bluuebunny/crossref_metadata_2025 huggingface dataset:
Formation of Niobium Carbides in High-Dose Carbon-Ion-Implanted and Annealed Niobium
Authors: Huang J. S.
Published: March 2011

Polycrystalline niobium was implanted with 200-keV C+ ions to a total fluence of 7 × 1017 carbon ions per cm2 (C/cm2). Auger electron spectroscopy (AES) analysis showed that the carbon concentration varied from 5 to 50 at.% within a depth of about 4000 Å. Glancing-angle x-ray diffraction analysis (XRDA) and transmission electron microscopy (TEM) analysis indicated that no Nb2C phase was formed and that a buried fee NbC layer was formed in the region where carbon content exceeds about 40 at.%. The absence of Nb2C was attributed to its narrow range of solubility for carbon and the low diffusivity of carbon atoms. The possibility of the NbC precipitation by nucleation and growth or by a diffusionless martensitic transformation is discussed. When the implanted samples were annealed at 1273 K for 1 h, an orthorhombic Nb2C phase formed as spherical precipitates and the implanted carbon redistributed.
Strengthening of Aluminum by Oxygen Implantation: Experimental Results and Mechanical Modeling
Authors: Bourcier Roy J. , Follstaedt David M. , Myers Samuel M. , Polonis Douglas H.
Published: March 2011

The microstructuTe and mechanical properties of high purity aluminum implanted with 20 at.% oxygen to a depth of roughly 500 nm and subjected to various thermal histories have been examined. Transmission electron microscopy and Rutherford-backscattering spectrometry were used to characterize the depth and nature of the implanted zone. As implanted, the material appears to contain a homogeneous distribution of disordered precipitates with sizes of 1.5-3.5 nm. Annealing at 450 or 550ΰC for 1 hour, induces ordering of the precipitates but only causes slight coarsening. Ultra-low load indentation hardness testing was used to probe the mechanical response of the surface-modified material. The data from the hardness tests were interpreted through the use of a finite-element model; the results indicate the flow stresses of an implanted and annealed layer are as high as 1600 MPa. The as-implanted material is much harder, approaching 3300 MPa. The degree of strengthening expected for the as-implanted and post-annealed material on the basis of the observed microstructure was estimated using several micromechanical models, and the results conform to the findings from indentation testing.
Computer Simulation of Ion Beam Enhanced Deposition of Titanium Nitride Films
Authors: Xi Wang , Jiankun Zhou , Youshan Chen , Xianghuai Liu , Shichang Zou
Published: March 2011

A Monte-Carlo computer simulation has been performed to describe, at atomic level, the growth of titanium nitride films formed by ion beam enhanced deposition (IBED). The simulation is based on a random target, fixed free path of moving particles and binary collisions. An alternate process of deposition of titanium atoms and implantation of nitrogen ions is applied instead of the actual continuous and synchronous process of IBED. According to the actual conditions, the adsorption of nitrogen gas, which is leaked out from the ion source, at the fresh titanium layer surface has been considered. In addition, the change of the composition profile and the density profile during film growth is taken into account. It is demonstrated that the width of the intermixed region between the film and substrate increases with the increase of the atomic arrival ratio, R, of implanted nitrogen ions to deposited titanium atoms. When the titanium deposition rate is low, the nitrogen concentration of the film is relatively insensitive to R, indicating that a dominant contribution to the nitrogen concentration is derived from the nitrogen gas leaked out from the ion source. The results obtained in this study are in agreement with the experimental measurements.
Low Temperature Interlevel SiO2 Layers by Photoinduced Processing
Authors: Sigmund H. , Klumpp A. , Springholz G.
Published: March 2011

Polysiloxane layers were deposited from the gas phase by photoinduced polymerization reaction of tetraethylorthosilicate (TEOS) and 02/N20. The deposition kinetics can be described by a gas phase polymerization and the subsequent condensation of the siloxane molecules. As UV light sources an ArF excimer laser (193 nm) anda 185/253 nm low pressure Hg—discharge lamp were used, the polysiloxane deposition rates are 2000 Å/min or 1200 Å/min respectively. Ina second thermal or combined thermal/ photoinduced process step the as deposited siloxane layers are transformed by hydrolysis and condensation reactions to pure Si02. The composition of the as deposited and transformed polysiloxane layers were investigated by FTIR spectroscopy. Typical examples of the step coverage and planarizing properties of the SiO2 layers for the use as interlevel dielectrics are presented.
X-Ray Photoemission Investigation of Excimer Laser Induced Etching of InP
Authors: Matz R. , Meiler J. , Haarer D.
Published: March 2011

ArF excimer laser induced etching of InP in various etch gases (HBr, HCI, CI2) is discussed with regard to its spatial resolution capability. X-ray photoemission spectra and large-area etch rate measurements published before lead to fundamental understanding and interpretation of the characteristics of etched test structures. HBr and HCI require gas phase photodissociation. CI2' in contrast, has the advantage to react spontaneously.
Local Laser Induced Etching of Copper Films by Chlorine
Authors: Tang Hua , Herman Irving P.
Published: March 2011

A focused argon ion laser was used to induce local thermal etching of copper films in the presence of chlorine gas. Raman scattering was used to follow the transformation of the copper film in situ to CuC1 and CuCl2. In some regimes the laser only induced transformation of copper to copper chloride, while in others the laser produced copper chloride and also desorbed it.
A Process Model for Reactive Ion Etching and Study of the Effects of Magnetron Enhancement
Authors: Meyyappan M. , Buggeln R. C.
Published: March 2011

