bluuebunny/crossref_metadata_2025 huggingface dataset:
Ion Beam Modification of TI-Ba-Ca-Cu-O Type High Temperature Superconductors During Irradiation
Authors: Newcomer P.P. , Wang L. M. , Morosin B.
Published: April 2011

Microstructural modification of high temperature superconductor (HTS) single-crystal plates of T1-1212 and T1-2212 (numbers designate the Tl/Ba/Ca/Cu cation ratio) was studied during 1.5 MeV Kr+ and Xe+ ion irradiation with in-situ electron diffraction and after ion irradiation with high resolution TEM (HRTEM). Similar in-situ temperature dependence effects are seen for both phases. During irradiations from 22K to 673K, an amorphous halo develops after very low ion dose or fluence (l.7X1012 ions/cm2). During irradiation at 100K and 300K, complete amorphization is obtained, while at 22K and ≥533K, the halo fades slightly and a polycrystalline ring pattern develops, indicating ion irradiation induced crystallization occurred. After a low ion dose (8.5XlO12ions/cm2) at 100K and 300K, HRTEM reveals amorphous regions 5 -20 nm in size which are not columnar and do not all penetrate the entire sample thickness. At 22K and ≥533K, Moire fringes and misoriented crystallites of cascade size are observed. The 4 - 6nm crystallites are thallium-rich.
Production of Defects in Metals by Collision Cascades: Tem Experiments
Authors: Kirk M. A.
Published: April 2011

I will review our experimental TEM data on the production of dislocation loops by low energy ion bombardment to low doses, as simulations of similar collision cascades produced by fast neutron irradiation, in various metals and alloys. The dependence of vacancy dislocation loop formation on recoil energy, sample temperature, and specific metal or alloy will be examined. Special emphasis will be placed on the effects of dilute alloy additions. A model for cascade melting will be employed to understand these effects, and will require an examination of the role of electron-phonon coupling in cascade cooling and recrystallization. The formation of interstitial dislocation loops as cascade defects, and the influence of the nearby surfaces in these experiments will be briefly discussed.
Cascade Damage in the Ordered Alloy Ni3AI
Authors: Bui Tho X. , Robertson I.M. , Kirk M. A.
Published: April 2011

The damage (disordered zones and vacancy loops) produced in the ordered alloy Ni3AI by irradiation with different ions (Ar+, Kr+, Xe+), ion energies (30 and 50 keV), and at 30 and 300 K has been investigated by using transmission electron microscopy. At room temperature and at constant ion energy, the average size of the disordered zones increases as the ion mass increases from Ar+ to Kr+and to Xe+ ions. This trend is opposite to that of the collisional volume which decreases with increasing ion mass and highlights the importance of the thermal spike in causing disorder. At room temperature and at constant ion mass, the zone size increases with increasing ion energy. At 30K, for the same ion mass and ion energy, the size of the disordered zones is smaller than at room temperature. At both irradiation temperatures, the dislocation loop yield increases with increasing ion energy and ion mass. The loop yield was lower for irradiations at 30K compared to at 300 K. Comparison of the dislocation loop yield and the size of the disordered zones indicates that the probability for forming a loop increases with the size of the disordered zone.
Excited State Absorption in Cubane-Like Transition Metal Clusters
Authors: Ji W. , Du H. J. , Shi S.
Published: April 2011

We report an investigation of excited-state absorption in cubane-like transition metal clusters. The fluence-dependent transmittances of the clusters have been measured with using 8-ns laser pulses. Time-resolved transmission measurements show that the triplet-triplet absorption occurs within a few nanoseconds. We have also developed a five-level (two singlet states, two triplet states, and one ionized state) model to simulate the excited-state absorption in these cluster compounds. The comparison between the model and the experimental measurements indicates that the population of the triplet states is created mainly by an ionization-recombination process and the triplet-triplet transitions are responsible for the observed nonlinear absorption.
Spectral Properties and Chi(3) of Metallo Meso-Tetra-Substituted Tetrabenzporphyrins
Authors: Nakashima Masato , Roach Joseph F. , Yeomans Walter G. , Alabran David M.
Published: April 2011

We have reported high Chi(3) values observed for metallo meso-tetra (substituted phenyl) tetrabenzporphyrins (metallo TPTBP). In order to find the relationship between the molecular structures and the Chi(3) values, we have attempted to find relationships between these values and the electronic spectral properties of the compounds. For a series of Zn TPTBPs, we found that the B and Q band peak wavelengths and the peak height ratio between these two bands are related as one would expect from such a series of porphyrins. The Chi(3) values appear to be directly related to the Q/B peak height ratio. For a series of metallo meso-tetra(p-methoxyphenyl) tetrabenzporphyrins, such a correlation of Chi(3) with the spectral properties of various metal species was not apparent. Strategies to increase the Chi(3) values of metallo TPTBP on the basis of these observations are discussed.
Optical Limiting in Protonic Doped Bis-Benzothiazole
Authors: Tang N. , Hellwarth R. W. , Partanen J. P. , Sun S. , Dalton L. R.
Published: April 2011

A ∼13% increase in the absorption coefficient is seen by a weak probe beam to build-up exponentially in ∼50 ps and decay in ∼1.4 ns after a ∼30 ps intense pump pulse (∼220 mJ/cm2 ) at 532 nm goes through a bis-benzothiazole/H2SO4 solution. We propose a three-level model to explain the effect and obtain the basic parameters by fitting our data to the model.
Approaches for Optimizing and Tuning the Optical Limiting Response of Phthalocyanine Complexes
Authors: Perry J. W. , Mansour K. , Marder S. R. , Chen C.-T. , Miles P. , Kenney M. E. , Kwag G.
Published: April 2011

