bluuebunny/crossref_metadata_2025 huggingface dataset:
Organic Thin Film Transiators on Synthesis Paper
Authors: Cheng Hua-Chi , Peng Yu-Rung , Chung Chao-An , Hou Wei-Hsin , Pei Zing-Way
Published: April 2011

We have demonstrated organic thin-film transistor devices on synthesis paper of polypropylene (PP). All the fabrications are in solution-based processes except electrodes. As a barrier and smoother layer, photosensitive epoxy, 5μm-thich was coated on the paper substrate by using slit die coating. Polyvinyl phenol (PVP) was mixed with poly (melamine-co-formaldehyde) methylated, filmed by spin coating and ultraviolet (UV) cross linked to provide the gate dielectric layer. Using poly (3-hexylthiophene) as an active layer, a high-performance organic transistor with field effect mobility up to 0.006 cm2/ V s and an on/off ratio of 50 can be achieved. For the applications in flexible and disposable electronics, to built organic transistors on a cheap synthesis paper substrate can extremely lower the cost.
The Electronic Structure and the Energy Level Alignment at the Interface Between Organic Molecules and Metals
Authors: Kawabe Eiji , Yamane Hiroyuki , Koizumi Kenji , Sumii Ryohei , Kanai Kaname , Ouchi Yukio , Seki Kazuhiko
Published: April 2011

We investigated the electronic structure and the energy level alignment at the interfaces between perylene-3,4,9,10-tetracarboxylic dianhydride (PTCDA) and metals (Au, Cu and Co) by ultraviolet photoelectron spectroscopy (UPS). In the case of PTCDA/Au interface, the apparent interface states and charge transfer (CT) states were not observed in its UPS spectra. In the case of PTCDA/Cu and Co interfaces, however, we found that the CT from metal to PTCDA occurred, and that the apparent CT states were observed at PTCDA/Cu interface.
Very High On/Off Ratio in Vertical-Type Metal-Base Organic Transistors
Authors: Nakayama Ken-ichi , Yokoyama Masaaki
Published: April 2011

The on/off ratio of the vertical-type metal-base organic transistors was drastically improved by heat treatment in air. The heat treatment after deposition of the collector layer and base electrode reduced the leakage current between the base and collector, resulting in remarkable suppression of the off current. As a result, in addition to the advantage of low voltage and high current operation based on the vertical structure, very high on/off ratio exceeding 105 was achieved.
Direct Local Strain Measurement In Damascene Interconnects
Authors: Kasbari Moustafa , Rivero Christian , Blayac Sylvain , Cacho Florian , Bostrom Ola , Fortunier Roland
Published: April 2011

A new mechanical stress characterization method has been developed for Damascene copper interconnects. The micro strain gauge based on a rotating beam has been fabricatedin situon a standard industrial CMOS production line. Comparison of the beam deviation in the fabricated sensor with usual geometrical model is discussed. The saturation of the beam deviation leads to an analytical model which takes the stiffness of the anchoring points into account. This model gives a direct value of the local stress in the copper line for different annealing times. We show that this value is different from the one given by a curvature measurement method. The microstructure of the Damascene copper induces a higher stress level than full sheet deposition copper. The sensor was developed to be compatible within a CMOS process. It is suitable for in situ mechanical stress monitoring in Damascene lines and process optimization.
RRAM electronics and Switching Mechanism
Authors: Hsu Sheng Teng , Li TingKai
Published: April 2011

The property of PCMO RRAM memory devices have been studied in terms of electrical pulse width, Pulse polarity, voltage ramping, film thickness, resistivity distribution, and temperature dependent of resistance. The PCMO material is deposited using MOD, PVD, or PLD process. The experimental results clearly indicated the resistance increase is due to localization of valence electrons. The narrow pulse induced resistance increase near the cathode indicated the localization of valence electrons is the effect of high density of excessive non-equilibrium electrons through the well known Jahn-Teller effect. High density of non-equilibrium electrons may also be induced by any other means such as displacement current, space charge limited current, SCLC, and radiation. High field intensity collapses the localized valence electrons and returns the device to the low resistance state. This is the intrinsic property of transition metal oxides. We expect all doped and un-doped transition metal oxides to exhibit resistance switching property.
Stress and Mechanical Constants Characterizations of Phase-change SbTe-alloys: Influence of the Film Thickness and Substrate
Authors: Lisoni Judit , Gille T. , Goux L. , Delhougne R. , Jossart N. , Attenborough K. , Wouters D. J.
Published: April 2011

We have characterized the in-film stress and the mechanical constants of a growth-dominated phase-change SbTe-alloy, a material beneficially used in the line-cell phase change memory architecture. The influence of the thickness of the films (5-120 nm) and of the substrate used for its deposition (Si, SiO2 and SiC) was studied. The characterizations were carried out on both amorphous and crystalline films. The crystallization temperature was determined by the resistance changes as a function of the temperature. The mechanical characteristics of the films were measured by the wafer curvature method. We observed that the mechanical behavior of these films was strongly dependent on their thicknesses and on the substrate material. For the thinnest amorphous films, the in-film stress was highly compressive (with the largest compressive stress for films on SiC), while it tended to be very low (fully relaxed films) for films thicker than 20 nm. The amorphous films furthermore did not reveal any stress relaxation in time-dependent stress measurements. Therefore, it was not possible to quantify the viscosity of the SbTe-alloy. This result maybe related to a lower defect state in the very thin films used, or to a blocking of the defects by enhanced reactivity of these thin SbTe-alloy films with their surroundings, both resulting in the absence of relaxation in the amorphous state. Finally, the coefficients of thermal expansion (CTE) of the amorphous and crystalline SbTe-alloys were similar, 1–3×10−6 K−1. These values were comparable to the CTE's of the substrates, clearly indicating that for thin films the substrates dominate their thermal expansion behavior.
Temperature-dependent Degradation Modes in CdS/CdTe Devices
Authors: Albin David , Demtsu Samuel H , Duda Anna M , Metzger Wyatt K
Published: April 2011

