bluuebunny/crossref_metadata_2025_split huggingface dataset:
Photoreflectance and Double Crystal X-Ray Study of Strained InGaAsP Layers on InP Substrates
Authors: Flemish J. R. , Shen H. , Dutta M. , Jones K.A. , Ban V.S. 
Published: March 2011

ABSTRACTDetermining the composition of quaternary epitaxial films requires accurate measurements of both the lattice parameter and the bandgap energy. Complications arise in lattice-mismatched material, because the mismatch produces tetragonal distortion of the epi-layer and splitting of the valence band energies in a manner which depends on the film composition. We present studies on strained InGaAsP grown on (100) InP. Using room temperature photoreflectance (PR) we observe shifting of the band gap and splitting of the valence band energies, and using the (115) and (004) reflections from double crystal x-ray diffraction (DXRD) we determine the values of the parallel and perpendicular lattice constants. By combining the lattice parameter measurements with band splitting data, we accurately determine the quaternary composition from a self-consistent model using an iterative procedure. By linear interpolation of the elastic-stiffness constants, C11 and C12. as well as the shear and hydrostatic deformation potentials for the four binary compounds in the InGaAsP system, we relate the state of biaxial stress to the induced shifts in the valence band energies.
Low Temperature Infrared Measurements and Photo-Induced Persistent Changes of Intersubband Transitions in GaAs/AlGaAs Multiple Quantum Wells.
Authors: Dischler B. , Ralston J.D. , Koidl P. , Hiesinger P. , Ramsteiner M. , Maier M. 
Published: March 2011

ABSTRACTUtilizing infrared absorption and Hall measurements, a detailed study is presented of the temperature dependence (10 K < T < 300 K) of the intersubband transition and related doping behaviour in GaAs/Al0.32Ga0.68As multiple quantum well structures with Si doping concentrations between 1×1018 and 8×1018 cm−3 in the quantum wells. The intersubband transition frequency increases with decreasing temperature, which can be adequately modelled by considering the different effective masses and the thermal populations of the two electron subbands. This model also accounts for the decrease in linewidth of the infrared absorption resonance upon cooling. In Hall measurements a persistent photo-induced decrease in the free electron concentration within the GaAs quantum wells is observed for Si doping levels exceeding 5×1018 cm−3. Corresponding decreases are observed both in the integrated absorption and the absolute frequency of the intersubband transition, the latter arising from a reduction in the depolarization shift. The spectral dependence of the photo-induced changes over the energy range 1.2 eV < hν < 2.5 eV, along with thermal regeneration over the temperature range 70 K < T < 150 K, have been studied.
Properties of Graphite Interconnect Circuit Boards with Anisotropic Thermal Expansion
Authors: Malamas J. , Bambha R.P. , Ramsey J.B. , Garrett W.C. , Kelso E.G. , Hahn T.A. 
Published: March 2011

ABSTRACTWe report the investigation of an interconnect circuit board (ICB) with anisotropic thermal expansion for use with bump bonded, indirect hybrid, scanning focal plane arrays. This ICB is designed to reduce significantly the thermal stresses on the indium bump bonds during thermal cycling. Highly oriented pyrolitic graphite (HOPG) was chosen because its anisotropic thermal expansion meets the criteria for forming an indirect hybrid ICB using silicon processor circuits and mecury cadmium telluride detectors. Properties of HOPG influencing its performance as an ICB have been investigated including thermal expansion, electrical conductivity, durability, and adherence of electrically insulating thin films.
Long-Wavelength Germanium Photodetectors by Ion Implantation
Authors: Wu I.C. , Beeman J.W. , Luke P.N. , Hansen W.L. , Haller E.E. 
Published: March 2011

ABSTRACTExtrinsic far-infrared photoconductivity in thin high-purity germanium wafers implanted with multiple-energy boron ions has been investigated. Initial results from Fourier transform spectrometer(FTS) measurements have demonstrated that photodetectors fabricated from this material have an extended longwavelength threshold near 192μm. Due to the high-purity substrate, the ability to block the hopping conduction in the implanted IR-active layer yields dark currents of less than 100 electrons/sec at temperatures below 1.3K under an operating bias of up to 70mV. Optimum peak responsivity and noise equivalent power(NEP) for these sensitive detectors are 0.9A/W and 5×10−16 W/Hz1/2 at 99μm, respectively. The dependence of the performance of devices on the residual donor concentration in the implanted layer will be discussed.
II-VI / III-V Strained-Layer Superlattice Materials and Devices
Authors: Fuxi Gan , Hailong Wang , Jie Cui 
Published: March 2011