Recent progress on the use of molecular engineering approaches for the enhancement and spectral tuning of the optical limiting responses of phthalocyanine complexes is presented. Examples are given involving the use of the heavy-atom approach to enhance the limiting response of naphthalocyanines and of donor substitution of naphthalocyanines to red shift the optical limiting response, as demonstrated for indium and tin octabutoxynaphthalocyanines. These approaches have led to new materials for optical limiting with potential for high performance. An experimental demonstration of the “bottleneck” limiter concept, in which the optical-limiting material is distributed nonhomogeneously to permit strong pumping of excited-state population throughout the interaction region, is presented and shows an order-of-magnitude increase in pulse suppression compared to a homogeneous distribution, without an increase in linear absorbance.
Nonlinear Optical Properties of Tetrabenzporphyrins
Authors: Wood Gary L. , Mott Andrew G. , Miller Mary J. , Nakashima Masato , Roach Joseph F.
Published: April 2011

Optical limiting in a solution of tetrabenzporphyrin (TBP) dissolved in tetrahydrofuran (THF) was measured in an f/5 optical focusing arrangement using 532 nm wavelength laser light with a 9 ns pulse duration. The performance of this solution was compared to a variety of other materials. In order to better understand the nonlinear behavior of this material, apertured and unapertured Z-scans were performed. From these measurements it was determined that the excited-state cross section and its ratio to ground-state cross section were large. The nonlinear refraction of this material is made up of contributions from thermal density change and population redistribution. Limiter performance was modeled in an f/64 limiter. The limiter behavior of a slightly modified compound and an additional solvent were measured.
Thermally Activated Transmissive Optical Elements for Rejection of Laser Radiation
Authors: Marcy H. O. , Warren L. F. , Cunningham P. H.
Published: April 2011

The sacrificial thermal shutter/reflector concept is suitable for optical power limiting in optical systems containing an intermediate focus and uses a thermally activated chemical process to form a mirror that reflects a large fraction of the incident laser light. Under normal illumination, the thermal reflector component is a transmissive optical element at or near a focal plane of an optical system. A pulse from an incident laser beam heats a film of precursor chemicals on the optical element and thereby converts it to a localized reflective metallic mirror. For visible laser pulses longer than 0.1 ms, the thermal shutter provides optical limiting at energies below the ANSI Maximum Permissible Exposure (MPE) standard for laser eye protection. For shorter pulses, near-MPE limiting is achieved. See-through during exposure is also possible with these elements. Various thermal shutter chemistries and efforts to form optically clear thin precursor films are described. The laser testing results highlight the importance of the substrate and absorber in these devices.
U.V Induced Visible Band Excited State Absorption in Liquid Crystal Media.
Authors: McEwan Kenneth J. , Hollins Richard C.
Published: April 2011

The transient absorption, in the visible band, induced by a UV laser pulse at 337nm in three different liquid crystal materials is studied. Two decay channels are observed and assigned to the relaxation of the singlet and triplet excited state populations. The fluorescence is also measured under both UV and two-photon (590nm) excitation and the rate of decay is found to compare well with the rapidly relaxing component of the induced absorption. A strong temperature dependence on both the fluorescence and absorption transients is observed and this is discussed in the context of excimer formation.
Polymer Hosts for Non-Linear Absorbing Materials
Authors: McGeoch Stephen P , Christie Alan , Bahra Gurmit S , Welford Kevin R
Published: April 2011

There is a recognised requirement for solid-phase, non-linear absorbing devices. We present data for a range of non-linear absorbing dyes in polymer hosts. We identify polycarbonate as a useful host material. We recognise that progress will be required to increase the laser-induced damage threshold of the dyed polymers if practical devices are to be realised.
Novel Polycarbonate Diacetylene Materials for Optical Limiting
Authors: Sandman Daniel J. , Conroy Jeffrey L. , Piche Joseph
Published: April 2011

In the interest of finding useful materials systems for optical limiting, we have sought to combine the attractive third order nonlinear optical properties of polydiacetylenes (PDA) with the desirable ballistic and mechanical properties of polycarbonates in our study of two different systems. Composites of Lexan polycarbonate with the PDA from 1,6-di-N-carbazolyl-2,4-hexadiyne have attractive laser power transmission characteristics. Macromonomers derived from the chloroformates of bis -phenols A and F and diacetylene diols were synthesized, their spectral, molecular weight, and thermal properties were studied, and the crosslinking of the macromonomers to PDA structures was investigated.
Grain Formation in Polycrystalline Silicon Films Deposition on SiO2 at Very Low Temperatures
Authors: Wang Kun-Chih , Wang Ruo-Yu , Yew Tri-Rung , Loferski Joseph J. , Hwang Huey-Liang
Published: April 2011

This paper describes the grain formation in very low temperature polycrystalline silicon (poly-Si) growth on SiO2. The silicon films were deposited by electron cyclotron resonance chemical vapor deposition with hydrogen dilution at 250°C and without any thermal annealing. The largest grain sizes observed in the poly-Si film is about 1 μm. The grains have a leaf-like shape as observed in plan-view transmission electron microscopy. The grain morphologies were determined by cross-sectional transmission electron microscopy and atomic force microscopy. Raman scattering spectrum was used to determine the crystalline fraction. X-ray diffraction patterns were used to study the film crystallinity. A simple model of grain formation is proposed.
Defects, Energies, Hydrogen, and Structural Properties of Molecular-Dynamics Modeled a-Si:H
Authors: Fedders P. A.
Published: April 2011

