bluuebunny/crossref_metadata_2025 huggingface dataset:
Direct Evidence of Diffusion of Self-Interstitials in Silicon
Authors: Das Gobinda
Published: March 2011

High temperature (1200°C) HCI oxidation treatment has been employed to float-zone (FZ) silicon wafers (625μm thick) containing swirl defects in order to study their diffusion characteristics. In treated wafers, swirl defects can be eliminated from both surfaces up to a depth of ∼30μm. In the bulk of the wafers, however, large swirl defects (A-swirls) rearrange themselves into many small defects. The untreated portions of wafers contain large swirl defects (A-swirls) that extend up to both surfaces. Since swirl defects are primarily clusters of silicon self-interstitials, their rearrangement in the bulk and elimination from the surfaces demonstrate that migration of interstitials takes place on a large scale and is not confined to SiO2/ silicon interface only. The above observations appear to provide direct evidence for the dominant role of self interstitials for diffusion mechanism in silicon at high temperature and can be rationalized in terms of an interstitialcy mechanism. Alternatively, however, dominance of interstitials can be related to a higher migration energy of vacancies proposed in a model where both species coexist at high temperature. The preference of one model over another must await theoretical calculations of diffusion energetics derived from both models.
The Causes of Property Variations of Ibad-Titanium Nitride
Authors: Kant R. A. , Dillich S. A. , Sartwell B. D. , Sprague J. A.
Published: March 2011

The influence of the growth conditions on the composition, microstructure, and mechanical properties of TiN formed with low energy Ar+ ion bombardment during reactive physical vapor deposition was studied. The ratios of the incident ion and atom fluxes at the growth surface were varied systematically and were found to have a strong influence on both the composition and the microstructure of the films. These changes correlated well with measured changes in mechanical and optical properties. The films were examined using Auger electron spectroscopy, transmission electron microscopy, and their mechanical properties were studied using hardness, friction, and wear testing.
Microstructural Studies of IAD and PVD Cr Coatings by Cross Section Transmission Electron Microscopy
Authors: Cheng C. C. , Erck R. A. , Fenske G. R.
Published: March 2011

Cross section transmission electron microscopy was used to study the microstructure and interface structure of Cr films deposited by ion-assisted deposition as a function of the incident ion energy. High-energy ion bombardment (1 keV) was found to enhance the adhesion of the deposited film owing to the formation of an intermixed layer, whereas deposition with lowenergy ions (100 eV) was found to reduce or eliminate grain boundary porosity. A tailored Cr film with excellent adhesion and no grain boundary porosity was deposited by combining highand low-energy ion bombardment.
In-Vacuo, Tribological Properties of “High-Rate” Sputtered MoS2 Applied to Metal and Ceramic Substrates.
Authors: Roberts E W , Price W B
Published: March 2011

Studies of the tribological properties of molybdenum disulphide deposited at the high rates afforded by magnetron sputtering have shown such films to exhibit low friction and high endurance under vacuum. However such studies have mostly been confined to bearing steels. This paper reports on the extension of such studies by presenting measurements of friction coefficient and endurance obtained for thin films of “high-rate” molybdenum disulphide applied to substrates of 440C steel, 52100 steel, titanium alloy 318 andsilicon nitride. The results are interpreted in terms of substrate-related parameters such as film adhesion and elastic modulus of substrate materials. Preliminary evidence relating the degree of film adhesion to the existence of interfacial chemical compounds, identified using surface analytical techniques (XPS, SIMS), is presented.
Future Application Trends - a Case for Mechanistic Approaches
Authors: Fehrenbacher Larry L.
Published: March 2011

This paper reviews moving mechanical assembly (MMA) and component technology shortfalls imposed by demanding ground, naval and aerospace system requirements of the future. The tribology development needs for specific harsh environment applications such as high temperature engines, chemical reactant turbopumps, precision acquisition, tracking and pointing MMAs surveillance systems and laser communications components are identified. Development goals for lightweight bearing and gear alloys and ceramics, ultra low friction and wide temperature range solid lubricants, self lubricating composites and real time health monitoring devices are translated into a rationale for mechanistic, more fundamental research approaches.
A Study of Subsurface Damage Generation by Single Scratches of Silicon
Authors: Ahn J.H. , Danyluk S.
Published: March 2011

This paper describes the use of electrical resistivity to quantify the damage produced asa result of the scratching of single crystal silicon.

The change in resistivity was measured as a function of time as a scratching diamond passed between four electrical contacts of a specially designed printed circuit and while thesilicon was heated to temperatures up to 300ºC. The data shows that the resistivity increases during scratching and reaches a steady state value if the silicon temperatureis below 200ºC. The conductivity recovers when the silicon temperature is 200ºC.
Stick-Slip\Smooth Slip as a Function of Ambient Gases and Pressures Disproving Previous Models of Adhesive Wear
Authors: Gao Chao , Kuhlmann-Wilsdorf Doris , Makel David D.
Published: March 2011

