bluuebunny/crossref_metadata_2025_split huggingface dataset:
Properties of GaN Epitaxial Layer Grown by MOVPE on MgAl2O4 Substrate
Authors: Kuramata A. , Horino K. , Domen K. , Soejima R. , Sudo H. , Tanahashi T. 
Published: April 2011

ABSTRACTWe propose a MgAl2O4 substrate for GaN-based laser diodes. We grew GaN epitaxial layers using metal-organic vapor phase epitaxy on a MgAl2O4 substrate. The GaN on the MgAl2O4 showed a narrow X-ray diffraction peak of 310 arcsec, a photoluminescence dominated by the band-edge emission, and good electronic properties. The optical cavity was fabricated by cleaving the GaN on the MgAl2O4, and the stimulated emission from the cavity using optical pumping was observed. We also fabricated a light emitting diode (LED) with a AlGaN/InGaN double-heterostructure. The electroluminescence was dominated by the band-edge emission of InGaN with a narrow FWHM of 13.5 nm. The characteristics of LED on the MgAl2O4 were comparable to that on a A12O3 substrate. MgAl2O4 is feasible as a substrate for laser applications.
Theory of Point Defects and Complexes in GaN
Authors: Neugebauer Jörg , Van de Walle Chris G. 
Published: April 2011

ABSTRACTWe have studied the electronic and energetic properties of native defects, impurities and complexes in GaN applying state-of-the-art first-principles calculations. An analysis of the numerical results gives direct insight into defect concentrations and impurity solubility with respect to growth parameters (temperature, chemical potentials) and into the mechanisms limiting the doping levels in GaN. We show how compensation and passivation by native defects or impurities, solubility issues, and incorporation of dopants on other sites influence the acceptor doping levels. The role of hydrogen in enhancing the p-type doping is explained in detail. We also discuss the mechanisms responsible for the experimentally observed limitation of the free-carrier concentration in p-type GaN.
Electron cyclotron resonance etching characteristics of GaN in plasmas with and without hydrogen
Authors: Zhang L. , Ramer J. , Brown J. , Zheng K. , Lester L.F. , Hersee S.D. 
Published: April 2011

ABSTRACTElectron cyclotron resonance (ECR) plasma etching characteristics of gallium nitride (GaN) are investigated using low pressure (4-10 mTorr) SiCl4/Ar and Cl2/H2/Ar ECR discharges. The purpose of this effort is to develop a dry etching process for making laser mirrors on GaN and to examine dry etching processes of GaN that do not require hydrogen, which is known to cause carrier compensation in GaN. The etch rate is found to increase near-linearly with increasing DC bias, and a minimum DC bias of 100V is required to initiate etching in SiCl4/Ar. We have also found that the material quality significantly affects the etch rate. The latter decreases with x-ray rocking curve half-width and increases with defect density. A reasonable etch rate of 660Ǻ/min and good surface morphologies obtained in SiCl/Ar ECR etching make this process suitable for gate recess of an FET. An etch rate of 5270Ǻ/min has been achieved in Cl2/H2/Ar plasmas. This is the highest reported etch rate of GaN so far. The smooth and vertical etch sidewalls (etch to mask selectivity of 16 is obtained) make this process promising for dry-etched laser mirrors on GaN.
Properties of Zn Implanted GaN
Authors: Strite S. , Epperlein P. W. , Dommann A. , Rockett A. , Broom R. F. 
Published: April 2011

ABSTRACTWe report the optical and structural properties of ion implanted GaN:Zn. Post-implant annealing up to 1100 °C was performed under flowing N2 in both a tube furnace and a rapid thermal annealing (RTA) system, with and without SiNx encapsulation layers. The implantation damage is quantified by transmission electron microscopy (TEM). Secondary ion mass spectroscopy (SIMS) detects significant rearrangement of implanted Zn only at the highest temperatures and doses investigated. Strain reduction, observed in GaN:Zn annealed at or above 975 °C by high-resolution x-ray diffractometry (HRXRD), indicates successful damage removal. The optical activation of annealed GaN:Zn is measured by photoluminescence (PL). The room temperature (RT) Zn acceptor transition at ∼430 nm is consistently observed in annealed GaN:Zn, but at low efficiency. We conclude that residual implantation damage and/or N loss during annealing limits the optical quality of implanted GaN:Zn.
Interfacial Reactions Between Metal Thin Films and p-GaN
Authors: Trexler J.T. , Miller S.J. , Holloway P.H. , Khan M.A. 
Published: April 2011

