bluuebunny/crossref_metadata_2025_split huggingface dataset:
Calculated Electronic Structure and Transport Properties of La.67Ca.33MnO3
Authors: Butler W. H. , Zhang X.-G. , Maclaren J. M. 
Published: April 2011

ABSTRACTWe have calculated the electronic structure, total energy, magnetic moments and electrical resistivities of La.67Ca.33MnO3 using mean field band theory. The magnetic and structural properties seem to be in good agreement with experiment. The calculations predict that La.67Ca.33MnO3 is metallic for the majority spins and semiconducting for the minority spins.
Effects of SC-1 Dilution and Temperature Variations on Etch Rate and Surface Haze
Authors: Christenson K. K. , Smith S. M. 
Published: April 2011

ABSTRACTThe slight etch and accompanying roughening of the silicon by the APM solution are of great concern as device geometrys and gate oxide thicknesses decrease. This report covers the variations in the SiO2 etch rate and surface roughening of an APM solution as a function of NH4OH and H2O2 concentration and temperature. In general, the etch rate and roughening increased with increasing temperature and NH4OH concentration but was unaffected by H2O2 concentration. Other portions of the larger APM study covering the addition and removal of metals and the removal of particles by APM are published elsewhere. Together, these studies provide a complete set of process response surfaces for the SC-1 chemistry. These surfaces can be used to select the most promising regime of parameter space for any particular process.
New Method to Characterize Thin Oxide Reliability
Authors: Lin Heng-Chih , Snyder J. P. , Helms C. R. 
Published: April 2011

ABSTRACTNext generation ULSI devices will require ultra thin gate insulators where degradation due to contamination or surface microroughness is an even more important problem. Tunneling and breakdown characteristics are critical electrical testing methods, but unfortunately obtaining meaningful oxide integrity information on the one hand and tunneling IV's on the other is a tedious and time consuming process.In this research, we report on a new method to measure meaningful IV's, Qbd's, and Vbd's at the same time. This method uses a linear current ramp strategy where a voltage ramp to between 8–10 MV/cm is applied first followed by a linear current ramp until breakdown is reached. There are several advantages of this new method: The linear voltage ramp quickly and easily identifies low breakdown devices, whereas switching to a linear current ramp provides for nearly constant field stressing to obtain meaningful IV and Qbd
Properties of Gate-Quality SiO2 Films Prepared by Electron Cyclotron Resonance Chemical Vapour Deposition in an Ultrahigh Vacuum Processing System
Authors: Tao Y. , Landheer D. , Hulse J. E. , Xu D.-X. , Quance T. 
Published: April 2011

ABSTRACTWe have prepared thin SiO2 layers on Si(100) wafers by electron cyclotron resonance chemical vapour deposition (ECR-CVD) in a multi-chamber ultra-high vacuum (UHV) processing system. The oxides were characterized in-situ by single wavelength ellipsometry (SWE) and x-ray photoelectron spectroscopy (XPS) and ex-situ by Fourier transform infra-red spectroscopy (FTIR), spectroscopic ellipsometry (SE) and capacitance-voltage (CV) electrical measurements. Films deposited at higher pressures, low powers and low silane flow rates had excellent physical and electrical properties. Films deposited at 400 °C had better physical properties than those of thermal oxides grown in dry oxygen at 700 °C. A 1 minute anneal at 950 °C reduced the fast interface state density from 1.2×1011 to 7×1010 eV−1cm−2
Collisional Effects of Background Gases on Pulsed Laser Deposition Plasma Beams
Authors: Geohegan David B. , Puretzky Alex A. 
Published: April 2011