Five different slip modes have been identified for bundles of copper fiberssliding on a smooth copper substrate in atmospheric air, argon and nitrogenat pressures from atmospheric to 0.01 Torr. These are stick-slip, variable sliding, intermittent stick sliding and two kinds of smooth sliding, one apparently a basic property of clean surfaces and the other due to contaminants. These forms of sliding are rather persistent once established, and they follow some trends. Specifically, low-pressure smooth sliding is coordinated with a value of the coefficient of friction (μ) near 0.15 and is seen when the surface film is exceptionally thin, while intermittent stick sliding appears to be due to “pads” on the substrate surface,and variable sliding to small particles caught in between the fibers and the copper substrate. However, the five slip modes are erratic in that under the same conditions one or another or yet a third may be observed, even though the electrical contact resistance (R) depends rather reproducibly on time, load, velocity, ambient atmosphere and pressure. That dependence indicates an equilibrium between film destruction through sliding and film formation, overwhelmingly through the presence of oxygen. In the stick-slip mode the difference between pst tic and ųK itic appears to be roughly proportional to ų 0.15, i.e. tfiee xcess of e average value of the friction coefficient above 0.15, being about 20% for ų 0.3 andvanishing near ų =0.15. During slip episodes, R spikes roughly in proportion to their magnitude. Some tentative interpretations are offered, based on the concept that ų consists of three additive components, namely due to the bulk (ųBulk), due to debris (ųDebris), and dueto scoring of surface films (ųFilm).At any rate, the conclusion that the results contradict all previous models of “adhesive” wearis inescapable.
Selection of Scuffing-Resistant Materials Under Lubricated, High-Speed Sliding
Authors: Au J. J. , Corcoran M. W. , Yung J.-Y.
Published: March 2011

The scuffing resistance of materials under lubricated high-speed sliding was analyzed based on the thermalelastic instability (TEl) model. The model was used to select and rank scuffing-resistant materials.

The scuffing resistance was also determined experimentally by the Falex 6 thrust washer wear tests. There was good agreement between the experimental results and the analytical predictions.
Gas Plasma Treatment of Sputtered Carbon Thin Film and Enhancement of its Properties
Authors: Sharma J.P. , Narayan P.B. , Brar A.S.
Published: March 2011

In magnetic recording, the metallic magnetic media are protected from corrosion and wear by a thin sputtered carbon layer. The latter also acts as a self-lubricating film during the interaction of the media with the ceramic read \write head pad material. Since the surface energy of carbon is high, it tends to absorb and chemisorb environmental constituents such as oxygen, nitrogen, water vapor and hydrocarbons. These could then react with the head\media interface and form heterogeneous layers of “frictional polymers”. These changes in carbon lead to frictional instability and friction build-up. Low temperature gas plasma treatment of sputtered carbon layer was found to improve the surface properties and the frictional instability problems. Use of a mixture of argon and carbon tetrafluoride gases led to the formation of a very thin self-lubricating layer, probably a fluorocarbon. The surface also becomes smooth. This is because of thecombined reaction of chemical reaction, ion-diffusion, ion-penetration and plasma etching. This reaction product was found to be prominently present at the grain boundaries and other morphological inhomogeneities, thereby strengthening the weak areas and improving the tribo-performance of the media.
Effects of Grain Boundary Characteristics of Steel on Magnetoacoustic Emission Spectra
Authors: Namkung M. , Yost W. T. , Utrata D. , Grainger J. L. , Kushnick P. W.
Published: March 2011

The pulse height distribution of a magnetoacoustic emission (MAE) spectrum is expected to be generally Gaussian due to its random nature. The functional form of distribution depends on the microstructure of a ferromagnet since the domain wall-lattice defect interaction produces MAE. The present study investigated the effects of grain boundary characteristics on the properties of MAE spectra obtained by external AC magnetic field-driven domain wall motions. The results show the enhancement of domain wall-defect interaction as more grain boundary disorder is introduced to HY80 steel samples. This was confirmed by the growth of a non-Gaussian-like distribution in the tail section of histograms with increased population of impurities trapped at the grain boundaries causing embrittlement. It is found that the enhancement of domain wall-defect interaction, which is responsible for generation of high amplitude MAE pulses, also tends to reduce the rate of such MAE events by limiting domain wall motions. Application of a stronger AC magnetic field should increase the count rate of high amplitude MAE signals in more embrittled samples.
In-Situ NMR Study of Dislocation Jump Distance During Creep of Pure and Doped NACL Single Crystals
Authors: Murty K. Linga , Kanert O.
Published: March 2011

Nuclear magnetic resonance pulse techniques are used in-situ during creep of single crystals of NaCl to evaluate the contribution of mobile dislocations to spin relaxation. 23Na spin-lattice relaxation rates were measured in the rotating frame (T1ρ) during compression creep of single crystals of NaCl along [110] direction at 473K at an applied stress of 20 MPa. The relaxation rates are evaluated from the spin-echo height following π/2, locking and 67° pulse sequence. The height of the free induction decay decreased as soon as the load is applied followed by a gradual increase until the steady-state is reached, at which point a saturation value is observed corresponding to the constant steady-state creep-rate. The mean jump distance of the mobile dislocations, evaluated from the ratio of the signal heights without deformation and during creep, decreased with time/strain reaching a constant value during steady-state creep regime. The results are compared with the dislocation-dislocation spacing, subgrain size as well as the jump distance predicted from creep models. The effects of dilvalent Ca and solid solution with LiCl are examined.
The Use of Time-Temperature Superposition Techniques to Forecast Creep Behavior in Engineering Plastics
Authors: Overton B. J. , Taylor C. R. , Shea J. W.
Published: March 2011

