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Showing papers on "Amorphous solid published in 1998"


Journal ArticleDOI
TL;DR: The reflectance and the phase change on reflection from semiconductor-metal interfaces (including the case of metallic multilayers) can be accurately described by use of the proposed models for the optical functions of metallic films and the matrix method for multilayer calculations.
Abstract: We present models for the optical functions of 11 metals used as mirrors and contacts in optoelectronic and optical devices: noble metals (Ag, Au, Cu), aluminum, beryllium, and transition metals (Cr, Ni, Pd, Pt, Ti, W). We used two simple phenomenological models, the Lorentz-Drude (LD) and the Brendel-Bormann (BB), to interpret both the free-electron and the interband parts of the dielectric response of metals in a wide spectral range from 0.1 to 6 eV. Our results show that the BB model was needed to describe appropriately the interband absorption in noble metals, while for Al, Be, and the transition metals both models exhibit good agreement with the experimental data. A comparison with measurements on surface normal structures confirmed that the reflectance and the phase change on reflection from semiconductor-metal interfaces (including the case of metallic multilayers) can be accurately described by use of the proposed models for the optical functions of metallic films and the matrix method for multilayer calculations.

3,629 citations


Journal ArticleDOI
08 Oct 1998-Nature
TL;DR: A dye-sensitized heterojunction of TiO2 with the amorphous organic hole-transport material 2,2′,7,7′-tetrakis(N,N-di-p-methoxyphenyl-amine)9,9′-spirobifluorene (OMeTAD) was described in this article.
Abstract: Solar cells based on dye-sensitized mesoporous films of TiO2 arelow-cost alternatives to conventional solid-state devices1. Impressive solar-to-electrical energy conversion efficiencies have been achieved with such films when used in conjunction with liquid electrolytes2. Practical advantages may be gained by the replacement of the liquid electrolyte with a solid charge-transport material. Inorganic p-type semiconductors3,4 and organic materials5,6,7,8,9 have been tested in this regard, but in all cases the incident monochromatic photon-to-electron conversion efficiency remained low. Here we describe a dye-sensitized heterojunction of TiO2 with the amorphous organic hole-transport material 2,2′,7,7′-tetrakis(N,N-di-p-methoxyphenyl-amine)9,9′-spirobifluorene (OMeTAD; refs. 10 and 11). Photoinduced charge-carrier generation at the heterojunction is very efficient. A solar cell based on OMeTAD converts photons to electric current with a high yield of 33%.

3,386 citations


Journal ArticleDOI
01 Jul 1998-Nature
TL;DR: In this article, the authors showed that nanometre-sized ceramic powders can be used as solid plasticizers for polyethylene oxide (PEO) electrolytes to prevent crystallization on annealing from amorphous state above 60°C.
Abstract: Ionically conducting polymer membranes (polymer electrolytes) might enhance lithium-battery technology by replacing the liquid electrolyte currently in use and thereby enabling the fabrication of flexible, compact, laminated solid-state structures free from leaks and available in varied geometries1. Polymer electrolytes explored for these purposes are commonly complexes of a lithium salt (LiX) with a high-molecular-weight polymer such as polyethylene oxide (PEO). But PEO tends to crystallize below 60 °C, whereas fast ion transport is a characteristic of the amorphous phase. So the conductivity of PEO–LiX electrolytes reaches practically useful values (of about 10−4 S cm−1) only at temperatures of 60–80 °C. The most common approach for lowering the operational temperature has been to add liquid plasticizers, but this promotes deterioration of the electrolyte's mechanical properties and increases its reactivity towards the lithium metal anode. Here we show that nanometre-sized ceramic powders can perform as solid plasticizers for PEO, kinetically inhibiting crystallization on annealing from the amorphous state above 60 °C. We demonstrate conductivities of around 10−4 S cm−1 at 50 °C and 10−5 S cm−1 at 30 °C in a PEO–LiClO4 mixture containing powders of TiO2 and Al2O3 with particle sizes of 5.8–13 nm. Further optimization might lead to practical solid-state polymer electrolytes for lithium batteries.

2,695 citations



Journal ArticleDOI
TL;DR: In this paper, the field effect mobility in an organic thin-film transistor was studied theoretically. And the authors applied the theory to describe the experiments by Brown et al. on solution-processed amorphous organic transistors, made from polythienylene vinylene and from a small molecule (pentacene).
Abstract: The field-effect mobility in an organic thin-film transistor is studied theoretically. From a percolation model of hopping between localized states and a transistor model an analytic expression for the field-effect mobility is obtained. The theory is applied to describe the experiments by Brown et al. [Synth. Met. 88, 37 (1997)] on solution-processed amorphous organic transistors, made from a polymer (polythienylene vinylene) and from a small molecule (pentacene). Good agreement is obtained, with respect to both the gate voltage and the temperature dependence of the mobility.

