bluuebunny/crossref_metadata_2025 huggingface dataset:
Adhesive Wafer Bonding with SU-8 Intermediate Layers for Microfluidic Applications
Authors: Dragoi Viorel , Mittendorfer Gerald , Thanner Christine , Matthias Thorsten , Glinsner Thomas , Lindner Paul
Published: November 2006

Recently adhesive wafer bonding using SU-8 has gained a lot of interest for micro-fluidic devices e.g. lab-on-chip applications. Due to its specific properties as well as the capability to pattern thin and thick layers accurately, SU-8 is an ideal candidate for micro-fluidic components like channels, reservoirs and valves, but also for micro-optical components. Wafer bonding enables the capping and encapsulation of the devices. In this paper the state-of-the-art of SU-8 wafer bonding is presented with a higher emphasis on the impact of the pre- processing. Spin-, spray coating and dry film lamination are reviewed and the resulting bond properties are analyzed.
Anodic and Direct Bonding of Si and Glass - Similarities and Distinctions in Applications
Authors: Gabriel Markus , Cetin Volkan , Ludewig Thomas , Eichler Marko
Published: November 2006

Wafer bonding is an enabling technology in substrate engineering, MEMS manufacturing and packaging as well as for hybrid integration of MEMS and CMOS. The mainstream semiconductor industry is currently exploring wafer bonding as a possible technology for 3D integration of IC devices. Several Bonding Processes exist today and can be classified under different aspects. They can be more or less well controlled and have been established in volume production of MEMS devices. Cost is still a critical factor, but sometimes there are no alternatives to wafer bonding to ensure the device functionality. Among many bonding processes with intermediate layers there are only two processes not using intermediate layers, the anodic and direct bonding. In this paper these two processes of bonding Silicon to glass wafers, are compared in some details. Equipment, process flow as well variations and modifications of the basically described processes are explained and discussed.
The Effect of Water on the Nucleation Kinetics of ZnO Nanoparticles
Authors: Oskam G. , Soberanis Domínguez Orlando E.
Published: November 2006

The nucleation and growth kinetics for the synthesis of ZnO nanoparticles from ZnCl2 and NaOH in ethanol were determined as a function of the reactant concentrations and the concentration of added water. It was found that the presence of water is essential for the controlled nucleation of ZnO. The nucleation rate increases with increasing reactant concentrations, which is in agreement with classical nucleation theory.
Influence of Ionic Strength on Brookite Content in Sol-Gel Synthesized Titania before and after Hydrothermal Aging
Authors: Penn R. L. , Isley Sara L. L. , Anderson Eric R.
Published: November 2006

This work investigates the effect of increasing ionic strength on the phase composition of hydrothermally aged titania. Rietveld refinements were used to systematically track the brookite content and both anatase and brookite particle size. Results demonstrate that increasing ionic strength during hydrothermal aging has no effect on brookite content. The presence of chloride is concluded to have the most influence over the brookite content during the sol gel synthesis and that the addition of chloride to chloride-free, sol gel synthesized titania has no effect during hydrothermal aging. Photocatalysis results using particles of similar size but different phase composition suggest that particles with higher brookite content are less photocatalytically active than those with lower brookite content. Results suggest that substantial control over photocatalytic activity of titania nanoparticles can be achieved by modifying sol-gel synthesis and hydrothermal aging conditions
Synthesis and Characterization of Functional Nanostructured Zinc Oxide Thin Films
Authors: Chow Lee , Shishiyanu S. , Lupan Oleg , Shishiyanu Teodor
Published: November 2006

A novel aqueous relatively low-temperature thin film growth technique has been developed to fabricate a new generation of smart and functional nanostructured metal oxide thin film materials. This chemical synthetic route uses stable and inexpensive metal inorganic salts and environment-friendly solvents. The nanomaterials are obtained to analyze the physical and structural requirements of their applications in gas sensors and solar cells. The rapid photothermal processing at the 650 ºC of nanostructured zinc oxide leads to the suppression of deep-defect-level emission and improvement of near-band edge emission. The responses of the sensing elements when exposed to 100 ppm ammonia at temperatures between 20 ºC and 300 ºC have been assessed.
Alumina Porous Membranes Obtained by One-Step Anodizing Process in H2SO4 for MEMS Packaging
Authors: Hellin Rico Raquel , Celis Jean-Pierre , Du Bois Bert , Van Hoof Chris , Witvrouw Ann , Ruythooren Wouter
Published: November 2006

A MEMS packaging technique based on porous alumina films is proposed. This method allows for low temperature, wafer level packaging of the devices. We report on initial experiments indicating the feasibility of the technique. Patterned porous alumina films are created by anodizing aluminum films on wafer substrates using shulphuric acid electrolytes. Etching of the barrier layer through the porous membrane by plasma with CF4+O2 gas and evidence of pore opening required for the release of a sacrificial MEMS layer are presented.
Nano-Structured Ceramics by Gas-Phase Reaction
Authors: Carney Carmen , Akbar Sheikh
Published: November 2006

Single-crystalline nanofibers of tin dioxide (SnO2) were synthesized by a gas-phase reaction of solid SnO2 sintered disks in a reducing atmosphere between 700 and 800 C. The resulting nanostructures grew on regions of the disk that were coated with gold, which acted as a catalyst. The samples were analyzed with scanning electron microscopy, x-ray diffraction, and transmission electron microscopy. The nanofiber length was controlled by varying the reaction time and by the sintering agent used to densify the SnO2 disks.
Advances in Line Profile Analysis for the Study of Nanocrystalline Systems
Authors: Scardi Paolo , Leoni Matteo
Published: November 2006

