bluuebunny/crossref_metadata_2025 huggingface dataset:
Structure and Properties of WNx Thin Film on GaAs Substrate
Authors: Mao Dali , Yu Weili , Lin Dongliang , Lin T.L.
Published: March 2011

In this paper, the effect of sputtering parameters on the interfacial reaction and the electronic properties of the WNx system were reported.

The report showed that W and W2 N phases were observed in WNx film on GaAs substrate annealed at 800–900°C, in which no UN phase was found and W2N was the stable phase. Throughout the WNx film, W,N distributed uniformly. There was no interdiffusion between WN, films and GaAs substrate annealed at 80°C. However, at 900°C, there was some N in-diffusion to substrate, but no Ga or As out-diffusion. The electrical resistivity p of WNx films increased with increasing nitrogen partial pressure r. All the samples with r<0.2 showed the p below 200 µΩcm. By the I/V measurement, the Schottky Barrier Height was obtained with the value: øB=0.93ev, n=1.30 for WNx/n-GaAs contact that annealed at 850°C, 15 minutes.
Effect of Substrate Orientation on CdTe Film Growth by OMVPE
Authors: Snyder D.W. , Ko E.I. , Mahajan S. , Sides P.J.
Published: March 2011

Most CdTe epilayers grown by OMVPE have been deposited on two low index orientations: {111}Te and {100}. In this study we have examined the OMVPE of CdTe as a function of deposition temperature on CdTe substrates having the four low index orientations ({111}Te, P111}Cd, {110}, and {100}) and on the {211}Te and {211}Cd orientations. Results are presented for deposition rate, surface morphology, and structural quality of the epilayers.
Near Ir Emissions from Er, Tm, AND Pr Implanted GaAs and AlGaAs
Authors: Pomrenke G.S. , Yeo Y.K. , Hengehold R.L.
Published: March 2011

Optical properties of Er, Tr, and Pr ion implanted GaAs and A1xGa1−xAs were investigated using photoluminescenoe. For Er, the characteristic sharp emissions around 1.54 μm were observed at sample temperatures as high as 296 K, which are due to the transitions between the weakly crystal-field-split spin-orbit levels 4I13/2 and 4I15/2 of Er3+ (4f11) ; the strongest luminescence signal was from A10.4Ga0 6As. For Tm, the sharp 4f-emissions were observed between 1.22 to 1.33 μm at sample temperatures up to 200 K, and are due to the transitions between levels 3H5 and 3H6 of Tm3+ (4f12). For Pr, three sets of 4f-emissions were observed at 1.05, 1.35, and 1.6 μm due to transitions between levels 1G4∼3H4, 1G4∼3H5, and 3F3 ∼ 3H4 of Pr3+(4f2), respectively, and the highest temperature at which sharp emissions were observed was around 175 K.
II-VI Semiconductor Heterostructures: Pointers to Appropriate Analysis Techniques
Authors: Bithell Erica G.
Published: March 2011

Approximate methods are used, for a variety of II–VI semiconductor alloys, to estimate the sensitivity to composition change of quantitative transmission electron microscopy techniques which have proved successful in characterising III–V heterostructures. It is shown that bright field thickness fringe matching at the [001] axis is likely to prove relatively more successful than 200 dark field intensity measurement for many alloy systems. It is also noted that alternative methods would be necessary if quantitative characterisation of (Mn,Zn) compounds were required.
In Situ Spectroscopic Ellipsometry for Real Time Semiconductor Growth Monitor
Authors: Johs Blaine , Meyer Duane , Cooney Gerald , Yao Huade , Snyder Paul G. , Woollam John A. , Edwards John , Maracas George
Published: March 2011

A modular spectroscopic ellipsometer for in situ and ex situ materials analysis is described, and results for in situ MBE growth of GaAs/AlGaAs are reported.
Thermoelectric Power in Quantum Confined Bismuth Under Classically Large Magnetic Field
Authors: Ghatak Kamakhya P. , Biswas S. N.
Published: March 2011

In this paper we studied the thermoelectric power under classically large magnetic field (TPM) in quantum wells (QWs), quantum well wires (QWWS) and quantum dots (QDs) of Bi by formulating the respective electron dispersion laws. The TPM increases with increasing film thickness in an oscillatory manner in all the cases. The TPM in QD is greatest and the least for quantum wells respectively. The theoretical results are in agreement with the experimental observations as reported elsewhere.
On the Photoemission from Ternary and Quaternary Alloys Systems Under Strong Magnetic Quantization
Authors: Ghatak Kamakhya P.
Published: March 2011

We study the photomission from ternary and quanternary alloys systems by formulating the respective expressions considering the spin & broadening of Landau levels. It is found taking n-Hg1−x CdxTe and In1−xGaxAsyP1−y lattice matched to InP as examples of ternary and quaternary alloys respectively that the photoemission exhibits oscillatory magnetic field dependence and increases with increasing electron concentration in spiky manner for both the cases. The numerical magnitudes of photoemission in ternary alloys are greater than that of the quaternary systems and the theoretical formulations are in agreement with the experimental observations as reported elsewhere.
Micro-Ellipsometric Measurements of Strained Layer Structures
Authors: Xiong Yi-Ming , Snyder Paul G.
Published: March 2011

