bluuebunny/crossref_metadata_2025 huggingface dataset:
Effects of Composition on the Microstructures and Optical Properties of Hydrogenated Amorphous Silicon Carbide Films Prepared by Electron Cyclotron Resonance Plasma Chemical Vapor Deposition
Authors: Chan Lih-Hsiung , Chou Wei-Zen , Chou Lih-Hsin
Published: April 2011

Hydrogenated amorphous silicon carbide films (a -SiC:H) were prepared from CH4, SiH4, and Ar mixtures by Electron Cyclotron Resonance Plasma Chemical Vapor Deposition (ECR PCVD). The deposition of the thin films was proceeded with the following optimized conditions; microwave power: 900W, Ar flux : 90sccm, and total flux: 113.4 sccm. The substrate temperature was around 100∼120°C during deposition. For comparisons, the relative flux ratio of methane to silane was varied to produce thin films of different compositions to investigate the relationships between the associated compositions of films and their corresponding microstructures and optical properties. Moreover, both film's microstructures and their optical properties were analyzed to find out as to how they are interrelated. Furthermore, the surface morphology and amorphous microstructures were confirmed by Scanning Electron Microscopy (SEM) and Transmission Electron Microscopy (TEM), respectively. And, x-ray Photoelectron Spectroscopy (XPS) was employed to study the relative atomic ratio of C to Si along with the bonding conditions in the thin films. Finally, the Hydrogen concentration and the amounts of C-H and Si-H bonds were determined by Fourier transform infrared spectroscopy(FTIR), while the optical properties were measured by optical spectrophotometer.
Enzymatic Template Synthesis of Polyphenol
Authors: Bruno Ferdinando F. , Nagarajan Ramaswamy , Sidhartha Jena S. , Yang Ke , Kumar Jayant , Tripathy Sukant , Samuelson Lynne
Published: April 2011

An alternative, biocatalytic approach for the synthesis of a new class of water soluble and processable polyphenols is presented. In this approach, the enzyme horseradish peroxidase (HRP) is used to polymerize phenol in the presence of an ionic template. The template serves as a surfactant that can both emulsify the phenol monomer and growing polyphenol chains and provide water solubility of the final polyphenol/template complex. This approach is a simple, one step synthesis where the reaction conditions are remarkably mild and environmentally compatible. The final product is a water soluble, high molecular weight complex of polyphenol and the template used. The approach is also very versatile as numerous templates may be used to build in specific functionalities to the final polyphenol complex. Polystyrene sulfonates (SPS), lignin sulfonate and dodecyl benzene sulfonates (micelles) are the templates investigated in this study. Thermal analysis and UV-Vis spectroscopy shows that these complexes have exceptional thermal stability and a high degree of backbone conjugation. Electrical conductivities on the order of 10−5 S/cm and third order nonlinear optical susceptibilities (χ(3)) of 10−12 esu are also observed. In the case of the SPS template, under certain conditions, a sol gel complex may be formed. This enzymatic approach offers interesting opportunities in the synthesis and functionalization of a new class of processable polyphenolic materials.
Electroactive Nonionic Polymer Gel-Swift Bending and Crawling Motion
Authors: Hirai T. , Zheng J. , Watanabe M. , Shirai H. , Yamaguchi M.
Published: April 2011

We have found a nonionic polymer gel swollen with nonionic dielectric solvent can be actuated by applying an electric field. The motion was not only far much faster than conventional polyelectrolyte gel materials, but also far much bigger in deformation. The motion was completed, for instance, within 60 ms and the deformation reached over 100%. The heat loss is negligible compared to that of polyelectrolyte gels. The deformation is not only bending, but also crawling. The principle was suggested to be charge-injected solvent dragging in the gel. The force was suggested to be proportional to the square of the electric field and proportional to the dielectric constant of the solvent. The principle was suggested to be promising and applicable to other conventional polymers.
The Voltage and Composition Dependence of Switching in a Polymer Current Limiter Device
Authors: Duggal Anil R.
Published: April 2011

The high power electrical switching properties of a polymer current limiter device are studied as a function of applied voltage. It is shown that a dramatic change in switching behavior occurs at a characteristic voltage. Below this voltage, the device switches to a high resistance state whereas at higher applied voltages it does not. It is shown that the high voltage, low resistance state has similar electrical characteristics to an arc discharge. Material variation experiments are also described which demonstrate that the changeover depends sensitively on the contact resistance between the filler particles of the composite material.
Electro-Mechanical Properties of Electron Irradiated P(VDF-TrFE) Copolymers Under Different Mechanical Stresses
Authors: Cheng Z.-Y. , Gross S. J. , Bharti V. , Xu T.-B. , Mai T. , Zhang Q. M.
Published: April 2011

The electro-mechanical properties of high energy electron irradiated poly(vineylidene fluoride-trifluorethylene) (P(VF-TrFE)) copolymers under different mechanical stress conditions are reported. In stress free condition, the electric field induced longitudinal and transverse strains of the irradiated P(VDF-TrFE) copolymer films at room temperature (RT) can reach about 5% and more than 3% respectively. The longitudinal strain response of the material under hydrostatic a pressure up to 83 atmospheses was studied at RT. The transverse strain response of the material at RT was studied under uniaxial tensile stress. It was found that the material has a high load capability and for stretched films along the stretching direction the induced strain remains high, even at about 45 MPa. The temperature dependence of the strain response is also characterized. Both the temperature and stress dependence of the strain response indicate that the electric field induced strain response originates from the electric field induced local phase transition.
Ceramics Superplasticity
Authors: Wakai Fumihiro
Published: April 2011

