bluuebunny/crossref_metadata_2025_split huggingface dataset:
The Double Donor Issue of the EL2 Defect in GaAs.
Authors: Manasreh M. O. , Brown G. J. 
Published: March 2011

AbstractPhoto-induced changes in the infrared (IR) absorption spectrum of the EL2 defect in undoped and lightly alloyed unannealed GaAs materials grown by the liquid-encapsulated Czochralski technique were observed under a monochromatic light irradiation. These changes were attributed to the change of the charge states of EL2. The spectrum which is believed to be due to the charged EL2 exhibits a complex structure with two peaks at 1.07 and 1.32 eV and a shoulder at 0.94 eV. The EL2+/2+ → EL20/+ and EL20/+ → EL2+/2+ transitions were obtained by illuminating the sample with 0.7 ≤ hv ≤ 0.95 eV and 1.3 ≤ hv ≤1.5 eV, respectively. The transformation EL2+/2+ ↔ EL20/+ can be achieved in less than 10 sec and can be repeatedly switched back and forth between the two states. Fourier-transform photoconductivity (FTPC) measurements were performed on a large number of samples both semi-insulating and n-type. Two broad peaks were observed in the FTPC spectra with thresholds at 0.80 and 0.95 eV. The photoquenching and thermal recovery properties of these two peaks are identical to those of EL2. Both IR and FTPC results suggest strongly that EL2 is a double donor.
Absolute Pressure Dependence of the Second Ionization Level of EL2 in GaAs
Authors: Bliss D.E. , Walukiewicz W. , Nolte D.D. , Haller E.E. 
Published: March 2011

AbstractWe report the results of DLTS experiments under uniaxial stress on the second ionization level of EL2(++/+) in p-type GaAs. We measured the shift in the hole emission rate as a function of stress applied in the [100] and [110] directions. By modeling the valence band with two independently displacing bands and appropriately derived effective masses, we obtain a small absolute hydrostatic pressure derivative for the defect, 39 ±15 meV GPa-1. The shear contribution is negligible. This result is very different than for the first ionization level, EL2(+/o) with a emission energy pressure derivative of 90 ±15 meV GPa-1. The difference can be accounted for by the pressure dependence of the electron capture barrier of EL2(+/o), 49 ±15meV GPa-1. The absolute pressure derivatives of the two levels are then comparable and in good agreement with simple theory for Ga site point defects.
The Role of EL2 for the Mobility-Lifetime Product of Photoexcited Electrons in GaAs
Authors: Valley G. C. , von Bardeleben H.J. , Rajbenbach H. 
Published: March 2011

abstractThe mobility lifetime products for photo-electrons in semi-insulating GaAs, which fit successfully the results of photorefractive studies undertaken in the presence of electric fields are three orders of magnitude smaller than those inferred from transport measurements or from the photorefractive effect with no applied electrical field. Consideration of enhanced recombination via EL2 effective-mass states linked to the L-conduction band minimum allows us to fit the dependence of the photorefractive beam coupling gain coefficient on the grating period for both AC fields and moving gratings. A cascade-capture process, which is three orders of magnitude faster than recombination by multiphonon emission from the Γ band to EL2, leads to greatly reduced mobility-lifetime products for field strengths greater than 1 kV/cm. Our results establish the dominant influence of the EL2 defect properties on the recombination processes essential for modelling and optimizing the photorefractive effect in semi-insulating GaAs.
Electron Scattering by Native Defects in Uniformly and Modulation Doped Semiconductor Structures
Authors: Walukiewicz W. 
Published: March 2011

AbstractFormation of native defects in GaAs is described in terms of the amphoteric native defect model. It is shown that Fermi energy induced formation of gallium vacancies is responsible for the limitations of maximum free electron concentration in GaAs. The effect of the defects on electron mobility in heavily doped n-GaAs is quantitatively evaluated. Defect scattering explains the abrupt reduction of electron mobility at high doping levels. Also, it is demonstrated that native defects are responsible for the mobility reduction in inverted modulation doped GaAs/AlGaAs heterostructures. The amphoteric defect model also explains a distinct asymmetry in defect formation in n- and p-GaAs. In p-GaAs the Fermi level induced reduction of the defect formation energy is much smaller, and therefore the concentration of the native defects is negligible compared with the hole concentration.
Modified Optically Detected Magnetic Resonance Technique for Studies of Defects in Si and GaAs
Authors: Chen W.M. , Monemar B. 
Published: March 2011

