bluuebunny/crossref_metadata_2025 huggingface dataset:
Problems of Power Feeding in Large Area PECVD of Amorphous Silicon
Authors: Stephan U. , Kuske J. , Grüger H. , Kottwitz A.
Published: April 2011

The production of amorphous silicon, e.g. for solar cells, requires large area, high-deposition rate plasma reactors. Increasing the radio frequency from the conventional 13.56MHz up to VHF has demonstrated higher deposition and etch rates and lower particle generation, a reduced ion bombardement and lower breakdown, process and bias voltages.

But otherwise the use of VHF leads to some problems. The non-uniformity of deposition rate increase due to the generation of standing waves (TEM wave) and evanescent waveguide modes (TE waves) at the electrode surface.

Increasing the frequency and/or the deposition area the plasma impedance, the capacitic stray impedance of the RF electrode and other parasitic capacitive impedances decrease. Increasing the frequency and/or the RF power, the phase angle of the discharge and of the impedance at every point at the lines between the RF matching network an the RF electrode tends more and more towards -90°. This results in increasing currents and standing waves with extremly high local current maximas. Increasing resistances of lines and contacts due to the skin effect and loss-caused heating up of the lines the power losses increase extremely, up to 90% and more. In spite of the increasing of the coupled power, the plasma power does not increase. Thermal destructions of the lines due to extreme expansion or melting are possible.

Some solutions to reduce the non-uniformity of the deposition rate like multipower feeding, central backside power feeding, electrode segmentation, use of load impedances, published in former publications, will be discussed in connection with several reactor types (coaxial, large area, long plasma source) in view of the efficiency of power coupling and the practical realization. Solutions to minimize the power losses at the lines will be presented.
The Role of Vacancies and Dopants in Si Solid-Phase Epitaxial Crystallization
Authors: Chen C. M. , Rassiga S. , Gessmann T. , Petkov M. P. , Weber M. H. , Lynn K. G. , Atwater H. A.
Published: April 2011

The role and interaction of vacancies and dopants in the crystallization of amorphous Si (a-Si) by solid-phase epitaxy (SPE) was investigated. To this end, we studied: (i) the solid-phase epitaxy rate measured by time-resolved reflectivity (TRR), (ii) the dopant and carrier concentrations measured by secondary ion mass spectrometry (SIMS) and spreading resistance (SR) analysis, and (iii) the vacancy concentration measured by positron annihilation spectroscopy (PAS). Phosphorus was implanted into a-Si on Si (001), which was previously amorphized by 29Si+ implantation, to create a nonuniform P doping profile. Phosphorus doped samples compensated with a similar boron profile were also studied. Samples were vacuum annealed for various times so that the amorphous-crystal interface was stopped at various depths providing frozen frames of the SPE process. These samples were then studied with PAS to investigate the vacancy population and to identify the impurity-defect complexes. Using this method, we have observed a population of phosphorus-vacancy complexes in the epitaxial layer.
Possibility of Quasi-Single-Crystalline Semiconductor Films
Authors: Noguchi T. , Usui S. , Gosain D. P. , Ikeda Y.
Published: April 2011

The existence of a novel tetrahedral semiconductor Quasi-Single-Crystalline (QSC) phase is posited. In the QSC semiconductor phase, the films consist of grains with a diamond structure of tetrahedral elements, such as Si, Ge and C, and the grains have a preferred orientation, such as <111> or <100> normal to the film. The lattices perpendicular to the grain boundaries are quasi-matched with neighboring grains. The grains in the films form a regular array, and are distributed more uniformly than in conventional poly-crystalline semiconductor films. Because of the small-angle grain boundaries, a tetrahedral QSC semiconductor such as QSC Si films are expected to have extremely low energy barriers at the grain boundaries.
Medium-Range Order in a-Si:H Below and Above the Onset of Microcrystallinity
Authors: Williamson D.L.
Published: April 2011

Medium range order (MRO) and the formation of microcrystallites in a-Si:H prepared by plasma-enhanced chemical vapor deposition (PECVD) and hot-wire chemical vapor deposition (HWCVD) have been probed by systematic x-ray diffraction studies with films as thin as those used in solar cells. Effects of substrate temperature, hydrogen dilution, film thickness, and type of substrate have been examined. High-hydrogen-diluted films of 0.5 μm thickness, using optimized deposition parameters for solar cell efficiency and stability, are found to be partially microcrystalline (μc) if deposited directly on stainless steel (SS) substrates but are fully amorphous provided a thin (20 nm) n-layer of a-Si:H or μc-Si:H is first deposited on the SS. The latter predeposition does not prevent partially microcrystallinity if the films are grown thicker (1.5 to 2.5 μm) and this is consistent with a recently proposed phase diagram of thickness versus hydrogen dilution. Analysis of the first (lowest angle) scattering peak of the a-Si:H phase demonstrates that its width, directly related to MRO, is reduced by heavier hydrogen dilution in PECVD growth or by increased substrate temperature in HWCVD growth. The narrowest width of fully amorphous material correlates with better solar cell stability and this is not likely related to bonded hydrogen content since it is quite different in the optimized PECVD and HWCVD a-Si:H. A wide range of MRO apparently exists in the residual amorphous phase of the mixed a/μc material.
Structural Changes in a-Si:H Films Deposited on the Edge of Crystallinity
Authors: Mahan A.H. , Yang J. , Guha S. , Williamson D.L.
Published: April 2011