We use ab initio pseudopotential local-density-approximation methods to create and study related supercells containing 62 Si atoms and from 5 to 7 H atoms. In particular, we obtain energies and structural properties of H in different charge states that are passivating dangling bonds, in bond centered positions, and in other interstitial sites. The most striking result found is the rather large (of order 1 eV) spread of energies for a given type of defect, depending on its surroundings. We also find that changes in single particle energies or energy eigenvalues from defect to defect are not particular close to changes in the total energy and that the distinction, between bond centered H and a dangling bond plus an Si-H bond, is not as clear cut as one might think. The calculations also provide insights into possible migration mechanisms and energies for H movement.
Transient Mean-Field Reaction-Diffusion Model Applied to Hydrogen Evolution From Hydrogenated Amorphous Silicon
Authors: Franzi A. J. , Mavrikakis M. , Schwank J. W. , Gland J. L.
Published: April 2011

Hydrogen bulk mobility plays an important role in determining a wide range of materials and electronic properties of hydrogenated amorphous silicon (a-Si:H). The existence of two types of hydrogen traps plays an important role in controlling hydrogen mobility in, and evolution of hydrogen from a-Si:H, however, theoretical and experimental literature values for the trap energetics vary considerably. We have developed a mean-field reaction-diffusion model which explicitly includes two trap states and realistic surface processes to model hydrogen evolution from a-Si:H. Modern numerical techniques were required to solve this challenging problem over the wide range of temperatures and concentrations encountered in typical hydrogen evolution experiments. The model is based on a number of experimentally established parameters. Comparison of our rigorous model with temperature programmed hydrogen evolution experiments provides a powerful method for characterizing the energetics, trap concentrations and diffusivity of hydrogen in a-Si:H.
Is Thermal and Light-Induced Annealing of Met Astable Defects in a-Si:H Driven by Electrons?
Authors: Gleskova Helena , Wagner S.
Published: April 2011

We report results of a search for a unifying rate law for the annealing of metastable defects in hydrogenated amorphous silicon (a-Si:H). We tested the hypothesis that defect-annealing by both heating or illumination is driven by the density of free electrons. This hypothesis is formulated via the rate equation - dN/dt = A nα N f (T), where N is the defect density, t the time, A a constant, n the free electron density, and f (T) a function of temperature derived from a distribution of annealing energies. The model fits two sets of data, with light-intensity and electrical conductivity as the independent variables, reasonably well, with a ranging from 0.39 to 0.76, but not the third set, where we varied the temperature.
Telegraph Noise as A Probe of Microscopic Hydrogen Motion in Amorphous Silicon
Authors: Lust Lisa M. , Kakalios J.
Published: April 2011

Time traces of conductance fluctuations in the co-planar current of hydrogenated amorphous silicon (a-Si:H) display sharp jumps between discrete resistance levels, termed random telegraph switching noise (RTSN). Measurements of the temperature dependence and effects of light soaking of the RTSN in n-type doped a-Si:H are reported. The rise times between the two level fluctuators yield activation energies and attempt to hop frequencies for microscopic hydrogen motion which agree with those obtained from NMR experiments. Computer simulations of a dynamical percolation random resistor network support the suggestion that the RTSN arises from local diffusion processes altering the conductance of inhomogeneous current filaments.
Electron Drift Mobility in a-Si:H Prepared by Hot-Wire Deposition
Authors: Gu Qing , Schiff E. A. , Crandall R. S. , Iwaniczko E. , Nelson B.
Published: April 2011

We have measured the electron drift mobility in a-Si:H prepared by hot wire (HW) deposition using photocarrier time-of-flight. Initial work has shown that light-soaked HW material can have much better ambipolar diffusion lengths than the plasma-deposited material following extended light soaking. In a sample with about 2% H-concentration in the intrinsic layer, we find that the electron drift mobility is quite different from that of a-Si:H alloys prepared by normal glow-discharge CVD, even allowing for the reduced bandgap of the hot Wire material. This result challenges the principle that the bandgap of optimized amorphous silicon based material is sufficient to predict the electron drift mobility.
Phototransport Properties of a-SiC:H Alloys
Authors: Nery G. , Ramirez A. , Resto O. , Weisz S. Z. , Lubianiker Y. , Balberg I.
Published: April 2011

We report a study of the mobility-lifetime products of the two charge carriers in a-SiC:H alloys. The measurements were carried out as a function of the carbon concentration and the temperature. An analysis, relying on the interpretation of the corresponding light intensity exponents, indicates that neutral dangling bonds control the electrons' lifetime while another recombination center controls the holes' lifetime.
Time Dependence of Spatial Defect Profiles in a-Si:H Solar Cells with Light-Soaking
Authors: Caputo D. , Maggi M. , Masini G. , Palma F. , Vasanth K. , Wagner S.
Published: April 2011

We report on modeling the evolution of the spatial defect profile in the i-layer of a-Si:H solar cells combined with tests of the model against the efficiency decay of amorphous silicon (a-Si:H) p-i-n solar cells under various light-soaking conditions. We use a finite-element device simulator. The defect density during light-soaking is calculated as a function of time and of position. The defect density evolves due to the combined effects of light-induced generation, assumed proportional to the product of free carrier densities, and of light-induced annealing, assumed proportional to the sum of carrier densities. We find that in thick cells defects close to the p-i interface affect cell efficiency less than bulk defects, and that in thin cells the defect density increases significantly in the central portion of the i-layer. However, in thin cells the high electric field masks the effect of the defect density increase.
New Si CVD Precursors: Preparation and Pre-Screening
Authors: Gaines D. , Hop M. , Kuech T. , Redwing J. , Saulys D. , Thon A.
Published: April 2011