ABSTRACTThe optical and spectroscopy properties of Il-VI wide gap semiconductor SLSs have been studied. We report the first observation of the pulse compression in ZnS-ZnSe MQW and the folded LA phonon modes in ZnS-ZnSe SLS;The confined LOn phonon modes in ZnSe-ZnTe SLS are observed and the critical thickness of ZnSe-ZnTe SLS are determined,for the first time, by Raman scattering.
Reflection High-Energy-Electron Diffraction Study of Inp and InAs (100) In Gas-Source Molecular Beam Epitaxy
Authors: Chin T. P. , Liang B. W. , Hou H. Q. , Tu C. W. 
Published: March 2011

ABSTRACTInP and InAs (100) were grown by gas-source molecular-beam epitaxy (GSMBE) with arsine, phosphine, and elemental indium. Reflection high-energy-electron diffraction (RHEED) was used to monitor surface reconstructions and growth rates. (2×4) to (2×1) transition was observed on InP (100) as phosphine flow rate increased. (4×2) and (2×4) patterns were observed for In-stabilized and As-stabilized InAs surfaces, respectively. Both group-V and group-rn-induced RHEED oscillations were observed. The group-V surface desorption activation energy were measured to be 0.61 eV for InP and 0.19 eV for InAs. By this growth rate study, we are able to establish a precise control of V/HII atomic ratios in GSMBE of InP and InAs.
Infra-Red Photodiodes in Hg1-xCdxTe Grown by OMVPE
Authors: Parat K.K. , Taskar N.R. , Ehsani H. , Bhat I.B. , Ghandri S.K. 
Published: March 2011

ABSTRACTHg1-xCdxTe layers, grown by the organometallic vapor phase epitaxy (OMVPE), are p-type with carrier concentrations around 4 × 1016/cm3 due to the Group II vacancies in them. Following a Hg saturated anneal at 220°C, these layers become n-type with carrier concentrations around 4 × 1014/cm3. In order to fabricate p-n junction diodes, Hg1-xCdxTe layers were grown with a 0.5–0.8 μm thick CdTe cap. By opening windows in this CdTe cap, the underlying Hg1-xCdxTe Te layer was annealed in a selective manner, thus forming planar p-n junctions. The CdTe cap, which is used as the diffusion barrier for Hg during the selective anneal, also served as the junction passivant for the photodiodes. Details of device fabrication and characterization are presented in this paper.
Cone-Beam 3-D Reconstruction with Double Circular Trajectory
Authors: Rizo Ph. , Grangeat P. , Sire P. , Lemasson P. , Delageniere S. 
Published: March 2011

ABSTRACTIn X-ray cone-beam tomography, the only planar source trajectory that does not produce incomplete data is the infinite line. Such a source trajectory is not experimentally possible. To ensure complete data acquisition with cone-beam radiographs, a set of nonplanar trajectories has been studied. Among the trajectories proposed in the literature, a simple one is a set of two circular trajectories with intersection of the two trajectory axes. The angle between the two axes is related to the maximum aperture of the cone beam. We propose here an exact method for performing this reconstruction using the 3-D Radon transform of the object. The modulation transfer function of this algorithm remains identical to that for the central slice of reconstruction in a single circular trajectory. The relative mean square error for density stays within 2% for an aperture of ±30°. With a single circular trajectory, the relative mean square error may reach 20% at the same aperture. With a double circular trajectory, horizontal artifacts are nearly suppressed.
Three Dimensional (3D) Electron Paramagnetic Resonance Imaging Technique For Mapping Porosity in Ceramics
Authors: Kordas G. , Kang Y.H. 
Published: March 2011

ABSTRACTA three dimensional (3D) Electron Paramagnetic Resonance Imaging (EPRI) method has been developed to probe the structure and size of pores in ceramic materials. A computer control current source and magnetic field gradient coil assembly were added on the conventional EPR instrument as imaging devices. This added-on facility was tested using a phantom sample having cavities filled with DPPH (2,2-diphenyl-1-picrylhydrazyl) particles. Pumice was then used to demonstrate the feasibility of the technique. Porous pumice stone was immersed in a 0.5mM 15N-PDT-water solution to introduce the spin labels into the open volume of the sample. A two-dimensional image was reconstructed from a set of 1-D projections using a filtered back-projection technique. A three-dimensional image was derived from 22 2-D images each constructed by 22 1-D projections. At present, the facility allows a resolution of 69 and 46 μm for 2-D and 3-D imaging.
Fast Radial NMR Imaging of Transport Processes
Authors: Majors Paul D. , Smith Douglas M. , Caprihan Arvind 
Published: March 2011

