bluuebunny/crossref_metadata_2025 huggingface dataset:
μτ Products of 10−6 cm2V−1 Deduced from Eleverse-Bias Dependence of Carrier-Collection Measurements in High Drift Mobility a-Si:H
Authors: Ganguly Gautam , Matsuda Akihisa
Published: April 2011

The room temperature hole drift mobility measured by the ‘time-of-flight’ technique can be increased to 0.5 cm2/Vs with a valence band tail width of 25meV by optimizing the ion impingement energy during film growth using a triode configured PECVD reactor. The reverse bias dependence of the carrier collection in Au Schottky diodes formed on these specimens show significantly improved carrier collection which can be approximately quantified using the C-V measured voltage dependent depletion widths to yield μτ≈10−6cm2V−1.
Influence of Precursor Chemistry on Synthesis of Silicon-Carbon-Germanium Alloys
Authors: Todd Michael , Kouvetakis John , Matsunaga Phillip , Chandrasekhar D. , Smith David
Published: April 2011

We describe the synthesis and use of the novel molecular precursors C (SiH3) 4, CH3GeH3and SiH3GeH3 to generate silicon-carbon-germanium materials by ultrahigh vacuum chemical vapor deposition. By using these precursors in reactions with S1H4 and GeH4 between 470°C and 650°C we obtained: 1) heteroepitaxial Si1-x-y. GexCy (y=0.04–0.06) alloys with C (SiH3) 4; (2) polycrystalline alloys with carbon compositions ranging from 2–14 at.% with CH3GeH3; (3) mixtures of diamond cubic nanocrystals (Ge, Si1-xGex) and amorphous SiC with SiH3CH2GeH3. The effect of the precursor chemistry on composition, crystallinity, and microstructure of the materials as characterized by Rutherford backscattering spectroscopy (RBS), secondary ion mass spectrometry (SIMS) and transmission electron microscopy (TEM) is discussed.
Amorphous-to-Microcrystalline Silicon Transition in Hot-Wire Chemical Vapor Deposition
Authors: Brogueira P. , Chu V. , Conde J. P.
Published: April 2011

The conductivity and the structural properties of thin films deposited by Hot-Wire Chemical Vapor Deposition (HW-CVD) from silane and hydrogen at a substrate temperature of 220 °C are shown to be strongly dependent on the filament temperature, Tfil, and process pressure, p. Amorphous silicon films are obtained at low pressures, p < 3 × 10−2Torr, for Tfil ∼ 1900 °C and FH2 = FSiH4. At this TfilJU, high deposition rates are observed, both with and without hydrogen dilution, and no silicon was deposited on the filaments. At Tfil ∼ 1500 °C, a transition from a-Si:H for p > 0.3 Torr to microcrystalline silicon (μc-Si:H) for p < 0.1 Torr occurs. In this temperature regime, silicon growth on the filaments is observed. /ic-Si:H growth both without hydrogen dilution and also in very thin films (∼ 0.05 μm) is achieved. Raman and X-Ray spectra give typical grain sizes of 10 – 20 nm, with a crystalline fraction higher than 50%. For both, Tju ∼ 1500 °C, p > 0.3 Torr and Tfil ∼ 1900 °C and p ∼ 2.7 × 10−2Torr, an increase of the crystalline fraction from 0 to ∼ 30% is observed when the hydrogen dilution, FH2/FSiH4, increases from 1 to > 4.
Real Time Monitoring of Amorphous Silicon Solar Cell Fabrication
Authors: Lu Yiwei , Kim Sangbo , Burnham J. S. , Chen Ing-Shin , Lee Yeeheng , Strausser Y. E. , Wronski C. R. , Collins R. W.
Published: April 2011

We have applied real time spectroscopie ellipsometry (RTSE) to monitor the successive growth of p-type a-Si1-xCx:H and i-type a-Si:H on specular SnO2:F (i.e., the superstrate solar cell configuration) in a single-chamber deposition system. Both the microstructural evolution, which includes the surface roughness and bulk layer thicknesses versus time and bulk layer void volume fraction, as well as the optical properties, which include the dielectric function (1.5–4.0 eV) and optical gap of the individual layers, were determined from RTSE data collected during growth. The accuracy of our approach is demonstrated by correlating structural parameters obtained both by RTSE and atomic force microscopy. Based on prior information deduced by RTSE, the TCO/p/i structure was fabricated with optimized procedures that have sought to minimize TCO/'p and p/i interfacial problems. These studies illustrate that RTSE can be a valuable tool for identifying problems in the fabrication of a-Si:H solar cells and ultimately improving cell performance.
Low Temperature Deposition of Polycrystalline Silicon thin Films by Hot-Wire CVD
Authors: Yu Shuangying , Deshpande Sadanand , Gulari Erdogan , Kanicki Jerzy
Published: April 2011

In this study, we have deposited polycrystalline silicon (poly-Si) thin films by hot-wire Chemical Vapor Deposition (CVD) using hydrogen and disilane as the reactive gases. We selectively activate hydrogen and let disilane bypass the hot tungsten filament assembly and enter the reactor downstream from hydrogen. This may provide a better process chemistry, and by this approach, we have deposited poly-Si films at a substrate temperature as low as 310°C and at a growth rate as high as 100 Å/min. The substrate temperature is more than 2000C lower and the growth rate is more than twice higher compared to those of LPCVD poly-Si films. The effect of hydrogen flow rate, disilane flow rate and substrate temperature on the deposition rate and structural properties of the polysilicon films are investigated. The deposited films are characterized by transmission electron microscopy, scanning electron microscopy, Raman spectroscopy and X-ray diffraction.
Dielectric Effects in Laser-Crystallised Polycrystalline Silicon Thin Film Transistors
Authors: Masterton G. H. , Gibson R. A. G. , Hack M.
Published: April 2011

