bluuebunny/crossref_metadata_2025_split huggingface dataset:
Non-Equilibrium InSb/InAISb Diodes Grown by MBE
Authors: Johnson A D , Smout A B J , Cairns J W , Pryce G J , Pidduck A J , Jefferies R , Ashley T , Elliott C T 
Published: April 2011

AbstractThe application of non-equilibrium transport techniques to Molecular Beam Epitaxy (MBE) grown InSb/InAlSb heterostructure diodes has produced practical devices such as midinfrared LED's and negative luminescent sources that operate at room temperature. By extending the epitaxial growth to vicinal InSb substrates it has been demonstrated that the temperature window for high quality epitaxy can be lowered by ∼12°C, giving greatly improved epilayer morphology. The degree of misorientation needed for given growth temperatures is shown from Atomic Force Microscope (AFM) measurements to be only ∼2°. In addition, the lower growth temperature gives improved dopant activation, lower trap densities and lower reverse bias leakage currents, with consequent benefits to device performance.
GaAs/AlGaAs Intersubband MID-Infrared Emitter
Authors: Strasser G. , Gianordoli S. , Hvozdara L. , Bichl H. , Unterrainer K. , Gornik E. , Kruck P. , Helm M. , Heyman J. N. 
Published: April 2011

AbstractWe report here the growth and characterization of intersubband quantum well structures based on the GaAs/AlGaAs material system, designed to emit radiation at approximately 7 micrometers. We present transport behavior, infrared photocurrent spectra, and electroluminescence data. First attempts to fabricate a laser structure from this devices encountered difficulties with the electrical properties of the AIGaAs waveguide cladding layers. Thus, we present measurements with different waveguide concepts as doped AlAs cladding layers and doped superlattice cladding structures.
Germanium Far Infrared Blocked Impurity Band Detectors
Authors: Olsen C. S. , Beeman J. W. , Hansen W. L. , Hallerab E. E. 
Published: April 2011

AbstractWe report on the development of Germanium Blocked Impurity Band (BIB) photoconductors for long wavelength infrared detection in the 100 to 250.μm region. Liquid Phase Epitaxy (LPE) was used to grow the high purity blocking layer, and in some cases, the heavily doped infrared absorbing layer that comprise theses detectors. To achieve the stringent demands on purity and crystalline perfection we have developed a high purity LPE process which can be used for the growth of high purity as well as purely doped Ge epilayers. The low melting point, high purity metal, Pb, was used as a solvent. Pb has a negligible solubility <1017 cm−3 in Ge at 650°C and is isoelectronic with Ge. We have identified the residual impurities Bi, P, and Sb in the Ge epilayers and have determined that the Pb solvent is the source. Experiments are in progress to purify the Pb. The first tests of BIB structures with the purely doped absorbing layer grown on high purity substrates look very promising. The detectors exhibit extended wavelength cutoff when compared to standard Ge:Ga photoconductors (155 μm vs. 120 μm) and show the expected asymmetric current-voltage dependencies. We are currently optimizing doping and layer thickness to achieve the optimum responsivity, Noise Equivalent Power (NEP), and dark current in our devices.
Modular 64×64 CdZnTe Arrays With Multiplexer Readout for High-Resolution Nuclear Medicine Imaging
Authors: Woolfenden J. M. , Barber H. B. , Barrett H. H. , Dereniak E. L. , Eskin J. D. , Marks D. G. , Matherson K. J. , Young E. T. , Augustine F. L. 
Published: April 2011

AbstractWe are developing modular arrays of CdZnTe radiation detectors for high-resolution nuclear medicine imaging. Each detector is delineated into a 64×64 array of pixels; the pixel pitch is 380 ptm. Each pixel is connected to a corresponding pad on a multiplexer readout circuit. The imaging system is controlled by a personal computer. We obtained images of standard nuclear medicine phantoms in which the spatial resolution of approximately 1.5 mm was limited by the collimator that was used. Significant improvements in spatial resolution should be possible with different collimator designs. These results are promising for high-resolution nuclear medicine imaging.
Current Issues of High-Pressure Bridgman Growth of Semi-Insulating CdZnTe
Authors: Szeles Csaba , Eissler Elgin E. 
Published: April 2011

