bluuebunny/crossref_metadata_2025 huggingface dataset:
The Optical Properties of ION Implanted Silica
Authors: Smith C. C. , Ila D. , Williams E. K. , Poker D. B. , Hensley D. K.
Published: April 2011

We present the results of our investigation of the change in the optical properties of silica, "suprasil", after keV through MeV implantation of copper, tin, silver and gold and after annealing. Suprasil, name brand of silica glass produced by Hereaus Amersil, which is chemically highly pure with well known optical properties. Both linear and nonlinear optical properties of the implanted silica were investigated before and after thermal annealing. All implants showed strong optical absorption bands in agreement with Mie theory. For implants with a measurable optical absorption band we used Doyle's theory and the full width half maximum of the absorption band to calculate the predicted size of the formed nanoclusters at various heat treatment temperatures. These results are compared with those obtained from direct observation using transmission electron microscopic techniques.
High Quality in.Ga1−xas Heterostructures Grown on GaAs With Movpe
Authors: Bulsara M.T. , Fitzgerald E.A.
Published: April 2011

InxGa1−xAs structures with compositionally graded buffers were grown by metal-organic vapor phase epitaxy (MOVPE) on GaAs substrates and characterized with plan-view and cross-sectional transmission electron microscopy (PV-TEM and X-TEM), atomic force microscopy (AFM), and x-ray diffraction (XRD). The results show that surface roughness experiences a maximum at growth temperatures where phase separation occurs in InxGa1−xAs. The strain energy due misfit dislocations in the graded buffer indirectly influences phase separation. At growth temperatures above and below this temperature, the surface roughness is decreased significantly; however, only growth temperatures above this regime ensure nearly complete relaxed graded buffers with the most uniform composition caps. With the optimum growth temperature for grading InxGa1−xAs determined to be 700°C, it was possible to produce In0.33Ga0.67As diode structures on GaAs with threading dislocation densities < 8.5 × 106/cm2
Recent Progress in Crystal Growth and Conductivity Control of Wide Bandgap Group III Nitride Semiconductors
Authors: Akasaki I.
Published: April 2011

Recent progress in crystal growth of wide bandgap group III nitrides on highly-mismatched substrates has enabled us to produce high-quality GaN, A1GaN, GaInN and quantum well structures. High-performance blue and green light-emitting diodes and room temperature operation of nitride-based laser diodes have also been realized. Today, steady progress is being made in the areas of crystal growth and device performance. However, much further advances are required in many areas of materials science and device fabrication of the nitrides
Theoretical Analysis of the Minority Carrier Lifetime in a Multicrystalline Wafer with Spatially Varying Defect Distribution
Authors: Sopori Bhushan , Chen Wei , Ravindra N. M.
Published: April 2011

Multicrystalline Si (mc-Si) wafers, used for the commercial solar cell fabrication, have spatial nonuniformities in the material properties that cause strong variations in the minority carrier lifetime, τ. We present the results of two-dimensional modeling to show carrier generation, recombination and transport in such a material. These results are used to infer measurement conditions that can yield meaningful spatially weighted average value of τ.
Electrical Properties of Iron-Related Defects in Cz- And Fz-Grown N-Type Silicon
Authors: Kitagawa Hajime , Tanaka Shuji
Published: April 2011

Electrical properties of iron-related defects (IRD) introduced in n-type floating zoned (FZ) and Czochralski (CZ)-grown silicon are studied by deep level transient spectroscopy and Hall effect. Electrically active IRD have been observed for the first time in n-type CZ silicon. Enthalpy and entropy factors of electron emission rate of IRD are equivalent between those observed in CZ and FZ silicon. In-diffusion process at 1160° and isothermal annealing process at 150° also indicate the identical nature of IRD between CZ and FZ silicon, which can be understood in terms of the consecutive progress of iron-related complex-formation reactions including interstitial iron atoms (Fei) in the silicon crystal. The IRD is independent of oxygen and phosphorus atoms. Only a small fraction of Fei forms electrically ionizable complexes
The transformations of the EL6 deep level defect in n-GaAs: Is EL6 a DX-like center?
Authors: Reddy C.V. , Fung S. , Beling C.D.
Published: April 2011

Based on the charge redistribution effect, as observed by the present authors, and the earlier reported large lattice relaxation and persistent photoconductivity phenomena associated with the EL6 defect seen in doped, undoped, semiinsulating(SI) and low temperature grown GaAs LT-GaAs), it is suggested that this defect be classified as a DX-center. A tentative unified atomic model is proposed for all the native defects EL2, EL3, EL5, and EL6 observed in GaAs.
Baseline Particle Reduction of Downstream Oxide Etchers Etching Contacts and Vias
Authors: Williams Bradley
Published: April 2011

In the process of etching contact and via openings with a downstream oxide etcher, plasma etch byproducts form polymer that collects on process chamber components. Polymer build up over time will begin to separate from chamber components and deposit on the wafer, blocking the etch and creating incomplete contact and via openings, which result in device failure. When this phenomena occurs, complete disassembling and cleaning of the chamber (wet clean) is required before particle levels are acceptable again for processing wafers. Over half of the time wet cleans are performed at or before 1500 wafers processed.

Experimentation was performed to isolate one particular chamber component causing particle deposition on the wafer. Once a chamber component was isolated, possible solutions were designed so that original process parameters were not altered. The first experiment was a maintenance procedure to disassemble and clean one chamber component at set intervals between wet cleans. The second was a no wafer, high concentration Oxygen plasma chamber clean.