The international joint project “Ceramics Superplasticity” has been conducted from 1995 till 1999 by a cooperation between the Japan Science and Technology Corporation (JST) and Max-Planck-lnstitute for Metals Research (MPI-MF). The new type of covalent ceramics was developed through atomic level processing, and novel properties such as superplasticity were investigated. The development of local analysis technique of disordered structure combined the two research fields, grain boundary of crystalline solids and structure of amorphous.
The Industrial Application of Aluminum Superplastic Forming
Authors: Barnes A. J.
Published: April 2011

Over the past thirty years superplastic aluminum forming has advanced from a laboratory curiosity to a well established manufacturing route. Applications are now found in many and diverse markets, including: medical systems, specialist automobiles, rail cars, architectural panels and all types of aircraft.

This paper examines the reasons for success in these markets and explores future prospects including the potential for fast forming alloys currently under development.
Materials Design and Processings for Industrial High-Strain Rate Superplastic Forming
Authors: Hosokawa H. , Higashi K.
Published: April 2011

The optimum materials design in microstructural control could be developed for the highstrain-rate superplastic materials in the industrial scale. In the present work, it is reported that the high-performance-engine pistons with near-net-shape can be fabricated by the superplastic forging technology in the high-strain-rate superplastic PM Al-Si based alloy, which is produced by using this optimum materials design.
Influence of Equal-Channel Angular Pressing on the Superplastic Properties of Commercial Aluminum Alloys
Authors: Lee Sungwon , Langdon Terence G.
Published: April 2011

Equal-channel angular (ECA) pressing was used to refine the microstructure in two commercial aluminum alloys, Al-2024 and the Supral-100 Al-2004 alloy. The ECA pressing was conducted at room temperature and at elevated temperatures for both alloys using several different processing routes. Tensile testing was carried out at elevated temperatures on both pressed and unpressed samples of each alloy in order to evaluate the effect of the pressing. This paper describes the influence of the ECA pressing on the subsequent mechanical properties of these two alloys. For both alloys, it is shown that the optimum superplastic conditions are influenced by the ECA pressing, and in practice there tends to be a decrease in the optimum temperature for superplasticity and a corresponding increase in the optimum strain rate. In addition, there was evidence for high strain rate superplasticity (HSR SP) in both alloys after the ECA pressing procedure.
Superplastic Deformation Behavior of Zn-Al Alloys
Authors: Ha Tae Kwon , Koo Hyun Woo , Eom Tae Shin , Chang Young Won
Published: April 2011

The superplastic deformation behavior of a quasi-single phase Zn-0.3 wt.% Al and a microduplex Zn-22 wt.% Al eutectoid alloy has been investigated in this study within the framework of the internal variable theory of structural superplasticity (SSP). Load relaxation and tensile tests were conducted at room temperature for quasi-single phase alloy and at 200°C for eutectoid alloy. The flow curves obtained from load relaxation tests on superplastic Zn-Al alloys were shown to consist of the contributions from interface sliding (IS) and the accommodating plastic deformation due to dislocation activities. The IS behavior could be described as a viscous flow characterized by the power index value of Mg = 0.5. In the case of quasi-single phase Zn-0.3 wt.% Al alloy with the average grain size of 1 µm, a large elongation of about 1400 % was obtained at room temperature. In a relatively large-grained (10 µm) single-phase alloy, however, grain boundary sliding (GBS) was not expected from the analysis based on the internal variable theory of SSP.
Rapid-Solidified Metallic Actuator Materials Developed by Electromagnetic Nozzleless Melt Spinning Method
Authors: Furuya Y.
Published: April 2011

Electro-magnetic nozzleless melt-spinning method was developed by combining the control of the flow down of the molten metals after electromagnetic float-melting(i.e. levitation) with rapid solidification by rotating roll. The metallurgical grain microstructures can be changed by rotating roll speed. It was confinned that the produced, intermetallic TiNi and NiAl system alloy thin plates showed the strong crystal anisotropy, higher shape memory functional properties than those of the conventionally processed melt-worked samples having its same origin. As new SMAs by using this method, ferromagnetic shape memory, FePd alloy having very large magnetostriction and super high temperature shape memory, RuTa alloy having the transformation over 1000°C were developed. Moreover, our recent study on the advanced rapid-solidification machine to produce many kinds of short fibers as well as ribbons is introduced. Finally, harmonic material design for sensor/actuator stacking composite system, namely “Smart Board” for aircraft structures will be introduced.
Zero Hysteresis in Shape-Memory TI-NI-X Films (X = CU, PD) Under Constraint
Authors: Winzek B. , Quandt E.
Published: April 2011

The hysteresis of thin film shape memory actuators affects the frequency of actuators switching between martensite and austenite. Therefore the hysteresis properties of thin films of TiNi, Ti(Ni,Cu) and Ti(NiPd) deposited onto metallic substrates by DC-Magnetron sputtering have been investigated. The substrates have different expansion coefficients to establish biaxial tensile and compressive film stresses, respectively. The results show, that the hysteresis width is significantly affected by the stress state of the shape memory film and in principal depends on the temperature range of measurement. In contrast, the difference Af-Mf remains unchanged. In some alloys zero hysteresis width could be obtained.
Adaptive Composites with Embedded Shape Memory Alloy Wires
Authors: Balta J.A. , Parlinska M. , Michaud V. , Gotthardt R. , Manson J-A.E.
Published: April 2011