A set of 24 identically made CdS/CdTe devices were subjected to accelerated lifetime testing (ALT) under open-circuit bias, 1 sun illumination, and temperatures of 60, 80, 100, and 120 °C. A total of 6 identical devices were tested for statistical purposes at each temperature. Current density-voltage (JV) measurements were made on stressed cells for up to 2000+ hours. Device performance parameters were calculated as a function of temperature and stress time using discrete element circuit models. Forward current behavior was represented by two parallel diodes to simulate recombination currents in the quasi-neutral (QNR) and space-charge (SCR) regions. Backcontact behavior was studied using a parallel combination blocking diode and shunt conductance. A systematic pattern of degradation was apparent with increased stress temperature. At 60 °C, degradation associated with the CdTe/backcontact dominates. At temperatures above 80 °C, greater losses in fill factor (FF) and open-circuit voltage (Voc) were observed. Recombination current modeling of JV data attributes this to increased space-charge recombination. Calculated diffusion lengths based upon an Arrhenius-derived activation energy of 0.63 eV in this temperature-range suggests Cu diffusion into the SCR is mechanistically responsible for the observed increased recombination, and decreased Vocand FF. At lower temperatures (60 to 80 ºC), degradation was considerably slower with a measured activation energy of 2.9 eV.
Investigation of ZnO:Al Doping Level and Deposition Temperature Effects on CIGS Solar Cell Performance
Authors: Duenow Joel N. , Gessert Timothy A. , Wood David M. , Egaas Brian , Noufi Rommel , Coutts Timothy J.
Published: April 2011

Cu(In,Ga)Se2 (CIGS) photovoltaic cells require a highly conducting and transparent top electrode for optimum device performance. ZnO thin films doped with 2 wt.% Al (ZnO:Al) are commonly used to ensure sufficient conductivity while providing acceptable transparency to the active absorber layers. Deposition of transparent conducting oxide (TCO) films on CIGS cells often is performed at room temperature in the manufacturing process because of production advantages. However, material properties and reproducibility may be poorer at room temperature than at higher temperatures. Maximum mobilities of 2 wt.%-doped ZnO:Al grown at room temperature in pure Ar are typically ∼20-25 cm2V-1s-1. Relatively high carrier concentration is therefore required to achieve the desired conductivity. This high carrier concentration produces low infrared transmittance due to increased free-carrier absorption.

World-record CIGS cells produced at the National Renewable Energy Laboratory (NREL) are known to tolerate photolithographic processing temperatures of ∼100Â°C, though significant changes in device performance occur beyond 200Â°C. In this study, we investigate whether ZnO:Al films with superior material properties can be produced at the elevated temperatures consistent with CIGS processing parameters. We examine undoped ZnO and ZnO:Al with doping levels of 0.5, 1, and 2 wt.% Al2O3 for growth at substrate temperatures from 25Â° to 360Â°C using radio-frequency magnetron sputtering. For films grown in a 100% Ar ambient, optimal electrical and optical properties are achieved at ∼150Â°-200Â°C. Controlled incorporation of H2 in the Ar sputtering ambient at 200Â°C increases mobility to 48 cm2V-1s-1 for undoped ZnO and 36 cm2V-1s-1 for 0.5 wt.%-doped ZnO:Al. Both values are considerably higher than the 25 cm2V-1s-1 of 2 wt.%-doped ZnO:Al deposited at 200Â°C in 100% Ar. We have explored whether these higher-mobility films can be exploited in the design of high-quality CIGS devices produced at NREL. Preliminary results show similar open-circuit voltage and only slightly lower short-circuit current compared to devices utilizing the standard 2 wt.%-doped ZnO:Al deposited at room temperature. This suggests that higher-performance devices may result once the TCO thickness is optimized for the higher mobility.
InGaAs Solar Cells Grown on Wafer-Bonded InP/Si Epitaxial Templates
Authors: Zahler James M. , Tanabe Katsuaki , Ladous Corinne , Pinnington Tom , Newman Frederick D. , Atwater Harry A.
Published: April 2011

InP/Si engineered substrates formed by wafer bonding and layer transfer have the potential to significantly reduce the cost and weight of III-V compound semiconductor solar cells. InP/Si substrates were prepared by He implantation of InP prior to bonding to a thermally oxidized Si substrate and annealing to exfoliate an InP thin film. Following thinning to remove damage caused by the implantation and exfoliation from the surface of the InP transferred film, InGaAs solar cells lattice-matched to bulk InP were grown on those substrates using metal-organic chemical vapor deposition. The photovoltaic current-voltage characteristics of the InGaAs cells fabricated on the wafer-bonded InP/Si substrates were comparable to those synthesized on commercially available epi-ready InP substrates, thus providing an initial demonstration of wafer-bonded InP/Si substrates as an alternative to bulk InP substrates for solar cell applications.
Towards Lower Deposition Temperatures of Spray Deposited ZnO Films
Authors: Gledhill Sophie E. , Allsop Nicholas , Thier Pablo , Camus Christian , Lux-Steiner Martha , Fischer Christian Herbert
Published: April 2011

Highly transparent, conductive ZnO:Al doped films have been deposited by a non-vacuum spray deposition method. At substrate temperatures above 400C we attain resistivites of 5x10-3Ohmcm and free charge carrier concentrations of 10-20cm-3. ZnO film growth and quality are sensitive to the precursor solution. For a non-vacuum process the properties of the films are excellent.

