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  • C01B33/02—Silicon
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  • B22F1/00—Metallic powder; Treatment of metallic powder, e.g. to facilitate working or to improve properties
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  • B22F1/00—Metallic powder; Treatment of metallic powder, e.g. to facilitate working or to improve properties
  • B22F1/05—Metallic powder characterised by the size or surface area of the particles
  • B22F1/054—Nanosized particles
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  • B82—NANOTECHNOLOGY
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  • B82—NANOTECHNOLOGY
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  • C01B33/00—Silicon; Compounds thereof
  • C01B33/02—Silicon
  • C01B33/021—Preparation
  • C01B33/027—Preparation by decomposition or reduction of gaseous or vaporised silicon compounds other than silica or silica-containing material
  • C01B33/029—Preparation by decomposition or reduction of gaseous or vaporised silicon compounds other than silica or silica-containing material by decomposition of monosilane
• • H—ELECTRICITY
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  • H01L21/00—Processes or apparatus adapted for the manufacture or treatment of semiconductor or solid state devices or of parts thereof
  • H01L21/02—Manufacture or treatment of semiconductor devices or of parts thereof
  • H01L21/04—Manufacture or treatment of semiconductor devices or of parts thereof the devices having at least one potential-jump barrier or surface barrier, e.g. PN junction, depletion layer or carrier concentration layer
  • H01L21/18—Manufacture or treatment of semiconductor devices or of parts thereof the devices having at least one potential-jump barrier or surface barrier, e.g. PN junction, depletion layer or carrier concentration layer the devices having semiconductor bodies comprising elements of Group IV of the Periodic System or AIIIBV compounds with or without impurities, e.g. doping materials
  • H01L21/22—Diffusion of impurity materials, e.g. doping materials, electrode materials, into or out of a semiconductor body, or between semiconductor regions; Interactions between two or more impurities; Redistribution of impurities
  • H01L21/223—Diffusion of impurity materials, e.g. doping materials, electrode materials, into or out of a semiconductor body, or between semiconductor regions; Interactions between two or more impurities; Redistribution of impurities using diffusion into or out of a solid from or into a gaseous phase
  • H01L21/2236—Diffusion of impurity materials, e.g. doping materials, electrode materials, into or out of a semiconductor body, or between semiconductor regions; Interactions between two or more impurities; Redistribution of impurities using diffusion into or out of a solid from or into a gaseous phase from or into a plasma phase
• • H—ELECTRICITY
  • H01—ELECTRIC ELEMENTS
  • H01L—SEMICONDUCTOR DEVICES NOT COVERED BY CLASS H10
  • H01L29/00—Semiconductor devices adapted for rectifying, amplifying, oscillating or switching, or capacitors or resistors with at least one potential-jump barrier or surface barrier, e.g. PN junction depletion layer or carrier concentration layer; Details of semiconductor bodies or of electrodes thereof  ; Multistep manufacturing processes therefor
  • H01L29/02—Semiconductor bodies ; Multistep manufacturing processes therefor
  • H01L29/06—Semiconductor bodies ; Multistep manufacturing processes therefor characterised by their shape; characterised by the shapes, relative sizes, or dispositions of the semiconductor regions ; characterised by the concentration or distribution of impurities within semiconductor regions
  • H01L29/0657—Semiconductor bodies ; Multistep manufacturing processes therefor characterised by their shape; characterised by the shapes, relative sizes, or dispositions of the semiconductor regions ; characterised by the concentration or distribution of impurities within semiconductor regions characterised by the shape of the body
  • H01L29/0665—Semiconductor bodies ; Multistep manufacturing processes therefor characterised by their shape; characterised by the shapes, relative sizes, or dispositions of the semiconductor regions ; characterised by the concentration or distribution of impurities within semiconductor regions characterised by the shape of the body the shape of the body defining a nanostructure
• • H—ELECTRICITY
  • H01—ELECTRIC ELEMENTS