AbstractThe penetration of energetic pulsed ablation plumes through ambient gases is experimentally characterized to investigate a general phenomenon believed to be important to film growth by pulsed laser deposition (PLD). Under typical PLD conditions involving background gases, the ion flux in the ablation plume is observed to split into distinct fast and slow components over a limited range of distances1,2 the fast component is transmitted with near-initial velocities and high kinetic energies, potentially damaging to growing films at these distances. Formation of the second, significantly-slowed component correlates with the bright contact front3 formation observed1,4 in fast ICCD imaging studies. This general effect is explored in detail for the case of yttrium ablation into argon, a single-element target into an inert gas.5 Time-resolved optical absorption spectroscopy and optical emission spectroscopy are employed to simultaneously view the populations of both excited and ground states of Y and Y+ for comparison with quantitative intensified-CCD photography of the visible plume luminescence and ion flux measurements made with fast ion probes during this phenomenon. these measurements confirm that, in addition to the bright significantly-slowed front which has been described by shock or drag propagation models1, a fast-component of target material is transmitted to extended distances for some ambient pressures with near-initial velocities.
High-Pressure Pulsed Plasma Synthesis of Carbon-Nitride Thin Films
Authors: Gurarie V. N. , Orlov A. V. , A Bursill L. , JuLin Peng , Nugent K. W. , Prawer S. 
Published: April 2011

AbstractIn this study a high N2 pressure has been used to enhance the N incorporation into CN films produced by a shock plasma deposition method. auger spectroscopy indicates that increasing the nitrogen pressure from 0.1 atm to 10 atm results in an increase of nitrogen incorporation into CN films to a maximum of 43 at.%. Nitrogen distribution varies across the surface of the deposit, showing an increase of nitrogen content with depth in the center of the deposition and a decrease with depth at points away from the center. SEM and optical microscopy indicate that under increased nitrogen pressure the grain structure becomes finer. Raman spectra contain sharp peaks characteristic of a distinct crystalline CN phase. TEM diffraction patterns for the films produced under N2 pressure in the range of 0.05-0.1 atm unambiguously show the presence of micron-sized crystals displaying a cubic symmetry, and not the predicted β-Si3N4 type structure. PEELS data suggest that in the crystalline phase a significant fraction of the nitrogen atoms have sp2 trigonal bonds and there is a significant degree of sp3 character for the carbon atoms.
Low Temperature Deposition of Diamond Thin Films Using Electron Cyclotron Resonance Plasmas
Authors: Gilbert Donald R. , Singh Rajiv K. 
Published: April 2011

AbstractWe have used an electron cyclotron resonance enhanced plasma system to deposit films from methyl alcohol at a pressure of 1.00 Torr. Depositions occurred on silicon substrates at temperatures from 550 - 750 °C. Film morphology was examined using SEM. Structural characterization was conducted using Raman spectroscopy and x-ray diffraction. Based on these analyses, certain trends in film quality as a function of deposition temperature were determined.
Formation of artificially-Layered Thin-Film Compounds Using Pulsed-Laser Deposition
Authors: Norton David P. , Chakoumakos B. C. , Lowndes D. H. , Budai J. D. 
Published: April 2011

AbstractSuperlattice structures, consisting of SrCuO2, (Sr,Ca)CuO2, and BaCuO2 layers in the tetragonal, "infinite layer" crystal structure, have been grown by pulsed-laser deposition (PLD). Superlattice chemical modulation is observed for structures with component layers as thin as a single unit cell (~3.4 Å), indicating that unit-cell control of (Sr,Ca)CuO2 growth is possible using conventional pulsed-laser deposition over a wide oxygen pressure regime. X-ray diffraction intensity oscillations, due to the finite thickness of the film, indicate that these films are extremely flat with a thickness variation of only ~20 Å over a length scale of several thousand angstroms. Using the constraint of epitaxy to grow metastable cuprates in the infinite layer structure, novel high-temperature superconducting structural families have been formed. IN particular, epitaxially-stabilized SrCuO2/BaCuO2 superlattices, grown by sequentially depositing on lattice-matched (100) SrTiO3 from BaCuO2 and SrCuO2 ablation targets in a PLD system, show metallic conductivity and superconductivity at Tc(onset) ~70 K. these results show that pulsed-laser deposition and epitaxial stabilization have been used to effectively "engineer" artificially-layered thin-film materials.
Viscoelastic Characterization of an Epoxy-Based Molding Compound
Authors: Kenner V. H. , Julian M. R. , Popelar C. H. , Chengalva M. K. 
Published: April 2011

