bluuebunny/crossref_metadata_2025_split huggingface dataset:
Structural Changes in a-Si:H Studied by X-Ray Photoemission Spectroscopy
Authors: Sheng Shuran , Sacher Edward , Yelon Arthur , Branz Howard M. , Masson Denis P. 
Published: April 2011

AbstractX-ray irradiation-induced structural changes in undoped a-Si:H have been investigated in detail by X-ray photoemission spectroscopy (XPS). The Si2s and the Si2p peaks were found to shift simultaneously to lower bonding energies, by the same amount, with X-ray irradiation. The shifts are near saturation, at about 0.1 eV, after one hour of irradiation at the intensity used; they can be reversed almost completely, seemingly with an activation energy lower than that for the metastable changes in electronic properties (Staebler-Wronski effect). The present results suggest that essentially the whole Si network structure is affected by the X-ray irradiation.
Infrared Electroabsorption Spectra in Amorphous Silicon Solar Cells
Authors: Lyou J. H. , Schiff Eric A. , Hegedus Steven S. , Guha S. , Yang J. 
Published: April 2011

AbstractWe report measurements of the infrared spectrum detected by modulating the reverse-bias voltage across amorphous silicon pin solar cells and Schottky barrier diodes. We find a band with a peak energy of 0.8 eV. The existence of this band has not, to our knowledge, been reported previously. The strength of the infrared band depends linearly upon applied bias, as opposed to the quadratic dependence for interband electroabsorption in amorphous silicon.The band's peak energy agrees fairly well with the known optical transition energies for dangling bond defects, but the linear dependence on bias and the magnitude of the signal are surprising if interpreted using an analogy to interband electroabsorption. A model based on absorption by defects near the n/i interface of the diodes accounts well for the infrared spectrum.
Stable Amorphous Silicon and Improved Microcrystalline Silicon by Photon-Assisted Electron Cyclotron Resonance Chemical Vapor Deposition
Authors: Song Young J. , Anderson Wayne A. 
Published: April 2011

AbstractAmorphous (a-Si) and microcrystalline silicon (μc-Si) are widely used in photovoltaics and thin film transistors. These products suffer from instability and less than desired electrical properties. We have utilized photon-assisted electron cyclotron resonance chemical vapor deposition (PA-ECRCVD) resulting in great improvement in both areas. For example, PA-ECRCVD compared with conventional ECR-CVD gives carrier lifetime of 1.35 4ts compared to 0.17 μs, and photovoltaic solar cell efficiency of 10 % compared to 5.9 %. Moreover, the PAECRCVD cell only degraded to 9.8 % compared to the ECR-CVD cell degradation to 5.5 %, under long term exposure to tungsten lamp illumination. In addition, PA-ECRCVD gives much enhanced crystallinity in μc-Si as revealed by atomic force microscopy and Raman spectroscopy.
A Novel P-Type Nanocrystalline Si Buffer at the P/I Interface of A-SI Solar Cells for High Stabilized Efficiency
Authors: Lee Chang Hyun , Lim Koeng Su 
Published: April 2011

AbstractWe investigated the properties of a novel p-type nanocrystalline Si (p-nc-Si) prepared onto p-a-SiC and the effect of using the buffer with an energy bandgap over 1.9 eV at the p/i interface on the performance of p/i/n type amorphous silicon based solar cells. At the initial growth stage of the p-nc-Si onto p-a-SiC, Si nanocrystallites are proved to be formed in amorphous matrix within the thickness of less than 100Å. The open circuit voltage and the blue response of the cell were improved significantly by inserting the film at the p/i interface as a buffer as compared with the bufferless cell. We found from a numerical simulation using the Gummel-Sharfetter method that the buffering effect of the p-nc-Si is originated from the reduction of highly defective region with a short life-time in the vicinity of the p/i interface.
High Rates and Very Low Temperature Fabrication of Polycrystalline Silicon From Fluorinated Source GAS and Their Transport Properties
Authors: Kamiya T. , Nakahata K. , Ro K. , Fortmann C. M. , Shimizu I. 
Published: April 2011

