bluuebunny/crossref_metadata_2025_split huggingface dataset:
Thin Film Transistors of Microcrystalline Silicon Deposited by Plasma Enhanced-CVD
Authors: Chen Y. , Wagner S. 
Published: April 2011

AbstractWe fabricated top gate TFTs of microcrystalline silicon (μc-Si) deposited at 360 °C. The TFTs have field-effect electron mobilities of up to 7.9 cm2/Vs in the saturation regime and 5.8 cm2/Vs in the linear regime. The highest ION/IOFF ratio is 105. Typical values for Vth is 6.5 V and for the subthreshold slope is 1.7 V/decade. The μc-Si is grown by PE-CVD from a source gas mixture of SiH4, SiF4 and H2, with a typical flow ratio of 1:20:200, at a pressure of 120 Pa and a power density of 160 mW/cm2. The TFT structure is built on un-passivated Coming 7059 glass, with 300 n+ μc-Si, 60 nm n+ μc-Si source and drain contact layers, 200 nm SiO2 or 300 nm SiNx gate insulator, and 100 nm Al gate, source and drain electrodes.
Optical Filter for Fabricating Self-Aligned Amorphous Si TFTS
Authors: Mei P. , Lu J. P , Chua C. , Ho J. , Wang Y. , Boyce J. B. 
Published: April 2011

AbstractSelf-aligned structures for bottom-gate amorphous Si TFTs provide a number of advantages, including reduced parasitic capacitance, smaller device dimensions, and improved uniformity in device performance for large-area electronics. A difficult challenge in making self-aligned TFT structures is the necessity of making source/drain contacts that exhibit low contact resistances and that are precisely aligned relative to the gate electrode. In this article, we describe a novel process for fabricating self-aligned amorphous Si TFTs. This process utilizes a pulsed excimer laser (308 nm) to dope or to activate dopants in a-Si to form the source/drain contacts. An important feature of the device design is an optical filter to protect the a-Si channel region from radiation damage during the 308 nm laser process. However, the optical filter allows the transmission of the uv light for lithography exposure from the backside of the substrate to align the channel region with the gate electrode. This new process enables the fabrication of high performance self-aligned a-Si TFTs with poly-Si source and drain contacts.
Real Time Optics of Amorphous Silicon Solar Cellfabrication on Textured Tin-Oxide-Coated Glass
Authors: Rovira P. I. , Ferlauto A. S. , An Ilsin , Fujiwara H. , Koh Joohyun , Koval R. J. , Wronski C. R. , Collins R. W. 
Published: April 2011

AbstractA rotating-compensator multichannel ellipsometer has been used to measure the four spectra (1.4-4.0 eV) that describe the Stokes vector of the light beam reflected from the surface of an amorphous silicon (a-Si:H) p-i-n solar cell during fabrication on textured tin-oxide (SnO2) coated glass. The Stokes vector elements include the irradiance in the reflected beam (or the reflectance) and the parameters {(Q, χ), p} of the reflected beam, where Q and χ are the tilt and ellipticity angles of the polarization ellipse and p is the degree of polarization. The value of p deviates from unity in part due to the non-uniform nature of the textured SnO2 substrate film. An analysis of Q and χ that neglects the effects of the texture can provide the time evolution of the thicknesses, microscopic structure, and the optical properties of the component layers of the a-Si:H solar cell. Deviations of the measured reflectance spectra from those predicted on the basis of the (Q, χ) analysis provide the thickness dependence of the scattering and the evolution of the macroscopic structure of the solar cell. The measurement and analysis approach is important because of its potential application for real time monitoring of solar cell production. The analysis results also provide realistic inputs for optical modeling of the effects of texture in light trapping for solar cell efficiency enhancement.
Optical Modeling of a-Si Solar Cells
Authors: Sopori Bhushan , Madjdpour Jamal , Zhang Yi , Chen Wei , Guha Subhendu , Yang Jeff , Banerjee Arindam , Hegedus Steven 
Published: April 2011

AbstractWe describe applications of PV Optics to analyze the behavior of a metallic back-reflector on an a-Si solar cell. The calculated results from PV Optics agree well with the measured data on solar cells. Several unexpected results obtained from these calculations are qualitatively explained.
Amorphous Silicon Solar Cell Techniques for High Temperature and/or Reactive Deposition Conditions
Authors: Kanbe M. , Komaru T. , Fukutani K. , Kamiya T. , Fortmann C.M. , Shimizu I. 
Published: April 2011