ABSTRACTThe reactions between Au, Au/Ni and Au/C/Ni thin films on p-GaN have been studied using current-voltage (I-V) measurements, Auger electron spectroscopy (AES) and secondary ion mass spectrometry (SIMS). The metallization schemes consisted of ≈2000Ǻ sputtered Au, 1000Ǻ Au/500Ǻ Ni, and 1000Ǻ Au/100Ǻ C/500Ǻ Ni electron beam evaporated. The Au/Ni metallization scheme is of particular interest since it is the basis for the most commonly used ohmic p-type contacts for blue GaN LED’s. Au does not decompose the GaN matrix, while Ni has been shown to react with GaN above a temperature of 400° C for times longer than 5 minutes. Upon decomposition of the GaN by Ni, incorporation of C at the metal/GaN interface occurred. It is believed that a regrowth of GaN occurred, with the surface region being doped with C. Attempts at increasing this doping concentration by introducing an interfacial C layer were not successful.
Metallurgical Study of Contacts to Gallium Nitride
Authors: Mohney S.E. , Luther B.P. , Jackson T.N. , Khan M.A. 
Published: April 2011

ABSTRACTThermally stable contacts to GaN that also have desirable electrical characteristics are required for the further development of optoelectronic and high temperature devices based on GaN. To make improvements on existing contacts or to develop new ones, information on the metallurgy of potential contact systems is needed. In this work, the Metal-Ga-N ternary phase equilibria and the contact metallurgy are examined for Ti, Re, and Ni. Annealed contacts of these metals have been examined with x-ray diffraction and/or x-ray photoelectron spectroscopy, and the observed metallurgical reactions are discussed in light of estimated or experimentally determined Metal-Ga-N phase diagrams. Particular attention is paid to the gas phase equilibria and the role of the annealing environment on the metallurgical reactions. Finally, the consequences of this work for the design of thermally stable contacts are considered.
Pulsed Laser Deposition of ZnO: Energetic Rydberg State Atoms and Their Impact on Film Growth
Authors: Leuchtner Robert E. 
Published: April 2011

ABSTRACTA detailed comparison of the ZnO film microstructure prepared with both targets at two deposition pressures (0.01 and 0.1 torr) and a variety of substrate temperatures from 50-500°C was performed. The crystallographic and morphological results suggest that the condensation of highly electronically excited state particles, both ions and long-lived excited state neutrals likely affects film growth, and can enhance desirable surface processes, such as athermal recrystallizalion and surface mobility, that favor oriented crystal growth at lower substrate temperatures.
Excimer Laser Applications in Integrated Circuit Packaging
Authors: Lu Y. F. , Hong M. H. , Chan D. S. H. , Low T. S. 
Published: April 2011

ABSTRACTExcimer laser ablation is applied in the deflashing and demarking of IC packages. It is found that mold flash filled in the interface holes of IC leadframe can be removed completely by the laser deflashing in a short period of time. With appropriate selection of laser parameters, deflashing quality and efficiency can be greatly improved. The laser deflashing is more efficient for higher pin count packages. It is a superior alternative in future applications. In laser demarking, ink marks on package surfaces can also be removed completely in a short time. The surface after the processing has good conditions for remarking. The package remarking shows good permanency. The lifetime for good marking is much longer for IC packages after the laser demarking than those after hydrogen flame-off. Laser processing can be used to replace hydrogen flame-off in the ink printing of IC packages for high efficiency and safety.
On The Origin of Laser-Induced Surface Activation of Ceramics
Authors: Pedraza A.J. , Park J.W. , Lowndes D.H. , Cao S. , Allen W.R. 
Published: April 2011

ABSTRACTThe surfaces of Al2O3and AlN are modified by pulsed-laser irradiation This modification promotes the deposition of copper when the irradiated substrates are immersed in an electroless bath. In this paper the nature of the surface modification is analyzed using results from Auger Emission Spectroscopy (AES) and Cross Sectional Transmission Electron Microscopy (XTEM). During irradiation AlN thermally decomposes leaving a discontinuous metallic film on the surface. A film of Al2O3is detected at the surface of the irradiated AlN substrate, much thicker when the irradiation is performed in an oxidizing atmosphere than when done in a reducing one. Nanoparticles of metallic aluminum are generated during laser irradiation of Al2O3in a reducing atmosphere. When the irradiation of Al2O3is performed in an oxidizing atmosphere, regions containing aluminum or substoichiometric alumina are detected by AES. It is concluded that the presence of metallic aluminum is the main reason why electroless deposition can occur in both AlN and Al2O3. Deposition kinetics are completely consistent with this conclusion. It is very likely that also substoichiometric alumina helps to catalyze the electroless deposition.
Excimer Laser Processing of Tool Steel: Tribological Effects of Multiple Pulse Processing and Ti Alloying
Authors: Jervis T. R. , Nastasi M. , Griffin A. J. , Zocco T. G. , Taylor T. N. , Foltyn S. R. 
Published: April 2011

