bluuebunny/crossref_metadata_2025 huggingface dataset:
Interfacial Shear Strength of Ion Beam Modified UHMW-PE Fibers in Epoxy Matrix Composites
Authors: Ozzello A. , Grummon D. S. , Drzal L. T. , Kalantar J. , Loh I-H. , Moody R. A.
Published: March 2011

Ultra-high molecular weight polyethylene fibers possess exceptional strength and stiffness combined with low density. Their use as reinforcements in polymer matrix composites has, however, been limited by poor fiber adhesion. In the present study, individual fibers of UHMW-PE (Allied-Signal SPECTRA-1000) were modified by direct implantation of N+, Ti+ and Ar+ ions, at energies between 30 and 100 KeV, to doses ranging between 1x1014 and lx1015 ions/cm2. Fiber tensile strength was generally unaffected by these irradiations. Single-fiber droplet pull-off tests using DGEBA Epoxy with m-PDA curing agent have shown that ion beam surface modification of the fibers can give an increase of over 300% in interfacial shear strength (ISS). The improvements were found to vary with dose but were relatively insensitive to implant species. TEM observation of transverse microtomed sections confirmed a substantial improvement in fiber-matrix adhesion for ion beam modified UHMW-PE composites.
Electrophoretically Applied Dielectrics for Amorphous Metal Foils Used in Pulsed Power Saturable Reactors.
Authors: Sharp D. J. , Harjes H. C. , Mann G. A.
Published: March 2011

Amorphous metal foil-wound inductors have been tested as ferromagnetic saturable inductive elements for pulsed-power (multi-terawatt) switching modules in the inertial confinement fusion program at Sandia National Laboratories. Saturation switching may provide large 100 ns current bursts necessary to accelerate ion beams for the fusion fuel pellet implosion required, for example, in PBFA (particle beam fusion accelerator) operation.

In simulated capacitor testing premature dielectric breakdown of thin polyethylene terephthalate film insulation in the inductor windings occurs at considerably below 2500 V. This appears to be due to inadvertant dielectric damage from micro-spikes on the amorphous foil surface. Electron micrographs and dielectric breakdown data illustrate that electrophoretically-applied dielectric coatings, deposited from organic aqueous colloid dispersions, can be used to provide insulating coatings on the foil which provide a 240% improvement (6000 V) in the breakdown strength of wound amorphous foil inductors.

The theory and operation of a dedicated electrophoretic continuous coating system is described. The machine was constructed and successfully applied for dielectric coating of amorphous metal foil. Additional possible applications exist for practical dielectric coating of metallic films or foils used in various commercial wound-type capacitor structures.
Solvent and Curing Effects on Diffusion at Polyimide Interfaces
Authors: Tead S. F. , Kramer E. J. , Russell T. P. , Volksen W.
Published: March 2011

Interdiffusion at interfaces between deuterated polyamic acid (d-PAA) and polyimide (PI) films was investigated with forward recoil spectrometry, an ion beam analysis technique. The PI films were prepared by spin - coating a solution of PAA on a silicon substrate, followed by an anneal at a temperature Ti, which produced partial or complete conversion of the PAA to PI. An overlayer of d-PAA was added in one set of samples by spin - coating from solution and in another set by transferring (in the absence of solvents) a dry d-PAA film onto the PI surface. The bilayer samples were then either annealed at a temperature Td or allowed to stand at room temperature. Bilayers prepared by spin - coating d-PAA from solution directly on partially cured PI films had interdiffusion distances w that decreased with increasing values of Ti to immeasurable levels by Ti = 200 °C. The decrease in w with increasing Ti is thought to be caused by a positive Flory parameter between PAA and PI which increases with the imide fraction in the PI film; the result is an increasing immiscibility between the swollen polymer layers. No interdiffusion occurred in the solventless - transfer samples for any combination of temperatures Ti or Td from room temperature up to 400 °C. Post - annealing of spin - coated bilayers at a temperature Td up to 400 °C was ineffective in producing any additional interdiffusion. Both of these results indicate that thermally activated interdiffusion (even for initially unimidized samples) does not exist in the absence of solvents, an effect attributed to the rapid increase of the glass transition temperature of the polymer with imidization.
Determination of the Bond Strength of a Metal Coating on a Substrate
Authors: Sachse Wolfgang , Kim Kwang Yul , Conway H. D.
Published: March 2011

This paper reviews the principles and describes new procedures for determining the bond strength of a metal film on a substrate. Considered are mechanical, electrical, acoustical and thermal measurements. Particular attention is placed on techniques which permit an unambiguous connection to be made between measured quantitites and the parameters by which the adhesive strength of a coating on a substrate can be determined.
Characterization of Nanophase Materials by X-Ray Diffraction and Computer Simulation
Authors: Eastman J. A. , Thompson L. J.
Published: March 2011

X-ray diffraction experiments on nanophase Pd have been performed with the primary goal of determining the nature of grain boundary structures in nanophase materials. A kinematical diffraction analysis has been developed to interpret x-ray θ-2θ data by comparing actual scans with scans produced by computer simulation. This simulation program has been used to explore the effects on diffracted intensity of a variety of microstructural and grain boundary structural parameters such as void concentration, grain size, grain boundary width, and changes in interplanar spacing and density in grain boundary regions. It has been found that a reasonable match to experimental data is produced by at least two model structures; in one, the material contains randomly positioned voids or vacancies, while in the other, the interplanar spacings in grain boundary regions are varied with respect to the spacings found in the grain interiors.
Influence of Substrate on Cracking of Vapour-Deposited Thin Films Due to Residual Stresses
Authors: Fisher Robert M. , Duan J.Z.
Published: March 2011