A complete understanding of the time-temperature dependent, viscoelastic mechanical properties of polymeric materials is essential for their successful application to engineering designs. We describe a computer-based system for acquiring, reducing and storing the mechanical properties of polymers, from which the useful forms of the mechanical characteristics may easily be reproduced and compared. We provide several examples illustrating the variety of ways in which these properties are utilized to forecast the performance of polymeric components of engineering designs under extreme field conditions.
Study of Spherulites in a Semi-Crystalline Polymer Using Acoustic Microscopy
Authors: Duquesne J. Y. , Yamanaka K. , Neron C. , Jen C. K. , Piche L. , Lessard G.
Published: March 2011

Abstracts

The local elastic properties of a semi-crystalline polymer (isotactic polypropylene) have been investigated with the use of scanning acoustic microscopy (SAM) techniques. The operating frequency was 775 MHz and the temperatures ranged between 25 and 60°C. A new and effective signal processing method was developed to process the material signature V(z) curve. This method avoids complicated calibration procedures involved with operating the SAM lens at different temperatures. Longitudinal velocities VL(α) and VL(β) in individual α and β-type spherulites of isothermally crystalized samples have been measured. Acoustic velocity of a quenched sample was also obtained. It was found that vL(α) and VL(β) were nearly equal but the acoustic impedances of α and β-spherulites were unexpectedly very different.
Elastic Properties of Porous Ceramics
Authors: Ledbetter H. M. , Lei M. , Datta S. K.
Published: March 2011

Using theoretical models, we consider the sound velocities and elastic constants of ceramics containing pores. As an example, we consider alumina. However, the approach applies to all ceramics. As a point of departure, we consider spherical pores. For all the usual elastic constants–Young modulus, shear modulus, bulk modulus, Poisson ratio–we give relationships for both the forward and inverse cases: predicting the porous ceramic properties and estimating the pore-free ceramic properties. Following a suggestion by Hasselman and Fulrath that sintering or hot pressing can produce cylindrical pores, we derive a relationship for the elastic constants of a distribution of randomly oriented long cylinders (c/a + ∞, the prolate-spheroid limit). This model predicts elastic constants lower than for spherical pores, but well above measurement. We obtain agreement with observation by assuming the pores are oblate spheroids. For alumina, the necessary aspect ratio equals oneninth. Besides pore aspect ratio, the model requires only the pore-free alumina elastic constants. It contains no adjustable parameters.
Thermal Properties of Non-Metallic Films by Means of Thermal Wave Techniques
Authors: Frederikse H. P. R. , Ying X. T. , Feldman A.
Published: March 2011

The propagation of a thermal wave into a thin film or coating depends on the thermal properties of the material. Consequently, thermal wave generation and detection can be used to obtain the heat conductivity of the material. The method is also useful because thermal wave propagation is sensitive to inhomogeneity, porosity, inclusions, voids, and delaminations. The results of two specific applications of the thermal wave technique are presented, the heat resistance of oxide coatings and of diamond films.
Detecting Areas of High Chloride Concentration in Bridge Decks
Authors: Lim K. , Gress D. L. , Maser K.
Published: March 2011

The presence of chloride ions in New England bridge decks has caused severe damage and has contributed greatly in reducing service life. The source of the chloride ions is mainly from deicing salts applied for snow and ice removal to enable safer driving during the winter. The chloride ion acts as an accelerator in the corrosion of reinforcing bars causing expansion and therefore deterioration of the bridge deck concrete.

At present the method of determining the percentage of chloride present in bridge decks is a very time consuming, expensive and destructive process. The need for a fast nondestructive procedure to determine the amount of chloride in a concrete bridge deck is apparent. This paper introduces a means of utilizing ground penetrating radar as a viable nondestructive means of detecting areas of high chloride concentration in concrete bridge decks. The technique is based on the attenuation of a radar signal emitted from a radar unit in the presence of chloride.
Correlating Microstructure with Backscattered Ultrasonic Energy
Authors: Mittleman John , Mohr David W.
Published: March 2011

High frequency ultrasonic energy interacts with metallurgical microstructure to produce scattered energy fields that are useful in characterizing the material. By using a focused transducer whose focal spot size and ultrasonic wavelength are both comparable to the scale of grain structure in high purity copper specimens, the authors have shown a strong correlation between microstructure and the pattern of backscattered ultrasonic signals. A systematic series of experiments logged the ultrasonic returns from cold-rolled copper with the direction of the ultrasonic beam both parallel to and transverse to the rolling direction. Fourteen samples were annealed to various degrees, capturing several stages of recovery and recrystallization. Use of backscattered ultrasonic energy rather than specularly reflected energy allows isolation of grain boundary scattering in an otherwise quiet acoustic environment. Clear differences between returns of backscattered shear waves from parallel and transverse beam orientations relative to the rolling direction gradually disappear as the annealing process re-establishes a field of equiaxial crystals. Backscattered surface waves also show variations that appear to correspond with the relaxation of residual stresses before the onset of recrystallization, and preferred orientation after recrystallization.
Ultrasonic Characterization of Texture
Authors: Li Y. , Thompson R. B.
Published: March 2011

This paper will propose a new technique to characterize texture of rolled plates of cubic crystallites. This technique uses information from ultrasonic velocities of high order plate mode to improve the estimation of orientation distribution coefficients (ODC's), especially W400. Also discussed will be the generalization of this technique to the case of hexagonal crystallites.
Interaction of Thin Ga Overlayer with InP(110): a Photoemission Study
Authors: Cao R. , Miyano K. , Kendelewicz T. , Lindau I. , Spicer W. E.
Published: March 2011