AbstractLow temperature (50-300°C) growth of polycrystalline silicon (poly-Si) by very high frequency (100MHz) glow-discharge plasma enhanced CVD using SiF4 and H2mixtures was studied. The poly-Si microstructure was strongly affected by the SiF4/H2 gas flow ratio. For example, either (220) or (400) preferentially oriented films were prepared by appropriate SiF4/H2 ratio selection. The addition of small SiH4 flows to the SiF4/H2 mixtures could be used to increase the growth rate while the SiF4/H2 continued to control the film structures such as preferential orientation. Highly crystalline films were grown at a growth rate of 0.52nm/s using SiF4/H2/SiH4 flow rates of 30/90/2.Osccm (respectively). However, at higher SiH4 flows amorphous films were deposited. Under the small SiF4/H2 ratio condition, highly crystallized poly-Si was grown at temperatures as low as 50°C. N/i/Pt Schottky diode solar cells were prepared using these poly-Si for both the n- and the i-layers. These solar cells exhibited good performance; for example, open circuit voltages over 0.32V. N-i-p solar cell results are very promising with 6.2% of conversion efficiency being achieved in the initial trials.
Structure and Optoelectronic Properties as a Function of Hydrogen Dilution of Micro-Crystalline Silicon Films Prepared by Hot Wire Chemical Vapor Deposition
Authors: Yue Guozhen , Lin Jing , Wang Qi , Han Daxing 
Published: April 2011

AbstractFilms prepared by hot wire CVD using H dilution ratio, R=H 2/SiH4, from 1 to 20 were studied by X-ray, Raman, PL, and conductivity measurements. We found that (a) when the dilution ratio reached R=3, the structure transition from amorphous to microcrystalline growth occured; meanwhile, PL spectrum showed a dual-peak at 1.3 and 1.0 eV; (b) the total intensity, band width, and peak position of the low energy PL band decreased with increasing H dilution; (c) both the Raman and PL measured from the transparent substrate side showed that initial growth tends to be amorphous and a portion of μc-Si was formed when R ≥ 5; and (d) the conductivity activation energy first decreased from 0.68 to 0.15 eV when the film transition from a- to μc-Si; then increased slightly with increasing μc-Si fraction. The results demonstrate that the variation of the H-dilution ratio has significant effects on both the film structures and the optoelectric properties.
High Quality Microcrystalline Silicon-Carbide Films Prepared by Photo-CVD Method Using Ethylene Gas as a Carbon Source
Authors: Myong Seung Yeop , Lee Hyung Kew , Yoon Euisik , Lim Koeng Su 
Published: April 2011

AbstractHydrogenated boron-doped microcrystalline silicon-carbide (p-μc-SiC:H) films were grown by a photo chemical vapor deposition (photo-CVD) method from silane (SiH4), hydrogen (H2), diborane (B2H6), and ethylene (C2H4) gases. Since the photo-CVD is a mild process (~10mW/cm2), we can avoid the ion damage of the film, which is inevitable during the deposition of μc-SiC:H employing conventional PECVD technique. A dark conductivity as high as 5 × 10-1 S/cm, together with an optical bandgap of 2 eV, was obtained by the C2H4 addition, which is the first approach in photo-CVD systems. From the Raman and FTIR spectra, it is clear that our p-μc-SiC:H films are made up of crystalline silicon grains embedded in amorphous silicon-carbide tissue. We investigate the role of the hydrogen dilution and ethylene addition on the electrical, optical, and structural properties of p-μc-SiC:H films.
Quasi Drift and Quasi Diffusion: A Grain size Dependent Polysilicon Tft Model
Authors: Eccleston W. 
Published: April 2011

AbstractMost of the models for Thin Film Transistors take no account of the way that electrons move across grain boundaries. The purpose of this work is to produce an analytical model, physically based, that takes account of both the change in height of the potential barriers that separate the grains, and the change of carrier density in the grains with gate voltage. The high current and subthreshold regions are treated. The model enables the change of field effect mobility with grain size and temperature to be determined. Two closed form expressions are provided which should be of value to both device and circuit designers, as well as providing insight to the physical processes occurring in such devices. They form a close analogy with the electrical characteristics of MOSFETs on crystalline silicon, diffusion and drift being replaced by quasi-diffusion and primary quasi-drift.
Application of Self-Aligned Amorphous SI Thin-Film Transistors
Authors: Lu J.P. , Mei P. , Chua C. , Ho J. , Wang Y. , Boyce J. B. , Lujan R. 
Published: April 2011