We present experimental results on the transient response of the source-drain current of laser crystallised polycrystalline silicon (poly-Si) thin film transistors (TFTs) over many orders of magnitude in time after the application of a voltage pulse to the gate electrode. This work follows on from similar measurements performed on amorphous silicon (a-Si) TFTs. Results showed a definite change in transient behaviour dependent on the magnitude of the gate bias. At a gate voltage of 5V there was an initial decay then a marked increase in the source-drain current beyond 1000 seconds. This variation of transient behaviour with gate bias was not seen in the a-Si case. For poly-Si the transient behaviour could not be split into different regimes in time (beyond the carrier transit time) whereas for a-Si TFTs the source-drain current showed a logarithmic decay at room temperature up to 100 seconds followed by a power law decay beyond 100 seconds. Our results indicate perhaps that only one mechanism exists for the observed transient decay of current, unlike the a-Si case. Measurements carried out at elevated temperature showed the current decay was independent of temperature indicating that the transient decay may be caused by charge injection via a tunnelling process into interface states, gate dielectric or passivation dielectric. Finally by carrying out measurements on TFTs after moderate positive voltage stressing and on TFTs with specially fabricated gate and passivation dielectrics it has been established that the transient decay is dielectric related and not a defect generation process.
TFT Performance - Material Quality Correlation for a-Si:H Deposited at high Rates
Authors: Sherman S. , Lu P-Y. , Gottscho R. A. , Wagner S.
Published: April 2011

We evaluated the characteristics of a-Si:H/a-SiNx:H thin film transistors (TFTs), and of separately deposited a-Si:H films, as functions of the a-Si:H deposition power in a high-rate, large-area, 40 MHz PE-CVD system. TFT performance and a-Si:H film properties improve with decreasing power density and deposition rate. However, low defect density a-Si:H material was deposited at rates as high as 1500 Å/min. TFTs with gate nitride deposited at 1000 A/min show excellent I-V characteristics when the a-Si:H deposition power is low enough. The TFT electron mobility in the linear regime correlates well with the Urbach energy of the a-Si:H films, suggesting that the quality of the a-Si: H controls the performance of our TFTs.
Two Dimensional Amorphous Silicon Image Sensor Arrays
Authors: Street R. A. , Wu X. D. , Weisfield R. , Ready S. , Apte R. , Nguyen M. , Nylen P.
Published: April 2011

Large two dimensional amorphous silicon image sensor arrays offer a new approach to electronic document input and x-ray imaging. The sensor array technology is now capable of image capture at greater than 10 frames/sec and with resolution of 200–400 spi. We describe our new high resolution imaging system, comprising a page-sized sensor array with nearly 3 million pixels, and the accompanying high speed read out and processing electronics. The key technological issues of pixel resolution, sensor fill factor, leakage currents and noise are reviewed. Measurements of a new array architecture are described, in which the sensor is formed as a single continuous film on top of the matrix addressing components.
Thick Amorphous Silicon Layers Suitable for the Realization of Radiation Detectors
Authors: Hong W. S. , Petrova-Koch V. , Drewery J. , Jing T. , Lee H. , Perez-Mendez V.
Published: April 2011

Thick silicon films with good electronic quality have been prepared by glow discharge of He-diluted SiH4 at a substrate temperature ∼150°C and subsequent annealing at 160°C for about 100 hours. The stress in the films obtained this way decreased to ∼100 MPa compared to the 350 MPa in conventional a-Si:H. The post-annealing helped to reduce the ionized dangling bond density from 2.5 × 1015 cm−3 to 7 × 1014 cm−3 without changing the internal stress. IR spectroscopy and hydrogen effusion measurements implied the existence of microvoids and tiny crystallites in the material showing satisfactory electronic properties. P-I-N diodes for radiation detection applications have been realized out of the new material.
Adjustable Threshold a-Si/SiC:H Color Detectors
Authors: de Cesare Giampiero , Irrera Fernanda , Lemmi Francesco , Palmamario Tucci Fabrizio
Published: April 2011

We present the Adjustable Threshold Color Detectors (ATCDs) based on stacked heterojunctions of amorphous silicon (a-Si:H) and silicon carbide (a-SiC:H). These devices work as bias-controlled photocurrent sources with different values of the voltage threshold depending on the wavelength of the incident radiation. The ATCDs detect the three fundamental chromatic components (blue, green, red) by varying the external voltage within a few Volts.
Surface Passivation and the Ultrafast Optical Response of Low-Temperature-Grown GaAs
Authors: Wang H. H. , Whitaker J. F. , Al-Hemyari K. , Williamson S. L.
Published: April 2011

Metal-semiconductor-metal photodetectors fabricated using low-temperature-grown GaAs have been passivated using AlGaAs cap layers in order to understand the influence of surface states and fields on the properties of these detectors. It has been found that passivation has little effect on the time response or persistent photoconductive tails associated with the detectors, but that responsivity and dark current can be enhanced in certain circumstances. The dependence of the temporal response on optical fluence and dc-voltage bias were observed for both passivated and unpassivated detectors.
Incorporation of Hydrogen in SiO2 and Si3N4 Thin Films Deposited by ECR-CVD
Authors: Brown J. , Boudreau M. , Boumerzoug M. , Mascher P. , Jackman T. E. , Tong S. Y. , Haugen H.
Published: April 2011