AbstractSeveral promising new methods for amorphous silicon solar cell preparation involve high substrate temperatures and/or very reactive atmospheres. When incorporated into solar cells, the performance of these layers has often been less than expected due to enhanced diffusion and/or chemical reactions. This poor performance results from the harsh deposition environments. Deleterious effects include darken of TCO coated glass substrates due to hydrogen diffusion to and hydrogen reduction at the TCO interface when solar cells are prepared in the p-i-n deposition sequence. Alternatively, the deposition of TCO layers onto amorphous layers also involves rather harsh oxidizing conditions that have a deleterious effect on the top most amorphous silicon-based p-layers. Strategic use of blocking layers results in remarkably improved solar cell performance. A thin Cr layer (probably becoming Cr2O3) shows ability to improve the performance of both n-ip and p-i-n solar cells by inhibiting both O and H diffusion.
Buffer Layers for Narrow Bandgap A-SIGE Solar Cells
Authors: Liao X. B. , Walker J. , Deng X. 
Published: April 2011

AbstractIn high efficiency narrow bandgap (NBG) a-SiGe solar cells, thin buffer layers of unalloyed hydrogenated amorphous silicon (a-Si) are usually used at the interfaces between the a-SiGe intrinsic layer and the doped layers. We investigated the effect of inserting additional a-SiGe interface layers between these a-Si buffer layers and the a-SiGe absorber layer. We found that such additional interface layers increase solar cell VOC and FF sizably, most likely due to the reduction or elimination of the abrupt bandgap discontinuity between the a-SiGe absorber layer and the a-Si buffer layers. With these improved narrow bandgap solar cells incorporated into the fabrication of triple-junction a-Si based solar cells, we obtained triple cells with initial efficiency of 10.6%.
Characteristics of Different Thickness a-Si:H/Metal Schottky Barrier Cell Structures-Results and Analysis
Authors: Lu Zhou , Jiao Lihong , Koval Randy , Collins Robert W. , Wronski Christopher R. 
Published: April 2011

AbstractCurrent-voltage, light I-V and internal quantum efficiency characteristics have been investigated in specular TCO/n+(a-Si:H)/i(a-Si:H)/Nickel Schottky barrier cell structures with protocrystalline intrinsic layers. The studies were carried out on structures with different thickness i layers after a degraded steady state had been reached with AMI.5 illumination at 27°C. These characteristics were modeled using the Analysis of Microelectronic and Photonic Structures(AMPS) and a gap state distribution, which includes charged defects, used in the analysis of results of detailed studies on thin films[1]. Fits are obtained to these characteristics for the different thickness cell structures using the same parameters as those used to fit the results on the corresponding intrinsic thin films. The results obtained from this study offer an approach to more reliable modeling of solar cells at their “end of life”.
High Resolution, High Fill Factor A-SI:H Sensor Arrays for Optical Imaging
Authors: Rahn J.T. , Lemmi F. , Mei P. , Lu J.P. , Boyce J.B. , Street R.A. , Apte R.B. , Ready S.E. , Schuylenbergh K.F. van , Nylen P. , Ho J. , Fulks R.T. , Lau R. , Weisfield R.L. 
Published: April 2011

AbstractAmorphous silicon large area sensor arrays are in production for x-ray medical imaging. The most common pixel design works very well for many applications but is limited in spatial resolution because the available sensor area (the fill factor) vanishes in small pixels. One solution is a 3-dimensional structure in which the sensor is placed above the active matrix addressing. However, such high fill factor designs have previously introduce cross talk between pixels.We present data for a design in which the a-Si:H p-i-n photodiode sensor layer has a continuous i-layer and top p+-layer, and a patterned n+-layer contact to the pixel. Arrays of 64 μm and 75μm pitch have been fabricated and are the highest resolution a-Si:H arrays reported to date. The resolution matches the pixel size, and sensitivity has been improved by the high fill factor. Comparison is made between arrays with standard TFTs and TFTs with self-aligned source and drain contacts. Data line capacitance is improved by use of the self-aligned contacts.Measurements are included on the contact to bias capacitance. The high fill factor design greatly suppresses lateral leakage currents, while retaining ease of processing. Provided illumination levels remain below saturation, the resolution matches expectation for the pixel size.
More Insight into the Transient Photocurrent Response of Three-Color Detectors
Authors: Stiebig H. , Stannowski B. , Knipp D. , Wagner H. 
Published: April 2011