A new approach to the study of diffraction line profiles is briefly described and applied to a nanocrystalline cerium oxide powder. Results are compared with those obtained by traditional line profile analysis, like the Williamson-Hall plot and the Warren-Averbach method. The proposed approach is proven to be particularly suited to study finely dispersed systems like nanocrystalline oxides and heavily deformed materials as it provides deep and reliable information on the crystalline domain size distribution and lattice defects.
Ormosil-Nafion Composite Membranes for PEM Fuel Cells
Authors: Mecheri Barbara , D'Epifanio Alessandra , Traversa E. , Licoccia Silvia
Published: November 2006

Composite Nafion-based membranes were prepared and characterized, using an organosilane derivative (sulfonated diphenylsilanediol, SDPSD) as a filler. The formation of the composite substantially modified the properties of the Nafion matrix in terms of proton conductivity and thermal stability. The structural and electrochemical performance of the membranes were investigated by means of electrochemical impedance spectroscopy, differential scanning calorimetry (DSC), field emission scanning electron microscopy (FE-SEM) and water uptake measurements. Both conductivity values and thermal features of the composite Nafion/SDPSD demonstrated that it has satisfactory proton conductivity values up to 160{degree sign}C, and it is then suitable for application as an electrolyte in polymer electrolyte fuel cells operating at intermediate temperature.
Nanostructured Ceria-Zirconia as a Promising Anode Component for IT-SOFC: Synthesis and Characterization
Authors: Desinan Stefano , Miyayama Masaru , Traversa E.
Published: November 2006

Ceria-zirconia (CZO) is an attractive candidate as anode material for SOFCs due to its catalytic activity and its electronic and ionic conductivity. In this work, ceria-zirconia powders with different compositions were synthesized by citrate route and characterized using N2 physisorption, SEM, and XRD. TG/DTA curves of the precursors helped to optimize the synthesis method. The reduction at 1000{degree sign}C and the subsequent reoxidation at 600{degree sign}C originated some structural modifications in CZO. The porous powders were impregnated with 50 vol% of NiO by a liquid mixture technique to form model anodes, which were characterized by SEM.
Effect of TiO2 Addition on Phase Stability and Electrical Conductivity of Cubic Zirconia Used as an Electrolyte in Solid Oxide Fuel Cells
Authors: Tekeli Suleyman , Guru Metin , Akcimen Ali , Gurdal Osman
Published: November 2006

The influence of TiO2 addition on the phase stability and electrical conductivity of cubic zirconia was studied. XRD results showed that when the TiO2 amount was less than 5 wt %, the specimens were entirely in single cubic phase; further addition of TiO2 destabilized cubic zirconia phase and caused the formation of tetragonal phase. The amount of tetragonal phase increased with increasing TiO2 content in cubic zirconia matrix. The electrical conductivity of the specimens was measured using a frequency response analyzer in the frequency range of 5-13 MHz in air and in the temperature range of 300-800 oC. It was seen that the electrical conductivity of the TiO2 doped cubic zirconia decreased with increasing TiO2 content. This decrease was due to both a trapping of the oxygen ion vacancies at Ti ions and the formation of tetragonal phase which gives rise to a reduction in moving oxygen vacancies.
Preparation and Anion Sensing Properties of Perovskite-Type Oxide Thick-Film via EPD Method
Authors: Takase Satoko , Inagaki Toru , Shimizu Youichi
Published: November 2006

Perovskite-type oxide fine powders could be synthesized from polymer precursors prepared with ethylenediamine (EDA) as chelating agent and polyethylene glycol (PEG) as a polymer additive, respectively. A single phase LaCoO3 powder with large surface area was obtained by heat treatment at 380ºC. This fine powder could be applied for a preparation of an oxide thick-film for an anion sensing devise by an electrophoretic deposition (EPD) process in ethanol-based suspension with acetylacetone or polyvinylalcohol as a stabilizer. The LaCoO3 thick-film devise prepared by the EPD method showed good amperometric responses to hydrogen- phosphate ion with high stability.
Alternative Sol-Gel Routes for Synthesizing Gas Sensing Nanostructured Materials
Authors: Neri Giovanni , Bonavita Anna , Micali Giuseppe , Rizzo Giuseppe
Published: November 2006

Alternative sol-gel techniques, investigated in our laboratory with the aim to obtain nanostructured metal oxides powders with enhanced gas sensing properties, are reviewed. The synthesis of pure and doped In2O3 by a non aqueous sol-gel method and TiO2 by reactive microemulsion and gel-combustion, are described in detail. The morphological and microstructural characteristics are also described and related to the gas sensing characteristics of the synthesized nanopowders.
Efficient and Photostable ZnS-Passivated CdS:Mn Quantum Dots
Authors: Bera Debasis , Yang Heesun , Holloway Paul
Published: November 2006

Efficient photostable ZnS-passivated CdS:Mn (CdS:Mn/ZnS core/shell) luminescent quantum dots (Qdots) were synthesized using a reverse microemulsion process. Inorganically passivated Qdots with a core (CdS:Mn) diameter of ~2.3 nm and a ZnS-shell thickness of ~0.4 nm exhibited improved quantum yield (18 %), as compared to similar n-dodecanethiol-capped (organically passivated) CdS:Mn Qdots (3 %). Upon UV-irradiation in air for 3 hrs, CdS:Mn/ZnS Qdots exhibited photo-brightening and a stable emission with a quantum yield of 28 %. X-ray photoelectron spectroscopy (XPS) data revealed that this photo- brightening correlated with the development of a ZnSO4 layer on the Qdot surface. A direct current electroluminescence (EL) device with a hybrid organic/inorganic multilayer structure of ITO//PEDOT-PSS//PVK//CdS:Mn/ZnS//Al was tested. The EL data suggested that the electron-hole recombination zone was confined to Mn in the Qdot layer.
Defects Limiting Minorty Carrier Lifetime in 4H-SiC Epilayers
Authors: Klein Paul B. , Shanabrook Benjamin , Huh Sung Wook , Polyakov Alexander , Skowronski Marek , Sumakeris Joseph , O'Loughlin Michael
Published: November 2006