AbstractWe have successfully used self-aligned Amorphous Si Thin-Film Transistors, fabricated by a laser doping/annealing process, to construct dynamic shift register circuits, which can be used as gate-line drivers or in other peripheral circuits for flat-panel displays and imagers. Taking advantage of easily scaling down the TFT channel length in a self-aligned process, much higher circuit speeds can be achieved compared to that of circuits using conventional TFTs. We have successfully demonstrated a four-phase dynamic shift register, operating at a clock speed higher that 250 kHz (1 μs for each clock phase) built on 3 μm channel length TFTs. This new technology opens up possibilities for integrating peripheral circuits in flat-panel displays and imagers based on a-Si TFTs.
Signal Amplification and Leakage Current Suppression in Amorphous Silicon P-I-N Diodes by Field Profile Tailoring
Authors: Hong W.S. , Zhong F. , Mireshghi A. , Perez-Mendez V. 
Published: April 2011

AbstractThe performance of amorphous silicon p-i-n diodes as radiation detectors in terms of signal amplitude can be greatly improved when there is a built-in signal gain mechanism. We describe an avalanche gain mechanism which is achieved by introducing stacked intrinsic, p-type, and n-type layers into the diode structure. We replaced the intrinsic layer of the conventional p-i-n diode with i1-p-i2-n-i3 multilayers. The i2 layer (typically 1~3 μm) achieves an electric field > 106 V/cm, while maintaining the p-i interfaces to the metallic contact at electric fields < 7 × 104 V/cm, when the diode is fully depleted. For use in photo-diode applications the whole structure is less than 10 μm thick. Avalanche gains of 10~50 can be obtained when the diode is biased to ~500 V. Also, dividing the electrodes to strips of 2 μm width and 20 μm pitch reduced the leakage current up to an order of magnitude, and increased light transmission without creating inactive regions.
Noise of a-Si:H Pin Diode Pixels in Imagers at Different Operating Conditions
Authors: Blecher F. , Schneider B. , Sterzel J. , Böhm M. 
Published: April 2011

AbstractThe noise current spectral density of an a-Si:H pin diode can be calculated with experimentally determined flicker noise coefficients by superposition of the shot and flicker noise spectra of photocurrent and dark current. The dependence of the flicker noise current spectral density in pin diodes on the pixel area is calculated with our expansion of Hooge's law for flicker noise. We propose a new method for the calculation of dynamic range (DR) and signal-to-noise ratio (SNR) in pin diode pixels as a function of pixel area, dark current, photocurrent and the integration time of the imager. DR and SNR of the pin diodes are calculated for Thin Film on ASIC (TFA) image sensors.
Oriented Carbon Nanotube Growth for Field Emission Applications
Authors: Obraztsov A.N. , Pavlovsky I. , Volkov A.P. , Kuznetsov V.L. , Chuvilin A.L. 
Published: April 2011

ABSTRACTOriented carbon nanotube films were grown using a method of chemical vapor deposition in hydrogen/methane plasma activated by glow discharge. The film phase composition and structural features were studied by Raman, SEM, TEM, and HRTEM techniques. Field emission properties of the films were examined to obtain I-V characteristics and the field emission site distribution. The I-V curves in Fowler-Nordheim coordinates were linear, that is typical for the field emission, with the threshold average field about 1.5 V/μm and the emission current density up to 50 mA/cm2 at the field of 5 V/μm. The emission site density reached 107 cm2 at the same value of electrtic field.
Field Emission Properties of Thin Molybdenum Carbide and Diamond Films Deposited by Dielectrophoresis
Authors: Rouse Ambrosio A. , Bernhard John B. , Sosa Edward D. , Golden David E. 
Published: April 2011

ABSTRACTMolybdenum carbide and diamond films were deposited at room temperature by dielectrophoresis on molybdenum foil and field emission tips. Films deposited on flat surfaces were characterized with XPS, UPS and SEM. Field emission Fowler-Nordheim current-voltage characteristics and electron energy distribution measurements were obtained using films deposited on field emission tips as part of a single aperture gated diode in a VG ESCALAB II system. Molybdenum trioxide was present after molybdenum carbide deposition at room temperature on all samples. At a temperature of about 650 °C, the dominant oxide changes to molybdenum dioxide. At about 800 °C, the oxygen content of the films significantly decreases and molybdenum carbide with significant graphite content remains. The UPS data for these samples were obtained at different annealing temperatures and a number of photon energies to determine photoelectric work functions for molybdenum trioxide, molybdenum dioxide and molybdenum carbide. The same kind of data was obtained for diamond deposited on molybdenum and molybdenum carbide coated foils and field emission tips.
High-Dielectric Constant Insulators and the AMLCD Process: Is Amorphous BST a Candidate?
Authors: Andy P. , Neumayer D. , Duncombe P. , Dimitrakopoulos C. , Libsch F. , Laibowitz R. , Grill A. , Wisnieff R. 
Published: April 2011