AbstractWe discuss one of the major difficulties, namely the strong free carrier induced background signal, in studies of defects in Si and GaAs by optically detected magnetic resonance (ODMR) technique. A modified ODMR technique, namely delayed ODMR, is presented and is shown to be very successful in overcoming this difficulty.
Beryllium Doping in MBE-grown GaAs and AlGaAs
Authors: Pellegrino Joseph , Griffin James , Myers Leary , Spencer Michael 
Published: March 2011

AbstractBeryllium is an effective p-dopant in GaAs and AlGaAs and plays an important role in device characterizations of hetero bipolar transistors. This work addresses the doping and mobility properties for two series of beryllium-doped samples: GaAs and AlGaAs. Within each series the doping ranged between 3×1015cm-3 to levels of 5×1019cm-3. Mobility and carrier concentrations were obtained through Hall and Polaron measurements. The doping concentration results suggest the onset of carrier compensation at higher doping levels. One possible explanation is that for high doping levels, Be is incorporated as interstitial donors. A thermodynamic model is used to explain the observations.
Nitrogen and Phosphorous Impurities in Diamond
Authors: Jackson Koblar , Pederson Mark R. , Harrison Joseph G. 
Published: March 2011

AbstractIn this paper we use a first-principles local density approximation-based approach to study the properties of the n-type impurities nitrogen and phosphorous in diamond. We determine impurity donor level positions of 0.90 eV and 1.09 eV, respectively for C:N and C:P, measured relative to the bottom of the conduction band. We also study the energetics of impurity atom relaxation along the <111> direction in the diamond lattice. While experimental observations indicate a trigonal distortion about the impurity site, we find the on-center position for both impurity atoms to be stable against the simple <111> relaxation.
Ordering in III/V Alloys
Authors: Stringfellow G.B. 
Published: March 2011

AbstractSimple calculations using the delta-lattice-parameter (DLP) model indicate that the enthalpy of mixing is invariably larger than or equal to zero for III/V alloys, and increases with increasing difference in lattice constant for the constituent binary compounds. In terms of the regular solution model this suggests the occurrence of miscibility gaps. Solid phase immiscibility has indeed been observed in a number of systems. Nevertheless, such alloys can be grown by OMVPE, including the highly metastable alloys GaPSb and InPSb. Initially surprising was the occurrence of ordered structures in these same alloys. The regular solution model apparently specifically excludes immiscibility and ordering in the same system. However, when the positive enthalpy of mixing is due to strain energy effects, as in III/V alloys, Hume-Rothery recognized very early that such phenomena should be anticipated. This was later confirmed by detailed first principles calculations. In fact, the tendency for ordering is anticipated to increase as the difference in tetrahedral radii of the elements sharing a common sublattice increases. Thus, it is somewhat surprising that ordering was first observed in the AlGaAs system where Al and Ga have nearly equal sizes. Ordered structures have now been observed in several III/V alloy systems including the ternary systems GaAsSb and GalnP and the quaternaries GalnAsP, GalnAsSb, and AlGalnP. In this paper, ordering in other alloy systems such as GaPSb and InAsSb will be described. Surprisingly, no strong correlation between atomic size difference and the degree of ordering has been observed. Another unexpected observation is that the preferred ordered structure for most ternaries involves ordering along the {111}directions. Both first principles total energy and simple strain energy calculations indicate that such ordered structures are only slightly more stable than the disordered solid solution. Other ordered structures, including L10, where ordering occurs along the {100} directions, are considerably more stable. Both phenomena must be explained in terms of the surface kinetic processes occurring during epitaxial growth. Such an explanation is supported by the importance of kinetic parameters such as growth rate, temperature, and substrate orientation in determining both the degree of order and the specific ordered structures observed.
Ion Beam Etching of Silicon: Implantation and Diffusion of Noble Gas Atoms, and Gettering of Copper
Authors: Sawyer William D. , Schmälzlin Jörg , Weber Jörg 
Published: March 2011

