Showing papers by "Energy Conversion Devices published in 1980"

Threshold switching in chalcogenide-glass thin films

Abstract: The application of sufficiently high electric fields to any material eventually results in deviations from linearity in the observed current-voltage I(V) characteristic. There are two general classes of explanations for such non-Ohmic effects— thermal and electronic. Thermal effects arise because the electrons accelerated by the field always emit phonons in an attempt to return to equilibrium. Electronic effects are due to changes in the response of the charged carriers to high applied fields. In general, both effects must be considered in any quantitative analysis, and the two can produce a coupled response ofter called “electrothermal.” The use of the terminology electrothermal encompasses predominantly thermal and predominantly electronic processes as well as all intermediate cases, and therefore should not prejudice the casual observer into concluding that both effects are necessarily important. In a discussion of the physical mechanism in a particular sample, the major parameters controlling its operation must be identified and separated out from the less significant features.

Method for optimizing photoresponsive amorphous alloys and devices

Abstract: The production of improved photoresponsive amorphous alloys and devices, such as photovoltaic, photoreceptive devices and the like; having improved wavelength threshold characteristics is made possible by adding one or more band gap adjusting elements to the alloys and devices. The adjusting element or elements are added at least to the active photoresponsive regions of amorphous devices containing silicon and fluorine, and preferably hydrogen. One adjusting element is germanium which narrows the band gap from that of the materials without the adjusting element incorporated therein. Other adjusting elements can be used such as tin. The silicon and adjusting elements are concurrently combined and deposited as amorphous alloys by vapor deposition, sputtering or glow discharge decomposition. The addition of fluorine bonding and electronegativity to the alloy acts as a compensating or altering element to reduce the density of states in the energy gap thereof. The fluorine bond strength allows the adjusting element(s) to be added to the alloy to adjust the band gap without reducing the electronic qualities of the alloy. Hydrogen also acts as a compensating or altering element to compliment fluorine when utilized therewith. The compensating or altering element(s) can be added during deposition of the alloy or following deposition. The addition of the adjusting element(s) to the alloys adjusts the band gap to a selected optimum wavelength threshold for a particular device to increase the photoabsorption efficiency to enhance the device photoresponsive without adding states in the gap which decrease the efficiency of the devices. The adjusting element(s) can be added in varying amounts, in discrete layers or in substantially constant amounts in the alloys and devices.

Method of making p-doped silicon films

Abstract: The production of improved photovoltaic solar cells and the like comprising both p and n type deposited silicon film regions is made possible by a process which provides more efficient p-doped silicon films with higher acceptor concentrations. The process utilizes previously known p-dopant metal or boron gaseous materials in unique forms and conditions in a glow discharge silicon preferably hydrogen and fluorine compensated deposition process. Thus, p-dopant metals like aluminum may be used in an elemental evaporated form, rather than in a gaseous compound form heretofore ineffectively used and deposited with the glow discharge deposited silicon on substrates kept at lower temperatures where fluorine and hydrogen compensation is most effective. Preferably boron in a gaseous compound form like diborane and other p-dopant metals in a gaseous form are used uniquely during the glow discharge deposition of silicon by heating the substrate to heretofore believed undesirably higher temperatures, like at least about 450° C. to 800° C. where at least fluorine compensation, if desired, is still effective. The improved devices, such as solar cells, can be manufactured in a continuous process on a web type substrate moved through a plurality of film deposition chambers. Each of the chambers is dedicated to depositing a particular type of film layer (p, i or n) and is isolated from the other chambers.

Metal‐insulator‐semiconductor solar cells using amorphous Si:F:H alloys

Abstract: Metal‐insulator‐semiconductor‐type photovoltaic devices using amorphous Si:F:H alloys have been fabricated. Conversion efficiencies of up to 6.3% under AM:1 illumination have been observed. These represent the highest efficiencies yet reported for amorphous thin‐film solar cells.