ABSTRACTExcimer lasers were used to modify the surface of AISI type A-7 tool steel, a high C, high V, high Cr material used in many cutting applications. Multiple pulses of laser radiation at 248 nm were used to alter the composition of the surface alloy. Hardness and modulus were not significantly affected by the treatment, but friction in dry sliding against an alumina pin was reduced. The reduction was small but persistent for multiply melted and resolidified surfaces. These surfaces showed a marked increase in the surface Cr concentration. Greater reductions in friction were obtained from a Ti rich surface layer formed by laser mixing an evaporated Ti layer into the material. The friction coefficient of the Ti alloyed surface deteriorated after approximately 1,000 cycles, indicating wear-through of the modified surface. The observed properties will be discussed in terms of the excimer laser modification process and the microstructure and composition of the resulting surfaces.
Optimization of Bulk Hgcdte Growth in a Directional Solidification Furnace by Numerical Simulation
Authors: Bune A.V. , Gillies D.C. , Lehoczky S.L. 
Published: April 2011

ABSTRACTA numerical model of heat transfer by combined conduction, radiation and convection was developed using the FIDAP finite element code for NASA's Advanced Automated Directional Solidification Furnace (AADSF). The prediction of the temperature gradient in an ampoule with HgCdTe is a necessity for the evaluation of whether or not the temperature set points for furnace heaters and the details of cartridge design ensure optimal crystal growth conditions for this material and size of crystal. A prediction of crystal/melt interface shape and the flow patterns in HgCdTe are available using a separate complementary model.
Kinetics and Thermodynamics of the Formation of Thin Film Titanium Diselicide
Authors: Kasica R.J. , Cotts E.J. , Ahrens R.G. 
Published: April 2011

ABSTRACTMultilayered difiiision couples consisting of alternating layers of titanium (Ti) and amorphous silicon (a-Si) have been fabricated using sputter deposition with a range of modulation lengths corresponding to an average composition of Ti33 Si67. We have used differential scanning calorimetry to measure the enthalpy evolved during the solid state reaction a-Si + Ti → C49-TiSi2 and have characterized the phases formed using x-ray diffraction analysis. An average measured enthalpy of formation, ΔΗ was found to be ΔΗ = -58 + 9 kJ/g atom for thin film samples. Using scanning and isothermal calorimetry measurements, we have also characterized the kinetics involved during the initial intermixing stage.
Alloying in an Immiscible Cu-Nb System upon Solid-State Reaction
Authors: Pan F. , Ling Z.F. , Gao K.Y. , Liu B.X. 
Published: April 2011

ABSTRACTIn an immiscible Cu-Nb system, an amorphous alloy and two metastable crystalline phases were obtained by solid-state reaction of Cu-Nb multilayered films, and the formation of the alloy phases was found to be quite sensitive to the average composition of the films. At Nb concentration of 75at%, amorphization was achieved by 250°C annealing for 50 min, while in the films with compositions of 70 and 80 at% Nb, a simple cubic (a=0.405±0.005nm) and an orthorhombic phase (a=0.421, b=0.334, c=0.291±0.005nm) were observed, respectively. Thermodynamic calculation was conducted for the Nb-Cu alloy phases and the energetic state of the multilayers, which consisted of 9 Cu/Nb bilayers. It turned out that the excess free energy originating from the interfacial atoms could raise the multilayers to an energy level being higher than that of the amorphous or/and metastable crystalline phases both with a convex shape, and thus provided a major driving force for alloy phase formation in such immiscible system.
Hydrogen Release and Si-N Bond-Healing Infrared Study of Rapid Thermal Annealed Amorphous Silicon Nitride Thin Films
Authors: Santos-Filho P. , Stevens G. , Lu Z. , Koh K. , Lucovsky G. 
Published: April 2011