The defects controlling carrier lifetime in 4H-SiC n- epilayers have been investigated by DLTS and time- resolved photoluminescence. Measurements of the dependence upon layer thickness enabled the separation of bulk and surface contributions to the measured lifetimes. Only the Z1/Z2 defect exhibited consistent correlation with measured lifetimes, while the EH6/EH7 defect was correlated only in some cases. The dependence upon layer thickness revealed a bulk minority carrier lifetime that was linearly related to the Z1/Z2 concentration and a hole capture cross-section of 3x10-14 cm2. This corresponded well to DLTS measurements carried out in p-i-n diode structures, where a large hole capture cross-section, sp, was indicated for Z1/Z2 and a small sp for EH6/EH7. Consequently, these results suggest that Z1/Z2 acts alone as the lifetime killer in this material.
Growth of Self-Assembled Quantum Dots, Quantum Rings, and Lateral Bi-Quantum-Dot Molecules by Gas-Source Molecular Beam Epitaxy
Authors: Tu C. W. , Suraprapapich S. , Shen Y.M. , Fainman Y. , Panyakeow S.
Published: November 2006

Self-assembled InAs quantum dots, quantum rings, and lateral bi- quantum-dot molecules have been achieved using gas-source molecular beam epitaxy under As2 overpressure. Their morphologies and temperature-dependent photoluminescence of QDs and BQDMs are presented.
Fabrication and Optimization of Al Doped Ta2O5 Thin Films to Enable Temperature Stable Phase Shifters
Authors: Cole Melanie W. , Nothwang William , Hirsch Sanual , Hubbard Clifford , Ngo Eric
Published: November 2006

The premier candidate active material for tunable microwave phase shifter devices is single composition, paraelectric BaSrTiO3 (BST). However, there is concern that in practical applications the device performance will be compromised due to the temperature dependence of the BST based device capacitance. We report a device design which controls the magnitude and the sign of the temperature coefficient of capacitance (TCC) via a multilayer paraelectric BST/buffer layer/ferroelectric BST coplanar device structure. To realize this multilayer device structure we have designed, fabricated, and optimized a 10 mol% Al doped Ta2O5 barrier layer with low loss (tan δ=0.004), moderate permittivity (εr=42.8), low TCC (-20 ppm/oC), and a low bias stability of capacitance (0.4%). The thin film integration of the barrier layer with the BST layers was optimized for structure, microstructure, interfacial/surface morphology, and dielectric properties as a function of Al doping concentration, annealing temperature, material growth and integration process parameters.
Ohmic Contacts to p-Type III-V Semiconductors for the Base of Heterojunction Bipolar Transistors
Authors: Mohney Suzanne E. , Lysczek Eric , Wang Sammy , Robinson Joshua
Published: November 2006

Ohmic contacts to p-type In0.25Ga0.75Sb, InAs, and InAs0.8P0.2 have been investigated for the base of heterojunction bipolar transistors. On all these semiconductors, using Pd and/or Pt as the first layer in the metallization stack provided the lowest contact resistances. Specific contact resistances as low as 3 x 10-7 Ω-cm2 were measured for Au/W/Pd/p-InGaSb. Thin reactive layers of Pd or Pt were used beneath an unreactive W barrier to keep the contacts shallow, but contact resistance and thermal stability were sacrificed when 2 nm of Pd was used instead of 5 nm. The lowest contact resistance we measured on p-InAs was obtained with Pd/Pt/Au, but Pd/W/Au exhibited better thermal stability at 250 °C. For p-type InAsP, Pd/Ru/Au provided a specific contact resistance of 4 x 10-6 Ω-cm2 as deposited. The contact consumed only 4 {plus minus} 2 nm of InAsP after 3 days at 250 °C, and its resistance remained low.
Carbon Modified (CM)- n-Fe2O3 Thin Films for Efficient Photoelectrochemical Splitting of Water
Authors: Khan Shahed U. , Shaban Yasser A.
Published: November 2006

Carbon modified n-type Iron (III) oxide (CM-n-Fe2O3) photoelectrodes were synthesized by thermal oxidation of Fe metal sheets (Alfa Co. 0.25 mm thick) by heating at several temperatures for different lengths of time. Reference n-Fe2O3 films were prepared by electric oven for comparison. The photocatalytic activity of both CM-n-Fe2O3 and oven made n- Fe2O3 was evaluated by measuring the rate of water splitting reaction to hydrogen and oxygen, which is proportional to photocurrent density, jp. The photoelectrodes were illuminated by light intensity of 100 mW cm-2 from a 150 Watt Xenon arc lamp. At a potential of 0.0 V (V/SCE) and under illumination intensity of 100 mW cm-2 the photocurrent density increased from 5.1 mA cm-2 for oven made n-Fe2O3 to 8.75 mA cm-2 for carbon modified n-type Iron (III) oxide (CM-n-Fe2O3) photoelectrodes synthesized by thermal oxidation. The corresponding maximum photoconversion efficiency improved significantly from 3.6 % for oven made n-Fe2O3 to 6.5% for CM- n-Fe2O3 synthesized by thermal oxidation process. Both n-Fe2O3 electrodes were characterized by using UV-Vis spectra, scanning electron microscope (SEM), monochromatic photocurrent density analysis, and energy dispersive analysis by X-ray (EDAX).
Growth and Surface Reconstructions of GaN and AlN
Authors: Lee Chae-Deok
Published: November 2006