The challenge is to lower the deposition temperature to a maximum of 250C to be useful for Cu(In, Ga)(S, Se)2 solar cells and yet maintain the ZnO film quality and conductivity. As the deposition temperature decreases the resistivity of the ZnO drastically increases yet is conducting enough to be used undoped as the intrinsic ZnO layer. This is particularly relevant as the deposition technique is readily up-scalable to roll to roll coating processes.
Electroluminescence from Cu(In,Ga)Se2 Thin-film Solar Cells
Authors: Kirchartz Thomas , Mattheis Julian , Rau Uwe
Published: April 2011

We compare the electroluminescence (EL) of three polycrystalline ZnO/CdS/Cu(In,Ga)Se2 heterojunction solar cells with similar bandgaps but different open circuit voltages, indicating a difference in the electronic quality of the absorber. Temperature dependent electroluminescence measurements reveal that all cells feature transitions from donor-acceptor pair recombination at lower temperatures to band to band recombination at higher temperatures. However, the less efficient cells show a longer transition range with donor-acceptor pair recombination still apparent at room temperature. The thus broadened room temperature luminescence is one effect which reduces the open circuit voltage of the devices below the Shockley-Queisser-limit. The other effect is the existence of non-radiative recombination currents, which determine the efficiency of the device as light emitting diode. To quantify the open circuit voltage losses, we use reciprocity relations between electroluminescent and photovoltaic action of solar cells, which allow us to predict the light emitting diode efficiency. Measurements support the theory and show that Cu(In,Ga)Se2 solar cells reach external LED efficiencies approaching.
Analysis of Band Gap Fluctuations in Cu(In,Ga)Se2 by Confocal Optical Transmission and Photoluminescence
Authors: Gutay Levent , Bauer Gottfried H.
Published: April 2011

We present new insights into inhomogeneities of Cu(In,Ga)Se2 absorbers by confocal optical transmission (OT) and spectrally resolved photoluminescence (PL) with lateral resolution in the one-micron regime. We carry out scans for both measurands at identical positions and observe explicit local variations of the PL- and OT-spectra. The PL-yield shows fluctuations in the sub- and few-µm regime. As shown in previous papers we extract local variations of the splitting of quasi-Fermi-levels of about 40-50meV, which limits the open circuit voltage of cells, and of the optical threshold of the absorber of some tens of meV related to the local optical band gap. Local transmission spectra similarly show lateral variations in the few-µm regime. From these spectra we calculate local absorption coefficients and absorbance functions which yield variations of the optical threshold of the absorber of 20-30meV, amounting to the same range as PL-results. Via Planck's generalized law we are able to compute theoretical PL-spectra from the resulting absorbance functions. The discrepancies between measured and calculated hypothetical PL-spectra are discussed with respect to diffusion of excess charge carriers and fluctuations of the band gap in the sub-µm-regime below the spatial resolution of the experiment.
The Effect of Ionizing Radiations on the Structural, Electrical and Optical Properties of AIIBVI Polycrystalline Thin Films Used as Solar Cell Materials
Authors: Ion Lucian , Antohe Vlad Andrei , Ghenescu Marian , Ghenescu Oana , Bazavan Rosemary , Danila Mihai , Gugiu Marius Marin , Antohe Stefan
Published: April 2011

The effects of irradiation with high-energy protons (3 MeV, up to a fluency of 1013 protons/cm2), on structural, electrical and optical properties of polycrystalline CdS and CdTe thin films have been investigated. XRD investigation has revealed that the films contain wurtzite-type CdS, (001) preferentially oriented in the growth direction, and cubic phase CdTe, respectively. The defects induced by ionizing radiations have been studied by thermally stimulated currents spectroscopy (TSC). Parameters of identified defect levels were determined and their possible origin is discussed.
Influence of Metal Impurity Defects on the Electrical and Optical Properties of ITO Films on the PEN Substrates
Authors: Han Hauk , Alford Terry L
Published: April 2011

Indium tin oxide (ITO) has drawn a great deal of attention due to its potential use as transparent electrodes in organic light emitting diode (OLED) and photovoltaic applications. This work focuses on understanding the role of impurity defects on the electrical conduction and transmittance of ITO. Thin films of ITO with high carrier concentration have been deposited onto polyethylene napthalate (PEN) substrates by electron-beam deposition without introduction of oxygen into the chamber. The influence of air anneals on the electrical and optical properties of ITO/PEN samples can is evaluated in terms of the oxygen content and is explained in terms of changes in the free electron concentrations. Rutherford backscattering spectrometry and X-ray photoelectron spectroscopy analysis were used to determine the oxygen content in the film. A Hall effect measurement is used to determine the dependence of electrical properties on oxygen content. The electrical properties of the ITO films such as carrier concentration, electrical mobility, and resistivity abruptly changes after annealing in the air atmospheres. In addition, optical transmittance is improved from 7 to 71 % and optical band gap changes from 3.18 to 3.25 eV after heat treatment. The optical band gap narrowing behavior is because of impurity band and heavy carrier concentration. Metal impurity clusters form in the films as a result of oxygen deficiency and also generate defects and/or impurity states in the band gap and produces an optical band gap shift by merging of these impurity states and conduction band.
Study of the Electronic Properties of Matched Na-Containing and Reduced-Na CuInGaSe2 Samples Using Junction Capacitance Methods
Authors: Erslev Peter T , Halverson Adam , Shafarman William , Cohen J. David
Published: April 2011