Photoemission study of the Ga/InP(110) interface, in particular at the In 4d cooper minimum (CM) reveals that the growth of the deposited Ga on InP(110) at room temperature (RT) has two modes: chemisorption at low coverage and metallic island formation at high coverage, whereas the Ga overlayer is much more uniform at 80K low temperature (LT). A replacement reaction between Ga and InP is found to take place only underneath the Ga islands. Metal screening from the Ga islands is suggested to weaken the substrate bonds and enhance the replacement reaction. Distinct behavior of Fermi level pinning has been observed at different temperatures. This is correlated with the temperature dependence of the overlayer morphology as well as the interfacial reaction.
Exafs Studies of Multilayer Interfaces
Authors: Heald S. M. , Lamble G. M.
Published: March 2011

Important for the understanding of multilayer materials is a determination of their interface structure. The extended x-ray absorption fine structure (EXAFS) technique can be useful, particularly for interfaces with a high degree of structural disorder. This paper reviews the application of EXAFS to multilayers, and describes the standing wave enhancement of the EXAFS from multilayer interfaces. Examples are given for W-C and Ni- Ti multilayers.
Fluorescence Yield Near Edge Spectroscopy (Fynes) for Ultra Low Z Materials: an In-Situ Probe of Reaction Rates and Local Structure
Authors: Fischer D. A. , Gland J. L. , Meitzner G.
Published: March 2011

Fluorescence Yield Near Edge Spectroscopy (FYNES) of ultra low Z materials represents a synchrotron radiation milestone for in-situ determination of local structure for a range of materials problems from monolayers to bulk samples even in the presence of a reactive atmosphere. Two examples will be presented highlighting the broad range of materials problems addressed by the FYNES technique. First a study of the kinetics of CO displacement on Ni(100) by hydrogen at pressures up to.1 torr. These kinetic results highlight the unique capabilities of FYNES to directly characterize surface reaction rates in the presence of reactive gases. Second, a pioneering fluorescence EXAFS study characterizing low concentration fluorine materials will be discussed. Finally new opportunities in FYNES presented by increased photon flux from insertion-device- based sources will be explored.
Exafs Studies of Cobalt Silicide Formation Produced by High Dose Ion Implantation
Authors: Tan Z. , Budnick J. I. , Sanchez F. , Tourillon G. , Namavar F. , Hayden H. , Fasihuddin A. F.
Published: March 2011

The early stages of cobalt silicide formation in high dose (1.0 to 8.0× 1017Co/cm2) cobalt implanted Si(100) are studied by extended X-ray absorption fine structure (EXAFS), X-ray diffraction (XRD) and Rutherford backscattering spectroscopy (RBS). Locally ordered silicide that is not detectable in XRD has been observed with EXAFS in the as-implanted samples. Long-range ordered phases are observed in the 3 × 1017Co/cm2 samples. After thermal annealing at 700–750°C, single phase CoSi2 with (400) orientation is formed in all implants.
Structural Changes in Ag,Fe,Mn, and Ge Microclusters
Authors: Zhao J. , Ramanathanl M. , Montano P. A. , Shenoy G. K. , Schulze W.
Published: March 2011

The structures of Ag,Fe,Mn, and Ge microclusters were determined using EXAFS. The measurements were performed over a wide range of clusters sizes.The clusters were prepared using the gas aggregation technique and isolated in solid argon at 4.2 K. A strong contraction of the interatomic distances was observed for Ag dimers and multimers. Silver clusters larger than 17 A mean diameter show a small contraction of the nn distance and a structure consistent with an fcc lattice. By contrast smaller clusters show the presence of a small expansion and a strong reduction or absence of nnn in the EXAFS signal. This points towards a different crystallographic structure for Ag microclusters. In iron clusters we observed a gradual reduction of the nn distance as the cluster size decreases. The interatomic distance for iron dimers was determined to be 1.94 A, in good agreement with earlier measurements. The iron microclusters show a bcc structure down to a mean diameter of 9 A. Iron clusters with 9 A mean diameter show a structure consistent with an fcc or hcp lattice.Mn microclusters show a simpler crystallographic structure than α-Mn. The measurements on Ge clusters show the presence of only nearest neighbors. There was clear evidence of temporal annealing as determined by variations in the near edge structure of the K-absorption edge. Absorption edge measurements were also performed on free Ge clusters traveling perpendicular to the direction of the synchrotron radiation beam.
Application of Multilayer Structures to the Determination of Optical Constants in the X-Ray, Soft X-Ray and Extreme Ultra Violet Spectral Ranges
Authors: Barbee Troy W.
Published: March 2011

The dispersion of x-rays (XR), soft x-rays (SXR) and extreme ultraviolet (EUV) light by multilayer structures is dependent on the scattering and absorption cross-sections of the elements used to synthesize the multilayer. In this paper it will be shown that this dependence provides a means for the accurate experimental determination of the optical constants of the multilayer constituents. Two specific approaches will be presented and discussed. First, it will be shown that detailed analysis of the energy dependence of the reflectivity of a simple depth periodic multilayer allows the unfolding of the optical constants. Secondly a new optic structure, the multilayer diffraction grating, will be described and it will be demonstrated that such combined microstructure optics allow the scattering cross-sections of the multilayer constituents to be accurately determined over broad spectral ranges.
Imaging with Soft X-Rays
Authors: Shinozaki D. M.
Published: March 2011

A review of recent advances in soft X-ray imaging using synchrotron radiation is given.
Automatic Orientation Mapping with Synchrotron Radiation
Authors: Gottstein G.
Published: March 2011