It was found that changing a particular chamber component after 1250 wafers processed, and then again after 2500 wafers, made it possible to run to 3750 wafers before performing a wet clean. Overall particle levels were also reduced by 30% with the plasma cleans after every 100 wafers processed. The combined solutions resulted in a greater than 30% reduction in overall particle counts. Also, maintenance down time for particle failures was reduced from 57% to 19%. During the time frame of implementation of these solutions, overall factory defectivity of finished product wafers was reduced up to 25%, which relates to a 15 to 25% yield increase. The reduction of defects on the downstream oxide etcher is a contributing factor to device yield improvements.
Behavior of Electron Traps Induced by Phosphidization and Nitridation of GaAs Surfaces
Authors: Nozu Satoshi , Matsuda Koichiro , Sugino Takashi
Published: April 2011

GaAs is treated with remote PH3 and N2 plasmas. Electron traps induced by plasma treatments are investigated by isothermal capacitance transient spectroscopy measurements. The EL2 trap is detected in the as-grown GaAs. The TP1 trap(Ec-0.26eV) is generated in GaAs phosphidized for 10min, while the TN1 trap(Ec-0.66eV) is induced in GaAs nitrided for 30min. It is found that the TP1 trap is changed to the another trap with an energy level as shallow as 0.16eV below the conduction band edge and a capture cross section as small as 1.8×10−21cm2 by treating with N2 plasma subsequently after PH3 plasma treatment.
Carbon Doping into GaAs Using Low-Energy Hydrocarbon Ions
Authors: Sanpei Hirokazu , Shima Takayuki , Makita Yunosuke , Kimura Shinji , Fukuzawa Yasuhiro , Nakamura Yo-ichi , Sandhu Adarsh
Published: April 2011

The role of hydrogen (H) in carbon (C)-doped GaAs was examined by co-doping of C and H atoms using low-energy hydrocarbon (CH+ and CH3+) ions. Experiments were carried out using the combined ion beam and molecular beam epitaxy (CIBMBE) system. Samples were characterized by low-temperature photoluminescence at 2K and Hall effect measurements at room temperature. Results show that incorporated C atoms are optically and electrically activated as acceptors even by hydrocarbon ion impingement. The effect of H incorporation was found to be noticeable when impinged current density of CH3+ ion beam is high that produces equivalent net hole carrier concentration greater than ∼1018 cm−3
Underflow Process for Direct-Chip-Attachment Packaging
Authors: Li P. C. , Lehmann G. L. , Cascio J. , Driscoll T. , Huang Y. J. , Cotts E. J.
Published: April 2011

In flip-chip packaging an underfill mixture is placed into the chip-to-substrate standoff created by the array of solder bumps, using a capillary flow process. The flow behavior is a complex function of the mixture properties, the wetting properties, and the flow geometry. This paper reports on the use of a plane channel capillary flow to characterize underfill materials. The measured flow behavior provides evidence that both the contact angle (θ) and the suspension viscosity (μapp) vary with time under the Influence of changing flow conditions. This nonlinear fluid behavior is modeled for the flow of both model suspensions and commercial underfill materials using an extended Washburn model.
Effect of Humidity on Charge Profiles and Thermal Properties of 1.7 μM Polyimide Films on Silicon Substrates
Authors: Bloss P. , Reggi A. S. De , Schafer H.
Published: April 2011

Using an improved version of the thermal pulse (TP) method for determining electric field profiles and thermal parameters, we have obtained for the first time field profiles in 1.7 μm thick polyimide (PI) films spin-coated on Si wafers. As-coated films were found to have an internal field caused by negative charges within 200 nm of the free (pulsed) surface believed due to electrochemical reactions involving water. The change near the pulsed surface was stable up to 200 °C and would not be switched by applied fields of ±1 V/μm. The charge distribution and the thermal parameters were found to be sensitive to humidity
Direct Measurements of Thermal Stress Distributions in Large Die Bonds for Power Electronics
Authors: He Jun , Shaw M. C. , Sridhar N. , Cox B. N. , Clarke D. R.
Published: April 2011

Large semiconductor devices can be subject to significant mechanical stress resulting from thermal expansion mismatch between the devices and packaging materials. This stress can either cause mechanical failure or change the operational characteristics of the device. Furthermore, this stress governs the reliability of the system during use. Therefore, a complete understanding is required of the nature of stress evolution during packaging, and its time and temperature dependence during subsequent service. In the present investigation, the absolute magnitudes and spatial distributions of time-dependent thermal residual stress are measured directly by piezospectroscopic techniques. These measurements are performed with high stress (±15 MPa) and spatial (1 μm) resolution in silicon specimens attached to substrates. Measurements are performed at room temperature on 25 mm square specimens, with continuous, layered solder joints in model specimens of silicon/solder/copper. Room temperature creep relaxation is also investigated. The stress data are then analyzed according to fundamental micromechanical models.
Determination of Critical Volumes in Recording Media
Authors: O'Grady K. , Dova P. , Laidler H.
Published: April 2011