AbstractDefects introduced into silicon by ion beam etching are investigated by low-temperature photoluminescence (PL) and Rutherford backseattering (RBS) measurements. The RBS results show that during the ion beam etch a highly damaged surface layer is formed which contains a large concentration of Ar atoms. The Ar atoms then diffuse out of the surface and into the crystalline bulk by some form of radiation enhanced diffusion. Annealing of the etched samples at 350°C results in the formation of noble gas defects known from previous PL studies of ion implanted silicon. When the samples are annealed at 650βC PL lines due to new defects are formed. Although little is known about their structure, we show that the new Ar defects getter small copper contaminations very effectively.
Angle Resolved XPS Analysis of Surface Region Defects in Rapid Thermal Annealed Antimony Implanted Silicon
Authors: Kumar S.N. , Chaussemy G. , Laugier A. , Canut B. , Charbonnier M. 
Published: March 2011

AbstractAngle-resolved X-ray photoelectron spectroscopy characterization of the surface region of high-dose Sb+ ion implanted silicon, after rapid thermal treatments over various temperatures, is reported. The results obtained are compared with the Rutherford backscattering data and the capacitance-voltage measurements on the metal-oxide-semiconductor mesa structures built on them. Rapid anneal at 1100 °C of the 1.4×1016 Sb+/cm2 samples showed an anomalous deep oxygen diffusion inside the implanted region.
Twinning Structure of {113} Defects in High-Dose Oxygen Implanted Silicon-on-Insulator Material.
Authors: Visitserngtrakul S. , Barry J. , Krause S. 
Published: March 2011

AbstractConventional and high resolution electron microscopy (HREM) were used to study the structure of the {113} defects in high-dose oxygen implanted silicon. The defects are created with a density of 1011cm-2below the buried oxide layer in the substrate region. The {113} defects are similar to the ribbon-like defects in bulk silicon. Our HREM observations show that two crystalline phases are present in the defect. Portions of the defects exhibit the original cubic diamond structure which is twinned across {115} planes. The atomic model shows that the {115} interface is a coherent interface with alternating five- and seven-membered rings and no dangling bonds.
Environmentally Stable, Low Dielectric Polymers from Soluble Intermediates
Authors: Mates T. , Ober C. K. , Angelopolous B. , Martin H. 
Published: March 2011

AbstractWe have investigated new polymers of poly(phenylene vinylene), PPV and poly(phenylene), PP. Like polyimides, these polymers can be spin-coated from soluble intermediates and converted to their thermally stable forms by elimination of small groups during a heating cycle. As such, these polymers are insulating. Both poly(phenylene vinylene) and poly(phenylene) also have the potential for metallic conductivity when properly doped. During curing, the complete removal of the leaving groups is important in determining the final behavior of the aromatized polymer film. Elimination of the leaving groups was followed by means of Rutherford Backscattering (RBS) and Forward Recoil Spectrometry (FRES) analysis for various curing conditions and environments. We will describe the curing and film-forming properties of these polymers, and discuss both their dielectric characteristics and thermal stability as a function of the curing conditions.
Ceramic/Polymer Nanocomposite Properties for Microelectronic Packages
Authors: Das Amitabh , Srinivasan Thallam T. , Newnham Robert E. 
Published: March 2011