Properties of Amorphous Si:F:H Alloys

Abstract: Previously we have shown that amorphous silicon-based alloys containing F and H (1–7) possess desirable properties for photovoltaic application. Amorphous tetrahedral semiconductors ordinarily possess a very large density of states which act as traps leading to low values for drift mobility and low recombination lifetimes of free carriers. However, Spear and his group (8–10) reported that a-Si decomposed from SiH4 gas by r.f. glow discharge and deposited on a heated substrate produces a film which has a comparatively low density of states. However, materials prepared in this way possess a large concentration of H.(11) Because of the relatively low density of states, these types of films can be doped n type, albeit using relatively large concentration of the dopant. However, p-type doping using B2H6 is generally accompanied with the decrease in the band gap, indicating alloying action rather than conventional doping.(9) Furthermore, the material has apparently a sufficiently large carrier lifetime that efficiencies of photovoltaic devices exceeding 5% have been reported.(12)

New experiments on threshold switching in chalcogenide and non-chalcogenide alloys

Abstract: A systematic and detailed comparison was made between the threshold switching properties of a typical ovonic threshold material (Te 40 As 35 Ge 7 si 18 ) and a non-chalcogenide alloy (Cd 23 Ge 12 As 65 ) of nearly equal band gap but higher conductivity. All specimens (thickness 1 μm) were prepared by RF sputtering on molybdenum-on-glass substrates, and tested with hemispherical counter-electrodes of pyrolytic graphite. The results (ON and OFF characteristics, ac and pulse switching, temperature dependence, the TONC, recovery characteristics, forming phenomena, etc.) show great similarities and, in this way, suggest that no special role is played by lone pair electrons in the mechanism of threshold switching as such. On the other hand, the lone pair band in the chalcogenide alloy may well be responsible for its much higher degree of stability, i.e., its ability to withstand the intense excitation levels prevailing in the ON-state. The results also provide further evidence against thermal interpretations and thereby support electronic models of threshold switching for both materials.

Imaging film with improved passivating layers

Abstract: In an imaging film having a substrate over which is deposited a thin, opaque layer of an imaging material there is located on at least the outer side of said opaque imaging layer and, better still, on the opposite sides of said opaque layer of imaging material, thin, preferably vapor deposited, passivating layers forming a barrier against passage of oxygen and moisture. The passivating layer, or layers, in a flexible continuous amorphous film having a thickness generally no greater than about 500 Angstroms (A°) and preferably less than 200 A° and comprising an alloy or mixture of a Group IV oxide, most advantageously germanium oxide, and a stabilizing agent or agents, more particularly one or more different oxides of a metal or a semiconductor or a metal fluoride which stabilizes the amorphous character and chemical inertness of the Group IV oxide even when subjected to the elements of the surrounding atmosphere.

Catalytic electrolytic electrode

Abstract: A catalytic body which is substantially amorphous is formed from at least two materials vacuum deposited on a cool substrate or sprayed on a cool surface to provide a local order non-equilibrium structural configuration. The amorphous body comprises a composition of at least one metal and a second component which maintains the amorphous character of the composition. The body has an increased number and desired type of catalytically active sites. In most applications, the composition includes at least initially a component which is removed by leaching or vaporization to leave a rough surface with a large surface to volume ratio. The resulting composition is sometimes annealed to relax or modify the local structure thereof to provide a more reactive structural configuration. In an electrode form of the invention, the catalytic body is highly conductive, resistant to corrosion and degradation under current reversal and has low overvoltage characteristics when used in electrochemical cells.

Schottky barrier profiles in amorphous silicon-based materials

Abstract: The localized state density for a-Si:H and a-Si:H:F can be reasonably approximated by a hyperbolic function. Solution of Poisson's equation leads to potential profiles in the depletion region. The predicted width of the depletion region is in reasonable agreement with the results obtained from C-V experiments.