ABSTRACTFast NMR imaging techniques for the study of objects with circular or spherical symmetry are introduced. Quantitative, radially-resolved information for an object with circular symmetry is obtained by Abel inversion of a single one-dimensional (1D) NMR image or equivalently by Hankel transformation of the 1D time domain NMR signal. With adequate sensitivity, the entire image information is obtained in a single experimental iteration, providing snapshot temporal resolution. Thus these techniques are useful for the study of transport phenomena. Spherical objects can also be radially resolved from a 1D projection image by applying two sequential Abel inversions, or in one simple differentiation step. These radial imaging techniques are easy to implement and the computational and data storage requirements are nominal. These procedures are also applicable to microscopic and solids NMR imaging, as well as to X-ray CAT and other projective imaging techniques. Noise effects, and the detection and handling of distortions from circular symmetry are also considered.
Nondestructive Imaging of Materials Microstructures Using X-Ray Tomographic Microscopy
Authors: Kinney J.H. , Nichols M.C. , Bonse U. , Stock S.R. , Breunig T.M. , Guvenilir A. , Saroyan R.A. 
Published: March 2011

ABSTRACTA technique for nondestructively imaging microstructures of materials in situ, especially a technique capable of delineating the time evolution of chemical changes or damage, will greatly benefit studies of materials processing and failure. X-ray tomographic microscopy (XTM) is a high resolution, three-dimensional inspection method which is capable of imaging composite materials microstructures with a resolution of a few micrometers. Because XTM is nondestructive, it will be possible to examine materials under load or during processing, and obtain three-dimensional images of fiber positions, microcracks, and pores. This will allow direct imaging of microstructural evolution, and will provide time-dependent data for comparison to fracture mechanics and processing models.
Improved Light Soaking Stability of R.F. Sputter Deposited Amorphous Silicon
Authors: Wynveen A. , Fan J. , Kakalios J. , Shinar J. 
Published: March 2011

ABSTRACTStudies of r.f. sputter deposited hydrogenated amorphous silicon (a-Si:H) find that the light induced decrease in the dark conductivity and photoconductivity (the Staebler-Wronski effect) is reduced when the r.f. power used during deposition is increased. The slower Staebler-Wronski effect is not due to an increase in the initial defect density in the high r.f. power samples, but may result from either the lower hydrogen content or the smaller optical gap found in these films.
Thermal Annealing of Light-Induced K Centers in Hydrogenated Amorphous Silicon Nitride
Authors: Tober E. D. , Sigari E. , Kanicki J. , Crowder M. S. 
Published: March 2011

ABSTRACTThe thermally-induced decay of light-induced, paramagnetic neutral silicon dan-gling bonds(K centers ) in hydrogenated amorphous silicon nitride thin films is monitored using electron spin resonance. The nitride films are of gate-quality and nitrogen-rich and are deposited at two different temperatures (250 and 400 °C). The kinetics for isothermal annealing of the light-induced K° states is dependent upon sample deposition temperature and is observed to follow a stretched exponential dependence, exp {— (t/τ)β}, upon annealing time (t). The stretched exponential factor, β, shows a non-linear dependence upon annealing temperature including temperature independent regimes. Thermal annealing is thermally activated with an apparent activation energy of ∼ 0.4 eV and is independent of deposition temperature. These results indicate that annealing is a dispersive process which involves hopping and multiple trapping or trap controlled hopping in the thermal annealing of light induced K centers in amorphous SiN1.6:H.
Radiation Detection with Evaporated Csl(TI) Coupled to a-Si:H Photodiode Layers
Authors: Fujieda I. , Cho G. , Drewery J. , Gee T. , Jing T. , Kaplan S. N. , Perez-Mendez V. , Wildermuth D. 
Published: March 2011

ABSTRACTCsl(TI) layers 100–1000 μm thick were evaporated on glass substrates from a crystal Csl(TI). When they were exposed to calibrated X-ray pulses, their scintillation properties were found to be comparable to those of a crystal Csl(TI). Single p particles from radioisotopes were successfully detected by these layers coupled to a crystalline Si photodiode. The light spread inside evaporated Csl(TI) was measured by an amorphous Si (a-Si:H) photodiode array coupled to evaporated Csl(TI) layers. Monolithic X-ray detectors were fabricated by evaporating Csl(TI) on a-Si:H photodiodes directly. The signal yield and noise of this prototype were 1.5×10+4 electrons/MeV and 3×10+4 electrons FWHM, respectively. Larger signal size and lower noise are expected by optimizing the photodiode design.
Ferroelectric Liquid Crystal Light Valve Using SiO2 / A-Si:H Photodiode
Authors: Horikawa T. , Tahata S. , Kaho S. , Masumi T. , Mikami N. , Takahashi K. , Nunoshita M. , Nakajima H. , Nishi K. 
Published: March 2011