AbstractNipiin structures with controlled bandgap and mobility-life-time product exhibit excellent stationary properties. However, the photocurrent transients of these devices show reasonable delay times in the range of tens of milliseconds before reaching steady state. Hence, the transient behavior after light switching of three color detectors based on a nipiin structure was studied by a detailed analysis of experimentally determined and simulated data. The numerical simulation reproduces well the characteristic features. The delayed current onset and the sign reversal of the transient photocurrent response are explained by trapping of holes in the vicinity of the central p-layer.
Effects of Material Properties in Amorphous Silicon Color Detectors
Authors: Caputo D. , Colalongo L. , Irrera F. , Lemmi F. , Palma F. , Tucci M. 
Published: April 2011

AbstractIn this work we study the effects of material properties on the reading process of color detectors by using a two dimensional simulator for the transient regime. In particular, starting from the potential and charge distribution in the device, we describe effects of the density of defects on the self-bias process. Results show the possibility to engineer materials in order to optimize response speed of the device.
Low Hydrogen Content, High Quality Hydrogenated Amorphous Silicon Grown by Hot-Wire CVD
Authors: Nelson Brent P. , Crandall Richard S. , Iwaniczko Eugene , Mahan A. H. , Wang Qi , Xu Yueqin , Gao Wei 
Published: April 2011

AbstractWe grow hydrogenated amorphous silicon (a-Si:H) by Hot-Wire Chemical Vapor Deposition (HWCVD). Our early work with this technique has shown that we can grow a-Si:H that is different from typical a-Si:H materials. Specifically, we demonstrated the ability to grow a-Si:H of exceptional quality with very low hydrogen (H) contents (0.01 to 4 at. %). The deposition chambers in which this early work was done have two limitations: they hold only small-area substrates and they are incompatible with a load-lock. In our efforts to scale up to larger area chambers—that have load-lock compatibility—we encountered difficulty in growing high-quality films that also have a low H content. Substrate temperature has a direct effect on the H content of HWCVD grown a-Si:H. We found that making dramatic changes to the other deposition process parameters—at fixed substrate temperature and filament-to-substrate spacing—did not have much effect on the H content of the resulting films in our new chambers. However, these changes did have profound effects on film quality. We can grow high-quality a-Si:H in the new larger area chambers at 4 at. % H. For example, the lowest known stabilized defect density of a-Si:H is approximately 2 × 1016 cm-3, which we have grown in our new chamber at 18 Å/s. Making changes to our original chamber—making it more like our new reactor—did not increase the hydrogen content at a fixed substrate temperature and filament-to-substrate spacing. We continued to grow high quality films with low H content in spite of these changes. An interesting, and very useful, result of these experiments is that the orientation of the filament with respect to silane flow direction had no influence on film quality or the H content of the films. The condition of the filament is much more important to growing quality films than the geometry of the chamber due to tungsten-silicide formation on the filament.
Substrate Sensitivity of the Adhesion and Material Properties of RF-PECVD Amorphous Carbon
Authors: Paul Shashi , Clough F.J 
Published: April 2011

ABSTRACTHydrogenated amorphous carbon (a-C:H), deposited by the if-plasma enhanced chemical vapour deposition (rf-PECVD) technique, is a promising material for large area electronic and interlayer dielectric applications. The structural and electronic properties of rf-PECVD a-C:H, deposited at room temperature from CH4/He and CH4/Ar gas mixtures, are shown to be sensitive to the substrate on which the thin film is deposited. The choice of substrate (c-Si or C7059 glass), and the existence and geometrical dimensions of any metallic pattern on the substrate surface, can result in significant spatial variations in the a-C:H adhesion and material properties. The observed effects are attributed to potential variations across the metal patterned substrates which influence the ‘local’ dc self-bias. This leads to spatial variations in the growth conditions and hence material properties. For electronic device and dielectric isolation applications this effect can result in significant variations in operating performance. The nature of the substrate and any overlying metallisation pattern are therefore important considerations.
Three and Six Channel Sensors: Realization and Colorimetric Characterization
Authors: Knippa D. , Herzog P. , Stiebig H. , Siekmann H. , König F. , Wagner H. 
Published: April 2011