ABSTRACTWe address aspects of hydrogen bonding and its thermal evolution in amorphous Silicon nitride films grown by Remote Plasma Enhanced Chemical Vapor Deposition (RPECVD) from SiH4 and NH3 (or ND3) source gases. Rapid Thermal Annealing (RTA) decreases the Si-H(D) and SiN-H(D) bond populations. The hydrogen bonds break, and H2 (HD, D2) forms and evolves from the film with the heat treatment. This molecular hydrogen release is accompanied by Si- and N- bond healing as detected by a SiN infra red stretch mode signal gain. The ex-situ RTA experiment temperatures ranged from 400 °C to 1200 °C, in 100 °C steps and the film structural changes were monitored by Fourier Transform Infrared spectroscopy (FTIR) after each incremental anneal. Gas flow ratios R=NH3/SiH4 > 2 produced films in which SiN-H(D) bonds dissociated, and a gas desorption rate equation estimated an activation energy barrier of Ea = 0.3 eV. The release of hydrogen from the films in the form of H2 (D2) and ammonia radicals was detected by mass spectrometry and is shown here. The re-bonding of nitrogen to silicon upon thermal dissociation of hydrogen's is consistent with the improvement of the electrical properties of a-SiN:H films following RTA treatment.
In Situ Study of the Temperature Dependence of Irradiation-Induced Amorphization in A-Sic
Authors: Weber W. J. , Wang L. M. , Yu N. , Hess N. J. 
Published: April 2011

ABSTRACTIon-beam-induced amorphization in single crystal α-SiC has been studied as a function of temperature. Specimens have been irradiated with 1.5 MeV Xe+ ions over the temperature range from 20 to 475 K using the HVEM-Tandem Facility (ANL), and the evolution of the amorphous state has been followed in situ in the HVEM. Specimens also have been irradiated at 170, 300, and 370 K with 360 keV Ar+ ions, and the damage accumulation process followed in situ by Rutherford backscattering spectroscopy/channeling using the dual beam facilities at the Ion Beam Materials Laboratory (LANL). At 20 K, the displacement dose for complete amorphization is 0.25 dpa and increases with temperature in two stages. The activation energy associated with the simultaneous recovery processes above 100 K is 0.12 ± 0.02 eV. The critical temperature above which amorphization does not occur is 485 K under the 1.5 MeV Xe+ irradiation conditions. Ion channeling results suggest that the rate of simultaneous recovery increases with temperature only above a critical damage level. Raman spectroscopy indicates that rapid chemical disordering occurs during irradiation.
The Crystal-Melt Interface in Si or Ge
Authors: Spaepen Frans , Shao Yan 
Published: April 2011

ABSTRACTFrom the nucleation data on undercooling of liquid Si or Ge, crystal-melt interfacial tensions are calculated. Only a temperature-dependent tension can account simultaneously for the results of experiments on bulk and thin film Si. The observed temperature dependence can be accounted for by reasonable values of the interfacial entropy and enthalpy. The analysis is used to determine the temperature-dependent interfacial tension for Ge. A comparison of results for Ge and Si indicates that homogeneous nucleation has not been achieved in the undercooling of bulk liquid Si.
Microstructural Stability of Stressed Lamellar Eutectics
Authors: Sridhar N. , Rickman J.M. , Srolovitz D.J. 
Published: April 2011

ABSTRACTAt elevated temperatures, stresses enhance mass transport at the microstructural scale and under certain conditions, lead to microstructural instabilities. Using a linear stability analysis, we examine the effect of stresses on the morphological stability of plate-like phases and lamellar eutectic composites. These stresses can be either due to misfit strains and/or due to externally applied loads. We find that for misfitting plates, the nominally flat plate-matrix interface is unstable with respect to the growth of perturbations with wavelengths greater than a critical wavelength, provided that the reinforcing plates are elastically suffer than the surrounding matrix. On the other hand, for stresses generated by externally applied loads, the flat interface is always unstable as long as the plate modulus and the matrix modulus are not identical. In addition, the analysis reveals that misfit strains can either counteract or enhance the destabilizing influence of applied loads depending on the elastic properties of the plate and the matrix. Finally, we have developed stability diagrams that identify material properties and operating conditions required to maintain a stable interface in these lamellar eutectic composites.
A Kinetic Model of Precipitate Evolution
Authors: Lane Rohrer C. , Asta M. D. , Foiles S. M. , Hyland R. W. 
Published: April 2011