ABSTRACTA new type of ferroelectric liquid crystal light valve (FLCLV) is presented. The design of the FLCLV is based upon the linear equivalent circuit analyses. A photosensor in the FLCLV consists of a metal-insulator-semiconductor (MIS) photodiode. A-Si:H doped with boron and nitrogen [a-Si:(:N:B)] is used in the MIS diode. The a-Si:H(:B:N) film has a dark-conductivity of less than 1×1012 S/cm and a high photosensitivity.Consequently, the writing characteristics of the FLCLV for a two dimensional (2D) image are evaluated. Using writing light of 630 nm and 1 mW/cm2, a high resolution capability of 120∼140 1p/mm is obtained.
Influence of Deposition Conditions on the optical and Electronic Properties of a-Ge:H
Authors: Paul W. , Jones S. J. , Marques F. C. , Pang D. , Turner W. A. , Wetsel A. E. , Wickboldt P. , Chen J. H. 
Published: March 2011

ABSTRACTWe have measured the optical absorption edge spectra for absorption coefficients between 1 and 105 cm-1, the photoluminescence spectra at 77 K, the conductivity-temperature relations, and the photoconductivity magnitude and spectral dependence for a series of r.f. glow discharge films of a-Ge:H. The films were deposited at the powered cathode and unpowered anode of a diode capacitive reactor having very different electric fields and plasma conditions, while substrate temperature, H2 dilution of a GeH4 plasma and applied r.f. power were varied. The structure of the films are radically different, with the anode-deposited films displaying a microstructure of low density material (voids) and the cathode-deposited films displaying homogeneity similar to that of device-quality a-Si:H. A self consistent explanation of the differences in measured optical and electronic properties is given, taking full account of the structural observations. From this analysis the conditions required for the production of a-Ge:H of good photoelectronic quality may be inferred. Preliminary structural, optical and photoelectronic data for a-Si1.x Gex :H of large x, prepared under conditions extrapolated from the a-Ge study, indicate significant improvements from current data in the literature.
1 / f Noise in Hydrogenated Amorphous Silicon
Authors: Parman C. , Kakalios J. 
Published: March 2011

ABSTRACTMeasurements of co-planar current fluctuations in n-type doped hydrogenated amorphous silicon (a-Si:H) find that the spectral density of the noise accurately obeys a 1/f frequency dependence over the frequency range of 1 Hz to 1 kHz for temperatures ranging from room temperature to 450K. The noise displays a power law dependence on the d.c. curent passing through the sample, with a temperature dependent power law exponent. In addition, the resistance of the a-Si:H as a function of time displays switching phenomena; a surprising result given the effective volume ( ∼10-6 cm3) of the sample.
The Effect of Hydrogen Dilution on the Deposition of Sige Alloys and the Device Stability
Authors: Yang L. , Chen L. , Catalano A. 
Published: March 2011

ABSTRACTWe have studied the structural and transport properties of a-Si1−x Gex:H alloys made by DC glow discharge of SiH4 and GeH4 with substantial amount of H2 dilution. The dilution ratio, i.e. H2/(SiH4 + GeH4), was varied up to 40:1. IR spectroscopy revealed that H2 dilution greatly suppresses the tendency of forming microvoids due to Ge incorporation. Photoconductivity and ambipolar diffusion length, which represent transport properties of electrons and holes respectively, are also significantly improved by using H2 dilution. At a dilution ratio of 20:1, the electron υτ product reached 10-6 cm2/V at a bandgap 1.55 eV which is even larger than that of a device quality a-Si:H. Solar cells using alloy i-layers made with H2 dilution were fabricated. The stability of the devices under light exposure was found to be much improved with increasing H2 dilution, suggesting a strong correlation between the stability and the density of microvoids.
Temperature Dependence of the Growth and Saturation of Light-Induced Defects in a-Si:H
Authors: Isomura M. , Hata N. , Wagner S. 
Published: March 2011

ABSTRACTWe report new experimental data on the light-soaking of a-Si:H with a Kr-ion laser at an optical generation rate G of at least 4×1021 to 3×1022 cm-3s1. We studied the temperature and intensity dependence of the saturation of the defect density and found that the saturation value of light-induced defects (Nsat) is insensitive to temperature and light intensity below about 90°C. Above 90°C Nsat drops with increasing temperature. This behavior can be explained within the defect pool model by a limited number of defect sites coupled with an annealing process.
Amorphous Silicon Thin-Film Transistors Modified by Doping and Plasma Treatment of the Nitride
Authors: Nickel Norbert , Saleh Rosari , Fuhs Walther , Mell Helmut 
Published: March 2011