Recent studies in the surface structural analysis of GaN and AlN films grown by plasma-assisted molecular beam epitaxy are discussed. The GaN(0001) and AlN(0001) surfaces are all found to be terminated by metallic layers containing approximately one bilayer of Ga or Al atoms. However, in contrast to GaN (0001) where the Ga-bilayer exists in an incommensurate, fluid- like state at room temperature, the metallic layers for AlN (0001) form large-unit-cell commensurate structures with static atomic arrangements.
Approaches to Reduced-Defect Active Regions for III-N Devices
Authors: Eddy Charles R. , Mastro Michael , Bassim Nabil , Twigg Mark , Henry Richard , Holm Ronald , Culbertson James , Glembocki Orest , Caldwell Joshua D. , Neudeck Phillip , Trunek Andrew , Powell J. Anthony , Peckerar Martin , Ngu Yves , Yan Feng , Babu Sachidananda
Published: November 2006

Two approaches to achieving reduced-defect active regions in III-N devices are discussed - confined epitaxy and heteroepitaxy on step-free SiC surfaces. In confined epitaxy, sapphire substrates (either GaN coated or not) are patterned with a dielectric mask and then III-N device structures are selectively and vertically grown in the openings using metalorganic chemical vapor deposition (MOCVD). In heteroepitaxy on step-free SiC surfaces, SiC mesas are created that have surfaces completely free of atomic steps and then used as substrates for conventional MOCVD III-N growth. In both approaches significant reductions in extended defect densities (10-100x) are observed and manifest in improved electroluminescence efficiency of UV emitters and leakage currents in UV detectors. Extensions of these efforts and other structural characterization results will be presented. Modeling results suggesting directions for future efforts will also be discussed.
Microwave Wireless Power Transmission - A System Perspective
Authors: Lin Jenshan , Verma Ashok , Kim Jaeshin , Ko Sangwon , Wu Wenhsing , Ren F. , Jang Soohwan , Pearton Steve J.
Published: November 2006

In this paper, the concept and the historical developments of wireless power transmission are reviewed and the challenges are discussed from a system perspective. By transmitting at microwave frequency, the electromagnetic wave beam can be focused to improve overall efficiency. However, lightweight high power microwave devices and circuits operating with high efficiency are required. Among various semiconductor technologies, GaN has the best power density and power handling capability. High efficiency rectifier circuits using GaN diodes are used as examples and detailed analysis is presented.
Oxide Dielectrics for Reliable Passivation of AlGaN/GaN HEMTs and Insulated Gates
Authors: Gila Brent , Hlad Mark , Anderson Travis , Chen Jau-Jiun , Allums Kimberly , Gerger Andrew , Herrero Andrew , Jang Soohwan , Kang B.S. , Abernathy Cammy R. , Ren F. , Pearton Steve J.
Published: November 2006

Dielectric oxides of scandium and magnesium have been employed as a surface passivation on AlGaN/GaN HEMT devices. Research to discover a lower lattice mismatch oxide to further reduce the interface trap density and increase oxide/nitride stability has lead to adding calcium to the MgO to create a crystalline film of MgCaO that is a closer lattice match to GaN. Stability of the dielectric films was determined for environmental and thermal processes and a 5nm cap of Sc2O3 was found to increase the stability of the MgCaO over that of the MgO. Passivation effects of the oxide dielectrics maintained pulse currents that were twice that of SiNx passivation after 5 weeks of aging at 200{degree sign}C. A newer capping material of (Sc2O3)x(Ga2O3) 1-x has been developed that provides for double the breakdown field of the previous Sc2O3 capping layer.
Study of the Impact of Electron Traps on GaN HEMT Reliability
Authors: Katzer D. Scott , Mittereder Jeffrey , Binari Steven , Storm David , Roussos Jason , Klein Paul
Published: November 2006

In this paper, we will review work done at the Naval Research Laboratory that addresses GaN-based high electron mobility transistor (HEMT) reliability. Electron trapping effects are especially important in these wide bandgap devices, as they can limit microwave frequency performance and degrade reliability. We will review the utility of current collapse and gate lag measurements in characterizing nitride HEMT device performance. We will conclude with a discussion of the physical origin of these traps and work being done to reduce their density and mitigate their effects.
Performance, Reliability, and Manufacturability of AlGaN/GaN High Electron Mobility Transistors on Silicon Carbide Substrates
Authors: Brown Jeffrey D. , Gibb Shawn , McKenna Johnathan , Poulton Matthew , Lee Sangmin , Gratzer Kevin , Hosse Brook , Mercier Thomas , Yang Yinbao , Young Martin , Green Daniel , Vetury Ramakrishna , Shealy Jeffrey
Published: November 2006

AlGaN/GaN High Electron Mobility Transistors (HEMTs) are receiving considerable attention as a technology that is well suited for high power, high efficiency, radio frequency(RF) and microwave applications. The demonstration of attractive performance of GaN based HEMT technology for applications such as wireless basestations, has been successfully achieved by several organizations, including RFMD. Development efforts are now directed toward understanding and resolving the issues associated with the manufacturability and reliability of this technology. We report on the status of this technology at RFMD with respect to the goals delivering a manufacturable and reliable GaN HEMT device technology. The material growth and process technology will be described. Results of device performance, wafer fab repeatability, and technology reliability are reported.
Mechanisms of Enhanced Luminescence In Nanoscale Compositionally Inhomogeneous AlGaN
Authors: Shen P. H. , Sampath Arnand , Garrett Gregory , Wraback Michael
Published: November 2006

In this paper, we report a detailed optical investigation of the exciton transfer process in AlGaN epilayers with nanoscale compositional inhomogeneities (NCI). Temperature and time- dependent photoluminescence studies were performed. Modeling of the experimental data shows that the enhanced luminescence is due to a rapid transfer of the excitons from a wider band gap matrix to a narrower bandgap and lower dimensional NCI region with a short radiative lifetime. This effect greatly enhances luminescence efficiency.In this paper, we report a detailed optical investigation of the exciton transfer process in AlGaN epilayers with nanoscale compositional inhomogeneities (NCI). Temperature and time-dependent photoluminescence studies were performed. Modeling of the experimental data shows that the enhanced luminescence is due to a rapid transfer of the excitons from a wider band gap matrix to a narrower bandgap and possibly lower dimensional NCI region with a short radiative lifetime. This effect greatly enhances luminescence efficiency.
Hot Carrier Stress Effects of SiO2 Passivated AlGaN/GaN High Electron Mobility Transistors
Authors: Ha Min-Woo , Choi Young-Hwan , Park Joon-Hyun , Seo Kwang-Seok , Han Min-Koo
Published: November 2006