AbstractThis paper reviews some of the research efforts in microelectronic packaging to develop composites with dimensions of the fillers ranging down to nanometer dimensions. Some initial experiments have been conducted with nanocomposites, where the thermal and dielectric properties of polymer/fumed silica composites have been studied. The bulk samples were prepared in different ratios of polymer to silica using polydimethyl siloxane and Cab-O-Sil. Differential thermal analyses carried out on these samples showed no changes in the samples till 330°C. The dielectric constant of the 70:30 (Cab-O-Sil- Polymer by Wt.%) composite is 3.8, similar to that of the pure silica. For the same composite the value of the thermal expansion coefficient is 350 ppm, closer to the value of pure polymer (439 ppm). It is suggested that the key to model these nanocomposites with ceramic and polymer phases is to understand the interfaces and their chemical bonding.
Structure and Properties of C-Axis Oriented AlN Films Reactively Deposited by DC Planar Magnetron Sputtering
Authors: Takahashi Takakazu , Takeda Fumio , Naoe Masahiko 
Published: March 2011

AbstractAluminum nitride (AlN) films have been deposited by reactive DC planar magnetron sputtering at a low substrate temperature of 80°C. An Al disk and either N2 or NH3 were used as a target and an ambient gas, respectively. In films deposited in N2, the c-axis of AlN crystallites was perpendicular to the film plane. On the other hand, in NH3, X-ray diffraction peaks from (100), (110) and (200) were observed. The surface and the cross-sectional microstructures of AlN films deposited in N2 were significantly different from that deposited in NH3. The surface of films deposited in NH3 was smoother than that deposited in N2. The transmittivity of films deposited in NH3 was superior to that deposited in N2 in wavelength of 275∼450 nm. Resistivities of films deposited in N2 and in NH3 were 1014sim;1015 Ω · cm. Dielectric constants of films deposited in N2, and of that deposited in NH3, were 9.7, and 9, respectively, in a frequency range of 20 kHz to 20 MHz. The structure and the properties of AlN films deposited by this method depended on kind of ambient gas.
A Technique for Brazing Aluminum Nitride Substrates
Authors: Norton M. Grant , Kajda Jacek M. , Steele Brian C. H. 
Published: March 2011

AbstractA technique for brazing aluminum nitride (AIN) using conventional (non-active) brazing alloys has been investigated. The process involves the in-situ decomposition of a metal hydride. This process alters the surface chemistry of the substrate and improves the wettability of the molten braze. The development of high strength bonding between braze and ceramic results. The ceramic-braze interface was studied using scanning electron microscopy (SEM). The nature of the interfacial reactions and the reaction products have been identified using x-ray diffraction (XRD). The progress of the reaction has been followed using differential thermal analysis (DTA).The experimental results have been correlated with thermodynamic predictions of the reaction process. In addition to joining ceramic to ceramic, braze joints of AIN to a low expansion iron-nickel lead frame alloy were made.
Microstructure and Microchemistry of Tungsten and Tungsten Compound Reactions with Aluminum Nitride Substrates
Authors: Westwood Alistair D. , Notis Michael R. 
Published: March 2011

AbstractA clear understanding of the bonding process in the cofired tungsten-aluminum nitride (W-AIN) metallized system is not currently available. Therefore, in an attempt to obtain a fuller understanding of this process, reactions between metallic W, tungsten trioxide (WO3), and calcium tungstate (CaWO4) with aluminum nitride have been studied using a variety of electron microscopy techniques. The observed reaction was found to be similar in all cases, resulting in the formation of metallic tungsten particles within the AIN substrates. A reaction sequence is proposed to explain adhesion in the W-AIN metallized system; thermodynamic calculations support the proposed reaction sequence. The adhesion in this system is due to both a mechanical fastening by an interlocking and a chemical precipitation reaction. Finally thermal conductivity measurements across the interface have been made to assess the ability of the interface to transfer heat.
Contact Reactions at Thin Film Aluminium/Transition Metal Interfaces
Authors: Schuhmacher Bernd , Köster Uwe 
Published: March 2011