779 citations


Journal ArticleDOI
TL;DR: In this article, a large-scale synthesis of silica nanowires (SiONWs) using an excimer laser ablation method was reported. The SiONWs emit stable and high brightness blue light at energies of 2.65 and 3.0 eV.
Abstract: We report large-scale synthesis of silica nanowires (SiONWs) using an excimer laser ablation method. Silica was produced in the form of amorphous nanowires at a diameter of ∼15 nm and a length up to hundreds micrometers. The SiONWs emit stable and high brightness blue light at energies of 2.65 and 3.0 eV. The intensity of the emission is two orders of magnitude higher than that of porous silicon. The SiONWs may have potential applications in high-resolution optical heads of scanning near-field optical microscope or nanointerconnections in future integrated optical devices.

492 citations


Journal ArticleDOI
TL;DR: In this paper, the flow and relaxation of the Zr46.75Ti8.25Cu7.5Ni10Be27.5 bulk metallic glass forming alloy was investigated in the supercooled liquid state and the glass transition region using parallel plate rheometry, three-point beam bending as well as differential scanning calorimetry.

461 citations


Journal ArticleDOI
TL;DR: Very fine cobalt oxide xerogel powders were prepared using a unique solution chemistry associated with the sol-gel process as mentioned in this paper, and the effect of thermal treatment on the surrace area, pore volume, crystallinity, particle structure, and corresponding electrochemical properties was investigated and found to have significant effects on all of these properties.
Abstract: Very fine cobalt oxide xerogel powders were prepared using a unique solution chemistry associated with the sol-gel process The effect of thermal treatment on the surrace area, pore volume, crystallinity, particle structure, and corresponding electrochemical properties of the resulting xerogels was investigated and found to have significant effects on all of these properties The xerogel remained amorphous as Co(OH) 2 up to 160°C, and exhibited maxima in both the surface area and pore volume at this temperature With an increase in the temperature above 200°C, both the surface area and pore volume decreased sharply, because the amorphous Co(OH) 2 decomposed to form CoO that was subsequently oxidized to form crystalline Co 3 O 4 In addition, the changes in the surface area, pore volume, crystallinity, and particle structure all had significant but coupled effects on the electrochemical properties of the xerogels A maximum capacitance of 291 F/g was obtained for an electrode prepared with the CoO x xerogel calcined at 150°C, which was consistent with the maxima exhibited in both the surface area and pore volume; this capacitance was attributed solely to a surface redox mechanism The cycle life of this electrode was also very stable for many thousands of cycles

441 citations


Book
31 Oct 1998
TL;DR: The technology of amorphous and microcrystalline silicon solar cells has been studied in this paper, where the authors present an overview of the properties of solar cells and their properties in terms of optical, electronic and structural properties.
Abstract: Part I: Technology of Amorphous and Microcrystalline Silicon Solar Cells. 1. Introduction. 2. Deposition of Amorphous and Microcrystalline Silicon. 3. Optical, Electronic and Structural Properties. 4. Technology of Solar Cells. 5. Metastability. Part II: Modeling of Amorphous Silicon Solar Cells. 6. Electrical Device Modeling. 7. Optical Device Modeling. 8. Integrated Optical and Electrical Modeling. Index.

383 citations


Journal ArticleDOI
TL;DR: In this paper, a review of x-ray photoelectron spectroscopy studies on carbon nitride (CN) is presented, based on results obtained from CN thin films prepared by mass selected ion-beam deposition.
Abstract: This paper reviews x-ray photoelectron spectroscopy studies on carbon nitride (CN) and reports on results obtained from CN thin films prepared by mass selected ion-beam deposition. The core-level spectra of samples deposited at room temperature show that nitrogen is incorporated into the amorphous network in two different bonding configurations; carbon has three main bonding configurations whose relative contributions vary as a function of the nitrogen content. For samples deposited at elevated temperatures an ordering of the amorphous CN network towards a crystalline graphitelike structure is observed. Furthermore, both deposition at elevated temperatures (350 \ifmmode^\circ\else\textdegree\fi{}C) and post-deposition ion irradiation have a strong influence on the bonding configuration in the CN films. Based on these results and the results reported in the reviewed literature a picture of the microstructure of carbon nitride deposited using energetic species is developed.