The hot carrier stress with VDS=10 V, VGS=0 V and 5×104 sec is applied to AlGaN/GaN HEMTs before and after SiO2 passivation. The measured forward drain current of AlGaN/GaN HEMTs before and after SiO2 passivation decreases by 4.62 % and 5.46 % after the hot carrier stress. The SiO2 passivation suppresses the electron trapping in surface states so that the degradation due to the hot carrier stress is decreased. The threshold voltage is shifted to a positive direction after the hot carrier stress. The threshold voltage of SiO2 passivated and unpassivated AlGaN/GaN HEMTs after the hot carrier stress increases by 0.14 V and 0.22 V respectively. The leakage current of both devices decreases after the hot carrier stress due to the increased depletion.
Growth of High Quality ZnSe Epilayer on Si (100)
Authors: Yang Tsung-Hsi , Ku Jui Tai , Yang Tsung-Yeh , Luo Guangli , Chou Wu Ching , Chang Chun-Yen
Published: November 2006

Growth of high quality ZnSe epilayer on Ge/GeSi/Si (100) was demonstrated by using low temperature migration enhance epitaxy (LT-MEE) and LT-ZnSe buffer layer. In this study, the low dislocation density of Ge/GeSi/Si structure was grown utilizing an ultrahigh vacuum chemical vapor deposition (UHV/CVD) system. The LT-MEE and LT-ZnSe buffer layer was grown employing molecular beam epitaxy (MBE) system for suppressing the formation of the deep-level emission (DLE) in the ZnSe/Ge/GeSi/Si structure. The low-temperature PL measurements indicate that the sample with a LT-MEE and LT-ZnSe buffer layer can improve its optical characteristic effectively. The X-ray diffraction (XRD) analysis and transmission electron microscopy (TEM) results indicate that the use of a LT-MEE and LT-ZnSe buffer layer markedly improves the crystallinity of the ZnSe epilayer and reduced the number of dislocations in ZnSe epilayer grown-up on Ge/GeSi/Si.
Intrinsic Paramagnetic Defects in GaNP Alloys Grown on Silicon
Authors: Chen Weimin M. , Vorona I. P. , Buaynova Irina , Utsumi A. , Furukawa Y. , Moon S. , Wakahara Akihiro , Yonezu H.
Published: November 2006

We present our recent results of grown-in defects in the GaNP alloy lattice matched to Si, by optically detected magnetic resonance. One of the defects was identified as the Gai-B complex, commonly formed in dilute nitrides. The remaining defects are suggested to be probably related to intrinsic defects as well.
Sputter Deposition of In-Fe2O3 Films for Photoelectrochemical Hydrogen Production
Authors: Ingler William B. , Sporar Daniel , Deng Xunming
Published: November 2006

Stable indium (In) doped iron (III) oxide (Fe2O3) thin film electrodes exhibiting n-type behavior were synthesized by radio frequency (rf) powered sputter coating onto indium doped tin oxide (ITO) coated glass substrates. The highest photocurrent density of 33.4 μA/cm2 was observed for In-Fe2O3 deposited with a Fe2O3 power of 100W and an indium power of 20W, with a substrate temperature of 200{degree sign}C with an atmosphere of 5% oxygen in argon, and a chamber pressure of 6 mTorr. Total deposition time was 120 min.
Heteroepitaxial Growth of 3C-SiC on Silicon-Porous Silicon-Silicon (SPS) Substrates
Authors: Severino Andrea , D`Arrigo Giuseppe , Leone Stefano , Mauceri Marco , Abbondanza Giuseppe , Terrasi Antonio , La Via Francesco
Published: November 2006

This paper presents a new compliance substrate for heteroepitaxial growth of β-SiC on silicon able to partially relax the huge stress caused by both the lattice mismatch and the thermal expansion coefficient difference. We present substrate treatments to achieve the required SPS substrates. The porous region is characterized from a double porosity in order to make easier pores locking up on the surface through the growth of an ultra-thin silicon layer on it by using both APCVD reactor or UHV system (as SSMBE). On such substrates a preliminary study of SiC growth is performed and compared with SiC growth on Si(100) flat substrate. 3C-SiC growth is performed in an horizontal hot-wall CVD reactor by using hydrogen, sylane and ethylene gasses in a low-pressure regime. Moreover, this approach is very interesting in realization of free-standing 3C-SiC wafers disconnected from Si substrates and for thermal stress relief on the substrate only.
Light Enhanced MOCVD Growth of GaN
Authors: Escobosa Arturo , Sanchez-R Victor M. , Elyukhin Vyacheslav
Published: November 2006

The decomposition of ammonia in the MOCVD growth of GaN has been assisted by the use of strong illumination. Epitaxial growth was successful at 700ºC and ammonia flow rates as low as 50 sccm.
Recent Progress in the Development of Quantum Dot Light Emitting Diodes
Authors: Pagan Jennifer G. G. , Stokes E. B. , Patel Kinnari N.
Published: November 2006

Light emitting diodes (LEDs) with colloidal grown quantum dot active layers may serve as a solution to the efficiency gap in the deep green LED emission spectrum. CdSe quantum dots can be tuned for emission across the visible spectrum including the deep green. This work focuses on integrating a CdSe active layer into a GaN LED.
Novel Thermally Stable Contacts to GaN
Authors: Stafford Luc , Khanna Rohit , Voss Lars , Pearton Steve J. , Ren F. , Anderson Travis J. , Dabiran A. , Osinsky A.
Published: November 2006