AbstractContact reactions at thin film Al/TM interfaces (TM = W, Cr, Co, Zr and Ta) have been studied by means of cross sectional transmission electron microscopy. In all cases the first phase formed at the interface was the most aluminium-rich compound as given in the correspondent phase diagram: In the case of Al/W, Al/Cr as well as Al/Co growth of Al12W, Al7Cr, and Al9Co2, respectively, with rather smooth, planar morphology has been observed. On the other hand, Al/Zr and Al/Ta contacts exhibit a irregular growth morphology of Al3Zr, and Al3Ta, respectively.In addition, precipitation behaviour of rapidly solidified supersaturated Al(TM) solid solutions upon thermal annealing has been studied, in order to get a better insight on preferred orientation relationships between aluminium and the aluminides as well as on the influence of defects, e.g. grain boundaries.Based on the observed morphologies and orientation relationships a model will be proposed for the different modes of interfacial reactions, i.e. with planar or irregular growth morphology.
Phase Stability and Mechanical Behavior of Ternary Bismuth-Lead-Tin Solders
Authors: Whealon W. J. , Stone D. S. , Chang Y. A. 
Published: March 2011

AbstractResults from a phase stability study of the Bi-Pb-Sn ternary system and mechanical property data from the testing of the Bi-Pb-Sn ternary eutectic alloy are reported. It is found that the mechanical properties of the ternary eutectic alloy change considerably during cooling due to a solid state phase change at 79° C. After solidification, but prior to this phase transformation, the alloy exhibits brittle failure upon tensile loading. After the phase change high ductility is observed, bordering on superplasticity at low strain rates. Furthermore, having gone through the phase change once, the alloy remains ductile even after it is held at temperatures above 79° C. These results are interpreted in terms of the microstructures observed in the alloy.
Photosensitive Polyimides
Authors: Hiramoto Hiroo 
Published: March 2011

AbstractPhotosensitive polyimides are used as insulation and protection layers for microelectronics. They can easily give fine-patterned films with excellent characteristics of polyimides by photolithographic procedure.Photosensitive groups such as double bonds, azides, o-nitrobenzyl and o-naphthoquinonediazides. These photosensitive groups are incorporated to polymer chains through covalent bonds or acid-base ion bonds. Some polyimides have photosensitivity even without intentionally introduced photosensitive groups. Most of photosensitive polyimides are negative working, and a few of them are positive working.Characteristics of photosensitive polyimides are determined by two factors, the way of introducing photosensitive groups and the structures of polyimide backbone chains. Photosensitivity, resolution, purity and easiness of imidization mainly depends on the former factor. The film properties after curing are mainly determined by the latter. The film properties, however, are affected by the former when imide cyclization is imperfect.Photosensitive polyimides are widely used as protection and insulation layers of VLSI, multi-chip modules for computers, telecommunication, linephotosensors, thermal-heads, etc.
Microprobe Study of Chemical Inter-Grain Variation In Class-F Fly Ash: Application of Fuzzy C-Means Cluster Analysis and Non-Linear Mapping
Authors: Pietersen Hans S. , Vriend Simon P. , Poorter Rene E. P. , Bijen Jan M. 
Published: March 2011

AbstractThe chemistry of individual grains of several Class F fly ashes has been investigated by electron microprobe analysis. To interpret the analytical data-set, a combination of two multivariate statistical procedures was applied. The method involves the use of both fuzzy c-means cluster analysis (FCM) and non-linear mapping (NLM). It allows for a quick visual interpretation of the fly ash analysis and provides information which is not obtained through the use of the commonly used classical two-or three dimensional data representation plots alone. The method provides information on the occurrence of “outlying” samples, such as quartz grains, lime, calcium-sulfate or iron-containing particles. When the data-set is truncated for these outlying particles, cluster analysis of all ash data indicates that a model of 4–5 clusters can best explain chemical differences between the bulk of the particles of several class-F fly ashes. These clusters are related to each other by an inverse relation between the SiO2 and the A12O3 content, and some clusters display marked differences of either the oxides of Ti, Fe, Ca, Mg, K and/or K and Na. Inter-grain variation of one separate fly ash indicates that similar variations occur within individual fly ashes, only the absolute differences being smaller. The results are interpreted to represent either the coalescence or fusion of chemically different particles or small chemical differences in precursor clay minerals. The method of data-reduction presented here provides quick information on chemical relationships and is particularly suited to evaluate small data-sets. The method has potential to be combined with other input parameters, such as pozzolanic activity, glass content, particle size distribution and others.