ABSTRACTAs the active matrix flat panel market continues to grow, manufacturers are constantly looking for ways of gaining an advantage in the marketplace typically through increased performance, expanded functionality and/or reduced cost. The continuing trend of larger panel sizes and higher resolution poses interesting challenges for manufacturers in the areas of image quality and brightness. In particular, it has been clearly shown that as pixel dimensions shrink, relative crosstalk coupling coefficients increase while the area available for pixel electrodes and storage capacitors (Cδ,t) decreases, so that charge compensation drive schemes must be employed to eliminate visual artifacts. One approach to minimizing crosstalk and flicker is to increase Cδ,t, however this requires increased pixel area, usually at the expense of brightness due to smaller aperture ratio. Depending on design and process flow, it may be possible to replace the typical Cδ,t, insulator, SiNx:H, with a material of higher dielectric constant thereby vastly improving electrical performance without sacrificing brightness.
Modeling of Cathodoluminescence and Photoluminescence Properties of Pulsed Laser-Deposited Europium-Activated Yttrium Oxide Thin Film Phosphors
Authors: Cho K.G. , Kumar D. , Chen Z. , Holloway P. H. , Singh R. K. 
Published: April 2011

ABSTRACTEuropium-activated yttrium oxide (Eu:Y2O3) thin films were deposited on (100) silicon and (0001) sapphire substrates using 248 nm KrF pulsed laser. To investigate the effect of the Eu:Y2O3 film roughness on cathodoluminescence (CL) and photoluminescence (PL) properties, the substrate surfaces with various roughnesses were used. The roughness was found to play an important role in determining CL and PL brightness of the Eu:Y2O3 films. The improvement in brightness by increasing the film roughness is due to increase in total portion of light that escapes from the surface of the phosphor film. A model has been proposed which supports strongly this explanation. Our results show that depositions with slower growth rate and lower laser energy are more important parameters than increasing the roughness to improve CL brightness of the Eu:Y2O3 thin film phosphors.
A new laser Printing technique for the fabrication of thin film transistors
Authors: Toet D. , Smith P.M. , Sigmon T.W. , Thompson M.O. 
Published: April 2011

ABSTRACTWe present a new technique for the spatially selective deposition, or “printing”, of materials such as Si and Al. This transfer is effected by irradiating a hydrogenated amorphous silicon film deposited on a quartz substrate and coated with the material to be transferred with an excimer laser pulse. The resulting release and accumulation of hydrogen at the film/substrate interface generates pressures sufficient to propel the silicon, as well as any overlying material, onto an adjacent glass receptor wafer. Transient optical transmission measurements performed during the transfer of Si indicate that the amorphous film is melted by the laser pulse and breaks into droplets during ejection. These droplets travel towards the host substrate with a velocity of about 800 m/s and coalesce upon arrival. For fluences above 400 mJ/cm2, the resulting films adhere well to the receptors and can be smoothed using a second laser irradiation. We fabricated thin film transistors (TFTs) in the printed-and-smoothed Si using conventional lithography. The resulting devices show consistent switching behavior. We have also printed Si and Al lines with widths 5 to 15 µm by patterning the laser beam using a reflective grating mask defined on the target substrate. These lines are straight, show few discontinuities, and have sharp edges.
A μc-Si:H P-I-N Imager For 2-D Pattern Recognition
Authors: Martins J. , Fernandes M. , Sousa F. , Louro P. , MaçArico A. , Vieira M. 
Published: April 2011

ABSTRACTA TCO/ μc-p-i-n Si:H/AI imager is presented and analyzed. The μc-p-i-n Si:H photodiode acts as a sensing element. Contacts are used as an electrical interface. The image is acquired by a scan-out process. Sampling is performed on a rectangular grid, and the read-out of the photogenerated charges is achieved by measuring simultaneously both transverse photovoltages at the coplanar electrodes. The image representation in gray-tones is obtained by using low level processing algorithms. Basic image processing algorithms are developed for image enhancement and restoration.
Investigation of the Role of Chemical-Mechanical Polishing in Improving the Performance of Polysilicon TFTs
Authors: Lee B. , Quinn L.J. , Baine P.T. , Mitchell S.J.N. , Armstrong B.M. , Gamble H.S. 
Published: April 2011

