bluuebunny/crossref_metadata_2025_split huggingface dataset:
Measurement of Quasi-Fermi Levels in Quantum Well Lasers
Authors: Therrien J. , Mil'shtein S. , Chin A. 
Published: April 2011

AbstractHeterojunction Quantum Well Lasers were tested under forward and reverse bias, by Scanning Electron Microscopy (SEM) working in Differential Voltage Contrast(DVC) mode. DVC utilizes the impact of electrical potential across a device on the emission of secondary electrons. DVC consists of storing and subtracting two digitized images of the tested device under zero bias and in an operational regime. Calibration of the resultant image provides for quantitative measurements of the potential across the device. The question of whether the DVC technique measures the electron affinity of a material or its work function or the thermodynamic potential has been addressed in recent papers, however questions remained regarding discrepancies between the expected Quasi Fermi Energy (QFE) and the measured values. The experimental part of our work concentrated on taking (QFE) profiles by DVC across a single quantum well laser operating in inverse population, threshold, and high power emission modes of photoemission. The intensity was measured by a calibrated photodetector aligned with the laser in the SEM chamber. The cleaved and yet operational lasers have as a central part a layer of In0.2Ga0.8As 600nm thick between two undoped layers of Al0.3Ga0.7As 0.1 μm thick each with cladding layer of n-type Al0.6Ga0.4As on one side and a similar p-type layer on the other. The shape of QFE indicated that eletrons and photons contribute to total energy over the intrinsic area. This QFE profiling across the laser reveals areas of electron and photon confinement.
Rapid Cure Of Liquid Encapsulants And Structural Adhesives For Electronics Packaging Using Variable Frequency Microwave (Vfm) Energy
Authors: Fathi Zak , Tucker Denise A. , Wei Billy J. , Garard Richard S. , Mead Patricia F. , Balaji P. , Hutchins Charles L. 
Published: April 2011

AbstractThis paper reports on the use of an emerging process technique for curing of polymer encapsulants as used in the electronic packaging industry. Previous work performed in the area of materials processing has demonstrated the usefulness of sweeping operating frequencies in order to achieve high levels of electric field uniformity and process control. The use of controlled variable frequency microwave energy has been evaluated as a process technique compatible with electronic packaging requirements. The heating of a series of integrated circuits (ICs) and their subsequent characterization was performed. IC integrity was investigated using X‐Ray, Acoustic Microscopy, Decapsulation and Bond Pull. Processing of liquid encapsulants, underfills and glob‐tops, used in Flip Chip and Chip On Board (COB) applications, was performed. Differential Scanning Calorimetry was used to study cure extent. Further studies show that variable frequency microwave processing leads to fast curing of encapsulants. A reduction in cycle times from 15 to 20 times over conventional curing has been observed. Also, results have showed a reduction in the stresses induced by mismatches in coefficient of thermal expansion.
Viscoelastic Behavior of Polymer Thin‐Films Under Thermal Stresses
Authors: Bluestein Stephen D. , Bramono Dewi P. Y. , Miaoulis Ioannis N. , Wong Peter Y. 
Published: April 2011

AbstractStresses and deformation in microelectronic packaging are affected by the viscoelastic behavior of polymer materials during manufacture or operation. Predicting and measuring these thermo‐mechanical effects is important for new devices, components, and materials. The viscoelastic response of Nycoa 851 polyimide thin‐films during thermal loading is investigated. The time‐dependent relaxation of polyimide films was measured in‐situ, focusing on the change in thermo‐mechanical properties based on the thickness of the polyimide layer. The curvature change of the multilayer structure (silver‐polyimide‐quartz heterostructure) was obtained for different temperatures and polymer film thicknesses. The polyimide relaxation time constant and activation energy were determined. Results indicate that the thermo‐mechanical properties of polyimide thin films are dependent on the thickness of the polymer layer.
Novel Technique to Improve Adhesion Between Metal‐Polymer Interfaces
Authors: Menezes Marlon , Robertson I.M. , Birnbaum H.K. 
Published: April 2011

AbstractPartially embedded copper clusters within a polyimide substrate have been utilized to act as “nano‐nails” to anchor the bulk metal overlayer to the underlying polyimide substrate resulting in increased adhesion between the metal and substrate. Isolated nano‐sized copper clusters can be formed on a polyimide surface under UHV conditions using very slow deposition rates and temperatures that are high enough to induce mobility of copper atoms on the polyimide surface. Because copper has a high surface energy with respect to the copper/polyimide interface and the polymer surface, the copper clusters exert an embedding force on the polyimide substrate. These clusters can be made to embed in the polymer by annealing in vacuum at temperatures close to the glass transition temperature of the polymer. By regulating the time and temperature of post‐deposition anneals, the degree of embedding of the copper clusters can be controlled. Cross‐sectional TEM results will illustrate the various degrees of cluster embedding, while adhesion testing results will be presented to show the improved adhesion obtained from these interfaces.
Creep Study for Fatigue Life Assessment of Two Lead-Free High Temperature Solder Alloys
Authors: Liang J. , Lee P. S. , Gollhardt N. , Schroeder S. , Morris W. 
Published: April 2011