  • H01L—SEMICONDUCTOR DEVICES NOT COVERED BY CLASS H10
  • H01L29/00—Semiconductor devices adapted for rectifying, amplifying, oscillating or switching, or capacitors or resistors with at least one potential-jump barrier or surface barrier, e.g. PN junction depletion layer or carrier concentration layer; Details of semiconductor bodies or of electrodes thereof  ; Multistep manufacturing processes therefor
  • H01L29/02—Semiconductor bodies ; Multistep manufacturing processes therefor
  • H01L29/06—Semiconductor bodies ; Multistep manufacturing processes therefor characterised by their shape; characterised by the shapes, relative sizes, or dispositions of the semiconductor regions ; characterised by the concentration or distribution of impurities within semiconductor regions
  • H01L29/0657—Semiconductor bodies ; Multistep manufacturing processes therefor characterised by their shape; characterised by the shapes, relative sizes, or dispositions of the semiconductor regions ; characterised by the concentration or distribution of impurities within semiconductor regions characterised by the shape of the body
  • H01L29/0665—Semiconductor bodies ; Multistep manufacturing processes therefor characterised by their shape; characterised by the shapes, relative sizes, or dispositions of the semiconductor regions ; characterised by the concentration or distribution of impurities within semiconductor regions characterised by the shape of the body the shape of the body defining a nanostructure
  • H01L29/0669—Nanowires or nanotubes
  • H01L29/0673—Nanowires or nanotubes oriented parallel to a substrate
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  • H01—ELECTRIC ELEMENTS
  • H01L—SEMICONDUCTOR DEVICES NOT COVERED BY CLASS H10
  • H01L29/00—Semiconductor devices adapted for rectifying, amplifying, oscillating or switching, or capacitors or resistors with at least one potential-jump barrier or surface barrier, e.g. PN junction depletion layer or carrier concentration layer; Details of semiconductor bodies or of electrodes thereof  ; Multistep manufacturing processes therefor
  • H01L29/02—Semiconductor bodies ; Multistep manufacturing processes therefor
  • H01L29/06—Semiconductor bodies ; Multistep manufacturing processes therefor characterised by their shape; characterised by the shapes, relative sizes, or dispositions of the semiconductor regions ; characterised by the concentration or distribution of impurities within semiconductor regions
  • H01L29/0657—Semiconductor bodies ; Multistep manufacturing processes therefor characterised by their shape; characterised by the shapes, relative sizes, or dispositions of the semiconductor regions ; characterised by the concentration or distribution of impurities within semiconductor regions characterised by the shape of the body
  • H01L29/0665—Semiconductor bodies ; Multistep manufacturing processes therefor characterised by their shape; characterised by the shapes, relative sizes, or dispositions of the semiconductor regions ; characterised by the concentration or distribution of impurities within semiconductor regions characterised by the shape of the body the shape of the body defining a nanostructure
  • H01L29/0669—Nanowires or nanotubes
  • H01L29/068—Nanowires or nanotubes comprising a junction
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  • B22F2998/00—Supplementary information concerning processes or compositions relating to powder metallurgy
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  • B22F2999/00—Aspects linked to processes or compositions used in powder metallurgy

Definitions

• This disclosure relates in general to nanoparticles and in particular to Group IV nanoparticles and films comprising Group IV nanoparticles.
• Group IV semiconductors generally refer to those elements in the fourth column of the periodic table (e.g., carbon, silicon, germanium, etc.).
• a solid semiconductor tends to exist in three forms: crystalline, polycrystalline, and amorphous.
• crystalline form semiconductor atoms are positioned in a single unbroken crystal lattice with no grain boundaries.
• polycrystalline form the semiconductor atoms are positioned in many smaller and randomly oriented crystallites (smaller crystals). The crystallites are often referred to as grains.
• amorphous form the semiconductor atoms show no long-range positional order.
• conduction generally refers to the movement of electrically charged carriers, such as electrons or holes (i.e., lack of electrons), through a transmission medium.