Junction capacitance methods were used to examine a matched pair of CuInGaSe2 (CIGS) thin film solar cells, one with Na incorporated into the absorber and the other with a diffusion barrier to inhibit the Na incorporation from the soda-lime glass. Typical cells showed a 50% increase in efficiency with the addition of Na. Forward biased admittance spectroscopy revealed a large defect density located near the CdS/CIGS heterojunction in the reduced Na samples not present in the higher Na samples. This may be responsible for the lower Voc, contributing to the loss in efficiency when Na is not added. Drive-level capacitance profiles revealed free carrier densities of 3×1014cm-3 and 1.1×1014cm-3 for the higher and reduced Na samples, respectively. Transient photocapacitance spectra indicated a slight improvement in absorber properties with the addition of Na, but not enough to account for the large loss in efficiency.
High-resolution Raman imaging by optically tweezing a dielectric microsphere
Authors: Kasim Johnson , Yu T. , You Y. M. , Liu J. P. , See A. K. H. , Shen Z. X.
Published: April 2011

We show a different method in doing near-field Raman imaging with sub-diffraction limit spatial resolution. A dielectric microsphere (for example polystyrene microsphere) is trapped by optical tweezers. The microsphere is used to focus the laser to the sample, and also to collect the scattered Raman signals. We show the capability of this method in imaging various types of samples, such as SiGe/Si structures, gold nanopattern and carbon nanotubes. This method is comparatively easier to perform, better repeatability, and stronger signal than the normal near-field Raman techniques.
Electrostatic Force Microscopy of Nanofibers and Carbon Nanotubes: Quantitative Analysis Using Theory and Experiment
Authors: Datta Sujit Sankar , Staii Cristian , Pinto Nicholas J. , Strachan Douglas R. , Johnson AT Charlie
Published: April 2011

Electrostatic force microscopy (EFM) is a widely used scanning-probe technique for the characterization of electronic properties of nanoscale samples without the use of electrical contacts. Here we review the basic principles of EFM, developing a quantitative framework by which EFM measurements of extended nanostructures can be understood. We support our calculations with experimental data of EFM of carbon nanotubes and conducting or insulating electrospun polyaniline-based nanofibers. Furthermore, we explore routes towards extending EFM as a means of non-invasively probing the local electronic density of states of carbon nanotubes.
Attaching Biological Entities to AFM Cantilevers for Molecular Recognition Studies
Authors: Johnson W. Travis
Published: April 2011

Atomic force microscopy (AFM) is an important tool for high resolution studies in biophysics and mechanical studies directed at biological materials. A strong suit of AFM is its ability to measure hardness/elasticity, nonspecific adhesion or ligand-receptor interactions at the picoNewton scale. Molecular interactions are critical factors in a variety of biological phenomenon; such as the initiation, modulation and termination of DNA replication, transcription, enzyme activity, infection, immune responses, tissue generation, wound healing, cell differentiation, apotopsis and physiological responses from drugs, hormones or toxic agents. Using AFM, scientists can probe and quantify these interactions in their native, liquid environments at physiological pH or perform dynamic experiments in situ by removing or adding ions, solutes and reagents to the sample environment. Bioconjugation chemistry and surface chemistry are crucial because a selective ligand must be immobilized on the tip of an AFM probe so that the AFM can resolve the mechanical force required to separate the ligand and its target. The resulting data can be used to calculate forces of unbinding, derive rate constants and infer structural information about the binding pocket. Biomolecular recognition experiments with AFM can be greatly enhanced through the use of relatively short (~8-10 nm), heterobifunctional, elastic, polyethylene glycol (PEG) linkers to immobilize ligands. Heterobifunctional linkers are used in order to permit their sequential immobilization and bioconjugation, while minimizing undesirable polymerizations or self-conjugation. The linkers have an N-hydroxysuccinimide ester at one end to permit their attachment to aminated silicon or silicon nitride AFM probes. Other reactive functional groups, such as a biotin, maleimide, disulfide, aldehyde, or a photoreactive group reside at the opposite end of the linker to permit the direct or indirect attachment of intact antibodies, Fab fragments, peptides, nucleic acids or other biological entities. The PEG linkers are flexible, so an attached ligand has freedom to diffuse within a defined volume of space and approach the binding site in a thermodynamically favorable manner. PicoTREC, an accessory for the Agilent AFM, uses ligand-PEG modified cantilevers to generate a topography image and a recognition image of biomolecular interactions. As the modified cantilever gently oscillates at defined amplitude, it is scanned across a sample and PicoTREC converts the information derived from ligand-receptor interactions into a high resolution, nanometer-scale map. Consequently, the locations of discrete molecular interactions can be easily determined and compared with a topography image of the sample.
Variational Calculations of Donor Binding Energy in Rectangular Wurtzite Aluminium Gallium Nitride / Gallium Nitride Quantum Wires
Authors: Praharaj Choudhury Jayant
Published: April 2011