Carrier-generation efficiencies in a-Si : F : H-based photovoltaic devices

Abstract: Photocurrents in a Au Schottky-barrier a-Si : F : H photovoltaic cell configuration have been measured as a function of incident photon energy, temperature and applied electric field. Our results show a near-unity (> 0·95) carrier-generation efficiency in the visible region of the spectra and thereby eliminate geminate recombination as a limitation to the efficiency of solar cell devices using a-Si : F : H as an active component. We show that the short-circuit current can be accounted for by the effective absorption within the depletion width, which is estimated from a simple analysis of our data.

Method and apparatus for making a modified amorphous glass material

Abstract: The method for forming a metallic, dielectric or semiconductor modified amorphous glass material includes the steps of forming a fluid host matrix material on a substrate surface having relative movement thereto, such as a wheel; directing a fluid modifier material in a stream, as from a nozzle toward the substrate surface in a direction such that it converges with the host matrix material; maintaining the temperature of the substrate or wheel between 4.2° K and ambient room temperature while rotating the wheel at a velocity of 1000 to 5000 rpm to obtain a surface velocity of between 1000 to 4000 centimeters per second thereby to obtain rapid quenching of the host and modifier materials as they contact one another at a rate of from 104 to at least 108 C per second or more to produce a ribbon of modified amorphous glass material in which the electrical and optical transport properties and the number and type of electronic configurations can be controlled. The modified material can range from an alloy to various degrees of alloying and modification to one in which only modification and doping actions exist. This provides a new method of synthesizing materials in which modifier atoms can be incorporated at various intervals or layers or a bulk material whose surfaces can be distinctly chemically different from the bulk interior can be made by this process. The apparatus can include metal spinning apparati such as reservoirs, nozzles and the wheel for carrying out the method.

Some electrical and optical properties of a-Si:F:H alloys

Abstract: Amorphous Si:F:H with desirable properties for photovoltaic applications can be fabricated by the glow discharge of SiF4 and H2. The preparation conditions influence the properties of the resultant alloy. For instance, altering the ratio of SiF4 to H2 from 80 to 5 can alter the localized state density from 1019cm−3eV−1 to ≃ 1016cm−3eV-1, respectively. The conduction mechanisms are altered and there are vast changes in the photoconductivity as the density of recombination centers is decreased. The lower density of states achieved in the a-Si:F:H alloy reflects in the ease of doping. In addition, the lower density of states in a-Si:F:H alloy should result in a wider depletion region than reported for the a-Si:H alloy when fabricated within the device configuration. Results of C-V measurements using Au Schottky barrier devices confirm this.

The Chemistry of Glassy Materials and Their Relevance to Energy Conversion

Abstract: The problems of our modern society are directly related to materials. Depletable fossil fuels, shrinking silver supplies, the high cost of gold, platinum and other precious metals all are interfering with industrial growth and creating societal problems. The fossil fuels and uranium supply us with energy without which no society or civilization can endure. However, there is a tendency to focus only on the fuel aspects of materials and ignore the larger materials picture, that is, that materials such as platinum, palladium and iridium, which are the core of the catalytic and electrochemical industries, affect not only the generation but the use of energy in a dramatic fashion.

Apparatus for producing microform records at high speed from computer or other electrical data signal sources

Abstract: Apparatus for producing microform records from computer stored data or other electrical data signal sources forms on the screen of a cathode ray tube at rapidly occuring intervals successive hard copy-appearing images of such data which is reduced in size by a bundle of tapered fiber optic filaments with a wide light receiving end encompassing the screen of the cathode ray tube and a narrow light projecting end encompassing an area of the frame of a microfiche card. The successively produced images at the narrow end of the fiber optic filament bundle are applied to successive frames of a heat developable masking film strip requiring more time to develop than the imaging intervals and moved in step-by-step fashion past the narrow end of the fiber optic bundle, a heating bar and an image transfer station where a flash of light is passed through the masking film strip to transfer a negative image thereon to a frame of an archival add-on microfiche card-forming film. The transfer of a cathode ray tube image to the masking film, the application of a heating bar to a previously imaged frame of the masking strip and the transfer of a previously imaged portion of the masking film may take place simultaneously. The heating bar has a length several frame lengths long so that a frame of the masking film is completely developed over several imaging intervals.