In this overview paper the concept of thermal activation of magnetisation reversal is reviewed in terms of the Wohlfarth-Gaunt formalism. This formalism gave rise to the concept of an activation volume of reversal. Other techniques have been developed for the determination of activation or critical volumes of reversal and these are reviewed. It is found that these methods give the same approximate value for the activation volume but the only method based on micromagnetism is the waiting time experiment which is consistent with Gaunt. Factors which affect the activation volume such as incoherent reversal and intergranular coupling are discussed together with measures that may be required in order to generate ultrahigh density recording media that are relatively free from thermal loss of signal.
Structure and Magnetic Properties of Co, Ni, Mn, Cr and Cu Substituted Magnetites
Authors: Sorescu M. , Mihaila-Tarabasanu D. , Diamandescu L.
Published: April 2011

Co, Ni, Mn, Cr and Cu substituted magnetites were prepared by the hydrothermal method at 300°C, with concentrations x ranging from 8.2 to 12.5%. Transmission electron microscopy determined the average particle diameter <Φ> to be in the hundred of nm range and the morphological modifications induced by the various substitutions employed. Hysteresis loop measurements were performed to determine the coercive field Hc and saturation magnetic moment ms. While Hc decreased with increasing <Φ>, the particle shape was found to play an important role in explaining the dependence of ms on <Φ>. Transmission Mössbauer spectroscopy was used to determine the site preference of the substitutions and their effect on the hyperfine magnetic fields. The room temperature Mossbauer spectra were analyzed assuming a random distribution of substitutents using the binomial distribution from the ionic crystal point of view. Superparamagnetic particles were observed at room temperature in the case of Cu and Cr substituted magnetites.
A Method for Laser Zone Texturing of Glass Based Magnetic Media Using Nd:Yag Lasers
Authors: Rosenblum M. P. , Ross C. A.
Published: April 2011

Laser zone texturing of nickel-plated, aluminum based magnetic media has become a preferred method of providing a precisely controlled head landing zone. The Nd:YAG lasers used for this process are not suitable for directly texturing glass substrates. A novel method has been developed which allows the use of the existing Nd:YAG laser systems to zone texture glass based magnetic media.

An amorphous sputtered film of a non-magnetic Ni alloy provides a texturing layer which absorbs the laser pulse and controllably forms regular, small protrusions. Optimization of the alloy composition results in small cone-shaped bumps. Laser power sensitivity exhibits a region of invariance for a range of film thickness. This behavior provides a wide margin for manufacture by reducing the effect of thickness variation on laser bump height.

Disks fabricated using this form of laser zone texture exhibit excellent tribology performance. TEM images show the Ni alloy to be amorphous and featureless. The sputtered film does not influence the properties of the subsequently sputter deposited isotropic magnetic films.
Diluted Magnetic Semiconductor Magneto-Optic Waveguides for Monolithic-Integration with Semiconductor Optic Devices
Authors: Ando K. , Zaets W. , Watanabe K.
Published: April 2011

We propose to use a paramagnetic diluted magnetic semiconductor Cd1-xMnxTe for magneto-optic waveguides, which can be integrated with semiconductor optic devices. Single crystal Cd1-xMnxTe films are epitaxially grown on GaAs substrates by molecular beam epitaxy method. A good optical confinement is obtained in the waveguide by using a Cd1-yMnyTe clad layer with Mn concentration higher than that of the waveguide core layer.
Magnetic Second Harmonic Generation Studies of Co-Cu Granular Films
Authors: Misuryaev T.V. , Murzina T.V. , Ganshina E.A. , Gushin V.S. , Kazantsev D.V. , Aktsipetrov O.A.
Published: April 2011

Magneto-induced optical second harmonic generation (MSHG) is used to study the structural and magnetic properties of Co-Cu granular films. Azimuthal anisotropy of the SHG response reveals an existence of the regular structure of Co nanocrystals. The nonlinear magneto-optical Kerr effect (NOMOKE) is observed for the longitudinal and transverse configurations. The coherence of the SH responses from the nonmagnetic and magnetic subsystems of the Co-Cu granular films is demonstrated by the MSHG phase measurements (the MSHG interferometry).
Fabrication of Nanostructured Monoclinic Zirconia Ceramics by Colloidal Processing
Authors: Uchikoshi T. , Sakka Y. , Ozawa K. , Hiraga K.
Published: April 2011

Fabrication of fine-grained monoclinic zirconia ceramics has been attempted from acid and neutral zirconia sols, which have been prepared by different methods. Complete re-dispersion of flocculated particles for the neutral sol is impossible even by changing its pH, while no flocculation is observed for the acid sol. Chloride ions, which are inevitably present in the acid sol, are removed effectively by using anion exchange resin. Consolidation of the sols is performed by the pressure filtration method at 10 MPa, followed by CIP treatment at 400 MPa. It is possible to densify the compacts from both sols to >98% of theoretical density by pressureless sintering in air at 1100 °C. This temperature is lower than that for the monoclinic to tetragonal transformation of pure zirconia. Fine and homogenous-grained microstructures, which have an average grain size of 92 nm, are observed for monoclinic zirconia fabricated from the acid sol. However, more coarse and heterogeneous microstructures are observed for the compact fabricated from the neutral sol.
Producing Clay-Coated Quartz Powders for Semidry Pressing of Wall Ceramics
Authors: Kryukova G.N. , Simonov P.A. , Storozhenko G.I. , Boldyrev G.V.
Published: April 2011

This paper discusses the potential of mechanochemical activation of low grade raw materials with carbonaceous inclusions to achieve high-quality building ceramics. The procedure proposed enabled us to produce clay-coated quartz powders thus facilitating further processing steps of semidry pressing and firing of the bricks, tiles and flagstones.
Applications for Silica-Based Aerogel Products on an Industrial Scale
Authors: Schmidt M. , Schwertfeger F.
Published: April 2011

Aerogels, nanoporous lightweight materials, were discovered more than 60 years ago. The supercritical manufacturing process and expensive raw materials typically used to produce aerogels prohibited commercialization on an industrial scale. Recently a commercially attractive ambient pressure production process was developed which will allow broader commercialization of silica-aerogel products.

