bluuebunny/crossref_metadata_2025_split huggingface dataset:
In-Situ Study of the Optoelectronic Properties of Very thin P-TYPE μc-Si:H Films and the Potential Profile at the p-(μc-Si:H)/i-(a-Si:H) Interface
Authors: Hamma S. , Cabarrocas P. Rocai 
Published: April 2011

ABSTRACTIn-situ UV-visible ellipsometry and Kelvin probe measurements were performed to study the growth of boron-doped microcrystalline silicon (μc-Si:H) thin films and the band profiling at the p- (μc-Si:H)/i-(a-Si:H) interface. The in-situ UV-visible spectroscopic ellipsometry measurements, combined with dark conductivity measurements, performed at different stages of the growth show that p-type μc-Si:H formation can be achieved for a film thickness below 10 nm. These analyses also reveal that both the optical absorption, and the dark conductivity do not change significantly for a crystalline volume fraction above 50%. Moreover, the contact potential as measured by in- situ Kelvin probe shows a saturation just after the percolation threshold. These results indicate that highly crystallized doped layers are not necessary in device applications. From the Kelvin probe measurements, the potential profile through the p-(μc-Si:H)/ i-(a-Si:H) interface was measured. The microcrystalline silicon p-layers were successfully incorporated in single junction solar cells.
Scanning Tunnelling Microscopy Study of the Growth Mechanism for Hydrogenated Amorphous Silicon Produced by Plasma Enhanced Chemical Vapour Deposition
Authors: Flewitt A.J. , Milne W.I. , Robertson J. , Stephenson A.W. , Welland M.E. 
Published: April 2011

ABSTRACTThin films of hydrogenated amorphous silicon (a-Si:H) have been deposited by plasma-enhanced chemical vapour deposition (PECVD), and the resulting topography measured in-situ on a nanometre scale using a scanning tunnelling microscope (STM). An island structure is observed on the surface of device quality a-Si:H, which can be quantitatively analysed using a one dimensional Fourier transform of the topography. Results suggest that deposition is limited by the creation of dangling bonds on the a-Si:H surface and not by the surface transport of SiH 3 radicals at the deposition temperature (598 K). Island nucleation takes place through the abstraction of hydrogen atoms from the a-Si:H surface by plasma etching and the subsequent attachment of an SiH 3 radicals to the available sites. A thermally activated hydrogen effusion process around the edge of each island, where the step edge causes a high local hydrogen concentration, then creates further dangling bonds which allow the islands to grow. A simulation has been constructed, which confirms this two stage mechanism.
Changes in Short- and Medium-Range Order in a-Si:H Induced by Light-Soaking, Pseudodoping and Doping With Boron
Authors: Golikova O.A. , Kazanin M.M. , Kudoyarova V.Kh. , Adriaenssens G.J. , Eliat A. 
Published: April 2011

ABSTRACTA study of a-Si:H structure on the scales of short- and medium- range order has been carried out by the Raman spectroscopy method. Undoped a-Si:H films were deposited by the conventional rf- PECVD with some special variations in the process conditions ( pseudodoping technique); doping with boron was performed from a gas phase as well as by ion implantation. Changes in short- and medium- range order induced by light-soaking, pseudodoping and doping with boron were determined and compared.
INTERFACE CHARACTERISATION AND INTERNAL ELECTRIC FIELD EVALUATION OF a-Si:H PIN SOLAR CELL BY VARIABLE ENERGY POSITRON ANNIHILATION SPECTROSCOPY
Authors: Zou X. , Chan Y. C. , Webb D. P. , Lam Y. W. , Chan F. Y. M. , Lin S. H. , Hu Y. F. , Beling C. D. , Fung S. 
Published: April 2011

ABSTRACTBy means of the slow positron beam Doppler-broadening technique, the depth profile of microvoids across a p-i-n double junction solar cell has been resolved. VEPFIT fitting results indicate an approximately uniform density of the defects throughout the solar cell, but with an enhanced concentration at all of the interfaces possibly due to network mismatch. In order to evaluate the internal electric field, Variable Energy Positron Annihilation Spectroscopy (VEPAS) measurements have been performed on a single junction pin solar cell at different biases. The internal electric field effect on positrons has also been examined in terms of the bias dependence of positron drift in a-Si:H single junction pin solar cell.
Photoinduced Structural Changes in Hydrogenated Amorphous Silicon
Authors: Shimizu K. , Tabuchi T. , Hattori K. , Kida H. , Okamoto H. 
Published: April 2011