Ohmic and Schottky contact formation on n-GaN using novel boride-based metallization schemes was studied. The minimum specific contact resistance achieved is 1.6x10-6 ohm cm2 for Ti/Al/TiB2/Ti/Au after annealing over a broad range of temperatures (700-900oC). Boride/Ti/Au metallurgies exhibited rectifying behavior up to 700oC anneal, the barrier height being ~0.55 eV for all borides. Comparison of Ti/Al/TiB2/Ti/Au and conventional Ti/Al/Pt/Au metallizations for AlGaN/GaN high electron mobility transistors subjected to long-term annealing at 350oC show that the improved thermal stability of the boride-based Ohmic contacts has a beneficial effect on the long-term stability of the device.
4H- and 6H- SiC Avalanche Photodiodes
Authors: Campbell Joe C. , Guo Xiangyi , Beck Ariane , Liu Han-Din , McIntosh Dion
Published: November 2006

Ultraviolet detectors are becoming increasingly important in medical, military, and environmental applications, including biological agent detection and non-line-of-sight (NLOS) communications. SiC avalanche photodiodes (APDs) are an attractive candidate for those applications that place a premium on detectors that are compact, rugged, and inexpensive. This paper presents an overview of 4H- and 6H-SiC APDs.
1500V SiC DIMOSFET Development
Authors: Tucker Jesse B. , Matocha Kevin , Beaupre Rich , Tilak Viniyak , Arthur Stephen , Rao Ramakrishna , Balaji S
Published: November 2006

In the process of developing high voltage (1500V) SiC power DIMOSFETs, both channel mobility and gate reliability were investigated. Using a MOS-gated Hall structure, the sheet carrier concentration and electron mobility were measured versus gate bias at various temperatures. The Hall mobility increases with increasing temperature, indicating that Coulombic scattering limits the inversion-layer mobility in these SiC MOSFETs at these fields. The gate oxide reliability of thermally-grown oxides on SiC has been characterized by time-dependent dielectric breakdown (TDDB) measurements of MOS capacitors, lateral MOSFETs, and vertical DIMOSFETs fabricated on 4H-SiC. Simple MOS CV dots demonstrate the potential for >10^6 hours lifetime for a gate oxide field < 4MV/cm. However, fully processed lateral or vertical MOSFET devices demonstrated distinctly lower predicted lifetimes and even different failure modes.
The Effect of Surface Cleaning on Current Collapse in AlGaN/GaN HEMTs
Authors: Bardwell J. , Haffouz Soufien , McKinnon Ross , Storey Craig , Tang Haipeng , Sproule G. Irwin , Roth Daniel , Wang Rongzhu
Published: November 2006

The phenomenon of current collapse is a limiting factor in the performance of AlGaN/GaN high electron mobility transistors (HEMTs), and can be ameliorated by the deposition of a silicon nitride passivation film on the surface. The effect of three types of surface cleaning prior to the application of a silicon nitride passivation layer are studied. The best results were obtained when the wafers were cleaned using an air plasma descum followed by an HCl dip prior to the deposition of the silicon nitride passivation. Auger electron spectroscopy depth profiling indicated that the degree of collapse was correlated with the amount of residual carbon contamination at the silicon nitride/AlGaN interface.
Wide Bandgap Devices with Non-Ohmic Contacts
Authors: Simin Grigory
Published: November 2006

The paper proposes a novel approach to fabricate high performance microwave devices with non-ohmic contacts. Low contact impedance is achieved through a strong capacitive coupling between the metal electron and the high-density two- dimensional electron gas. This approach allows for a new device design with non-annealed or low-temperature annealed contacts and gate alignment-free technology. The application of capacitively coupled contacts for high-power microwave devices is demonstrated.
Optical Properties of GaN Nanowhiskers Produced by Photoelectrochemical Etching
Authors: Ng Hock Min , Geiss Reinhard , Chowdhury Aref , Sergent Mike , Srinivasan Sridhar , Ponce Fernando
Published: November 2006

The optical properties of GaN nanowhiskers with average diameters of 10 to 20 nm formed by photoelectrochemical etching were investigated using photoluminescence (PL) and cathodoluminescence (CL) spectroscopy and imaging. The main donor-bound exciton peak of the etched sample showed a red-shift of 9 meV compared to the unetched sample. CL mapping revealed that the luminescence originated from the surrounding matrix of GaN while the nanowhiskers themselves were non-radiative.
Doped Wide Bandgap Materials and Devices from Semiconducting Boron Carbide
Authors: Montag Benjamin W. , Platt Neil , Boag Neil M. , Brand Jennifer I. , Nelson Kyle A.
Published: November 2006

Semiconducting boron carbide is showing promise as a refractory and robust material with a tunable bandgap. Thin films and devices are easily grown with standard chemical vapor deposition techniques using a variety of boron and carbon precursors including the closo-dodecacarboranes (C2B10H12). Although undoped boron carbide films grown from orthocarborane (1,2- C2B10H12) are p-type, those grown from metacarborane (1,7- C2B10H12) and paracarborane (1,12-C2B10H12) are n-type allowing the production of all boron carbide diodes. In this experimental study, new precursors are used that contain phosphorus and yield new doped n-type films on deposition. The films were characterized by a variety of techniques using UV-Vis spectroscopy (optical bandgap), photoemission (PES) and inverse photoemission (IPES) (electronic structure) and FTIR spectroscopy. Performance evaluation of these new materials will be compared with previous materials.
Electrical Characterization of Novel GaN Light Emitting Diodes with II-VI Quantum Dot Active Layers
Authors: Patel Kinnari N. , Stokes E. B. , Pagan Jennifer G. G. , Burkhart Casey C. , Barletta Phillip
Published: November 2006