Some aerogel products for insulation applications and their preparation are described. Sound insulation properties including a remarkable absorption in the difficult low frequency range was found. In the case of insulation plates performance depends on binder and can be positively influenced by choosing the right binding material.
Numerical Modelling of the Strength of Highly Porous Aerated Autoclaved Concrete
Authors: Schneider Thomas , Schober Georg , Greil Peter
Published: April 2011

Highly porous building materials like aerated autoclaved concrete are characterized by low thermal conductivity and high mechanical strength, which both strongly depend on porosity. The influence of porosity distribution on the compressive strength of aerated autoclaved concrete was investigated by using finite element analysis and multiaxial Weibull theory. Calculations of failure probability of microstructures with ordered as well as random pore configurations show a dependence of compressive strength on the Weibull modulus of the matrix material and the size and arrangement of pores. The results of the calculations are compared to experimental data of aerated autoclaved concrete.
Fabrication and Properties of Syntactic Magnesium Foams
Authors: Hartmann M. , Reindel K. , Singer R. F.
Published: April 2011

Syntactic magnesium foams which consist of thin-walled hollow alumina spheres embedded in a magnesium matrix were fabricated by infiltrating a three-dimensional array of hollow spheres with a magnesium melt by using a gas pressure-assisted casting technique.

The resulting composite contains closed cells of homogeneous and isotropic morphology. The densities of the syntactic magnesium foams were between 1.0 and 1.4 g/cm3. The densities were controlled by variations in the bulk density of the hollow spheres with the volume fraction of spheres kept constant at approximately 63 %.

Compressive deformation characteristics of the composites were evaluated with respect to the influence of matrix strength and sphere wall thickness on characteristic variables such as compressive strength, plateau stress and energy absorption efficiency. Differences in the strength of the magnesium-based matrix materials investigated (cp-Mg, AM20, AM50, AZ91) had little influence on the compressive strength of the syntactic foam. However, an increasing relative wall thickness of the hollow ceramic spheres led to a significant strength enhancement. In all cases the ratio between compressive and plateau strength rose with increasing composite strength resulting in decreasing energy absorption efficiency.
Modeling of Fatigue for Cellular Materials
Authors: Huang J. S. , Lin J. Y.
Published: April 2011

Dimensional arguments are used to analyze the fatigue of cellular materials. A modeling describing the fatigue of foams with or without macrocrack is derived and compared to the existing experimental data of cementitious foams and phenolic foams; agreement is good.
Bending Properties of Foamed Aluminum Panels and Sandwiches
Authors: Simančik F. , Kováčik J. , Mináriková N.
Published: April 2011

The foamed panels and sandwiches were prepared by powder metallurgical route using various matrix alloys. The effect of the apparent density, geometry and structure of the foam on its bending stiffhess was studied with respect to the results of the four-point-bending. It has been shown that the modulus of elasticity of the foam cannot be related only to its apparent density, because the distribution of the cell-wall material along the thickness of the foamed panel is not uniform. Therefore the real moment of inertia of the foam's cross-section should be used for the calculation of bending stiffness. This moment can be determined from the square weight of the foamed sample.
Difference between Wafer Temperature and Thermocouple Reading during rapid Thermal Processing
Authors: Borca-Tasciuc T. , Achimov D. A. , Chen G.
Published: April 2011

Thermocouples are often used as a calibration standard for rapid thermal processing. Although it has been recognized that the thermocouple temperature can be different from the wafer temperature, the magnitude of the temperature difference is difficult to quantify. In this work, we present a simple analytical model to demonstrate the difference between the thermocouple temperature and the true wafer temperature. The results show that a large difference can exist between the thermocouple and the wafer temperature. This is because the optical and thermophysical properties of the thermocouple and the glue material are different from those of the wafer. The model results show that temperature measurement becomes more accurate if fine diameter thermocouple wires with very low emissivity are used.
Rapid Thermal Processes for Future Nanometer MOS Devices
Authors: Hauser John R.
Published: April 2011

Scaling of MOS devices is projected to continue down to device dimensions of at least 50 nm. However, there are many potential roadblocks to achieving such dimensions and many standard materials and front-end processes which must be significantly changed to achieve these goals. The most important areas for change include (a) gate dielectric materials, (b) gate contact material, (c) source/drain contacting structure and (d) fundamental bulk CMOS structure. These projected changes are reviewed along with possible applications of rapid thermal processing to achieving future nanometer scale MOS devices.
Defect Reduction in Remote Plasma Deposited Silicon Nitride by Post-Deposition Rapid Thermal Annealing
Authors: Lucovsky G. , Parker C. R. , Wu Y. , HAUSER J. R.
Published: April 2011