ABSTRACTA novel sensor concept for detecting the fundamental components of the visible light has been developed. The multi-channel sensors based on three stacked amorphous thin film detectors are color moiré or color aliasing free due to their vertical integration. The four terminal devices enable the generation of three or six linearly independent spectral response curves at the same spatial position. The 3-channel sensor based on three stacked pin-diodes generates a red-green- blue signal with one shot, whereas the 6-channel sensor with three stacked pinip structures allows the detection of up to six linearly independent spectral response curves. The reproducibility of the complex layer sequences is enhanced by introducing a textured TCO-layer in the rear part of the device, which leads to a distinct scattering of the incoming light for longer wavelengths.In order to gain information on how to improve the sensor performance, the sensors are characterized. The presented characterization model facilitates the quantification of color errors with regard to the human perception. Furthermore, the color errors of amorphous thin film sensors are compared with a commercial color CCD camera and a BiCMOS color-sensor.
A Study of The Viability of Poly(O-Methoxyanhine) Layer-by-Layer Films as Gas Sensors
Authors: Raposo M. , Oliveira O.N. 
Published: April 2011

ABSTRACTThe electrical properties of layer-by-layer films of poly(o-methoxyaniline) (POMA) alternated with poly(vinylsulfonic acid) (PVS) have been investigated as a function of the surrounding atmosphere, in order to probe the sensitivity of POMA/PVS as a gas sensor. The POMA films have their conductivity increased with increasing humidity, near to one order of magnitude higher for 100% relative humidity when compared to nitrogen. The d.c. applied field may affect the POMA films, for these films become practically insulating if the field is applied for a prolonged time (typically 10-20 h) in humid air. In order to circumvent this problem, a.c. impedance measurements were conducted. For samples in nitrogen, oxygen and carbon dioxide, the real part of the complex impedance increases only when the frequency is lowered below 10 kHz. In a humid atmosphere, the onset for the real part occurs at higher frequencies than for dry atmospheres. Furthermore, at a fixed frequency in the range from 10 to 100 kHz this impedance component increases with the relative humidity.
Supramolecular Assembly Strategies Using Alternate Adsorption of Polyelectrolytes: Applications in Pled And Lc Display Devices
Authors: Advincula R. C. , Inaoka S. , Roitman D. , Franka C. , Knoll W. , Baba A. , Kaneko F. 
Published: April 2011

ABSTRACTWe present work on the modification, processing, and analysis of ultrathin films for display devices primarily using the supramolecular assembly strategy. This involves the use of various molecular assembly techniques (organic, polymer, metal) in which layer order and functionality is achieved at defined length scales approaching that of ultrathin films (a few to several hundred nm thicknesses). The use of alternate polyelectrolyte deposition (APD) is primarily investigated in ultrathin films that have significance in the fabrication of display devices. The first application involves modifying a polymer light emitting diode (PLED) device fabricated using the ITO/MEH-PPV/Ca protocol with polyaniline derivatives. The second is the use of the “command layer” amplification concept and photo-induced alignment using polarized light with ultrathin films of azo dye/polyelectrolytes in a hybrid liquid crystal (LC) cell configuration. Both strategies rely on the use of surface sensitive spectroscopic and microscopic techniques to correlate device performance with layer ordering at the molecular level. The concept of functional ultrathin layers for device fabrication and modification is emphasized.
Doped Organic Light-Emitting Diodes Based on Random Copolymers Containing Both Hole and Electron Transport Groups
Authors: Jiang Xuezhong , Register Richard A. , Pschenitzka Florian , Sturm James C. , Killeen Kelly A. , Thompson Mark E. 
Published: April 2011

ABSTRACTDoped organic light-emitting diodes (OLEDs), such as PVK containing the electron transport molecule PBD and molecular dyes, have demonstrated three-color capabilities and efficiencies over 1%, but there are concerns about reliability due to recrystallization of the small molecule PBD. In this work we describe the incorporation of both hole and electron transport groups into a single copolymer to avoid recrystallization and phase segregation (which could occur if two separate polymers were used) as well as the application of such copolymers in dye-doped OLEDs. The polymers were synthesized through free radical copolymerization of the electron- donating monomer N-vinylcarbazole (NVK) with the electron-withdrawing monomer 2-(4-tert-butylphenyl)-5-{4-[(4'-vinyl)phenylmethoxy] phenyl}-1,3,4- oxadiazole (BVO). The radical reactivity ratios of the two monomers were estimated to be rNVK=0.052 and rBvo=12. The copolymers are transparent in the visible region, homogeneous as characterized by both GPC and DSC, and have good thermal stability. External quantum efficiencies of 0.07%, 0.3% and 0.4% were achieved in LEDs with device structures of ITO/COP:C47/Mg:Ag, ITO/COP:C6/Mg:Ag and ITO/COP:NR/Mg:Ag, respectively, where COP stands for copolymer, C47 for Coumarin 47, C6 for Coumarin 6 and NR for Nile Red. The introduction of the oxadiazole group balances the injection of holes and electrons by decreasing the hole injection and transport ability and enhancing the electron injection and transport ability of the copolymers relative to PVK.
Three-Color Doping of Polymer Oleds by Masked Dye Diffusion
Authors: Pschenitzka F. , Sturm J. C. 
Published: April 2011