ABSTRACTThis paper describes the viscoelastic characterization of a highly filled epoxy molding compound commonly used in electronic packaging applications. Both stress relaxation tests and constant strain rate tensile tests were conducted. The material was found to be nonlinear in its viscoelastic behavior and to be amenable to horizontal shifting to form master curves. A representation of the master stress relaxation curves in terms of a Prony series is given, and the use of this representation illustrated in the context of both linear and nonlinear representations of the viscoelastic behavior to predict the results of the constant strain rate experiments.
New Ferroelectric Liquid Crystal Polymers for Nonlinear Optics Applications
Authors: Thurmes William N. , More Kundalika M. , Vohra Rohini T. , Wand Michael D. , Walba David M. , Keller Patrick 
Published: April 2011

AbstractInitial results of a project directed towards the design and synthesis of ferroelectric liquid crystal polymers (FLCPs) for second order nonlinear optics (NLO) applications are described. FLCP glasses represent a novel type of solid, a truly noncrystalline solid with thermodynamically stable polar order. FLCPs with useful magnitude of the second order susceptibility χ(2) and processability not possible with poled polymers or crystals have been obtained.
Enhanced Photoluminescence from Erbium-Doped Gap Microdisk Resonator
Authors: Chu D. Y. , Wang X. Z. , Bi W. G. , Espindola R. P. , Wu S. L. , Wessels B. W. , Tu C. W. , Ho S. T. 
Published: April 2011

AbstractThe fabrication and optical properties of an erbium-doped gallium phosphide microdisk resonator pumped by a Ti-sapphire laser at 980 nm were investigated. Enhanced Er3+ intra-4f-shell photoluminescence was observed in the microdisk resonator compared to a thin film, and is attributed to a microcavity effect. At low pumping power intensity, the photoluminescence from erbium-doped gallium phosphide microdisks is an order of magnitude more intense than that from a thin film sample.
Poly(α-Hydroxy Ester)/Short Fiber Hydroxyapatite Composite Foams for Orthopedic Application
Authors: Thomson Robert C. , Yaszemski Michael J. , Powers John M. , Harrigan Timothy P. , Mikos Antonios G. 
Published: April 2011

AbstractA process has been developed to manufacture biodegradable composite foams of poly(DL-lactic- co-glycolic acid) (PLGA) and hydroxyapatite short fibers for use in bone regeneration. The processing technique allows the manufacture of three-dimensional foam scaffolds and involves the formation of a composite material consisting of a porogen material (either gelatin microspheres or salt particles) and hydroxyapatite short fibers embedded in a PLGA matrix. After the porogen is leached out, an open-cell composite foam remains which has a pore size and morphology defined by the porogen. The foam porosity can be controlled by altering the volume fraction of porogen used to make the composite material. Foams made using NaCl particles as a porogen were manufactured with porosities as high as 0.84±0.01 (n=3). The short hydroxyapatite fibers served to reinforce the PLGA. The compressive yield strength of foams manufactured using gelatin microspheres as a porogen was found to increase with fiber content. Foams with compressive yield strengths up to 2.82±0.63 MPa (n=3) with porosities of 0.47±0.01 (n=3) were manufactured using 30% by weight hydroxyapatite fibers in the initial composite prior to leaching. These composite foams with improved mechanical properties may also be expected to have enhanced osteoconductivity and hence provide a novel material which may prove useful in the field of bone regeneration.
Growth and Doping of AlxGa1−xN Deposited Directly on α(6H)-SiC(0001) Substrates via Organometallic Vapor Phase Epitaxy
Authors: Bremser M.D. , Perry W.G. , Edwards N.V. , Zheleva T. , Parikh N. , Aspines D.E. , Davis R.F. 
Published: April 2011