Magnetron reactive ion etching has been receiving much attention since it offers low pressure, and low bias etching conditions with little damage. We have developed a process model for this process and present simulation results for boron trichloride etching of GaAs. The computed etch rates are uniform in the center with higher rates at the edges of the wafer. Flow rates and pressure can be optimized to improve uniformity. The etch rates with the aid of the magnetron are shown to be higher than the rates tor conventional reactive ion etching.
Downstream Etching of GaAs and InP Using Molecular Chlorine and Chlorine Radicals
Authors: Lishan David G. , Hu Evelyn L.
Published: March 2011

The temperature dependent etching of GaAs and InP using both molecular and remote plasma activated Cl2 and HC1 is examined. GaAs etches nearly three times faster in a remotely generated C12 plasma than in a molecular Cl2 environment with plasma off. The temperature dependance from room temperature to 250°C is similar for both cases. Significant etch rates of GaAs are observed for HC1 remotely generated plasma even at room temperature (∼1000 Å/min). Although the etch rate for InP below 150°C is quite low for either C12 or HCl, the relatively fast, temperature independent etch rate above this temperature is comparable to that of GaAs. The results are compared to RIE and a thermodynamic model.
Hollow Cold Cathode Ion Source for Reactive Ion-Beam Etching
Authors: Stognij A.I. , Tokarev V.V.
Published: March 2011

A wide-aperture reactive gas ion source has been developed for various ion-beam processings in high vacuum (p < < 5×10−2 Pa). The peculiar feature of the ion source is that two-stage self-maintained low-pressure discharge is used here as a plasma emitter. This provides high operating parameters of the source along with simple diode-type structure.
Generation of Blind Via-Holes for a High Density Multi-Chip-Module Using Excimer Lasers
Authors: Bachmann Friedrich G.
Published: March 2011

In recent years the on-chip delay has gone down much more rapidly than the signal delay in packaged circuits. As a consequence of this the packaging delay times have had to be reduced drastically, which means that a greater packging density had to be implemented. A novel planar packaging technique, used in the new Siemens main frame computer 7500 H 90 has led to considerable progress in solving this problem. An essential part of this system is a multi-chip-module which can hold up to 144 bare chips. The carrier of these IC's is a 16-layer high density multilayer printed circuit board, which is fabricated in a sequential process. Interlayer contacts are formed by 80 µm wide blind via-holes, which are generated by excimer-laser ablation of the dielectric. The process desribed in this paper shows that it is possible to produce blind via-holes with an aspect ratio of about one in an extremely reliable and reproducible way. This process is already being successfully run on a production line. It is to our best knowledge the first time excimer lasers have been used on a large-scale in an industrial environment.
Laser Deposition and Patterning of High-Temperature Superconductors
Authors: BÅuerle D. , Heitz J. , Ludorf W. , Schwab P. , Wang X.Z.
Published: March 2011

Superconducting films of Y-Ba-Cu-O and Bi-Sr-Ca-Cu-O on (100) SrTiO3 and (100) MgO substrates have been fabricated by reactive excimer-laser sputtering from ceramic targets. Film patterning by laser-induced reduction/metallization, oxidation, and ablation has been investigated.
Ultrafast Imaging of Ultraviolet Laser Ablation and Etching of Polymethyl Methacrylate
Authors: Braren Bodil , Srinivasan R. , Casey Kelly G. , Yeh Mildred
Published: March 2011

Ablation and etching of the surface of polymethyl methacrylate (=PMMA) by pulses of 248 nm laser radiation ∼20 ns full width at half maximum (FWHM) have been probed by pulses of visible laser radiation (596 nm; < 1 ns FWHM). The results were recorded photographically in real time with a set time delay between the 248 nm ablation pulse and the 596 nm probe pulse. Modification of the surface structure of the polymer at a fluence ∼ 3 J/cm2 is first visible at 12 ns and appears to be complete in ∼ 60 ns. The first manifestation of the ablation does not occur until the UV pulse is over and consists of a nearly transparent shock-wave that has an initial velocity of 6 ∼ 104 cm/sec. Solid material from the ablated zone begins to leave the surface at ∼150 - 200 ns and reaches a maximum in intensity at 6 µs, continuing for ∼ 20 µs. The average velocity of the solid material, which is probably a low molecular weight polymer of PMMA, is 1.5 ∼ 104 cm/sec. The conclusion to be drawn from the present work is that the signal measured by photoacoustic detectors does not coincide with the bulk of the material leaving the surface.
Time-Resolved Studies of Surface Melting During Laser-Induced Chemical Vapor Deposition with Laser Intensity Modulation
Authors: Comita Paul B. , Price Peter E. , Kodas Toivo T.
Published: March 2011

Thermal laser-induced chemical vapor deposition of gold deposits has been studied using a modulated Ar+ laser. Deposition of gold from dimethylgold hexafluoroacetylacetonate is accompanied by surface melting of the deposit when laser source is modulated. Time-resolved reflectance measurements have been used to study the surface reflectance during growth with modulated and unmodulated laser source. The reflectance measurements indicated that surface melting does not occur under unmodulated cw irradiation at equivalent laser intensities. Variation in the modulation duty cycle indicates that there is a minimum laser-off cycle time length required for surface melting to be observed. Evidence is presented which suggests that surface melting is due to the heat released by the exothermic decomposition of reactant adsorbed during the time that the laser intensity is off.
An Interfacial Phase Transformation in CoSi2/Si(111)
Authors: Eaglesham D.J. , Tung R.T. , Headrick R.L. , Robinson I.K. , Schrey F.
Published: March 2011

