bluuebunny/crossref_metadata_2025_split huggingface dataset:
Atomic Force Microscopy Study of Initial Nucleation in the Deposition OF μc-Si:H
Authors: Brogueira P. , Chu V. , Conde J.P. 
Published: April 2011

AbstractThe initial stages of microcrystalline silicon growth of n+ doped films prepared by rf plasma enhanced chemical vapor deposition (PECVD) and of intrinsic films prepared by hot-wire chemical vapor deposition (HW-CVD) are studied using atomic force microscopy, Raman spectroscopy and parallel dark conductivity measurements. The effect of the use of a plasma hydrogen treatment, of chamber conditioning prior to this treatment, of the type of substrate (glass or c-Si) used and the effects of a seed layer on the film properties are discussed.
An Optical Gap Calibration Applied to the Case of Hydrogenated Amorphous Silicon
Authors: Sweenor D. E. , O'Leary S. K. , Foutz B. E. 
Published: April 2011

AbstractThere are many different empirical means whereby the optical gap of an amorphous semiconductor may be defined. We analyze some hydrogenated amorphous silicon data with respect to a number of these empirical measures for the optical gap. By plotting these various gap measures as a function of the breadth of the optical absorption tail, we provide a means of relating these disparate measures of the optical gap. The applicability of this calibration to another set of hydrogenated amorphous silicon data is investigated.
Amorphous Silicon Precipitates in (100) c-SI Films Grown by ECRCVD
Authors: Birkholz M. , Platen J. , Sieber I. , Bohne W. , Röhrich J. , Fuhs W. 
Published: April 2011

AbstractSilicon films were grown on (100) n-Si with an electron-cyclotron resonance chemical vapor deposition (ECRCVD) system by decomposition of SiH4 at 325°C. Structure and composition of thin films were investigated by SEM, Raman spectroscopy, elastic recoil detection analysis (ERDA) and TEM. Excellent epitaxial growth was achieved for some hundred nm thickness. For more than 1 μm thick films, however, SEM revealed the occurrence of conical structures orientated upside-down with their basal plane in the film surface. Depth-profiling of the elemental composition of thin films by means of ERDA showed the hydrogen content CH to exhibit a pronounced increase with increasing film thickness. Raman spectroscopy evidenced the coexistence of c-Si and a-Si:H by the occurrence of two bands at 520 and 480 cm-1, the ratio of which was found to depend sensitively upon the position of the laser spot on the sample. All experimental results could be consistently explained by assuming the conical precipitates to consist of a-Si:H which was finally proven by coherent electron beam diffraction (CEBD).
Microcrystalline Silicon Tunnel Junctions for Amorphous Silicon-Based Multijunction Solar Cells
Authors: Ferlauto A. S. , Koh Joohyun , Rovira P. I. , Wronski C. R. , Collins R. W. 
Published: April 2011

AbstractThe formation of tunnel junctions for applications in amorphous silicon (a-Si:H) based multijunction n-i-p solar cells has been studied using real time optics. The junction structure investigated in detail here consists of a thin (~200 Å) layer of n-type microcrystalline silicon (μc-Si:H) on top of an equally thin layer of p-type μc-Si:H, the latter deposited on thick (~2000 Å) intrinsic a-Si:H. Such a structure has been optimized in an attempt to obtain single-phase μc-Si:H with a high crystallite packing density and large grain size for both layers of the tunnel junction. We have explored the conditions under which grain growth is continuous across the p/n junction and conditions under which renucleation of n-layer grains can be ensured at the junction. One important finding of this study is that the optimum conditions for single-phase, high-density μc-Si:H n-layers are different depending on whether the substrate is a μc-Si:H p-layer or is a H2-plasma treated or untreated a-Si:H i-layer. Thus, the top-most μc-Si:H layer of the tunnel junction must be optimized in the multijunction device configuration, rather than in single cell configurations on a-Si:H i-layers. Our observations are explained using an evolutionary phase diagram for a-Si:H and μc-Si:H film growth versus thickness and H2-dilution ratio, in which the boundary between the two phases is strongly substrate-dependent.
Role of Bandgap Grading for the Performance of Microcrystalline Silicon Germanium Solar Cells
Authors: Krause M. , Carius R. , Stiebig H. , Finger F. , Lundszien D. , Wagner H. 
Published: April 2011