ABSTRACTMonocrystalline AlxGa1−xN(0001) (0.05 ≤ x ≤ 0.70) thin films, void of oriented domain structures and associated low-angle grain boundaries, have been grown at high temperatures via OMVPE directly on vicinal and on-axis α(6H)-SiC(0001) wafers using TEG, TEA and ammonia in a cold-wall, vertical, pancake-style reactor. The surface morphologies were smooth and die densities and distributions of dislocations were comparable to that observed in GaN(0001) films grown on high temperature A1N buffer layers. Double-crystal XRC measurements showed a FWHM value as low as 186 arc sec for the (0002) reflection. Spectra obtained via CL showed strong near band-edge emissions with FWHM values as low as 31 meV. The compositions of the AlxGa1−xN films were determined using EDX, AES and RBS and compared to the values of the bandgap as measured by spectral ellipsometry and CL emissions. A negative bowing parameter was found. Controlled n-type, Si-doping of AlxGa1−xN for x ≤ 0.4 has been achieved with net carrier concentrations ranging from ≈ 2 × 1017 cm−3 to 2 × 1019 cm−3. Acceptor doping with Mg for x < 0.13 was also successful.
A Modeling Study of GaN Growth by MOVPE
Authors: Safvi S.A. , Redwing J.M. , Tischler M.A. , Kuech T.F. 
Published: April 2011

ABSTRACTA model for the growth of gallium nitride in a vertical metalorganic vapor phase epitaxy reactor is presented. For a mixture of non-dilute gases, the flow temperature and concentration profiles are predicted. The results show that the growth of GaN epilayers is through an intermediate adduct of TMG and ammonia. Growth rates are predicted based on simple reaction mechanisms and compared with those obtained experimentally. Loss of adduct species due to polymerization leads to lowering in growth rate. An attempt to quantify loss of reacting species is made based on experimentally observed growth rates.
Photoluminescence and Sims Studies of Hydrogen Passivation of Mg-Doped P-Type Gallium Nitride
Authors: Li Y. , Lu Y. , Shen H. , Wraback M. , Hwang C.-Y. , Schurman M. , Mayo W. , Salagaj T. , Stall R. A. 
Published: April 2011

ABSTRACTThe effects of hydrogen passivation in MOCVD grown Mg doped p-type GaN were studied using low temperature (5K) photoluminescence (PL) and secondary-ion-mass spectroscopy (SIMS). GaN films with different Mg doping level were annealed at 700° C in N2 ambient with different annealing times. The SIMS results indicate that the hydrogen concentration increases with increasing Mg doping level in the as-grown Mg:GaN film. After 20 minutes of annealing, most of the hydrogen escapes from the film. The 3.455 eV PL peak before annealing and the 3.446 eV peak after annealing found in the Mg doped samples were attributed to the exciton bound to the Mg-H complex and to the Mg acceptor, respectively. The shift of the bound exciton peak to higher energy (3.465 eV) in the lightly doped sample is due to an effective n-type compensation associated with an annealing-induced increase in the nitrogen vacancies. In heavily doped Mg:GaN, the decreases in the integrated PL intensity after 700° C annealing may be associated with the hydrogen depassivation of nonradiative recombination centers in the film. The increase of PL intensity in the lightly doped sample after annealing is attributed to the reduction of defects by the annealing process.
The Microstructural Study of Aluminum Nitride Thin Films: Epitaxy on the Two Orientations of Sapphire and Texturing on Si
Authors: DOVIDENKO K. , OKTYABRSKY S. , NARAYAN J. , RAZEGHI M. 
Published: April 2011