A new type of phase transformation at the interface is described in CoSi2/Si(111) B (i.e. twinned) epilayers. Thin (25Å) CoSi2 films are codeposited at room temperature on Si (111) with a Si-rich surface layer, and subsequently annealed. Plan-view transmission electron microscopy (TEM) shows that these films have low symmetry, the interface being characterised by a shift “R” between (220) planes in CoSi2 and Si. X-ray diffraction from “R” films differs from otherwise identical films either grown without Si-rich surface layer, or not annealed, which have the conventional cubic structure (“C”); R-CoSi2 cannot be indexed on a single reciprocal lattice. Cross-section high-resolution TEM suggests the presence of a separate (non-cubic) layer ≈9Å thick at the interface in these films. Annealing of R-CoSi2in-situ in the TEM shows a reversible transformation R⇔C occuring at temperatures varying from 180°C to 150K, depending on layer stoichiometry. Rt⇔C is thus a quasi-equilibrium, diffusionless transformation. We propose that R-CoSi2 lowers interfacial free energy for certain stoichiometries, but that bulk constraints stop the entire layer from transforming.
Electronic Structure of Epitaxial SiO2/Si(100) Interfaces
Authors: Motooka T.
Published: March 2011

The local densities of states (LDOS) of epitaxial SiO, layers on Si(100) surfaces have been calculated using the recursion method combined with the Harrison's universal tight-binding model. The interface states associated with strained epitaxial layers of β-cristobalite (√2×√2)R45° and tridymite (1010)<0001> || Si(100)<011> were examined. In the β-cristobalite layer, gap states due to the surface Si dangling bonds appeared while they were eliminated by H termination. In the tridymite layer, the interface states primarily composed of the surface Si back bonds appeared near the Si conduction band minimum. Comparing the calculated DOS with photoelectron spectra for initial oxidation processes of clean Si(100), it was found that the valence band spectrum from the initial oxide formed at ∼300°C resembled that of the β-cristobalite layer.
The Structure of Interfaces in Oxide Heterojunctions Formed by CVD
Authors: Tietz Lisa A. , Summerfelt Scott. R. , Carter C. Barry
Published: March 2011

Weak-beam imaging is used to characterize the interface structure of hematite (α-Fe2O3)/ sapphire (α-Al2O3) heterojunctions parallel to (0001). The heterojunctions were prepared by lowpressure chemical vapor deposition of hematite directly onto electron-transparent sapphire substrates. Bright-field imaging and selected-area diffraction show that the growth is epitactic. The 5.5% lattice misfit at the interface is found to be accommodated by one of two different hexagonal dislocation networks: (1) b = 1/3<1210> or (2) b = 1/3<1010>. The latter are associated with a “basal twin”-type orientation relationship of the hematite and the alumina.
A New Defect on the Reconstructed Si(100) Surface: An AB Initio Molecular-Dynamics Study
Authors: Ihara Sigeo , Ho Shi Lun , Uda Tsuyoshi , Hirao Masahiko
Published: March 2011

An interstitial dimer, which is symmetric and recessed from the surface, is proposed as a new defect structure on reconstructed Si(100) surfaces. The structure of the interstitial dimer is studied using ab initio molecular-dynamics simulations, and shown to be stable. Possible arrangements of the new defects are discussed.
Imaging by Sliding Planes in Scanning Tunnelling Microscopy
Authors: Todd John D. , Pethica John B.
Published: March 2011

Scanning tunnelling microscope images of layered materials in a non-uhv environment exhibit various anomalous phenomena, including enhanced corrugation heights, periodicity over large areas and a marked absence of point defects. We have modified a precision indentation device to allow STM rastering of a tip across a surface, while simultaneously monitoring mechanical contact. Images we have obtained from this apparatus on an HOPG sample exhibit atomic scale resolution with contact areas much larger than a single atom. Contrast in the image results from periodic conductance fluctuations as the layers of the sample undergo shear in the region of the tip. We provide a model for this process, which explains a variety of curious, and otherwise unrelated phenomena occurring during STM imaging of these materials.
STM of Gold on Graphite
Authors: Thomas P. A. , Lee W. H. , Masel R. I.
Published: March 2011

Scanning Tunnelling Microscopy was used to examine the surface structure of gold films and supported gold particles. It was found that freshly evaporated gold films have a relatively smooth surface morphology. However, after 1 hr of annealing, a series of dendrites were clearly visible on the surface of the films. With additional annealing, the dendrites got larger, until the film broke into particles. STM images of annealed gold particles showed that annealed gold particles larger than 150 Å have a polyhederal shape and a smooth surface morphology. However, the surfaces of the particles smaller than 60 Å remained highly corrugated even after a long anneal. We believe that the difference in morphology of large and small particles may have some profound implications in supported metal catalysis.
μm-Scale Lateral Growth of Ga-Monolayers Observed In-Situ by Electron Microscopy
Authors: Osaka J. , Inoue N.
Published: March 2011

An ultra high vacuum scanning electron microscope equipped to an MBE system is utilized to study a transient of a surface atomic structure during MBE growth of GaAs and AlGaAs by the alternate supply method. Lateral growth of a Ga-monolayer over microns is realized utilizing Ga droplets. This is confirmed by discriminating the Ga and As top layer by using the secondary electron intensity difference between the Ga and As top layer. The growth mechanism of the Ga monolayer is discussed based on the results.
Interfacial Stability and Interdiffusion Examined at the Atomic Level
Authors: Kim Y. , Ourmazd A. , Malik R.J. , Rentschler J.A.
Published: March 2011

