bluuebunny/crossref_metadata_2025_split huggingface dataset:
A Semiconductor-based Field-effect Platform for (Bio-)Chemical and Physical sensors: From Capacitive EIS Sensors and LAPS over ISFETs to Nano-scale Devices
Authors: Schöning Michael J. , Abouzar Maryam H. , Wagner Torsten , Näther Niko , Rolka David , Yoshinobu Tatsuo , Kloock Joachim P. , Turek Monika , Ingebrandt Sven , Poghossian Arshak 
Published: April 2011

ABSTRACTThe coupling of semiconductor field-effect devices (FED) together with chemical and biological recognition elements, like functional intelligent materials, biomolecules and living cells, represents an attractive platform for the creation of different (bio-)chemical sensors, multi-parameter analysis systems and bio-chips. This paper summarises recent developments and current research activities in the field of (bio-)chemically modified FEDs, scaling down from capacitive EIS (electrolyte-insulator-semiconductor) sensors and LAPS (light-addressable potentiometric sensor) to ISFETs (ion-sensitive field-effect transistor) that have been realised in our laboratory. Selected examples of application of ISFETs for the detection of physical parameters in liquids are presented, too. With the aim of future development of nano-devices for the detection of single biomolecules, the possibility of a simple preparation of different self-aligned nano-structures by using conventional photolithography and pattern-size reduction technique has been experimentally demonstrated.
Ferroelectric PTCR Films for Photonic Crystal Gas Sensor
Authors: RaviPrakash J. , Trolier-McKinstry Susan , Cheng Jing-Gong , McNeal Mark , Greenwald Anton , Puscasu Irina , Johnson Edward , Pralle Martin , Shah Ashak 
Published: April 2011

ABSTRACTWe examined lanthanum doped lead barium titanate films for temperature measurements of photonic crystal - MEMS devices. Films were deposited by sol-gel techniques and crystallized in air above 650°C. X-ray diffraction spectra consistent with the perovskite structure were detected. The room temperature dielectric constant was ∼570 at 10 kHz of La-doped (0.3 mol%) Pb0.3Ba0.7TiO3 films. These films had a remanent polarization of ∼20μC/cm2 and a coercive field of 145 kV/cm. The leakage current density was ∼ 2×10−7 amps/cm2 at 100 kV/cm field. The resistivity of the films extracted from the linear region of the I-V data (electric fields in excess of 100 kV/cm) measured as a function of temperature shows an increase in resistivity at temperatures above Tc (120°C for BaTiO3 and 240°C for Pb0.3Ba0.7TiO3) of the film consistent with positive coefficient of resistance (PTCR) effect. However, the change in resistance was small when compared to bulk samples of similar compositions.
Thermo-Reversible Protein Fibrillar Hydrogels
Authors: Miller Aline , Saiani Alberto , Yan Hui 
Published: April 2011

ABSTRACTHen egg white lysozyme (HEWL) was exposed to various physical and chemical denaturing environments to encourage protein denaturation and consequent gelation. Its phase behavior was examined as a function of pH, temperature and also in the presence of the reductant dithiothreitol (DTT). Transparent viscoelastic gels form at low pH values while opaque gels form under alkaline conditions. No increase in viscosity was observed for systems in pure water unless 20 mM of DTT was added, which is known to break the disulfide bridges present in HEWL. The microstructure of the gel was studied using transmission electron microscopy (TEM) and environmental scanning electron microscopy (ESEM). Gels formed at low pH contain fibrils ∼10 nm in diameter with various lengths while at high pH the gels are dominated by particulate aggregates. Thinner fibrils that are 4-6 nm in diameter are observed in the gels formed in the presence of DTT. In this case the distinct feature of the gels is they are thermoreversible and can be melted and reformed easily by varying the temperature.
Spin-Orbit Coupling and Zero-Field Electron Spin Splitting in AlGaN/AlN/GaN Heterostructures with a Polarization Induced Two-Dimensional Electron Gas
Authors: Kurdak Ç. , Biyikli N. , Cheng H. , Ozgur U. , Morkoç H. , Litvinov V. I. 
Published: April 2011

ABSTRACTWe studied spin-orbit coupling in wurtzite AlxGa1−xN/AlN/GaN heterostructures with different Al concentrations using weak antilocalization measurements at 1.6 K. Using the persistent photoconductivity effect we change the carrier density in controllable manner. We find that the electron spin splitting energies does not scale linearly with the Fermi wavevector at high carrier densities. From this deviation, for the first time, we are able to extract the cubic spin-orbit parameter for this material system.
Epitaxial Growth of ZrO2 on GaN by MOMBE for High Dielectric Material Applications
Authors: Gu Xing , Xie Jinqiao , Chevtchenko Serguei , Izyumskaya Natalia , Avrutin Vataliy , Morkoç Hadis 
Published: April 2011