ABSTRACTPolarized electroabsorption method has been used to study photo-induced structural changes in hydrogenated amorphous silicon. The field-modulated absorption signal consists of two components, one of which is the true polarization-dependent electroabsorption serving as an indicator of the structural disorder, and the other is the thermoabsorption resulted from the temperature modulation due to Joule heating. The thermoabsorption component has removed from the observed field-modulated absorption signal to make an accurate and reliable evaluation of structural disorder by phase-separation procedure. As a result, about 15-25 % of the observed signal arises from the thermoabsorption effect for the Tauc gap region. Nevertheless, any essential alteration is not needed for our previous PEA results. The internal stress as well as density have been measured to provide another evidences for the photo-induced structural change. It is found that amorphous silicon film expands and the density tends to decrease upon light-exposure, the temporal behaviors of which coincide with that of the PEA ratio factor indicating disorderness of the amorphous network structure. The results permit us to conclude that a large scaled change in the amorphous network structure occurs under light-exposure, which might proceed the light-induced creation of metastable dangling bond defects.
Low Defect Density Microcrystalline-Si Deposited by the Hot Wire Technique
Authors: Mahan A. H. , Vanecek M. , Poruba A. , Vorlicek V. , Crandall R. S. , Williamson D. L. 
Published: April 2011

ABSTRACTThe optical and electronic properties of a series of microcrystalline silicon (μ-Si) films, deposited by the hot wire (HW) technique, are reported. Preliminary results suggest, using moderate H2 /SiH4 dilution ratios and substrate temperatures (320°C), high filament temperatures, and no H gas purifier, that the subgap absorption for these films, measured using the constant photocurrent (CPM) method, can be as low as that obtained for films deposited by the very high frequency glow discharge (VHF-GD) technique. The film dark conductivities of the HW samples, ranging as low as 2.0 × 10−8 (ohm cm)−1, lend further credance to these low defect values. At the same time, the optical absorption in the region > 1.6 eV is higher than that previously observed for the VHF-GD deposited samples. The present results, discussed in the context of the film microcrystalline fraction, suggest that there is no unique, good quality, low defect density μ-Si material, and that different deposition techniques can be used to successfully deposit device quality gc-Si. We also present optical and structural data for films deposited at lower substrate temperatures and higher deposition rates, and suggest combinations of deposition parameters to be used that may further improve the electronic properties of these films.
The Effect of Hydrogen Dilution on Hot-Wire Thin-Film Transistors
Authors: Conde J.P. , Silva H. , Chu V. 
Published: April 2011

ABSTRACTBottom-gate thin film transistors (TFT) were fabricated with amorphous and microcrystalline silicon active layers deposited by hot-wire (HW) chemical vapor deposition using different levels of hydrogen dilution. As the hydrogen dilution was increased above 80%, the active layer made a transition from amorphous to microcrystalline. This transition resulted in an increase of the TFT off-current and in an increase of the TFT subthreshold slope. The TFT on- current and the TFT mobility remained at levels comparable to those of the a-Si:H HW TFTs. A comparison is made between TFTs with amorphous and microcrystalline silicon active layers prepared both by rf glow discharge and HW. HW TFTs with an active layer consisting of a thin layer deposited with high hydrogen dilution underlying a thicker amorphous silicon layer are also compared to TFTs with an active layer of the same total active layer thickness consisting only of the high hydrogen dilution film.
Structural Characterization and Crystallization Process of Nanostructured Silicon Thin Films Produced in Low-Pressure Silane Plasma
Authors: Viera G. , Cabarrocas Proca i , Costa J. , Martínez S. , Bertran E. 
Published: April 2011