AbstractThe optical absorption of microcrystalline silicon germanium alloys (μc-Si1-xGex:H) increases in the near infrared region with increasing germanium content. Therefore, these alloys are promising candidates for the application as intrinsic absorber material in thin film solar cells with tandem and triple structure or IR-detectors. The material properties for a germanium content (x) up to 0.6 and the performance of solar cells based on this material were investigated. Graded bandgap structures are used to optimize the cell performance. For cells with x > 0.3 a continuously graded bandgap in the rear 20 nm of the i-layer (at the i/n interface) results in an enhancement of the open circuit voltage by 40-80 mV compared to an abrupt bandgap discontinuity. When the design of the p/i interface region is changed in a similar way no effect on Voc is observed.
High Rate Deposition of Microcrystalline Silicon Using Resonance Plasma Source (HELIX) – Plasma Properties and Deposition Results
Authors: Grtiger H. , Terasa R. , Haiduk A. , Kottwitz A. 
Published: April 2011

AbstractMicrocrystalline silicon layers have been deposited by PECVD using a resonance plasma source (Helix) operating at frequencies of 46, 68, 113 and 163 MHz. The plasma discharges in hydrogen and various hydrogen/silane mixtures were investigated by optical emission spectroscopy (OES) and mass spectroscopy (MS). Growth rate, crystalline fraction and hydrogen content of the layers were studied for different gas compositions, excitation frequencies and plasma powers.Plasma monitoring revealed preferably the formation of positive ions. The density of positive hydrogen ions increased steadily 15 times by raising the frequency from 46 MHz to 163 MHz, whereas the ion energy was reduced from 75 eV to 23 eV and the radiation from hydrogen decreased to 50 %. Growth rates up to 1.5 μm/h have been achieved for microcrystalline layers at 230 °C deposition temperature. The content of hydrogen was below 15 at.%. Raman spectroscopy measurements reveal that 20 to 70 % of the silicon was crystalline depending on the silane concentration.
Integrated Amorphous and Polycrystalline Silicon TFTs with a Single Silicon Layer
Authors: Pangal K. , Chen Y. , Sturm J.C. , Wagner S. 
Published: April 2011

AbstractSelective exposure of an a-Si:H film to a room temperature hydrogen plasma using a patterned SiNx, capping layer and a subsequent anneal at 600°C, resulted in polycrystalline and amorphous silicon regions in a single silicon layer on the same glass substrate. Top-gate non-self-aligned TFTs were fabricated in both the amorphous and polycrystalline regions with all shared processing steps and no laser processing using a re-hydrogenation step. The TFTs had good characteristics, with field-effect mobilities upto 1.2 cm2/Vs and 15 cm2/Vs for the a-Si:H and the poly-Si TFTs, respectively, and ON/OFF ratios >105 in either case.
A New Method to Characterize TCO/P Contact Resistance in a-SI Solar Cells
Authors: Hegedus Steven S. , Gibson Michael , Ganguly Gautam , Arya Rajeewa 
Published: April 2011

AbstractA method is presented to characterize the TCO/p contact and the TCO sheet resistance in a-Si based p-i-n superstrate devices. It requires having scribed TCO strips, which are electrically isolated before a-Si deposition, then fabricating rows of individual devices on each strip. Analysis of 4-terminal measurements in different V-sensing configurations yields the TCO/p contact and TCO sheet resistance in a straightforward manner. The method is applied to devices fabricated on 3 brands of commercial SnO2 substrates. The TCO/p contact resistance is found to be ~2 Ω-cm2 and the sheet resistance decreases by 2-4 Ω/sq after a-Si deposition on all 3 brands of SnO2 substrates.
Low Temperature Deposition of Amorphous Silicon Based Solar Cells
Authors: Koch Christian , Ito Manabu , Schubert Markus , Werner Jurgen H. 
Published: April 2011

AbstractOur investigations study the influence of various deposition parameters on the structural and optoelectronic properties of a-Si:H deposited at temperatures of 100 °C and below. Despite a significant material quality deterioration at low substrate temperatures, we observe remarkable improvements of charge carrier transport properties due to an increased H2-dilution of the process gases. In case of doped layers, we restore the electrical conductivity of low temperature n-type a-Si:H to standard values, whereas the p-layer quality is still inferior. We incorporate our optimized low temperature layers into a variety of solar cell types, including single and tandem cell structures. In addition to our conventional pin-structures we also successfully develop nip-cells for growth on opaque polymer substrates. From pinpin tandem cells, we record initial efficiencies of 6.0 % at a deposition temperature of 100 °C and 3.8 % at 75 °C. Interestingly, our nipnip tandem structures attain similar values which offers the possibility for deposition on low-cost plastic substrates. The mechanical flexibility of such substrates offers a wide variety of novel applications.
A Numerical Model for Hot-Wire Chemical Vapor Deposition of Amorphous Silicon
Authors: Goodwin D. G. 
Published: April 2011