In this work we present preliminary results of MOCVD grown n- GaN and MBE grown p-GaN p-n junctions on a sapphire substrate, with and without II-IV active layers. Circular transmission line method (CTLM) test structures were used to measure sheet resistance, contact resistance and to calculate resistivity of the p-GaN layer in both cases. Atomic force microscopy (AFM) was deployed to characterize the surface morphology of the p-type GaN. LED structures fabricated using standard methods were tested for IV characteristics and electroluminescence was demonstrated
Surface Study of P-Type MBE Gallium Nitride Growth over CdSe Quantum Dots
Authors: Burkhart Casey C. , Patel Kinnari N. , Pagan Jennifer G. G. , Barletta Phillip , Stokes E. B.
Published: November 2006

The objective of our current work is to observe the effects of MBE p-GaN growth over II-VI semiconductor nanocrystals on an MOCVD n-GaN template. The starting material was approximately 2 microns of n-type GaN MOCVD material atop a sapphire wafer. CdSe quantum dots were applied through drop and spin casting. A p-type MBE GaN layer of 2500 A was grown using a nitrogen plasma source. MBE allowed precise growth while SIMS analysis showed the relatively low temperature associated with this method, versus MOCVD, preserved the quantum dots. The surface was investigated using atomic force microscopy in tapping mode for samples at various high/low substrate and magnesium cell temperatures.
Sensors Based on Spectroelectrochemistry: Detection of Metal Ions
Authors: Heineman William R. , Seliskar Carl J. , Morris Laura K. , Andria Sara E. , Wansapura Chamika , Shtoyko Tanya
Published: November 2006

Spectroelectrochemical sensors for detecting metal ions have been developed by combining electrochemistry, spectroscopy, and selective partitioning into a single device. The sensor consists of an optically transparent electrode (OTE) coated with a thin (20-500 nm thick) charge-selective film. Sensing is based on the change in optical signal for attenuated total reflectance (ATR) at the OTE accompanying electrochemical modulation of the analyte that has partitioned into the film. Two properties of the analyte that are important for its sensitive detection are a large optical signal from one of the two oxidation states involved in electrochemical modulation and high loading into the charge-selective film. However, not all metal ions have appropriate spectroscopic properties for sensitive detection. This paper focuses on two strategies for improving sensitivity for metal ions: (a) increasing the molar absorptivity difference between the electromodulated oxidation states and (b) enhancing preconcentration of analyte into the charge-selective film.
Electrochemical Detection of Catechol/Neurotransmitter in the Presence of Ascorbic Acid at Conducting Poly (2,2-bithiophene) Platinum Electrode
Authors: Lunsford Suzanne K. , Stinson Jelynn A. , Widera Justyna
Published: November 2006

Preparation of poly(2,2-bithiophene) modified platinum electrode to detect catechol in the presence of a common interferent have illustrated improved electrochemical reversibility, selectivity and sensitivity compared to conventional electrodes. Cyclic voltammograms and Scanning Electron Microscopy data will be discussed to explain the optimization of preparation of the poly(2,2- bithiophene) -modified platinum electrode for the detection of catechol in the presence of a common interferent such as ascorbic acid.
TCP Electrochemical Detection.
Authors: Simonian Aleksandr , Vertelov Grigory , Gale William
Published: November 2006

In this paper we are describing a new approach for TCP determination in solutions. TCP (tricresyl phosphate) hydrolysis has been accelerated for the first time, using microwave irradiation. The detection of TCP was done through the analysis of alkali hydrolysis medium, where cresols were detected electrochemically using carbon paste electrodes. These carbon paste electrodes were composed of graphite powder and silicone oils. Linear sweep voltammograms were recorded; the detection limit for TCP was 3×10-8 M.
Ion Spectroscopy Using Microfluidic FlowFETs
Authors: Tabib-Azar Massood , Xie Yan , Mutlu Senol , Mastrangelo Carlos , Wang Run
Published: November 2006

FlowFETs consisting of drain and source contacts to liquids in microfluidic channels and an isolated gate electrode were used to analyze the ionic content (H+ and Cu++) of fluids for the first time. Compared to ion-selective electrodes, a flowFET is faster and its gate region acts as a programmable membrane with its selectivity determined by the gate potential. Both DC and AC measurement results using aqueous solutions of NaCl and CuSO4 in the 10-3-10-7 molar range are discussed.
Non-Equilibrium Potentiometric CO Sensor Using (BaxLa1-x)2In2O5 (0.4<=x<=0.6) Electrolyte
Authors: Li Xiaogan , Kale Girish
Published: November 2006

Dense (BaxLa1-x)2In2O5 (BLIO) ceramic electrolytes with different compositions (x=0.4, 0.5, 0.6) were synthesised by Pechini method during which the obtained sintered BLIO electrolytes showed high relative density of ~98% and indicated a pure single cubic phase. The CO sensing properties of as-fabricated planar-type BLIO-based sensors coupled with ITO and Pt as the sensing electrode and reference electrode, respectively was investigated. The sensors showed good sensitivity to different concentrations of CO from 0 to 500ppm and excellent selectivity over low-concentrations of methane (<500ppm). However, the sensors with dense electrolyte indicated more sluggish response compared with the sensors coupled with corresponding porous electrolyte as previously reported. The long-term stability of the sensor for the detection of CO was also investigated which indicated a reasonably stable sensor signal after the initial declination.
Amperometric Sensor for Applications in Hydrodynamic Regimen
Authors: Garcia de la Rosa Luis A. , Alatorre Ordaz Alejandro , De Leon Rodriguez L. M. , Gutierrez Granados S.
Published: November 2006