AbstractThe availability of large-size, detector-grade CdZnTe crystals in large volume and at affordable cost is a key to the further development of radiation-detector applications based on this II-VI compound. The high pressure Bridgman technique that supplies the bulk of semiinsulating CdZnTe crystals used in X-ray, γ-ray detector and imaging devices at present is hampered by material issues that limit the yield of large-size and high-quality crystals. These include ingot cracking, formation of pipes, material homogeneity and the reproducibility of the material from growth to growth. The incorporation of macro defects in the material during crystal growth poses both material quality limitations and technological problems for detector fabrication. The effects of macro defects such as Te inclusions and pipes on the charge-transport properties of CdZnTe are discussed in this paper. Growth experiments designed to study the origin and formation of large defects are described. The importance of material-crucible interactions and control of thermodynamic parameters during crystal growth are also addressed. Opportunities for growth improvements and yield increases are identified.
Dopants in HgCdTe
Authors: Berding M. A. , Sher A. 
Published: April 2011

AbstractIn this paper we discuss our ab initio calculations of native point defect and impurity densities in HgCdTe. Our calculations have explained the experimental finding in general, and in particular have explained the in-active incorporation of the group VII elements under mercury-deficient conditions; have shown that the group I elements have a large fraction of interstitial incorporation, thereby explaining their fast diffusion; and have described a microscopic mechanism for the amphoteric behavior of the group V elements. We discuss the trends found among the compounds in terms of the underlying bond strengths to understand why the various elements behave the way they do.
Substrate Misorientation Effects on Epitaxial GaInAsSb
Authors: Wang C. A. , Choi H. K. , Oakley D. C. , Charache G. W. 
Published: April 2011

AbstractThe effect of substrate misorientation on the growth of GaInAsSb was studied for epilayers grown lattice matched to GaSb substrates by low-pressure organometallic vapor phase epitaxy. The substrates were (100) misoriented 2 or 6° toward (110), (111)A, or (111)B. The surface is mirror-like and featureless for layers grown with a 6° toward (111)B misorientation, while a slight texture was observed for layers grown on all other misorientations. The optical quality of layers, as determined by the full width at half-maximum of photoluminescence spectra measured at 4K, is significantly better for layers grown on substrates with a 6° toward (111)B misorientation. The incorporation of Zn as a p-type dopant in GaInAsSb is about 1.5 times more efficient on substrates with 60 toward (111)B misorientation compared to 2° toward (110) misorientation. The external quantum efficiency of thermophotovoltaic devices is not, however, significantly affected by substrate misorientation.
Dark Soliton Formation for Light-Induced Waveguiding in Photorefractive inP:Fe
Authors: Chauvet M. , Hawkins S. A. , Salamo G. J. , Segev M. , Bliss D. F. , Bryant G. 
Published: April 2011

AbstractWe present experimental evidence for the observation of steady-state dark photorefractive screening solitons trapped in bulk InP:Fe.
Photoacoustic Study of The Effect of 0.9 eV Light Illumination in Semi-Insulating GaAs
Authors: Fukuyama Atsuhiko , Akashi Yoshito , Yoshino Kenji , Maeda Kouji , Ikari Tetsuo 
Published: April 2011

AbstractThe effect of the secondary light illumination of hv = 0.9 eV on the photoquenched and the enhanced states in semi-insulating GaAs are investigated by using piezoelectric photoacoustic (PPA) measurements at 80 K. It is found that the secondary light causes an optical recovery from EL2* to EL2° and this is in agrezment with the result reported by using infrared optical absorption measurements. We observed a broad peak around 0.9 eV after the secondary light illumination for the first time. The most important finding is that the PPA spectra after the secondary light illumination on the quenched and the enhanced states are the same in the whole photon energy region. We concluded that the secondary light of hv = 0.9 eV induces both an optical recovery and generation of metastable state of the EL6 level. The difference of the transformation rates of these two processes explains well the observed complex natures of the PPA signal under the secondary light illumination.
High Resolution X-Ray Reflectometry and Diffraction of CaF2/Si(111) Structures Grown by Molecular Beam Epitaxy
Authors: Abramof E. , Ferreira S. O. , Rappl P. H. O , Ueta A. Y. , Boschetti C. , Closs H. , Motisuke P. , Bandeira I. N. 
Published: April 2011