Pre-strained martensitic Shape Memory Alloy wires embeddedz into a composite material act against the stiffness of the host material if they are heated above their retransformation temperature, biasing their strain recovery. As a result, recovery stresses are generated in the composite, leading to a shift in resonance vibration frequency if the wires are placed along the neutral axis of a composite beam. Guidelines for quantification of the effects produced, as a function of SMA wire composition, volume fraction, level of pre-strain, and of host material stiffness are not available yet. In order to investigate the governing mechanisms of activation, adaptive composite materials based on Kevlar fiber reinforced epoxy matrices have been produced by embedding thin Shape Memory Alloy wires, 150 microns in diameter, during processing in an autoclave. A mold was specially designed to pre-strain the SMA wires and prevent their recovery during the cure cycle. Values of the degree of activation in the composite materials, in terms of maximal recovery force and of the corresponding maximal resonance vibration frequency shift will be presented as a function of the stiffness of the host material and SMA volume fraction. Preliminary guidelines for the optimization of these materials will thus be given.
Radial Bragg Grating Package for Temperature Compensation in Interferometric Hydrophone Arrays
Authors: Carreiro L.G. , Ames G.H. , Ramotowski T.S. , Curry P.D.
Published: April 2011

A new method of packaging fiber Bragg gratings to stabilize their wavelength over temperature variations was developed using a grating mount fabricated from zirconium tungstate (ZrW2O8), a ceramic with a negative coefficient of thermal expansion (CTE). The principle of operation is based on the differences in CTE of the Bragg grating and grating mount, with the mount serving as a compensator for the thermo-optic effects of the fiber. As the temperature is elevated, the refractive index of the grating increases, shifting the reflection wavelength to longer wavelength. At the same time the ceramic grating mount contracts relieving some of the tension on the grating, causing a shift to shorter wavelength. Since these two effects offset each other, the thermal wavelength shift of the grating can be minimized or even eliminated. In addition to a description of the temperature-compensating device, the properties of zirconium tungstate are briefly discussed with emphasis on the processing of the ceramic grating mount. Thermal analysis data is given for zirconium tungstate with 5% polymer binder addition.
PbZr0.52Ti0.48O3 Ferroelectric Thin Films on Silicon by KrF Excimer Laser Ablation
Authors: Ebihara K. , Mitsugi F. , Yamazato M. , Ikegami T. , Narayan J.
Published: April 2011

The Au / PbZrxTi1-xO3 (PZT) ferroelectrics / YBa2Cu3O7-x (YBCO) superconductor / yttria-stabilized zirconia (YSZ) heterostructures were prepared on Si (100) substrate by KrF excimer laser ablation technique. The x-ray diffraction patterns showed that the PZT films prepared on YBCO / YSZ /Si at 550°C, O2 100 mTorr and a laser energy density of 2 J/cm2(5Hz) are pure perovskite and highly oriented with the (00l) orientation. The polarization (P)-electric field (E) characteristics showed the remanent polarization Pr of 23 µC/cm2 and coercive field Ec, of 35 kV/cm. Pr of the PZT capacitor degraded to one half of initial value after about 1010 switching cycles (50 kHz).
Electrical Conductivity of Piezoelectric Strontium Bismuth Titanate Under Controlled Oxygen Partial Pressure
Authors: Voisard C. , Martin P. Duran , Damjanovic D. , Settier N.
Published: April 2011

Hysteresis free and linear piezoelectric behavior of SrBi4Ti4O15 (SrBIT) is very promising for precise sensors/actuators devices. Despite a quite low longitudinal piezoelectric coefficient (around 15 pC/N), its elevated ferroelectric phase transition temperature (540°C) allows its use above 300°C. Electrical conductivity at such temperatures should be kept as low as possible in order to avoid loss of piezoelectric properties or charge drifts. Under reducing conditions, however, the electrical conductivity may change considerably. The electrical conductivity of SrBi4Ti4O15 (SrBIT) has been measured under controlled oxygen partial pressure at elevated temperatures (700-900°C) from 1 atm down to 10−15atm. From 1 atm down to 10−15 atm pO2, above 700°C, the conductivity of SrBIT exhibits a -1/4 slope in log-log scale indicating n-type conductivity and an impurity controlled oxygen vacancy concentration. A conductivity minimum is observed around 0.2 atm for undoped SrBIT at 800°C. Acceptor doping (Mn) raises the minimum and flattens the conductivity curve with slope around -1/10 at 700°C, and -1/6 at 900°C. Ionic conductivity and defect ionization are discussed to account for this. Preliminary results indicate the possibility of a large, pO2 independent, region, down to 10−15atm pO2. The ionic transport number was found to be 0.42 at 800°C for undoped SrBIT and 0.75 for Mn doped SrBIT. The activation energies of undoped (1.35 eV) and Mn doped (1.44 eV) samples are close to each other as expected for a common mechanism
Triboluminescence of Rare-Earth-Doped Aluminosilicates and Its Application to Sensing of Structural Damage
Authors: Tanaka Katsuhisa , Ishihara Tsuguo , Fujita Koji , Hirao Kazuyuki
Published: April 2011