• electrically charged carriers such as electrons or holes (i.e., lack of electrons)
• Metals tend to have substantial amounts of electrically charged particles available, whereas insulators have very few.
• dopants In the absence of impurities (called dopants), a semiconductor tends to behave as insulator, inhibiting the flow of an electric current. However, after the addition of relatively small amounts of dopants, the electrical characteristics of a semiconductor can dramatically change to a conductor increasing the amount of electrically charged carriers.
• a doped region of a semiconductor can have more electrons (n-type) or more holes (p-type).
• n-type electrons
• p-type holes
• a p-type region is placed next to an n-type region in order to create a (p-n) junction with an electric field. Consequently, electrons on the p-type side of the junction within the electric field may then be attracted to the n-type region and repelled from the p-type region, whereas holes within the electric field on the n-type side of the junction may then be attracted to the p-type region and repelled from the n-type region.
• the n-type region and/or the p-type region can each respectively be comprised of varying levels of relative dopant concentration, often shown as n-, n+, n++, p-, p+, p++, etc.
• a junction may be created by placing an intrinsic (undoped) intrinsic semiconductor layer between the n-type region and the p-type region in order to mitigate the effects of quantum tunneling, a quantum-mechanical effect in which an electron transitions through a classically- forbidden energy state. For example, without an intrinsic separation layer, if the p-n junction is small enough, an electron can travel against the electric field and degrade the performance of the p-n junction.
• a metal junction may be created by placing the n-type region and/or the p-type region next to a metal region in order to form an ohmic (low- impedance) contact.
• One method of adding the impurities into the semiconductor involves depositing a doped glass on a semiconductor substrate, such as a Si wafer. Once exposed to relatively high temperature (e.g., 900-1000°C), the dopants will tend to diffuse from the highly-doped glass into the substrate.
• relatively high temperature e.g., 900-1000°C
• Annealing is generally the process of heating a material above a critical or recrystallisation temperature in order to reduce the materials internal stresses, and or improve its physical and electrical
• annealing allows the dopant atoms to properly position themselves in the lattice, such that the additional electrons or holes are available for the transmission of current. This is generally called activation and is critical for the creation of an efficient junction.
• doped glass is often applied via a silk-screen.
• Silk-screening is generally a printing technique that makes use of a squeegee to mechanically force a liquid, such as a highly doped glass paste, directly onto a substrate. Consequently, this downward mechanical force tends to subject the substrate to additional stresses, and hence may detrimentally affect the electrical and physically characteristics of the substrate.
• creating alternating n-type and p-type regions on the same side of the substrate with a doped glass, such as with back contact solar cells is difficult without the use of multiple and costly time-consuming printing steps.
• Another method of adding the impurities into the semiconductor involves depositing dopants in a crystalline or polycrystalline substrate through ion implantation.
• Ion implantation generally accelerates dopant ions into the substrate at high energy.
• the substrate must also generally be annealed at a high temperature to repair the substrate and activate the dopants.
• dopant dosage may be controlled with high precision, ion implantation tends to be very expense since it requires the use of specialized and expensive semiconductor manufacturing equipment.
• doped (thin) film layers may be formed using deposition techniques such as chemical vapor deposition (CVD).
• CVD chemical vapor deposition
• a substrate which can be an insulator, a semiconductor, or metal
• volatile precursors which react and/or decompose on the substrate surface to produce a doped film.
• CVD is expensive since it requires specialized and expensive semiconductor manufacturing equipment.
• CVD also tends to be very slow, as the film layers are built up a single atom at a time.
• the invention relates, in one embodiment, to a set of nanoparticles, wherein each nanoparticle of the set of nanoparticles is comprised of a set of Group IV atoms arranged in a substantially spherical configuration.
• Each nanoparticle of the set of nanoparticles further having a sphericity of between about 1.0 and about 2.0; a diameter of between about 4 nm and about 100 nm; and a sintering temperature less than a melting temperature of the set of bonded Group IV atoms.