AbstractA Direct Simulation Monte Carlo numerical model for hot-wire CVD is described that includes detailed gas-phase chemistry and accurately models gas-phase transport, from the low-pressure ballistic regime to the high-pressure diffusive regime. Model predictions for an idealized reactor geometry are shown to agree qualitatively with experimental trends.
Dependence of Image Transient Behavior on Operating Parameters of Amorphous Silicon Image Sensors
Authors: Aflatooni Koorosh , Weisfield Richard , Zhong Fan , Bornstein Jon , Hack Mike , Gomcz Carlos 
Published: April 2011

AbstractThe growing interests for real-time applications of our amorphous silicon X-ray image sensors requires a better understanding of transient behavior in imaging characteristics. In our pixel structure, which consists of a p-i-n photodiode and an addressing thin film transistor (TFT), the image lag can stem from a number of mechanisms, including charge retention on the photodiode, TFT charge transfer efficiency, and data-line charge sharing. The exact prevailing mechanism depends on the array design and the operating conditions of the sensors. This paper describes the results of our systematic studies on image lag, and its dependence on various operating conditions of the image sensors, such as applied bias, light intensity, frame time, and applied gate voltages. We find that the charge retention in the intrinsic region of the photodiode is an important source of the image lag, and it is correlated to the forward transient characteristics of the diode. This correlation can be explained by the common underlying mechanisms leading to depletion region formation and charge transport through the diode. Furthermore, we notice that the time dependent decay of the image lag, originated mainly from charge retention in the diode, presents power-law time dependence, which is consistent with the release of trapped charges from a continuous distribution of defect states. We also find only a small variation in the image lag, <%3, for a wide range of gate on-periods, 10μs-80μs, and gate on-voltages, 15V- 30V, which indicates an efficient charge transfer by the switching TFT. These results demonstrate that in our devices, the image lag is controlled by the intrinsic defect levels in the a-Si:H photodiode.
Photoinduced Space Charge Effects in a-Si:H Solar Cells
Authors: Unold T. , Binnewies T. , Brüggemann R. , Bauer G.H. 
Published: April 2011

AbstractWe have investigated charge collection in thin amorphous silicon solar cells under light bias illumination, both experimentally and by numerical simulation. In such charge collection experiments, space charge due to trapped bias-light generated carriers leads to an enhancement of a small signal probe beam charge collection. It is found that this enhancement of the small signal charge collection is strongly dependent on the diode thickness and the defect density in the samples. In particular for thin diodes (d < 0.5 microns) the charge collection enhancement can be shown to increase with light-induced degradation of the devices. The effect of these material parameters as well as other experimental parameters, such as light bias and probe beam photon flux, will be demonstrated by means of numerical simulation.
Artificial Formation of Nucleation Seed in Excimer Laser Recrystallization Of Poly-Si
Authors: Jeon Jae-Hong , Park Kee-Chan , Kang Ji-Hoon , Lee Min-Cheol , Han Min-Koo 
Published: April 2011

ABSTARCTExcimer laser annealing method employing artificial nucleation seed is proposed to increase the grain size of polycrystalline silicon(poly-Si). We utilize Si component incorporated in aluminum(Al)-sputtering source for the nucleation seed. Si clusters which are to be used as nucleation seed are successfully formed on the substrate by deposition and etch-back of Si-incorporated Al layer. Irradiation of excimer laser on amorphous silicon(a-Si) film deposited on the substrate prepared by our method results in enlargement of poly-Si grains, compared with conventional laser recrystallization. Poly-Si thin film transistor also shows much improved electrical perfbrmance which directly reflects the quality of poly-Si film recrystallized by our method.
From A Reaction Mechanism to New PPV'S for High Performance Polymer-Leds
Authors: Spreitzer H. , Becker H. , Kreuder W. , Kluge E. , Schenk H. 
Published: April 2011