Intense triboluminescence has been observed in rare-earth-doped aluminosilicates such as BaAl2Si2O8and SrAl2Si2O8doped with Eu2+, Tb3+, or Dy3+. The triboluminescence is caused by the excitation of and emission from rare-earth ions doped in the crystals. A discrepancy in the wavelength of maximum emission intensity between triboluminescence and photoluminescence spectra is observed for the 4f65d-4f7 transition of Eu2+, whereas the peak positions and the relative intensities of emission lines in triboluminescence and photoluminescence spectra are almost the same as each other for the 4f-4f transitions of Th3+ and Dy3+. This is because the 5d levels, which are more significantly affected by ligand fields than the 4f levels, contribute to the transition of Eu2+. It is thought that the difference in local environment around the Eu2+ between on the fractured surface and within the bulk brings about the discrepancy between triboluminescence and photoluminescence spectra
Composite Piezoelectric Materials for Health Monitoring of Composite Structures
Authors: Blanas P. , Das-Gupta K.
Published: April 2011

Composites of ferroelectric ceramic in polymer matrix have been developed and characterized for their ability to be employed as embedded sensors for the health monitoring of olymer composite structures. In this paper results illustrating the response of embedded composite sensors to dynamic loads are presented and discussed. Furthermore, the ability of the composite sensors to act as actuators, generating diagnostic waves in composite structures, has been investigated.
Fatigue Testing Machine of Micro-Sized Specimens for MEMS Applications
Authors: Higo Y. , Takashima K. , Shimojo M. , Sugiura S. , Pfister B. , Swain M. V.
Published: April 2011

A new type of fatigue testing machine for micro-sized specimens for MEMS applications has been developed. This fatigue testing machine consists of a magnetostrictive actuator which is able to impart small displacements to a specimen upto 20 νm with resolution of 5 nm. The actuator is connected to a metal shaft and a diamond tip of 5 νm in radius is attached to the end of the shaft. Small displacements are applied to the specimen through the diamond tip. This makes it possible to construct a high stiffness loading fixture. The magnitude of load applied to the specimen is measured by a strain gauge type load cell with a load resolution of 10 νN. The specimen stage and load cell can be moved to adjust the loading position precisely by a stepping motor at a translation resolution of 0.1 νm. Cantilever beam type specimens with dimensions of 10 × 12 × 50 νm3 were prepared from a Ni-P amorphous thin film by focused ion beam machining. Very small cyclic load (ΔP = 0.1 - 40 mN) was able to be applied to the specimen successfully. This machine appears to be promising for evaluation of fatigue properties for micro-sized specimens for MEMS applications.
Built-In Strain in Polysilicon: Measurement and Application to Sensor Fabrication
Authors: Guckel H.
Published: April 2011

The built-in strain in deposited polysilicon films depends on film morphology. The strain may be compressive or tensile. Its magnitude and uniformity may be measured by using surface micro machining with test structures which require a single photomask level and use Euler buckling. Anneal cycles may be used to convert compressive strain to tensile or zero strain. Deposition and anneal cycles may be optimized to produce fine grained polysilicon with isotropic mechanical behavior.

Strain field control can improve yield by reducing surface sticking. This mechanical stiffening is used in, for instance, pressure transducer construction. Built-in and applied axial strain are used to change the resonant frequencies of clamped-clamped beams in a vacuum envelope where quality factors up to 300,000 have been measured.
Properties of Low Residual Stress Silicon Oxynitrides Used as a Sacrificial Layer
Authors: Habermehl S. , Glenzinski A. K. , Halliburton W. M. , Sniegowski J. J.
Published: April 2011

Low residual stress silicon oxynitride thin films are investigated for use as a replacement for silicon dioxide (SiO2) as sacrificial layer in surface micromachined microelectrical-mechanical systems (MEMS). It is observed that the level of residual stress in oxynitrides is a function of the nitrogen content in the film. MEMS film stacks are prepared using both SiO2 and oxynitride sacrificial layers. Wafer bow measurements indicate that wafers processed with oxynitride release layers are significantly flatter. Polycrystalline Si (poly-Si) cantilevers fabricated under the same conditions are observed to be flatter when processed with oxynitride rather than SiO2 sacrificial layers. These results are attributed to the lower post-processing residual stress of oxynitride compared to SiO2.
Characterization of Metallized Plastic MEMS
Authors: Chu Charles , Bachman Mark , Chiang Yuh-Min , Gonzales Fernando , Li G. P.
Published: April 2011

Metallization of plastic devices is of interest to newer non-silicon based MEMS which are being developed for biomedical and other applications. The electrical properties of the metallization will depend, in part, on the material on which they are patterned, and the method of deposition. Of interest are the electrical characterizations during usage which must be studied to allow plastic MEMS designs to proceed wisely. Flexible microdevices may develop open circuits or shorts after excessive bending; joule heating may adversely affect the plastic substrates, leading to failure. We present some experimental studies on electrical characterization of metallized plastics as it relates to various processing conditons and usage scenarios.
Iron Sulfide (FeS2) Thin Films From Single-Source Precursors by Aerosol-Assisted Chemical Vapor Deposition (AACVD)
Authors: O'Brien Paul , Otway David J. , Park Jin-Ho
Published: April 2011