ABSTRACTPolycrystalline silicon thin-film transistors (TFTs) have been fabricated on glass substrates using a low temperature top-gate self-aligned process. The interface between the polysilicon active layer and the silicon dioxide oxide gate dielectric is of vital importance in order to achieve good thin-film transistor electrical characteristics. Carrier transport takes place within 10nm of this interface, and any roughness in this region, corresponding to the initial surface roughness of the polysilicon layer, causes scattering of the carriers and a higher density of interface traps. Chemical-mechanical polishing has been used to reduce the initial surface roughness of the polysilicon. Electrical parameters of polished TFTs, such as mobility and threshold voltage, show a marked improvement compared to unpolished devices.
Growth Mechanism of thin Film Wide-Gap Semiconductors by Chemical Bath Deposition Technique
Authors: Nair P. K. , Parmananda P. , Nair M. T. S. 
Published: April 2011

ABSTRACTChemical bath deposition is a thin film technique in which semiconductor thin films of typically 0.02 – 1 μm thickness are deposited on substrates immersed in dilute baths containing metal ions and a source of sulfide or selenide ions. Many I–VI, II–VI, IV–VI, and V–VI semiconductors are included in the list of materials deposited by this technique, II–VI compounds CdS, CdSe, ZnS and ZnSe being the most investigated. However, a mathematical model describing the growth mechanism of these films still remains to be established. The deposition process consists of a nucleation phase, growth phase, and a terminal phase, each of which depends on the concentration of the ions in the deposition bath, its temperature, dissociation constants of the metal complex ions, etc. In this paper we propose a mathematical model, which can qualitatively account for most of the features of the experimental growth curves of chemically deposited semiconductor films.
Electroluminescence and Photoluminescence of Fluorene-Carbazole Copolymer
Authors: Stephan O. , Vial J.C. 
Published: April 2011

ABSTRACTThin layers of poly(dihexylfluorene-co-N-hexylcarbazole) sandwiched between ITO and aluminium electrodes show stable photoluminescence and electro-luminescence at room temperature and ambient atmosphere. I(V) and Electro-luminescence versus voltage curves present a much lower threshold than device made up of poly(dihexylfluorene) homopolymer. When using the copolymer, the barrier height for hole injection is reduced to a value close to 0.17 eV to be compared to 0.83 eV for the homopolymer. This difference in offsets has been confirmed by electrochemical investigations.
Performing Accurate Cathodoluminescence Measurements of Phosphor Powders and Screens
Authors: Shea L. E. , Walko R. J. 
Published: April 2011

ABSTRACTIn the field of display phosphors, the efficiency of the cathodoluminescence process is a characteristic that is often used to assess the potential of a phosphor for use in flat-panel display applications such as field emission displays (FEDs). Cathodoluminescence characterization in a demountable vacuum chamber is important for preliminary evaluation and lifetesting of phosphor powders and screens prior to incorporation into an actual display device. There are many experimental factors that influence accurate measurement and calculation of the cathodoluminescence efficiency. These include electron beam profile (uniform, Gaussian), current density, electron accelerating voltage, secondary electron collection, and optical detection system. This paper will present some methods for achieving improved accuracy of cathodoluminescence measurements in systems at Sandia National Laboratories, using Y2O3:Eu as a representative phosphor.
Energy and Charge Transfer in Electroluminescent Polymer/Porphyrin Blends
Authors: Cleave V. , Yahioglu G. , Barny P. Le , Friend R.H. , Tessler N. , Hwang D.H. , Holmes A.B. 
Published: April 2011

ABSTRACTWe present a study of the effects of blending electroluminescent polymers with platinum (II) octaethylporphyrin (PtOEP). We find that in the case of polymers which are measured to have HOMO and LUMO levels respectively below and above those of the PtOEP, and which have emission spectra overlapping the PtOEP absorption spectra, energy transfer occurs as expected. We find further evidence, in the form of steady state and time-resolved electroluminescence and photoluminescence measurements, which indicates additional transfer of triplet excitons between polymer and porphyrin. Where the polymers have emission spectra overlapping the absorption spectra of PtOEP, but which are measured to have a HOMO or LUMO level between those of the porphyrin, quenching of the photoluminescence efficiency occurs. We propose this is due to charge separation between the porphyrin and the polymer, and show evidence for this in the form of photoinduced absorption measurements.