ABSTRACTEpitaxial growth of ZrO2 has been achieved on MOCVD grown GaN template by oxides MBE using a reactive H2O2 oxygen source. Using the low temperature buffer followed by high temperature in-situ annealing and high-temperature growth, monoclinic, (100)-oriented ZrO2 thin film with decent structural quality and smooth surface morphology was achieved. The full width at half maximum of ZrO2 (100) rocking curve is 0.4 arc degree and the rms roughness for a 5μm by 5 μm AFM scan is 4.1Å. The use of epitaxially grown ZrO2 in the AlGaN/GaN HFET structure as a gate dielectric layer have resulted in the increase of the saturation-current density and pinch-off voltage as well as showed near symmetrical gate-drain I-V behavior.
Defects in Electron and Neutron Irradiated n-GaN: Disordered Regions Versus Point Defects
Authors: Polyakov Alexander Y , Smirnov Nikolai B , Govorkov Anatoliy V , Markov Alexander V , Lee Cheul-Ro , Lee In-Hwan , Kolin Nikolai G , Merkurisov Denis I , Boiko Vladimir M , Wright James S , Pearton Stephen J 
Published: April 2011

ABSTRACTEffects of 10 MeV electron and fast reactor neutron irradiations on carrier removal rate and deep traps spectra were compared for undoped n-GaN samples. It is shown that for electron irradiation the carrier removal rate is well accounted for by the difference in introduction rates of nitrogen-vacancy-related donors with activation energy 0.2 eV and of nitrogen-interstitial-related acceptors at Ec-1.2 eV. In the case of neutron irradiation the introduction rate of all deep traps was much lower than the carrier removal rate indicating that the main contribution to electron removal was due to disordered regions. These regions give rise to a marked persistent photocapacitance signal and a hole-trap-like feature in deep traps spectra. The Fermi level position in the core of disordered regions is located near Ec-(0.85-1) eV.
Defect reduction in (11-20) a-plane GaN by two-step epitaxial lateral overgrowth
Authors: Ni X. , Özgür Ü. , Fu Y. , Biyikli N. , Morkoç H. , Liliental-Weber Z. 
Published: April 2011

ABSTRACTWe report a two-step growth method to obtain uniformly coalesced epitaxial lateral overgrown a-plane GaN by metalorganic chemical vapor deposition (MOCVD). By obtaining a large wing height to width aspect ratio in the first step followed by enhanced lateral growth in the second step via controlling the growth temperature, we reduced the tilt angle between the advancing Ga-polar and N-polar wings for improved properties. Transmission electron microscopy (TEM) showed that the threading dislocation density in the wing area was 1.0×108cm−2, more than two orders of magnitude lower than that in the window area (4.2×1010cm−2). However, a high density of basal stacking faults, 1.2×104cm−1, was still observed in the wing area. Near field scanning optical microscopy (NSOM) at room temperature revealed that the luminescence was mainly from the wing regions with very little contribution from the windows and meeting fronts. These observations suggest that due to significant reduction of threading dislocations radiative recombination is enhanced in the wings.
Localisation of Excitation in InGaN Epilayers and Quantum wells
Authors: O'Donnell Kevin Peter 
Published: April 2011

ABSTRACTUsing a synchrotron radiation source, extended X-Ray Absorption Fine Structure (EXAFS) measurements were performed at the gallium and indium K-edges of a range of (In,Ga)N samples, grown either by MBE or MOCVD. The resulting determinations of local alloy structure, complemented in selected cases by asymmetric x-ray diffraction reciprocal space mapping (XRD-RSM), show an inequality in the “mixed cation” separations, Ga-In and In-Ga, for samples with InN content less than about 50%. This asymmetry, whichincreaseswith decreasing InN content of the layers, is related to the high luminescence efficiency of the materials through a combination of percolation and localisation of excitation on the GaN and InN sub-lattices, respectively.
Estimation of Junction Temperature in Operating Light Emitting Diodes
Authors: Sakhawat Md. Shahrukh , Guha Arindra N , Akpa Okechukwu , Hagler Ping Z , Wang Dake , Park Minseo , Das Kalyankumar 
Published: April 2011