Dialkyl (or mixed alkyl)-dithiocarbamato iron(III) complexes have been used for the deposition of iron sulfide thin films using chemical vapor deposition techniques. The single-source precursors used in this work have been prepared by the reaction of FeCl3with dialkyldithiocarbamate sodium salts and characterized by a number of analytical techniques. Good quality thin films of FeS2 have been prepared from the single-source metal organic precursor, [Fe(S2CNMeiPr)3], by AACVD. XRD patterns of the films indicated crystalline iron sulfide (FeS2) grown at between 375 – 450 °C. SEM images show the films to have reasonable morphology and to be crystalline.
MOCVD of CuInE2 (Where E = S or Se) and Related Materials for Solar Cell Devices
Authors: Kemmler Michael , Lazell Michael , O'brien Paul , Otwaya David J.
Published: April 2011

Thin film(s) of chalcopyrite CuInE2(where E = S or Se) have been grown by low-pressure metal-organic chemical vapour deposition (LP-MOCVD) using the precursors [In(E2CNMenHexyl)3] and [Cu(E2CNMenHexyl)2]. Similarly, thin films of ME (where M = Zn, Cd; E = S, Se) have been deposited from precursors of general formula [M(E2CNMenHex)2]x. Films were grown on glass between 400 - 500 °C, and characterized by X-ray diffraction, optical spectroscopy (UV/Vis), EDAX and scanning electron microscopy.
Wet-Chemical Synthesis of Thin-Film Solar Cells
Authors: Raffaelle R.P , Junek W. , Gorse J. , Thompson T. , Harris J.D , Cowen J. , Hehemann D. , Rybicki G. , Hepp A.F.
Published: April 2011

We have been working on the development of wet-chemical processing methods that can be used to create thin film photovoltaic solar cells. Electrochemically deposition methods have been used to produce copper indium diselenide (CIS) thin films on molybdenum coated polymer substrates. CIS has an extremely high optical absorption coefficient, excellent radiation resistance, and good electrical conductivity and thus has proved to be an ideal absorber material for thin film solar cells. A series of compositionally different p-type CIS films were produced by using different electrochemical deposition potentials. Cadmium sulfide (CdS) window layers were deposited directly on these CIS films using a chemical bath process. CdS is a naturally ntype wide-bandgap semiconductor which has good transparency and is well lattice-matched to CIS. Zinc oxide thin films were grown by electrochemical deposition directly on the CdS films. ZnO is a transparent and conductive thin film that serves as the top contact of the cells. The structural and elemental properties of the individual ZnO, CdS and CIS films were characterized by x-ray diffraction and energy dispersive spectroscopy. The electrical behavior of the CdS on CIS junctions was determined using current versus voltage measurements. We will discuss the performance of these devices based on the physical properties of the component films and the processing methods employed in their fabrication.
Pentadionate: An Alternate Sol-Gel Method for the Synthesis of Ferroelectric Ba1−xSrxTiO3
Authors: Sharma Pramod K. , Jose K. A. , Varadan V. V. , Varadan V. K.
Published: April 2011

Sol-gel synthesis of transitional metal oxides is one of the important technique to obtain the pure and homogenous materials at low temperature. In this work, Barium strontium titantate (BST) was synthesized by sol-gel processing using 2,4-pentadionate as the precursors of metal oxides. The Ba1−xSrxTiO3 was prepared for four values of x i.e. 0.2, 0.4, 0.5 and 0.6. The obtained powders were heated from 400 °C to 800 °C at the interval of 100 °C to determine the temperature of crystallization. The phase of the final products was investigated by x-ray diffraction (XRD). Two particle sizes (< 100 nm and 200-400 nm) were observed under the scanning electron microscope (SEM) of the heat treated xerogel. The dielectric properties were determined by impedance analyzer at the frequency of 1MHz and explained in detail for the different values of x.
Effect of Layer Relaxation on the Internal Photoemission in Pt/Si1−xGex Schottky Barrier Type Infrared Detectors
Authors: Aslan B. , Turan R. , Nur O. , Karlsteen M. , Willander M.
Published: April 2011

A Schottky type infrared detector fabricated on a p-type Si1−xGex substrate has a higher cut-off wavelength than one on a pure Si substrate because the barrier height of the Schottky junction on p-type Si1−xGex decreases with the Ge content and the induced strain in the Si1−xGex layer. We have studied the effect of the strain relaxation on the internal photoemission and I-V characteristics of a Pt/Si1−xGex Schottky junction with x=0.14. It is shown that the cut-off wavelength of the diode made on a strained Si0.86Ge0.14 layer is higher than that on a Si substrate as expected. This shows the possibility of tuning the range of these detectors in the mid-infrared region. However, the thermal relaxation in the Si0.86Ge0.14 layer is found to reduce the cut-off wavelength to lower values, showing that the difference between the Fermi level of the metal and the valence band edge increases with the layer relaxation. This effect should be taken into account when a Schottky type infrared detector is manufactured on a strained Si1−xGex film. I-V characteristics of the junctions also indicate an increase of the barrier height with the relaxation of Si1−xGex. These results demonstrate the band edge movements in a Si ixGex layer experimentally agree with the expected changes in the band structure of the Si1−xGex layer with strain relaxation.
Infrared Photosensitivity Due to the Yb-Induced Defect States in Pb1−xGexTe Alloys
Authors: Skipetrov E.P. , Chernova N.A. , Zvereva E.A. , Slyn'ko E.I.
Published: April 2011