• the invention relates, in another embodiment, to a set of doped Group IV nanoparticles made by a process comprising introducing a Group IV precursor gas and a dopant gas into a plasma reactor.
• the process further includes striking a radiofrequency plasma in the plasma reactor, and forming a set of substantially spherical doped nanoparticles, wherein each nanoparticle of the set of substantially spherical doped nanoparticles has a diameter of between about 4 nm and about 100 nm.
• FIG. 1. shows a simplified diagram comparing surface area/volume to diameter for a set of Si nanoparticles, in accordance with the present invention
• FIG. 2 shows a simplified diagram of sphericity for a Group IV nanoparticle, in accordance with the present invention
• FIG. 3 shows a simplified comparison of surface contamination and melting temperature to diameter for Si nanoparticles, in accordance with the present invention
• FIGS. 4A-C show a set of schematic diagrams for a concentric flow-through plasma reactor, in accordance with the present invention
• FIG. 5 A shows a set of secondary ion mass spectroscopy (SIMS) results for an intrinsic (undoped) film and a p-type film, in accordance with the present invention
• FIG. 5B shows a set of dark current versus voltage curves, in accordance with the present invention.
• FIG. 6 shows a comparison of conductivity of an amorphous n-type nanoparticle film to a crystalline n-type nanoparticle film, in accordance with the present invention
• FIG. 7 shows a particle size distribution for crystalline n-type Si nanoparticles, in accordance with the present invention.
• FIG. 8 shows a comparison of the degree of crystallinity of a crystalline n-type Si nanoparticle to an amorphous n-type Si nanoparticle, in accordance with the present invention
• FIG. 9 shows the size distribution for three types of Si nanoparticle inks using dynamic light scattering, in accordance with the present invention.
• FIG. 10 shows a set of n-type Si nanoparticle colloidal dispersions of varying viscosity, in accordance with the present invention.
• a set of Group IV nanoparticles may be created such that an efficient junction (e.g., p-n, metal-silicon, etc.) may be formed at a substantially lower cost than alternate methods, hi one configuration, the formed junction includes at least one film, hi another configuration, the Group IV nanoparticles are substantially spherical and preferably between about 4 ran and about 100 ran in diameter, hi yet another configuration, the Group IV nanoparticles are substantially spherical and more preferably between about
• the Group IV nanoparticles are substantially spherical and most preferably 7.0 ran.
• a nanoparticle is a microscopic particle with at least one dimension less than 100 ran.
• the term "Group IV nanoparticle” generally refers to hydrogen terminated Group rv nanoparticles having an average diameter between about 1 ran to 100 ran, and composed of silicon, germanium, carbon, or combinations thereof.
• the term “Group IV nanoparticle” also includes Group IV nanoparticles that are doped.
• nanoparticles may have physical properties that are size dependent, and hence useful for applications such as junctions.
• semiconductor nanoparticles may be more easily and cheaply patterned p-n junctions when compared to alternate methods, such as silk-screening or deposition.
• Group IV nanoparticles also tend to be very susceptible to contamination.
• contamination often occurs from such chemical reactions such as oxidation and/or hydrolysis. Consequently, even small amounts of contamination may inhibit sintering (i.e., interfering with the physical connection of the Group rv nanoparticles), delay dense layer formation (i.e., increasing material porosity and thus decreasing conductivity), and provide electron-hole recombination sites (i.e., attenuating current generation in the assembled junction).
• the Group IV nanoparticles may be formed into a substantially spherical shape in order to minimize contamination.
• a sphere is the one with the smallest surface area.
• the sphere is the one having the greatest volume. Consequently, a spherical nanoparticle will tend to shield the greatest number of Group IV atoms from contamination, and hence is beneficial to junction creation.
• semiconductor nanoparticles typically must be formed into dense connected regions in order to create a junction.
• One such method is sintering.