ABSTRACTChemical reaction rate theory is used to model the kinetics of precipitation reactions in Al alloys, including the effects of continuous cooling and thermally generated point defects. The computational method models the processes of nucleation, growth, and coarsening within a single framework. Calculated time and temperature dependent precipitate number densities and sizes during the homogeneous precipitation of the A13Sc phase in an Al-.11 at% Sc alloy are shown to compare favorably with experimental observations.
Ordering Kinetics and Magnetic Properties in the Pt1co1–xNix Alloy System
Authors: Tu Huan , Ruiz Eduardo , Orehotsky J. 
Published: April 2011

ABSTRACTOrdering kinetics were measured of various alloys in the order-disorder Pt1Co1–xNix (0 ≤ x<0.5) magnetic alloy system.The kinetics of all the investigated alloys were found to be characterized by an Arrhenius temperature dependence. The associated activation energy as a parametric representation of the kinetics was evaluated as a function of the nickel content. This result was correlated with measured values of the saturation magnetization and Curie temperature of these alloys in both the atomically ordered and disordered states. A strong correlation was discovered between the activation energy and the saturation magnetization of the disordered ternary alloys.
Investigation of Phase Transformations and Ordering During Combustion Synthesis
Authors: Kachelmyer C.R. , Varma A. , Khomenko I.O. , Rogachev A.S. , Merzhanov A.G. 
Published: April 2011

ABSTRACTTwo complementary experimental techniques are presented that describe the mechanisms during the combustion synthesis of NiAl and Ti5Si3. The first involves quenching a reacting wedge-shaped sample imbedded in a copper block where the propagating combustion front extinguishes while traveling to the apex. The second technique, time-resolved X-ray diffraction (TRXRD), provides a direct in-situ observation of the sequence of high temperature phase transformations. The information obtained from this investigation will be useful in developing improved process models of combustion synthesis, which can lead to the production of advanced materials with tailored microstructure and properties.
Phase Separation of β-SN in Strained, Compositionally Metastable Ge1-xSnx Alloys
Authors: Kriesel Joshua W. , Lee Susanne M. 
Published: April 2011

ABSTRACTUsing rf sputtering and post-deposition annealing in a differential scanning calorimeter (DSC), we manufactured bulk (4000 nm) films of crystalline Ge0.83Sn0.17. This Sn concentration is much greater than the solid solubility limit of Sn in Ge (x ≤ 0.01). Continued annealing thermally induces Sn phase separation from the alloy, limiting the ultimate attainable grain size in the metastable crystals. We examine, here, the mechanisms and kinetics of the processes limiting the size of the Ge0.83Sn0.17 polycrystals. From a combination of DSC, electron microprobe, and x-ray diffraction (XRD) measurements, we propose phase transformation mechanisms corresponding to crystallization of amorphous Ge0.83Sn0.17, crystallization of an as-yet unidentified phase of Sn, and phase separation of Sn from the Ge1-xSnx crystals. We were unable to observe the unidentified phase of Sn in XRD, but the phase must be present in the material to account for the quantitative discrepancies (as much as 8 at.%) in Sn percentages determined from each of the DSC, XRD, and electron microprobe measurements. Our models for the various transformation kinetics were corroborated by the subsequent phase-separated Sn melting behavior observed in the DSC: two Sn melting endotherms, one of which was 20–100°C lower than the bulk melting temperature of Sn. This depressed temperature endotherm we speculate represents liquefaction of nanometer-sized (β–Sn clusters.
Molecular Beam Epitaxy of InGaP Films Grown on Si(001) Substrates with Various Kinds of Initial Buffer Layers
Authors: Kawanami H. , Sekigawa T. 
Published: April 2011

ABSTRACTSingle domain InxGa(1-x)P (x=0.4) films were successfully grown on Si(001) misoriented substrates by molecular beam epitaxy with solid phosphorous source. The effects of the initial 100 nm thick interfacial buffer layer such as InGaP (i.e. direct growth without buffer layer), GaP, AJP, and GaAs were examined. Superior surface morphologies were indicated for the films with GaP, A1P, and GaAs buffer layers compared with the films on InGaP buffer layer. The results indicated the necessity of some kind of initial buffer layer different from the film.
Interfacial Coarsening in an MBE Growth without Slope Selection
Authors: Golubović Leonardo 
Published: April 2011

ABSTRACTWe study the dynamics of an MBE growth in the presence of the interfacial instabilities inducing a pyramidal or mound-type interfacial growth. By using a novel collective coordinates method similar to Bray’s theory of phase ordering, we discuss the statistics of the growing interfaces in the absence of slope selection, when the mounds slope indefinitely increases with time.