Ellipsometric measurements are extremely sensitive (on the monolayer scale) to layer thicknesses and surface or interfacial roughness. However, lateral resolution is poor, because of the need for a highly collimated ( ≤0.05° ) and therefore large diameter (typically 1 mm) optical beam. Many materials are inhomogeneous on a smaller lateral scale, in which case conventional ellipsometry simply measures some average value. Focusing the beam leads, for an incoherent light source, to an uncollimated beam and a consequential spread in the angle of incidence, which in turn degrades the sensitivity. We describe here a technique for focusing a coherent, Gaussian laser beam to a minimum spot size of about 30μm × 130μm, while maintaining a negligible effective spread in angle of incidence. The technique was used to measure semi-insulating (S.I.) GaAs, laser annealed ion implanted GaAs, and InIGa1−xAs strained layer structures.
Ion Milling Damage in InP and GaAs
Authors: Pearton S. J. , Chakrabarti U. K. , Perley A. P.
Published: March 2011

Near-surface damage created by Ar+ ion milling in InP and GaAs was characterized by capacitance-voltage, current-voltage, photoluminescence, ion channeling and transmission electron microscopy. We find no evidence of amorphous layer formation in either material even for Ar+ ion energies of 800eV. Low ion energies (200eV) create thin (≤100 Å) damaged regions which can be removed by annealing at 500°C. Higher ion energies (≤500 eV) create more thermally stable damaged layers which actually show higher backscattering yields after 500°C annealing. Heating to 800°C is required to restore the near-surface crystallinity, although a layer of extended defects forms in GaAs after such a treatment. No dislocations are observed in InP after this type of annealing. The electrical characteristics of both InP and GaAs after ion milling at ≥500 eV cannot be restored by annealing, and it is necessary to remove the damaged surface by wet chemical etching. For the same Ar+ ion energies the damaged layers are deeper for InP than for GaAs-after 500 eV ion milling at 45° incidence angle, removal of ∼485 Å and ∼650 Å from GaAs and InP respectively restores the initial current-voltage charaeteristics of simple Schottky diodes.
SiGe/Si Heterojunction Internal Photoemission Long-Wavelength Infrared Detectors
Authors: Lin T. L. , Ksendzov A. , Dejewski S. M. , Jones E. W. , Fathauer R. W. , Krabach T. N. , Maserjian J. , Terhune R. W.
Published: March 2011

There is a great need of long-wavelength (8-17μm) infrared (LWIR) focal plane arrays (FPAs) for a variety of space and defense applications. Si-based infrared detectors offers several important advantages, including good uniformity, low cost, and easy integration with Si readout circuitry either monolithically or by indium bump bonding to form large arrays. We report here a novel SiGe/Si heterojunction internal photoemission (HIP) long-wavelength infrared (LWIR) detector fabricated by molecular beam epitaxy [1].
Traps and Trap-Assisted Tunneling in HgCdTe Photodiodes
Authors: Rosenfeld D. , Bahir G.
Published: March 2011

The performance of HgCdTe photodiodes, realized for the purpose of thermal imaging in the 8–12μm atmospheric window, is often limited by traps and by the tunneling mechanism associated with them. This mechanism dominates the leakage current and the dynamic resistance in diodes operated in reverse bias above 1OOmV and at temperatures below 77K. In usual working conditions, namely low reverse bias and a temperature of 77K, the presence of traps and the tunneling mechanism associated with them, degrades the performance of the diodes. Although the diffusion mechanism dominating the leakage current and the dynamic resistance in diodes operated under the above conditions is of major concern, the presence of the traps should not be ignored. The traps result in shorter electron lifetime in the bulk as well as in the generation of 1/f noise, which degrades the device's figures of merit such as NETD. Therefore, a thorough understanding of the trapassisted tunneling mechanism is a prerequisite to studying its impact on the device performance.

In this paper we present a model which describes the connection between the leakage current associated with the traps and the trap characteristics: concentration, energy level and capture cross-section. The validity of the model is confirmed by the good fit between measured and calculated characteristics of the diodes.
Advances in Cone-Beam Reconstruction for the Analysis of Materials
Authors: Smith Bruce D.
Published: March 2011

The utility of cone-beam tomography in the analysis of material has been demonstrated by Feldkamp et al [1]. Recent advances in cone-beam tomography will enhance its usefulness in the analysis of material.
Three-Dimensional Nuclear Magnetic Resonance and X-Ray Microtomographic Imaging of Composite Materials
Authors: Dieckman S.L. , Rizo P. , Gopalsami N. , Botto R. E.
Published: March 2011

This paper presents a new, three-dimensional (3-D) nuclear magnetic resonance (NMR) imaging technique for spatially mapping proton distributions in green-state ceramic composites. The technique is based on a 3-D back-projection protocol for data acquisition, and a reconstruction technique based on 3-D Radon transform inversion. In principle, the 3-D methodology provides higher spatial resolution of solid materials than is possible with conventional slice-selection protocols. The applicability of 3-D NMR imaging has been demonstrated by mapping the organic additive distribution (2.5 wt.%) in cold-pressed Si34 whisker-reinforced Si34 ceramic composites. Three-dimensional X-ray computed tomography (CT) also has been employed for mapping voids and inclusions within the composite specimen. Combining information from both imaging modalities provides an extremely powerful nondestructive evaluation tool for materials characterization.
Characterization of Low Density Carbon Foams by X-ray Computed Tomography (CT) and Ion Microtomography (IMT)
Authors: Moddeman W. E. , Kramer D. P. , Firsich D. W. , Trainer P. D. , Yancy R. N. , Weirup D. L. , Logan C. M. , Pontau A. E. , Antolak A. J. , Morse D. H.
Published: March 2011