Hydrogen incorporation in ECR-CVD silicon oxynitride films deposited using tris dimemylaminosilane (TDAS) as the silicon precursor was investigated. The as-deposited silicon dioxide films were shown to contain little hydrogen (<2%) as determined by both FTTR and nuclear reaction analysis (15N profiling). Films were obtained with high breakdown fields (>10 MV/cm) and low interface state densities (2×l011cm−2) on silicon without special surface preparation. Silicon nitride films were found to contain large hydrogen concentrations, both bonded and unbonded, which evolved from the film due to beam irradiation during 15N profiling. We were able to demonstrate that dilution of the nitrogen plasma with both hydrogen and argon was effective in avoiding problems of trace oxygen contamination and poor film adhesion, and reducing the hydrogen concentration in the nitride films.
Atomic Structure of Deep Level Defects in Dimethylaluminum Methoxide-Doped GaAs
Authors: Park Y , Skowronski M
Published: April 2011

GaAs epilayers doped with dimethylaluminum methoxide (DMA1MO), an alkoxide bearing a pre-formed Al-O molecule, have been investigated using local vibrational mode (LVM) absorption and deep level transient spectroscopy measurements. LVM measurements indicated that oxygen and aluminum atoms are incorporated into GaAs layer as a complex and remain bound in the volume of the crystal. Electron traps with activation energies of 0.74 and 0.93 eV below the conduction band are main deep level defects responsible for the electrical and optical properties of the layers. Interpretation of the relationship between trap concentration and growth conditions led to the conclusion that the 0.93 and 0.74 eV traps have the atomic structures in which oxygen atom is bonded to one (AlO) and two aluminum atoms (A12O), respectively.
Very Low Deep Level AlxGa1−xAs (x=0.22) Layer Grown by Metalorganic Chemical Vapor Deposition
Authors: Huang Z. C. , Yang Bing , Chen H. K. , Chen J. C.
Published: April 2011

We have achieved deep-level-free Al0.22Ga0.78As epitaxial layers using low selenium (Se)-doping (8.4 × l016 cm−3) grown by metalorganic chemical vapor deposition (MOCVD). Deep levels in various Al0.22Ga0.78As layers grown on GaAs substrates were measured by deep level transient spectroscopy (DLTS). We have found that the commonly observed oxygen contamination-related deep levels at EC-0.53 and 0.70 eV and germanium-related level at EC-0.30 eV in MOCVD-grown Al0.22Ga0.78 As can be eliminated by low Se-doping. In addition, a deep hole level located at Ev+0.65 eV was found for the first time in highly Se-doped Al0.22Ga0.78 As epilayers. We suggest that low Se-doping (<2 × 1017 cm−3) produces a passivation effect and then deactivates other deep levels in Al0.22Ga0.78As.
Spectroscopic Ellipsometric Characterization of Low Temperature GaAs
Authors: Gao X. , Snyder P. G. , Yu P. W. , Zhang Y. Q. , Peng Z. F.
Published: April 2011

Pseudodielectric functions of low temperature grown GaAs (LT GaAs) measured by spectroscopic ellipsometry are presented. The spectral range includes the El (2.92eV) and El+ΔAl (3.13eV) critical point structure of GaAs. A Lorentz-oscillator model was used to fit the dielectric function of LT GaAs for samples with nominal growth temperatures (Tg) varying from 200°C to 580°C. For Tg of 200°C, 30% and 19% broadenings and −0.01 leV and −0.007eV red shifts were found for the El and El+Δl structures respectively, compared with normal GaAs. The red shift can be explained in terms of a strain effect in the LT layer. In annealed LT GaAs the broadening decreased significantly and no red shift was found.
Transition-Metal Impurity Luminescence in GaAs and its Application to Material Characterization
Authors: Nishino T.
Published: April 2011

A number of sharp characteristic luminescence lines has been observed for GaAs doped with 3d transition-metal impurities in the near-infrared region, the origin being attributed to the zero-phonon intracenter transitions between the energy levels of the metal ions split by the crystal field of the GaAs lattice. It is also known that these luminescence lines are very sensitive to the surrounding field of the transition-metal impurities. The luminescence of Cr-doped GaAs has been most extensively studied, the spectrum revealing a very sharp luminescence line at 0.839 eV. In this paper we review the results on the successful applications of this Cr-related luminescence line to characterization of in-depth profiles of arsenic vacancy in thermally annealed GaAs, local strain field in In-doped GaAs and interface stress at heterostructures grown on Cr-doped GaAs substrate.
Coupling of Electronic and Structural Properties of Hydrogen in Crystalline Silicon
Authors: Csaszar Wolfgang , Endrös Arthur L.
Published: April 2011

Theory has made great progress during recent years in calculating the fundamental properties of monatomic hydrogen in crystalline silicon. By applying the DLTS and DDLTS method we use the hydrogen-carbon complex which consists of an electronically inactive carbon atom on a substitutional lattice site and a hydrogen atom near the bond-center position to detect theoretically predicted properties of hydrogen in silicon. The results of two independent experiments show that there exists a coupling of the electronic and structural properties of monatomic hydrogen, as predicted by theory.
Interaction of Atomic Hydrogen with Chalcogens in Gaas
Authors: Vetterhöffer J. , Weber J.
Published: April 2011

The passivation by hydrogen of the shallow donors sulfur, selenium, and tellurium in GaAs was studied by infrared absorption spectroscopy (FTIR), capacitance-voltage (CV) depth profiling, and secondary ion mass spectroscopy (SIMS). Local vibrational mode (LVM) frequencies due to hydrogen-donor complexes agree with a microscopic model where the hydrogen atom is bound in the antibonding position to one of the donor’s neighboring gallium atoms. Our results suggest a hydrogen penetration depth much greater than the passivated region, however the infrared active region coincides with the passivated part of the material.
Plasma-Induced Electron Traps in n-InP
Authors: Sakamoto Yoshifumi , Sugino Takashi , Matsuda Koichiro , Shirafuji Junji
Published: April 2011