Synchrotron radiation can be utilized to obtain Laue back reflection patterns of microscopic areas with very short exposure time. A method is presented to fully automatically evaluate Laue patterns. The experimental setup and procedure are outlined to determine the orientations of a large number of contiguous grains, and consequently to enable orientation mapping. Preliminary experimental results are presented.
X-ray Scatiering Studies of the Melting of Lead Surfaces.
Authors: Fuoss P. H. , Norton L. J. , Brennan S.
Published: March 2011

Of fundamental importance in understanding melting is the question of premelting (i.e. do surfaces melt at a lower temperature than the bulk). We report the results of an x-ray scattering experiment that has directly measured liquid correlations in Pb(110) and Pb(111) surfaces at temperatures substantially below the bulk melting point of Pb. Surprisingly, significant liquid scattering is observed at ≈230°K or >1/2Tm on both the (110) and the (111) surfaces. On the (110) surface, analysis of the scattered intensity yields 2–3 monolayers of liquid from 575°K to 599°K while substantially less than 1 monolayer of liquid is present on the (111) surface at 599°K.
Metals in Beta-Rhombohedral Boron
Authors: Wong Joe , Slack Glen A.
Published: March 2011

The bonding and local atomic structure of a series of 3d metal-beta boron solid solution are investigated using a combination of x-ray absorption near-edge structure (XANES) and extended fine structure (EXAFS) technique utilizing intense synchrotron radiation as a light source. The corresponding metal diborides MB2, (M = Sc, Ti, V, Cr).were also measured and used to model the coordination environment of these metal sites in beta-boron.
Exafs of Near Monolayer and Submonolayer Coverage Films
Authors: Barbee Troy W. , Wong Joe
Published: March 2011

The high intensities available using synchrotron source insertion devices potentially extend the range of adatom surface coverage on well prepared surfaces that may be experimentally studied to very low levels. In this paper we report the results of a fluoresence EXAFS study of a 0.5 nm thick hafnium film in the vicinity of its LIII absorption edge (9561 eV). This film was deposited on a platinum-carbon nmultilayer having a period of 31.7Å. These results indicate that EXAFS studies of species at surface coverages of 0.01 monolayer are easily experimentally accessible.
Surface Lattice Strain and the Electronic Structure of Thin Mercury Overlayers
Authors: Varma Shikha , Kime Y. J. , Dowben P. A. , Onelliont M.
Published: March 2011

The stress in the surface of a thin (0–10 monolayer) film of mercury can be relieved by either changing the substrate and consequently changing adlayer lattice constants or by growing thicker films. An empirical relationship between strain and the valence electronic structure of mercury overlayers can be demonstrated, though we present evidence that this relationship can be altered and destroyed by crystallography changes.
Growth of CdTe Thin Films on Polar and Nonpolar Semiconductor Substrates by Metalorganic Chemical Vapor Deposition.
Authors: Grodzinski P. , Mazur J.H. , Nouhi A. , Stirn R.J. , Sudharsananu R.
Published: March 2011

Electron diffraction and high resolution electron microscopy (HREM) have been used to investigate the origin of multiple orientation-relationships and defect structure of CdTe thin films grown on (100) GaAs and Si substrates by metal- organic chemical vapor deposition (MOCVD). It has been determined that growth at 370°C with pre-exposure of the GaAs surface to Te following oxide desorption treatment at 600°C resulted in non-parallel epitaxy ((111)CdTe // (100)GaAs), while growth at 300°C following oxide desorption at 500°C with no exposure to Te resulted in parallel epitaxy ((100)CdTe // (100)GaAs). Both epitaxial orientation-relationships were observed on the same substrate for growth at 300°C temperature after 600°C oxide desorption treatment, but with no pre-exposure of the GaAs surface to Te. Preliminary results of growth of CdTe on Si are also reported.
AES and EELFS Studies of Initial Stages of Growth of GaAs/InAs/GaAs Heterostructures.
Authors: Schowengerdt F. D. , Grunthaner F. J. , Liu John K.
Published: March 2011

We report on a systematic study of the composition and structure of GaAs/InAs/GaAs quantum wells using Auger Electron Spectroscopy (AES), Extended Energy Loss Fine Structure (EELFS), and Reflection High Energy Electron Diffraction (RHEED) techniques. Double heterostructures with InAs thickness ranging from 2 to 10 monolayers, capped by 2 to 10 monolayers of GaAs, were grown by MBE using a variety of techniques, including those employing sequential, interrupted, and delayed shutter timing sequences. AES peak ratios are compared with model calculations to monitor compositional development of the multilayers. The AES results are correlated with RHEED measurements to determine MBE growth parameters for optimal control of the stoichiometry and surface morphology. EELFS was used to monitor strain in the buried InAs layers. The AES results show departure from smooth laminar growth of layers of stoichiometric InAs on GaAs at temperatures below 420 C and above 470 C. AES results on the quantum well structures suggest floating InAs layers on top of the GaAs and/or facet formation in the GaAs layers. The EELFS results, when compared to bulk InAs, indicate the presence of strain in the buried InAs quantum well.
Characterization of III-V Semiconductor Structures Using Electron Beam Electroreflectance (EBER) spectroscopy.
Authors: Herman M. H. , Ward I. D. , Buttrill S. E. , Francke G. L.
Published: March 2011

EBER is a form of modulated reflectance spectroscopy in which a low energy electron beam alters the sample surface potential. For III-V semiconductors, the spectra are characteristic of electroreflectance, including excitonic, interband, and impurity transitions. The study of these transitions provides accurate estimations of band gaps in bulk and thick film samples. Measurements of the band gap energy in compounds such as AlxGa1-xAs provide highly precise evaluations of their composition.