Two NDT techniques were used to characterize low-density, microcellular, carbon foams fabricated from a salt replica process. The two techniques are x-ray computed tomography (CT) and ion microtomography (IMT); data are presented on carbon foams that contain high-density regions. The data show that densities which differ by <10% are easily observable for these low density (<100 mg/cm3) materials. The data reveal that the carbon foams produced by this replica process have small density variations; the density being ∼30% greater at the outer edges than when compared to the interior of the foam. In addition, the density gradient is found to be rather sharp, that is the density drops-off rapidly from the outer edges to a uniform one in the interior of the foam. This edge build-up in carbon density was explained in terms of polymer concentrating on the foam exterior during drying which immediately followed a polymer infusion processing step. Supporting analytical data from other techniques show the foam material to be >99.9 % carbon
NMR Imaging of Elastomers and Porous Media
Authors: Komoroski Richard A. , Sarkar Subhendra N.
Published: March 2011

NMR imaging has been applied to some elastomeric materials of industrial interest. The T2s of common elastomers, Particularly after filling and curing, are sufficiently short That spin-echo sequences at submillisecond echo times cannot Produce T2 independent images. The sensitivity to T2 Potentially makes spin echo imaging a good probe of elastomer Blend composition, as demonstrated for a series of filled and Cured cis-polybutadiene, styrene-butadiene rubber blends. The Technique can be used to distinguish good and bad carbon black Dispersion in actual tire tread samples. The configuration of Polyester tire cord, voids, rubber layer boundaries, differences of molecular mobility and composition, and other inhomogeneities can be detected in end-product tire samples. The value of isotropic voxels at 80–100 um and the effect of resolution Relative to pore size are demonstrated on a model, H2O-saturated Porous glass disk of 200-um average pore size. The feasibility of multinuclear NMR imaging for fluid-specific characterization of porous materials such as oil cores is demonstrated for 7Li and 19F
Development of Quantitative X-Ray Microtomography
Authors: Deckman H. W. , Dunsmuir J. H. , D'Amico K. L. , Ferguson S. R. , Flannery B. P.
Published: March 2011

We have developed several x-ray microtomography systems which function as quantitative three dimensional x-ray microscopes. In this paper we describe the evolutionary path followed from making the first high resolution experimental microscopes to later generations which can be routinely used for investigating materials. Developing the instrumentation for reliable quantitative x-ray microscopy using synchrotron and laboratory based x-ray sources has led to other imaging modalities for obtaining temporal and spatial two dimensional information.
Temperature Dependent Defect Density Calculated from Activated Conductivity of a-Si:H
Authors: Drusedau T. , Kirbs V. , Fiedler H.
Published: March 2011

Thermally activated conductivity of a—Si:H at a slow cooling rate of 0.3 K/min is connected with temperature dependent changes of the mobility gap states. By means of the Fermi—level shift calculated from these data and a density of states model it is possible to determine this dependence. The results mainly reveal a decrease of the defect state density by about a tenth between 375 K and 400 K.
Defect Creation by Forward Bias in Amorphous Silicon P-I-N Diodes
Authors: Street R. A. , Hack M.
Published: March 2011

Metastable defects are induced in a-Si:H p-i-n devices by a forward bias current. The defect density increases approximately as the square root of time, reaching saturation at long inducing times, and with a weak temperature dependence. Current-induced defect annihilation is observed, in which the current causes a reduction in the previously induced defect density. Calculations of the changes in the forward bias current for different bulk defect densities are able to account for the measured results.
Metastable Defects in a-SiOx:H and a-SiCx:H
Authors: Deng X.-M. , Hamed A. , Fritzsche H. , Tran M. Q.
Published: March 2011

Metastable defects are created in hydrogenated amorphous silicon alloys presumably by the same mechanism as in a-Si:H. We find metastable defects created in a-SiCx:H and a-SiOx:H by hopping injection of photocarriers from adjacent a-Si:H layers. In a-SiCx:H the defects can be created only below T=150K, they anneal at TE=400K. In a-SiOx:H they are created at or below T=300K, they anneal at TE=480K. The anneal temperature is nearly independent of the creation temperature. The defects are detected by their charge exchange with adjacent a-Si:H layers whose conductance is thereby changed.
Characterization of A-Si : H and A-SiGe : H Films in Liquid Crystal Light Valve
Authors: Qiao Jianmin , Han Gaorong , Du Piyi , Han Weiqiang , Huang Wanquan , Ding Zishang
Published: March 2011

A-Si : H and a-Si : H/a-SiGe : H heterojunctions have been prepared as the photoconductors in the liquid crystal light valves. The impedance matching conditions of the a-Si : H and the heterojunction in the valves have been carefully analysed, which has shown that the adjustment for the capacitance of the photoconductor is the key procedure for the matching, but the low photocapacitance effect in the a-Si : H limits the further improvements on the matching. The formation of the a-Si : H/a-SiGe : H diode promotes the photocapacitance effect in the photoconductor, and the matching behavior in the valve is greatly improved.
Theoretical and Experimental Analysis of Amorphous Silicon Image Sensor
Authors: Su Chih-Yuang , Su Ying-Wen , Hwang Huey-Liang
Published: March 2011

The experimental results for different structures of contact image sensor are reported in this paper, which includes Schottky barrier, p-i junction, p-l-n junction, and MIS structures. The J-V characteristics of p-i-n a-Si: H contact image sensor under dark and illuminated conditions have been simulated by solving the Poisson's equation and the continuity equations, and the results are correlated with the experiments. The dependence of the dark and photo currents on the parameters such as the density of states in the gap, intrinsic layer width, dopant concentrations of p* layer and n+ layer are discussed.
Characteristics of a-Si:H Schottky Photodiode by Using Mo Barrier Metal at Al/ITO Contact
Authors: Sakai Yoshihiko , Hotta Hiroyuki , Hamada Tsutomu , Ito Hisao , Ozawa Takashi
Published: March 2011

An ITO/a-Si:H Schottky Photodiode(PD) with Mo as a barrier metal at Al/ITO contact has been made and it shows its useful characteristics. The PD without Mo had high dark current proportional to the contact-via-hole area and quite a large resistance at the contact area. The XPS analysis of the Al/ITO interface indicated that Al and O in ITO mutually diffused around the interface, resulting in the degradation of ITO/a-Si:H Schottky barrier. Most of the diffused Al formed aluminum oxide (AI2O3) at the Al/ITO interface, and which caused high resistance of the contact area.