ABSTRACTThin—film transistors (TFTs) were prepared by the glow—discharge deposition of amorphous silicon nitride (a—SiNx:H) and amorphous silicon (a—Si:H). The properties of these TFTs were varied in two ways: a) doping of the amorphous silicon film with phosphine or diborane and b) exposure of the a—SiNx:H film to an oxygen plasma prior to the deposition of the a—Si:H layer. The TFTs are characterized by measurements of the transfer characteristic, ISD(VG) and of the effective density of interface states, Ni(E), using a transient current spectroscopy (TCS). The dependence of Ni(E) on the Fermi—level position in the a—Si:H film suggests that for EC—EF > 0.6eV this quantity is mainly determined by interface related defect states whereas for Ec,—EF <0.6eV it is determined by doping—induced defect states. The exposure to the oxygen plasma results in a reduction of Ni in both the upper and lower half of the gap and in an improvement of the characteristic, in particular in p—channel TFTs. These changes are discussed in terms of the chemical-equilibrium or defect—pool concept.
The Application of Hydrogenation to Amorphous Silicon Thin Film Transistors for the Decrease of the off Current
Authors: Kobayashi K. , Murai H. , Hayama M. , Yamazaki T. 
Published: March 2011

ABSTRACTThe influence of hydrogenation on OFF current of TFTs with a bottom gate staggered structure has been investigated. The hydrogenation is done by exposing the surface of the a-Si:H channel layer to H2 plasma. The hydrogenation decreases the OFF current by more than one order of magnitude. The decrease in the OFF current is attributed to the increase in the density of states at the interface between the a-Si:H channel layer and the SiN passivating layer.
Reduction of Threshold Voltage Shift by Bias Annealing of Hydrogenated Amorphous Silicon Thin Film Transistors
Authors: Deane S. C. , Milne W. I. , Powell M. J. 
Published: March 2011

ABSTRACTWe show that bias annealing modifies the rate of threshold voltage shift under bias stress in the regime where state creation dominates. Previously we have shown that the deep state distribution near the interface of a-Si:H TFTs can be altered by bias annealing. In particular the energy position of the defects can be made high or low in the energy gap, consistent with the defect pool model.In this paper, we relate the kinetics of new state creation at room temperature to a particular equilibrated defect distribution. In particular we show that the rate of state creation can be reduced by prior bias annealing.
Amorphous Silicon Thin—Film Transistors with Non—Uniform Distribution of Gap States
Authors: Saleh Rosari , Nickel Norbert , Fuhs Walther , Mell Helmut 
Published: March 2011

ABSTRACTA theoretical study of the properties of a-Si:H thin-film transistors (TFTs) has been performed using uniform and non-uniform distributions of gap states in the a-Si:H layer. The potential profile in the semiconductor is calculated in a straightforward way by solving Poisson's equation numerically. From the band bending the source-drain current ISD(VG) of the TFT is predicted. In addition we calculate the transient discharge current I(t) generated by switching the gate voltage from positive to negative values. In experimental studies such transients are analyzed to obtain an effective density of interface states, Ni(E). We find that N;(E) depends little on the spatial variation of gap states, N(E,x), but sensitively on the energy distribution of N(E,x). It is shown that experimental N;(E) curves and ISD(VG) characteristics from the same sample can be fitted by the same N(E,x) which however cannot be unequivocally determined.
The Study of the Optoelectronic Properties of a-SiGe:H Photodiodes
Authors: Kuo L. C. , Lee C. C. , Chen K. H. , Fang Y. K. , Yu C. H. 
Published: March 2011

ABSTRACTWe have studied the spectrum of various types of a-SiGe:H alloys for pin and Schottky barrier photodlodes, in which the band gaps of the a-SiGe:H vary between 1.75 eV and 1.35 eV. It has been found that the spectral re-ponse of the Schottky barrier diode shifts significantly to longer wavelength and the quantum efficiency decreases with an increase in i layer thickness. However, for the pin diode, an increase in the i layer thickness can hardly shift the spectrum to longer wavelength. For both pin and Schottky barrier diodes, the quantum efficiency can be increased by increasing the reverse bias. Therefore, an enhanced spectrum with a maximum at 800nm and a tail to lun can be achieved for a reverse-biased a-SiGe:H Schottky barrier diode. The results indicate that a-SiGe:H has a great potential for a low cost infrared photodetector.