Using infrared, H evolution and x-ray diffraction (XRD), the structure of high H dilution, glow discharge deposited a-Si:H films ‘on the edge of crystallinity’ is examined. From the Si-H wag mode peak frequency and the XRD results, we postulate the existence of very small Si crystallites contained within the as-grown amorphous matrix, with the vast majority of the bonded H located on these crystallite surfaces. Upon annealing at ramp rates of 8-15°C/min, a H evolution peak at ~400°C appears, and film crystallization is observed at temperatures as low as 500°C, both of which are far below those observed for a-Si:H films grown without H dilution using similar rates. While the crystallite volume fraction is too small to be detected by XRD in the as-grown films, these crystallites enable the crystallization of the remainder of the amorphous matrix upon moderate annealing, thus explaining the existence of the low temperature H evolution peak.
Interstitial Trapped Hydrogen Molecules in Pecvdamorphous Silicon
Authors: Borzi R. , Mascarenhas F. , Fedders P. A. , Leopold D. J. , Norberg R. E. , Wickboldt P. , Paul W.
Published: April 2011

New NMR measurements show that interstitial T site-trapped molecular hydrogen can amount to more than one third of the contained hydrogen in high quality PECVD amorphous silicon. Microvoid-contained dense molecular hydrogen is negligible in these good films. Experiments on a sequence of hydrogenated and/or deuterated a-Si films have characterized individually-trapped molecular HD and D2 in films deposited from SiD4, and from SiH4+D2. The T site-trapped molecular hydrogen fraction observed here is larger than previously reported because of recent efforts to measure very slowly relaxing molecular components and the employment of radiofrequency pulse sequences to detect ortho-D2 with nuclear spin I=2. The population of interstitially trapped molecular hydrogen increases with increasing photovoltaic quality over a range of an order of magnitude in photoresponse product ημτ. Above 200 K, hopping transport of molecular hydrogen among the amorphous equivalent of interstitial T sites occurs with an activation energy near 50 meV.
Nmr Study of Ortho-Molecular Hydrogen in Hydrogenated Amorphous Silicon
Authors: Su Tining , Taylor P.C. , Chen Shenlin , Crandall R.S. , Mahan A.H.
Published: April 2011

A Jeener-Broekaert three-pulse sequence is used to investigate ortho-molecular hydrogen (o-H2) in device quality amorphous silicon films prepared by plasma enhanced chemical vapor deposition (PECVD) and hot wire CVD (HWCVD). For the PECVD sample, the concentration of hydrogen molecules is ~ 11% of the total hydrogen concentration, one order of magnitude larger than that inferred from spin-lattice relaxation time measurements (~1%). Hence, most of the hydrogen molecules do not serve as effective relaxation centers. For HWCVD samples with ~3 to 4% hydrogen and very low void densities, the concentrations of hydrogen molecules are ~1% of the total hydrogen concentration. In these samples, spin-lattice relaxation measurements for bonded hydrogen indicate that the concentration of hydrogen molecules that contribute to spin-lattice relaxation is at most 0.1% of the total hydrogen concentration. Spin-lattice relaxation time (T1) measurements of ortho-molecular hydrogen indicate two very different T1's. The longer T1 is ~ 0.6 s, possibly due to an electric quadrupole-quadrupole (EQQ) interaction between o-H2 molecules and, the shorter T1 is ~ 3 ms, very close to that calculated for a two-phonon Raman process for rotating o-H2.
Anisotropy in Hydrogenated Amorphous Silicon Films as Observed Using Polarized Ftir-Atr Spectroscopy
Authors: Webb J. D. , Gedvilas L. M. , Crandall R. S. , Iwaniczko E. , Nelson B. P. , Mahan A. H. , Reedy R. , Matson R. J.
Published: April 2011

We used polarized attenuated total reflection (ATR) measurements together with Fourier transform infrared (FTIR) spectroscopy to investigate the vibrational spectra of hydrogenated amorphous silicon (a-SiHx) films 0.5-1.0 microns in thickness. We deposited the films using hot-wire or plasma-enhanced chemical vapor deposition methods (HWCVD or PECVD, respectively) on crystalline silicon and cadmium telluride substrates. Our ATR technique gave a spectral range from 2100-400 cm-1, although the Si-H wagging mode absorption band at 640 cm-1 was somewhat distorted in the a-SiHx/Si samples by impurity and lattice absorption in the silicon ATR substrates. We report the identification of a Si-O-C impurity band with maximum intensity at 1240-1230 cm-1. The assignment of this band to a Si-O-C vibration is supported by secondary-ion mass spectrometry (SIMS) measurements. Our polarized FTIR-ATR spectra of HWCVD and PECVD a-SiHx films on <111> Si ATR substrates show that the impurity dipoles are oriented strongly parallel to the film growth direction. The wagging mode absorbance band is more intense in the film plane. This trend is less pronounced for the Si-H stretching vibrations. These observations are consistent with some degree of anisotropy or medium-range order in the films. The anisotropy in the Si-H bands may be related to residual stress in the films. Our scanning electron microscopy (SEM) analyses of the samples offer additional evidence of bulk structural anisotropy in the a-SiHx/Si films. However, the Si-O-C impurity band was not observed in the polarized ATR-FTIR spectra of the a-SiHx/CdTe samples, thus indicating that the Si substrates influence formation of the impurity in the a-SiHx/Si films.
Simulation of Quantum Efficiency Spectroscopy for Amorphous Silicon P-I-N Junctions
Authors: Estwick Rodney , Dalal Vikram L.
Published: April 2011