AbstractCreep of two lead-free high temperature solder alloys, 95Sn-5Ag and 99Sn-1.0Cu was studied in this investigation. Room and high temperature creep tests were performed to examine deformation mechanisms and to establish mathematical models of creep deformation for the alloys. A state variable creep model was introduced to model both primary and secondary creep deformation of these two alloys which show a very significant primary creep. Fatigue life models of the alloys were established based on an energy-based failure criteria, which was deduced from variable strain amplitude tests at a constant strain rate of 0.003/sec, and from variable strain rates tests with two constant strain amplitudes of 0.005 and 0.01. Applications of the creep model includes determination of peak loads and hysteresis strain energy density in strain-controlled fatigue tests. It is demonstrated that the creep model can be very helpful to establish fatigue failure criteria and to assess fatigue lives of these two alloys.
Thermodynamic and Kinetic Study of Phase Transformations in Solder/Metal Systems
Authors: Chromik R.R. , Cotts E.J. 
Published: April 2011

AbstractDiffusion in both the Pd‐Sn and Cu‐Sn systems has been investigated using differential scanning calorimetry. Averaged interdiffusion coefficients for the PdSn4, PdSn2 and Cu3Sn intermetallics have been calculated, where equilibrium concentrations in the diffusion couples are assumed. There is an obvious hierarchy within the Pd‐Sn system where diffusion is fastest in the most Sn‐rich intermetallic. Comparisons within each system, including consideration of the solute diffusion coefficients in pure Sn, provide evidence that in the most Sn rich phase (e.g. PdSn4) the interstitial diffusion of metal atoms is the dominant reaction mechanism. In contrast, the diffusion coefficient for the Cu‐rich phase Cu3Sn was found to be five orders of magnitude smaller than the solute diffusion coefficient for Cu in pure Sn.
Electron Emission from Cold Cathodes
Authors: Pryor R. W. , Li Lihua , Busta H. H. 
Published: April 2011

ABSTRACTNew observations are presented on the emission of electrons from n-type polycrystalline diamond and n-type boron nitride (BN) cold cathode films, both as synthesized and after post-synthesis annealing. The films have been observed to show an increase in electron emission after annealing by one to several orders of magnitude, depending upon the type of emitter and the specific surface treatment. Observations from both plasma and laser annealing treatments will be presented.The annealed BN cold cathodes have been observed to yield stable emission currents as high as 2 A cm−2 (∼4 mA total current) at fields as low as ∼30 V μm−1. This is believed to be the highest reported current density yet observed from a planar film cold cathode emitter.
Design Consideration of GaN-Based Surface Emitting Lasers
Authors: Honda T. , Koyama F. , Iga K. 
Published: April 2011

ABSTRACTThe threshold current density of GaN-based vertical cavity surface emitting lasers (VCSELs) has been estimated. It is clarified that the introduction of a quantum well structure as an active layer is very effective for a low threshold operation and that high reflective mirrors are required for low threshold GaN-based VCSELs. Also, attempts on micro-fabrication process of GaN is presented.
Realization and Characterization of Optically-Pumped GaInN-DFB Lasers
Authors: Hofmann R. , Wagner V. , Gauggel H-P. , Adler F. , Ernst P. , Sohmer A. , Bolay H. , Scholz F. , Schweizer H. 
Published: April 2011

ABSTRACTWe demonstrate room temperature laser activity of optically pumped GaN/GalnN-DFB-lasers. The ridge-waveguide DFB lasers were realized on GaN/GalnN double heterostructures grown by low-pressure metal-organic vapor phase epitaxy. The best laser threshold we achieved is 1.9 MW/cm2.By varying the grating period, the laser emission wavelength could be tuned from 399 to 415 nm. This allows to determine the dispersion relation of the effective refractive index neff(λ) and the spectral dependence of the pump power density at the laser threshold Pth(λ) over the whole emission range. Furthermore, the shift of the emission wavelength with temperature of the DFB-lasers is investigated and is found to be small compared to the emission wavelength shift of the gain maximum.
Study of IBAD Deposited AlN Films for Vacuum Diode Electron Emission
Authors: Forsythe E.W. , Sprague J.A. , Khan B.A. , Metha S. , Smith D.A. , Murzin I.H. , Ahern B. , Weyburne D. W. , Tompa G. S. 
Published: April 2011