Silanes and their organo-derivatives are of interest as precursors and dopants in chemical vapor deposition (CVD) to prepare (modified) thin films with unique surface properties. Applications of these films are widespread: transitors, laser diodes, optoelectronic devices, etc. Film growth, however, is capital intensive and mechanistically complex, while film characterization is time-consuming and often requires sophisticated instrumentation. A tool is needed to prescreen precursors' CVD behavior, preferrably a technique requiring a minimum of time and sample to provide information directly related to aspects of the film growth process.
Deuterium Incorporation into Glow-Discharge Deposited Deuterated-Hydrogenated Amorphous Silicon
Authors: Sidhu L. S. , Gaspari F. , O'Leary S. K. , Zukotynski S.
Published: April 2011

We investigate deuterium incorporation into deuterated-hydrogenated amorphous silicon grown by the saddle-field glow-discharge of deuterium and silane. The presence of HD and SiH3D in the discharge suggests strong gas phase mixing. The dominant process of deuterium incorporation into the growing film appears to be the direct reaction between deuterium and the growth surface.
Passivation Studies on AlGaAs Surfaces Suitable for High Power Laser Development
Authors: Edirisinghe C. , Ruda H. E. , Koutzarov I. , Liu Q. , Jedral L. , Boudreau M. G. , Boumerzoug M. , Brown J. , Mascher P. , Moore A. , Henderson R.
Published: April 2011

We report on the optical characterization of sulphur (S) passivated AlxGa1−xAs/GaAs surfaces using photoluminescence (PL) and surface photovoltage (SPV) measurements. Both techniques show an enhancement in the near bandgap signal intensity, implying a reduction of the non-radiative recombination rate at the surface. To counter the instability of S-passivation, due to re-oxidation, dielectric layers of silicon nitride were deposited using electron cyclotron resonance plasma enhanced chemical vapour deposition (ECR-PECVD); the deposition of dielectric layers up to lOOnm thick does not appear to cause significant deterioration or stress at the insulator/AlGaAs interface. The dielectric layers are shown to be resistant to oxidation, and effective in maintaining the passivation effect over a period of weeks.
Deep Impurities in AlGaAs Grown by MOCVD Using Different Hydrogen and Nitrogen as Carrier Gases
Authors: Chen J. C. , Huang Z. C. , Yang Bing , Chen H. K. , Lee K. J.
Published: April 2011

A study was carried out to characterize the deep impurities in AlxGa1-x As grown by metal-organic chemical vapor deposition (MOCVD) using different carrier gases. Since AlxGai1-x As is very sensitive to any impurities, especially moisture and oxygen, in the growth process, the concentration of impurities in AlxGai1-xAs can serve as a measure of the purity of carrier gases. The undoped AlGaAs layers grown by using H2 have n-type background concentrations from 3×1015 to 10×1015/cc. The concentrations of oxygen-related traps (Ec−0.53 and 0.7 eV) are 0.2−9×1013 and 3.4−5×1014/cc for Pd- and Li-purified H2, respectively. Low-temperature photoluminescence (PL) measurements show better PL efficiency in samples grown by using Pd- purified H2. AlxGa1-xAs grown by using N2 is p-type (p∼6×1016/cc) with an oxygen-related trap and two hole traps. The concentration of oxygen-related trap is more than one order of magnitude higher than that of AlGaAs using Pd-purified H2. The memory effect due to impurities from carrier gas left in source materials is also studied.
Low Deep Impurity InxGa1-xP Grown by Metalorganic Chemical Vapor Deposition
Authors: Huang Z. C. , Yang Bing , Chen H. K. , Chen J. C.
Published: April 2011

InxGai-xP (x=0.49) layers lattice-matched to GaAs have been grown by metalorganic chemical vapor deposition (MOCVD). We did not observe any deep levels in the temperature range of 30-380K by deep level transient spectroscopy (DLTS) in undoped In0.49Ga0.51P layers which have a background concentration of 3.1×1015 cm−3. The deep levels, if they exist, have a concentration of less than 5×1011 cm−3, which is the lowest deep level concentration found so far in InxGa1-xP materials. Moreover, lattice-mismatched InxGa1-xP/GaAs heterojunctions were deliberately grown by varying the In-composition ranging from 0.43 to 0.57. No deep levels were created in 1-μm-thick InxGa1-xP layers due to lattice mismatch when 0.469 < x < 0.532. However, we have observed a shallow electron trap at EC - 60 meV in InxGa1-xP layers with x < 469, and a deep electron trap located at Ec - 0.85 eV in the samples with x > 0.532. We suggest that the lattice-mismatch-induced-defects in InxGa1-xP are either electrically inactive or resided outside the bandgap when In content ranging from 0.469 to 0.532.
Optical Absorptions and EL2-Like Defects in Low Temperature Grown Molecular-Beam-Epitaxial GaAs
Authors: So S. K. , Chan M. H. , Chan K. T.
Published: April 2011