Using chemical lattice imaging in combination with vector pattern recognition, we obtain quantitative profiles of the chemical change across single interfaces with atomic plane resolution. We thus study interdiffusiuon across single GaAs/AlGaAs interfaces as a function of temperature, depth of interface beneath the surface, and doping. Since our technique is sensitive to interdiffusion coefficients as small as 10−20 cm2/s, we can study atomic level changes at a single interface at the low temperatures used for many device processing steps (∼700C). Our results show interdiffusion, and hence the layer stability depend not only on temperature and doping, but also on the distance of the interface from the surface. The implications of these results for the stability of multilayered structures are discussed.
Atomistic Simulation Study of Interfaces in Nanophase Silicon
Authors: Lupo James A. , Sabochick Michael J.
Published: March 2011

Nanophase silicon was investigated using atomistic simulation. The simulations employed a modified Stillinger-Weber potential appropriate for crystalline and amorphous silicon. Computer “samples” of nanophase material were formed by compressing together three grains of several hundred atoms each, using Fletcher-Powell minimization and external pressures of 0.5 to 13.5 GPa. Relative densities obtained in the samples ranged from 65% to 98% as compared to the perfect crystal. The nanophase materials maintained crystalline order up to the interfaces and no highly disordered interfaces were observed. Calculated bulk moduli exhibited a linear dependence with respect to density, with no significant dependence on structure. The calculated thermal expansion coefficients were up to twice as large as that in the perfect crystal and were structure dependent.
High-Resolution Electron Microscopy of Interfaces In Ain - Braze Metal Alloy Systems
Authors: Carim A. H.
Published: March 2011

The microstructural aspects of active brazing of AIN with a Ag-Cu-Ti alloy have been investigated. A series of reaction product layers are formed. TiN is produced in contact with the polycrystalline, bulk AIN. High-resolution transmission electron microscopy and microdiffraction demonstrate that some of the TiN grains at the interface display specific orientation relationships with respect to the adjoining AIN crystallites. As has sometimes been observed in studies of epitaxy in other systems, these relationships are not necessarily those that provide the minimum geometrical mismatch between one or more sets of lattice planes. Farther from the substrate, an fl-type nitride phase with composition (Ti,Cu,Al)6N occurs as a reaction product. High-resolution images confirm the absence of amorphous or crystalline intervening phases at the TiN-ŋ interface and at ŋ grain boundaries.
Novel Compact and High-Resolution Ion Backscattering Analysis System,Chiribas
Authors: Kido Yoshiaki , Kawano Akira , Konomi Ichiro
Published: March 2011

The design and performance of CHIRIBAS(Compact and High-Resolution Ion Backscattering Analysis System) are presented. The system consists of a 60 kV duoplasmatron and unique energy analysis systems connected to a microcomputer. The 5–60 keV H, He, and He+ beams are backscattered to 180° and their energies are analyzed by a time-of-flight technique or with an electrostatic deflector combined with a position sensitive microchannel plate. The probing depth and depth resolution are estimated to be up to 50 nm and better than 0.5 nm, respectively. The computer-simulated spectrum analysis allows rapid and accurate determination of surface and interface structures such as depth profiles of elemental compositions and lattice defects. CHIRIBAS also makes it possible to measure excited state populations using Stark ionization for 5–10 keV H neutralized at the exit surface and thus provides the possibility to determine the energy and spatial distributions of the valence electrons extending outward from the top surface. The present article includes the beam parameters achieved and the preliminary data on reactive-ion etched Si surfaces.
Spectroscopic Ellipsometry as a Non-Destructive Technique for Characterization of Atomic-Scale Interfaces
Authors: Stehle J.L. , Piel J.P. , Lecat J.H. , Pickering C. , Hammond L.C.
Published: March 2011

Analysis of oxide interfaces with semi-conductor substrates, such as crystalline silicon, gallium arsenide, or indium phosphide is critical in processing and electrical performances. Interfaces can be characterized by spectroscopic ellipsometry (SE), which has a wide spectral range (1.3 to 5.3 eV ) allowing an optical penetration depth of 10 nm to a few microns.

A multilayer stack can be characterized in terms of its layer thicknesses and composition. These physical parameters must be calculated through a mathematical model. Linear regression analysis is used to minimize the differences between the measured spectrum and the calculated model. If necessary, an interlayer can be introduced into the model to enhance the fit. This can be complemented by a new method involving calculation of apparent index values which amplifies interface sensivity allowing the thickness to be measured to better than 2 Angstroms. Examples will be given.
Numerical Model of Bond Strength Measurements
Authors: Nutt Gerald L.
Published: March 2011

We have reported bond strength measurements of metal/ceramic interfaces using shock waves to separate the bond by spallation[1,2]. The technique relies on the interpretation of the free surface velocity of the metal film as it is spalled from the substrate.