AbstractCaF2 layers were grown by molecular beam epitaxy on differently prepared Si(111) substrates. X-ray reflectivity spectra were measured and fitted. From the fitting process, the thickness of the CaF2 layer was precisely (within 1 Å) determined and the CaF2/Si interface roughness was also obtained. This roughness was used as an evaluation parameter for the quality of the layers. The CaF2/Si sample from which the intentional oxide was desorpted at 800°C inside the growth chamber exhibited the most clear x-ray reflectivity spectrum with very well resolved interference fringes. The epitaxial relations of the CaF2/Si samples grown at temperatures between 250 and 700°C were determined from x-ray diffraction analysis.
Auger Recombination in Antimony-Based, Strain-Balanced, Narrow-Band-Gap Superlattics
Authors: Olesberg J. T. , Boggess Thomas F. , Anson S. A. , Jan D.-J. , Flatté M. E. , Hasenberg T. C. , Grein C. H. 
Published: April 2011

AbstractTime-resolved all-optical techniques are used to measure the density and temperature dependence of electron-hole recombination in an InAs/GaInSb/InAs/AlGaInAsSb strain-balanced superlattice grown by molecular beam expitaxy on GaSb. This 4 μm bandgap structure, which has been designed for suppressed Auger recombination, is a candidate material for the active region of mid-infrared lasers. While carrier lifetime measurements at room temperature show unambiguous evidence of Auger recombination, the extracted Auger recombination rates are considerably lower than those reported for bulk materials of comparable bandgap energy. We find that the Auger rate saturates at carrier densities comparable to those required for degeneracy of the valence band, illustrating the impact of Fermi statistics on the Auger process. The measured results are compared with theoretical Auger rates computed using a band structure obtained from a semi-empirical 8-band K.p model. We find excellent agreement between theoretical and experimental results when Umklapp processes in the growth direction are included in the calculation. Measured recombination rates from 50 to 300 K are combined with calculated threshold carrier densities to determine a material To value for the superlattice.
Metal Oxide / Silicon Heterostructures: New Solutions for Different Optoelectronic Applications
Authors: Malik A. , Martins R. 
Published: April 2011

AbstractIn this paper we report the success in fabricating FTO/Si surface-barrier photodiodes produced by spray pyrolysis deposition technique, under ambient conditions. Three types of photodetectors for low-voltage-bias operation were developed based on high-resistivity silicon: 1. X-Ray detectors with energy resolution of 16.5% at 661.5 keV (137Cs source), consisting of surface-barrier PIN photodiode with an active area of 50 mm2 operating at 5V reverse bias, scintillator based on monocrystalline Bi4Ge3O12 and preamplifier (noise of 250 e− RMS.); 2. Fastresponse surface-barrier FTO/I n−-n+ silicon epitaxial photodiodes, operating at 10 V bias with rise times of 2 ns at λ = 0.85 μm; 3. Radiation-resistant drift epitaxial surface-barrier PIN photodiodes for unbiased operating conditions, with an exponential impurity distribution in a 8 μm thick epitaxial layer. A built-in electrical field due to the carrier concentration distribution in the epitaxial layer provides a considerable improvement in the “critical fluence” value (3× 1014 cm−2 ) for neutron irradiation.
Scintillator - Photodiode Linear Arrays for X-Ray Inspection System
Authors: Ignatov S. M. , Potapov V.N. , Fedin A. V. , Chirkin V. M. , Urutskoev L. I. , Gostilo V. V. , Kondrashov V. V. , Sokolov A. D. 
Published: April 2011

AbstractThe evaluations of the following performances of detectors for design of the radiographic system were carried out by mathematical simulation method and experimentally: sensitivity to absorbed energy, noise level, form of apparatus function for spatial resolution of detectors array.The results of calculations were used for designing of CdWO4-Si arrays with optimal sizes of scintillator and photodiode for resolution ability. At the given stage the quality of radiation detectors was evaluated by spectroscopic methods. At the bias voltage on photodiode 24 V, the sensitivity of detectors has made up (0,95–1,00) × 10−21 C / eV, noise level - (1,50–1,75) ×10−16 C together with electronic noise. Dynamic range at absorbed energy by separate detector is more than 105, what is sufficient to get required image contrast.
Photochromic Liquid Hydrogels as Hosts for Holographic Materials
Authors: White R. L. , Hsu Y. Y. , Cooper T. M. , Gresser J. D. , Wise D. L. , Trantolo D. J. 
Published: April 2011