ABSTRACTPoly(p-phenylene vinylene)s (PPVs) are very promising materials for optoelectronic applications, especially for displays based on polymer light emitting diodes (PLEDs). We report here our findings concerning defect structures in this materials and the influence of the discovered irregularities on an important property of the materials, i.e. the operational life in a PLED. Recent improvements, which were deviated from this findings are presented: optimized PPVs with a lower amount of defects result in a strong increase of operational lifetime.
Jet Printing of Copper Lines at 200°C Maximum Process Temperature
Authors: Hong C.M. , Wagner S. 
Published: April 2011

ABSTRACTWe describe a new technique for making copper lines by printing a precursor pattern that is converted to copper, at a maximum process temperature of 200°C. We formed copper metallization patterns on 80 μm thick Coming 0211 glass substrates by jet printing. Continuous lines of copper with resistivity of 10 μΩcm have been obtained. We successfully applied this technique to the direct printing of copper source and drain contacts for amorphous silicon thinfilm transistors. The TFTs are bottom gate back-channel etched structures, with the silicon stack made by RF excited PE-CVD. The TFT process uses only printing for all masking steps, by employing laser-printed toner etch masks, and using the printed copper as the mask for the back channel etch. The transistor ON/OFF current ratio is 105. The process for copper printing represents a further step toward an all-printed TFT technology.
Polymer Leds Based on N-Alkylsulfinyl Ppv Precursor Polymers
Authors: Kiebooms R. , Resel R. , Vanderzande D. , Leising G. 
Published: April 2011

ABSTRACTA new class of precursor polymers, as first described by Louwet et al. [1], was used to make organic LEDs. Device properties are relatively independent from the side chain to be eliminated. However introduction of two methyl groups onto the phenyl ring introduces significant changes in absorption, photoluminescence (PL) emission, PL quantum efficiency and electroluminescence spectra. From XRD there is an indication that this effect might be related to a different packing of the polymer chains.
Improved electroluminescence lifetime and efficiency of polymer light- emitting diodes with plasma-treated indium tin oxide anodes
Authors: Kim J. S. , Friend R. H. , Cacialli F. 
Published: April 2011

ABSTRACTWe studied the influence of various surface treatments of indium-tin oxide anodes on the operational stability of high-efficiency green-emitting polymer light-emitting diodes, fabilicated with a doped poly(3,4-ethylene dioxythiophene) PEDOT hole transport layer, a polyfluorene-based emissive layer, and Ca-Al cathodes. The anodes were modified by physical (oxygen-plasma), chemical (aquaregia), or combined treatments. Oxygen-plasma improves the stability under constant current over all the other anodes, with half-brightness lifetimes (initial brightness, 200 cd/m2) two to five times longer than for untreated samples, and 1000 times longer than for aquaregia ones. We derive two major indications for optimisation of PLEDs. First, thermal management of the diode is of the uppermost importance. Second, the ITO anode and in general the electrical properties of the hole-injecting contact are crucial to device operation, even in the presence of a hole transport layer.
Energy Level Alignment at Tpd/Etal Interfaces Studied by Kelvin Method
Authors: Hayashi N. , Ito E. , Ishii H. , Ouchi Y. , Seki K. 
Published: April 2011

ABSTRACTThe vacuum level shift A was determined by Kelvin probe method for TPD/metal systems prepared in ultrahigh vacuum (TPD: N, N'-bis(3-methylphenyl)-N, N'-diphenyl-[1, 1'-biphenyl]-4,4'-diamine). The energy of the vacuum level sharply changed at the initial stage of depositing TPD on the metal substrates, and further bending was not observed up to 100 nm thickness of TPD. This result is consistent with our previous studies of ultraviolet photoelectron spectroscopy. These results indicate the invalidity of traditional model with a common vacuum level at organic/metal interface. We discussed the dependence of the vacuum level shift on the work function Φm of the metal substrate (Au, Cu, Ag, Mg, and Ca). A liner correlation between Δ and Φm was observed only in the region of 3.8 eV < Φm < 4.5 eV, indicating that Fermi level alignment is not achieved at least for some interfaces. We found that Δ for TPD film on the air-exposed metal substrate is smaller than that of TPD on clean metals and was observed a liner relation between Φm and Δ except for the Cu substrate.
1.5 μm Luminescence from ErQ Based Organic Light Emitting Diodes
Authors: Curry R.J. , Gillin W.P. 
Published: April 2011