The influence of the substrate material on the column and grain microstructure, the residual stresses, crack patterns and delamination of Cr films has been investigated using TEM, SEM, and X-ray diffraction. The inter-influence of these factors which determine the long term reliability of microelectronics is discussed. When interfacial adhesion is very low, as may be the case with some polymer substrates, cracking occurs discontinuously during film formation each time the stress exceeds the critical value for fracture.
Kinetic and Thermodynamic Properties of Nanocrystalline Materials
Authors: Averback R.S. , Hahn H. , Hö;fler H.J. , Logas J.L. , Shen T.C.
Published: March 2011

A new class of materials with ultra small grain size has recently been synthesized by combining the methods of inert gas condensation of metal vapors and in situ powder compaction. These ‘nanocrystalline’ materials, with grain sizes of 5-10 nm, can have over 30% of their atoms lying in the highly disordered interfaces or grain boundaries. Because of their unique atomic structure, nanocrystalline materials often have properties far different from their bulk counterparts. In addition, kinetic processes can be rapidly accelerated due to the short diffusion distances between grains. In this review, we will report on the thermodynamic properties and reaction kinetics of nanocrystalline metals and on such kinetic properties as sintering and grain growth in nanocrystalline ceramics.
Measurement of Bond Strength at Metal/Ceramic Interfaces
Authors: Nutt Gerald L. , Lai William , Froeschner Kenneth E. , King Wayne E.
Published: March 2011

We report on a novel method for measuring the bond strength of metal/ceramic interfaces. Test specimens are created by vapor depositing a metal film on a ceramic substrate. The specimen is impacted with a thin metal flyer sending a short planar shock pulse into the ceramic. If the shape and amplitude of the wave is properly controlled the interface will spontaneously debond creating new free surfaces.

Measurements indicate the debonding process occurs in less than 1.0 ns, which we believe is too short for crack propagation along existing flaws. Therefore, we conclude that simultanious breaking of atomic bonds rather than propagation and coalescence of cracks is the means by which the film and substrate are separated. The free surface velocity of the metal overlayer is monitored during spall by laser interferometry. The data constitute a direct measurement of the bond strength. The measured bond strengths are reproducible and do not show a dependence on shock amplitude for identically prepared specimens.
Continuous-Film Thickness Determination by AES of Cr Overlayers on Cu Surfaces
Authors: Lefakis H. , Ho P.S.
Published: March 2011

The characteristics of Cr coverage of Cu surfaces, including determination of tc, the minimum average film thickness required for formation of a continuous film, have been studied in-situ by Auger Electron Spectroscopy (AES). Auger signal intensities of substrate and deposit were monitored during Cr film growth by vapor deposition in UHV. It was shown that substrate surface morphology (roughness) has a dominant effect on coverage rate and tc. Slower coverage rates and larger tc′s were effected by the presence of native oxides, substrate heating (to 330°C) and H2O-vapor rich (5×10−5 Torr) ambient during Cr deposition. Surface oxides seemed to affect more the coverage of a smooth than a rough surface. Conversely, substrate heating affected more the coverage of a rough surface. The combined effect of substrate heating and water vapor rich atmosphere was pronounced for both smooth and rough surface coverages. Some of the main factors controlling these effects are discussed.
Electron Microscopy Analysis of Aluminous Porcelain-Tin Oxide Coated Platinum Bonds
Authors: Ji Huaxia , Marquis P. M. , Loretto M. H.
Published: March 2011

The structure of the bond between dental aluminous porcelain and tin oxide coated platinum foils, used in dental jacket crowns, has been studied using analytical electron microscopy of crosssectioned specimens. It has been shown that the tin oxide is in the form of stannic oxide (SnO2) and that some of the oxide dissolves into the glass. It has also been demonstrated that the platinum foil is strained immediately adjacent to the interface.
Atomic Matching Across Internal Interfaces
Authors: Merkle Karl L.
Published: March 2011

The atomic structure of internal interfaces in dense-packed systems has been investigated by high-resolution electron microscopy (HREM). Similarities between the atomic relaxations in heterophase Interfaces and certain largeangle grain boundaries have been observed. In both types of interfaces localization of misfit leads to regions of good atomic matching within the interface separated by misfit dislocation-like defects. It appears that, whenever possible, the GB structures assume configurations in which the atomic coordination is not too much different from the ideal lattice. It is suggested that these kinds of relaxations primarily occur whenever the translational periods along the GB are large or when the interatomic distances are incommensurate. Incorporation of low index planes into the GB appears to lead to preferred, i.e. low energy structures, that can be quite dense with good atomic matching across a large fraction of the interface.
The Study of Contamination of Carbon, Boron, and Oxygen in LEC-GaAs
Authors: Itoh Y. , Takai M. , Fukushima H. , Kirita H.
Published: March 2011

Carbon in LEC GaAs was found to be introduced as CO from the ambient atmosphere; the oxygen concentration in the crystals decreased with increase in the duration of melting. An equilibrium segregation coefficient of oxygen in GaAs crystals was found by charged particle activation analysis to be 0.1, the value of which was smaller by a factor of 3~4 than that reported before.
Depth Sensitive Imaging of Defects in Epilayers and Single Crystals Using White Beam Synchrotron Radiation Topography in Grazing Bragg-Laue Geometry.
Authors: Dudley M. , Yao G.-D. , Wu J. , Liu H.-Y.
Published: March 2011

The technique of Synchrotron White Beam topographic imaging in grazing Bragg-Laue geometries has been developed at the Stony Brook synchrotron topography station at the NSLS. This technique enables imaging of defects in subsurface regions of thickness which can range from hundreds of Angstroms to hundreds of microns as determined by the penetration depth of the X-rays. This penetration depth, which is shown to be determined by the kinematical theory of X-ray diffraction, can be conveniently varied, in a controlled manner, by simple manipulation of the diffraction geometry, thereby enabling a depth profiling of the defect content.