AbstractThe goal of this project is to develop, fabricate, and test advanced optical materials for potential applications to real-time holography based on liquid crystalline polymer hydrogels. In this project, we are investigating the feasibility of increasing holographic capacity and lifetime by coupling a photochromic spyropyran dye to in a liquid crystalline polymer in which cholesteric order has been ‘captured.’ ‘Capture’ is being approached using a unique in-plane poling process with the helical polypeptide poly(α-benzyl-L-glutamate), PBLG, a biopolymer which is capable of maintaining cholesteric order in a liquid crystalline state. Subsequent in situ crosslinking of this aligned biopolymer is projected to offer increased birefringence of the host in the writing of a hologram. Given that a key issue is the magnitude of the real component of the refractive index, increasing the bireflingence may be a useful approach. In writing the hologram, the liquid crystals (LC's) go from isotropic to an ordered dispersion, a property which can be captured via crosslinking to improve holographic lifetime. In the following, the characterization of an aligned host LC system based on the biopolymer poly(α-benzyl-L-glutamate), PBLG, is presented. Inplane alignment is shown to depend on a number of variables, most notably the choice of solvent, polymer molecular weight, and field strength. The results show that optimal alignment of the PBLG LC is achieved with a 2.5% (w/w) concentration of a 118kD biopolymer in methylene chloride in an applied field of 10 kV/cm. Subsequent work will exploit this system as a host for a spiropyran dye for improved holographics.
Synthesis and Electroluminescence Study of a Novel Copolymer:Poly(Phenylene Vinylene-Co-Quinoline Vinylene)
Authors: Kasim Ramesh K. , Derecskei Bela , Pomerantz Martin , Elsenbaumer Ronald L. 
Published: April 2011

AbstractHigh-efficiency polymer light-emitting diodes (LEDs) are often fabricated using multilayered structures with separate carrier transport and light emission layers. Recently, we reported on the synthesis and electroluminescence (EL) characteristics of poly(2,6-quinoline vinylene) (PQV) and its potential for use as an electron transport layer in poly(phenylene vinylene) (PPV) LEDs. To take advantage of the high emission efficiency of PPV and electron accepting ability of PQV, a copolymer of PPV and PQV, poly(phenylene vinylene-co-quinoline vinylene) (PPVQV) was synthesized via the precursor polymer route and converted to the conjugated form by thermal elimination. When used as the emissive layer with Indium-Tin Oxide (ITO) and aluminum as positive and negative electrodes respectively, PPVQV emitted blue light at an onset electric field of 1.05x 106 V/cm and emission efficiency of 0.08%. Improved efficiencies of the order of 0.15% were obtained when blends of copolymer with PPV were used in conjunction with PPV in a multi-layered structure. Along with copolymer chemical characterization data, results from EL studies on single and multi-layered devices are discussed. We also report on a simple and costeffective chemical deposition of silver for the negative electrode in polymer LEDs.
Organic Metals and Superconductors: Facile Synthetic Methodologies Bypassing Coupling and Chromatography
Authors: Meline Ronald L. , Elsenbaumer Ronald L. 
Published: April 2011

AbstractThe organic donor tetrathiafulvalene (TTF, 1) and its derivatives are synthesized from tetrathianaphthalene (TTN, 2) in a one pot reaction. The reaction takes advantage of an isomerization of lithiated TTN into lithiated TTF and subsequent substitution with novel disulfide electrophiles yielding substituted T donors. The isomerization approach eliminates the need for a chemical coupling reaction of oxones or thiones (a yield limiting procedure), and simple byproducts eliminate the need for tedious purification. The novel methodology allows for a high yield preparation of bis(ethylenedithio)tetrathiafulvalene (BEDT-TTF, 3a, 80%) and bis(propylenedithio)tetrathiafulvalene (BPDT-TTF, 3b), previously unavailable directly from TTF. A high yield of bis(phenylenedithio)tetrathiafulvalene (BPhDT-TTF, 3c, unavailable from dimercaptoisotrithione “DMIT”) is also achieved using the synthetic scheme. The method is general, and can be used to prepare a variety of novel organic donors based on TTF. Synthetic procedures along with all relevant characterization are presented.
Improved Electron Injection in Organic Light Emitting Devices by Applying Thin Insulating Layers
Authors: Pairleitner R. , Tasch S. , Leising G. , Scherf U. 
Published: April 2011