Galvanomagnetic properties and photoconductivity kinetics of Pb1−xGexTe(x≤0.04) alloys doped with Yb have been investigated. The alloys exhibit high infrared photosensitivity at temperature under 40 K; at helium temperature, the effect of persistent photoconductivity has been observed. The photoconductivity kinetics after terminating of infrared illumination consists of a fast and a long-term relaxation regions. We explain the observed effects by a capture of electrons into the Yb-induced states, that are subjected to the Jahn-Teller instability. The parameters of the Jahn-Teller states are estimated.
Strained SiGe Materials for High Quantum Efficiency Photodiodes at µ = 1.3 to 1.5µm
Authors: Giovane L. M. , Luan H.-C. , Fitzgerald E. A. , Kimerling L. C.
Published: April 2011

Silicon-gemanium is a promising materials system for delivering near-IR photodetection on the ubiquitous silicon substrate. The 4% lattice mismatch leads to biaxial strain for SiGe films grown coherently on (100) Si substrates, which both extends the long wavelength detection limit by reducing the band gap and defines the critical thickness for the SiGe film. We have studied the use of strained-layer superlattices grown on high quality relaxed SiGe buffers. Graded buffers are ideal virtual substrates for achieving a complete range of compositions and strains for GeSi alloys. A physical model has been created to map out the absorption coefficient as a function of Ge fraction and (100) biaxial strain. Based on calculated absorption spectra as a function of composition and strain, we have designed and grown a Ge/Ge0.5Si0.5 strain-balanced superlattice on a high quality Ge0.75Si0.25 relaxed buffer using UHV-CVD. The strain-balanced superlattice has an effective absorption coefficient of 5000 cm−1. The relaxed buffer serves as a virtual substrate with relatively low threading dislocation density (106 cm-−2). The effect of the threading dislocations on the leakage current of P-I-N junctions is also investigated. Electron beam induced current (EBIC) is used to determine the dislocation density of SiGe relaxed buffer junctions grown with different grading rates. Mesa isolated devices are used to determine bulk leakage current densities for the SiGe junctions. The bulk leakage current density scales directly with the dislocation density. Bulk leakage currents density per dislocation length (2×10−5 A cml) agrees with deep level transient spectroscopy (DLTS) determined literature values for SiGe capture cross-section and defect density per dislocation in Si.
Progress in Antimonide-Based Mid-IR Lasers
Authors: Turner G.W. , Manfra M.J. , Choi H.K. , Goyal A.K. , Buchter S.C. , Calawa S.D. , Sanchez A. , Spears D.L.
Published: April 2011

Mid-infrared optically pumped semiconductor lasers (OPSLs) are presently being investigated for a variety of commercial and military applications. Active regions in such optically pumped lasers must meet the dual requirements of high gain and low loss at mid-IR wavelengths, combined with sufficient absorption of the optical pump at shorter wavelengths for efficient power conversion. In this paper we report the successful growth, fabrication, and characterization of high-performance OPSLs that employ novel active regions consisting of combinations of GalnAsSb integrated-absorber layers with type-II GaInSb/InAs quantum well regions. With 1.85-µm optical pumping at 85 K, OPSLs with such active regions have exhibited a peak output power of 2.1 W at 3.9 pm, improved beam quality, power conversion efficiency of ∼8%, and characteristic temperatures of ∼47 K.
Photoluminescence and EPR of Phosphorus Vacancies in ZnGep2
Authors: Moldovan M. , Stevens K. T. , Halliburton L. E. , Schunemann P. G. , Pollak T. M. , Setzler S. D. , Giles N. C.
Published: April 2011

Zinc germanium diphosphide (ZnGeP2) is a nonlinear optical material used in mid-infrared optical parametric oscillators. The near-infrared photoluminescence (PL) from single crystals of bulk ZnGeP2 has been studied as a function of excitation power, wavelength, temperature, and polarization. At 5 K, a broad PL band extending from 0.7 µm to beyond 1 µm is typically observed. Two distinct emissions with different polarization, power, and temperature behaviors have been resolved. These bands have peaks in intensity near 1.6 eV and 1.4 eV. The relative intensities of these two bands were found to correlate with the presence of phosphorus vacancies, as determined by electron paramagnetic resonance (EPR). A resonance in the intensity of the 1.6-eV band occurs when pumping into a level ∼90 meV below the minimum conduction band. This level is tentatively assigned to the shallow state.
Analysis of Cr-Doped CdGeAs2 Using Thermal Admittance Spectroscopy
Authors: Smith S.R. , Evwaraye A.O. , Ohmer M.C. , Saxler A. W. , Goldstein J. T. , Solomona J. , Schunemann P. G. , Pollak T. M.
Published: April 2011

The optical and electrical properties of chrome-doped CdGeAs2 (CGA), an important non-linear optical material, are reported. CGA, a chalcopyrite semiconductor of the pseudo- III-V type, is a close ternary analog to GaAs, possessing significant differences. To date, the electrical and optical properties of as-grown undoped CGA have been controlled by a somewhat shallow dominant residual acceptor which it is the source of significant undesirable optical absorption. Highly transparent semi-insulating CGA should be attainable using compensation and counterdoping schemes similar to those used for GaAs. However, identifying suitable deep and shallow n-type and p-type dopants will require extensive empirical studies. As a starting point of survey to find deep levels, the properties of CGA:Cr have been investigated. Cr is a reasonable choice as it has been used extensively to provide a deep level in GaAs. Thermal Admittance Spectroscopy was used to examine the electrically active levels in this material. These measurements were correlated with temperature dependent Hall effect measurements, and IR absorption measurements. SIMS analysis was utilized to estimate the Cr concentration as the segregation coefficient for Cr in CGA has not been reported.. The results show that there is a p-type level introduced into the band gap at about 0.16 eV above the valence band, a value nominally 50% deeper than that of the native acceptor. The background doping as measured by Capacitance-Voltage measurements was determined to be 8 × 1016 cm−3 near the surface, and 1.0 × 1017 cm−3 in the bulk. These results are compared to similar measurements in undoped material.
Influence of SiOx Capping Layer Quality on Impurity-Free Interdiffusion in GaAs/AlGaAs Quantum Wells
Authors: Deenapanray P.N.K. , Tan H.H. , Jagadish C.
Published: April 2011