The fundamentals of the technique are described, and its advantages and disadvantages compared to existing techniques are discussed in detail. Examples of application of the technique in the characterization of defects in thin epitaxial films of GaAs on Si, are given, and the general applicability of the technique is discussed.
Formation of Three Red-Shift Emissions in Heavily Germanium-Doped P-Type GaAs Grown By MBE
Authors: Makita Y. , Yamada A. , Shibata H. , Asakura H. , Ohnishi N. , Beye A. C. , Mayer K. M. , Kutsuwada N.
Published: March 2011

Molecular beam epitaxy (MBE) of Ge-doped GaAs was made, in which As4 to Ga flux ratio :γ and Ge concentration :[Ge] were used as growth parameters. Photoluminescence (PL) spectra at 2K for slightly Ge-doped GaAs revealed that for γ =1 the emission of excitons bound to neutral Ge acceptors (A°,X) was the dominant one. With increasing γ ,(A°,X) was found to be steeply suppressed and at around γ=1.1, (A°,X) was totally quenched. For γ higher than 1.4, the emission of excitons bound at neutral Ge donors (D°,X) was gradually enhanced and for γ =11, (D°,X) became the principal one. Through van der Pauw measurements, samples with [Ge] around 1×1017cm-3 presented type conversion at around γ=1.7. In this series, the sample with γ =1.0 indicated a strong specific emission, [ g-g], which is formed just below (A°,X) and exhibited a strong energy shift towards lower energy sides (red shift) with increasing [Ge]. [g-g] was theoretically attributed to the pairs between excited-state acceptors. Since [g-g] is known to be easily quenched by small amount of donors, the formation of predominant [g-g] for γ =1 assures that very low-compensated p-type GaAs were grown by using this typically am-photeric impurity. We fabricated a series of p-type Ge-doped GaAs by keeping γ =1 in which the net hole concentration, │ NA-ND │ as high as 1×1020cm-3 was attained. We found four emissions which exhibited significant energy shifts with increasing │ NA-ND │ . From │ NA-ND │ ~1×1016 cm-3, [g-g] begins to appear as a dominant emission and at │ NA-ND │ ~ 1×1017 cm-3, another red shift emission, [g-g]2 begins to be formed parralelly on the higher energy side of [g-g]. It is interesting to note that both [g-g] and [g-g]2 seem to be totally quenched by the further increase of [Ge]. The emission due to band to Ge acceptor,(e,Ge) does not change its central energy until [Ge]= 5×-1018cm-3 and for larger [Ge] it turned into a new broad emission,[g-g]β showing a steep red energy shift. [g-g]α was formed on the higher energy side of (e,Ge) and indicated a systematic blue energy shift with growing [Ge] larger than 1×1019cm-3. [g-g]α was theoretically explained to be the emission due to the pairs between ground-state acceptors.
Photoluminescence Study of GaAs Diffused with Li
Authors: Gislason H. P. , Sveinbjörnsson E. Ö. , Monemar B. , Linnarsson M.
Published: March 2011

We present a detailed study of the photoluminescence (PL) properties of a wide range of GaAs material diffused with the group I element Li. The effects of the Li diffusion are investigated through its effects on existing photoluminescence bands in the as-grown material as well as the appearence of new such bands. Among new PL bands resulting from the Li doping of n-type and semi-insulating material the most pronounced ones are a strong deep band at 1.34 eV and shallower bands at 1.45 and 1.48 eV. The origin of these PL bands will be discussed.
The Role of Oxygen in p-Type InP
Authors: Michel J. , Jeong J. , Lee K.M. , Kimerling L.C.
Published: March 2011

We have studied the influence of oxygen on the optical properties of Be implanted InP. Be implanted p-type InP without oxygen shows a strong deep photoluminescence (PL) band at 0.82 eV following anneal. As the oxygen concentration increases, the 0.82 eV PL-band disappears. We attribute the disappearance of this PL-band to the formation of oxygen complexes with the implantation induced defects. In epitaxial grown, nominally undoped InP a new PL-line is observed at ~1.2 eV. The paramagnetic state of the phosphorus on indium P^ antisite is observed by optically detected magnetic resonance (ODMR) as a modulation of the photoluminescence in all Be implanted samples without oxygen. The antisite resonance is detected as a reduction of the 0.82 eV PL-band and the 1.2 eV PL-band. The observation of the Fe3+ resonance by ODMR spectroscopy is reported for the first time.
Mid-Infrared Spectral Photoresponse of Semi-Insulating GaAs
Authors: Brown G.J. , Mitchel W.C.
Published: March 2011