Apparatus for producing microform records from hard copy, cathode ray tube image or transparency data-containing sources

Abstract: Apparatus for producing microform records includes an image-reducing projection system positioned above a hard copy and transparency-receiving imaging station defining a horizontal document plane. An opaque platform is located at the document plane for supporting hard copy and a transparent plate is located at or near the document plane for supporting a transparency. Overhead lamps are provided to direct light downwardly upon the hard copy, and a light source, preferably a cathode ray tube, is provided below this document plane to project light upwardly through the document plane. The cathode ray tube or other light source produces a uniform light field or image-containing light field, the former when a transparency is placed at said document plane, the latter either when a transparency is or is not located at or near said document plane. When an image-containing light field is directed through a transparency at the document station, the microform record produced includes both the image in the image-containing light field and the object of the transparency as an overlay of the same.

Heat-sink imaging apparatus for live skin tissue using pulsed energy source

Abstract: The imaging layers coated side of a heat-responsive recording medium is selectively heat-sinked by the raised portions of live skin tissue contacting the same so that only the unheat-sinked portions of the recording medium will reach an imaging temperature. The source of heat for the film may be a flash lamp directed against the opposite substrate side of the film where the electromagnetic energy thereof is converted into heat when absorbed by the substrate, or may be a source of externally applied heat transmitted through the substrate to the imaging layer of the film. In the latter case, the recording medium is preferably initially in spaced relationship with a heat contact plate which is to be contacted by a heat source, which may be the end face of a piston either pre-heated to a given temperature or having a current heatable resistance thereon to be pulsed with current. In the former case the polymer end face preferably has a low heat conductivity coating thereon. The live skin tissue, like a finger, is pressed against the imaging layer coated side of the recording medium to bring the substrate side thereof against the heat contact plate which receives heat from the piston end face. The plunger is automatically withdrawn from the heat contact plate a short time after the recording medium is pressed against the heat contact plate to prevent any discomfort or burning of the finger.

Effect of An Interfacial Oxide On Amorphous Si:F:H Alloy Based Metal Insulated Semiconductor (MIS) Devices

Abstract: We discuss the effect of oxides on the forward and reverse bias J-V characteristics in a-Si:F:H MIS type devices. Data are also presented for the variation of the open circuit voltage with the work function of the Schottky contact. We conclude that the density of interface states is low.© (1980) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.

Raman Scattering Characterization of Bonding Defects in Silicon

Abstract: Raman scattering is used for the characterization of defects in Si. Damage is produced in single crystal silicon by ion-implantation of As and Si. The phonon structure of the damaged layer is that of the typical amorphous Si. After irradiation by pulsed laser(10ns,532nm) at energy density of approximately 0.1J/cm2, a Raman peak appears at a frequency between 508 cm−1 and 517 cm−1 depending on implant dosage. The higher the implant dosage, the lower is the frequency. We explain this in terms of the residual bonding defects caused by the presence of extraneous atoms such as oxygen. On the other hand, irradiation at an energy density in excess of 0.5 J/cm2, a Raman peak appears at a frequency close to that of the single crystal except for small shifts due to Fano-shift. For implant dosage in excess of 4×1016 As/cm2, we have found additional peaks at 222 cm−1 and 267 cm−1 which are close to the metallic arsenic modes indicating the presence of arsenic clusters.

Optical Recording With Amorphous Materials

Abstract: Amorphous materials can be used in a variety of configurations for optical recording and storing of information. Focused laser beams yield changes in state between crystalline and amorphous giving high quality images without ablation or post processing of the film. Tailoring material compositions to a particular application results in films that can be read in reflection or transmission, and store information in a read-only or erasable form. The materials inherently provide permanence of storage, even in the case of erasable films, due to threshold imaging mechanisms. Films can be coated on a variety of substrates, including flexible plastic, sheet plastic, and glass, depending on reading and writing system requirements.© (1980) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.