We answer several questions relating to the details of the interaction of the shock with the interface. Specifically, we examine the role of sound speeds in the measurements. We also calculate the plastic strain in the the bond region and verify the theory relating to the jumpoff velocity of the scab to the bond strength.
Plan-View CBED Studies of Nio-Zro2(CaO) Interfaces
Authors: Dravid V.P. , Notis M.R. , Lyman C.E. , Revcolevschi A.
Published: March 2011

Low energy lamellar interfaces in the directionally solidified eutectic (DSE) NiO-ZrO2(CaO) have been investigated using transmission electron diffraction and imaging. The symmetry of this bicrystal and an aspect of interfacial relaxations in the form of symmetry lowering in-plane rigid body translation (RBT) have been explored by performing convergent beam electron diffraction (CBED) experiments of plan-view bicrystals. Edge-on interfaces have also been studied by conventional and high resolution transmission electron microscopy (CTEM and HRTEM respectively), and electron diffraction fine structure analysis. Despite certain experimental difficulties due to interfacial defects and strain, plan-view CBED patterns offered valuable information concerning bicrystal symmetry and indicated no symmetry lowering RBT in this bicrystal. The suitability of plan-view CBED is briefly discussed in view of its potential as a technique to determine bicrystal symmetry and RBT.
Bi4Ge3O12 (BGO) - A Scintillator Replacement for NaI(Tl)
Authors: Farukhi M. R.
Published: March 2011

Scintillation performance of recent (2X) grown BGO is studied. Results indicate BGO to perform better than 8% 137Cs FWHM NaI(Tl) at energies 2.6 Mev and higher. Even the low energy performance of BGO is suitable for considering it in lieu of NaI(Tl) for many spectroscopic applications.
Materials Aspects of Germanium Radiation Detector Fabrication
Authors: Scott Hubbard G.
Published: March 2011

An overview of the present status and future requirements of material for germanium radiation detectors is presented. Fabrication and storage problems for both lithium-drifted, doped germanium and high-purity germanium are compared to demonstrate the reasons for the recent complete dominance of the latter in commercially available radiation detectors. The effect of electrically active point and line defects on the resolution and operating characteristic of high-purity germanium radiation detectors is discussed. Emphasis is placed on deep impurities and dislocations. Present and future applications of high-purity germanium radiation detectors are reviewed.
Microdiffraction from Cleaved Si-Si1-xGex Multilayers
Authors: Pike W. T.
Published: March 2011

Using the nanometer probe available in the dedicated scanning transmission electron microscope (STEM) local structural information can be obtained from individual layers in [100] grown Si-Si1-xGex multilayer structures. Furthermore the small probe size enables cleaved specimens with their very large wedge angles to be analyzed in cross-section. Diffraction patterns are shown from multilayers of varying periodicity. Analysis of the patterns concentrates on the higher order Laue zone (holz) reflections in the high angle excess ring . The behaviour of the excess holz reflections indicates the transition from a strained layer superiattice to a dislocated structure as the thickness of the layers increases for a given composition.
Structural and Electronic Properties of GaAs/InGaAs/GaAs Heterostructures
Authors: Bonar J. M. , Hull R. , Malik R. J. , Ryan R. W. , Walker J. F.
Published: March 2011

We have made a study of GaAs/InGaAs/GaAs (001) strained layer heterostructures using Transmission Electron Microscopy (TEM) as a structural tool to determine the misfit dislocation structure and density as a function of Indium concentration. The average misfit dislocation spacing varies from > 10 µm for x < 0.3, to a few microns at x = 0.3, and drops to a few hundred Angstroms at x = 0.5. We did in-situ annealing experiments in order to study the strain relaxation process, measuring the temperature at which the structure begins to relax, and the dislocation velocities. Dislocation velocities are a few microns per second at the growth temperature of 450 ° C, and tens of microns per second at 690 ° C. In addition to interfacial dislocations in the usual <110> directions, in samples where x ≥ 0.4, we observed dislocations running in <100> directions. A study of the electrical characteristics of the material was made in parallel with the structural measurements: the mobility of the InGaAs layer was measured, the material was processed into Heterojunction Bipolar Transistors (HBT’s) and the gain was measured. The electrical characteristics initially improved with the addition of In, peaking at x = 0.1 and dropping sharply for higher x.
Effect of Annealing on Strained InGaAs/GaAs Quantum Wells
Authors: Koteles Emil S. , Elman B. , Melman P. , Armiento C.A.
Published: March 2011

We have demonstrated that shallow ion (75As+) implantation and rapid thermal annealing (RTA) of strained InGaAs/GaAs quantum well (QW) structures can modify the optical properties of these epitaxial semiconductor heterostructures in a spatially selective manner. After RTA, exciton QW energies, determined from peaks in the photoluminescence spectra, shifted significantly to higher values only in the implanted regions. The magnitudes of the shifts were dependent on QW widths, RTA temperatures, and implantation fluences. The shifts were interpreted as resulting from the modification of the shapes of the as-grown QWs from square (abrupt interfaces) to rounded (gradual interfaces) due to enhanced indium diffusion out of the well layers in irradiated areas as a consequence of the diffusion of vacancies generated near the surface by the implantation. The thermal processing had only a small effect on the strain present in the quantum well layers due to the difference in the lattice constant of the well and barrier layers.
A Tem study of Epitaxial FE/AG and MN/AG Superlattices
Authors: Nahm S. , Salamanca — Riba L. , Jonker B. T. , Prinz G. A.
Published: March 2011