We have developed a characterization technique using spectral photoconductivity that is capable of identifying deep energy levels in gallium arsenide. Our technique requires less sample processing than deep level transient spectroscopy (DLTS) and can be used on semi-insulating (si) gallium arsenide. The technique uses a mid-infrared fourier transform spectrometer for rapid photoresponse versus wavelength measurements. Using this technique we have observed evidence of several below mid-gap energy levels in undoped si gallium arsenide by the spectral PC technique. Spectral PC measurements were made on si GaAs before and after illuminating the cooled samples with high intensity white light at 8K. The PC spectrum typically showed a broad photoresponse that was attributed to multiple energy levels being present in the material. The observed energy levels were: 0.54 eV, 0.44 eV, 0.25 eV, 0.17 eV, 0.14 eV and ~0.10 eV. The shallow photoresponse from the carbon acceptor was not observed. The most striking spectral feature was a sharp ionization edge at about 0.44 eV in all of the samples studied. This energy level correlates to the 0.43 eV intrinsic defect level that has been observed by temperature dependent Hall effect measurements. The 0.44 eV level was also observed in our PC spectrum of a n-type Bridgman grown sample that had shown the 0.43 Hall effect level. The presence of additional deep levels in concentrations comparable to those of EL2 and carbon indicates that the simple model for compensation in si GaAs which invokes only EL2 and shallow impurities needs revision.
Deep Level Luminescence in InP: Phonon Feature Analysis
Authors: Banerjee S. , Srivastava A.K. , Arora B.M.
Published: March 2011

The phonon features in the deep level luminescence (PL) bands related to Fe and Mn and native defects in InP have been clearly identified and the lineshape of the bands are analysed using configuration coordinate model. A consistent set of phonon parameters are determined for the first time.
The Nature of Native Defects in LEC grown Semi-Insulating GaAs by Thermally Stimulated Current Spectroscopy
Authors: Fang Zhaoqiang , Shan Lei , Schlesinger T. E. , Milnes A. G.
Published: March 2011

Traps have been studied by thermally stimulated current spectroscopy (TSC) with intrinsic (1.96 eV) and extrinsic (1.15 eV) light for both In doped and undoped LEC materials grown under various non-stoichiometric conditions. Significant differences are seen in the bulk trap spectra associated with Ga-rich and As-rich material and with isoelectronic In doping. Proximity wafer-annealing at 950° C has been shown to improve minority carrier lifetime in n-type GaAs and we show that in semi-insulating GaAs this causes changes in trap structure. From such thermal studies and the effects of non-stoichiometric growth, the probable nature of the traps commonly seen is inferred.
Comparative Optical Studies of Cu, Mn, and C Impurities in Bulk Lec grown GaAs by Electron Beam Electroreflectance (EBER) and Photoluminescence (PL).
Authors: Herman M. H. , Pearah P. J. , Elcess K. , Ward I. D.
Published: March 2011

We have used 300K Electron Beam Electroreflectance (EBER) and 4. 2K photoluminescence (PL) to measure optical transitions in a series of LEC grown GaAs samples. The contaminants primarily consisted of the individual elements Cu, Mn, and C at levels above 1016/cm3. In unmodified control samples we find evidence of strong excitonic effects in the EBER lineshape even at 300K. For the contaminated samples, we find characteristic impurity transitions below the E0 bandgap of the GaAs in both optical spectroscopies. However, in general the estimated impurity binding energies by EBER are not equivalent to established PL or DLTS values. Specifically, from EBER data we find below E0 (1.424eV at 300K) a Cu peak near 49meV (1.375eV) and a C peak about 39meV (1.385eV) below E0 . An EBER spectrum of the Cu-contaminated sample at 124K shows an asymmetric Cu impurity peak 47meV below E0 . The C feature has been ascribed to either Si or Ge from corresponding PL energies by several earlier researchers. Two samples which had been implanted with Mn and annealed show a peak about 43meV below E0 (1.381eV), and what appears to be a sharp, excitonic transition 10 to 16meV above the E0 . Although these features may be due to Mn alone, the latter observation is suggestive of strain-induced valence band splitting.

The correlated appearance of impurity peaks below the split-off E0 +Δ0 band may allow their assignment to either donors or acceptors in modulated reflectance studies [1,2]. None of the present cases showed corresponding transitions below E0 +Δ0 , suggesting that the observed impurity features arise only from acceptor transitions. Alternatively, the reduction of light penetration into the GaAs above the E0 bandgap, reducing the sample interaction volume, may also explain this null observation.
Ge Related Deep Level Luminescence in InGaAs Lattice Matched to InP
Authors: Chandvankar S.S. , Srivastava A.K. , Arora B.M. , Sharma D.K.
Published: March 2011

Photoluminescence and Hall measurements are reported on Ge doped InGaAs layers lattice matched to InP. Ge doping of these samples results in highly compensated material, with the highest Ge content sample giving a p type conductivity with carrier concentration of 5 ×1017 cm-3. Low temperature PL spectra of these samples show a broad peak from 0.55 to 0.77 eV due to Ge. The peak of luminescence shifts to lower energy with increasing Ge content. The peak position shifts to higher energy with increasing excitation like in a D-A pair transition. The PL spectra have been explained on the basis of a model which assumes tail states near the band edges due to disorder produced by the presence of Ge in the lattice.
High Performance Photoluminescence Spectroscopy using Fourier Transform Interferometry
Authors: Thewalt M.L.W. , Nissen M.K. , Beckett D.J.S. , Lundgren K.R.
Published: March 2011

We present recent results on the applications of Fourier transform techniques to photoluminescence spectroscopy as it relates to both basic and characterization-related semiconductor research. The emphasis here is on demonstrating the advantages of these methods in situations requiring very high spectral resolution and/or very high sensitivity. We also provide an example of the utility of interferometry in performing photoluminescence excitation spectroscopy in spectral regions where broadly tunable laser sources are not readily available.
Photoconductivity Study of CrB and CrI in Silicon
Authors: Schlette A. , Klenle R. , Dörnen A. , Kürner W. , Thonke K.
Published: March 2011