AbstractWe present the fabrication and characterization of organic light emitting devices (OLEDs) using thin insulating layers for improved electron injection. The OLEDs are constructed with an ITO anode and an aluminum cathode. For the active layer we use either ladder-type Polyparaphenylene (m-LPPP) or Parahexaphenyl (PHP). A thin film of an insulating material is applied between the active layer and the cathode, in order to achieve a better tunnel injection due to a higher electric field at the interface. We compared different insulating materials with various thickness. The best results are obtained by using a LiF-layer with a thickness between 10 Å and 15 Å. Thereby the onset voltage decreases and the current density in the device increases significantly.
Poly(2-Butyne-1,4-Diyl)S as Precursors to Novel Substituted Polyacetylenes
Authors: Pollack Steven K. , Fiseha Ashebir 
Published: April 2011

AbstractThermally-induced polymerization of 1,4-diphenyl-1,2,3-butatriene affords poly(1,4-diphenyl- 2-butyne-1,4-diyl) as a soluble high molecular weight material. Structure is characterized by 13C and vibrational spectroscopy. When treated with base, this material rearranges to a soluble red poly(acetylene) with a unique substitution pattern.
Deformed Helix Ferroelectric Liquid Crystals with Large Tilt Angles in Optically Addressed Spatial Light Modulators for Dynamical Holography Applications
Authors: Beresnev L. A. , Haase W. , Onokhov A. P. , Dultz W. , Isaev M. V. , Feoktistov N. A. , Ivanova N. L. , Konshina E. A. , Chaika A. N. , Berenberg V. A. , Weyrauch T. 
Published: April 2011

AbstractOptically addressed spatial light modulators (OASLMs) based on deformed helix ferroelectric liquid crystals (DHFLC) with high tilt angles on order of 40° and helical pitches less than 0.2μm were developed. The diffraction efficiency reached the order of 20%. The light induced deviation of the optical axis of the DHFLC layer was measured in sandwich structures consisting of photoconductors and liquid crystals. The photoelectric parameters of photoconductive amorphous silicon carbide a-SiC:H and a photoconductive polymeric films were measured with and without light blocking and reflecting layers. The application of the developed OASLMs in a holographic image corrector was demonstrated.
Oxygen-Induced Inhibition of Noble Metal Silicide Formation: Implications for Electrode/Barrier Structures used with Perovskite Materials
Authors: Saenger K. L. , Grill A. , Kotecki D. E. 
Published: April 2011

ABSTRACTWe describe how the inhibitory effect of ambient oxygen on suicide formation may be exploited in designing noble metal electrode structures suitable for perovskite-based memory devices. Reactions of Pt and Ir films with substrates of silicon and tungsten suicide (WSi2.8/Si) were examined after anneals in atmospheric pressure ambients of oxygen or nitrogen al temperatures of 640 °C for various initial noble metal film thicknesses. Metal/silicon reactions and phase formation were studied by Rutherford Backscattering Spectroscopy, X-ray diffraction. and electrical resistance measurements. While annealing in nitrogen resulted in complete noble metal silicidation in the all samples, some Pt and most to all of the Ir remained after equivalent anneals in oxygen. Oxygen exhibited a greater inhibitory effect on silicidation in thin Ir samples, where no suicide formation was observed. The consistent presence of unreacted noble metal M after oxygen annealing is attributed to the formation of an oxygen-containing M-O-Si barrier which interferes with the silicidation reaction. Qualitative through-film resistance measurements indicate that these in-situ formed M-O-Si barrier layers can be at least moderately conductive, a prerequisite for their possible use as a replacement for deposited barrier materials.
Microstructure Investigations and Structure-Property Correlations in Ferroelectric thin film Capacitors
Authors: Li H. , Yang B. , Dhote A. , Aggarwal S. , Salamanca-Riba L. , Ramesh R. 
Published: April 2011

ABSTRACTEpitaxial 0%, 3% and 10% La doped PZT capacitors with a LSCO bottom electrode grown by pulsed laser deposition on Si using a Ti(Al)N/Pt conducting barrier layer were systematically studied. Ferroelectric capacitors substituted with 10% La show a significantly lower coercive voltage compared to capacitors with 0% and 3% La. This is attributed to the systematic variation of the domain structure of the PLZT film with the increase of La concentration. The in-plane orientation relationship of this heterostructure is: [110]PLZT/[110]LSCO/[110]Pt/[110]Ti(AI)N[110]si. The morphology of the domains as a function of La concentration was studied using high resolution transmission electron microscopy(HREM). The Pt/Ti(Al)N conducting barrier layer stack is intact after the deposition of the LSCO/PLZT/LSCO stack. All Ti(Al)N layers in the samples studied consist of column-like structures with a [110] texture.