Inserting Mo barrier metal 500Å thick, the dark current got less dependent on the contact area and decreased by 2/3 on 254×227 μm PD with 106×106//m contact-via-hole. The contact resistance also decreased significantly to 1/105 of those of the conventional ones. From the XPS analysis of interface, it was also found that Mo barrier metal prevented Al diffusion into the ITO and formation of aluminum oxide at the interface.
Results from First Principles Molecular Dynamics Simulations on a-Si
Authors: Fedders Peter A. , Drabold David D.
Published: March 2011

We report on some recent results of first principles molecular dynamics simulations on a-Si. These simulations yield interesting results that challenge the standard beliefs about what constitutes a defect, how light induced defects arise, and about the origins of conduction band tailing.
Effects of Annealing Time and Temperature on Hydrogen in Doped and Intrinsic Amorphous Silicon
Authors: Ready S. E. , Boyce J. B.
Published: March 2011

The local environment and diffusion of hydrogen in hydrogenated amorphous silicon (a-Si:H) depend on both temperature and doping. Previous studies of hydrogen evolution indicate that the manner in which hydrogen diffuses and desorbs from the material depends on doping and may occur at relatively low temperatures over extended time frames. We have examined the microstructure of hydrogen in intrinsic, boron doped and phosphorous doped a-Si:H as a function of annealing temperature and annealing time using hydrogen NMR. Changes in both the H NMR spectrum and spin-lattice relaxation times occur. We find annealing time has only a small effect on these parameters, whereas the annealing temperature has a substantial effect. The bonded-H content drops and the molecular-H2 content is seen to decrease slightly as the samples are annealed to higher temperatures. However the bonded-H remains essentially constant for long time, low-temperature anneals, while the molecular-H2 content is also seen to diminish slightly. The changes are more profound for B-doped samples than for P-doped or intrinsic material, consistent with the conclusions of other studies.
In Situ IR Absorption Study of H Bonding in a-Si:H Thin Films
Authors: Katiyar M. , Feng G. F. , Abelson J. R. , Maley N.
Published: March 2011

We have used real time, in situ infrared reflectance spectroscopy to study the evolution of Si-H bonding during the growth of hydrogenated amorphous silicon (a-Si:H) by dc magnetron reactive sputtering. The surface Si-H stretching mode (2100 cm-l) is observed in films 5 Å thick and the 2000 cm-l mode, which has been attributed to isolated monohydrides in the bulk, appears for thickness (d) < 10–15 Å For larger thicknesses the intensity of both modes increases approximately linearly. These trends are interpreted in terms of the nucleation and coalescence of islands for d> 15 Å followed by bulk-like growth.
Lattice Relaxation of Deep Defects in Light-Soaked N-Type Hydrogenated Amorphous Silicon
Authors: Leen Thomas M. , David Cohen J.
Published: March 2011

We report evidence for a deep defect exhibiting very large lattice relaxation in n-type a-Si:H. In light-soaked partially-annealed samples with low phosphorus doping levels one obtains large controlled variation of the Fermi energy position in the mobility gap. Examination by photocapacitance spectroscopy of a sample having a Fermi energy near the minimum in the density of states shows dramatic change in the shape of the photocapacitance spectra. We interpret this as strong evidence for lattice relaxation of deep defects.
Excimer Laser Crystallized Amorphous Silicon Films: Effects of Shot Density and Substrate Temperature
Authors: Johnson R. I. , Anderson G. B. , Ready S. E. , Boyce J. B.
Published: March 2011

Laser crystallization of a-Si thin films has been shown to produce materials with enhanced electrical properties and devices that are faster and capable of carrying higher currents. The quality of these polycrystalline films depends on a number of parameters such as laser energy density, shot density, substrate temperature, and the quality of the starting material. We find that the average grain size and transport properties of laser crystallized amorphous silicon films increase substantially with laser energy density, increase only slightly with laser shot density, and are unaffected by substrate temperatures of up to 400°C. The best films are those processed in vacuum but films of fair quality can also be obtained in air and nitrogen atmospheres.
Annealing Characteristics of Amorphous Silicon Alloy Solar Cells Irradiated with 1.00 MeV Protons
Authors: Abdulaziz Salman S. , Woodyard James R.
Published: March 2011

a-Si:H solar cells were irradiated with 1.00 MeV proton fluences in the range of 1.00E14 to 1.2 5E15 cm-2. Annealing of the short-circuit current density was studied at 0, 22, 50, 100 and 150 °C. Annealing times ranged from an hour to several days. The measurements confirmed that annealing occurs at O °C and the initial characteristics of the cells are restored by annealing at 200 °C. It is proposed that the degradation in the short-circuit current density with irradiation is due to carrier recombination through the fraction of D° states bounded by the guasi-Fermi energies. The time dependence of the rate of annealing in the short-circuit current density appears to be consistent with the interpretation that there is dispersive transport mechanism which leads to the annealing of the irradiation induced defects.
Highly Conductive Microcrystalline Silicon Layers for Tunnel Junctions in Stacked Amorphous Silicon based Solar Cells.
Authors: Prasad K. , Kroll U. , Finger F. , Shah A. , Dorter J-L. , Howling A. , Baumann J. , Schubert M.
Published: March 2011