In this work we propose the use of Horse Radish Peroxidase (HRP) to determinate if its amino-acid structure is kept unchanged after being immobilized on a VC electrode. HRP presents enzymatic the transformation reaction of ortophenilendiamine (OPD) to 2,3-Diaminophenazine (DAP). Also, the Nafion membrane will be studied as a matrix for enzymes and antibodies, with the purpose to obtain specific sensors. We also report the electrochemical characterization of CV-Nafion-HRP electrodes. Their response to the presence of OPD was evaluated. It was found that the potential to be used by SSBA was 0.2 V, where each addition of an analyte was of 0.1 mM and the stirring speed was of 800 rpm. Furthermore an UV-Vis spectroscopy analysis was carried out. It was observed that the immobilized HRP on Nafion matrix doesn't present any desnaturalization nor loses of enzymatic activity. The amperometric curve shows the feasibility of Nafion as an immobilization matrix.
Manganese Salen Complex Immobilized by Electrostatic Interactions with Nafion and its Application as a Peroxynitrite Anion Sensor
Authors: Sandoval José , Gutierrez Sivia , Bedioui Fethi , Alatorre Ordaz Alejandro , López Jorge A.
Published: November 2006

Vitreous carbon electrodes modified with Nafion® and MnSalen complex were studied as sensors of peroxynitrite anion. The Nafion/MnSalen electrodes proved to be sensitive and robust for the detection of peroxynitrite concentration ranging from 2.24x10-4 to 1.1x10-3 M at pH 10.5.
Development of the Electrical DNA Sensor
Authors: Shiigi Hiroshi , Tokonami Shiho , Nagaoka Tsutomu
Published: November 2006

We have fabricated a precisely controlled nano-gapped electrode consisting of a nanoparticle - alkylchain - nanoparticle repeated sequence with a self-assembly process of Au and alkylthiol. The electrode was applied to the label-free DNA detection enabling us to read out the response purely by electronic protocols. After an addition of target DNA to the probe modified film, the resistance of the film dropped rapidly and then became constant within 30 s. The resistance reduction is attributed to the conductivity of the hybridized DNA, which can be explained by the dense π overlapping of adjacent base pairs in the double helix forming between the Au particles. The resistance changes depended on the number of mismatching bases in the DNA. Moreover, a significant difference in the resistance change was observed between complementary and 1 base pair mismatching DNA, which suggests that the film is characterized as an important diagnostic advantage on detecting single nucleotide polymorphism.
Screen-Printed Carbon Electrode Modified with Poly-L-Histidine Applied to Voltammetric Determination of Chromium (VI)
Authors: Boldrin Zanoni Maria Valnice , Bergamini Marcio F. , dos Santos Daniela P.
Published: November 2006

The present work reports the use of a Screen printed carbon electrode (SPCE) modified by poly-L-histidine film to determine Chromium (VI). Stable films can be formed by direct addition of PH solution 1% (w/v) on the electrode surface, followed by heating at 800C during 5 min. Calibration curves can be constructed for Cr(VI) from 1.0 x 10-5 mol L-1 to 7.0 x 10-5 mol L-1 Cr (VI) in acetate buffer pH 4 using a pre-concentration step of 60s at open circuit potential. A relative standard deviation of 3.2% was for five determination of 4.0 x 10-5 mol L-1 Cr (VI). The method was successful applied to determination of Cr(VI) in wastewater samples from a leather dyeing industry.
Development of a Novel Composite Sensor Based on Doped Pyrrole Selective to Nitrate Iones
Authors: Alvarez Romero Giaan A. , Galán Vidal Carlos , Palomar-Pardavé Manuel , Ramírez-Silva María Teresa
Published: November 2006

In this work the results obtained on the manufacturing and evaluation of a novel sensor built with a composite material, highly selective to nitrate ions using doped polypyrrole as a recognition agent, are presented. When the ratio recognition agent-graphite was optimized to 1:1 the sensitivities found closely approached nernstian behaviour. The response times were smaller than 20 s. Batch characterization of the sensor displayed a sensitivity of 57.10 mV/decade of nitrate ion activity and a detection limit of 5.37 x 10-5 M, which are comparable to those reported for commercial sensors. The evaluation of the selectivity coefficients showed high affinity to nitrate ions, superior to that of other commercial sensors. The composite material gives the sensor a prolonged service life. Coupling the sensor and a solid state, composite-type, reference electrode to a flow injection analytical system, FIA, permitted to achieve an effective overall assessment of the system.
A Solid Electrolyte Impedancemetric NOx Sensor Using Oxide Receptor
Authors: Koba Daisuke , Takase Satoko , Shimizu Youichi
Published: November 2006

Solid-electrolyte impedance-metric NOx sensor devices composed of a lithium ionic solid electrolyte: Li1.5Al0.5Ti1.5(PO4)3 (LATP) as a transducer and a ceramic oxide as a receptor, respectively, have been systematically investigated for the detection of NOx (NO and NO2) in the range 10-200ppm at 400- 500ºC. Responses of the sensors were able to divide component between resistance and capacitance, and it was found that the device was applicable to the selective detection of NO or NO2 concentration in each ingredient. Especially, those using TiO2, SnO2 (n-type semiconductor) and perovskite-type oxide based receptors gave good responses to NO and NO2.
Influence of H2O on NOx Sensors
Authors: Soltis Rick , Ding Yi , Kubinski David J. , Visser Jacobus H.
Published: November 2006

Highly sensitive and accurate NOx sensors are required to manage the complicated aftertreatment systems that will enable fuel-efficient lean burn engine systems to meet future emissions standards. Several automotive suppliers have developed sensors capable of measuring ppm levels of NOx in the exhaust stream of a vehicle. The response of these highly sophisticated sensors is determined in part by the electrochemistry occurring at the electrode, electrolyte, and interfaces of the various pumping cells comprising these devices. Water, in particular, shows evidence of a complex behavior resulting in both increased and decreased response in the sensor output depending upon the concentration level and operating conditions. This study examines these effects and provides some insight into possible mechanisms responsible for this behavior.