Deep electron traps in n-InP introduced during plasma exposure have been studied by means of isothermal capacitance transient spectroscopy (ICTS). Three electron traps, (Ec–0.21 eV), (Ec–0.34 eV) and (Ec–0.54 eV), which are designated E2, E3 and E4, respectively, are detected in n-InP treated with H2 plasma and by subsequent annealing. The E2 trap is induced by plasma exposure and the E3 trap is produced by thermal annealing. The E4 trap is generated by both plasma exposure and thermal annealing. These three traps are passivated with hydrogen atoms. The E2 trap density near the surface of hydrogen-plasma-treated samples is strongly enhanced by applying electric field because of dissociation of hydrogen from E2 trap. The E2 trap is annealed out with the activation energy of 1.5 eV and the attempt-to-escape frequency of 3.2 × 1014 s−1. Phosphine plasma treatment is effective in suppressing generation of these electron traps.
Hydrogen Diffusion and Passivation in InGaAIN Alloys
Authors: Pearton S. J. , Abernathy C. R. , MacKenzie J. D. , Vartuli C. B. , Wilson R. G. , Zavada J. M. , Shul R. J.
Published: April 2011

Hydrogen is found to readily diffuse into InGaN, InAIN and InGaAIN epitaxial layers during plasma exposures at 170 – 250 °C for 40 sec - 30 min. The diffusivity of hydrogen is > 10−11 cm2-s−1 at 170 °C, and the native donor species are passivated by association with the hydrogen. Reactivation of these species occurs at 450–500°C, but the hydrogen remains in the material until ≥ 800 °C.
Photoconductivity as a Function of Temperature in MOCVD Grown Gallium Nitride Films
Authors: Qiu C. H. , Melton W. , Pankove J. I.
Published: April 2011

The optical absorption in gallium nitride (GaN) films was studied by photoconductivity (PC) spectroscopy at various temperatures. At all the measured temperatures, the photoconductivity per incident photon increases with photon energy hv from 1.8 eV to 3.0 eV approximately as exp(hv/E0). Surprisingly, the measured photoconductivity tail to the infrared becomes more pronounced in magnitude at lower temperatures. We suggest from the data that the photoconductivity is dominated by majority carriers, and that the quantum efficiency η for conducting electron and hole generation by across-gap excitation increases with increasing temperature.
Surface-Oriented Oxygen Mass Transport During Implantation
Authors: Danilin A. B. , Charnyi L. A. , Nemirovski A. W. , Saraikin V. V.
Published: April 2011

The effect of implantation conditions on the localization of oxygen implanted with substoichiometric doses has been studied. Oxygen ions were implanted into Si wafers coated with a thin oxide film, which was etched off after the implantation. We used various implantation modes. After the implantation, the specimens were studied using SIMS and X-ray diffractometry. The concentration profiles suggest that at the lower implantation temperature, part of oxygen migrates toward the Si-SiO2 interface. The effect does not refer to the usual enhancement of SIMS signal at the surface because the concentration peak is at a depth of about 25 nm. Calculated deformation profiles indicate a compression at the same depth, the effect being the strongest for the low current density. The result suggests that the superficial layer is rich in vacancial-type defects. The coincidence of the deformation and oxygen concentration maxima leads to the conclusion that oxygen migrates toward the surface in the form of A-centers. A similar phenomenon has been observed for sequential low-temperature implantation of oxygen and nitrogen.
Observation of Vacancy-Oxygen Complexes in Silicon Implanted with Substoichiometric Doses of Oxygen Ions
Authors: Belogorokhov A. I. , Charnyi L. A. , Danilin A. B. , Nemirovski A. W.
Published: April 2011

Cz-grown p-Si(111) specimens were implanted with O+ ions at an energy of 150 keV and doses of 0.25, 0.5, and 1.0 (·1017) cm−2. The implantation temperatures used were 350 and 650 °C. After the implantation, some of the specimens were annealed at 1000 °C for 1 h in a nitrogen atmosphere. IR data indicated the presence of vacancy-oxygen complexes both before and after annealing, irrespective of implantation temperature. Double-crystal X-ray rocking curves also showed that vacancy-type defects are present.
Defects and Future Silicon Technology
Authors: Palm J. , Kimerling L.C.
Published: April 2011

The interaction between device technology and the control of defects has been strong since the first transistor. The rapid and unparalled development of this technology can be monitored by changes in device size and process complexity, or reciprocally, in defect density. In the future the emphasis on computation functionality will shift to imaging and learning. In addition high volume manufacturing will cast an emphasis on capital cost, yield, effluent control and safety. These foci require the development of new sensitive defect assessment tools, the modelling of complex defect systems and the understanding of defect properties on the atomic scale. We shall illustrate this interplay between technology and materials science by topics in ULSI circuits, silicon photovoltaics and silicon microphotonics. For ULSI the control of both bulk and surface defects is decisive. The physical chemistry at the silicon surface plays a key role in metal contamination. We shall discuss the use of RF-PCD for in-line monitoring and investigation of reaction kinetics. Silicon for low cost, photovoltaic applications confronts problems involving complex defect systems, but comparatively simple processes. The goal is to optimize growth and cell processing. The objective of silicon microphotonics is to establish an IC compatible process technology for integration of optical interconnection with silicon electronics. By building the first silicon-based LED operating at λ = 1.54 μm at room temperature it has been shown that erbium doping is a viable approach. Codoping with F or O largely enhances the light output. We will show a process simulator for the Si:Er:F system as an example for ligand field engineering.
Electrical and Structural Properties of MeV Si+ Ion Implantation in Silicon
Authors: Agarwal Aditya , Koveshnikov S. , Christensen K. , Rozgonyi G. A.
Published: April 2011