376 citations


Journal ArticleDOI
TL;DR: In this article, a large-scale synthesis of silicon nanowires (SiNWs) using a simple but effective approach was reported, where high purity SiNWs of uniform diameters around 15 nm were obtained by sublimating a hot-pressed silicon powder target at 1200 °C in a flowing carrier gas environment.
Abstract: We report the large-scale synthesis of silicon nanowires (SiNWs) using a simple but effective approach. High purity SiNWs of uniform diameters around 15 nm were obtained by sublimating a hot-pressed silicon powder target at 1200 °C in a flowing carrier gas environment. The SiNWs emit stable blue light which seems unrelated to quantum confinement, but related to an amorphous overcoating layer of silicon oxide. Our approach can be used, in principle, as a general method for synthesis of other one-dimensional semiconducting, or conducting nanowires.

Journal ArticleDOI
TL;DR: In this paper, the amorphous nature of CoFe2O4 particles was confirmed by various techniques, such as scanning and transmission electron microscopy (SEM and TEM), electron microdiffraction, and X-ray diffractograms.
Abstract: Nanostructured CoFe2O4 particles were prepared by a sonochemical approach, first by preparation of the amorphous precursor powders, followed by heat treatment at relatively very low temperatures. The precursor was prepared by sonochemical decomposition of solutions of volatile organic precursors, Fe(CO)5 and Co(NO)(CO)3, in Decalin at 273 K, under an oxygen pressure of 100−150 kPa. The amorphous nature of these particles was confirmed by various techniques, such as scanning and transmission electron microscopy (SEM and TEM), electron microdiffraction, and X-ray diffractograms. Magnetic measurements, Mossbauer, and electron paramagnetic resonance (EPR) spectral studies indicated that the as-prepared amorphous particles were superparamagnetic. The Mossbauer parameters and the significantly low (45 emu/g) observed saturation of magnetization of the annealed sample, compared to that of the bulk sample (72 emu/g), reflected its nanocrystalline nature.

Journal ArticleDOI
TL;DR: In this paper, the morphological evolution of the amorphous towards the polycrystalline phase is investigated by transmission electron microscopy and it is interpreted in terms of a physical model containing few free parameters related to the thermodynamical properties of ammorphous silicon and to the kinetical mechanisms of crystal grain growth.
Abstract: The solid phase crystallization of chemical vapor deposited amorphous silicon films onto oxidized silicon wafers, induced either by thermal annealing or by ion beam irradiation at high substrate temperatures, has been extensively developed and it is reviewed here. We report and discuss a large variety of processing conditions. The structural and thermodynamical properties of the starting phase are emphasized. The morphological evolution of the amorphous towards the polycrystalline phase is investigated by transmission electron microscopy and it is interpreted in terms of a physical model containing few free parameters related to the thermodynamical properties of amorphous silicon and to the kinetical mechanisms of crystal grain growth. A direct extension of this model explains also the data concerning the ion-assisted crystal grain nucleation.

Journal ArticleDOI
TL;DR: In this paper, the authors investigated the reversible capacity of thin-film negative electrodes for lithium-ion batteries and found that the substantial irreversibility during the first cycle can be explained by the formation of metallic tin and amorphous lithium oxide.
Abstract: Crystalline SnO{sub 2} thin films have been investigated as possible negative electrodes for lithium-ion batteries. The films have been cycled electrochemically vs. lithium and shown reversible capacity as high as 500 mAh/g over more than 100 cycles. The substantial irreversibility during the first cycle can be explained by the formation of metallic tin and amorphous lithium oxide. This last phase probably plays an important role in allowing the thin-film electrode to contract and expand during the cycling process.

Journal ArticleDOI
B. Stellwag1
TL;DR: In this paper, a double-layer structure of the inner layer consists of a chromium-rich spinel and is covered by an outer layer of magnetite or iron-nickel spinel.