ABSTRACTWe have demonstrated the basic operation of a vacuum diode based on the negative electron affinity polycrystalline AlN thin film emitters. The AlN films, both undoped and Ge doped, were deposited by ion beam assisted deposition (IBAD). The IBAD process utilizes thermal evaporation from either electron-beam or resistance heated sources with ion bombardment from Kaufman-type ion sources at energies from 50 to 1500 eV. Films were post-annealed by rapid thermal annealing and long-time tube furnace annealing in a N2 atmosphere to test improvements in crystallinity. The electrical and transport properties of the films were tested by DC l-V measurements. The structure of the AlN films was investigated by TEM, SIMS, optical absorption, and RBS as a function of growth parameters and annealing. The field emission was tested for films with different Ge doping concentrations, film thickness, diode voltage, and post annealing conditions. Field emission was observed for the undoped AlN films with a thickness of approximately 10 nm.
Pressure-Controlled GaN MBE Growth Using a Hollow Anode Nitrogen Ion Source
Authors: Leung M. S. H. , Klockenbrink R. , Kisielowski C. , Fujii H. , Krüger J. , Sudhir G. S. , Anders A. , Liliental-Weber Z. , Rubin M. , Weber E. R. 
Published: April 2011

ABSTRACTGaN films were grown on sapphire substrates at temperatures below 1000 K utilizing a Hollow Anode nitrogen ion source. A Ga flux limited growth rate of ~ 0.5 µm/h is demonstrated. Active utilization of strain and the assistance of a nitrogen partial pressure during buffer layer growth are found to be crucial issues that can improve the film quality. The best films exhibit a full width at half maximum of the x-ray rocking curves of 80 arcsec and 1.85 meV for the excitonic photoluminescence measured at 4 K. A Volmer-Weber three dimensional growth mode and the spontaneous formation of cubic GaN inclusions in the hexagonal matrix are observed in the investigated growth temperature range. It is argued that this growth mode contributes to a limitation of the carrier mobility in these films that did not exceed 120 cm2/Vs though a minimum carrier concentration of ~ 1015 cm−3 was achieved.
MOVPE Growth and Optical Characterization of GaPN Metastable Alloy Semiconductor
Authors: Onabe K. 
Published: April 2011

ABSTRACTThe Gap1–x Nx, alloy semiconductor has been grown with the N concentration as high as 6.3% by inetalorganic vapor phase epitaxy (MOVPE) using 1,1-dimethylhydrazine (DMHy) as the N source. The growth characteristics show the key role of the non-equilibrium circumstances during the growth, where the N desorption from the surface limits the N incorporaton. The band-edge states have been studied using time-resolved PL and PL excitation spectroscopies. The PL takes place via the tail states below the absorption edge. The band edge, which shifts to lower energies with increasing N concentration, originates from the A-line energy (i.e. isolated N states) rather than the indirect-gap energy of GaP in the limit x = 0.
Large Area Supersonic Jet Epitaxy of AlN, GaN, and SiC on Silicon
Authors: Lauhon L.J. , Ustin S. A. , Ho W. 
Published: April 2011

ABSTRACTAlN, GaN, and SiC thin films were grown on 100 mm diameter Si(111) and Si(100) substrates using Supersonic Jet Epitaxy (SJE). Precursor gases were seeded in lighter mass carrier gases and free jets were formed using novel slit-jet apertures. The jet design, combined with substrate rotation, allowed for a uniform flux distribution over a large area of a 100 mm wafer at growth pressures of 1–20 mTorr. Triethylaluminum, triethylgailium, and ammonia were used for nitride growth, while disilane, acetylene, and methylsilane were used for SiC growth. The films were characterized by in situ optical reflectivity, x-ray diffraction (XRD), atomic force microscopy (AFM), and spectroscopic ellipsometry (SE).
Effect of Growth Parameters and Local Gas-Phase Concentrations on the Uniformity and Material Properties of GaN/Sapphire Grown by Hydride Vapor-Phase Epitaxy
Authors: Safvi S. A. , Perkins N. R. , Horton M. N. , Kuech T. F. 
Published: April 2011