This paper describes a novel synthesis route for producing defect-free siliclon nitride films that are demonstrated to provide state of the art electrical performance in MOS devices with stacked oxidenitride gate dielectrics in both nmos and pmos devices. High concentrations of bonded hydrogen are introduced into the as-deposited nitride films during a 300°C remote plasma-enhanced deposition, and then the majority of this hydrogen is evolved during a 30 second rapid thermal anneal (RTA) at 900°C. The nitride formed in this way is effectively “defect-free” and qualitatively different from nitride films formed by conventional chemical vapor deposition processes.
A Study of Transistor Optimization in A 0.25 Micron Cmos Flow Using Source/Drain and Silicide Process Modules and Their Interactions
Authors: Vasanth K. , Apte P. , Davis J. , Saxena S. , Burch R. , Rao S. , Mozumder P. K.
Published: April 2011

A modular approach to CMOS process development requires an understanding of individual process modules (channel, gate etc.) and their interactions. The reverse short channel effect (RSCE) in NMOS devices is one such interaction between the channel and source/drain (S/D) modules. Similarly the interaction between the S/D and silicide modules affects the contact and gate sheet resistance. This paper presents (a) an investigation of the effects of S/D processing (As and P implant conditions) on the RSCE, (b) effects of S/D and silicide processing on the contact and gate sheet resistance, (c) the use of an integrated system to optimize process modules and their interactions and (d) the validity of the modules and system in process development by obtaining a 4% improvement in drive current of a 0.25 micron NMOS device.
The Two-Step Rapid Thermal Annealing Effect of the Prepatterned A-SI Films
Authors: Park Kee-Chan , Choi Kwon-Young , Lee Min-Cheol , Han Min-Koo , Yoon Chan-Eui
Published: April 2011

Hydrogenated amorphous silicon (a-Si:H) films which were deposited by plasma enhanced chemical vapor deposition (PECVD) have been recrystallized by the two-step rapid thermal annealing (RTA) employing the halogen lamp. The a-Si:H films evolve hydrogen explosively during the high temperature crystallization step. In result, the recrystallized polycrystalline silicon (poly-Si) films have poor surface morphology. In order to avoid the hydrogen evolution, the films have undergone the dehydrogenation step prior to the crystallization step.

Before the RTA process, the active area of thin film transistors (TFT's) was patterned. The prepatterning of the a-Si:H active islands may reduce the thermal damage to the glass substrate during the recrystallization. The computer generated simulation shows the heat propagation from the a-Si:H islands into the glass substrate. We have fabricated the poly-Si TFT's on silicon wafers. The maximum ON/OFF current ratio of the devices was over 10.
Comparative Studies of Pb/Cu(001) by TEM, AFM and STM
Authors: Bocquet Franck , Cohen Camille , Schmaus Didier , Rocher André , Crestou Jacques , Gauthier Sèbastien
Published: April 2011

The same specimen of Pb/Cu grown under Ultra High Vacuum (UHV) conditions has been investigated by Scanning Tunneling Microscopy (STM), Atomic Force Microscopy (AFM) and Transmission Electron Microscopy (TEM). We show that the information obtained by these techniques is consistent when comparable, and complementary. In particular, three different morphologies of Pb islands with specific orientation relationship are observed; AFM reveals the faceted shape of the islands; STM permits an accurate determination of the atomic structure of the facets; TEM moir6 patterns reveal that Pb islands are well relaxed.
Fluctuations of Step Edges: Revelations About Atomic Processes Underlying Surface Mass Transport
Authors: Einstein T. L. , Khare S. V. , Pierre-Louis O.
Published: April 2011

Experimental advances in recent years make possible quantitative observations of step-edge fluctuations. By applying a capillary-wave analysis to these fluctuations, one can extract characteristic times, from which one learns about the mass-transport mechanisms that underlie the motion as well as the associated kinetic coefficients [1-3]. The latter do not require a priori insight about the microscopic energy barriers and can be applied to situations away from equilibrium. We have studied a large number of limiting cases and, by means of a unified formalism, the crossover between many of these cases[4]. Monte Carlo simulations have been used to corroborate these ideas. We have considered both isolated steps and vicinal surfaces; illustrations will be drawn from noble-metal systems, though semiconductors have also been studied. Attachment asymmetries associated with Ehrlich-Schwoebel barriers play a role in this behavior. We have adapted the formalism for nearly straight steps to nearly circular steps in order to describe the Brownian motion of single-layer clusters of adatoms or vacancies on metal surfaces, again in concert with active experimental activity [3,5]. We are investigating the role of external influences, particularly electromigration, on the fluctuations.
Nucleation of Islands During Epitaxial Growth: Influence of a Second Species
Authors: Ranade Pushkar S. , Chrzan D. C.
Published: April 2011

The theory of the nucleation and growth of islands is maturing rapidly. This advance is driven by the increased availability of experimental data, as well as the need for better control over growth processes. Recently, a number of authors have studied the effects of introducing a second species onto the surface in order to influence the ultimate growth morphology. In some situations, the addition of a second species results in a signficant change (approximately a factor of 1000) in the nucleated island density. The origin of this increase in density has been linked to the anomalous diffusion induced by the presence of the additional species of atoms. In the current paper, this dependence is explored further. In particular, earlier work focused on nucleation and growth in the regime in which the second species is essentially immobile. This constraint is relaxed here, and the subsequent model studied through application of a self-consistent mean-field theory. Predictions for the total island density are presented.
Epitaxy of Thin Ternary Co1−xFexSi2 Silicide Films on SI(111)
Authors: Khouchaf L. , Berling D. , Pierron-Bohnes V. , Pirri C. , Hong S. , Wetzel P. , Gewinner G. , Tuilier M. H. , Lefebvre S. , Cortts R.
Published: April 2011