Journal ArticleDOI
TL;DR: In this paper, the structural properties of a series of films grown under a variation of the dilution of the process gas silane in hydrogen, which induces a transition from highly crystalline to amorphous growth, were investigated.
Abstract: The growth of microcrystalline silicon prepared by plasma-enhanced chemical vapour deposition depends on the deposition conditions and yields films with variable content of crystalline grains, amorphous network, grain boundaries and voids. The changes in the structural properties of a series of films grown under a variation of the dilution of the process gas silane in hydrogen, which induces a transition from highly crystalline to amorphous growth, were investigated. The evolution of the crystalline volume fraction was quantitatively analysed by Raman spectroscopy and X-ray diffraction. The results confirm the need for proper correction of the Raman data for optical absorption and Raman cross-section. Transmission electron microscopy was used to investigate the characteristics and the variation in the microstructure. Upon increasing the silane concentration the strong columnar growth with narrow grain boundaries degrades towards the growth of small irregularly shaped grains enclosed in an amorpho...

Journal ArticleDOI
TL;DR: In this article, it was shown that modification by electronic excitation can be achieved in a far wider range of materials, such as alkali halides, alkaline earth fluorides and fused quartz.
Abstract: Excitonic mechanisms of defect formation and of sputtering from surfaces, induced as a consequence of exciton relaxation, are effective in a limited class of wide-gap materials, such as alkali halides, alkaline earth fluorides and fused quartz. In this paper, we point out that modification by electronic excitation can be achieved in a far wider range of materials. First, referring to STM observations of semiconductor surfaces irradiated by laser or intense-electron beams, we show that atomic emissions with electronic origin do take place even in materials in which the bandgap energy is smaller than the energy to remove an atom from the surface. The yield of this process is linear with the beam intensity for higher incident energies, but superlinear for lower incident energies. Secondly we analyse the phenomena of laser damage and laser ablation in a variety of wide-gap materials, emphasizing the role played by defect creation in the bulk, and atomic emissions from surfaces originating from excitation of existing defects. Finally, we discuss the amorphisation of less-ionic oxides and semiconductors by electron- and ion-beam irradiation in terms of nucleation followed by radiation-induced reactions at the interface between the crystalline and amorphous regions. The similarities and differences of the interface reactions induced by electronic excitation and by hot zones in collision cascades are discussed.

BookDOI
01 Jan 1998
TL;DR: In this paper, the authors investigated the effect of tunneling defects on the acoustic properties of disordered solids and proposed a softpotential model for tunneling in amorphous solids.
Abstract: 1. Introduction.- 2. Heat Release in Solids.- 3. Crossover to Phonon-Assisted Tunneling in Insulators and Metals.- 4. Influence of Tunneling Systems on the Acoustic Properties of Disordered Solids.- 5. Interactions Between Tunneling Defects in Amorphous Solids.- 6. Investigation of Tunneling Dynamics by Optical Hole-Burning Spectroscopy.- 7. Tunneling of H and D in Metals and Semiconductors.- 8. Microscopic View of the Low-Temperature Anomalies in Glasses.- 9. Beyond the Standard Tunneling Model: The Soft-Potential Model.- References.

Patent
09 Jul 1998
TL;DR: In this paper, a conductive, non-stick coating (62) is provided using a ceramic material which is conductive and flexible and provides a surface which exhibits the property of lubricity.
Abstract: A conductive, non-stick coating (62) is provided using a ceramic material which is conductive, flexible and provides a surface which exhibits the property of lubricity. A room or near room temperature manufacturing process produces a coating of titanium nitride on a substrate, where the coating is amorphous if the substrate is a solid material including plastics, composites, metals, magnets and ceramics, enabling the substrate to bend without damaging the coating. The coating can also be applied as a conformal coating on a variety of substrate shapes, depending upon the application. The coating is biocompatible and can be applied to a variety of medical devices.

Journal ArticleDOI
TL;DR: In this article, the influence of plastic deformation on the structural state of amorphous Pd40Ni40P20 is investigated by means of tensile test measurements as a function of temperature, strain rate and pre-annealing time.

Journal ArticleDOI
TL;DR: In this paper, a-Si under and near the Ni-covered regions was found to be crystallized after heat treatment at 500 ˚°C from 1 to 90 h.
Abstract: Nickel (Ni) induced crystallization of amorphous silicon (a-Si) has been studied by selective deposition of Ni on a-Si thin films. The a-Si under and near the Ni-covered regions was found to be crystallized after heat treatment at 500 °C from 1 to 90 h. Micro-Auger electron spectroscopy revealed that a large amount of Ni stayed in the region under the original Ni coverage, but no Ni was detected either in the crystallized region next to the Ni coverage or in the amorphous region beyond the front of the laterally crystallized Si. X-ray photoelectron spectroscopy revealed a nonuniform Ni distribution through the depth of the crystallized film under the original Ni coverage. In particular, a Ni concentration peak was found to exist at the interface of the crystallized Si and the buried oxide. It was found that a layer of 5-nm-thick Ni could effectively induce lateral crystallization of over 100 μm of a-Si, but the lateral crystallization rate was found to decrease upon extended heat treatment. Transmission e...