ABSTRACTNanostructured silicon thin films (ns-Si:H), consisting of a two-phase mixture of amorphous and ordered material, were obtained by plasma-enhanced chemical vapor deposition (PECVD) under a wide range of plasma conditions. The key to embedding Si-ordered particles in the amorphous Si matrix was the formation of silicon clusters in the gas phase (diameter < 2nm) under conditions of plasma polymerization, and their incorporation into the growing films. The crystallization induced by thermal annealing in these nanostructured films can be attained faster than in conventional a-Si:H thin films, because the silicon-ordered particles cause a heterogeneous nucleation process in which they act as seeds for crystallization. In this work, we present a detailed structural characterization by using electron and X-ray diffraction patterns and Raman spectroscopy. The crystallization dynamics were studied in-situ by Raman spectroscopy.
Raman and Spectroscopic Ellipsometry Studies of P-Doped Poly-Si
Authors: Zollner Stefan , Liu Ran , Christiansen Jim , Chen Wei , Monarch Kathy , Lee Tan-Chen , Singh Rana , Yater Jane , Paulson Wayne M. , Feng Chris 
Published: April 2011

ABSTRACTPhosphorus-doped poly-Si films were studied with Raman spectroscopy and spectroscopic ellipsometry. We determine strain and grain size and compare with a structural analysis using plan-view transmission electron microscopy and atomic force microscopy. We analyze the derivatives of our ellipsometry data (peak shifts and broadenings) using analytical lineshapes, which are affected by grain size, film thickness, doping, and inhomogeneity, but only minimally by macroscopic biaxial strain.
Facetting Growth of Low Temperature Polycrystalline Silicon by Ecr-Cvd with Hydrogen Dilution Method
Authors: Hsiao H.-L. , Yang A.-B. , Hwang H.-L. 
Published: April 2011

ABSTRACTThe polycrystalline silicon films with grain size of 1 μ m have been successful deposited on glass substrates using ECR-CVD with hydrogen dilution method at 250°C and without any thermal annealing. The deposited poly-Si films exhibit severe “hill and valley” surface roughness and facets structures. The X-ray diffraction spectra show that the dominant crystal textures are <220> and <111> orientations. The leaf-like two-fold symmetrical grain shape and the corresponding crystallography diffraction pattern indicate the orientation of largest grain is <110>. The dark field TEM image also shows the upside octahedral facets shape. Considering the effect of orientation on deposition rate and symmetry, the possible facets orientation should be <311>. Moreover, the grain sizes of poly-Si thin films deposited on bare Si wafer and on oxidized Si substrates or glass are almost the same. The facetting and textural structures can be attributed to the surface free energy change induced by the adatom quasi-liquid layer which is composed by the radicals and energetic atomic hydrogen. This adatom quasi-liquid layer would dramatically change the surface diffusion processes of adsorbed precursors and surface free energy of low index planes. Therefore, the SiHn radicals and SinHm molecular precursors with enhanced surface mobility would relax to their stable sites and form the crystalline silicon clusters.
Material Issues in the Commercialization of Amorphous Silicon Alloy Thin-Film Photovoltaic Technology
Authors: Guha S. , Yang J. , Banerjee A. , Sugiyama S. 
Published: April 2011

ABSTRACTTwo significant developments took place in 1997 in the field of amorphous silicon alloy photovoltaic technology. First, a world record stable cell efficiency of 13% was demonstrated using a spectral-splitting, triple-junction structure. Second, a triple-junction photovoltaic manufacturing facility of an annual capacity of 5 MW was commissioned. In order to make the transition from R&D to production, critical material issues and deposition methods which ensure the lowest module cost per delivered watt needed to be evaluated. In this paper, we discuss some of these issues with special reference to the cell materials.
Low-Temperature, High-Quality Silicon Dioxide Thin Films Deposited Using Tetramethylsilane (TMS)
Authors: Reber D. M. , Fonash S. J. 
Published: April 2011

AbstractSilicon dioxide thin films have been deposited at temperatures from 40°C to 250°C by plasma enhanced chemical vapor deposition (PECVD) using tetramethylsilane (TMS) as the silicon containing precursor. The properties of the PECVD TMS oxides (PETMS-Oxs) were analyzed with Fourier Transform Infrared (FTIR) transmission spectroscopy, BOE and P-etch rates and both current-voltage (I-V) and capacitance-voltage (C-V) electrical characterization. At both 130 °C and 250 °C, deposition conditions were identified which formed high quality as-deposited oxide films. Under the best conditions, unannealed Al/PETMS-Ox/c-Si capacitor structures displayed flat band voltages of Vfb = -2.5 V and breakdown fields (Vbd) in excess of 8 MV/cm. These PETMS-Ox films also show low leakage current densities <10-9 A/cm2 which can be maintained up to fields in excess of 4.5 MV/cm. The PETMS oxide electrical quality and process simplicity combine to make a very attractive oxide deposition technology for low temperature, large area applications.
a-Si:H Thin-Film Transistors on Rollable 25-µ;m Thick Steel Foil
Authors: Ma E.Y. , Wagner S. 
Published: April 2011