The optical absorptions and the defect densities of GaAs grown by low temperature molecular-beam-epitaxy at growth temperatures between 200-580 °C were evaluated by photothermal deflection spectroscopy. The shapes of the absorption spectra exhibit EL2-like characteristics. Defect densities were found to be in the range of 1018-1019 cm−3. The PDS phase spectra were shown to be useful to differentiate the absorptions of the epilayer from those of the bulk.
On the Recombination Activity of Oxygen Precipitation Related Lattice Defects in Silicon
Authors: Vanhellemont J. , Kaniava A. , Libezny M. , Simoen E. , Kissinger G. , Gaubas E. , Claeys C. , Clauws P.
Published: April 2011

The recombination activity of oxygen precipitation related lattice defects in p- and n-type silicon is studied with photoluminescence (PL) and microwave absorption (MWA) techniques. A direct correlation is observed between the amount of precipitated oxygen and the extended defect density on one hand and the minority carrier lifetime and PL activity on the other hand. The PL analyses show as dominant features in the spectra the Dl and D2 lines. The relative amplitude of the D-lines in the different samples is investigated as a function of the oxygen content, defect density and excitation level. The results are correlated with those of complementary techniques and are interrelated on the basis of Shockley-Read-Hall (SRH) theory.
ECR Hydrogen Plasma Treatment of Si: Defect Activation Under Thermal Anneal
Authors: Nam C. W. , Ashok S.
Published: April 2011

Si wafers subject to short-time (4–12 min.), low-temperature atomic hydrogen cleaning in an electron cyclotron resonance (ESR) plasma system have been annealed subsequently in the temperature range 300–750 °C for 20 mins. While only a small broad peak is seen immediately after hydrogenation, several pronounced and distinct majority carrier trap levels show up in deep level transient spectroscopy (DLTS) measurements of subsequently fabricated Schottky diodes on samples annealed at 450 °C and above. The concentrations of these deep levels reach a maximum at anneal temperatures around 500 °C and drop substantially beyond 750 °C. This phenomenon appears to be unrelated to the presence of oxygen in Si and is of potential importance in silicon processing technology.
Hydrogen and Lithium Passivation of Gold in Silicon: A Comparative Study
Authors: Sveinbjörnsson E. ö. , Kristjansson S. , Engström O. , Gislason H. P.
Published: April 2011

We report studies of passivation of the gold center in silicon by hydrogen and lithium using deep level transient spectroscopy (DLTS), capacitance voltage (CV) profiling and secondary ion mass spectroscopy (SIMS). Both lithium and hydrogen are able to remove the electrical activity of the gold center from the silicon band gap but the passivation mechanisms are different. In the case of lithium the passivation is most likely due to a Coulomb attraction between lithium donors Li+ and gold acceptors Au−. No complex formation is observed between Li+ and Au0. In contrast, hydrogen is able to passivate the gold center without the need of opposite charge states of the species involved. Two Au-H complexes are observed, one (G) electrically active, and another (PA) passive. Based on the annealing kinetics of these complexes we propose that the active complex is a Au-H pair and that the passive complex contains two H atoms (Au-H2).
Hydrogen-Induced Passivation of Deep Traps in n-GaAs:Si Grown on LT-GaAs
Authors: Paloura E. C. , Ginoudi A. , Theys B. , Chevallier J. , Lioutas C. B. , Kalomiros J. , Lagadas M. , Hatzopoulos Z.
Published: April 2011

We study the hydrogen-induced passivation of interface traps in n-GaAs:Si, grown by MBE at 580°C, with a buffer layer grown at 200 to 250°C (LT-buffer). In the as-grown samples, the LT-buffer contains As-precipitates, with a density of 4×1016 cm−3 and a diameter that depends on the LT-buffer growth temperature and takes values in the range 4–8nm. The epilayer/LT-buffer interface in the as-grown samples is characterised by interface related traps which dominate the electrical behaviour of the epitaxial layer. Secondary ion mass spectroscopy profiling of deuterated samples reveals that 2H has a nearly uniform concentration throughout the epilayer, while it accumulates at the interface. Hydrogenation induces a reduction of the interface trap concentration and a significant improvement of the carrier mobility values.
High Resistivity InAIN by Nitrogen or Oxygen Implantation
Authors: Zolper J. C. , Pearton S. J. , Abernathy C. R. , Vartuli C. B.
Published: April 2011

We report on the isolation properties of In0.75Al0.25N implanted with either N or O for several doses and post-implant anneal temperatures. Sheet resistance versus anneal temperature data are reported for the various implants with a maximum sheet resistance of <1×109 Ω/□ achieved for a high dose N-implant annealed at 600 or 700 °C and <5×108 Ω/□ achieved for a high dose O-implant annealed at 600 °C. These sheet resistances correspond to a greater than three order of magnitude increase over the as-grown values. The compensating defect level for the highest resistance N-implanted sample has an estimate ionization level 580 meV below the conduction band edge. Implant isolation of InAIN is also compared to oxygen implant isolation of InxGa1-xN — where only a 50 to 100 fold increase in sheet resistance is observed — to study the effect of Al in the isolation scheme.
Silicon Delta Doping in GaAs: An Ongoing Enigma
Authors: Newman R. C. , Ashwin M. J. , Wagner J. , Fahy M. R. , Hart L. , Holmes S. N. , Roberts C.
Published: April 2011