We have investigated the influence of substrate temperature on the optoelectronic and structural properties of heavily doped μc-Si:H, prepared with the Very High Frequency Glow Discharge process. At substrate temperatures as low as 160°C we obtain, for films with 0.5μm thickness, maximum conductivities of 100 S/cm and 20 S/cm for  and
 material, respectively. Starting from these values the deposition parameters were optimised for ultrathin layers having thicknesses in the range of 100 to 500Å. We observe that boron doping plays a critical role in the crystallisation of ultrathin films. The thinnest layers investigated so far show conductivities of 0.2 S/cm at d=100Å for , and 0.2 S/cm at d=250Å for
 material. These properties make μc-Si:H films attractive candidates to form tunnel junctions in tandem solar cells.
Improvement of a-Si:H P-I-N Devices using Zinc Oxide based Back-Reflectors
Authors: Kothandaraman C. , Tonon T. , Huang C. , Delahoy A. E.
Published: March 2011

The conversion efficiency of a-Si:H P-I-N photovoltaic devices was improved using aluminum doped zinc oxide thin films between the n-layer and the metal electrode. The improvement is due to the increase in the quantum efficiency, mainly in the wavelengths between 550 – 750 nm, and is attributed to the increased reflectivity of the zinc oxide/metal layer over the conventional metal electrode. The dependence of the enhancement, on the thickness of the zinc oxide layer and the back metal electrode was studied and the optimal configuration was identified as 800 angstroms of zinc oxide backed by a silver electrode. Photostability studies of devices containing these back-reflectors showed that their stability to light-soaking was comparable to conventional devices establishing the use of zinc oxide back-reflectors as a viable way of increasing the efficiency of a-Si:H devices without compromising their stability.
Amorphous Hydrogenated Silicon (a-Si:H) Photovoltaic Thin Films Deposited onto Ultra-Low Density Aerogels
Authors: Hotaling S. P. , Proni F. P.
Published: March 2011

Amorphous Hydrogenated Silicon (a-Si:H) photovoltaic thin films have been deposited onto ultra low density (ULD) silica aerogel substrates using plasma enhanced chemical vapor deposition (PECVD). The techniques and results of ULD aerogel fabrication, surface treatment, thin film deposition and photovoltaic (PV) characterization are discussed. DC photbcurrent and transient time of flight measurements were performed for the PV characterization, while ellipsometry, transmission optical spectrophotometry, scanning electron microscopy (SEM) and low magnification optical microscopy (×64) were used to obtain qualitative and quantitative surface morphology, microstructure and film thickness data. This research indicates that ULD aerogels may be used as substrates for dielectric and metallic thin films which have electrical, optical and mechanical properties comparable to films deposited onto conventional substrates such as glass, metals or plastics. These data taken together with the lightweight of the ULD aerogels may be of interest to the space based sensor community as a possible route to large, lightweight photonic sensors or PV arrays. These results thus indicate that ULD aerogels could be used as substrate materials for other thin films of interest to the PV community, for example, we have produced ultra lightweight reflective optics using this fusion of solgel and thin film technologies [1].
Ultra-High-Sensitive Image Pickup Tubes Using Avalanche Multiplication in a-Se.
Authors: Tsuji K. , Ohshima T. , Hirai T. , Gotoh N. , Tanioka K. , Shidara K.
Published: March 2011

Extremely high-sensitive image pickup tubes with sensitivities 1000 times higher than those of conventional tubes are fabricated using the avalanche phenomenon in a-Se as photoconductive targets. The excess avalanche noise of a video signal is found to be much less than that expected, based on the carrier ionization rates. The frequency spectra of the noise currents of both the pickup tubes and sandwich-type photocells are examined. The results are compared with those of a simulation, and it is found that the excess noise can be reduced by the charge-storage operation of imaging devices.
Characteristics of a-Si Pixel Arrays for Radiation Imaging
Authors: Fujieda I. , Nelson S. , Street R. A. , Weisfield R. L.
Published: March 2011

Two-dimensional a-Si photodiode arrays with the a-Si TFT readout scheme were fabricated. Some performance characteristics were investigated for detecting visible light, X-ray and γ ray. Arrays of 64×40 1mm2-pixels have good uniformity with ± 1 % in linearity variation, ± 10 % dark current variation and ± 5 % sensitivity variation. The cross-talk between adjacent pixels was found to be negligible so that the intrinsic spatial resolution was determined entirely by the pixel size. Due to the high resistivity of a-Si photodiodes and TFTs, charges generated by pulsed light illumination were retained in photodiodes for a long period of time. This enables the accumulation-mode operation for detecting low-intensity light, where only one image is obtained over a long integration time. An encapsulated Co-57 source (3 μ.Ci) was successfully imaged with 5 sec integration. Alternatively, the array can be operated by the cine-mode for detecting high-intensity light, where a number of images are obtained successively.
Defect Equilibration and Metastability in Low-Spin-Density a-Si:H
Authors: McMahon T. J.
Published: March 2011