The electrical properties of residual MeV ion implantation damage in Si after annealing from 600 to 1100°C for 1 hour have been investigated using Deep Level Transient Spectroscopy, Capaciatance-Voltage, and Current-Voltage measurements. These data have been correlated with structural defects imaged by Transmission Electron Microscopy. It is shown that at least 4 deep levels are associated with the buried layer of extended defects after annealing at 800, 900, 1000 and 1100°C. Additionally, for the wafer annealed at 800°C at least 5 more deep level centers are present in the device layer above the buried defects.
Effects of Light on the Resonant Tunneling in Silicon Quantum Dot Diode
Authors: Ding Chen , Tsu Raphael
Published: April 2011

The resonant tunneling via nanoscale silicon particles embedded in an a-SiO2 matrix in a diode structure has revealed a range of intriguing observations such as extremely sharp peaks and steps and periodic oscillations in (conductance-voltage) G-V measurements. Recently we have discovered a drastic sharpening of the conductance peak with light. Phase measurements show that the effects of light may be understood by invoking the filling of charged traps.
Space Charge Layers at the Porous Silicon Surface
Authors: Weisz S. Z. , Avalos J. , Gomez M. , Many A. , Goldstein Y. , Savir E.
Published: April 2011

Pulse measurements on the porous-Si/electrolyte system are employed to determine the surface effective area and the surface-state density at various stages of the anodization process used to produce the porous material. Such measurements were combined with studies of the luminescence spectra and scanning tunneling microscopy (STM). Both the effective area and the luminescence intensity are found to increase with anodization time, reaching maximum values for the same anodization time (1–2 minutes). In most cases, they decrease monotonically with further anodization. The surface state density, on the other hand, decreases with anodization time from the initial value of ∼1012 cm−2 for the virgin surface, down to ∼1011 cm−2 at the common anodization time for which both the effective area and the luminescence intensity are peaked. The surface-state density increases upon further anodization, reaching a value of at least 1013 cm−2 after ∼10 minutes of anodization. Apart from its intensity, the luminescence spectrum is essentially independent of anodization time. The common peak of the spectra is at about 700 nm. The STM measurements reveal a pronounced surface roughness. Preliminary results indicate that for 1 - 2 minute anodization (maximum effective area), the roughness scale is of the order of 1 -2 nm. After 10-minutes anodization, on the other hand, the roughness microstructure becomes finer (roughness scale of only 0.5 - 0.7 nm). These findings indicate that the various characteristics studied are closely interrelated. Such information may help in understanding the luminescence mechanism, but further work is required in order to interpret more fully the results presented.
Nanotesla Detection Using the Planar Hall Effect
Authors: Schuhl A. , Van Dau F. Nguyen , Childress J.R.
Published: April 2011

A magnetic field sensor based on the planar Hall effect has been developed using epitaxial permalloy (Ni80Fe20) ultrathin films (1-10 nm). The magnetic and magnetotransport properties of these films have been studied in detail. For thicknesses above 5 nm, the resistivity of the permalloy film is below 5μΩ-cm, and its magnetoresistance ratio is 2%. By using the transverse resistivity for detection, we have reduced thermal drift effects by five orders of magnitude. We also make use of a weak uniaxial anisotropy induced in the permalloy through exchange coupling with a 6 nm-thick Fe/Pd multilayer, itself grown directly on the MgO substrate. Magnetic sensors based on these films have been used successfully to detect fields below 10 nT at 1Hz. Since the lateral dimensions of the sensing element are small (<30μm), and because of the ferromagnetic coupling with the Fe/Pd structure, it consists of a single magnetic domain. Sensitivities above 100 V/T-A have been obtained, with deviations from linearity of less than 2% over 4 decades.
Structural Coherence and Magnetic Coupling in Fe/Si
Authors: Foiles C.L. , Franklin M.R. , Loloee R.
Published: April 2011

A number of studies have inferred the presence of an Fe-silicide in Fe/Si multilayers. Our transmission electron diffraction data provide direct evidence for the presence of an Fe-silicide. Despite similarities in structural coherence and saturation magnetization behavior for Fe/Si and Fe/{FeSi}, direct evidence for Fe-silicide only occurs for the Fe/{FeSi} multilayers.
Process-Induced Uniaxial Magnetic Anisotropy in Epitaxial Fe and Ni80Fe20 Films
Authors: Childress J.R. , Durand O. , Nguyen Van F. , Galtier P. , Bisaro R. , Schuhl A.
Published: April 2011

The occurrence of a weak in-plane uniaxial magnetic anisotropy in Fe thin films grown by molecular beam epitaxy onto (001)-oriented MgO substrates has been previously reported. We explain the occurrence of this anisotropy by measuring the in-plane tetragonal distortion of the cubic Fe lattice in a 800Å-thick film. The analysis of the full x-ray diffraction spectrum reveals a 0.1% difference between the two in-plane parameters. This small difference is sufficient to fully explain the observed anisotropy (≈20 Oe) using a standard magnetoelastic model. Although it is established that the uniaxial anisotropy results from the angle of incidence of the Fe atomic flux during deposition, the relationship between angle of incidence and in-plane tetragonalization is still unexplained. However, this anisotropy is shown to also occur in other epitaxial systems such as Ni80Fe20 on (111)Si. Control of this effect can help design epitaxial multilayer films with specific and reproducible magnetic states.
Magnetic Structures in Nonmag-/MAG-/Nonmag-Netic Sandwiches
Authors: Kawazoe Yoshiyuki , Hu Xiao
Published: April 2011