Quantum efficiency(QE) spectroscopy of amorphous silicon and alloy solar cells has been used for many years now to determine the mobility-lifetime products for minority carriers. Similarly, matching of I(V) curves, assuming a linear model for collection as a function of applied voltage, has been used to quantify the effects of degradation on cell performance by estimating changes in the collection length [or range] of holes. In this paper, we do a numerical simulation of these techniques, using the AMPS I-D model developed by Fonash and his coworkers. The simulation shows that neither the lifetime nor the electric field in the devices is constant as a function of position. Nor is the electric field a linear function of applied voltage, particularly when the voltage exceeds about half the built-in voltage. The uniformity of the lifetime depends on the applied bias and on the defect densities in the material. This variation in electric field and lifetime and nonlinearity with applied voltage makes questionable some of the conclusions drawn from fitting device I(V) curves, particularly under forward bias. However, when one uses only a limited range of forward bias, or, preferably, make measurements in cells with thicker i layers under reverse bias, one c.an make reasonable estimates of the hole mobility-lifetime(μτ) product or the collection lengthl The simulations also show that indeed, it is the hole μτ product which is the limiting parameter.
Hydrogen Diffusion in the Hydrogen Collision Model of Amorphous Silicon Metastability
Authors: Branz Howard M.
Published: April 2011

The trap-controlled model of H diffusion that underpins the H collision model of amorphous silicon metastability provides new insight into thermal and light-enhanced H diffusion in a-Si:H. The longstanding puzzle of the linear DB-dependence of diffusion coefficient with doping is resolved. Expressions for the light-induced H diffusion coefficient are derived with and without D-for-H exchange reactions. It is shown that D-for-H exchange does not affect the long-time diffusion coefficient that is measured under illumination.
The Properties of a-SiC:H and a-SiGe:H Films Deposited by 55 kHz PECVD
Authors: Budaguan B.G. , Sherchenkov A.A. , Berdnikov A.E. , Metselaar J.W. , Aivazov A.A.
Published: April 2011

The deposition processes and the properties of a-SiC:H and a-SiGe:H films in 55 kHz glow discharge were investigated. The analysis of deposition rate and RBS measurements showed that the chemical reactions between SiHn spices and CH4 control the incorporation of C in a-SiC:H films. High deposition rates of a-SiC:H and a-SiGe:H films fabricated by 55 kHz PECVD is caused by the increase of radical fluxes to the growth surface. The specific features of a-SiC:H and a-SiGe:H microstructure were revealed by IR and AFM analysis. In a-SiC:H films the islands of low size were distinguished on the surfaces of large islands. The large variation of the total hydrogen content in a-SiGe:H did not affect the optical bandgap, while the hydrogen related microstructure controlled the electronic properties such as dark conductivity, 11p.r product, defect density and Urbach slope.

The results of optoelectronic properties and SW effect measurements of 55 kHz a-SiC:H and a-SiGe:H films demonstrated the increased stability in comparison with a-Si:H.
Step Response of a-Si:H Photodiodes
Authors: Mulato M. , Ramón M. , Wagner S.
Published: April 2011

We correlate the dark current-transients of a-Si:H p-i-n photodiodes with solar cell performance and quantum efficiency. For devices with solar cell efficiency varying from 7.2 to 2.2 % subjected to ±1 V and a sampling frequency of 21 kHz: i) the reverse-bias charging time is shorter, with the initial charging time being reduced by ~ 1.5 μs, while the time for final current stabilization is reduced by - 5 μs.; ii) the forward-bias time for the onset of space charge limited current dominated regime is ~ 1 μs faster, the final current limit is achieved also in shorter time (~ 9 μs), and the individual final limit current is diminished by ~ 8 % due to carriers trapping, while the relative final limit current between different diodes is diminished by ~ 50 %.
Optical Transitions in Light-Emitting Nanocrystalline Silicon Thin Films
Authors: Toyama T. , Kotani Y. , Shimode A. , Abo S. , Okamoto H.
Published: April 2011

Optical transitions in nanocrystalline Si (nc-Si) thin films with different mean crystal sizes ranging from < 2 nm to ~3 nm have been studied by electroreflectance (ER) spectroscopy. At 293 K, ER signals are observed at 1.20-1.37 eV to be corresponding to fundamental gap in bulk crystalline Si. With a decrease in the mean crystal sizes of nc-Si, the transition energy of the fundamental gap is increased and the ER signal is intensified. The bandgap widening would be due to quantum confinement (QC) in nc-Si, and the increased signal indicates appearance of direct transition nature. The ER signals are also observed at 2.2 eV and at E1 (E0’) direct gap of 3.1-3.4 eV, while photoluminescence (PL) peak energies are located at 1.65-1.75 eV and at 2.3 eV. With the reduced mean crystal size, the 1.7-eV PL peak energy is also increased, suggesting that QC is also responsible for the increased PL peak energy.
Charge Transport in the Transition From Hydrogenated Amorphous Silicon to Microcrystalline Silicon
Authors: Kattwinkel A. , Braunstein R. , Sun G. , Wang Qi
Published: April 2011

The electronic transport properties of a series of samples prepared by hot-wire chemical vapor deposition with a transition from a-Si:H to μc-Si:H were measured applying the photoconductive frequency mixing technique. We found both improved stability against light-soaking and different values for the photomixing electron lifetime and mobility close to the onset of microcrystallinity as compared to the amorphous state. In particular, the mobility-lifetime product of charge carriers in some of the μc-Si:H samples turns out to lie about two orders of magnitude higher than that of a-Si:H films. The mobility on the other hand, is shown rather to decrease in the transition to the μc-region. Additional measurements of the range and the depth of long range potential fluctuations yield a possible explanation for our results in that grain boundaries may serve as scattering centers and barriers against recombination.
Anisotropic Transport in Microcrystalline P-I-N Devices
Authors: Vieira M. , Fantoni A. , Fernandes M. , Maçarico A. , Martins I. , Louro P. , Schwarz R.
Published: April 2011

Entirely μc-Si:H p-i-n structures presenting an enhanced sensitivity to the near infrared region and a positive spectral response under forward bias higher than the open circuit voltage are analysed under different external voltage bias and illumination conditions.