We observe in photoconductivity (PC) measurements EMT-like excited states of the pseudodonor CrB, which are responsible for the capture of free electrons due to their short lifetime. The energetic position of the ground state can be located at Ev + (292 ± 5) meV. A finestructure of the (CrB)° transition consisting of at least 15 components is observed in PC and high-resolution Fourier transform photoluminescence. In acceptor-free silicon a step in photoconductivity at 205 ± 10 meV is ascribed to interstitial Cr, whereas a second step at ~ 425 meV could be due to substitutional Cr.
Formation of In-Cu Pairs in Silicon During Chemomechanical Polishing
Authors: Wichert Th. , Keller R. , Deicher M. , Pfeiffer W. , Skudlik H. , Steiner D.
Published: March 2011

Using the perturbed γγ angular correlation technique (PAC) the pairing of Cu with the radioactive acceptor atom 111In in Si is detected. Because of the identity of the electric field gradients the so-called X defect, observed after chemomechanical polishing of Si wafers and known of neutralizing acceptor atoms in Si, is identified as a Cu atom. It is also shown that as-delivered Si wafers already contain Cu atoms which neutralize acceptor atoms if the wafers are annealed at 1173 K.
Strain Induced Intrinsic Quantum wells as the Origin of Broad Band Photoluminescence in Silicon Containing Extended Defects
Authors: Weman H. , Monemar B.
Published: March 2011

A new recombination mechanism occuring in semiconductors containing extended defects is presented. The model is based on experimental data both from hydrogen plasma treated silicon, containing extended defects like platelets, and from oxygen precipitated silicon. The broad photoluminescence bands from these samples are attributed to the heavily damaged regions surrounding the extended defects, where electrons and holes can be localized in the strain-induced potential wells. From a theoretical calculation it is shown that the compressive strain field surrounding [111] and [100] platelets are sufficient to cause a local band gap reduction of as much as 0.3 eV, consistent with the experimental data.
Identification of Radiation-Induced Defects in Si:Al
Authors: Latushko Ya.I. , Petrov V.V.
Published: March 2011

Radiation-induced defects (RD) in Si.:Al have been investigated by means of infrared absorption (IRA) and photoluminescence (PL) methods. It has been found that the main Al containing RD in electron-irradiated Si is an interstitial Al atom (Al1). In the process of annealing at about 225 °C the production of Al1-Al1 pairs takes place. The activatin energy of this RD production is 0.95 eV, which corresponds to Al1 migration energy along hexagonal interstitials. Al1 is shown to be a two - charge donor with the energy level E(+/++) = Ev + 0.20 eV. Besides the above mentioned defect as well as acceptor type defect with Ev + 0.21 eV level a number of other defects has been revealed in neutron-irradiated Si:Al. These centers give rise to a great number of IRA and PL lines in the spectral range from 0.1 to 1.2 eV. The classification of the observed defects has been done on the basis of the annealing results and uniaxial stress measurements.
Excitoic Recombination at a Transititon-Metal Related Defect in Silicon
Authors: Mcguigan K.G. , Henry M.O. , Lightowlers E.C. , Nazare M.H.
Published: March 2011

A new photoluminescence system is reported for copper-doped silicon. The luminescence system consists of two doublet zero phonon lines at 1033.51±.05 meV, 1033.62±.05 meV, 1040.05±.05 meV and 1040.17±.05 meV. We establish from Zeeman studies that the lower energy lines are isotropic magnetic triplets, and the upper energy lines are singlets. From temperature dependence measurements the energy separation between triplet and singlet states is determined to be approximately 6 meV, in agreement with the spectroscopic separation. Also from temperature dependence PL we show that the transition probability ratio for the higher and lower states is 210. We conclude that the main features of the luminescence agree with radiative recombination of excitons bound to an axial isoelectronic defect. The chemical identity of the constituent(s) involved is uncertain although the participation of copper is likely.
Light- and Heavy-Hole Bound Exciton Transitions and Free to Bound Transitions in GaxAl1-xAs/GaAs Quantum Wells
Authors: Reynolds Donald C. , Bajaj K.K.
Published: March 2011

Excitons bound to neutral donors in AlxGa1-xAs/GaAs quantum wells were observed by high resolution resonant excitation photoluminescence, and temperature dependent photoluminescence measurements. Changes in the binding energy of excitons are observed when the donors are located in the center of the well, at the edge of the well, or in the center of the barrier. The variations in these binding energies are reported as a function of well size from 75–350Å. The binding energies increased as the well size was reduced to about 100Å, with further reductions in well size they decreased.

Light-hole free excitons bound to neutral donors were observed in AlxGa1-xAs/GaAs quantum wells. The transitions were observed, using selective excitation photoluminescence spectroscopy, in the energy region between the light-hole and heavy-hole free exciton transitions where no other intrinsic transitions exist. The neutral donor-bound heavy-hole free-exciton transitions were also observed when the light-hole bound exciton transitions were observed. Quantum well structures which showed no evidence of a heavy-hole donor bound exciton also showed no evidence of a light-hole donor bound exciton.