Spin-reorientation transition in magnetic thin film sandwiched by nonmagnetic materials is clarified by means of the variational formalism. Phase diagrams of the magnetization configuration are presented. Scaling relations among the film thickness, exchange coupling and magnetic anisotropies are revealed. A formula for the interface anisotropy is presented.
Induced Magnetic Anisotropy of Sputter NiFe Thin Films on Thin Tantalum Nitride Underlayer
Authors: Yeh T. , Berg L. , Falenschek J. , Yue J.
Published: April 2011

The structure and properties of sputter NiFe thin film deposited on both thermal oxide and thin tantalum nitride have been studied. The magnetic anisotropy field HK increases to 8.2 Oe when the NiFe film was deposited on a thin tantalum nitride underlayer. Anisotropic stress was found on the sample film with tantalum nitride underlayer. Results of X-ray diffraction show that a thin tantalum nitride underlayer appears to promote a preferred crystalline orientation formation of the NiFe film. The induced magnetic anisotropy is attributed to the formation of the preferred crystalline orientation and the induced anisotropic magnetoelastic energy which is associated with the anisotropic stress of the sample film.
Structural and Magnetic Characterization of Bi-Substituted Garnet on Si and GaAs
Authors: Ring Ken M. , Shapiro A.L. , Deng F. , Goldman R.S. , Spada F. , Hellman F. , Cheeks T.L. , Kavanagh K.L. , Suzuki Takao
Published: April 2011

Novel material structures that combine magneto-optic (MO) and semiconductor devices have potential applications in monolithic microwave systems and optoelectronics. We have investigated the materials issues pertaining to the film structure, interface uniformity, and magnetic/MO properties of (BiDy)3(FeGa)5O12 (Bi-DyIG) thin films sputter deposited on Si and GaAs. The rapid thermally annealed films were polycrystalline with a nominal grain size of 20 nm. The magnetic and MO properties were strongly dependent on the type of substrate such that square hysteresis loops and coercivities of 0.1 to 0.9 kOe were observed for Bi-DyIG/Si structures while Bi-DyIG/GaAs structures showed much lower coercivity values (0.03 kOe). A comparison of the magnetic properties, microstructure and substrate composition was carried out with plan-view and cross-section transmission electron microscopy, as well as electron and x-ray diffraction. The results suggest that grain orientation effects, stress, and compositional inhomogeneity due to interfacial reactions or diffusion introduced by the substrate strongly influence the magnetic and MO properties of the films.
Selective one-step Chemical Etching of the Silicon Nitride/Silicon PBL stack for 0.5μm device Fabrication
Authors: Ziger David , Vitkavage Susan , Oberdorfer Charles , Eisenberg Juli , Hughes Michael
Published: April 2011

Abstract Wet chemical removal of a silicon nitride/silicon Poly Buffer LOCUS (PBL) film stack with a phosphoric/nitric acid solution was characterized. Though silicon nitride etch rates remain constant, silicon etch rates decrease as a function of loading which severely limits the usable lifetime of the bath. This is caused by buildup of etching products which limits the amount of silicon that can be dissolved in the solution. Addition of HF to the phosphoric/nitric acid solution enhances the dissolution chemistry presumably by decomposing the silica reaction products and shifting the equilibrium. Characterization of this process was done to determine whether it could be applied towards PBL removal. Depending on the relative amounts of HF and HNO3 added, silicon etch rates could be enhanced by two orders of magnitude (200–400A/min) and silicon nitride etch rates by a factor of two. Selectivities for etching silicon to oxide and silicon nitride to oxide were typically between 8–12:1 and 8–20:1 respectively.
Monitoring of the Surface Species on Silicon After Chemical Cleaning by FTIR Spectroscopy
Authors: Chung Chan-Hwa , Kim Chang-Koo , Moon Sang Heup
Published: April 2011

For the analysis of as-cleaned surface, we have used a the unique IR method that uses a highsurface-area porous sample. We have observed by experiments that the oxide growth rate on silicon is reduced to a minimum when the surface is treated with a proper amount of HF vapor obtained from 1% I-IF solution. FTIR and XPS observations of the treated surface suggest that the oxide growth rate is closely related to the amount of the surface fluorides. In UV/O2 cleaning process, we have observed experimentally that addition of water vapor to cleaning gas stream enhances the cleaning efficiency by as much as 1.3 times.
Pre-Gate Oxidation Cleaning of Silicon Wafer by Electric Arc Plasma Jet Treatment
Authors: Pavlov G. Ya.
Published: April 2011

The effect of arc plasma jet treatment (APJT) of silicon surface used for pre-gate oxidation cleaning on the electrophysical parameters of MOS structures (Si/SiO2/Si*/Al) has been studied- We show that APJT etching cleaning considerably improves the constant current charge to breakdown of MOS structures in comparison with conventional wet chemical cleaning. We have analyzed the effect of plasma cleaning conditions on the quality of gate oxide and SiO2/Si interface.
Ion-Beam-Induced Epitaxy and Solid Phase Epitaxy of Sigec on Si Formed by Ge and C Ion Implantation and their Structural and Optical Properties
Authors: Kobayashi N. , Katsumata H. , Makita Y. , Hasegawa M. , Hayashi N. , Shibata H. , Uekusa S. , Hishita S.
Published: April 2011