AbstractWe report the first amorphous silicon thin film transistors (TFTs) on flexible, ultra-thin substrates of 25 µm thick stainless steel foil. The transistors remain operational under convex or concave bending down to 2.5 mm radius of curvature. Taking advantage of the flexibility and resiliency of these devices, we have successfully fabricated TFTs using only xerographic toner masks printed directly on to the steel substrate and using mechanical alignment in the laser printer to obtain the necessary overlay accuracy. The goal of our work is to develop a foldable active-matrix transistor backplane, at low cost and high throughput, for use in highly rugged and portable applications such as foldable intelligent maps. Our results suggest that such foldable backplane circuits are feasible.
Low-Temperature Floating Plasma Oxidation of Poly-SiGe
Authors: Fan Zhineng , Zhao Gang , Chu Paul K. , Jin Zhonghe , Kwok Hoi S. , Wong Man 
Published: April 2011

AbstractorLow temperature oxidation is an essential process for thin-film transistors (TFT) used in active-matrix liquid crystal displays (AMLCD). However, low temperature oxidation gives rise to defects at SiO2/poly-SiGe interfaces. We have recently developed a novel plasma oxidation method for poly-SiGe materials. The poly-SiGe wafers are soaked in 0.1 Torr pure oxygen RF (Radio Frequency) plasma and isolated. That is, the sample voltage is the same as the sheath potential of the floating wall, which is always negative since electrons move faster than ions.The defects caused by ion impact can therefore be reduced. No heating is applied during oxidation, as the sample is heated slightly by the plasma. Under our conditions, the temperature is below 100°C even after oxidation for two hours. Depth profiles are acquired by AES and the oxide/substrate interface is examined by XPS. NMOS devices fabricated using this gate oxide show good characteristics.
Effect of Ni and Al on the Low-Temperature Field Aided Lateral Crystallization (FALC)
Authors: Park Sang-Hyun , Jun Seung-Ik , Lee Chan-Jae , Yang Yong-Ho , Choi Duck-Kyun 
Published: April 2011

AbstractThere have been many reports on the low temperature crystallization of amorphous silicon films by introducing a trace amount of metal impurity for low temperature poly-Si TFTs applications. MIC (Metal Induced Crystallization) uses various metals, to lower crystallization temperature. In this study, a new crystallization method called FALC (Field Aided Lateral Crystallization) in which an electric field is applied during the crystallization was explored. Among possible alloying elements with Si, Ni and Al were selected to compare the effects of these impurities on the FALC.A trace of Ni lowered the crystallization temperature of a-Si down to 5001C and induced lateral crystal growth along the electric field into the metal free region. But Al exhibited no such effect. A new crystallization method, FALC, showed considerably enhanced speed of lateral crystallization and a strong preferred orientation in crystallized Si-films.
High Sensitivity Polymer Photosensors for Image Sensing Applications
Authors: Yu Gang , Wang Jian , McElvain Jon , Heeger Alan J. 
Published: April 2011

AbstractConjugated polymers and polymer blends were developed for photosensing applications. Large size photosensors fabricated in ITO/polymer/metal configuration show high photosensitivity, 0.1-0.4 A/Watt in visible and near UV, as good as that made with inorganic semiconductors. The processability of the polymeric materials allows these photosensors be made in large size, onto substrates in desire shape, or even in flexible form, hybridized or integrated with optical devices or electronic devices. Large area, full-color, digital image sensing is demonstrated using photodiode arrays made from semiconducting polymers. The photodiode arrays, fabricated by casting the semiconducting polymer from solution at room temperature, have high photosensitivity, low dark current and large dynamic range. Photo-detection with desired spectral response or multi-band selection are also demonstrated.
Production of Strontium Sulfide Coatings by Metal Organic Chemical Vapor Deposition
Authors: Moss T.S. , Dye R.C. , Tuenge R.T. 
Published: April 2011