Low-energy electron diffraction, x-ray diffraction, and x-ray absorption techniques are used to investigate the atomic structure of ternary silicides (MSi2, M = Co, Fe). 100 Å thick Co1−xFexSi2 films (with 0 ≤ × ≤ 1) were grown by codeposition onto a Si(111) substrate held at room temperature. The as-deposited films are metallic and adopt an ordered cubic structure of CsCl-type with essentially random vacancies, very similar to that of room-temperature grown FeSi2 and CoSi2 silicides. Upon annealing at 650°C, Fe-rich (x ≥ 0.85) films invariably convert into a semiconducting phase with a structure similar to the orthorhombic β-FeSi2 one. Yet, most interestingly, an almost cubic structure is preserved for x ≤ 0.85. Nevertheless, x-ray diffraction reveals a demixion into a Co rich CaF2-type silicide and a Fe-rich phase with a nearly cubic α-FeSi2 type structure. Extended x-ray absorption fine structure measurements indicate a local environment of Fe atoms similar to that in CsCl-type or α-FeSi2-type structure over the whole 0 < x < 0.85 composition range, showing that Fe does not merely substitute for Co atoms in a perfect CaF2-type CoSi2 structure, even for very low Fe content. In contrast, the local environment of Co atoms is similar to that in CoSi2 for Co-rich ternary compounds. Substantial modifications around Co sites are although observed in Fe richer silicides, suggesting that for x < 0.5, an appreciable amount of Co is incorporated in the α-FeSi2-type silicide phase.
Contribution to Optical Fiber Lifetime Modelling in Very Harsh Installation and Environment Conditions:Influence of the Temperature and pH on Optical Fiber Mechanical Behaviour.
Authors: Evanno Noëlla , Poulain Marcel , Gouronnec Alain
Published: April 2011

Today, during their use, optical fibers are subject to harsher installation and environmental conditions. So to evaluate optical fiber lifetime with higher precision, it is necessary to study the mechanical behaviour of optical fibers in extreme conditions : high stress and harsh environment.

This paper presents the results of static bending tests in distilled water at temperatures between 20°C and 70°C and in buffer solutions with a pH between 4 and 9.The stresses applied on optical fiber were between 3 and 3.5 GPa.

We observed a dependence of the failure time on temperature. This dependence can be described by the Arrhenius model, where the activation energy is one of the main parameters. The n-value seems also to change regularly with temperature. The results obtained in buffer solutions show that the pH influence on optical fiber strength may depend on coating characteristics.
Metallization of Silica Optical Fibers
Authors: Filas Robert W.
Published: April 2011

A review is presented of metallization processes of silica optical fiber. Fiber strengths and fatigue data are summarized and compared for liquid metal freezing, chemical vapor deposition, sputtering, electroless and electrolytic coatings. Both continuous in-line and termination-only processes are considered. Details of an electroless Ni-P plating process are presented which can be used to prepare fiber ends for soldering into hermetic packages.
Silicone Optical Attenuators
Authors: Lambert W. R. , Filas R. W. , King W. W.
Published: April 2011

Lucent Technologies manufactures and markets a family of SC and ST singlemode optical attenuator products which are low cost and easy to use. The attenuator elements are available in the attenuation range of 3 to 20 dB and are housed in buildout barrels which snap into companion buildout blocks to form complete optical couplings. The attenuator element is a 0.086-inch diameter thermoplastic material which, depending upon the attenuation level, has a thickness from 0.006 to 0.065 inches. In order to meet the full range of customer performance requirements, the attenuator element should not creep at temperatures up to 80°C and exhibit a reflection of less than -55 dB at optical telecommunication wavelengths. Commercially available thermoplastic materials cannot meet these requirements.
Visible and Infrared Rare-Earth Activated Electroluminescence From Erbium Doped GaN
Authors: Garter M. , Birkhahn R. , Steckl A. J. , Scofield J.
Published: April 2011

Room temperature visible and IR light electroluminescence (EL) has been obtained from Er-doped GaN Schottky barrier diodes. The GaN was grown by molecular beam epitaxy on Si substrates using solid sources (for Ga and Er) and a plasma source for N2. Transparent contacts utilizing indium tin oxide were employed. Strong green light emission was observed under reverse bias due to electron impact excitation of the Er atoms. Weaker emission was present under forward bias. The emission spectrum consists of two narrow green lines at 537 and 558 nm and minor peaks at 413, 461, 665, and 706 nm. There is also emission at 1000 nm and 1540 nm in the IR. The green emission lines have been identified as Er transitions from the 2H11/2 and 4S3/2 levels to the 4I15/2 ground state. The IR emission lines have been identified as transitions from the 4I13/2 and 4I13/2 levels to the 4I15/2 ground state. EL intensity for visible and IR light has a sub-unity power law dependence on bias current. An external quantum efficiency of 0.1% has also been demonstrated under a reverse bias current of 3.85 mA.
Optical Gain Spectra in InGaN/GaN Quantum Wells with the Compositional Fluctuations
Authors: Uenoyama Takeshi
Published: April 2011

