2011

AbstractWe perform parametrized density-functional calculations to predict the stability and formation mechanism of GaN nanotubes. Strain energies of GaN nanotubes are comparable to those of carbon nanotubes, suggesting the possibility for the formation of GaN nanotubes. We note that an intermediate phase with [4,6,10] polygons exist at armchair tube edge, which may play as a nucleation seed of further tube growth.
Crystal Structure and Defects in Nitrogen-Deficient GaN
Authors: Oktyabrsky S. , Dovidenko K. , Sharma A. K. , Joshkin V. , Narayan J. 
Published: April 2011

AbstractWe have studied crystal structure and associated defects in GaN films grown on sapphire under nitrogen-deficient conditions by metalorganic chemical vapor deposition (MOCVD) and pulsed laser deposition (PLD). The structural quality of the PLD films grown at 750 °C was comparable with those grown by MOCVD at 1050 °C having threading dislocations density of about 1010 cm-2 at a film thickness 150-200 nm. Microstructure of the PLD films grown at temperatures above 780°C was found to be similar to that of nitrogen-deficient MOCVD films indicating the loss of nitrogen due to thermal decomposition of the nitride layers. Nitrogen-deficient MOCVD and PLD films exhibit polycrystalline structure with a mixture of cubic zinc-blende and wurtzite hexagonal GaN grains retaining tetragonal bonding across the boundaries and hence the epitaxial orientations and polarity. Renucleation of the wurtzite phase at different {111} planes of cubic GaN results in a rough and faceted surface of the film. Most of the stoichiometric films displayed (0001) Ga-face polarity, but the renucleated inclined wurtzite grains grew in the opposite N-face polarity. The major defects related to the cubic structural metastability are stacking faults and microtwins which being nuclei of the metastable cubic phase have an extremely low energy. We elucidate that the cubic phase is more stable under the nitrogen deficiency and, therefore, can exist without decomposition at higher nitrogen vacancy concentrations in the material.
NIIN As an Ohmic Contact to P-GAN
Authors: Ingerly D. B. , Chang Y. A. , Chen Y. 
Published: April 2011

AbstractBased on the criteria for the solid state exchange reaction with p-GaN, we have investigated the intermetallic compound Niln as a possible ohmic contact. The contacts were fabricated by depositing Niln on p-GaN films (p ∼ 2 × 1017 cm-3) using RF sputtering from a compound target. The as-deposited, Niun contacts were found to be rectifying and using I-V characterization a Schottky barrier height of 0.82 eV was measured. Rapid thermal annealing of the contacts was shown to significantly decrease their resistance, with contacts annealed at 800°C for I min yielding the lowest resistance. When annealed at 800°C for 1 min Niln contacts exhibited a specific contact resistance of 8-9 × 10-3 Ωcm2, as measured by the circular transmission line model. To allow a more universal comparison the more traditional Ni/Au contacts, processed under the same conditions, were used as a standard. Their measured specific contact resistance (ρc = 1.2 - 2.1 x 10-2 Ωcm2) was significantly higher than that of the Niln contacts. Demonstrating that Niln has promise as an ohmic contact to p-GaN and should be studied in greater detail.
Temperature-Dependent Onset of Yielding in Dislocation-Free Silicon: Evidence of a Brittle-To-Ductile Transition
Authors: Folk R. H. , Khantha M. , Pope D. P. , Vitek V. 
Published: April 2011

AbstractAn investigation of the brittle-to-ductile transition (BDT) in silicon has been conducted on essentially dislocation-free silicon test specimens made by photolithography. No pre-cracks or additional dislocation sources were introduced into the samples. Three-point bending tests of the samples reveals a well defined transition from brittle fracture of the specimens to complete yielding near 732°C at a crosshead displacement rate of 0.1 mm/min. Limited plasticity is observed below 732°C but is insufficient to prevent crack propagation suggesting that yielding is not dislocation mobility limited. Instead the transition may be controlled by the nucleation of a sufficient density of dislocations. Further support comes from the results of experiments conducted at temperatures below 732°C in which samples were rapidly pre-loaded within the linearly elastic regime, then immediately retested. This rapid pre-loading results in a lower transition temperature. This would not be expected if dislocation mobility controlled the BDT. Instead, it is believed that the transition only occurs when a sufficient density of dislocations has nucleated within the sample. In these experiments, the pre-loading event may increase the dislocation nucleation rate. The source of the dislocations in these defect free samples is still under investigation.
Molecular Dynamics Studies of Interfacial Crack Propagation in Heterogeneous Media
Authors: Corbett John M. , Selinger Robin L. B. 
Published: April 2011

AbstractWe use molecular dynamics simulation to investigate the evolution of a crack front in interfacial fracture in three dimensions. We find that when a crack passes through a localized region of heterogeneous toughness, crack front waves are initiated and propagate laterally. We also investigate the development of roughness of the crack front when the crack propagates in a region of heterogeneous toughness. We find that in steady state the mean square width W of the front scales with system size L as W∼L0.35, in agreement with recent theoretical predictions.
Dry Etching of PZT Films with CF4/Ar High Density Plasma
Authors: Park Chanro , Cho Jun Hee , Choi Chang Ju , Seol Yeo Song , Choi Il Hyun 
Published: April 2011