Journal ArticleDOI
TL;DR: In this paper, an improved equivalent circuit for hydrogenated amorphous silicon (a-Si:H) solar cells and modules is presented, based on the classic combination of a diode with an exponential current-voltage characteristic, of a photocurrent source plus a new term representing additional recombination losses in the i-layer of the device.
Abstract: An improved equivalent circuit for hydrogenated amorphous silicon (a-Si:H) solar cells and modules is presented. It is based on the classic combination of a diode with an exponential current-voltage characteristic, of a photocurrent source plus a new term representing additional recombination losses in the i-layer of the device. This model/equivalent circuit matches the I(V) curves of a-Si:H cells over an illumination range of six orders of magnitude. The model clearly separates effects related to the technology of the device (series and parallel resistance) and effects related to the physics of the p-i-n junction (recombination losses). It also allows an effective /spl mu//spl tau/ product in the i-layer of the device to be determined, characterizing its state of degradation.

Journal ArticleDOI
08 May 1998-Science
TL;DR: High-pressure x-ray diffraction and Raman scattering experiments showed that ZrW2O8 becomes progressively amorphous from 1.5 to 3.5 gigapascals, indicating a general trend between negative thermal expansion and pressure-induced amorphization in highly flexible framework structures.
Abstract: It has recently been shown that zirconium tungstate (ZrW2O8) exhibits isotropic negative thermal expansion over its entire temperature range of stability. This rather unusual behavior makes this compound particularly suitable for testing model predictions of a connection between negative thermal expansion and pressure-induced amorphization. High-pressure x-ray diffraction and Raman scattering experiments showed that ZrW2O8 becomes progressively amorphous from 1.5 to 3.5 gigapascals. The amorphous phase was retained after pressure release, but the original crystalline phase returned after annealing at 923 kelvin. The results indicate a general trend between negative thermal expansion and pressure-induced amorphization in highly flexible framework structures.

Journal ArticleDOI
TL;DR: In this article, the relative contribution of C=N and C-N bonds is found to change with the variation of the nitrogen content in the samples, which shows a similar trend with the shift of the G peak to a higher wave number and the increase of the ID/IG ratio.
Abstract: Studies on structure and electronic properties of amorphous nitrogenated carbon films prepared in dual electron cyclotron resonance–radio frequency plasma from a mixture of methane and nitrogen are presently reported. These films are characterized by Fourier transform infrared spectroscopy (FTIR), Raman spectroscopy, x-ray photoemission spectroscopy (XPS), ultraviolet photoemission spectroscopy (UPS), electrical conductivity measurement, and optical absorption spectroscopy. Symmetry breaking of aromatic rings are at a very small amount of nitrogen incorporation is understood from FTIR spectra. The relative contribution of C=N and C–N bonds is found to change with the variation of the nitrogen content in the samples, which shows a similar trend with the shift of the G peak to a higher wave number and the increase of the ID/IG ratio. From decomposition of XPS C 1s and N 1s peaks a three-phase model of CN bonds is proposed. UPS valence band spectra obtained by using a Helium II source, are decomposed into p-...

Journal ArticleDOI
01 Nov 1998-Wear
TL;DR: In this paper, the results of amorphous hydrogenated carbon films (a-C:H) and hydrogen-free hard carbon (aC:C) are reported in terms of their tribological performance in dry, water and oil-lubricated conditions.

Journal ArticleDOI
TL;DR: In this article, the effects of changes in the notch root radius from 250 m to a fatigue precrack on the fracture toughness of a bulk amorphous glass were determined, and it was shown that the average toughness obtained from 6 fatigue precracked specimens was 18.4 {+-} 1.4 MPa {radical}m, while the notch toughness obtained on specimens with notch root radii ranging from 65 microm-250 microm were in the range of 101--131 MPa{ radical}m.