ABSTRACTOrganic light emitting diodes have been fabricated using erbium tris(8-hydroxy-quinoline) as the emitting layer and N, N'-diphenyl-N, N'-bis(3-methylphenyl)-1,1'-biphenyl-4,4'-diamine (TPD) as the hole transporting layer. Room temperature electroluminescence was observed at 1.5 μm due to intra-atomic transitions between the 4I13/2 and 4I15/2 levels in the Er3+, ion. These results make the possibility of producing silicon compatible 1.5 μm technology based on such devices a reality.
Frequency Resolved Photoluminescence (PL), Delayed Fluorescence and Triplet-Triplet Annihilation in Φ-Conjugated Polymers
Authors: Partee J. , Frankevich E. L. , Uhlhorn B. , Shinar J. , Ding Y. , Barton T. J. 
Published: April 2011

ABSTRACTThe delayed fluorescence of poly(p-phenylene vinylene) (PPV) and poly(p-phenylene ethynylene) (PPE) derivative solids and frozen solutions at 20 K is described. It provides strong evidence for triplet-triplet annihilation to singlets excitons accounting for up to ∼3% of the total emission in PPV films and ∼1.5% in PPE powder. It also yields triplet lifetimes of 70 and 110 μs in PPV films and frozen solutions, and ∼200 and ∼500 μs in PPE powder and frozen solutions, respectively.
The Physics of Organic Light-Emitting Devices
Authors: Scott J. Campbell , Malliaras George G. , Bozano Luisa , Carter Sue A. , Ramos Sergio 
Published: April 2011

ABSTRACTQualitatively, the basic principles behind the operation of OLEDs are well established. In order to optimize device parameters such as power efficiency and operating voltage, to explore the limits of performance and to understand changes in the electrical properties as diodes age, it is necessary to develop a quantitative understanding of each of the relevant processes: injection of electrons and holes at the cathode and anode, charge transport, recombination and exciton formation, and emission. In this paper, we summarize our experimental, theoretical and numerical studies to address these issues.
Properties of Si/Cs/O nanocluster thin films with negative electron affinity
Authors: Dinh L. N. , McLean W. , Schildbach M. A. , Balooch M. 
Published: April 2011

ABSTRACTThin films of Si/Cs/O nanoclusters have been synthesized by the technique of supersaturated thermal vaporization of Si and Cs in an oxygen background gas. These films, which were deposited onto conducting or semiconducting substrates, exhibit negative electron affinity (NEA) as evidenced by ultraviolet photoemission spectroscopy (UPS). Photo and field electron emission properties of these nanocluster films were investigated with photo-electron emission microscopy (PEEM), field electron emission microscopy (FEEM), and current-voltage measurements. Flat cathodes covered with thin films of Si/Cs/O nanoclusters exhibited high current outputs and low turn-on fields. The films' NEA is unaffected by air exposure and is stable to high temperature annealing (550 TC). A field emission display unit with a simple diode structure containing a flat cathode coated with a patterned thin film of Si/Cs/O nanoclusters has also been built to demonstrate the potential application of this material in cold cathode electron emitting devices, particularly field emission flat panel displays.
High Current Field Emission from ZrC with Differing Cone Angles
Authors: Mackie W. A. , Xie Tianbao , Lee K.S. , McCalluma A.T. , Kirby M.J. , Davis P. R. 
Published: April 2011

ABSTRACTWe briefly report on progress in forming field emitter array (FEA) cones from zirconium carbide. The major advances are on high current emission from single carbide emitters. These unique carbide materials have electron emission properties making them attractive for several applications. These could include video displays, microwave applications, high current and small spot electron sources (accelerators and FELs) and for operation at tube pressures or in poor vacuums (FEAs, vacuum detectors, neutralizing beams for ion thrusters, and charge dissipation on spacecraft).The significant recent outcomes are in high current electron emission from single emitters with and without extraction apertures. A new processing technique has been developed to allow in-situ sharpening of arced emitters. This method also yields large emitter-cone half angles yet preserves the small emitter radii of electrochemically etched emitters. So far, this geometry translates into currents as high as 15 mA dc, the highest yet measured from single emitters, and enhanced beam confinement. This geometry may also lead to new considerations in forming transition metal carbide emitter cones for FEAs.