Additionally, EBER spectra of quantum well structures and heterojunctions provide useful information about the composition and quality of materials and interfaces. For quantum wells, detected features suggest the presence of allowed, disallowed, and resonant states. In EBER spectra of HEMT structures, peaks are apparent resulting from transitions between the valence band and the states in which the electrons are confined. We present examples of EBER determination of AlGaAs composition, single GaAs/AlGaAs quantum well evaluation, and HEMT characterization.
The Effect of Substrate Orientation on the Properties of (Ga, Al)As Grown by Gas Source Molecular Beam Epitaxy
Authors: Sandhu A. , FUJII T. , Ando H. , Ishikawa H. , Miyauchi E.
Published: March 2011

We have carried out the first systemmatic investigation on the effect of substrate temperature and arsenic partial pressure on the morphology, growth rate, and compensation ratio of Si-doped GaAs, and the Al content of AlxGa1−xAs grown on just-cut (100), (110), (111)A&B, (311)A&B orientated GaAs substrates by gas source MBE (GSMBE). Triethylgallium ( TEG, Ga(C2H5)3 ) and triethylaluminium ( TEA, Al(C2H5)3 ) were used as group III sources, and solid arsenic ( As4 ) and silicon as a group V and IV sources, respectively. The best GaAs mophology was obtained at relatively high temperatures and arsenic pressures. The A orientations were identified as ‘fast surfaces,’ with the GaAs growth rate being comparable to the (100) orientation. The B orientations were identified as ‘slow surfaces,’ with the GaAs growth rate being much less (approximately 50% for the (111)B orientation ) than on the (100) orientation. The least compensated Si-doped GaAs was grown on the (311)A orientated substrate. The Al content, x, (nominally x=0.27 for (100)) of AlxGas1−xAs grown on (110), (111)A&B, was less than 0.05 and not affected by the growth conditions. The Al content of epilayers grown on (311)A&B ranged between x=0.1 to 0.27, strongly depending on the growth temperature.

These results show that using GSMBE we can selectively modifying a large range of (Ga,Al)As crystal properties. Potential applications include the selective growth and realisation of ultra-fine and planar structures and devices.
Photoluminescence of InP/GaAs/Si Heterostructures
Authors: Mazzi V.P. , Haegel N.M. , Vernon S.M. , Haven V.E.
Published: March 2011

Low temperature photoluminescence results from MOCVD epitaxial InP grown on GaAs/Si substrates are presented as a function of thickness of the GaAs buffer layer. As a consequence of thermal expansion mismatch of the heterostructure, the InP layer contains residual stress which causes the band gap to shift and splits the valence band degeneracy of the mj = ± 3/2 and the mj = ± 1/2 bands. Both the shifting and splitting phenomena are clearly seen in tite PL results and are shown to depend on the GaAs buffer layer thickness.
Migration-Enhanced Molecular Beam Epitaxial Growth and Characterization of GaAs on Si Substrates
Authors: Kim J.H. , Sakai S. , Liu J.K. , Raohakrishnan G. , Chang S.S. , Katz J. , El-Masry N.A.
Published: March 2011

We first report on migration-enhanced molecular beam epitaxial (MEMBE) growth and characterization of the GaAs layers on Si substrates (GaAs/Si). Excellent surface morphology GaAs layers were successfully grown on (100) Sisubstrates misoriented 4 toward [110] direction. The MEMBE growth method isdescribed and material properties are compared with those of normal two-step MBE-grown or in-situ annealed layers. Micrographs of cross-sectional view transmission electron microscopy (TEM) and scanning surface electron microscopy (SEM) of MEMBE-grown GaAs/Si showed dislocation densities of 107 cm-2 over ten times lower than those of two-step MBE-grown or in-situ annealedlayers. AlGaAs/GaAs double heterostructure lasers and light-emitting diodeshave been successfully grown on MEMBE GaAs/Si by both metal organic chemical vapor deposition and liquid phase epitaxy. MOCVD-grown lasers showed peak output power as high as 184 mW/facet, pulsed threshold currents as low as150 mA at 300 K, and differential quantum efficiencies of up to 30 %. The LPE-grown light-emitting diodes showed output powers of 1.5 mW and external quantum efficiencies of 3.3 mW/A per facet.
Thermal Stability of EL2 in GaAs
Authors: Boddaert X. , Letartre X. , Stievenard D. , Bourgoin J. C.
Published: March 2011

Different samples originating from the same LEC ingot have been used in order to determine the variation of the EL2 concentration versus depth after different types of thermal annealing ( 450 and 850°C : the temperatures generally used in technological processes ). The annealing of EL2 near the surface at 850°C has been interpreted as the result of the deviation from the stoichiometry near the surface, due to [As] variation induced by vacancy diffusion. At 450°C, the annealing of EL2 can only be explained by the dissociation of a complex, followed by the migration of one of the constituants, confirming that the EL2 defect is the complex AsGa- Asi.
X-Ray Studies of GaAs/Si and ZnS/Si
Authors: Kim H. M. , Choi Y-W , Vernon S. , Moise P. S. , Wie C. R.
Published: March 2011