AbstractLead-Zirconate-Titanate (PZT) films were etched with CF4/Ar mixed gases in high-density plasmas. Etch characteristics of the PZT film were investigated by using in-situ plasma diagnostic tools in conjunction with the surface analysis after etching. Densities of ionic species such as F+ and CFx+(x=1∼3) and their ion energy distributions within the plasma were measured by a mass spectrometer. Characteristics of the CF4/Ar plasma were obtained by using Langmuir probe measurements. Etch rate of the PZT film was sharply increased up to a peak at 30 % CF4 as the gas ratio of CF4/(Ar+CF4) increased, and then was gradually decreased. After etching, the surface of PZT film was covered with fluorine that was bonded chemically with underlying PZT film. Ion assisted etching mechanism for the PZT was proposed and its validity was confirmed by using the results of the plasma diagnostics.
In Situ Mass Spectroscopy of Recoiled Ion Studies of Degradation Processes in SrBi2Ta2O9 Thin Films During Hydrogen Gas Annealing
Authors: Im J. , Auciello O. , Krauss A.R. , Gruen D.M. , Chang R.P.H. , Kim S.H. , Kingon A.I. 
Published: April 2011

AbstractIt is known that the forming gas (N2-H2 mixture) annealing process required for microcircuit fabrication results in an unacceptable electrical degradation of SrBi2Ta2O9 (SBT) ferroelectric capacitors due mainly to the interaction of H2 with the ferroelectric layer of the capacitor. We have found a strong relationship between changes in the surface composition of the ferroelectric layer and the electrical properties of SBT capacitors as a result of hydrogen annealing. Mass spectroscopy of recoiled ions (MSRI) analysis revealed a strong reduction in the Bi signal as a function of exposure to hydrogen at high temperatures (∼500°C). The Bi signal reduction correlates with Bi depletion in the SBT surface region. Subsequent annealing in oxygen at temperatures in the range of 700–800°C resulted in the recovery of the MSRI Bi signal, corresponding to the replenishment of Bi in the previously Bi-depleted surface region. XRD analysis (probing the whole SBT film thickness) showed little difference in the XRD spectra of the SBT films before and after hydrogen and oxygen-recovery annealing. The combined results of the MSRI and XRD analyses can be interpreted as an indication that the degradation of the electrical properties of the SBT capacitors, after hydrogen annealing, is mainly due to the degradation of the near surface region of the SBT layer.
Micro-Raman Study of Pb(Zr,Ti)O3 Thin Films in Feram
Authors: Kimura Takahiro , Horii Yoshimasa , Nakamura Tomoji , Honda Koichiro 
Published: April 2011

AbstractWe examined the Raman spectra of the tetragonal Pb(Zr, Ti)O3 (PZT) films between FeRAM cells with a micro-Raman apparatus. We found that a Raman light peaked at 600cm−1 polarized linearly perpendicular to the polarization of the exciting light had a different intensity for each of the film.We showed that the difference in the intensities can be explained by the differing distributions of grain orientations in the films. Based on this knowledge, we estimated the volume fraction of 90° domains as well as the average spontaneous polarization of the grains.
Size Effect of Ferroelectric and Ferromagnetic Properties of Bi-based Perovskite Type Materials
Authors: Tabata H. , Ueda K. , Kawai T 
Published: April 2011

AbstractBismuth-based-layer-structured ferroelectric films have been formed epitaxially on Nb-doped SrTiO3 substrates by pulsed laser deposition (PLD). These films show an atomically smooth surface with a wide terrace of 100 nm∼200 nm, as observed by atomic force microscopy (AFM) which is ideal for measuring such properties. Thin films of (Bi0.7, Ba0.) (Fe0.7, Ti0.3)O3 exhibit both ferroelectric and ferromagnetic (weak ferromagnetism) properties at room temperature. In these samples, a size effect is discussed at the same time.
SrTiO3/BaTiO3 Artificial Superlattices Obtained by Injection MOCVD
Authors: Lindner J. , Weiss F. , Haessler W. , Kobernik G. , Senateur J.-P. , Oswald S. , Santiso J. , Figueras A. 
Published: April 2011

AbstractSrTiO3/BaTiO3 superlattices were deposited using injection MOCVD. The films obtained on LaAlO3(LAO), Al2O3, SrTiO3(STO) and SrTiO3:Nb(STO:Nb) were charcterized using X-ray diffraction. While the films on LaAlO3 (012), SrTiO3(100) and SrTiO3:Nb (100) were epitaxial, the multilayers deposited on Al2O3(0001)were highly oriented, but displaying two different in-plane orientations. To our knowledge, this is the first time that BTO/STO superlattices were deposited by MOCVD.