Free to bound transitions, free hole to bound electron, have also been observed in the AlxGa1-xAs/GaAs quantum wells. The diamagnetic shift of these transitions was used to distinguish them from excitonic transitions.
Decay Measurements of Free and Bound Exciton Recombination in Doped GaAs/GaAIAs Quantum Wells
Authors: Bergman J.P. , Holtz P.O. , Monemar B. , Sundaram M. , Merz J.L , Gossard A.C.
Published: March 2011

In this study we present photoluminescence decay measurements of free exciton (FE) and bound exciton (BE) recombination in doped GaAs/AIGaAs quantum wells (QW). It is found that the FE decay time is reduced in the doped QW’s compared to similar undoped samples. The low temperature decay time of the BE is slightly longer than for the FE, with BE decay times from 300 to 600 ps for well widths of 50 to 150 Å, respectively. It is also found that the observed decay of the BE is strongly influenced by the decay time of the FE. This is especially observed in the similarity of the temperature dependence for the FE and BE decay time.
ODMR of Shallow Donors in Zn-Doped Lec-Grown InP
Authors: Trombetta J. M. , Kennedy T. A.
Published: March 2011

ODMR spectra observed while monitoring the shallow donor-shallow acceptor pair emission in Zn-doped LEC-grown InP display strong features in the region near the conduction electron value of g=1.20. In addition to a previously observed narrow line, we observe a much broader resonance which dominates at low photoexcitation intensity. This broader line is interpreted as the unresolved exchange split resonances of electrons bound to residual shallow donors. The exchange broadening arises from interactions with nearby paramagnetic centers. Both resonances result in a decrease in the shallow-donor-to-shallow-acceptor radiative recombination and give evidence for pair recombination processes which compete with this emission.
Defect Induced Luminescence from MBE Prepared Si/Si1-xGex Superlattices
Authors: Northrop G.A. , Iyer S.S. , Wolford D.J.
Published: March 2011

We report the first definitive observation of photoluminescence from Si/Si1-xGex superlattice heterostructures. Excitons bound to a deep-level radiation damage center (I1) are observed in a series of low Ge content (x = 0.05) unrelaxed structures. We also present preliminary results on photoluminescence from as-grown narrow period (Si6Ge4) superlattices.
Fermi Resonance Effects on the Vibration Modes of Hydrogen-Passivated Boron in Silicon
Authors: Watkins G.D. , Fowler W.B. , Deleo G.G. , Stavola M. , Kozuch D.M. , Pearton S.J. , Lopata J.
Published: March 2011

10B - 11B isotope shifts have been reported recently for the vibrational frequencies of hydrogen (H) and its isotope deuterium (D) in the H-B complex in silicon. The D-10 B - D11 B shift was found to be anomalously large. We show that this effect finds a natural explanation in a phenomenon called “Fermi resonance”, arising from a weak anharmonic coupling between the second harmonic of the transverse B vibration and the longitudinal D vibration. We first present a simple classical explanation of the effect in terms of a “parametric oscillator”, or a child pumping a swing. We then outline a simple quantum mechanical treatment that provides a satisfactory quantitative explanation of the results. Our calculations also predict infrared absorption at the boron second harmonic frequencies. These are observed for both 10B and 11B with intensities and polarization as predicted, providing direct confirmation of the interpretation. The Pankove Si-H-B model, therefore, remains intact.
Hydrogen Diffusion in Boron-Doped Silicon
Authors: Herrero C.P. , Stutzmann M. , Breitschwerdt A.
Published: March 2011

Infrared reflectance spectroscopy is employed to obtain hydrogen depth profiles in boron-doped silicon, hydrogenated under various plasma conditions. From the obtained profiles, H-diffusion coefficients are calculated for different temperatures and dopant concentrations. Our results are interpreted by assuming that diffusion in the bulk is limited by trapping at the acceptor sites. A binding energy of 0.6 eV is deduced for B-H pairs. We also analyze the influence of a bias applied to the sample on the hydrogenation process. This sample bias can favor or completely hinder the diffusion of hydrogen into the silicon bulk. Also, a surface oxide layer can drastically inhibit the hydrogen in-diffusion.
Structure and Metastabiltty of Muonium Centers in Semiconductors and their Simulation of Isolated Hydrogen Centers
Authors: Estle T.L. , Kiefl R.F. , Schneider J.W. , Schwab C.
Published: March 2011

The study of isolated hydrogen in semiconductors is difficult because of the tendency for hydrogen to form complexes. An alternative to direct studies of hydrogen is the study of tnuonium in semiconductors. In such experiments the muon is essentially an isotope of hydrogen with th the mass of the proton. Twenty isolated muonium centers have been observed in tetrahedrally-coordinated crystals ranging from Si to the cuprous halides. Muon level-crossing resonance has provided detailed information on neutral interstitial muonium located at a bond center in Si (the analog of the hydrogen center seen by EPR) and very near a bond center in CaP and GaAs. This paper reviews these measurements and discusses the structures and their metastabilities. Comparison is made to EPR for Si and to theoretical studies. Recent results on the metastable and stable muonium centers in CuCl are discussed.
Analysis of Real-Time Hydrogenation data from P and N-Type Silicon
Authors: Seager Carleton H. , Anderson Robert A.
Published: March 2011

Hydrogenation of metal/thin oxide/p-type silicon and metal/n-type silicon diodes has been studied using high frequency capacitance profiling. In situ observations of acceptor and donor passivation were made while H ions were implanted through thin gate metallizations. Direct measurement of ion transits at a variety of electric fields establish that a unique mobility can be assigned to positive H ions, and modeling of low and high field data in both n and p-type samples is consistent with the notion that the positive charge state is occupied ~1/10 of the time. The time dependence of hydrogen penetration for both p and n-type diodes indicates that hydrogen is, in addition to being trapped at unpassivated shallow donors or acceptors, becoming immobilized at other sites in silicon. The density of these secondary trapping sites correlates well with the shallow dopant population suggesting that additional hydrogen atoms may become trapped near already-passivated dopant atoms.
Hydrogen Segregation at the Al/Si Interface Studied Using a Nuclear Resonant Reaction
Authors: Liu Joyce C. , Marwick A.D. , Legoues F.K.
Published: March 2011