AbstractThis work was focused on the MOCVD of the cerium-doped strontium sulfide (SrS:Ce) phosphor for use in thin film electroluminescent displays (TFELs). Following previous research on a small scale reactor, a feasibility scale-up using a commercially available reactor enlarged the size of the deposition area to a 4” diameter wafer or a 2” by 2” glass slide. Films were deposited from the reaction of Sr(thd)2, Ce(thd)4, and H2S at 450 °C and 5 torr. This system employed a liquid delivery system for the accurate and repeatable delivery of the metal organic reagents. The deposition from this reactor was shown to be crystalline-as-deposited SrS with a (200) orientation, possibly a result of the thin nature of the coating and the involvement of (200) grains in the initial nucleation process. The wafers showed good uniformity, but had some thickness variation near the outer radius of the wafer resulting from the addition of H2S from the outside edge. There were eighteen total deposition experiments, of which nine were characterized for EL performance. The highest brightness observed was 5 fL. The samples were exceedingly thin as a result of the fifteen fold increase in the surface area between the deposition reactors. Increasing the sample thickness to 7,000 Å or higher will dramatically increase the brightness of the emission.
Hybrid Amorphous and Polycrystalline Silicon Devices for Large-Area Electronics
Authors: Mei P. , Boyce J. B. , Fork D. K. , Anderson G. , Ho J. , Lu J. 
Published: April 2011

AbstractDistinct features of amorphous and polycrystalline silicon are attractive for large-area electronics. These features can be utilized in a hybrid structure which consists of both amorphous and polycrystalline silicon materials. For example, an extension of active matrix technology is the integration of peripheral drivers for the improvement of reliability, cost reduction and compactness of the packaging for large-area electronics. This goal can be approached by a combination of amorphous silicon pixel switches and polysilicon drivers. A monolithic fabrication process has been developed based on a simple modification of the amorphous silicon transistor process which uses selective area laser crystallization. This approach allows us to share many of the process steps involved in making both the amorphous and polysilicon devices. Another example of the hybrid device structure is a self-aligned amorphous silicon thin film transistor with polysilicon source and drain contacts. The advantages of the self-aligned transistor are reduction of the parasitic capacitance and scaling down of the device dimension. With a selective laser doping technique, self-aligned and short-channel amorphous silicon thin film transistors have been demonstrated.
Enhanced Luminescence Properties of Pulsed Laser-Deposited Eu:Y2O3 Thin Film Phosphors Using Diamond Buffer Layer
Authors: Cho K.G. , Kumar D. , Lee D.G. , Holloway P.H. , Singh R.K. 
Published: April 2011

AbstractEuropium-activated yttrium oxide (Eu:Y2O3) phosphor films have been grown in-situ on (100) bare silicon and diamond-coated silicon substrates using a pulsed laser deposition technique. Diamond-coated silicon substrates were prepared by hot filament chemical vapor deposition on (100) silicon wafer. Measurements of photoluminescence and cathodoluminescence properties of Eu:Y2O3 films showed that the films grown on diamond-coated silicon substrates are brighter than the films grown on bare silicon substrates. The improved brightness of the Eu:Y2O3 films on diamond-coated silicon substrates is attributed to reduced internal reflection and enhanced scattering of incident beam with lattice. These effects are primarily brought about by the presence of a rough diamond buffer layer between the phosphor film and substrate. Oxygen environment during deposition is necessary for better crystallinity but excess oxygenation of the Eu:Y2O3 films during cooling degrades the brightness of the films.
Passivation of Poly-Si Thin-Film Transistors With Ion-Implanted Deuterium
Authors: Wang Albert W. , Saraswat Krishna C. 
Published: April 2011

AbstractA comparison of ion-implanted deuterium and ion implanted hydrogen for passivation of grain boundary states in poly-Si thin film transistors (TFTs) is presented for the first time. Gate-drain bias stressing was carried out after anneals at 350 °C, 400 °C, and 450 °C. Under stress, deuterated TFTs are more resistant to bias stress than hydrogenated TFTs in terms of most PMOS performance parameters and NMOS leakage current, but are markedly less resistant to NMOS threshold degradation. While still showing promise, these results are not as impressive as those shown for hot carrier degradation in very large scale integration (VLSI) MOS devices. After 350 °C activation anneal, deuterium is less effective than hydrogen at initial device passivation, probably as a result of excessive implant damage. After anneals at 400 or 450 °C, deuterium becomes more effective at passivation than hydrogen, possibly due to differences in diffusion between hydrogen and deuterium.