The compositional fluctuations of the In content were found in InGaN/GaN quantum wells and it caused the localized states by the potential fluctuation. We have evaluated the optical gain of GaN based quantum well structures with localized states. The localized states are treated as the subband states of the quantum disk-like dots in the well. It was found that the inhomogeneous broadening played an important role in the optical gain and that it should be reduced to use the benefit of the localized states for laser oscillations.
Defect Complexes and Non-Equilibrium Processes Underlying the P-Type Doping of GaN
Authors: Reboredo Fernando A. , Pantelides Sokrates T.
Published: April 2011

It is well known that hydrogen plays a key role in p-type doping of GaN. It is believed that H passivates substitutional Mg during growth by forming a Mgs-N-Hi complex; in subsequent annealing, H is removed, resulting in p-type doping. Several open questions have remained, however, such as experimental evidence for other complexes involving Mg and H and difficulties in accounting for the relatively high-temperature anneal needed to remove H. We present first principles calculations in terms of which we show that the doping process is in fact significantly more complex. In particular, interstitial Mg plays a major role in limiting p-type doping. Overall, several substitutional/interstitial complexes form and can bind H, with vibrational frequencies that account for hitherto unidentified observed lines. We predict that these defects, which limit doping efficiency, can be eliminated by annealing in an atmosphere of H and N prior to the final anneal that removes H.
Interface Effects on the Persistent Photoconductivity in Thin GaN and AlGaN Films
Authors: Seifert O. P. , Kirfel O. , Munzel M. , Hirsch M. T. , Parisi J. , Kelly M. , Ambacher O. , Stutzmann M.
Published: April 2011

Thin films of GaN and its alloy AlGaN are investigated with respect to their properties of the persistent photoconductivity (PPC). In this work, we show that the film-substrate interface plays an important role for the metastable electrical effect. Strongly absorbed bandgap light causes an increase of photoconductivity which is about one order of magnitude higher when the sample is illuminated from the substrate side near the interface than from the growth side. To access the interface properties at the substrate, we use temperature-dependent Hall effect measurements. The smallest PPC effect was observed for the GaN film with the best interface properties grown on SiC.
Thermal Annealing of InGaN/GaN Strained-Layer Quantum Well
Authors: Chan Michael C.Y. , Tsang Kwok-On , Li E. Herbert , Denbaars Steven P.
Published: April 2011

Quantum well (QW) material engineering has attracted a considerable amount of interest from many people because of its ability to produce a number of optoelectronic devices. QW composition intermixing is a thermal induced interdiffusion of the constituent atoms through the hetero-interface. The intermixing process is an attractive way to achieve the modification of the QW band structure. It is known that the band structure is a fundamental determinant for such electronic and optical properties of materials as the optical gain, the refractive index and the absorption. During the process, the as-grown square-QW compositional profile is modified to a graded profile, thereby altering the confinement profile and the subband structure in the QW. The blue-shifting of the wavelength in the intermixed QW structure is found in this process.

In recent years, III-nitride semiconductors have attracted much attention. This is mainly due to their large bandgap range from 1.89eV (wurtzite InN) to 3.44eV (wurtzite GaN). InGaN/GaN quantum well structures have been used to achieve high lumens blue and green light emitting diodes. Such structures also facilitate the production of full colour LED displays by complementing the colour spectrum of available LEDs.

In this paper, the effects of thermal annealing on the strained-layer InGaN/GaN QW will be presented. The effects of intermixing on the confinement potential of InGaN/GaN QWs have been theoretically analysed, with sublattices interdiffusion as the basis. This process is described by Fick's law, with constant diffusion coefficients in both the well and the barrier layers. The diffusion coefficients depend on the annealing temperature, time and the activation energy of constituent atoms. The optical properties of intermixed InGaN/GaN QW structure of different interdiffusion rates have been theoretically analyzed for applications of novel optical devices. The photoluminescence studies and the intermixed QW modeling have been used to understand the effects of intermixing.
Thermal Stability of GaN Investigated by Raman Scattering
Authors: Kuball M. , Demangeot F. , Frandon J. , Renucci M.A. , Grandjean N. , Briot O.
Published: April 2011

We have investigated the thermal stability of GaN using Raman scattering. Noninvasive optical monitoring of the degradation of GaN during high-temperature processing has been demonstrated. GaN samples grown by molecular-beam epitaxy (MBE) and metalorganic vapor phase epitaxy (MOCVD) were studied. Characteristic features in the Raman spectrum identify three thermal stability regimes: (1) annealing below 900°C does not affect the GaN Raman spectrum; (2) annealing between 900°C and 1000°C results in the appearance of disorder-induced Raman scattering between the E2 and A1(LO) phonon; (3) annealing at temperatures higher than 1000°C gives rise to distinct Raman modes at 630 cm-1, 656 cm-1 and 770 cm-1. The evolution of the Raman spectrum of GaN with increasing annealing temperature is discussed in terms of disorder-induced Raman scattering. We find clear indications for an interfacial reaction between GaN and sapphire for annealing temperatures higher than 1000°C.
Study of Thin Films Polarity of Group III Nitrides
Authors: Dovidenko K. , Oktyabrsky S. , Narayan J. , Razeghi M.
Published: April 2011