The MOCVD-grown layers of GaAs/Si(001), InP/GaAs/Si(001), and ZnS/Si(111) were studied using X-ray rocking curve (XRC), double crystal topography (DCT), and Nomarski phase contrast microscopy. The layer qualities of GaAs/Si, InP/GaAs, and InP/GaAs/Si from the XRC full width at half maximum (FWHM) agreed well with these determined from the Nomarski phase contrast microscopy. The in-plane lattice mismatch (parallel X-ray strain) was 3.71% for GaAs/Si. In the double heteroepitaxial layer (InP/GaAs/Si), the parallel X-ray strain of GaAs was 4.03% with respect to Si. The parallel X-ray strain was larger than the perpendicular X-ray strain in GaAs/Si, perhaps due to the mismatch in thermal expansion coefficients between GaAs and Si. Dislocation densities estimated from the rocking curve linewidth were 5.30 × 107 cm−2 for GaAs/Si, 3.27 × 108 cm−2 for InP/GaAs. We also present the double crystal X-ray topographs of the III-V/Si and II-VI/Si samples.
Relationship Between Electrical Activation and Residual Defects in MeV Si Implanted GaAs.
Authors: Braunstein G. , Zheng L.-R. , Chen Samuel , Lee S.-Tong , Peterson D.L. , Ko K.-Y. , Rajeswaran G.
Published: March 2011

We have investigated the relationship between electrical activation and residual defects in GaAs implanted with 1 MeV Si ions to a fluence of 3×1015 cm−2 and subsequently annealed, using rapid thermal annealing (RTA) for 10 seconds, at temperatures up to 1050°C. Hall measurements show n-type activation that increases in magnitude with increasing annealing temperature to reach a sheet carrier concentration of 2.6×1014 cm−2 after RTA at 1050°C. Two main types of extended defects, perfect and partial dislocation loops, had previously been identified in the as-implanted samples. In addition, a large number of discrete point defect complexes are certainly created but escape detection. We show here a correlation between the annealing of the defects and the recovery of the electrical transport properties. Most of the point defects anneal out between room temperature and 700°C, and it is in this temperature regime that the transport properties show their most significant improvement. For annealing temperatures between 700°C and 1050°C, the mobility of the carriers decreases slightly while the carrier concentration gradually approaches saturation. Concurrently, the loops grow in size while decreasing in number and eventually anneal out. However, after annealing at 1050°C, while most of the extended defects have disappeared, only about 9% of the implanted atoms had been activated, suggesting that residual point defect centers control the activation of Si dopants in MeV implanted GaAs.
Rapid Thermal Annealing and Ion Implantation of Heteroepitaxial ZnSe/GaAs
Authors: Skromme B.J. , Stoffel N.G. , Gozdz A.S. , Tamargo M.C. , Shibli S.M.
Published: March 2011

We describe the effects of rapid thermal annealing on the photoluminescence (PL) and electrical properties of heteroepitaxial ZnSe grown by molecular beam epitaxy on GaAs, using either no cap or plasma-deposited SiO2, Si3N4, or diamond-like C caps, and annealing temperatures from 500 to 800°C. Capless anneals (in contact with GaAs) produce badly degraded PL properties, while capped anneals can prevent this degradation. We show that Si3N4 is significantly more effective in preventing Zn out-diffusion through t e cap than previously employed SiO2 films, as evidenced by less pronounced PL features related to the creation of Zn vacancies during the anneal. Implant damage tends to enhance the Zn vacancy formation. Rapid thermal annealing with Si3N4 caps is shown to optically activate shallow N acceptor implants.
GaAs/AlGaAs Quantum Well Mixing Using Low Energy Ion Implantation and Rapid Thermal Annealing
Authors: Elman B. , Koteles Emil S. , Melman P. , Armiento C. A.
Published: March 2011

Low energy ion implantation followed by rapid thermal annealing (RTA) was utilized to modify exciton transition energies of MBE- rown GaAs/AlGaAs quantum wells (QW). The samples were irradiated with an 75As ion beam with an energy low enough that the depth of the disordered region was spatially separated from the QWs. After RTA, exciton energies (determined using optical spectroscopy) showed large increases which were dependent on QW widths and the implantation fluence with no significant increases in peak linewidths. These energy shifts were interpreted as resulting from the modification of the shapes of the as-grown QWs from square (abrupt interfaces) to rounded due to enhanced Ga and Al interdiffusion in irradiated areas. These results are similar to our data on the RTA of the same structures capped with SiO2 and are consistent with the model of enhanced intermixing of Al and Ga atoms due to diffusion of vacancies generated near the surface.
Mechanisms for Ion and Te-Induced Intermixing of GaAs-AlGaAs Interfaces.
Authors: Kahen K. B. , Rajeswaran G.
Published: March 2011

Recently, GaAs-AlGaAs interfaces have been interdiffused following furnace and rapid thermal annealing (RTA) of samples containing impurities. Two models are proposed to explain the events occurring during the annealing processes. Te was chosen as the impurity for furnace annealing, whereas for the case of RTA, the impurities were introduced via ion implantation. The Te-induced interdiffusion process is modeled using an ensemble Monte Carlo simulation. The results of the simulation are in good agreement with the Te intermixing data. In the case of ion implantation followed by RTA, the intermixing model is based on the solution of coupled diffusion equations involving the excess vacancies and the Al distribution following ion implantation. Both initial distributions are obtained from the solution of a three-dimensional Monte Carlo simulation of ion implantation into a heterostructure sample. The excess interstitials calculated in the simulation are coupled to the vacancy diffusion via a phenomenological decay constant. Having established the value of the decay constant from one set of experimental results, the model is able to predict accurately other independent experimental results.
Gallium Arsenide Surface Inversion using a Novel Silicon–Silicon Dioxide Insulator Structure
Authors: Fountain G.G. , Rudder R.A. , Hattangady S.V. , Markunas R.J. , Vitkavage D.J.
Published: March 2011