Hydrogen segregation at the interface between an epitaxial Al film and a Si (111) substrate is studied using the 1H(15N, αγ)12C nuclear resonant reaction. Hydrogen depth profiles show that H atoms diffuse through the 1600 Å thick Al layer during 500 eV H implantation and are trapped at the Al/Si interface. The total amount of interface H is about 2 × 1015 /cm2 after a 1.4 × 1018 H/cm2 implantation, and the H atoms are narrowly distributed in the direction normal to the interface. During an isothermal anneal at 360 K, the amount of interface H decreases exponentially with annealing time; and during ramp annealing from 110 to 500 K, an abrupt release of the interface H is observed at temperature around 380 K. The release rates in both cases are controlled by a first order thermally activated de-trapping process with a binding energy of 0.86 eV/atom.
Surface and Bulk Properties which Influence Ion-Beam Hydrogenation of Silicon
Authors: Anderson Robert A. , Seager Carleton H.
Published: March 2011

The time evolution of dopant passivation in p and n-type silicon Schottky and MIS barriers has been investigated for low-energy H ions implanted directly into the silicon through a 400-Å front-electrode metallization. Knowledge of the dependence of the near-surface hydrogen concentration on time and experimental parameters is crucial to the analysis of these experiments. Hydrogenation effects are observed to vanish at ion energies below 800 eV, which suggests that the front electrode, rather than being a source of H, will behave as a sink for H diffusing in the silicon. Accordingly, we show that a steady-state H concentration proportional to the ion-deposition flux and deposition depth is established in a time interval less than a second near the electrode. Although some of the mobile H appears to be in a positively charged state, we calculate that the bias voltage applied to samples has only a small influence on the near-surface H concentration. An extensive study of the effects of sample temperature, beam flux, and ion energy supports these concepts and has revealed no evidence of ion-damage induced H trapping. The possible importance of H.H recombination is suggested by data obtained at the higher H concentrations.
The Electronic Structure of Interstitial Iron in Silicon
Authors: Thilderkvist A , Grossmann G , Kleverman M , Grimmeiss H G
Published: March 2011

A donor-like spectrum in Fe-doped silicon has been studied by means of high-resolution Zeeman spectroscopy. Previous work had unambigouosly identified the center as the interstitial iron impurity and the spectrum was interpreted as due to the transitions , where an electron is excited to shallow effective-masslike donor states. In this paper, we can, by studying the transitions in a magnetic field, verify the effective-mass-like character of the loosely bound electron. Furthermore, we also obtain information on the impurity core whose level structure is reflected in the observed superposition of donor-hke Rydeberg series and whose g values determines the Zeeman splitting pattern.
Atomic Diffusion Processes in Silicon
Authors: Pantelides Sokrates T.
Published: March 2011

The mechanisms of self-diffusion and dopant impurity diffusion in silicon have been the subject of intense debate since the 1960’s. Until the mid-1980’s, there was only limited experimental information and virtually no theory. In the last five years, however, first-principles calculations of many key quantities and new experimental data have led to significant progress. This paper traces the major theoretical advances and the key experimental data that have resolved many controversies and have provided a fairly comprehensive picture of diffusion processes. Theory has also recently provided detailed microscopic information about the diffusion of interstitial hydrogen.
Pressure and Strain Effects on Diffusion
Authors: Antonelli A. , Bernholc J.
Published: March 2011

We have investigated, via parameter-free calculations, the effects of hydrostatic and nonhydrostatic strains on the energetics of defect formation and self-diffusion in silicon. The three microscopic mechanisms, vacancy, interstitial, and concerted exchange, have very similar activation enthalpies at zero pressure but exhibit different behavior with hydrostatic pressure. Our results suggest that experiments performed at different pressures can determine the relative contributions of each of these mechanisms. The calculations also show that the neutral Si vacancy has a negative relaxation volume, with the nearest neighbors of the vacancy relaxing inwards, in contrast to the Si (111) surface. Large nonhydrostatic strains, which are present in e.g. Si/GexSi1-x pseudomorphic heterostractures, substantially reduce the formation energy of the tetrahedral interstitial, but do not affect the formation energy of the vacancy. These findings suggest that, aside from being another useful tool for the investigation of self-diffusion in Si, nonhydrostatic strain may significantly affect annealing and impurity diffusion in strained heterostructures. In particular, the interstitial-assisted impurity diffusion may proceed more rapidly in Si lattice-matched to GexSi1-x, but be slowed down in GexSi1-x lattice-matched to Si. The compressed GexSi1-x layers may thus act as diffusion barriers for impurities diffusing with help of native interstitials, such as B or P.
Low-Temperature Diffusion of Dopants in Silicon
Authors: Fahey P. , Wittmer M.
Published: March 2011

It has been reported that diffusion of substitutional dopant atoms in silicon occurs during the formation of transition-metal suicides at temperatures below 300°C. By observing the diffusion enhancements of buried marker layers of Sb-, Ga-, Ge-, and B-doped silicon layers, we provide solid experimental evidence that the diffusion enhancement induced by Pd2Si formation at low temperatures is due to point defects generated by the suicide reactions. Diffusion enhancement is observed at temperatures as low as 200°C. We have found the surprising result that diffusion is asymmetric: diffusion occurs preferentially towards the suiciding interface.
Measurements of Enhanced Diffusion of Buried Layers in Silicon Membrane Structures During Oxidation
Authors: Dunham Scott T. , Agarwal Anuradha M. , Jeng Nanseng
Published: March 2011