Epitaxial layers of Si1-x-yGexCy on Si(100) (x=0.13 and y=0.014 at peak concentration) were formed by ion implantation of Ge ions and C ions at room temperature (RT) and by subsequent IBIEC (ion-beam-induced epitaxial crystallization) process with 400keV Ge and ar ions at 300-400°C and SPEG (solid phase epitaxial growth) process up to 840°C. Crystallization up to the surface both by IBIEC and SPEG processes has been confirmed with RBS-channeling analysis. X-ray diffraction experiments have demonstrated strain compensation by incorporation of C atoms for IBIEC-grown Si1-x-yGexCy/Si samples, whereas strain accommodation due to C precipitation has been observed for SPEG-grown Si1-x-yGexCy/Si samples. Photoluminescence (PL) observed at 2K from IBIEC-grown samples has shown intense I1 peak with/without I1 related (Ar) peak and that from SPEG-grown samples has shown G line emission. these optical properties could suggest that small vacancy agglomeration is dominant in IBIEC-grown samples and C agglomeration is dominant in SPEG-grown samples, respectively.
Film Synthesis on Powders by Cathodic ARC Plasma Deposition
Authors: Anders André , Anders Simone , Brown Ian G. , Ivanov Igor C.
Published: April 2011

Cathodic arc plasma deposition was used to coat Al2O3 powder (mesh size 60) with platinum. the power particles were moved during deposition using a mechanical system operating at a resonance frequency of 20 Hz. Scanning electron microscopy and auger electron microscopy show that all particles are completely coated with a platinum film having a thickness of about 100 nm. the actual deposition time was only 20 s, thus the deposition rate was very high (5 nm/s).
Corrosion Protection of Aluminum-Matrix Composites
Authors: Hou Jiangyuan , Chung D. D. L.
Published: April 2011

Aluminum-matrix composites are attractive in their combination of low CTE and high thermal conductivity. Anodizing is an effective surface treatment for improving the corrosion resistance of aluminum-matrix composites. ForSiC filled aluminum, anodizing was performed successfully in an acid electrolyte, as usual. However, for AIN filled aluminum, anodizing needed to be performed in an alkaline (NaOH) electrolyte instead of an acid electrolyte, because NaOH reduced the reaction between AIN and water, whereas an acid enhanced this reaction. The concentration of NaOH in the electrolyte was critical; too high a concentration of NaOH caused the dissolution of the anodizing product (A12O3) by the NaOH, whereas too low a concentration of NaOH did not provide enough ions for the electrochemical process.
Nickel Filament Polymer-Matrix Composites with Low Surface Impedance and High Electromagnetic Interference Shielding Effectiveness
Authors: Shui Xiaoping , Chung D. D. L.
Published: April 2011

Nickel filaments of 0.4 μm diameter gave polyethersulfone-matrix composites with high electromagnetic interference shielding effectiveness and low surface impedance at 1–2 GHz. With 7 vol.% nickel filaments, the composite exhibited shielding effectiveness 87 dB (compared to 90 dB for solid copper), surface impedance 1.2 Ω (same as for solid copper), tensile strength 52 MPa, modulus 5 GPa, ductility 1.0% and density 1.87 g/cm3. The low surface impedance is valuable for microwave waveguides.
Excimer Laser Direct Write Aluminum on Aluminum Nitride
Authors: Li Hua , Lumpp Janet K.
Published: April 2011

Fabrication of metal lines on aluminum nitride (AIN) ceramic is important for application of AIN as a microcircuit board. An Al line can be made directly from AIN by excimer laser exposure. All lines in this paper were written by pulsed KrF excimer laser (248 nm) in air and vacuum at different scan speeds with a constant laser energy. The morphology of the Al lines was observed by optical and scanning electron microscopies. The lines become more metallic when the scan speed decreases. Consequently the resistance, measured by the four-point probe technique, decreased to a minimum value in the scan speed range of 400 μm/s to 900 μm/s for the samples made in air. The resistance of Al lines written in air is greater than that in vacuum because of oxidation. The samples made in air with scan speed lower than 400 μm/s were heavily oxidized. SAXPS spectra showed a strong oxidation state and that the excimer laser exposure depletes nitrogen from AMN. The Al lines produced by laser-induced decomposition of AMN board are being evaluated as catalysts for laser assisted CVD and conventional electroless plating. The oxidation layer on the surface of Al lines may effect the adhesion between the Al lines and the deposited or plated metal.
Adhesion Strength of CuCr Alloy Films to Polyimide
Authors: Ahn E. C. , Yu Jin , Park I. S.
Published: April 2011

In the present work, CuCr alloys with varying Cr content were sputter deposited on polyimide films, and the metal/polyimide thin films were maintained under 85° C/85%R.H. (T/H) conditions for the reliability measurements. Results showed that the peel strength without T/H treatments increased proportionally with the Cr content in the CuCr alloy layer(x) up to 17 at. %, and then saturated. Among the samples studied, the peel strength decreased with hold time under T/H conditions for all the cases, but most drastically for the sample with x=8.5. The very poor peel strength of that sample (x=8.5) was attributed to the occurrence of interfacial failures which were thought to take place along Cr-oxide/polyimide interfaces.
Sol-Gel Derived Polyvinylpyrrolidone/Silicon Oxide Composite Materials and Novel Fabrication Technique for Channel Waveguide
Authors: Yoshida Makoto , Prasad Paras N.
Published: April 2011

Sol-gel derived composite materials of polyvinylpyrrolidone (PVP), SiO2 and TiO2 were studied to achieve low optical propagation loss and high thermal stability in slab waveguides. PVP is a thermally crosslinkable polymer. However, the thermal crosslinking and thermal decomposition take place around the same temperature, 200 °C, resulting in high optical propagation loss. The incorporation of sol-gel processed SiO2 prevents thermal decomposition of PVP and produces remarkably low optical propagation loss even after being baked at 230 °C. We have achieved 0.2 dB/cm optical propagation loss at 633 nm. Furthermore, little index change was observed at 110 °C for 1,000 hours after initial slight increase. Impregnation of sol-gel processed TiO2 into the PVP/SiO2 system was also studied to increase refractive index. A broad manipulation of refractive index, from 1.49 to 1.65, with an optical propagation loss of less than 0.6 dB/cm at 633 nm was accomplished by a careful selection of Ti alkoxide and optimized reaction conditions. PVP/SiO2 slab waveguides were then used to fabricate channel waveguides by using a laser densification technique utilizing metal lines as light absorbent and an Ar laser. An optical propagation loss of 0.9 dB/cm was achieved at 633 nm.
Non-Radiative Competition in the Excitation of Erbium Implanted Silicon Light Emitting Devices
Authors: Taskin T , Huda Q , Scholes A , Evans J H , Peaker A R , Hemment P , Jeynes C , Jafri Z
Published: April 2011