We have studied the epitaxial growth and structural properities of single crystal Fe/Ag and Mn/Ag superlattices grown on (001) GaAs substrates using transmission electron microscopy. A buffer layer of Ag (001) was grown on a 5 monolayer Fe seed layer on the (001) GaAs substrate before the growth of the superlattice to obtain good quality films. For some samples an intermediate buffer layer of ZnSe was used, as well. Both Fe/Ag and Mn/Ag superlattices with a Ag buffer layer show very sharp interfaces. The densities of dislocations in the film and the buffer layer are the same suggesting that the dislocations originate at the film/substrate interface. We have observed evidence for a strain modulation of ≈ 8 Å in the Mn layer for thick (≈ 22 Å) Mn layers in the superlattice samples but not in samples with a thin Mn layer.
Columnar Epitaxy of CoSi2 on Si(111), Si(100), and Si(110)
Authors: Fathauer R.W. , Nieh C.W. , Xiao Q.F. , Hashimoto Shin
Published: March 2011

Epitaxial columns of CoSi2 are produced when Si and Co are codeposited on heated Si substrates. These columns are surrounded by epitaxial Si with defect densities below the detection limit of transmission electron microscopy. This phenomenon has been studied as functions of substrate temperature, Si:Co ratio, deposition rate, thickness of the epitaxial layer, and substrate orientation. These data suggest that the distribution of columns is dictated by the nucleation of CoSi2 islands during the initial stages of the deposition.
The Mechanism of Epitaxial Si-Ge/Si Heterostructure Formation by Wet Oxidation of Amorphous Si-Ge Thin Films
Authors: Prokes S.M. , Rai A.K. , Carlos W.E.
Published: March 2011

Epitaxial SiGe/Si heterostructures have been formed by wet oxidation from amorphous SiGe films deposited on Si(100). Amorphous SixGe1-x films were deposited at a vacuum of 10-7 Torr. The presence of an initial native oxide precluded solid phase epitaxy under standard annealing conditions, but epitaxy could be achieved by the use of wet oxidation. The samples were oxidized at 900°C for various times and examined in reflection electron diffraction, ellipsometry, cross-sectional and plan-view transmission electron diffraction, and electron spin resonance. The formation of the epitaxial layer and oxide has been examined, and an epitaxial growth model is suggested.
Heteroepitaxial Growth of Germanium Films by Supersonic Free Jet Chemical Beam Epitaxy
Authors: Eres Djula , Sharp J. W. , Lowndes D. H.
Published: March 2011

A supersonic free jet operated in continuous wave and pulsed mode was used to grow Ge films on (100) GaAs and (100) Si substrates. The Ge-bearing source molecule digermane (Ge2H6) was seeded (at 5% concentration) in a helium carrier gas. A free jet expansion of this gas mixture was directed toward the heated substrate surface, where Ge film growth took place by surface-induced thermal decomposition of the ballistically impinging digermane molecules. The thickness distribution across the substrate surface was fitted by a cosmJ distribution. The values of m spanned the range 6–35. The upper limit on growth resulting from “background” gas scattered out of the jet was found to be less than 10% of the Ge film thickness for growth on (100) GaAs, and around 25% for growth on (100) Si.
The Effect of Indium Depletion on the Composition of OMVPE Grown GaInAs
Authors: Agnello Paul D. , Chinoy Percy B. , Ghandhi Sorab K.
Published: March 2011

This paper describes an experimental and theoretical study of indium depletion during the OMVPE growth of GaInAs. A mathematical model for mass, momentum and energy transfer, together with decomposition of the indium species was developed. The model was compared with experimental results over a range of growth parameters that included susceptor temperature, slope, reactor pressure and reactant partial pressures. Excellent agreement was obtained for a model based on the homogeneous decomposition of a triethylindium-arsine adduct to a stable product via an irreversible bimolecular reaction, with an activation energy of 11.9 kcal/gmol. The model may be used for optimization of compositional uniformity and growth over a wide range of reactor conditions.
A High Resolution Cross-Section Transmission Electron Microscopy Study of Epitaxial rare Earth Fluoride / GaAs(111) Interfaces Prepared by Molecular Beam Epitaxy
Authors: Chien C.J. , Farrow R.F.C. , Bravman J.C.
Published: March 2011

We report the first HRXTEM study of epitaxial rare earth fluoride/ GaAs(111) interfaces. Such interfaces are of interest because they are the starting point for growth of buried epitaxial rare earth / rare earth fluoride sandwich structures which exhibit interesting and non bulk-like magnetic properties. Also, the optical transitions in ultrathin epitaxial NdF3 films may be influenced by strain and defects in the NdF3 film and the nature of the interface to GaAs.

We find that the rare earth fluoride / GaAs interfaces are semi- coherent but chemically abrupt with the transition taking place within 3Å. However, the interface is physically rough and multiple monolayer steps in the GaAs surface tend to lead to tilt boundaries in the fluoride. The origin of these steps is believed to be thermal etching of the GaAs during the heat-cleaning stage prior to epitaxy. The surface of the fluoride film is much smoother than the initial GaAs surface indicating planarization during epitaxy.
X-Ray Topographic Analysis of Strain Fields Associated with Micron-Sized Gratings on Si(100) Surfaces
Authors: Jardine A.P. , Dudley M. , Tolis G. , Yao G-D. , Durbin S.M.
Published: March 2011

Si(100) single crystals containing circular gratings etched into the surface using reactive ion etching were analysed using both monochromatic and white beam reflection X-ray topography. Some features of observed X-ray topographic contrast associated with the gratings were modelled using a diffracting zone model, based on a simple radial in-plane strain field. Reasonable agreement was obtained between this model and observations.
Structural Stability of Amorphous Semiconductor Superlattices
Authors: Persans P. D. , Ruppert A. F. , Abeles B. , Wu Y. J. , Pantojas V. , Liang K. S. , Hughes G.
Published: March 2011