ABSTRACTThe effects of flowrate variation and geometry on the growth rate, growth uniformity and crystal quality were investigated in a horizontal Gallium Nitride vapor phase epitaxy reactor. To better understand the effects of these parameters, numerical model predictions are compared to experimentally observed values. Parasitic gas phase reactions between group III and group V sources and deposition of material on the wall are shown to lead to reduced overall growth rates and may be responsible for inferior crystal quality. A low ammonia concentration is correlated with the deposition of polycrystalline films. A low V/III ratio and an ammonia concentration lead to poor crystalline quality and increased yellow luminescence. An optimum HVPE growth process requires selection of reactor geometry and operating conditions to minimize these parasitic reactions and wall deposition while providing a uniform reactant distribution across the substrate.
New Pathways to Heteroepitaxial GaN by Inorganic CVD Synthesis and Characterization of Related Ga-C-N Novel Systems
Authors: Kouvetakis J. , O’Keeffe M. , Brouseau Louis , McMurran J. , Williams Darrick , Smith D. J. 
Published: April 2011

ABSTRACTWe describe the development of a new deposition method for thin oriented films of GaN on basal plane sapphire using an exclusively inorganic single-source precursor free of carbon and hydrogen, Cl2GaN3. The films have been characterized by Rutherford backscattering spectroscopy (RBS) and cross sectional transmission electron microscopy (TEM) for composition morphology and structure. RBS analysis confirmed stoichiometric GaN and TEM observations of the highly conformal films revealed heteroepitaxial columnar growth of crystalline wurrtzite material on sapphire. Auger and RBS oxygen and carbon resonance profiles indicated that the films were pure and highly homogeneous. We also report the reactions of Cl2GaN3 with organometallic nitriles to yield a crystalline, novel gallium carbon nitride of composition GaC3N3. Quantitative X-ray powder diffraction has been used to refine the cubic structure of this material which consists of Ga atoms octahedrally surrounded by on the average three C and three N atoms. The structurally analogous LiGaC4N4 phase has also been prepared and characterized.
Thin Film Growth of Group III Nitrides by Mass Separated Ion Beam Deposition
Authors: Ronning C. , Dreher E. , Feldermann H. , Sebastian M. , Zweck J. , Fischer R. , HofsÄss H. 
Published: April 2011

ABSTRACTWe have grown gallium nitride (GaN), aluminum nitride (AIN) and boron nitride (BN) thin films by mass separated ion beam deposition. All deposited films were found to be almost stoichiometric. AIN and GaN films are crystalline even after room temperature deposition whereas for the formation of crystalline boron nitride temperatures above 150°C are necessary. The influence on the phase formation and the film structure of ion energy and substrate temperature on the one hand, and bond ionicity on the other hand, was investigated for these three systems.
Nanopipes and Inversion Domains in High-Quality GaN Epitaxial Layers
Authors: Ponce F. A. , Young W. T. , Cherns D. , Steeds J. W. , Nakamura S. 
Published: April 2011

ABSTRACTIn this paper we report that, in addition to dislocations, two other types of defects are observed in high quality GaN thin films. These defects have a filamentary nature, are oriented along the <0001> direction. and may not be easily distinguished from the pure dislocations. Using a combination of conventional electron microscopy with convergent beam electron diffraction techniques we show that one of these types of dislocations consist of nanopipes, which are coreless dislocations with Burgers vectors <0001>. The other type of observed defects consist of inversion domains with [0001 ] orientation within the [0001] matrix. The origin of the inversion domains and nanopipes is discussed.
Structural and Optical Characterization of High-Quality Cubic GaN Epilayers Grown on GaAs and 3C-SiC Substrates by Gas-Source MBE Using RHEED In Situ Monitoring
Authors: Okumura H. , Balakrishnan K. , Feuillet G. , Ohta K. , Hamaguchi H. , Chichibu S. , Ishida Y. , Yoshida S. 
Published: April 2011

ABSTRACTBy monitoring RHEED reconstruction patterns during gas source molecular beam epitaxy growth, the optimization of the growth for cubic GaN was carried out successfully. Cubic GaN epilayer having a X-ray diffraction width of 16min and a low temperature photoluminescence emission width of 19meV was obtained on a 3C-SiC substrate by adjusting the effective III/V ratioin-situduring the growth, which can be inferred from the surface reconstruction transitions. It was found that the surface reconstructions of cubic GaN surfaces are good indices for the optimization of growth parameters.
Comparison of the Microstructure of AlN Films Grown by MOCVD and by PLD on Sapphire Substrates
Authors: Li Yun-Xin , Salamanca-Riba Lourdes , Talyan V. , Venkatesan T. , Wongchigul C. , Zhou P. , Tang X. , Spencer M. G. 
Published: April 2011