We have investigated the influence of SiOx capping layer quality on impurity-free vacancy interdiffusion in GaAs/Al0.54Ga0.46As quantum wells. Dielectric layers were deposited by plasmaenhanced chemical vapor deposition, and properties of layers were changed by varying either the flow rate of silane or deposition temperature. The extent of intermixing in our samples is discussed in terms of the 0 content and incorporation of N in capping layers, and also on their porosity. We also report on the electrically active defects which are introduced in Si02 capped and annealed n-GaAs, and relate them to the intermixing process.
Degradation of Intersubband Transitions in Electron Irradiated GaAs/AlGaAs Multiple Quantum Wells With Superlattice Barriers
Authors: Morath C.P. , Manasreh M.O. , Gingrich H.S. , Bardeleben H.J. von , Ballet P. , Smathers J.B. , Salamo G.J.
Published: April 2011

Intersubband transitions in GaAs/AIGaAs multiple quantum wells (MQWs) are studied as a function of 2 MeV electron irradiation doses using the optical absorption technique. The MQW structure was designed with a 5 period Al.4Ga.6As/GaAs superlattice barrier, and two transitions are observed in the spectra. These transitions occur from the ground state to the first excited state and to the miniband formed by the superlattice barrier. The total integrated area from both transition spectra are studied as a function of temperature and electron irradiation dose. For the ground state to first excited state transition the total integrated area decreases exponentially as the irradiation dose increases, which could be explained in terms of the trapping of the 2D-electron gas in the quantum well by the irradiation induced defects. In comparison, the intensity of the ground state to miniband transition was found to increase exponentially as a function of the irradiation dose. Two possible explanations for this behavior are suggested. The temperature dependence of the integrated area of both transitions is also presented.
Compound Semiconductor Applications for Automotive Sensors
Authors: Pelczynski M. W. , Heremans J. J. , Schwed S.
Published: April 2011

Compound semiconductors find extensive application as magnetic position sensors in the automotive environment. Typical applications involve the sensor element, a permanent magnet attached to the sensor, and a moving magnetic circuit -a target wheel. Wider mechanical gaps in the magnetic circuit can be utilized with a sensor of higher sensitivity, and thus high sensitivity is valuable. Further limitations on the choice of materials are imposed by temperature sensitivity, as the automotive environment is characterized by wide temperature operating ranges (-40°C up to 200°C). The magnetic signal may be hidden by the temperature drift in the sensor output, andthus temperature stability limits the sensor's resolution. Automotive position sensors find use in ignition timing and misfire detection (cam and crank sensors), as wheel speed sensors (anti-lock brakes and other types of active wheel-control), in brushless electric motors and several other applications. This work reviews progress achieved to refine the use of InSb for automotive sensing applications.
Correlation Between GaInAsSb Surface Step Structure and Phase Separation
Authors: WANG C.A.
Published: April 2011

A strong correlation between the surface step structure and phase separation in metastable GaInAsSb epitaxial layers grown by organometallic vapor phase epitaxy has been identified. The full width at half maximum (FWHM) of 4-K photoluminescence (PL) peak energy is used as a semi-quantitative measure of the degree of phase separation. The step structure of GaInAsSb grown at 525 °C is vicinal, while it is step-bunched for layers grown at 575 °C. The corresponding 4-K PL FWHM data indicate that the degree of phase separation is minimized when the layers aregrown at the lower growth temperature. It is proposed that the longer terrace lengths of a step-bunched surface are associated with a longer adatom lifetime compared to a vicinal surface, and thus the adatoms have more time to cluster and phase separate, which is the preferred equilibrium state. Increasing the growth rate, which reduces the adatom lifetime, also reduces the PL FWHM, and thus, the degree of phase separation.
Microcrystalline Si and (Si,Ge) Solar Cells
Authors: Dalal Vikram L. , Maxson Tim , Han Kay
Published: April 2011

We report on the growth of microcrystalline Si and (Si,Ge) cells on stainless steel substrates. The devices were grown using a remote, low pressure, ECR growth technique at low temperatures (250-350 C). The precursor gases were silane, germane and hydrogen. The devices were of the p-i-n type, with light incident on the p layer. The p layer was a-(Si,C). A novel interface buffer layer, consisting of an amorphous alloy whose bandgap was graded from 1.3 eV to 1.9 eV was used to match the crystalline base layer with the higher gap p layer. It was found that the properties of this buffer layer were critical in determining the properties of the resulting device. The buffer layer was found to increase the voltage by almost 20%. Cells with high fill factors were made using this technique. The quantum efficiency data indicated that the base layers had absorption characteristic of crystalline materials.
Effects of Structural Properties of νc-Si:H Absorber Layers on Solar Cell Performance
Authors: Vetterl O. , Carius R. , Houben L. , Scholten C. , Luysberg M. , Lambertz A. , Finger F. , Wagner H.
Published: April 2011