We present variational calculations of donor binding energy in rectangular wurtzite aluminium gallium nitride / gallium nitride quantum wires. We explicitly take into account the effect of spontaneous and piezoelectric polarization on the energy levels of donors in quantum wires. Wurtzite structure nitride semiconductors have spontaneous polarization even in the absence of externally applied electric fields. They also have large piezoelectric polarization when grown as pseudomorphic layers. The magnitude of both polarization components is of the order of 1013 electrons per cm2, and has a non-trivial effect on the potential profile seen by electrons. Due to the large built-in electric fields resulting from the polarization discontinuities at heterojunctions, the binding energies of donors is a strong function of the position inside the quantum wire. The potential profile in the 0001 direction can vary by as much as 1.5eV due to polarization effects for vertical dimensions of the quantum wire up to 20 angstroms. The probability density of electrons tends to concentrate near the minimum of the conduction band profile in the 0001 direction. Donors located close to this minimum tend to have a larger concentration of electron density compared to those located closer to the maximum. As a consequence, the binding energy of the former are higher compared to the latter. We use Lorentzian variational wavefunctions to calculate the binding energy as a function of donor position. The confinement potential enhances the binding by a factor of about 3 compared to donors in bulk nitride semiconductors, from about 30 meV to about 90 meV. The variation of binding energy with position is calculated to be more than 50% for typical compositions of the quantum wire regions. Our calculations will be useful for understanding device applications involving n-type doped nitride semiconductor quantum wires.
A Role of the Built-in Piezoelectric Field in InGaN/AlGaN/GaN Multiple Quantum Wells in the Electroferlectance Experiments
Authors: Bokov Pavel , Avakyants Lev , Badgutdinov Mansur , Chervyakov Anatoly , Shirokov Stanislav , Yunovich Alexander , Vasileva Elena , Snegov Feodor , Bauman Dmitry , Yavich Boris
Published: April 2011

The influence of built in piezoelectric field in the light-emitting diodes based on InGaN/AlGaN/GaN heterostructures on the electroreflectance spectra have been studied. The structures were grown by MOCVD technology and «flip-chip» mounted. Light was emitted or reflected through sapphire substrate. The built in electric field in the structure was modulated by pulses of reverse bias from -6 to +1 V applied to the contacts of diode. Observed blue shift of spectral line from InGaN/GaN multiply quantum wells region with the increasing reverse bias voltage has been explained as the result of lowering of the electric field in the quantum well.
Formation of Aluminum Nitrides by Precipitate-Accommodated Plasma Nitriding
Authors: Aizawa Tatsuhiko , Vissutipitukul Patama
Published: April 2011

Precipitate accommodated nitriding is proposed as a new, non-traditional surface treatment of aluminum alloys. In the case of nitriding the aluminum-copper alloys, Al2Cu plays an important role as a nucleation site to form AlN by the two step reactions of Al2Cu + 2N → 2AlN + Cu and Cu + 2Al → Al2Cu and as a helper to preserve the fast nitrogen diffusion path. In this precipitate accommodation, AlN islands form on Al2Cu in coherent, and, gradually cover the matrix surface by the AlN layer. This Al2Cu accommodation in nucleation reduces the pre-sputtering time and shortens the incubation time prior to formation of AlN layer. Furthermore, the interface between Al2Cu and AlN plays a nitrogen diffusion path across the nitrided layer. This Al2Cu accommodation in growth of AlN accelerates the growth rate of AlN layer in practice. The formation rate of AlN approaches to 7 μm/ks in the present nitriding. This reduction of processing time is much favored for industrial manufacturing of automotive parts and electrical components in practice. Low friction and wear is also attained in dry sliding condition by this AlN-layered specimen: μ = 0.13 and Ws = 1.5 × 10−5 mm3N−1m−1. Since Al2Cu is common precipitate to most of aluminum alloys, this AlN-layer formation is also favored to protective coating for automotive parts and electric components.
DEFECT SELECTIVE ETCHING OF THICK AlN LAYERS GROWN ON 6H-SIC SEEDS – A TRANSMISSION ELECTRON MICROSCOPY STUDY
Authors: Nyakiti Luke Owuor , Chaudhuri Jharna , Kenik Ed A , Lu Peng , Edgar James H
Published: April 2011

In the present study, the type and densities of defects in AlN crystals grown on 6H-SiC seeds by the sublimation-recombination method were assessed. The positions of the defects in AlN were first identified by defect selective etching (DSE) in molten NaOH-KOH at 400 °C for 2 minutes. Etching produced pits of three different sizes: 1.77 ìm, 2.35 ìm , and 2.86 ìm. The etch pits were either aligned together forming a sub-grain boundary or randomly distributed. The smaller etch pits were either isolated or associated with larger etch pits. After preparing cross-sections of the pits by the focused ion beam (FIB) technique, transmission electron microscopy (TEM) was performed to determine which dislocation type (edge, mixed or screw) produced a specific etch pit sizes. Preliminary TEM bright field and dark field study using different zone axes and diffraction vectors indicates an edge dislocation with a Burgers vector 1/3 is associated with the smallest etch pit size.
Delamination of Oil Paints on Acrylic Grounds
Authors: Maor Yonah , Murray Alison
Published: April 2011

In a set of composite samples of oil or alkyd paints, over acrylic grounds, naturally aged for eight years, some of the samples delaminated. Samples were analyzed with X-ray fluorescence (XRF), inductively coupled plasma (ICP), Fourier transform infrared - attenuated total reflectance (FTIR-ATR) and atomic force microscopy (AFM) as well as other techniques not detailed in this paper. Results indicate the main cause of delamination is metal soaps in the oil paint and particularly zinc soaps. The ground is a minor consideration as well, rougher grounds providing better adhesion than smooth ones.
Fabrication of Carbon Nanotube Field-Effect Transistors with Metal and Semiconductor Electrodes
Authors: Sharma Himani , Xiao Zhigang
Published: April 2011