Reported calculations of the diffusion coefficient of silicon self interstitials vary over several orders of magnitude at temperatures of interest for integrated circuit fabrication. In this work, we measure the enhanced diffusion of phosphorus buried layers while interstitials are injected at a wafer surface via thermal oxidation. The starting substrates were either float-zone silicon or Czochralski silicon with a pre-treatment to precipitate excess oxygen. The samples were prepared by implantation of phosphorus followed by the growth of a 40-60µm epitaxial layer. They were then etched anisotropically from the frontside or backside to yield membrane structures. Local oxidation was performed at 1100°C on either the frontside or backside of each wafer and buried layer diffusion was monitored, yielding information about interstitial diffusion in silicon and it’s dependence on bulk properties.
Migrations of Interstitial Atoms in Semiconductors (Surface Diffusion and Kick-Out Mechanism)
Authors: Wada Takao , Takeda Akihiro , Ichimura Masaya , Takeda Michihiko
Published: March 2011

Ge and Zn atoms were introduced into the unirradiated regions of Si at 150°C and GaAs wafers at 50°C, respectively by using the electron-beam doping method. The surfaces of Si and GaAs substrates were covered partially by the overlayers of Ge and Zn sheets, respectively. The only surfaces of the Ge and Zn sheets were irradiated locally. with high energy electrons at 7MeV with the fluences of 5×1017 – 1×1018 electrons cm-2 . Even at a distance of ~10mm from the irradiated overlayers in the Si and GaAs substrates, Ge and Zn atoms respectively, whose interstitials may migrate the unirradiated regions, were detected by SIMS measurements. PL signal due to band-to-acceptor (ZnGa ) transition at 1.48eV becomes observable after annealing at 800°C for 20mm in the unirradiated GaAs region, which is separated from Zn sheet by nearly 10mm.
High and Low Temperature Measurements of the Chromium Diffusivity in Silicon
Authors: Zhu J. , Barbier D.
Published: March 2011

By grouping high and low temperature diffusivity measurements in boron-doped silicon, a new diffusivity law for chromium in the 20–1050 °C temperature range has been established. High temperature diffusivities were deduced from erfc fits of chromium-boron pair profiles measured by means of Deep Level Transient Spectroscopy in chromium-plated substrates, after annealing for a short time in a lamp furnace. Low temperature diffusivities were derived from the association time constants of the chromium-boron pairing reaction in chromium-contaminated specimens. The whole data points were well fitted using the following expression for the diffusion coefficient: D= 2.6×10-3 exp(-0.81 ± 0.02 eV/kT). Because of the wide 1/T interval available, the migration enthalpy value is more accurate than the previous determinations using only high temperature diffusivity results.
Precipitation of Copper and Cobalt at Grain Boundaries in Silicon
Authors: Jendrich U. , Möller H. J.
Published: March 2011

The precipitation of copper and (radioactive) cobalt at low energy grain boundaries in polycrystalline silicon and bicrystals is investigated. The metals are diffused in from a surface source between 800 - 1000 °C and the precipitation after cooling down is studied by TEM (for Cu) and Mößbauer spectroscopy (for Co). The precipitates are metal suicides. For copper it is shown that they appear in form of colonies containing hundreds of precipitates with a particle size between 5-60 nm. In the grain boundary they nucleate preferentially at dislocations and steps. The distribution and size of the precipitates depend on the cooling rate after the diffusion. In the vicinity of the grain boundary the volume is depleted from the impurities.
Annealing of Ion Implanted Tin in Silicon: a RBS/ Channeling, Mössbauer Spectroscopy and Tem Investigation of Solubility and Residual Defects.
Authors: Kringhøj P. , Nylandsted Larsen A. , Petersen J. W.
Published: March 2011

By combining RBS/channeling, Mössbauer spectroscopy, and TEM measurements on implanted Sn in Silicon, the solid solubility has been determined at 1025°C, 1075°C, and 1188°C to be respectively, 6.1 , 4.8 , 3.1·1020 cm-3.
A Comparison of the Diffusivity of As and Ge in Si at high Donor Concentrations
Authors: Kyllesbech Larsen K. , Gaiduk P. , Nylandsted Larsen A.
Published: March 2011

The effect of high background doping (8×1019 - 5×1020 cm-3 ) on the diffusion of Ge and As in Si has been studied. A strong enhancement is found for As for donor concentrations higher than ~2×1020 cm-3 , but not for Ge. These experimental findings are discussed within the percolation model.
Diffusion of Ga Vacancies and Si in GaAs
Authors: Kahen K.B. , Lawrence D.J. , Peterson D.L. , Rajeswaran G.
Published: March 2011

Using the Si-pair diffusion formalism of Greiner and Gibbons, a new Si diffusion model is developed based on the dominant diffusion species being SiGa+ - VGa- pairs, where VGa is the Ga vacancy. In the model, the unknown parameters are the pair diffusion coefficient (Dp) and the equilibrium constant, which are fitted to the experimental data. Dp is also derived to be equal to one-half the Ga vacancy diffusivity. To verify this relation, an experiment to determine the VGa diffusivity, Dv, is performed. A relation for Dv of the form 0.962 exp(-2.72 eV/kT) cm2/s is obtained, and it is shown that the fitted Dp values are indeed approximately equal to 0.5 Dv.