A two phase model to explain the transport properties is proposed using as input parameters the measured experimental data. The results suggest that the transport is preferentially concentrated inside the crystalline grains. The conduction within the amorphous regions is poor. The percolation path is different for electrons and holes and is determined by the local fields at the boundaries. These local fields are independent of the externally applied condition, and they can be related to the persistence of the small photocurrent observed when a bias voltage higher than the open circuit voltage is applied.
Laser Crystallized Polysilicon TFT'S Using LPCVD, PECVD and PVD Silicon Channel Materials-A Comparative Study
Authors: Fulks R.T. , Boyce J. B. , Ho J. , Davis G. A. , Aebi V.
Published: April 2011

In this work polysilicon TFI's were fabricated by excimer laser crystallization of active channel silicon which was deposited by three different methods: I) LPCVD at 550 °C; 2) PECVD at 225 °C; and 3) PVD at room temperature. CMOS devices were produced with the same low temperature (less than 600 °C) top gate process and the laser anneal condition was optimized for the material type and thickness. For PECVD material a pre-anneal step of 450 °C for 1 hour was required before crystallization to avoid bubbling and ablation due to hydrogen evolution, but no such anneal was required for either LPCVD or PVD material due to their low hydrogen and Ar content. For 50 nm films, laser energy densities were typically in the range of 300-400 miJ/cm2. Excellent device results were obtained for both LPCVD and PECVD material with n-channel field effect mobilities greater than 100 cm2/Vs and on/off ratios greater than 108 at 5 V drain bias. Good results were also obtained for PVD films that can be further improved by optimizing deposition and anneal conditions. In moving toward very low temperature polysilicon processing (less than 230 °C) both PECVD and PVD channel films appear to be viable candidates.
Thin Film Transistors based on Microcrystalline Silicon on Polyimiide Substrates
Authors: Constant A.P. , Witt T. , Bratland K.A. , Shanks H.R. , Landin A.R.
Published: April 2011

This study reports on the fabrication of inverted gate TFT devices and circuits using a low temperature microcrystalline silicon deposition process compatible with polyimide substrates. Results from the electrical and material characterization of μ-Si:H based TFT's are presented. Device performance is compared with that of α-Si:H based TFT's constructed on polyimide. Results indicate that the anticipated improvement in device performance due to an increase in the α-Si:H Hall mobility (~10 cm2/V-sec) over that of α-Si:H (~1 cm2/V-sec) is not realized. Properties of μ-Si:H films are related to deposition parameters.
Investigation of Textured Back Reflectors for Microcrystalline Silicon Based Solar Cells
Authors: Kluth O. , Vetterl O. , Carius R. , Finger F. , Wieder S. , Rech B. , Wagner H.
Published: April 2011

Microcrystalline silicon (μc-Si:H) solar cells require an effective light trapping in the near infrared (NIR) to enhance the long wavelength spectral response. For this purpose we investigated back reflectors based on texture-etched ZnO/Ag stacks prepared on glass substrates by magnetron sputtering. With decreasing sputter pressure the resulting surface texture of the glass/Ag/ZnO substrates after etching exhibits a larger feature size and root mean square roughness. The increase in feature size corresponds to an increase of diffuse reflectivity. Applied in microcrystalline solar cells prepared by VHF plasma enhanced chemical vapour deposition (PECVD), the reflectors showing the largest feature size (prepared at the lowest possible sputter pressure) yielded the highest long wavelength spectral response. The μc-Si n-i-p cells prepared on the latter back reflector exhibited efficiencies of 6.9 % (short circuit current density jsc= 18.8 mA/cm2) and 7.5 % (jsc=25 mA/cm2) for an i-layer thickness of 1 μm and 3.5 μm, respectively.
UV Imager in TFA Technology
Authors: Motze F. , Seibel K. , Schneider B. , Hillebrand M. , Blecher F. , Lulé T. , Keller H. , Rieve P. , Wagner M. , Böhm M.
Published: April 2011

An image sensor with enhanced sensitivity for near ultraviolet radiation (UVA) has been fabricated in TFA (Thin Film on ASIC) technology. The device employs an amorphous silicon pin detector optimized for UV detection by carbonization and layer thickness variation. The front electrode consists of an Al grid or TCO. Measurements show a peak responsivity of 90 mAW-1 at 380 nm. The UV Imager prototype consists of 128 × 128 pixels with a size of 25 μm × 25 [tim each, fabricated in a 0.7 μm CMOS process. Global sensitivity control serves to achieve a dynamic range in excess of 80 dB. The sensor can be used in fields such as chemical, medical and astronomical applications. Furthermore, a UV monitor has been developed, suited to warn of excessive sunlight exposure, considering skin type and sun protection factor.
Directional Breakdown of Metal/a-Si:H/c-Si Heterostructures and its Application to PROMs
Authors: Zhu Hong , Kalkan Ali Kaan , Cuiffi Joseph , Fonash Stephen J
Published: April 2011