ABSTRACTThe microstructural study of wide-band gap semiconductor AlN thin films grown on (0001) and (1012) sapphire and (111), (100) Si was carried out using plan-view and cross-sectional high-resolution electron microscopy and x-ray diffraction. The films were grown by MOCVD from TMAl + NH3 + N2 gas mixture. Epitaxial relationship for AIN grown on (0001)α 01-Al2O3 was determined to be the following: (0001)AIN ║ (0001)sap with the 30° in-plane rotation - [0110]AIN ║ [1210]sap. We report also TEM observation of the following epitaxial relationship of the AlN/(1012)α-Al2O3 heterostructure: (1120)AIN ║ (1012)sap; [0001]AIN ║ [1011]sap and [1100] AIN ║ [1210]sap. These epitaxial relationships were determined to be controlled by the bonding of Al and O ions at the interface. The study of interfaces and the defects present in the film was also carried out. Main type of defects were established to be inverted domain boundaries, misfit and threading dislocations - in the films on (0001) sapphire, and stacking faults of high density in the films on (1012) sapphire. The epitaxial AIN films on (0001) sapphire contained dislocation density about 1010 cm−2 and exhibited device quality electrical characteristics. The films on both orientations of Si were found to be highly <0001> textured polycrystalline.
Identification of Transition Metals in GaN
Authors: Pressel K. , Heitz R. , Eckey L. , Loa I. , Thurian P. , Hoffmann A. , Meyer B.K. , Fischer S. , Wetzel C. , Haller E.E. 
Published: April 2011

ABSTRACTWe present a photoluminescence study of residual transition metal contaminants in hexagonal GaN layers. We observe three no-phonon lines peaking at 1.3 eV, 1.19 eV and 1.047 eV. The no-phonon line at 1.3 eV is caused by the internal electronic transition 4T 1→ 6A1 of Fe3+. The 1.19 eV emission, which was first attributed to Cr4+, is caused by Ti2+. GaN layers intentionally doped with Cr, V, or Ti during growth have been investigated. Only the Ti doped samples snow an intense sienal of the 1.19 eV emission. The experimental data of the luminescence center at 1.047 ev, which appears as natural contaminant only in GaN layers grown by the sandwich technique, fit best to the 4T2(F) → 4A2(F) transition of Co2+. The three no-phonon lines show characteristic phonon sidebands. Most of them correspond to phonon modes observed in Raman spectroscopy.
Optical Properties of Mg-GaN, GaN/AlGaN SCH structures, and GaN on ZnO Substrates
Authors: Morkoç H. , Kim W. , Aktas Ö. , Salvador A. , Botchkarev A. , Reynolds D. C. , Look D. C. , Smith M. , Chen G. D. , Lin J. Y. , Jiang H. X. , Schmidt T.J. , Yang X.H. , Shan W. , Song J.J. , Goldenberg B. , Litton C. W. , Evans K. 
Published: April 2011

ABSTRACTGaN films and GaN/AlGaN heterostructures have been gro wn by MBE. GaN films doped with varying levels of Mg indicate effective mass acceptor at low doping concentrations, as determined from strong photoluminescence emission at about 380 nm. As the Mg concentration is increased the photoluminescence emission line red shifts considerably, indicating the formation of Mg-related or induced complexes whose lifetimes are relatively short. GaN/AlGaN separate confinement heterostructures grown on sapphire show strong near ultraviolet stimulated emission at room temperature in a side-pumping configuration. The pumping threshold for stimulated emission at room temperature was found to be ∼90 kW/cm2. Initial GaN films grown on ZnO substrates show the A exciton in low temperature photoluminescence. ZnO is being considered for nitride growth because of its stacking order and close lattice match.
Temperature Dependence of the Absorption Band Gap Edge of GaN
Authors: Manasreh M. O. , Sharma A. K. 
Published: April 2011