Thin film microcrystalline silicon solar cells with absorber layers of various structural composition have been prepared. The highest conversion efficiency is observed at preparation conditions close to the transition to the amorphous growth regime, i.e. crystalline volume fraction is high but not at its maximum. The optimized material consists of crystalline “fibers” with small diameter which extend through the whole absorber layer. On further approach to the transition regime a set in of amorphous growth can be observed, resulting in decreasing solar cell performance. Surprisingly, material prepared under conditions favoring highly crystalline growth exhibits a less efficient carrier extraction if applied to the solar cell. We discuss increasing bulk recombination as possible cause for this observation. The maximum conversion efficiency obtained was 8.7 % for a 1 νm single junction solar cell. Using our optimized deposition conditions with simultaneously higher discharge powers the deposition rate can be increased up to 4.6 Å/s at the high efficiency of 8.3 %.
Amorphous Silicon Alloy Solar Cells Near the Threshold of Amorphous-to-Microcrystalline Transition
Authors: Yang Jeffrey , Lord Kenneth , Guha Subhendu , Ovshinsky S.R.
Published: April 2011

A systematic study has been made of amorphous silicon (a-Si) alloy solar cells using various hydrogen dilutions during the growth of the intrinsic (i) layer. We find that the open-circuit voltage (Voc) of the cells increases as the dilution increases; it then reaches a maximum before it decreases dramatically. This sudden drop in Voc is attributed to the transition from amorphous silicon to microcrystalline inclusions in the i layer. We study i-layer thicknesses ranging from 1000 Å to 5000 Å and find that the transition occurs in all thicknesses investigated. Based on this study, a-Si alloy p i n solar cells suitable for use in the top cell of a high efficiency triple-junction structure are made. By selecting an appropriate dilution, cells with Voc greater than 1 V can be achieved readily. Solar cells made near the threshold not only exhibit higher initial characteristics but also better stability against light soaking. We have compared top cells made near the threshold with our previous best data, and found that both the initial and stable efficiencies are superior for the near-threshold cells. For an a-Si/a-Si double-junction device, a Voc value exceeding 2 V has been obtained using thin component cells. Thicker component cells give rise to an initial active-area efficiency of 11.9% for this tandem structure.
Protocrystalline Growth of Silicon below 80°C
Authors: Koch Christian , Ito Manabu , Svrcek Vlado , Schubert Markus B. , Werner Jürgen H.
Published: April 2011

Protocrystalline silicon deposited at temperatures below 80°C exhibits an extraordinary photosensitivity and superior stability against light-soaking. This material growths at the borderline of the amorphous and nanocrystalline phases in plasma-enhanced chemical vapor deposition. After thermal annealing and subsequent light-soaking, the photosensitivity is comparable to the values after deposition, while amorphous silicon strongly drops off. A structural and optical characterization reveals a small fraction of silicon crystallites embedded in an amorphous well-ordered matrix. We investigate the morphology of silicon films deposited at the edge of crystallinity by the absolute Constant Photocurrent Method and observe a phase transition from amorphous to nanocrystalline silicon. This thickness dependant morphology is of crucial importance for solar cell design. We attain protocrystalline absorber which reflect in a strongly improved fill factor compared to amorphous silicon based solar cells.
Early Research On Amorphous Silicon: Errors and Missed Opportunities
Authors: Fritzsche Hellmut
Published: April 2011

It is instructive to reflect on the past research of an entirely new material such as hydrogenated amorphous silicon in order to analyze which impediments lay in the way of reaching our present understanding. What in retrospect appears to be clear and important evidence was often not recognized as such and, therefore, not incorporated into a coherent picture for a surprisingly long time. One reason for the inability to see and understand is one's mode of thinking, which is conditioned by training and prior experience. Other impediments to progress are some persuasive, but erroneous, views of respected members of the scientific community. A third factor that tends to slow progress is a false sense of competition which, for example, prevents research laboratories from a fruitful exchange of materials and samples. It appears that human faults run neck to neck with nature's intricacies in slowing the pace of our understanding.
Composition and Structure of SiCx:H Films Formed by Plasma Immersion ION Implantation From A Methane Plasma
Authors: Volz K. , Klatt Ch. , Ensinger W.
Published: April 2011

Hydrocarbon ions are implanted into silicon by pulse biasing Si to a high voltage of -45 kV in a methane plasma. The resulting SiCx:H films are examined with respect to their composition and chemical binding by RBS, NRA and IR spectroscopy. The process may yield all C/Si ratios, up to pure C films. The H depth profile is shown to be strongly governed by the C depth profile. Silicon carbide bonding as well as C–H bonds can be proven in the implanted region.
Fast In-diffusion of Hydrogen at the Initial Stage of Hydrogen Plasma Treatment on a-Si:H Films Observed by In-situ ESR Measurements
Authors: Das Ujjwal Kr. , Yasuda Tetsuji , Yamasaki Satoshi
Published: April 2011

Time evolution of Si dangling bonds (dbs) was monitored during atomic hydrogen treatment of a-Si:H films using an in-situ electron-spin-resonance (ESR) technique. A high diffusion coefficient (>10−10 cm2s−1) of free atomic H in a-Si:H was detected at the very initial stage of H exposure. Atomic H diffuses into the bulk of the film (∼100 nm) and creates additional metastable dbs. The spatial distribution of such metastable dbs becomes deeper at lower treatment temperatures. An activated type of db creation reaction determines the distribution of these dbs.