Thin films of GaN grown by MOCVD on (0001) sapphire were studied by transmission electron microscopy in order to correlate the observed extended defects with crystal polarity of the films. We propose relatively simple and unambiguous method of polarity determination for wurtzite group III nitrides based on the dependence of the intensity of diffracted beams upon thickness of the specimen. Due to the dynamic scattering by polar structure, the convergent beam electron diffraction patterns lose inversion symmetry and become in fact fingerprints of the structure carrying information about crystal polarity. In this study, we have used the thinnest regions of the specimens (< 15 nm) and multiple diffraction spots in high-symmetry orientation for polarity determination. The films were found to have Ga-polar surfaces, either being unipolar, or containing thin (10-30 nm in diameter) columnar inversion domains (IDs) of N-polarity. The occurrence of IDs was correlated with specific types of dislocation distribution in the films.
Room Temperature Laser Action in Laterally Overgrown GaN Pyramids on (111) Silicon
Authors: Bidnyk S. , Little B. D. , Cho Y. H. , Krasinski J. , Song J. J. , Yang W. , McPherson S. A.
Published: April 2011

Single and multi-mode room temperature laser action was observed in GaN pyramids under strong optical pumping. The 5- and 15-micron-wide hexagonal-based pyramids were laterally overgrown on a patterned GaN/AlN seeding layer grown on a (111) silicon substrate by metal-organic chemical vapor deposition. The pyramids were individually pumped, imaged, and spectrally analyzed through a high magnification optical system using a high density pulsed excitation source. We suggest that the cavity formed in a pyramid is of a ring type, formed by total internal reflections of light off the pyramids' surfaces. The mode spacing of the laser emission was found to be correlated to the size of pyramids. The effects of pyramid geometry and pulse excitation on the nature of laser oscillations inside of the pyramids is discussed.
Base Transit Time in Abrupt GaN/InGaN/GaN and AlGaN/GaN/AlGaN HBTs
Authors: Chiu Shean-Yih , Anwar A. F. M. , Wu Shangli
Published: April 2011

Base transit time, τb, in abrupt npn GaN/InGaN/GaN and AlGaN/GaN/AlGaN double heterojunction bipolar transistors (DHBTs) is reported. Base transit time strongly depends not only on the quasi-neutral base width, but also on the low field electron mobility, μn, in the neutral base region and the effective electron velocity, Sc, at the edge of base-collector heterojunction. μn and Sc are temperature-dependent parameters. A unity gain cut-off frequency of 10.6 GHz is obtained in AlGaN/GaN/AlGaN DHBTs and 19.1 GHz in GaN/InGaN/GaN DHBTs for a neutral base width of 0.05um. It is also shown that non-stationary transport is not required to study τb for neutral base width in the range of 0.05um for GaN-based HBTs.
Generation Recombination Noise in GaN Photoconducting Detectors
Authors: Misra M. , Doppalapudi D. , Sampath A.V. , Moustakas T.D. , McDonald P.H.
Published: April 2011

Low frequency noise measurements are a powerful tool for detecting deep traps in semiconductor devices and investigating trapping-recombination mechanisms. We have performed low frequency noise measurements on a number of photoconducting detectors fabricated on autodoped n-GaN films grown by ECR-MBE. At room temperature, the noise spectrum is dominated by 1/f noise and thermal noise for low resistivity material and by generation-recombination (G-R) noise for high resistivity material. Noise characteristics were measured as a function of temperature in the 80K to 300K range. At temperatures below 150K, 1/f noise is dominant and at temperatures above 150K, G-R noise is dominant. Optical excitation revealed the presence of traps not observed in the dark, at room temperature.
The Charge Redistributon Accompanying Slip and Cleavage: Electronic Structure Calculations in Alloy Design
Authors: Eberhart M.E. , Woodward C. , Giamei A.F.
Published: April 2011

Extracting full information from electronic structure calculations requires the ability to compare differences in bonding between two molecules or solids. Often these comparisons use qualitative models of the chemical bond in an unsuccessful attempt to account for subtle variations in molecular properties. Correlating electronic structure with properties requires an unambiguous and quantifiable description of the chemical bond. Here, we show that such a description is contained within the geometric properties of the charge density, which can be obtained from quantum mechanical calculations. This description is used to rationalize the previously unexplained variation in the mechanical properties of a series of ordered intermetallic alloys. The ease with which this description of chemical bonding can be applied to problems, which have defied simple bonding explanations, suggests that it may be useful in accounting for the properties of any molecular system which arise from the making, breaking, or rearrangement of bonds.
Experimental Analysis of Deformation Induced Microstructure Near a Crack Tip in a Hardened Copper Crystal
Authors: Bastawros A.-F. , Kim K.-S.
Published: April 2011

The incremental in-plane Green-Lagrange strain tensor was measured near a stationary crack tip in a cyclically work-hardened copper single crystal. Measurements were made on the surface of a four-point bend specimen, using a finite-deformation laser moiré interferometer. The measurement showed the existence of a narrow asymptotic field beyond a distance of 300 μm from the crack tip. The inner boundary of the asymptotic zone was almost fixed at acharacteristic distanceahead of the crack tip. This length scale is thought to arise from a microstructural evolution near the crack tip. The inhomogeneous hardening due to glide-band clustering and patchy slip in a small volume near the crack tip triggered such an evolution. The outer boundary of the asymptotic zone radially grew with the increasing load. The deformation field was found to be very sensitive to additional mode II loading.