ABSTRACT(0001) aluminium nitride thin films were grown epitaxially on (0001) Sapphire substrates by MOCVD at 1200° C and PLD at 800° C. Both films have the same epitaxial growth relationship: (0001)AlN//(0001)Sap, and the same in-plane relationship which shows a 30° rotation between A1N and Sapphire: [ 12 10]AlN//[0 110]Sap and [10 10]AlN //[ 2110]Sap. The full width at half maximum (FWHM) of x-ray rocking curve of the MOCVD A1N film was 0.16° and PLD A1N film was 0.2°. Films grown by both MOCVD and PLD showed high crystalline quality. HRTEM images showed that these films are single crystalline with very low density of defects.Dislocations in the film parallel to the film / substrate interface were observed in both A1N films. Atomic force microscopy images showed that the MOCVD films have flatter and larger terraces than the PLD films. The PLD technique for A1N growth needs to be improved further. But both films have a surface roughness of approximately 100nm.
Characterization of OMVPE-Grown AlGaInN Heterostructures
Authors: Bour D. P. , Chung H. F. , Götz W. , Romano L. , Krusor B. S. , Hofstetter D. , Rudaz S. , Kuo C. P. , Ponce F. A. , Johnson N. M. , Craford M. G. , Bringans R. D. 
Published: April 2011

ABSTRACTWe report on the OMVPE growth and characterization of AlGalnN and its heterostructures, including measurements of electrical properties (Hall), optical properties (photo- and cathodo- luminescence), structural characteristics (x-ray diffraction and TEM); and also the emission of InGaN/AlGaN heterostructures subject to optical and electrical pumping.
Thickness Dependence of Electronic Properties of GaN Epi-layers
Authors: Götz W. , Walker J. , Romano L.T. , Johnson N.M. , Molnar R.J. 
Published: April 2011

ABSTRACTThe electronic properties of heteroepitaxial GaN were investigated for unintentionally doped, n-type films grown by hydride vapor phase epitaxy on sapphire substrates. The GaN layers were characterized by variable temperature Hall-effect measurement, capacitance-voltage (C-V) measurements, and deep level transient spectroscopy (DLTS). The measurements were performed on as-grown, 13 μn thick films and repeated after thinning by mechanical polishing to 7 μm and 1.2 μm. The room temperature electron concentrations as determined by the Hall-effect measurements were found to increase from ∼1017 cm−3 (13 μm) to ∼1020 cm−3 (1.2 μm) with decreasing film thickness. However, the C-V and DLTS measurements revealed that the ionized, effective donor and deep level concentrations, respectively, remained unchanged in regions close to the top surface of the films. These findings are consistent with the presence of a thin, highly conductive near interface layer which acts as a parasitic, parallel conduction path. Possible sources of such a shunt near the GaN/sapphire interface include oxygen contamination from the sapphire substrate or a structurally highly defective, 300 nm thick interface layer.
Persistent Photoconductivity in p-Type GaN Epilayers and n-Type AlGaN/GaN Heterostructures
Authors: Li J. Z. , Lin J. Y. , Jiang H. X. , Khan M. A. , Chen Q. , Salvador A. , Botchkarev A. , Morkoc H. 
Published: April 2011

ABSTRACTPersistent photoconductivity (PPC) effect has been observed in p-type GaN epilayers grown both by metal-organic chemical vapor deposition (MOCVD) and reactive molecular beam epitaxy (MBE) as well as in a two-dimensional electron gas (2DEG) system formed by an AlGaN/GaN heterostructure grown by MOCVD. Its properties have been investigated at different conditions.
P-Type Conductivity with a High Hole Mobility in Cubic GaN/GaAs Epilayers
Authors: As D. J. , Rüther A. , Lübbers M. , Mimkes J. , Lischka K. , Schikora D. 
Published: April 2011

ABSTRACTTemperature dependent Hall-Effect-measurements on unintentionally doped cubic GaN epilayers grown by molecular beam epitaxy (MBE) are reported. The cubic GaN layers have been deposited on semiinsulating (001) GaAs-substrates under N-stabilized growth conditions which were controlled by in-situ reflection high energy electron diffraction (RHEED) measurements. GaN-layers, which were fabricated under N-stabilized conditions have a (2×2) surface reconstruction during growth and show p-type conductivity. At room temperature the measured hole concentrations and mobilities are p = 9.7* 1012 cm-3, μp ≅ 350 cm2/Vs, respectively. Temperature dependent measurements of the carrier concentration yield an acceptor activation energy of EA = 0.445 eV. The nature of these defects will be discussed in view of intrinsic defects proposed by theoretical calculations already published in literature. The temperature dependence of the mobility is dominated by polar optical phonon scattering in the investigated temperature range.