Carbon nanotube field-effect transistors (CNTFETs) were fabricated with metal material (gold) and semiconductor material (bismuth telluride) as the source and drain materials. Highly-purified HiPCO-grown single-walled carbon nanotubes (CNTs) from Carbon Nanotechnologies, Inc. (CNI) were used for the fabrication of CNTFETs. The single-walled carbon nanotubes were ultrasonically dispersed in toluene and dimethylformamide (DMF) with trifluoroacetic acid (TFA), as co-solvent. Dielectrophoresis (DEP) method was used to deposit, align, and assemble carbon nanotubes (CNTs) to bridge the gap between the source and drain of CNTFETs to form the channel. The structure of CNTFET is similar to a conventional field-effect transistor with substrate acting as a back-side gate. Electron-beam evaporation was used to deposit gold and bismuth telluride thin films. Microfabrication techniques such as photolithography, e-beam lithography, and lift-off process were used to define and fabricate the source, drain, and gate of CNTFETs. The gap between the source and drain varied from 800 nm to 3 µm. The drain-source current (IDS) of the fabricated CNTFETs versus the drain-source voltage (VDS) and the gate voltage (VG) was characterized. It was found that in the case of gold (Au) electrodes, the IV curves of CNTFETs clearly show behavior of the CNT (metallic or semiconducting) aligned across the source and drain of CNTFETs, while in the case of bismuth telluride (Bi2Te3) electrodes, the I-V curves are less dependent on the type of CNTs (metallic or semiconducting). The developed carbon nanotube field-effect transistors (CNTFETs) can be a good candidate for the application of nanoelectronics and integrated circuits with a high mobility and fast switching.
Transistor Level Integration of Compound Semiconductor Devices and CMOS (CoSMOS
Authors: Elliott Kenneth , Patterson Pamela , Li James C. , Royter Yakov , Hussain Tahir
Published: April 2011

In the COSMOS program, HRL Laboratories, LLC. is developing technology for intimate integration of CMOS devices with 400 GHz InP HBTs to form complex integrated circuits. This research is investigating innovative approaches to the transistor-scale integration of compound semiconductor and silicon-based transistors so as to enable revolutionary advances in science, devices, circuits, and systems.
Enhancement Mode GaN MOSFETs on Silicon Substrates with High Field-effect Mobility
Authors: Kambayashi Hiroshi , Niiyama Yuki , Ootomo Shinya , Nomura Takehiko , Iwami Masayuki , Satoh Yoshihiro , Kato Sadahiro , Yoshida Seikoh
Published: April 2011

In this report, we have demonstrated enhancement-mode n-channel GaN MOSFETs on silicon (111) substrates. We observe a high field-effect mobility of 115 cm2/Vs, the best report for GaN MOSFET fabricated on a silicon substrate to our knowledge. The threshold voltage was estimated to be +2.7 V, and the maximum operation current was over 3.5 A. This value is the largest which have ever been reports.
Molecular Beam Epitaxy of AlN Layers on Si (111)
Authors: Moreno Jean-Christophe , Frayssinet Eric , Semond Fabrice , Massies Jean
Published: April 2011

In this work, we present a study of epitaxial Aluminium Nitride (AlN) for thin film bulk acoustic wave (BAW) applications. Molecular beam epitaxy (MBE) was used to perform high crystalline quality AlN thin films growth on different silicon substrate preparations. A morphological study was performed by atomic force microscopy (AFM) and scanning electron microscopy (SEM), while structural properties and acoustic wave speed were respectively assessed by X-ray diffraction and acoustic picoseconds.
Condensation Mechanism for the Formation of Relaxed SiGe Layer Grown-on-Insulator
Authors: Lee Hun-Joo , Lee Gon-Sub , Han Young-Soo , Hong Seuck-Hoon , Shim Tae-Hun , Park Jae-Gun
Published: April 2011

The condensation method to grow a strained SiGe layer-on-insulator (ε-SGOI) has attracted interests for the application of high speed complementary metal–oxide–semiconductor field-effect transistors (CMOSFETs) because of high quality properties and effective process cost. Although many reports presented its superiority in a device performance to bonding and dislocation sink technologies, the mechanism by which the condensation method produces ε-SGOI has also not been clearly explained and the surface properties have not been evaluated. Thus, we investigated condensation mechanism in detail by characterizing a surface property and Ge profile in SiGe layer. For the experiment, first, a SiGe layer on silicon-on-insulator layer was epitaxally grown at 550 °C, and three different oxidation thicknesses were grown at 950 °C, i.e., 40, 60, 90 nm. From our investigation results, we found that there are three steps in producing ε-SGOI. For the first step, by the 40-nm-thick oxidation, a diffusion of Ge atoms in SiGe layer into Si layer-on-insulator was generated and Ge atoms were segregated into only surface oxide. It was observed that Ge profile of SiGe layer was shown a less graded profile. And, in the second step with 60-nm-thick oxidation, Ge atoms in SiGe layer into Si layer-on-insulator was diffused further than a first step did and Ge atoms were segregated into surface oxide. It was observed that Si layer was shown a fully graded profile. Lastly, in the third step with 90-nm-thick oxidation, the diffusion of Ge atoms in SiGe layer into Si layer-on-insulator was finished completely and Ge atoms were segregated into both surface and buried oxides. It was confirm that Ge profile of SiGe layer was shown a Gaussian profile rather than a graded profile, and dislocation sink occurred. Therefore, our talk will focus on the explanation for the mechanism by which condensation method produces ε-SGOI via characterizing a surface property, SiGe thickness, a remained Si thickness on insulator, and Ge concentration in SiGe layer.
Growth of AlGaN/GaN HEMTs on Silicon Substrates by MBE
Authors: Semond Fabrice , Cordier Yvon , Natali Franck , Le Louarn Arnaud , Vézian Stéphane , Joblot Sylvain , Chenot Sébastien , Baron Nicolas , Frayssinet Eric , Moreno Jean-Christophe , Massies Jean
Published: April 2011