We report recent results of studies of the structure and thermal stability of periodic multilayers based on hydrogenated amorphous silicon, hydrogenated amorphous germanium, silicon nitride and silicon oxide. By varying the sublayer thickness from 1 nm to 20 nm it is possible to extract information on the range and magnitude of relaxation and interdiffusion in these metastable materials. It is also possible to gain information on the influence of interfaces on crystallization and relaxation. The principal techniques discussed here are Raman scattering, optical absorption and high resolution x-ray reflectivity.
Structural and Electronic Properties of Pb/Cu Multilayers
Authors: Neerinck D. , Temst K. , Vanderstraeten H. , Van Haesendonck C. , Bruynseraede Y. , Gilabert A. , Schuller Ivan K.
Published: March 2011

We have performed extensive structural and electronic transport measurements of Pb/Cu multilayered structures. The high-angle x-ray diffraction spectrum indicates the presence of continuous interfacial disorder. In the low-angle x-ray spectrum, pronounced minima occur at positions given by q = 2π/Λ, where Λ is the bilayer thickness. This is in sharp contrast to the results for Pb/Ge (crystalline/amorphous) multilayers, where minima are observed at positions q = 2π / tPb with tPb the Pb thickness. These low-angle x-ray spectra can be explained by taking into account lateral coherence and continuously distributed thickness fluctuations. The effect of this interfacial disorder on the electronic properties is investigated by measuring the low-temperature resistivity and the superconducting transition temperature of the multilayers. The calculated values for the elastic mean free path in the individual layers confirm the presence of strong interfacial scattering. The thickness dependence of the critical temperature is explained by taking into account an interfacial barrier with penetration probability σ ≃ 0.5.
Structural Stability of Heat Treated W/B4C Multilayers
Authors: Jankowski A.F.
Published: March 2011

The utilization of W/B4C multilayer structures as Bragg diffractors rests in their reflective efficiency and dependability, both of which rely on the stability of the layered structure. The layers within the vapor deposited multilayers, often amorphous, are typically metastable, hence susceptible to thermally induced structural change. In fact, crystallization and compound formation are known to occur in annealed multilayer systems. In this study, multilayers of W/C and W/B4C were vacuum heat treated, then structurally examined. A comparison between the pre- and post- heat treated structures of the two multilayer systems, accomplished using diffraction and electron microscopy, indicate structural stability in the W/B4C multilayers as opposed to structural degradation noted for the W/C system.
Photoreflectance of a GaAs/In0.5 Ga0.5 P (ordered) Single Quantum Well Grown by Atomic Layer Epitaxy
Authors: Yin X. , Pollak Fred H. , McDermott B.T. , Reid K.G. , Bedair S.M.
Published: March 2011

We have studied the photoreflectance spectrum at 300K from a GaAs/In0.5 Ga0.5p (ordered) single quantum well fabricated by atomic layer epitaxy. Comparison of the energies of the observed intersubband and barrier transitions with an envelope function model calculation yields a valence band offset of 350 ± 20 meV.
Electrical and Optical Characterization of InSb Grown on GaAs by MBE
Authors: Thompson Phillip E. , Waterman James , Kurtgaskill D. , Stahlbush Robert , Gammon Daniel , Davis John L.
Published: March 2011

InSb has been grown on semi-insulating GaAs substrates by molecular beam epitaxy. By growing an InSb buffer layer at 300 C prior to the main InSb layer growth at 420 C, the effect of the 14% lattice mismatch between GaAs and InSb was minimized. A typical 5 µrn InSb film had a room temperature carrier concentration and electron Hall mobility of 2 × 1016/cm3 and 6×104 cm2/Vs, respectively. At 77 K these values became 2 × 1015/cm3 and 1.1 ×105 cm2/Vs. Temperature dependent Hall measurements revealed a peak in the mobility at 85 K and 70 K for the 5 and 10 µm samples. Capacitance-voltage measurements using MIS capacitors produced 77 K carrier concentrations in agreement with the low fieldHall measurements. Carrier lifetimes were determined by photoconductive response measurements. Lifetimes of 20 ns and 50 ns were determined for the 5 and 10 µm films. For comparison, the carrier lifetime in bulk n-type InSb was found to be 200 ns. Optical characterization by room temperature IR transmission spectroscopy showed a broad absorption edge, with an absorption coefficient of 1.4 × 103/cm at a wavelength of 6 µm. Epilayer thickness was determined from observed interference fringes. Raman spectroscopy showed that each epitaxial layer had a spectrum equivalent to that of bulk InSb.
Magneto-Optical Studies of GaAs-AlGaAs Modulation Doped Quantum Wells Under Hydrostatic Pressure
Authors: Zhou Weimin , Perry Clive H. , Worlock John M.
Published: March 2011

High pressure photoluminescence measurements on modulation doped GaAs-AlGaAs quantum well structures have been performed for the first time with applied magnetic fields up to 15 Tesla. We have observed Landau fans from interband transitions of the 2D free electron gas between 0 and 8.5 kbar. In this pressure range the electron effective mass in GaAs increased at the rate of 2.6% per kbar. Above 9 kbar, the free Landau transitions disappeared and bound magneto-exiton behaviour dominated the spectrum. The influence of pressure on the band-gaps causes a controlled trapping of the free electron from the GaAs well to Si donors (DX centers) in the AlGaAs layers. Above 9 kbar the pressure coefficient of the GaAs band gap was found to be 10.4 meV/kbar which is comparable to the accepted value in undoped GaAs quantum well structures.
Index of Refraction Anisotropy in InGaAs/InP Heterostructures Measured by Ellipsometry
Authors: Bennett Brian R. , Del Alamo Jesús A.
Published: March 2011