To first order, the relaxation kinetics of thermally generated defects with spin observed in two differently prepared, 60-μm-thick undoped hydrogenated amorphous silicon (a-Si:H) films are consistent with a two-level system having a formation energy of 0.35 eV and an anneal barrier of 2.1 eV. However, closer examination of how relaxation depends on thermal treatments reveals the complexity that might be expected from a disordered material. For example, the stabilization of many spins quenched in from 260°C can be increased by annealing at an intermediate temperature: It appears that, some 260°C defects equilibrating further at 205°C will relax and become more locked-in configurationally than defects simply equilibrated at 260°C. Crossover of annealing data is the result. Crossover cannot be explained with two-level system approaches. Models in which a spin can be stabilized with alternate structural configurations must be invoked.
Comments on the Determination of Defect Density in a-Si:H Alloys by Integrating the Sub-Bandgap Optical Absorption Coefficient
Authors: Li Y.-M. , Paul W.
Published: March 2011

The validity of determining the defect density in a-Si:H and its alloys by integrating the sub-bandgap optical absorption coefficient is examined. It is shown that a formula derived for estimating Si-H bond density has been incorrectly applied to defect related absorption. In addition, the complex defect absorption processes have been oversimplified, by assumption, to the case of a single type of transition. Further, in practice, the defect absorption spectrum can not be unambiguously obtained at energies near and above the low end of the optical absorption edge. It is concluded that die integration method for quantitative defect density determination should be viewed at best as an empirical practice with considerable arbitrariness.
Defect States in Hydrogenated Amorphous Silicon-Sulphur Alloys by ESR and PAS
Authors: Han Gaorong , Qiao Jianmin , Du Piyi , Jiang Zhonghua , Ding Zishang
Published: March 2011

We have presented ESR and PAS measurements for a series of a-SiS:H and a-Si: H films deposited by glow discharge at different parameters. The spin density in a-SiS:H alloys measured by ESR is essentially independent of the sulphur content, while the density of defects measured by PAS increases significantly with the increasing of sulphur content. The ESR signals in a-SiS:H alloys strongly depend on both annealing and illumination. The spin density increases up to 540°C and then decreases with raising annealing temperature for a-SiS:H and a-Si:H alloys. The results suggest that some new defects such as molecular hydrogen and microvoids are appeared when addition of sulphur to a-Si:H films.
Nuclear Spin-Lattice Relaxation Via Paramagnetic Centers in Amorphous Hydrogenated Silicon (a-Si:H)
Authors: Cheung Man Ken , Petrich Mark A.
Published: March 2011

This is the first NMR study of a-Si:H which measures the 29Si spin-lattice relaxation time, T1. Measurements of T1 are useful in learning about the silicon network structure and the localized states within the mobility gap. Dangling-bonds are randomly distributed in device quality materials but are inhomogeneously distributed in nondevice quality materials. There are two simultaneously occurring dangling-bond spin-lattice relaxation mechanisms: one is through the spin-orbit coupling modulated by thermal excitation of “two-level systems”, and the other is through hopping conduction between localized states near the Fermi level.
Problems in Large Size Amorphous Silicon Plate Manufacturing
Authors: Schmttt J. P. M.
Published: March 2011

The growing aSi:H based component industry needs large PECVD machines for high throughput coating of flat substrates up to 1 meter in size. Deposition uniformity can be affected by gas depletion in diffusion and laminar gas flow geometries. Deposition rate is shown to be in conflict with large size uniformity. Main uniformity problems are found to originate from uneven RF voltage distribution, the effect is shown to be amplified near plasma equilibrium transitions. Contamination, a key factor for production quality, is controlled by the hot pressurized plasma box by both reducing unwanted background gas near UHV level and by allowing systematic fast plasma cleaning without machine corrosion or post contamination. Powder formation and dynamic is discussed based on several novel experiments and powder formation threshold is shown to be pushed away if the plasma is made intermittent.
Characterization of Electron Cyclotron Resonance Plasma-Deposited Hydrogenated Amorphous Silicon and Related Alloy Films
Authors: Essick J. M. , Pool F. S. , Shing Y. H. , Holboke M. J.
Published: March 2011

We characterized a-Si:H films deposited by the electron cyclotron resonance (ECR) microwave plasma-enhanced CVD technique with the purpose of comparing ECR film quality widi that of films deposited by the rf plasma-enhanced CVD method. These ECR films were deposited in the 1–10 mT pressure region under a variety of growth conditions. Our investigations reveal the following typical properties for intrinsic ECR-deposited a-Si:H: (1) high photosensitivity as indicated by a light-to-dark DC conductivity ratio of up to 2×106, (2) a Tauc gap in the range of 1.75–1.85 eV, (3) an Urbach slope of 45–60 meV as determined by CPM and (4) an integrated deep defect density of 0.5–2×1016 cm-3 with Ec - Ef = 0.74–0.87 eV as determined by drive level profiling and junction capacitance vs. temperature scans. Variations of these quantities with deposition temperature, hydrogen dilution and magnetic field profile are discussed. Our results indicate that ECR-deposited a-Si:H is of comparable quality to a-Si:H deposited by the rf plasma glow discharge technique. ECR deposition conditions for a highly conductive type of a-Si:H film also are discussed. This material, while only slightly photosensitive and possessing an Urbach slope of over 100 meV, has a light DC conductivity of 3×10-4 (Ωcm)-1. Boron doping of this material produces a conductivity of 5×10-2 (Ωcm)-1.
Growth and Characterization of Hydrogenated Amorphous Silicon using Liquid Organic Sources
Authors: Gaughan K. , Hershgold S. , Viner J. M. , Taylor P. C.
Published: March 2011