During the last ten years, we have developed an efficient growth process of nitrides on silicon substrates by molecular beam epitaxy. In collaboration with partners AlGaN/GaN HEMTs on Si having promising performances have been fabricated. Focusing on the growth aspect and underlying some of the key issues, we present in this paper an overview of our contribution in the field of AlGaN/GaN HEMTs on Si substrates.
Strong Light-Matter Coupling in GaN-Based Microcavities Grown on Silicon Substrates
Authors: Semond Fabrice , Sellers Ian Roberts , Ollier Nadège , Natali Franck , Byrne Declan , Réveret François , Stokker-Cheregi Flavian , Bejtka Katarzyna , Gurioli Maximo , Vinattieri Anna , Vasson Aimé , Disseix Pierre , Leymarie Joël , Leroux Mathieu , Massies Jean
Published: April 2011

We present an overview of our work concerning the fabrication of GaN-based microcavities grown on silicon substrates dedicated to the observation of the strong light-matter coupling regime. In the view of recent promising results in the field, prospects regarding the improvement of heterostructures in order to observe room temperature polariton lasing from a GaN-based microcavity grown on a silicon substrate will be discussed.
AlGaN Transition Layers on Si (111) Substrates - Observations of Microstructure and Impact on Material Quality
Authors: Roberts John C. , Cook James W. , Rajagopal Pradeep , Piner Edwin L. , Linthicum Kevin J.
Published: April 2011

III-nitride materials have different crystal structures and properties than the substrates commonly used for their deposition, including silicon, silicon carbide and sapphire. These differences, such as thermal expansion coefficient and lattice constant, necessitate the use of a transition layer to accommodate the resulting stress between substrate and the epitaxially grown III-N layers. AlxGa1−xN based transition layers are one proven solution used for the growth of device quality GaN layers on Si (111) substrates. The use of such transition layers enables the deposition of state of the art AlGaN/GaN high electron mobility transistor epitaxial structures that, upon fabrication into devices, exhibit high performance and excellent reliability.

Examination of the microstructure of these AlxGa1−xN transition layers, by transmission electron microscopy (TEM) and other methods, reveals some interesting properties that can help explain how high quality III-N epitaxy can be performed in a system with significant thermal and lattice mismatch. Observations that will be reported on and discussed in this presentation are (1) the role that a thin strain absorbing amorphous SiNx layer at the Si substrate/transition layer interface plays in the reduction of the formation of misfit dislocations, (2) the low screw dislocation density (less than ȼ107/cm2) in these III-N films relative to edge and mixed dislocation densities, and (3) the role that the substrate type and quality can play on dislocation type and density.
Epitaxial Growth of High-κ Dielectrics for GaN MOSFETs
Authors: Jur Jesse S. , Wheeler Ginger D. , Veety Matthew T. , Lichtenwalner Daniel J. , Barlage Douglas W. , Johnson Mark A. L.
Published: April 2011

High-dielectric constant (high-κ) oxide growth on hexagonal-GaN (on sapphire) is examined for potential use in enhancement-mode metal oxide semiconductor field effect transistor (MOSFET). Enhancement-mode MOSFET devices (ns > 4×1013 cm−2) offer significant performance advantages, such as greater efficiency and scalability, as compared to heterojunction field effect transistor (HFET) devices for use in high power and high frequency GaN-based devices. High leakage current and current collapse at high drive conditions suggests that the use of a high-κ insulating layer is principle for enhancement-mode MOSFET development. In this work, rare earth oxides (Sc, La, etc.) are explored due to their ideal combination of permittivity and high band gap energy. However, a substantial lattice mismatch (9-21%) between the rare earth oxides and the GaN substrate results in mid-gap defect state densities and growth dislocations. The epitaxial growth of the rare earth oxides by molecular beam epitaxy (MBE) on native oxide passivated-GaN is examined in an effort to minimize these growth related defects and other growth-related limitations. Growth of the oxide on GaN is characterized analytically by RHEED, XRD, and XPS. Preliminary MOS electrical analysis of a 50 Å La2O3 on GaN shows superior leakage performance as compared to significantly thicker Si3N4 dielectric.
Flash Memory Scaling: From Material Selection to Performance Improvement
Authors: Hou Tuo-Hung , Lee Jaegoo , Shaw Jonathan T. , Kan Edwin C.
Published: April 2011