ABSTRACTLight emitting diodes (LEDs) are normally operated at high current levels resulting in substantial junction heating. However, the junction temperature cannot be measured directly. In the study reported here, it was attempted to estimate junction temperature in LEDs with peak emission 400 nm. Temperature was estimated from current-voltage (I-V) measurements as a function temperature and peak-shift of optical emission spectra with increasing temperature. For a diode operated at a current-level of 100 mA, a temperature of 100 °C was estimate from current voltage measurement and 160 °C from the peak-shift in the optical emission spectra. The difference in temperature estimated using the two different technique is not understood at this point.
Traps in Si-doped AlxGa1-xN Grown by Molecular Beam Epitaxy on Sapphire Characterized by Deep Level Transient Spectroscopy
Authors: Ahoujja Mo , Elhamri S , Hogsed M , Yeo Y. K. , Hengehold R. L. 
Published: April 2011

ABSTRACTDeep levels in Si doped AlxGa1−xN samples, with Al mole fraction in the range of x = 0 to 0.30, grown by radio-frequency plasma activated molecular beam epitaxy on sapphire substrates were characterized by deep level transient spectroscopy (DLTS). DLTS measurements show two significant electron traps, P1 and P2, in AlGaN at all aluminum mole fractions. The electron trap, P2, appears to be a superposition of traps A and B , both of which are observed in GaN grown by various growth techniques and are thought to be related to VGa-shallow donor complexes. Trap P1 is related to line defects and N-related point defects. Both of these traps are distributed throughout the bulk of the epitaxial layer. An additional trap P0 which was observed in Al0.20Ga0.80N and Al0.30Ga0.70N is of unknown origin, but like P1 and P2, it exhibits dislocation-related capture kinetics. The activation energy measured from the conduction band of the defects is found to increase with Al mole content, a behavior consistent with other III-V semiconductors.
Characterization of GaN/Si Using Capacitance Spectroscopies
Authors: Smith Steven R. , Roberts John C. , Rajagopal P. , Cook J. W. , Piner E. L. , Linthicum K. J. , Elhamri Said 
Published: April 2011

ABSTRACTLayers of GaN deposited on Si substrates have been studied using Thermal Admittance Spectroscopy (TAS) and Optical Admittance Spectroscopy (OAS). Transparent front-side contacts were used to facilitate the optical measurements. Six specimens were cut from the same location in two different wafers, and three samples were randomly chosen from other growths. A shallow level at EC − 0.051 eV was found in all the specimens using TAS. In some specimens this peak was asymmetric, indicating more than one level near this energy. Deeper levels were also seen in the high-temperature portion of the spectra, but were poorly resolved in most specimens. Illuminating the specimen with UV light at 25 K resulted in the thermal position of the peak shifting to a lower temperature, and hence, the calculated energy, of the peak shifting lower. The amplitude of the peak also decreased. Transient OAS measurements revealed the interesting phenomenon of negative persistent photo conductance at room temperature in some of the specimens when the illumination photon energy was less than the bandgap. The negative response time was very short. At lower temperatures, below 100 K, the negative response diminished, but the response time was still short. At wavelengths above the bandgap energy, normal transient response was seen, with a longer time constant.
GaAsN Thin Film Growth by Chemical Beam Epitaxy with Source Gas Flow Rate Modulation
Authors: Ohshita Yoshio , Saito Kenji , Nishimura Kenichi , Suzuki Toshihide , Yamaguchi Masafumi 
Published: April 2011

ABSTRACTThe amount of residual carbon in the GaAsN film deposited by chemical beam epitaxy (CBE) is decreased by the flow rate modulation growth method (FM-CBE). The number of carbon atoms remained in the grown film increases as the growth temperature decreases. At low temperatures below 440°C, the carbon atoms are mainly originated from the nitrogen source gas mono-methylhydrazine. However, increasing the substrate temperature during the growth causes the deterioration of film qualities and the high growth temperature is not the solution for reducing the impurities. On the other hand, by intermitting the supply of gallium source triethylgallium while the arsenic and nitrogen sources are continuously supplied, the carbon concentration drastically decreases as compared with that grown by the conventional CBE growth. The results of temperature programmed desorption and ab initio calculations suggest that the desorption of adsorbates that contain C atom, such as, NHCH3, is enhanced by the FM-CBE growth, resulting in the decrease of the residual C concentration.
Thinking about Diamond
Authors: Stoneham A. Marshall 
Published: April 2011

ABSTRACTDiamond is valued mainly as a symbol of power and value (the girl's best friend) and as a solution to many materials processing problems (the engineer's best friend). The 1950s saw both striking developments in diamond synthesis and the beginnings of the rise of silicon as the semiconductor of choice. Since then, silicon has transformed the world. Diamond has reinforced its known roles, and found niches that exploit its special qualities. It is also one of the carbon materials that, in combination, have a variety of superb properties. Could there be bigger opportunities for diamond, more than mere niches, arising from the major social needs: the life sciences, the information technologies, energy, and perhaps others. I attempt to identify areas that might develop formidably.
Device Simulation and Design Optimization for Diamond Based Insulated-gate Bipolar Transistors
Authors: Ye Haitao , Tumilty Niall , Garner David , Jackman Richard B. 
Published: April 2011