ABSTRACTA method to locally pattern the distribution of dye by diffusion into the polymer film of organic light-emitting diodes is introduced. Using a large-area diffusion source, the diffusion of dye into the polymer film can be controlled with a shadow mask. The materials used are the polymer poly(9-vinylcarbazole) (PVK) combined with electron transport molecules (PBD), and the dyes bimane, coumarin 6 and Nile red. The temperature dependence of the diffusion is investigated along with the effect of annealing of the polymer film. A model of the dye distribution is introduced and estimations of the dye profile based on this model and PL measurement are discussed. A 3-color integrated device was demonstrated.
Some «Exotic» Aspects of Physics With Microtips
Authors: Baptist R. 
Published: April 2011

ABSTRACTThis paper focuses on some experiments done using field emitter arrays (FEAs) produced at CEA-LETI, experiments which are outside of the display or microwave amplifier contexts. Among various studies done at CEA-LETI with FEAs we have selected:- the search towards a spin polarized electron source,- a study on the spatial coherence of the electron beam emitted by a single emitter,- the incorporation of an optical command in a FEA and finally,- the application of a FEA to electron injection into rare gas liquids.
Towards the Realization of a INP/CDS/LAS Cold Cathode
Authors: Cahay M. , Malhotra A. , Modukuru Y. , Tang H. , Bresser W. , Boolchand P. , Mumford P. , Friz W. 
Published: April 2011

ABSTRACTIn the past, we have proposed a new cold cathode emitter which consists of a thin region of CdS (Cadmium Sulfide) sandwiched between a heavily doped InP (Indium Phosphide) substrate and a low work function LaS (Lanthanum Sulfide) semimetallic thin film. In this paper, we briefly review the principle of operation of the cathode and discuss the preliminary experimental steps undertaken to realize prototypes of the device. More specifically, we describe the growth of bulk samples of LaS which is used to achieve Negative Electron Affinity of the CdS/LaS surface. X-ray diffraction and micro-Raman experiments show the successful growth of the fcc cubic phase of LaS samples.
Film Preparation Conditions and Characterization of co-Deposited Tungsten Doped Zinc Oxide Phosphor
Authors: Sobti Jasleen Bombra , Bhatia V. , Babuchna P. M. , Weichold Mark H. 
Published: April 2011

ABSTRACTNeed for efficient blue light emitting source for optoelectronic device applications such as flat panel displays has made the research in luminescent material ever so important. Tungsten doped zinc oxide (ZnO:W) has been identified as a blue light emitting phosphor exhibiting cathodoluminescence near 490 nm. This paper details work done on ZnO:W phosphor preparation conditions for efficient light emission from the phosphor. Material characterization to identify the possible source of blue light emission will also be discussed.
High Temperature Annealing Behaviors of Luminescent Siox:H Films
Authors: Ma Zhixun , Xiang Xianbi , Sheng Shuran , Liao Xianbo , Shao Chunlin , Umeno Masayoshi 
Published: April 2011

ABSTRACTThe effects of high temperature annealing on the microstructure and optical properties of luminescent SiOx:H films have been investigated. Micro-Raman scattering and IR absorption, in combination with atomic force microscopy (AFM), provide evidence for the existence of both a-Si clusters in the as-grown a-SiOx:H and Si nanocrystals in the 1170°C annealed films. The dependence of optical coefficients (μ) on photon energy (hv) near the absorption edge (Eg) is found to follow the square root law: (μhv)½ μ (Eg – hv), indicating that nano-Si embedded in Si02 is still an indirect material. A comparison of the deduced absorption edge with the PL spectra shows an obvious Stokes shift, suggesting that phonons should be involved in the optical transition process.