Below the 65-nm technology node, scaling of Flash memory, NAND, NOR or embedded, needs smart and heterogeneous integration of materials in the entire device structure. In addition to maintaining retention, in the order of importance, we need to continuously make functional density (bits/cm2) higher, cycling endurance longer, program/erase (P/E) voltage lower (negated by the read disturbance, multi-level possibility and noise margin), and P/E time faster (helped by inserting SRAM buffer at system interface). From both theory and experiments, we will compare the advantages and disadvantages in various material choices in view of 3D electrostatics, quantum transport and CMOS process compatibility.
Realization of Hybrid Silicon core/silicon Nitride Shell Nanodots by LPCVD for NVM Application
Authors: Colonna Jean Philippe , Molas Gabriel , Gely Marc W , Bocquet Marc , Jalaguier Eric , De Slavo Barbara , Grampeix Helen , Brianceau Pierre , Yckache Karim , Papon Anne-Marie , Auvert Geoffroy , Bongiorno Corrado , Lombardo Salvatore
Published: April 2011

We present the realization of hybrid silicon core/silicon nitride shell nanodots by Low Pressure Chemical Vapor Deposition (LPCVD) and their application as floating gate in Non Volatile Memory (NVM) devices. The LPCVD process includes three steps: nucleation using SiH4, selective growth of the silicon nuclei using SiH2Cl2 and finally selective growth of silicon nitride using a mixture of SiH2Cl2 and NH3 around the silicon dot. The two first steps have already been described in literature. We will therefore focus on the selective growth of a nitride layer on silicon dots. Morphological characterization using Scanning Electron Microscopy (SEM) allows control over dots size – 5 to 10nm – and density – up to 1E12/cm2. High Resolution Transmission Electron Microscopy (HRTEM) shows a crystalline silicon core and an outer shell of amorphous silicon nitride. Energy Filtered TEM pictures confirm that the nitride layer is deposited only around the silicon dots and not on the oxide. Oxidation resistance of the silicon nitride shell is also investigated. A 2nm thick silicon nitride layer is an efficient barrier to an oxidation at 800°C in dry oxygen for 5 minutes. We thus have a very thin high quality stoechiometric nitride layer. Such a high quality nitride film can only be achieved using in-situ deposition i.e. on an oxide-free silicon surface. Finally, hybrid Si/SiN nanodots are integrated in a single memory cell with high-K interpoly dielectric. Electrical results show large threshold voltage shift of 6V. The use of silicon nitride shells on the silicon dots has therefore two main advantages: it provides both oxidation resistance and charge storage enhancement.
Metallurgical Effects of Solution Heat Treatment Temperatures of Alloy Haynes™ HR-120™ for Land-Based Turbine Application
Authors: Covarrubias O. , Elizarrarás Osvaldo
Published: April 2011

Haynes™ HR-120™ alloy is a solid-solution-strengthened heat resistant alloy. The main characteristics of this alloy are strength at elevated temperature combined with resistance to carburizing and sulfidizing environments. Typical solution heat treatment for this alloy is usually performed above 1100°C. Solution heat treatment promotes non-desired precipitates to dissolve and, if deformation parameters are adequate, re-crystallization after forging procedures. It is reported that the solution temperature can also promote non-controlled grain coarsening. This investigation summarizes results on the effect of solution heat treatment on the microstructure of forgings when it is performed at 1000°C, 1050°C and above 1100°C. The experimental conditions resemble industrial environments. The obtained results include the alloy microstructural evolution by optical microscopy and Scanning Electron Microscopy (SEM) and the effect of these heat treatments on mechanical properties such as tensile, hardness and stress-rupture properties.
Cross-Sectional Scanning Tunneling Microscopy of III-V Semiconductor Structures
Authors: Feenstra R. M. , Vaterlaus A. , Woodall J. M. , Collins D. A. , McGill T. C.
Published: April 2011

The method of cross-sectional scanning tunneling microscopy (STM) is described. Illustrative examples are given of studies of III-V semiconductor systems, including low-temperature-grown (LT) GaAs, and InAs/GaSb superlattices. In each case, the STM permits the observation of structural features on an atomic scale. The associated electronic spectroscopy for states a few eV on either side of the Fermi-level can be determined. Such information is relevant for the operation of devices constructed from these layered semiconductor systems.
High Resolution Tem Applied to Nanoscale Structure Studies
Authors: Rio L. Beltran Del , Yacaman M.Jose , Tehuacanero S. , Gomez A.
Published: April 2011

In this work, digital image processing techniques are used to study the structure of small metallic particles imaged under high resolution conditions. An algorithm is devised to extract directly from the micrographs the coordinates of columns of atoms in such a way that the crystal structure of the particles and their boundaries can be determined. For distorted regions (such as grain boundaries) the actual positions can be compared to the ones in the ideal lattice so that a general trend of the distortion field can be elucidated.
Elemental Mapping by Energy-Filtered Electron Microscopy
Authors: Krivanek Ondrej L. , Kundmann Michael K. , Bourrat Xavier
Published: April 2011

Energy-filtered imaging in a transmission electron microscope provides a fast and quantitative technique for mapping the distribution of elements in solids at nm-level resolution. The technique and its instrumental requirements are reviewed, and illustrated in the context of materials science.
Quantitative Hrtem: Measuring Projected Potential, Surface Roughness and Chemical Composition
Authors: Schwander P. , Kisielowski C. , Baumann F.H. , Kim Y.O. , Ourmazd A.
Published: April 2011

We describe how general lattice images may be used to measure the variation of the potential in crystalline solids in any projection, with no knowledge of the imaging conditions. This approach is applicable to structurally perfect samples, in which interfacial topography, or changes in composition are of interest. We present the first atomic-level topographic map of a Si/SiO2 interface in plan-view, and the first microscopic compositional map of a Si/GeSi/Si quantum well in cross-section.