This paper gives the first report of a directional breakdown phenomenon present in specially constructed amorphous silicon / crystalline silicon heterojunction structures. After breakdown, the forward current can be greatly increased, but the reverse leakage current remains unchanged or even lowered. We use the Analysis of Microelectronic and Photonic Structures (AMPS) [1] device simulation tool to study this phenomenon and show that the structures can provide a new approach to producing Programmable Read Only Memory (PROM).
Why SiNx:H is the Preferred Gate Dielectric for Amorphous Si Thin Film Transistors (TFTS) and SiO2 is the Preferred Gate Dielectric for Polycrystalline Si TFTs
Authors: Lucovsky Gerald , Phillips J.C.
Published: April 2011

Constraint theory developed for bulk glasses and recently applied to thin films and single crystalline Si (C-Si) dielectric interfaces is extended in this paper to a-Si:H and polycrystalline-Si (poly-Si) dielectric interfaces in TFTs where it provides guidelines for device optimization. The constraining effects of network bonding forces are a linear function of the average bonding coordination, Nav. Nav ∼ 3 separates low-defect density networks as in Si02 (Nav =2.67), from highly-defective networks such as non-hydrogenated Si3N4 (Nay = 3.43). Nay ∼ 3 also separates device-quality from highly-defective Si-dielectric interfaces. These criteria are applied to Si-Si02 and Si-SiNx:H interfaces that are integral components of TFT devices.
Gate Current Suppressed Lateral FEAs with Integrated TFTs
Authors: Lim Moo-Sup , Park Cheol-Min , Han Min-Koo
Published: April 2011

Lateral FEAs which have three terminals, stable anode current, and suppressed gate current are proposed and fabricated. In order to eliminate the path of electrons between tips and anode, the proposed FEAs are sealed by evaporation of oxide while Molybdenium in our privious work. Experimental results such as controllibility of gate electrode, a portion of the gate current for the anode current, and stability of the anode current are given. The proposed FEAs exhibit an excellent controllibility by gate electrode and stability of the emission current. The gate current of new FEAs is negligible compared with the ande current while that of the privious FEAs is about 20% of the anode current.
A Novel Two-Pass Excimer Laser Crystallization Process to Obtain Homogeneous Large Grain Polysilicon
Authors: Mariucci L. , Carluccio R. , Pecora A. , Foglietti V. , Fortunato G. , Sala D.Della
Published: April 2011

New approach to control the lateral growth mechanism through the opportune spatial modulation of the absorbed laser energy and with a two-pass excimer laser crystallization process is presented. In the first pass, spatial modulation of the light intensity has been obtained by irradiating the sample through a patterned mask in contact with the sample. Lateral growth is triggered when the irradiated regions are fully melted and a lateral extension of the grains in excess to 1 μm has been observed for samples irradiated at RT. In order to homogeneously crystallize the sample, the film can be re-irradiated (second pass) without the mask. By using opportune energy densities it can be induced a complete melting of the residual a-Si regions (masked areas during the first pass), while partially melting the polysilicon regions (unmasked areas during the first pass). Different mask geometries have been investigated and for optimized conditions, the sample area can be fully covered with laterally grown grains. The proposed novel technique can be rather attractive for polysilicon TFT fabrication, being characterized by only a two laser-shot process and wide energy density windows.
Properties of Polysilicon films Oxidized in Inductively Coupled Plasma and its Effect on thin-Film Transistors
Authors: Choi Yong Woo , Ahn Jin Hyung , Ahn Byung Tae
Published: April 2011

We investigated the properties of polycrystalline silicon (poly-Si) films oxidized in inductively coupled plasma (ICP) and the characteristics of poly-Si thin film transistors (TFTs) with an ICP/LPCVD gate oxide. The ICP oxidation reduced the interface traps and passivated dangling bonds by hydrogen incorporation. The ICP oxidation did not change the roughness of the Si/SiO2, while thermal oxidation increased the roughness largely. The characteristics of the TFTs with ICP/LPCVD oxide were improved due to the reduced interface trap density.
Structure and Properties of Quasi-Monocrystalline Silicon Thin-Films
Authors: Rinke Titus J. , Bergmann Ralf B. , Werner Jürgen H.
Published: April 2011

This contribution describes the preparation of a single crystalline Si thin-film separable from a reusable Si wafer. The method relies on: i) etching of a porous silicon layer ii) high-temperature annealing and iii) transfer of the recrystallized film to a foreign substrate. As a result of the process we obtain 1 to 30 μm thick monocrystalline Si films that contain voids with a size of several 100 nm. Due to its “swiss-cheese-like” structure the material is termed as “quasi-monocrystalline Si”. Sub micrometer thin layers are almost compact, while in several micron thick films voids cause scattering of incident light. This effect increases the effective absorption coefficient by light trapping and seems promising for the application of our quasi-monocrystalline films in thin film solar cells. Quasi-monocrystalline p-type silicon reaches a hole mobility of 78 cm2/ Vs measured by room-temperature Hall-effect. High carrier mobility and adjustable optical characteristics make these films suitable for display and photovoltaic applications. Quasi-monocrystalline films are processed using conventional high-temperature Si processing; finished devices can be transferred to a foreign substrate such as glass, while the starting wafer can be reused several times.
Novel Device Concept for Voltage-Bias Controlled Color Detection in Amorphous Silicon Sensitized Cmos Cameras
Authors: Neidlinger T. , Harendt C. , Glökner J. , Schubert M. B.
Published: April 2011