ABSTRACTA diamond based insulated gate bipolar transistor is incorporated into a two-dimensional device simulator (MEDICI) to examine the current gain (β) and potential distribution across the device. Initially, work has focused on an important component of IGBT structure, the PNP bipolar transistor, which has been simulated and is reported upon in this paper. Empirical parameters for emitter and collector regions were used. Various carrier concentrations for base region were used to optimize the simulation. It was found that decreasing the thickness of base region leads to an increase in current gain. A buffer layer is needed to prevent the punch-through at low carrier concentration in the base region. Various approaches of increasing the current gain are also discussed in this paper.
Electrical Transport and Defect Spectroscopy of Free Standing Single Crystal CVD Diamond Prepared from Methane Rich Mixtures
Authors: Bogdan Andrey , Bogdan Ganna , De Ceuninck Ward , Haenen Ken , Nesladek Milos 
Published: April 2011

ABSTRACTTransient photocurrent measurements in the Time-of-Flight (TOF) configuration were used to study the electrical transport in single crystalline diamond layers using a Nd:YAG - pumped OPO (2.7 nsec) laser pulse excitation source working at a wavelength of ∼ 218 nm. The amount of collected charge was measured and the hole and electron drift mobilities were determined at room temperature for natural IIa diamond and intrinsic single crystalline CVD diamond samples. A variation of the laser intensity over several orders of magnitude enabled switching between the so called “small signal TOF” and “space charge limited current” (SCLC) modes. Experiments were done using electrical fields in the range of 0.05-1.2 V/μm.
Diamond-like Carbon Film Deposition on an Artificial Heart Blood Pump Using a Flexible Type Electrode with r.f. Plasma CVD Processing
Authors: Kanasugi Kazuya , Ohgoe Yasuharu , Tsuchimoto Katsuya , Sato Keisuke , Hirakuri Kenji K. , Miyashita Osamu , Funakubo Akio , Fukui Yasuhiro 
Published: April 2011

ABSTRACTDiamond-like carbon (DLC) film was deposited uniformly on an irregular structure such as a polyurethane artificial heart blood pump using a special 3-dimensional type electrode. Process of applying the DLC film coating is accomplished by inserting a large number of small metallic balls (φ0.8 mm chromium balls). It is then possible to adjust the shape of the electrode in such a way that the DLC film coating can be applied to the irregular surface of the artificial heart. In investigating the availability of the electrode, under helium (He) plasma, the plasma states were measured using double probe analysis. Lateral profiles of the electron temperature were higher in the centre and decreased towards the edges of the electrode. On the other hand, the plasma density profiles were lower in the centre part than at the edges. The electrode kept ion sheath on the artificial heart blood pump's surface at self-bias voltage uniformly. The results were that the DLC film was deposited completely on the artificial heart blood pump at the film thickness of approximately 350 - 380 nm. Additionally the film structure was uniform.
Electrochemical Charge Transfer to Diamond
Authors: Chakrapani Vidhya , Angus John C. , Anderson Alfred B. , Sumanasekera Gamini U. 
Published: April 2011

ABSTRACTElectrochemically mediated charge transfer has been primarily studied by its effect on the surface conductivity of diamond. In this paper we show that the effect is not restricted to diamond, but may occur in other material systems as well, for example, semiconducting single-walled carbon nanotubes and gallium nitride.
DNA-ISFETs from Single Crystalline Diamond
Authors: Nebel Christoph E. , Shin Dongchan , Yamamoto Tomoko , Nakamura Takako 
Published: April 2011

ABSTRACTDNA sensitive field-effect transistors (DNA-FET) have been realized using single crystalline diamond grown by plasma-enhanced chemical vapor deposition (CVD). To bond DNA to diamond, amine linker-molecules are covalently attached by photochemical means to H-terminated diamond surfaces. Using hetero-bifunctional cross-linker and thiol-modified single-strand (ss) marker DNA, the gate of diamond FETs is modified to sense hybridization of DNA, forming double-strand (ds) DNA molecules on the gate. The density of DNA bonded to diamond is varied between 1012 and 1013 cm−2 to explore sensitivity enhancements by reduction of the DNA molecule density. DNA-FET characterization in 1M NaCl buffer solution (pH 7.2) reveal gate-potential threshold shifts by hybridization in the range 30 mV to 100 mV with decreasing DNA density. The variation is discussed based on the transfer doping model which predicts with decreasing pH increasing hole-densities in the surface conductive layer of diamond.
Temperature Dependent Hall Measurements on PLD Thin Films
Authors: von Wenckstern Holger , Brandt Matthias , Zimmermann Gregor , Lenzner Jörg , Hochmuth Holger , Lorenz Michael , Grundmann Marius 
Published: April 2011