Journal ArticleDOI
TL;DR: In this paper, the authors measured the absorption coefficient per unit mass of cosmic dust analog grains, crystalline fayalite and forsterite, amorphous faysalite, and two kinds of disordered carbon grains, between 20 μm and 2 mm over the temperature range 295-24 K.
Abstract: We have measured the absorption coefficient per unit mass of cosmic dust analog grains, crystalline fayalite and forsterite, amorphous fayalite, and two kinds of disordered carbon grains, between 20 μm and 2 mm over the temperature range 295-24 K. The results provide evidence of a significant dependence on temperature. The opacity systematically decreases with decreasing temperature; at 1 mm, it varies by a factor of between 1.9 and 5.8, depending on the material, from room temperature to 24 K. The variations are more marked for the amorphous grains. The wavelength dependence of the absorption coefficient is well fitted by a power law with exponent β that varies with temperature. For the two amorphous carbons, β(24 K) ~1.2 with increases of 24% and 50% with respect to the room-temperature values. A 50% increase is found for amorphous fayalite, characterized by β(24 K) = 2. A less pronounced change of β with temperature, 14% and 10%, is observed for crystalline forsterite, β(24 K) = 2.2, and fayalite, β(24 K) = 2.3, respectively. For amorphous fayalite grains, the millimeter opacity at 24 K is larger by a factor of ~4 than that of the crystalline counterpart. In addition, a temperature dependence of the infrared bands present in the spectrum of the two crystalline silicates is found. The features become more intense, sharpen, and shift to slightly higher frequencies with decreasing temperature. The results are discussed in terms of intrinsic far-infrared-millimeter absorption mechanisms. The linear dependence of the millimeter absorption on temperature suggests that two-phonon difference processes play a dominant role. The absorption coefficients reported in this work can be useful in obtaining a more realistic simulation of a variety of astronomical data concerning dust at low temperatures and give hints to better identify its actual properties. In particular, they are used to discuss the origin of the diffuse far-infrared-millimeter interstellar dust emission spectrum. It is proposed that composite particles formed of silicate and amorphous carbon grains can reproduce the observations. The presence of these particles in the diffuse medium is consistent with the recent interstellar extinction model by Mathis.

Journal ArticleDOI
TL;DR: In contrast to the previously known crystalline titania photocatalysts, which are active only when excited with UV light, the amorphous semiconductors modified with platinum, rhodium, and gold chloride enable both processes also with visible light.
Abstract: Amorphous, microporous TiO2 hybrid semiconductors modified with transition metals induce generation of a photocurrent and photocatalytic degradation of the water contaminant 4-chlorophenol through photoinduced charge separation (the postulated mechanism is shown in the picture, Ar=4-ClC6 H4 ). In contrast to the previously known crystalline titania photocatalysts, which are active only when excited with UV light, the amorphous semiconductors modified with platinum, rhodium, and gold chloride enable both processes also with visible light.

Journal ArticleDOI
TL;DR: In this paper, electroluminescence degradation studies of tris (8-hydroxyquinoline) aluminum (Alq3) organic light-emitting devices (OLEDs) under ambient conditions were performed.
Abstract: We report electroluminescence degradation studies of tris (8-hydroxyquinoline) aluminum (Alq3) organic light-emitting devices (OLEDs) under ambient conditions. Alq3 films and organic bilayer anode/naphthyl-substituted benzidine derivative/Alq3/cathode devices are studied via electroluminescence, photoluminescence, polarization microscopy and atomic force microscopy, and via microscopic infrared spectroscopy. Results reveal that humidity induces the formation of crystalline Alq3 structures in originally amorphous films. The same phenomenon is found to occur in OLEDs and causes cathode delamination at the Alq3/cathode interface that results in the formation of black (nonemissive) spots in the devices.

Journal ArticleDOI
TL;DR: In this article, a two-stage i-layer growth process was designed such that the initial stage of the i layer (∼200 A) is deposited at much higher R than the bulk to ensure that the film remains within the amorphous side of the a→μc phase boundary, yet as close as possible to this boundary at low I-layer thicknesses.
Abstract: Hydrogenated amorphous silicon (a-Si:H) p–i–n solar cell performance has been optimized using a two-step i-layer growth process. This effort has been guided by real-time spectroscopic ellipsometry (RTSE) studies of the nucleation and growth of a-Si:H films by plasma-enhanced chemical vapor deposition at 200 °C using a variable H2-dilution gas flow ratio R=[H2]/[SiH4]. RTSE studies during film growth with R>15 reveal a transition from the amorphous to microcrystalline (a→μc) phase at a critical thickness that decreases with increasing R. From such results, the optimum two-step process was designed such that the initial stage of the i layer (∼200 A) is deposited at much higher R than the bulk to ensure that the film remains within the amorphous side of the a→μc phase boundary, yet as close as possible to this boundary at low i-layer thicknesses.