The uses of liquid sources such as tertiarybutylphosphine (TBP) for n-type doping in hydrogenated amorphous silicon (a-Si:H) and ditertiarybutylsilane (DTBS) and n-butylsilane (NBS) for hydrogenated amorphous silicon-carbon alloys (a-SiC:H) are described. A rf glow discharge process is employed to produce the doped a-Si:H and a-SiC:H thin films. Tertiarybutylphosphine (TBP) may ultimately be preferred over phosphine because TBP is less toxic, less pyrophoric and safer to implement. The gross doping properties of a-Si:H doped with TBP are the same as those obtained with phosphine, but there are some differences. N-butylsilane (NBS) and DTBS have been used to produce wide band gap (E04 3 ≈ eV) a-SiC:H.
Measurement of Intrinsic Stress in a-Si:H thin films Deposited in a Remote Hydrogen Plasma Reactor
Authors: Stevens K. S. , Johnson N. M.
Published: March 2011

The effects of deposition conditions on the intrinsic stress in a-Si:H films deposited in a remote hydrogen plasma reactor are reported. The intrinsic stress is calculated from the change in substrate curvature induced by the a-Si:H film, as measured by the optical lever technique, and the results are compared with those for rf glow discharge deposited a-Si:H films.
Study of Oxidation Properties of Amorphous Si:B Films
Authors: Yang G.-R. , Nason T. C. , Wu Y.-J. , Tong B. Y. , Wong S. K.
Published: March 2011

Thin films of an amorphous silicon-boron alloy with boron content 1–50 at.% have been deposited by low pressure chemical vapor deposition (LPCVD). The boron content and film thickness of the samples were controlled by regulating the ratio of diborane and silane gases during the deposition. It was observed that the crystallization of the amorphous alloy took place at higher temperatures as boron concentration was increased. After a thermal oxidation was performed, the stoichiometry of die resulting oxide layers on various samples was determined by the secondary ion mass spectrometry and Auger depth profile methods. While the threshold temperature for thermal oxidation was determined to be inversely proportional to the boron concentration, the oxidation rate showed a dramatic increase with boron content. In particular, an alloy containing 30% boron was readily oxidized at 500°C. Mechanisms for the enhancement of oxidation consistent with stoichiometric and spectroscopic properties of the oxide layers are discussed.
An Investigation of the Influence of Plasma Characteristics on the Electronic and Optical Properties of Device Quality a-Si:H Grown by Electron Cyclotron Resonance Plasma Deposition
Authors: Knox Ralph D. , Dalal V. L. , Moradi B.
Published: March 2011

The electronic and optical properties of device quality hydrogenated amorphous silicon (a-Si:H) films grown by electron cyclotron resonance (ECR) plasma deposition were studied together with in-situ plasma characteristics. Hydrogen and helium plasmas, excited by 50–250 watts of 2.45 GHz microwave power under ECR conditions, were used to decompose silane at 6 to 20 mtorr pressures during the deposition of a-Si:H films at a 297 C substrate temperature. Both the electron temperature and density, and ion flux are measured near the deposition surface using plane and cylindrical Langmuir probes. An attempt is made to correlate these plasma properties with the light and dark photoconductivity, optical gap, refractive index, and subband gap photoconductivity.
The Influence of Nitrogen Content on the Properties of Sputtered a-Si56Ge44:N:H Films
Authors: Drusedau T.
Published: March 2011

Nitrogen related absorption bands of the IR spectra are used to determine the content of nitrogen and N—H bonds in a—Si56 Ge44 films. A preferential attachment of nitrogen to silicon is observed. Nitrogen incorporation enhances the normalized photoconductivity to 5 · 107 cm2/V at maximum. This is related to N—H complexes acting as donors. A correlation between optical gap and single oscillator energy is reported.
Hydrogen Stability in Hydrogenated Amorphous Silicon-Based Alloys
Authors: Beyer W. , Herion J. , Wagner H. , Zastrow U.
Published: March 2011

The thermal stability of hydrogen in amorphous silicon-based alloy films was studied by deuterium/hydrogen interdiffusion and hydrogen effusion experiments. Depending on the film structure, hydrogen stability is limited by hydrogen surface desorption or hydrogen diffusion. The hydrogen surface desorption energy is found to decrease with rising germanium content and to increase with rising nitrogen and carbon content. At T = 400°C, hydrogen diffusion is found to proceed in the germanium subnetwork for a-SiGe alloys and in the silicon subnetwork for a-SiN and a-SiC alloys.
The Investigation of Fluorine Effects on Charge Trapping and Interface State Generation in Mos Structures
Authors: Xie Dunxian D. , Lin Ta-Cheng , Young Donald R.
Published: March 2011

The bulk and interface charge trapping phenomena of fluorinated oxides have been studied by various electronic measurements. Fluorine is introduced into dry oxides by low energy (25kev) implantation followed by a 1000°C N2 ambient anneal to remove physical damage. Both the flat band and the mid gap voltage shifts of such MOS devices are measured during avalanche electron injection. We have developed techniques to separate effects due to interface state generation from bulk trapping effects. The bulk electron traps in the fluorinated oxides have a different cross section from the known water-related traps in conventional oxides. The generation of fast and slow interface states for different dosages of fluorine implantation is discussed based on Q-V and C-V measurements. The fast interface donor states, generated during avalanche injection, are charged at flat band but discharged at mid gap and beyond. An optimum dosage of fluorine implantation is found to suppress the so called turn-around effect during avalanche injection due to the formation of slow donor states. Finally, injection under high temperature (120°C-150°C) anneals out most of these donor states.
Interface Effects on Photocarrier Transport in a-Si:H
Authors: Persans P. D. , Arnzen D. , Possin G. , D'Anna L. , Zhao X. S. , Breton K.
Published: March 2011

We discuss the absorption-length and film thickness dependence of photoconductivity in amorphous silicon using measurements of the ambipolar diffusion length and the Debye screening length.
Steady State Photocarrier Charge Collection in a-Si:H for Electrons and Holes
Authors: Abel C.-D. , Paes H. R. , Bauer G. H.
Published: March 2011

Carrier transport in amorphous silicon pin-diodes has been analyzed by steady state photocarrier charge collection applying strongly absorbed light. For low intensities at room temperature electron charge collection is limited by recombination in the generation region. For increasing intensity ø and/or decreasing temperature charge collection becomes nonlinear in ø and shows S-like characteristics versus voltage.