We present a novel sensor concept comprising a new contacting scheme for voltage-bias con- trolled thin film photodiode arrays on CMOS readout chips. Our unilateral contact structure greatly facilitates manufacturing of the sensor system. Moreover, the novel contacting scheme most efficiently suppresses crosstalk between neighboring pixels. The respective devices are ready for operation and testing directly after deposition of the amorphous silicon based sensor layers. No extra transparent front contact is needed, no patterning and no connection between the topmost layer of the thin film stack and the underlying readout chip. Due to the lack of a metal oxide front contact, contamination of CMOS manufacturing equipment with tin, zinc or similar materials is definitely avoided. Thus, for the first time, a sensor concept with complete CMOS process compatibility is demonstrated. Our new sensor structure allows for a considerable reduction in manufacturing cost of high performance optical detection systems. As a proof of concept, we present detailed investiga- tions on current-voltage characteristics, dynamic behavior and spectral response of 0.1-inch test structures. Down-scaling to pixel sizes in the micron range is evaluated by semi-empirical numerical modeling and proves easily feasible.
Photoluminescent Polymer Films for Display Applications
Authors: Palmans Anja , Montali Andrea , Weder Christoph , Smith Paul
Published: April 2011

Novel poly(p-phenylene ethynylene) polymers, ANT-OPPE and COU-OPPE, have been prepared, in which anthracene and coumarin sensitizer molecules are covalently attached to the conjugated polymer backbone via a flexible spacer. These polymers show efficient energy transfer from the pendent sensitizer molecule to the PPE backbone, both in dilute solution as well as in an oriented polyethylene matrix. In case of ANT-OPPE, we found that the PPE backbone adapts the orientation of the matrix and is efficiently oriented, while the anthracene moiety remains essentially isotropic, resulting in a state-of-the-art polarizing energy transfer for this system.
Optical Properties and Characterization of Eu3+ Activated Pmma:Paac Copolymer Samples: Eu Concentration Effects
Authors: F. R. Sosa , Flores M. , T. R. Rodríguez , F. A. Muñoz
Published: April 2011

Samples of Eu3+-activated PMMA:PAAc copolymers were prepared in order to investigate their spectroscopic properties. The densities, refractive indices, UV-Visible absorption and emission spectra and fluorescence decay times were obtained experimentally. These data were used in conjunction with Judd-Ofelt theory to calculate the spontaneous emission probabilities and branching ratios, as a function of the europium content. The range of the concentration was 0.1 to 2.5 % mol. Our results are combined with previous information on the optical properties of rare-earth activated polymers in order to get a better understanding of the role played by the Eu3+ ions on the polymerization process in our samples.
Photoluminescence of Poly(P-Phenylene Vinylene) Encapsulated in Mesoporous Silica
Authors: Pattantyus-Abraham Andras G. , Wolf Michael O.
Published: April 2011

The preparation of poly(p-phenylene vinylene) (PPV) encapsulated in a mesoporous silica, MCM-41, is reported. In situ polymerization of xylylene bis(tetrahydrothiophenium chloride) yields a highly luminescent, yellow powder with a fluorescence spectrum matching that of unencapsulated PPV. Nitrogen adsorption isotherms show that the pore size of the PPV- loaded MCM-41 is significantly smaller than that of empty MCM-41 and a polymer loading of ca. 8% by weight is obtained by thermogravimetric analysis. Photoluminescence data for the encapsulated PPV are presented.
New Poly-Si TFT'S with Selectively Doped Region in The Channel
Authors: Lee Min-Cheol , Jeon Jae-hong , Yoo Juhn-suk , Park Kee-chan , Han Min-koo , Yoon Chan-Eui
Published: April 2011

We propose new poly-Si TFT's with selectively doped region in the center of channel in order to reduce large leakage current. In proposed TFT's, the selectively doped region redistributes total induced electric field in the channel. For VGS<0, VDS> 0 in the n-channel proposed TFT's, most of the high electric field applies in the depletion regions which exist the drain/undoped region and undoped region/selectively doped region which faces to the source. Comparing with conventional TFT's, the electric field induced near the drain junction reduces to about 1/2, therefore, electron-hole pairs generated in drain junction are considerably reduced. Furthermore, the ON-current of proposed TFT's is the same or slightly lower than that of conventional ones. Consequently, the experimental data show the considerable improvement of the ON/OFF current ratio.
Back Gate Effects in N-Channel Monocrystalline Silicon Devices-on-Glass and their Suppression by Boron Ion Implantation
Authors: Baine Paul , Mitchell S.J.N , Gamble H.S , Armstrong B.M
Published: April 2011

Initial N-channel self aligned polycrystalline silicon gate transistors fabricated on 1.5μm -2μm single crystal Silicon-O-Glass(SOG) layers exhibited poor transfer characteristics. Measured threshold voltages and On/Off current ratios were in the order of -8V and 10 respectively. This is due to the presence of fixed charge at the bond interface introducing back gate effects which degrade and distort device performance. These back gate effects were suppressed by implantation of boron into the silicon substrate prior to oxidation and bonding, with energy 40keV and dose 7.4×1012cm−2. This resulted in an improvement in device performance with a threshold voltage of-0.54V. On/Off current ratio increased to 1840 and field effect mobility increased from 274cm2/Vs to 357cm2 Vs
Heteroepitaxial Growth of In203 on Ysz (100) Single Crystal Surface
Authors: Orita M. , Ohta H. , Tanji H. , Hosono H. , Kawazoe H.
Published: April 2011