ABSTRACTThe optical absorption near the fundamental absorption edge in GaN thin films grown on sapphire substrates is studied as a function of temperature. The absorption band edge was determined from either the energy position of the exciton line in samples grown by metalorganic chemical vapor deposition technique, or from the first derivative of the absorption spectra in samples grown by molecular beam epitaxy technique. The band edge energies determined in the temperature range of 13 – 300 K were fitted with Varshni empirical relationship: Eg(K) = Eg(0) – α T2/(T + θD) and with the expression: Eg(K) = Eg(0) – κ/[exp(θE/T) – 1]. It is found that Eg(0), α, θD, and θE to be sample-dependent, which suggests that defects and dislocations significantly affect the optical band edge in GaN.
Fine Structure of the 3.42 eV Emission Band in GaN
Authors: Fischer S. , Wetzel C. , Walukiewicz W. , Haller E.E. 
Published: April 2011

ABSTRACTA luminescence band centered around 3.42 eV is commonly observed in GaN. Its appearance has been tentatively assigned to an oxygen donor level. Stimulated laser activity has also been reported at this energy. We present a study of this band in GaN grown by high temperature vapor phase epitaxy (HTVPE). The high quality of this material, with an excitonic line width as narrow as 3 meV, allows us to distingish four different peak positions of this luminescence band. They appear at 3.4066, 3.4121, 3.4186, and 3.4238 eV (T = 6 K). Within the experimental error the lines exhibit an equidistant spacing of 6 meV. They show a pressure behavior similar to shallow levels described by effective mass theory. We discuss our results in the context of incorporation of oxygen and structural defects in GaN.
Light Generating Carrier Recombination and Impurities in Wurtzite GaN/Al2O3Grown by MOCVD
Authors: Kaufmann U. , Kunzer M. , Merz C. , Akasaki I. , Amano H. 
Published: April 2011

ABSTRACTWe have studied by photoluminescence (PL) and optically detected magnetic resonance (ODMR) un-doped, n-doped and p-doped thin wurtzite GaN layers grown by metal-organic chemical vapor deposition on sapphire substrates. From the PL data for free excitons an accurate value of the free A-type exciton binding energy and a more accurate estimate for the hole effective mass is deduced. The localization energies of the Mg and the Zn neutral acceptor bound excitons are found to be in good agreement with Haynes’ rule. A sharp emission line, assigned to free electron recombination at a 116 meV shallow acceptor, together with three additional weak zero-phonon-lines (ZPLs), assigned to distant donor-acceptor (DA) pairs, are reported for the first time. The chemical nature of this acceptor and that of three residual donors, inferred from the DA pair ZPLs, is discussed. The effects of strain in thin GaN layers on a dissimilar substrate like sapphire are emphasized with respect to the energetic position of narrow PL lines. The ODMR data obtained for undoped, Mg-doped and Zn-doped GaN layers provide insight into the recombination mechanisms responsible for the broad yellow (2.25 eV), the violet (3.15 eV) and the blue (2.8 eV) PL bands, respectively. The ODMR results for Mg and Zn also show that these acceptors donotbehave effective mass like and indicate that the acceptor hole is mainly localized in the nearest neighbor shell surrounding the acceptor core.
Exciton Lifetimes in GaN
Authors: Bergman J.P. , Harris C. , Monemar B. , Amano H. , Akasaki I. 
Published: April 2011

ABSTRACTWe have performed time resolved photoluminescence measurements of the exciton recombination in different GaN samples at low temperatures. In epitaxial layers the decay time of the free exciton is typically faster than 100 ps. This is due to a dominating non-radiative recombination process. In thick bulk samples we have resolved and measured the decay time of the free exciton with a value of about 200 ps. We believe that this value is close to the radiative lifetime for free excitons in GaN. We have also shown that excitation transfer occurs between free and bound exciton states. We have furthermore measured the decay of the donor and acceptor bound excitons, and obtained values of the decay time of 250 ps and 1200 ps, respectively.