We present a model for this behaviour, including space charge limitation which e.g. for holes in a-Si:H limits charge collection even at room temperature due to low extended state mobility of holes and dark Fermi level position above midgap.
Thermal Quenching of Photoconductivity and the Sign of Photocarriers in Doped a-Si:H
Authors: Yoon B.-G. , Fritzsche H. , Tran M. Q. , Chi D.-Z.
Published: March 2011

Thermal quenching (TQ) of photoconductivity σp occurs when the demarkation level of minority carriers passes through recombination centers having small capture cross section for majority carriers compared to other centers present but normal cross section for minority carriers. The photoconductivity becomes superlinear with light intensity at the temperature of maximum TQ. We discovered TQ not only in n-type but also p-type a-Si:H. This cannot happen with the same centers unless the sign of the majority carriers changes. We present evidence that in p-type and undoped films majority carriers are electrons at T below TQ and holes above TQ. The nature of these special centers will be discussed.
Elastic Moduli of H2O: Liquid, Ice VI and Ice VII
Authors: Grimsditch M. , Rahman A. , Poliant A.
Published: March 2011

The results of a Brillouin scattering study of the room temperature phases of H2;O (liquid, ice VI and ice VII) up to 30 GPa are presented. Longitudinal elastic moduli thus obtained are compared with values of the bulk modulus obtained from density measurements [1] and with both static and molecular dynamics calculations of the bulk modulus using potentials which have been proposed in studies of the liquid state. The calculations indicate that the potentials are not capable of describing the high pressure region of ice VII.
Raman Spectra of Fluids in Elastohydrodynamic Contacts
Authors: Gardiner D.J. , Baird E. , Gorvin A.C. , Marshall W.E. , Dare-Edwards M.P.
Published: March 2011

Initial results of a novel Raman spectroscopic method for studying fluid lubricant characteristics in a simulated elastohydrodynamic contact are reported. The method uses a Raman microscope which allows spectra to be obtained from a small volume (∼ 0.1 nl) of lubricant entrapped in the elastic deformation formed when a loaded glass plate falls onto a lubricated steel ball. The work described here was undertaken to obtain direct pressure measurements from an entrapped fluid at equilibrium after the initial impact. Our results indicate that pressures in twofold excess of the maximum Hertzian pressure can be generated in ball-plate entrapments of the polyphenyl ether 5P4E. In addition 5P4E has been studied as a pure liquid and as a solution in CCl4 using a diamond anvil cell (DAC). Preliminary results on 2,4-dicyclohexyl-2-methylpentane studied using a DAC and a hydrostatic equilibrium cell are also described.
Luminescence in Solutions Under Pressure
Authors: Offen H. W. , Turley W. D. , Fetterolf M. L.
Published: March 2011

Probe molecules P placed in dilute solution and absorbing radiation Ia produce electronically excited species P* which can return to thermal equilibrium by radiative (luminescence) kR and nonradiative (heat) kNR processes. The relative probabilities of the two decay channels are determined by measuring the lifetime τ of P* and the luminescence quantum yield φ = I/Ia, where I is the luminescent intensity. The kinetic scheme and relevant relations are
The Collapse or Ballooning Pressure of Thick-Walled Pressure Vessels
Authors: Crossland B.
Published: March 2011

Discussion of the proposed extension of the ASME pressure vessel code to cover operating pressures up to 1.4 GPa (200000 lbf/in2 ) has generated the proposal that two criteria should be used, of which one would be the collapse or ballooning pressure not the bursting pressure. The present paper examines this proposal in relation to extensive data on the collapse and bursting of thick-walled vessels available to the author.

It is concluded that the collapse pressure is only readily calculable for materials which approach the behaviour of an elastic/perfectly plastic material. It also appears for materials with significant strain hardening characteristics, such as mild steel, that the collapse pressure considerably underestimates the bursting pressure, whereas for a material which behaves as an elastic/perfectly plastic material the collapse pressure is nearly coincident with the bursting pressure. Consequently if the collapse pressure was adopted and if the factor of safety against collapse was adequate for one material it might be more or less than adequate for another material, which would appear to be unacceptable.
The Fatigue Strength of Thick-Walled Cylinders
Authors: Karl Erich
Published: March 2011

ASME recently formed two committees which were given thetask of drafting a new Vessel Code and a new Piping Code for pressures ranging from approximately 70 Mpa (10,000 psi) up to 1,400 Mpa (200,000 psi). Pressure vessels and pipework operating in this pressure range are, in many cases, employed for batch-type operations or are subjected to pulsating pressures, for example in LDPE (low-density polyethylene) plants, in isostatic pressing processes, or in the production of synthetic crystals. For this reason, it is very important to design the pressure-bearing components so that they can safely tolerate the load cycles which are to be imposed on them.