ABSTRACTThe electrical properties of epitaxial ZnO thin films grown on sapphire substrates by pulsed laser deposition were investigated by temperature dependent Hall measurents. The thin films investigated were grown at different oxygen partial pressures ranging from 10-2 mbar to 1 mbar. The formation of a degenerate layer, determining the low temperature Hall data, depends on the oxygen partial pressure applied during growth. Further, the formation of such a layer can be correlated to the grain size of the samples. The thermal activation energy of dominant donors decreases in tendency with increasing oxygen partial pressure p(O2); it is about 100 meV for p(O2) ≤ 3 × 10-2 mbar and about 30 meV for p(O2) ≥ 0.1 mar. The concentration of donors and compensating acceptors increases with increasing p(O2).
Vertically Aligned Single Crystalline ZnO Nanorods Grown by Hydrothermal Synthesis and the Theoretical Model for Predicting the Rod Density
Authors: Chua Soo Jin , LE Hong Quang , TAY Chuan Beng , LOH Kian Ping , Fitzgerald Eugene 
Published: April 2011

ABSTRACTZnO nanorods are grown by hydrothermal synthesis on a GaN substrate. The nanorods are charcterised by X-ray diffraction, photoluminescence and electron diffraction. A phenomenological model is proposed to predict the areal density and rod length.
ZnO-Sn Bilayer Ultraviolet (UV) Photon Detector with Improved Responsitivity
Authors: Yadav Harish Kumar , Sreenivas K. , Gupta Vinay 
Published: April 2011

ABSTRACTThe influence of the integration of ultra-thin layer of different metals (Al, Cu, Sn, Te, Pb and Au) with the c-axis oriented ZnO thin film on the ultraviolet (UV) photoresponse is investigated. The transfer of electrons from the metal layer to the semiconductor at the interface compensate the surface states which otherwise takes electrons from the interior of ZnO layer and thereby increases the conductivity under UV illumination. The Sn/ZnO sample exhibits a responsivity of the order of 8.5 KV/W at a low UV intensity of 140 μW/cm2 (⎻ = 365 nm) with a fast rise and fall time of 105 and 400 ms respectively.
Two-Dimensional Organization of Single Crystal ZnO Nanopillars
Authors: Cui Jingbiao , Gibson Ursula J 
Published: April 2011

ABSTRACTPeriodically ordered ZnO nanopillar arrays were fabricated by a combination of soft templates created by e-beam lithography and an electrochemical process. Growth at 90 °C in an aqueous solution ensured compatibility with the polymethyl methacrylate used as a template material. We demonstrate that individual ZnO nanopillars with diameters around 100 nm can be precisely placed in desired locations to form two-dimensional periodic structures. This approach provides a new method for design and fabrication of ZnO photonic materials. The process is compatible with standard microfabrication techniques and may have potential applications in the manufacture of photonic and optoelectronic devices.
Donors and Acceptors in Bulk ZnO Grown by the Hydrothermal, Vapor-phase, and Melt Processes
Authors: Look David 
Published: April 2011

ABSTRACTThe optical and electrical properties of commercially available bulk ZnO samples grown by the hydrothermal, vapor-phase, and melt methods are compared. Low-temperature photoluminescence (PL) is used to identify the presence of common impurities, such as H, Al, Ga, and In, and temperature-dependent Hall-effect (T-Hall) measurements are used to obtain donor energies and to quantify donor and acceptor concentrations. All three types of material produce sharp donor-bound-exciton (D0X) PL lines, I4, I6, I8, and I9, generally associated with H, Al, Ga, and In, respectively. However, the I4 and I9 lines are weak in hydrothermal ZnO, and the I4 line is also weak in melt material. Another D0X line I5, possibly associated with donors near the surface, appears in some hydrothermal samples. Electrically, hydrothermal ZnO has a much lower bulk conductivity than vapor-phase or melt ZnO, partly because the donor concentration is lower, but also because the acceptor concentration is higher. A consequence of the low bulk conductance is that surface conductance becomes much more important and must be included in the Hall-effect modeling. An interesting result of this study is a close correlation between the PL-derived Al (I6) donor energy of 51 meV, and the T-Hall-derived energy of 52 meV.