Infrared (IR) absorption and Raman scattering are reported from the localized vibrational modes (LVM) of Al and Si δ-layer superlattices in MBE (100) GaAs grown at 400°C as a function of the total areal concentrations, [A1]A and [Si]A respectively. The Al superlattices show the expected behavior on passing from sub-monolayer (ML) to thicker layers (thin AlAs) since the impurities still occupy only Ga-sites. The behavior is very different from that found for Si δ-layers. In addition to SiGa reported previously, we now show that SiAs, SiGa-SiAs pairs and the electron trap Si-X are also present in Si δ-layers and superlattices for 0.05 ≤ [Si]A≤ 0.5 ML. The conductivity of these structures and the concentrations of substitutional Si in GaAs at all sites fall to zero for [Si]A> 0.5 ML but a Raman feature at 470–490 cm−1, attributed to the vibrations of covalent Si-Si bonds is then detected. This feature is not observed in structures containing very closely spaced dilute (0.01 ML) Si δ-planes. It is inferred that long-range Si diffusion does not occur in the bulk crystal, although there could be surface diffusion during Si deposition. The maximum measured carrier concentrations are always less than 2 × 1019 cm−3, the DX limit. The redistribution of Si amongst the various lattice sites is discussed in terms of SiGa DX-like displacements occurring during growth, followed by local thermally activated diffusion jumps. It is speculated that AsGa antisite defects and Ga-vacancies are produced by this process. The reason why the Si δ-layer is non-conducting remains unclear.
Activation of Implanted Phosphorus Ions into Silicon by Followed Hydrogen Ion Implantations
Authors: Hasebe Y. , Ohshima H. , Hattori T. , Usami A. , Tokuda Y.
Published: April 2011

The activation of phosphorus implanted into n-type silicon (100) substrate by followed hydrogen ion(H +) implantation was studied by means of spreading resistance technique(SR), secondary ion mass spectroscopy(SIMS) and transmission electron microscopy(TEM).

“The activation ratio” defined by carrier concentration divided by phosphorus concentration was used as a measure of activation of phosphorus. The H + energy, dose and dose rate dependence of activation ratio of phosphorus was investigated.

In the case of thermal annealing at 400 °C for 200 minutes the phosphorus atoms were not activated, on the other hand in the case of H + implantation at 400 °C the phosphorus atoms were activated and the activation ratio was increased almost proportionally with the dose. The SIMS data suggested that the depth profile of phosphorus atoms was not changed after activation by H + implantation. The activation ratio was increased with decreasing the dose rate. The TEM data suggested that the density of residual defects was reduced in the case of lower dose rate. The depth profile of activation ratio was similar to that of hydrogen atoms implanted at 20 °C. From these results the activation and recrystalization mechanism is discussed in the view of contribution of elastic collision process between H + ions and substrate atoms.
A Model for the Frequency Dependence of Charge Pumping Current in Polycrystalline Silicon Thin Film Transistor
Authors: Lee Ga-Won , Lee Jung-Yeal , Choi Deuk-Sung , Hur Sung-Hoi , Kim Choong-Ki , Han Chul-Hi
Published: April 2011

Making a comparative study between MOSFET and polycrystalline silicon thin film transistor(poly-Si TFT) in applying the charge pumping method(CPM), the most distinctive difference was found in the relation of the charge pumping current(Icp) versus the gate pulse frequency. According to the conventional theory, Icp increases linearly with the gate pulse frequency. In poly-Si TFT, however, Icp shows complicated dependence on frequency. We modeled the frequency dependence of Icp in poly-Si TFT by considering the resistance of active poly-Si film. According to this model we can extract the parameters such as grain boundary trap density, substrate resistance, and capture cross section.
Investigation of Resistivity Distributions in CdTe Crystals by Time Dependent Charge Measurements (TDCM)
Authors: Eiche C. , Joerger W. , Fiederle M. , Schwarz R. , Salk M. , Ebling D. G. , Benz K. W.
Published: April 2011

Spatially resolved resistivity measurements of CdTe crystals doped with Titanium (Ti) and Vanadium (V) were performed. From the temperature dependence of the resistivity the spatial variation of the thermal activation energy was deduced. Variations in axial as well as radial direction were observed and qualitatively explained by a combined segregation and compensation model. It is based on the deep donor levels of Ti and V at 0.95 eV below the conduction band.
Temperature Dependence of Metal-Semiconductor Contacts on 6H-SiC.
Authors: Smith S.R. , Evwaraye A.O. , Mitchel W.C.
Published: April 2011

We have examined the temperature dependence of the barrier height of Au, Ag, Ni, and Al, metal-semiconductor contacts on n-type 6H-SiC, and Al metal-semiconductor contacts on p-type 6H-SiC. The barrier height was determined from the (1/C2) vs VRcharacteristics of the contacts at temperatures ranging from 300K to 670K. The measurements were made at 1 MHz. These measurements were compared to I-V measurements at various temperatures, and to the behavior predicted by standard models.
Classical and Rapid Thermal Process Effects on Oxygen and Carbon Precipitation in Silicon
Authors: Mahfoud K. , Loghmarti M. , Muller J. C. , Siffert P.
Published: April 2011

We report observations on the effects of rapid thermal annealing on oxygen and carbon content of different single and multicrystalline silicon materials.