We applied ellipsometry to characterize layers of InxGa1-xAs grown by molecular beam epitaxy on (001) InP. Samples with mismatched layers exhibit significant anisotropy in the index of refraction. We explain these observations by the presence of misfit dislocations which form in an asymmetric pattern. This results in asymmetric strain and, via piezo-optical effects, an anisotropy in the optical properties. This effect makes ellipsometry a more sensitive technique than double-crystal x-ray diffraction for detecting misfit dislocations in these heterostructures.
Stress Evaluation Method using Raman Spectroscopy
Authors: Mashimoto Y.
Published: March 2011

Local stress measurement is becoming very important to evaluate electrical and reliability property of semiconductor. Raman spectroscopic method has been established to measure local stress at the area of one micron in diameter. The measurement problems came from the characteristics of a spectrometer have been solved by the following.

–Ar Plasma line is utilized to calibrate wave numbers.

–Gaussian and Lorentz distribution are utilized to determine the peaks of Plasma line and RAMAN shift.

This method with introduction of a certain assumption can be applied to the stress measurement not only for Silicon single crystal like trench structure, but for deposited thin layers like silicon oxide or silicon nitride, and plastic packaging material.

This paper describes the measurement methods of local stress, data processing techniques of measurement data and several examples of the measurement on a semiconductor thin layer and packaging plastic.
X-Ray Diffraction Study of Inalas-Ingaas on Inp High Electron Mobility Transistor Structure Prepared by Molecular-Beam Epitaxy
Authors: Liu H.Y. , Kao Y.C. , Kim T.S.
Published: March 2011

High-Electron Mobility Transistors (HEMTs) can be prepared by growing alternating epitaxial layers of InAlAs and InGaAs on InP substrates. Lattice matched HEMTs are obtained by growing layers of InxAl(1-x)As and InyGa(1-y)As with x ≃ 0.5227 and y ≃ 0.5324. Varying the values of x and y by controlling the individual flux during molecular-beam epitaxial (MBE) growth, one can obtain pseudomorphic HEMTs. Pseudomorphic HEMTs may have superior electronic transport properties and larger conduction band discontinuity when compared to an unstrained one. The precise control of the composition is thus important to the properties of HEMTs. This control is however very difficult and the values of x and y may vary from run to run.

We will demonstrate in this paper the capability of a double crystal rocking curve (DCRC) on the structure characterization. All the structure information: including composition and thickness of both the buffer and top InAlAs layers and the active channel InGaAs layer, can be obtained from one x-ray diffraction measurement. It is accomplished through a computer simulation process of DCRCs. The structure parameters of the epitaxial layers are used to calculate (simulate) the DCRCs. The simulated one is then to compare with the experimental curves. During the simulation one or more of these structure parameters are adjusted until the best fitted DCRC is obtained. The limitation of DCRC in measuring small variations in layer thickness as well as the small changes in composition for both InAlAs and InGaAs layers will be discussed.
Heterojuncion Study of Ga0.92In08as(P+)/GaAs(n) Diodes: Correlation of Electrical and Strucrural Characteristics
Authors: Choi Y.W. , Wie C.R. , Evans K.R. , Stutz C.E.
Published: March 2011

Different in-plane mismatch was introduced by varying the Ga 0.92In0.08As(p+) epilayer thickness (h-0.1, 0.25, 0.5 and lum) on GaAs(n)/GaAs(n+) structure. For sample with h-lum, quasi-Fermi level pinning effect was observed in low temperature forward Current-Voltage characteristic due to high density misfit dislocation. From Vint measurement at low frequency limit in C-2 vs Voltage plot, interface state density Nss was obtained. From Capacitance-Voltage measurements at different frequencies, single-level interface state density Ns was estimated using Schokley-Read-Hall statistics. Both Nss and Ns show their linear relation with epilayer in-plane mismatch. Admittance Spectroscopy shows an interface trap level at about Ev + 0.36 eV with the hole capture cross section cp = 2.7×10-15 cm-2 for the h-lum sample, and at Ev + 0.21 eV with cP = 2.4×10-16 cm-2 for the h-0.5um sample.
Thermal Stability of Si/Si0.85Ge0.15/Si Modulation Doped Double Heterostructures
Authors: Wang P.J. , Meyerson B.S. , Fahey P.M. , LeGoues F. , Scilla G.J. , Cotte J. M.
Published: March 2011

The thermal stability of Si/Si0.85Ge0.15/Si p-type modulation doped double heterostructures grown by the Ultra High Vacuum/ Chemical Vapor Deposition technique has been examined by Hall measurement, transmission electron microscopy, secondary ion mass spectroscopy, and Raman spectroscopy. As deposited heterostructures showed two-dimensional hole gas formation at the abrupt Si/SiGe and SiGe/Si interfaces. Annealing at 800 °C. for 1 hr. caused the diffusion of boron acceptors to the heterointerfaces, degrading the hole mobilities observed in the two dimensional hole gas. Rapid redistribution of boron, causing a loss of the 2 dimensional carrier behavior, was observed after a 900 °C, 0.5 hr. anneal. Neither Ge interdiffusion nor the generation of misfit dislocations were observed in the annealed heterostructures, evincing the defect-free crystal quality of these as-grown strained heteroepitaxial layers. The superior stability of these heterostructures have strong positive implications for Si:Ge heterojunction devices.