In203 films were deposited on YSZ (001) single crystal surface at 800°C at an oxygen pressure of 14 Pa by pulsed laser deposition (PLD) method. A heteroepitaxial relationship between the film and the substrate was seen in TEM photographs and X-ray diffraction measurements. The w locking curve full width of half maximum (FWHM) of the In203 (004) x-ray diffraction was 0.06°. Film conductivities were ∼10 S/cm or less, while carriers on the order of lO18/cm3 were generated.
Spin-on Polymer Gate Dielectric for High Performance Organic Thin Film Transistors
Authors: Sheraw C.D. , Gundlach D.J. , Jackson T.N.
Published: April 2011

We have investigated the polymeric insulators benzocyclobutene (BCB), parylene C and polyimide for use as gate dielectrics in pentacene organic thin film transistors (TFTs). Atomic force microscopy (AFM) was used to examine the surface roughness of the polymeric dielectrics and the morphology of pentacene films deposited onto them. X-ray diffraction was used to examine the molecular ordering of pentacene films deposited onto the polymeric dielectrics. We find a correlation between the surface roughness of the gate dielectric and the grain size in deposited pentacene films, with smooth surfaces yielding larger, more dendritic grains. Despite significant changes in film morphology, pentacene TFTs using BCB, parylene C, or polyimide as the gate dielectric have performance comparable to devices using SiO2 as the gate dielectric. These results suggest that there is not a strong correlation between pentacene film grain size and field-effect mobility for these devices. Pentacene TFTs using BCB as the gate dielectric had field-effect mobility as high as 0.7 cm2/V-s, on/off ratio > 107, subthreshold slope less than 2 V/decade, and negative threshold voltage, making them an attractive candidate for use in organic-based large-area electronic applications on flexible substrates.
Self-Assembly Processes for Organic Led Transport Layers and Electrode Passivation
Authors: Malinsky J.E. , Li W. , Wang Q. , Cui J. , Chou H. , Marks T.J. , Jabbourt G.E. , Shaheen S.E. , Anderson J.D. , Lee P. , Richter A.G. , Kippelen B. , Dutta P. , Peyghambarian N. , Armstrong N.
Published: April 2011

This contribution describes the use of self-limiting siloxane chemisoroption processes to self-assemble building blocks for the modification of vacuum-deposited organic LED (OLED) devices. One approach consists of the use of self-assembling OLED hole transport materials for application in hybrid self-assembled + vapor deposited two-layer devices. Another approach involves the application of self-limiting, chemisorptive self-assembly techniques to introduce thin dielectric films between the anode and hole transport layer of a vapor deposited two-layer OLED device.
Polyquinolines: Multifunctional Polymers for Electro-Optic and Light-Emitting Applications
Authors: Jen Alex K.-Y. , Ma Hong
Published: April 2011

A versatile, and generally applicable modular approach for making second-order nonlinear optical (NLO) side-chain aromatic polyquinolines has been developed. This approach emphasizes the ease of incorporating NLO chromophores onto the pendent phenyl moieties of parent polyquinolines at the final stage via mild Mitsunobu reaction. This method provides the synthesis of polyquinolines with a broad variation of the polymer backbones and great flexibility in the selection of NLO chromophores. These side-chain NLO polyquinolines demonstrate high electro-optic (E-O) activity (up to 35 pm/V at 830 nm and 22 pm/V at 1300 nm, respectively) and a good combination of thermal, optical, electrical and mechanical properties.

Comparatively, two new electroluminescent (EL) polyquinolines have been prepared via the Friedlander condensation and nucleophilic reaction. The resulting polymers contain a bipolar property with both an efficient hole-transporting moiety, tetraphenyldiaminobiphenyl (TPD), and an electron affinitive light-emitting moiety, bis-quinoline. In addition, they possess high thermal stability, excellent electrochemical reversibility, good thin film-forming ability, and bright light-emitting property. Electrical characterization of two-layer diode devices based on the configurations of ITO/CuPc/TPD-PQ or TPD-PQE/Al showed excellent electroluminescence performance (a rectification ratio greater than 105 and a low turn-on voltage of less than 4 V).
Cathode Lifetime Issues in Field Emission Displays
Authors: Reuss Robert H. , Chalamala Babu R.
Published: April 2011

Field emission displays are currently undergoing rapid transition from laboratory prototypes into commercial display components. Display lifetime and reliability are critical issues that will determine success of these displays in the marketplace. In this paper, we will summarize issues affecting field emission display lifetime and a roadmap for creating long life field emission display devices.
Long-Term Degradation Mechanism of Organic Light Emitting Devices Based on Small Molecules
Authors: Aziz Hany , Popovic Zoran D. , Hu Nan-Xing , Hor Ah-Mee , Xu Gu
Published: April 2011

The intrinsic degradation of tris(8-hydroxyquinoline) aluminum (AlQ3)-based organic light emitting devices, that leads to the long-term decrease in the electroluminescence efficiency of the devices operated under constant current conditions, is studied. The injection of holes in A1Q3 is found to be the main factor responsible for device degradation. OLEDs with dual HTLs in different arrangements are also presented to demonstrate the proposed degradation mechanism. The role of various approaches to increase OLED lifetime, such as, doping the hole transport layer, introducing a buffer layer at the hole-injecting contact, or using a mixed emitting layer of hole and electron transporting molecules, is explained.
Field Emission Energy Distribution and Current-Voltage Characteristics Using Single Tip Gated Diodes
Authors: Bernhard John M , Rouse Ambrosio A. , Sosa Edward D. , Gnade Bruce E. , Golden David E. , Chalamala Babu R. , Aggarwal Sanjeev , Ramesh R.
Published: April 2011