From the comparison between the resulting effects of conventional and short thermal annealing, we can deduce that the increase of the concentration of interstitial oxygen after a rapid thermal annealing (RTA) is due to the dissociation of some microprecipitates in silicon, which is significantly affected by the initial oxygen content, thermal history, defects and impurity content such as carbon.
Large In-Plane Lattice Expansion in NiAs-MnSb Thin Films Induced by ns Laser Recrystallization
Authors: Kubota Yukiko , Gorman Grace L. , Marinero Ernesto E.
Published: April 2011

Sputter deposited MnSb thin films were annealed utilizing KrF excimer laser pulses (16ns), and the resulting structural and magnetic changes investigated. These changes are compared to those observed when the samples are subjected to isothermal and rapid thermal annealing treatments. Isothermal and rapid thermal annealing induce significant lateral grain growth, whereas the laser treatment produces vertical grain size refinement with no appreciable lateral growth. Annealing is shown to increase the hexagonal c-axis, reaching an expansion value of 7% for the laser annealed samples. This c-axis expansion has a strong influence on the magnetic properties of the thin films. Mechanisms for the c-axis expansion are discussed.
Time Dependent Magnetic Switching in Spin Valve Structures
Authors: Restorff J. B. , Wun-Fogle M. , Cheng S. F. , Hathaway K. B.
Published: April 2011

We have observed time dependent magnetic switching in spin-valve sandwich structures of Cu/Co/Cu/Fe films grown on silicon and Kapton substrates and Permalloy/Co/Cu/Co films grown on NiO or NiO/CoO coated Si substrates. The giant magnetoresistance (MR) values ranged from 1 to 3 percent at room temperature. The films were grown by DC magnetron sputter deposition. Measurements were made on the time required for the MR to stabilize to about 1 part in 104 after the applied field was incremented. This time depends almost linearly on the amplitude of the timedependent MR change with a slope (time / ΔMR) of 20 000 to 30 000 s. Some samples took as long as 70 s to stabilize. The time dependent effects may be important for devices operating in these regions of the magnetoresistance curve. In addition, measurements were made on the time history of the MR value for a period of 75 s following a step change in the field from saturation. We observed that the time dependent behavior of the MR values of both experiments produced an excellent fit to a function of the form ΔMR(t) = α + β;ln(t) where ɑ and β are constants. This time dependence was consistent with the behavior of the magnetic aftereffect.
Calculated Electronic Structure and Transport Properties of La.67Ca.33MnO3
Authors: Butler W. H. , Zhang X.-G. , Maclaren J. M.
Published: April 2011

We have calculated the electronic structure, total energy, magnetic moments and electrical resistivities of La.67Ca.33MnO3 using mean field band theory. The magnetic and structural properties seem to be in good agreement with experiment. The calculations predict that La.67Ca.33MnO3 is metallic for the majority spins and semiconducting for the minority spins.
The Connection of Sum Rule and Branching Ratio Analyses of Magnetic X-Ray Circular Dichroism in 3d Systems
Authors: Tobin J.G. , Waddill G.D. , Jankowski A.F. , Sterne P.A. , Pappas D.P.
Published: April 2011

In the recent past, Carra, et al. derived a sum rule for electric dipole transitions in a single ion model that could be used to extract an elementally-specific spin-magnetic-moment (μSPIN) from magnetic x-ray circular dichroism (MXCD) spectra. Earlier, we proposed the utilization of a branching ratio analysis for the determination of μSPIN, based upon a simplified oneelectron, atomic picture which assumed complete orbital quenching. Here, it will be shown that these two approaches are essentially related in the case of 3d ferromagnetic materials. Both methods are based upon a comparison of the integrated intensity in the L3(J=3/2) white line peak versus the sum of the intensities in the L3(J=3/2) and L2(J=l/2) peaks, after background removal. An error estimate will also be presented. A more complete description of our work is under preparation.
Effects of SC-1 Dilution and Temperature Variations on Etch Rate and Surface Haze
Authors: Christenson K. K. , Smith S. M.
Published: April 2011

The slight etch and accompanying roughening of the silicon by the APM solution are of great concern as device geometrys and gate oxide thicknesses decrease. This report covers the variations in the SiO2 etch rate and surface roughening of an APM solution as a function of NH4OH and H2O2 concentration and temperature. In general, the etch rate and roughening increased with increasing temperature and NH4OH concentration but was unaffected by H2O2 concentration. Other portions of the larger APM study covering the addition and removal of metals and the removal of particles by APM are published elsewhere. Together, these studies provide a complete set of process response surfaces for the SC-1 chemistry. These surfaces can be used to select the most promising regime of parameter space for any particular process.
New Method to Characterize Thin Oxide Reliability
Authors: Lin Heng-Chih , Snyder J. P. , Helms C. R.
Published: April 2011

Next generation ULSI devices will require ultra thin gate insulators where degradation due to contamination or surface microroughness is an even more important problem. Tunneling and breakdown characteristics are critical electrical testing methods, but unfortunately obtaining meaningful oxide integrity information on the one hand and tunneling IV's on the other is a tedious and time consuming process.

In this research, we report on a new method to measure meaningful IV's, Qbd's, and Vbd's at the same time. This method uses a linear current ramp strategy where a voltage ramp to between 8–10 MV/cm is applied first followed by a linear current ramp until breakdown is reached. There are several advantages of this new method: The linear voltage ramp quickly and easily identifies low breakdown devices, whereas switching to a linear current ramp provides for nearly constant field stressing to obtain meaningful IV and Qbd
Properties of Gate-Quality SiO2 Films Prepared by Electron Cyclotron Resonance Chemical Vapour Deposition in an Ultrahigh Vacuum Processing System
Authors: Tao Y. , Landheer D. , Hulse J. E. , Xu D.-X. , Quance T.
Published: April 2011