A novel GaAs metal insulator semiconductor (MIS) structure in which the surface of the GaAs is unpinned and inverted is reported. The structure utilizes a thinsingle crystalline Si interlayer between the GaAs surface and a SiO2 insulator. The Si and SiO2 are deposited using low temperature remote plasma chemical vapor deposition techniques. Characteristics of the Si layer have been examined using reflecting high energy electron diffraction, Xray photoelectron spectroscopy, and He ion scattering spectroscopy. The complete MIS structure has been characterized using capacitance-voltage data taken at frequencies ranging from near D.C. (quasistatic) to 100 MHz. The structure exhibits deep depletion and inversion behavior. Calculation of the surface potential variation using quasistatic data indicates that the surface potential is varied by 0.83 V with an applied electric field from −1.6 to 3.2 MV- cm−1.
A Tem Study of Optically Annealed Ohmic Contacts to GaAs Using a Zirconium Diboride Diffusion Barrier
Authors: Grimshaw Mike , Staton-Bevan Anne
Published: March 2011

The morphology of a Ni(5nm), Au(45nm), Ge(20nm) ohmic contact with a ZrB2 (50nm) diffusion barrier, annealed to temperatures between 355°C and 485°C, was studied by TEM. The barrier was found to remain intact and unreacted after annealing. The contact annealed to 355°C reacted in the solid state to form αAu-Ga, Ge and orthorhombic NiGe phases. The morphology of contacts annealed above the melting point (∼ 380°C) consisted of two regions; type A contained αAu-Ca and NiGeAs, and type B contained αAu-Ga α′Au-Ga, NiGe and epitaxial Ge. αAu-Ga segregated to the contact pad edges at and above 403°C. The transition from rectifying to ohmic properties corresponded to annealing above the melting point of the contact. It was found that variations in contact resistance with temperature could be explained either by changes in the bulk or in the edge morphology.
Thermodynamically Stable Conducting Films of Intermetallic PtGa2 on Gallium Arsenide
Authors: Sadwick Larry P. , Wang Kang L. , Shuh David K. , Kim Young K. , Williams R. Stanley
Published: March 2011

The first epitaxial platinum gallium two (PtGa2) films have been grown on gallium arsenide (GaAs) (100) by co-evaporation of the elements under ultra-high vacuum conditions. An electron beam evaporator and a Knudsen cell were used to produce the platinum and gallium beams, respectively. The resulting films and bulk PtGa2 have been characterized by x-ray diffraction, Auger electron spectroscopy, and x-ray photoelectron spectroscopy. The data confirm the PtGa2 stoichiometry and crystal structure of the films, and demonstrate their chemical stability on GaAs (100). This study supports the contention that PtGa2 can be a suitable, temperature stable contact material on GaAs substrates.
Amorphous WSi0.45 Metallization for Self-Aligned GaAs MESFETs
Authors: Lahav Alex
Published: March 2011

Crystallization temperature (Tc) of amorphous WSix films on GaAs was studied as a function of the Si/W ratio. The highest Tc of 875°C for a 20 min anneal was obtained for co-sputtered WSMi films with the Si/W ratio of 0.45 (31 at.% Si). The WSi0.45 films remained amorphous following implant activation anneal and served as a barrier to Ga and As outdiffusion. Pitting of GaAs under the contact was also prevented. The WSi0.45 composition corresponds to the eutectic point between the W and W5Si3 phases, which was explained by the strong glass-forming tendency of eutectic alloys. Amorpous WSi0.45 films formed stable Schottky contacts to n-GaAs and produced minimum reduction of carrier concentration in the substrate. Therefore, the Si/W ratio of 0.45 is suggested as optimal for the WSix refractory gate metallization in self-aligned GaAs MESFErs.
High Barrier Height MIS Diodes on n-InP Using Pd, Ni and Au on a Chemical Oxide
Authors: Lee Y. S. , Anderson W. A.
Published: March 2011

MIS diodes were fabricated using Pd, Ni and Au- contacts on n-InP covered by a 40 Å chemically-grown oxide. The oxide had a refractive index of 1.4–1.6 with a composition of mainly In2O3 + some InPO3 near the surface and mixed oxide + InP near the interface. Pd-devices gave the highest barrigr height of 0.80 eV and lowest reverse saturation current density of 3×10−8A/cm2. I-V-T and C-V-T data gave temperature dependence of barrier height and revealed an interface state recombination current mechanism. Richardson plots gave good straight lines when empirically corrected using øB/n instead of just øB.
The Challenge of GaAs Heterojunction Bipolar Transistor Integrated Circuit Technology.
Authors: Yuan Han-Tzong
Published: March 2011

The status and progress of AlGaAs/GaAs heterojunction bipolar transistor integrated circuits are reviewed. The challenge of fabricating large-scale integrated circuits using heterojunction bipolar transistors is discussed. Specifically, the issues related to low defect epitaxial materials, localized impurity doping techniques, simple and reliable ohmic contacts, and multilevel interconnects are examined.