Field emission current-voltage characteristics and simultaneous field emission electron energy distributions have been measured using single tip gate diodes. An energy distribution is generated at each step of a current-voltage characteristic using a compact low-cost simulated hemispherical energy analyzer. A PC programmed with graphics-based data acquisition software is used for data acquisition and control. The PC is connected to a CAMAC crate and a picoammeter through a GPIB interface. The picoammeter measures the current leaving the tip and the field emission electrons are energy analyzed, detected and processed in the CAMAC crate. The CAMAC crate also sends control voltages. to the gate anode and the energy analyzer. This apparatus was used to measure tip work functions and Fowler-Nordheim tip shape parameters for Mo and IrO2 field emission tips. Work function measurements from field emission tips are compared to photoelectric work function measurements from flat surfaces.
Selective Area Laser Induced Deposition of Metal Boride Thin Films
Authors: Zhong Z.C. , Holmes V. , Dowben P.A. , Sellmyer D.J.
Published: April 2011

We have developed a novel technique for the selective area deposition of rare earth hexaborides: laser-induced solution deposition (LISD). This technique is both simple and efficient and combines many advantages of both chemical vapor deposition and electrolytic deposition. The results of LISD deposition show that the polycrystalline thin films of rare earth hexaborides and sub-borides such as MB6, MB4, and MB2 (M = Gd, La) are formed through the light initiated chemical reaction of nido-decaborane (B10H14) and rare earth chloride in solution. These films grow with a strong texture growth axis and morphology that is dependent both on the selection of solvents and laser wavelengths and power used in LISD.
Lifetime and Stability of Carbon Cold Cathodes
Authors: Fink R. L. , Thuesen L. H. , Tolt Z. Li , Yaniv Zvi , Marrese Colleen M.
Published: April 2011

We present the results of tests measuring the life of carbon cold cathodes and determining what conditions limit the life of the cathode. Cathode life and stability are important for a broad range of applications, including displays, electron sources for satellite thrusters, x-ray tubes and microwave devices. Cathodes were tested in vacuum chambers using different gas environments as well as in sealed and gettered glass envelopes. We measured emission current half-lives of 10,000 - 20,000 hours or more in sealed display devices, depending on operating conditions. The presence of a significant oxygen or water partial pressure degrades the life of the cathode. After removing the gases the decay rate was restored to near the original value. A similar partial pressure of hydrogen gas has little or no effect on the life of the cathode. Initial results of operation in a xenon environment indicate carbon cold cathodes are much more robust compared to microtip cathodes. These results will be discussed with respect to the various applications considered for carbon cold cathodes.
Er3+ Doped Silica Glass by Sol-Gel Processing with Organic Complexation
Authors: Han Xiuhong , Cao Guozhong , Pratum Tom
Published: April 2011

Er3+-doped silica glass (up to 10 wt%) was synthesized by sol-gel processing with the addition of 3- aminopropyl trimethoxysilane (APS) as a complexing agent. Er3+ ions reacted with amino groups and, thus, linked to the silica network during the sol preparation. As a result, the motion of Er3+ ions was restricted and the formation of Er3+ clusters was inhibited. Both fluorescence spectra and magic-angle spinning (MAS) nuclear magnetic resonance (NMR) indicated that the addition of the complexing agent APS resulted in a homogeneous dispersion of high-level Er+3 doping in the resultant gels. After the removal of organic components, however, Er+3 clustering occurs when firing at a high temperature for a long period of time, e.g. at 1000°C for 10 hrs, due to enhanced Er3+ diffusion.
The Effect of Post-Anodization Chemical Etching on Porous Silicon Investigated by Means of Photoluminescence and Ir Spectroscopy
Authors: Uehara Nobutomo , Yamazaki Tetsuya , Kobayashi Akiharu , Fujihara Shinji , Ohmukai Masato , Tsutsumi Yasuo
Published: April 2011

We studied the effect of post-anodization chemical etching on porous silicon by means of photoluminescence (PL), Fourier transform infrared (FTIR) absorption and Raman spectroscopy. We performed these measurements with repeating etching and then observed the variation of the spectra. On the basis of the correlation between PL and FTIR spectral changes, the PL emission at 660 and 730 nm in PL spectra stems from Si-H2, and Si-H clusters at surface, respectively. Raman spectra show a close relation between PL emission at 850 nm and nanocrystallites in porous silicon. In addition, chemical etching contributes to the promotion of nanocrystallites and to dissolving them.
Photoluminescent Polymer Films for Display Applications
Authors: Palmans Anja , Montali Andrea , Weder Christoph , Smith Paul
Published: April 2011

Novel poly(ρ-phenylene ethynylene) polymers, ANT-OPPE and COU-OPPE, have been prepared, in which anthracene and coumarin sensitizer molecules are covalently attached to the conjugated polymer backbone via a flexible spacer. These polymers show efficient energy transfer from the pendent sensitizer molecule to the PPE backbone, both in dilute solution as well as in an oriented polyethylene matrix. In case of ANT-OPPE, we found that the PPE backbone adapts the orientation of the matrix and is efficiently oriented, while the anthracene moiety remains essentially isotropic, resulting in a state-of-the-art polarizing energy transfer for this system.
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

Poly(ρ-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.