We have prepared thin SiO2 layers on Si(100) wafers by electron cyclotron resonance chemical vapour deposition (ECR-CVD) in a multi-chamber ultra-high vacuum (UHV) processing system. The oxides were characterized in-situ by single wavelength ellipsometry (SWE) and x-ray photoelectron spectroscopy (XPS) and ex-situ by Fourier transform infra-red spectroscopy (FTIR), spectroscopic ellipsometry (SE) and capacitance-voltage (CV) electrical measurements. Films deposited at higher pressures, low powers and low silane flow rates had excellent physical and electrical properties. Films deposited at 400 °C had better physical properties than those of thermal oxides grown in dry oxygen at 700 °C. A 1 minute anneal at 950 °C reduced the fast interface state density from 1.2×1011 to 7×1010 eV−1cm−2
Collisional Effects of Background Gases on Pulsed Laser Deposition Plasma Beams
Authors: Geohegan David B. , Puretzky Alex A.
Published: April 2011

The penetration of energetic pulsed ablation plumes through ambient gases is experimentally characterized to investigate a general phenomenon believed to be important to film growth by pulsed laser deposition (PLD). Under typical PLD conditions involving background gases, the ion flux in the ablation plume is observed to split into distinct fast and slow components over a limited range of distances1,2 the fast component is transmitted with near-initial velocities and high kinetic energies, potentially damaging to growing films at these distances. Formation of the second, significantly-slowed component correlates with the bright contact front3 formation observed1,4 in fast ICCD imaging studies. This general effect is explored in detail for the case of yttrium ablation into argon, a single-element target into an inert gas.5 Time-resolved optical absorption spectroscopy and optical emission spectroscopy are employed to simultaneously view the populations of both excited and ground states of Y and Y+ for comparison with quantitative intensified-CCD photography of the visible plume luminescence and ion flux measurements made with fast ion probes during this phenomenon. these measurements confirm that, in addition to the bright significantly-slowed front which has been described by shock or drag propagation models1, a fast-component of target material is transmitted to extended distances for some ambient pressures with near-initial velocities.
High-Pressure Pulsed Plasma Synthesis of Carbon-Nitride Thin Films
Authors: Gurarie V. N. , Orlov A. V. , A Bursill L. , JuLin Peng , Nugent K. W. , Prawer S.
Published: April 2011

In this study a high N2 pressure has been used to enhance the N incorporation into CN films produced by a shock plasma deposition method. auger spectroscopy indicates that increasing the nitrogen pressure from 0.1 atm to 10 atm results in an increase of nitrogen incorporation into CN films to a maximum of 43 at.%. Nitrogen distribution varies across the surface of the deposit, showing an increase of nitrogen content with depth in the center of the deposition and a decrease with depth at points away from the center. SEM and optical microscopy indicate that under increased nitrogen pressure the grain structure becomes finer. Raman spectra contain sharp peaks characteristic of a distinct crystalline CN phase. TEM diffraction patterns for the films produced under N2 pressure in the range of 0.05-0.1 atm unambiguously show the presence of micron-sized crystals displaying a cubic symmetry, and not the predicted β-Si3N4 type structure. PEELS data suggest that in the crystalline phase a significant fraction of the nitrogen atoms have sp2 trigonal bonds and there is a significant degree of sp3 character for the carbon atoms.
Low Temperature Deposition of Diamond Thin Films Using Electron Cyclotron Resonance Plasmas
Authors: Gilbert Donald R. , Singh Rajiv K.
Published: April 2011

We have used an electron cyclotron resonance enhanced plasma system to deposit films from methyl alcohol at a pressure of 1.00 Torr. Depositions occurred on silicon substrates at temperatures from 550 - 750 °C. Film morphology was examined using SEM. Structural characterization was conducted using Raman spectroscopy and x-ray diffraction. Based on these analyses, certain trends in film quality as a function of deposition temperature were determined.
Formation of artificially-Layered Thin-Film Compounds Using Pulsed-Laser Deposition
Authors: Norton David P. , Chakoumakos B. C. , Lowndes D. H. , Budai J. D.
Published: April 2011

Superlattice structures, consisting of SrCuO2, (Sr,Ca)CuO2, and BaCuO2 layers in the tetragonal, "infinite layer" crystal structure, have been grown by pulsed-laser deposition (PLD). Superlattice chemical modulation is observed for structures with component layers as thin as a single unit cell (~3.4 Å), indicating that unit-cell control of (Sr,Ca)CuO2 growth is possible using conventional pulsed-laser deposition over a wide oxygen pressure regime. X-ray diffraction intensity oscillations, due to the finite thickness of the film, indicate that these films are extremely flat with a thickness variation of only ~20 Å over a length scale of several thousand angstroms. Using the constraint of epitaxy to grow metastable cuprates in the infinite layer structure, novel high-temperature superconducting structural families have been formed. IN particular, epitaxially-stabilized SrCuO2/BaCuO2 superlattices, grown by sequentially depositing on lattice-matched (100) SrTiO3 from BaCuO2 and SrCuO2 ablation targets in a PLD system, show metallic conductivity and superconductivity at Tc(onset) ~70 K. these results show that pulsed-laser deposition and epitaxial stabilization have been used to effectively "engineer" artificially-layered thin-film materials.
Viscoelastic Characterization of an Epoxy-Based Molding Compound
Authors: Kenner V. H. , Julian M. R. , Popelar C. H. , Chengalva M. K.
Published: April 2011

This paper describes the viscoelastic characterization of a highly filled epoxy molding compound commonly used in electronic packaging applications. Both stress relaxation tests and constant strain rate tensile tests were conducted. The material was found to be nonlinear in its viscoelastic behavior and to be amenable to horizontal shifting to form master curves. A representation of the master stress relaxation curves in terms of a Prony series is given, and the use of this representation illustrated in the context of both linear and nonlinear representations of the viscoelastic behavior to predict the results of the constant strain rate experiments.