This paper reports a study of the non-radiative processes competing with the excitation of the erbium ion in layers implanted with high concentrations of erbium and oxygen. These processes reduce the luminescence efficiency of the Si:Er system and dramatically increase the threshold current density calculated to be necessary for an ultimate goal, the Si/Ge:Er LASER. Using cross sectional TEM, photoluminescence as a function of temperature and DLTS, it is demonstrated that a two stage anneal procedure which avoids the formation of extended defects and removes specific deep states is necessary to obtain efficient Er3+ excitation at high erbium concentrations. Comparisons are made with damage resulting from germanium implantation into silicon. The role of multiple stage anneals is discussed in relation to the removal of Shockley-Hall-Read recombination centres
Polymeric Thin Films for Electro-Optic Modulator and High Density Optical Memory Applications
Authors: Dalton Larry R. , Harper Aaron W. , Liang Zhiyong , Zhu Jingsong , Efron Uzi , Wu Chiung-Shieng , Au Anson
Published: April 2011

Chromophores capable of undergoing conformational changes when exposed to ultraviolet or visible light have been synthesized with functional groups permitting attachment to polymer matrices. One class of such chromophores, containing reactive functionalities at both ends of the chromophore, are referred to as double-end crosslinkable (DEC) chromophores. These chromophores are used in the synthesis of hardened nonlinear optically active lattices and in the fabrication of buried channel nonlinear optical waveguides by photoprocessing; development of such waveguides represents a critical step in the production of polymeric electro-optic modulators. Such chromophores are also crucial to the phenomena of laser-assisted poling (also known as photochemically-induced poling). Finally, these chromophores are attached to the surface of polystyrene beads permitting the realization of room temperature spectral hole burning exploiting morphology-dependent resonances. Such resonances provide the basis of wavelength coding for the development of high density optical memories.
Natural Poly(Hydroxybutyrate-Hydroxyvalerate) Polymers as Degradable Biomatertals.
Authors: Chaput Cyril , Yahia L'Hocine , Selmani Amine , Rivard Charles-Hilaire
Published: April 2011

Poly(ß-hydroxybutyrate-co-13-hydroxyvalerate) have been recently proposed as degradable biomaterials for drug delivery systems, sutures, bone plates and short-term implants. Three P-B\HV (7, 14 & 22 % HV) films were analyzed for in vitro cytotoxicity and aqueous accelerated degradation, in vivo degradation and tissue reactions. The PHB/HV materials and extracts elicit few or mild toxic responses, do not lead in vivo to tissue necrosis or abscess formation, but provoke acute inflammatory reactions slightly decreasing with the time. The degradation of PHB/HV polymers present low rates in vitro as well as in vivo. The weight loss rate generally increases with the copolymer composition (HV content) and ranges from 0.15- 0.30 (in vitro) to 0.25 %/day (in vivo). Compositional and physico-chemical changes in PHB/HV materials were rapidly detected during the accelerated hydrolysis, but were much slower to appear in vivo. The structural and mechanical integrity of PHB/HV materials tend to disappear early in vitro as well as in vivo. After 90 wks in dorsal muscular tissues of adult sheep, there was no significant dissolution of the PHB/HV polymer, 50–60% of the initial weight still remaining. PHB/HV polymers are biodegradable materials, either by hydrolysis or implantation, but with extremely low dissolution or degradation rates.
Tissue Engineering of Tendon
Authors: Caoa Y. , Vacanti J. P. , Ma P. X. , Ibarra C. , Paige K.T. , Upton J. , Langer R. , Vacanti C. A.
Published: April 2011

We studied the feasibility of creating new tissue engineered tendons, using bovine tendon fibroblasts (tenocytes) attached to synthetic biodegradable polymer scaffolds in athymic mice. Calffore- and hind-limbs were obtained from a local slaughterhouse within 6 hours of sacrifice. Tenocytes were isolated from the calf tendons. Cells were seeded onto an array of fibers composed of polymer (PGA) configured either as a random mesh of fibers, or as an array of parallel fibers. Fifty cell-polymer constructs were implanted subcutaneously in athymic mice and harvested at 3, 6, 8, 10 and 12 weeks. Grossly, all excised specimens resembled the tendons from which the cells had been isolated. Histologic sections stained with hematoxylin and eosin (H&E) and Masson's trichrome showed cells arranged longitudinally within parallel collagen fibers in the periphery. Centrally, collagen fibers were more randomly arranged, although they seemed to attain a parallel arrangement of cells and fibers over time. By 10 weeks, specimens showed very similar histologic characteristics to normal tendon. Histologically, 12-week samples were virtually identical to normal tendon. When longitudinal polymer fibers seeded with cell had been implanted, the collagen fibers seen in the neo-tendons became organized at an earlier interval of time. Biomechanical tests demonstrated linear increase in tensile strength of the neo-tendons over time. Eight-week specimens showed 30% the tensile strength of normal tendon samples of similar size. By 12 weeks, tensile strength was already 57% that of normal bovine tendon.