• a method for making particles adhere to each other, interacting nanocrystals sinter before size-dependent melting occurs.
• A.N. Goldstein The melting of silicon nanocrystals: Submicron thin-film structures derived from nanocrystal precursors, APPLIED PHYSICS, 1996. Consequently, Group IV nanoparticles that are substantially spherical and preferably between about 4 nm and about 100 nm in diameter tend to sinter at lower temperatures, and hence are beneficial to create junctions.
• FIG. 1 a simplified diagram is shown comparing surface area/volume to diameter for a set of Si nanoparticles, in accordance with the present invention.
• Horizontal axis 104 shows Si nanoparticle diameter in nanometers
• vertical axis 106 shows Si surface area/volume in meters "1 .
• Si atoms have an atomic radius of about 0.118 nm and tend to form a diamond crystal structure with a cell dimension of about 0.5431 nm.
• Ge with an atomic radius of about 0.125 nm and a cell dimension of about 0.566 nm, will have a area/volume to diameter curve that is substantially similar to that of Si.
• the surface area/volume ratio starts to substantially increase, from about 1.5 m "1 (at about 4 nm) to about 6.0 m "1 (at 1 nm).
• Si atoms are essentially surface or shell atoms, and the likelihood of contamination is extremely high.
• Group IV nanoparticles should be greater than about 4 nm in diameter.
• FIG. 2 a simplified diagram showing sphericity for a Group IV nanoparticle is shown, in accordance with the present invention.
• a metric for particle shape uniformity or sphericity may be obtained by using transmission electron microscopy images.
• a transmission electron microscopy (TEM) is an imaging technique whereby a beam of electrons is transmitted through a specimen, then an image is formed, magnified and directed to appear either on a fluorescent screen or layer of photographic film (see electron microscope), or to be detected by a sensor such as a CCD camera.
• Particle sizes may be measured by identifying individual particles and drawing a straight line cross a particles shortest and longest dimensions as shown in the graphical example. Uniformity may be defined as the ratio of the maximum diameter over the minimum diameter of a particle. By measuring the particle dimension defined as the ratio of the longest Ll over the shortest dimension L2, one can obtain the metric L1/L2 as the level of sphericity. For example, for an ideal spherical particle, uniformity is equal to about 1.0. For an irregular particle, uniformity is generally substantially larger than about 1.0. For example, if a particle is rod or needle shaped, the L1/L2 ratio may be greater than 5. Optimal sphericity is generally between about 1.0 and about 2.0. Aside from surface contamination, a L1/L2 ratio of below 2 is beneficial to nanoparticle application techniques, such as inkjet printing.
• FIG. 3 surface contamination and melting temperature are compared to diameter for Si nanoparticles, in accordance with the present invention.
• Horizontal axis 306 shows Si nanoparticle diameter.
• Left-side vertical axis 308 shows particle surface contaminants whereas right-side vertical axis 310 shows temperature in degrees Celsius ( 0 C).
• Si particle surface contamination is about 1.02 x 10 21 atoms/cm 3 , corresponding to a surface area/volume ratio of about 1.5 m "1 as previously shown.
• Si particle surface contamination increases above about 1.02 x 10 21 atoms/cm 3 in the catastrophic contaminating region (102), sintering, dense layer formation, and electron- hole recombination are aggravated, as previous stated.
• the sintering temperature of a Si nanoparticle sharply decreases with corresponding decrease in diameter size.
• the sintering temperature gradually increases with a corresponding increase in diameter size, eventually reaching about 947 0 C, or 67% of the melting temperature of Si (about 1414°C).
• germanium it is believed that the sintering temperature also gradually increases with a corresponding increase in diameter size, eventually reaching about 628 0 C, or 67% of the melting temperature of Si (about 938°C).
• sintering is generally a method for making particles adhere to each other and inducing densification of films. Consequently, because their small radii of
• nanoparticles generally begin to sinter when a temperature of about 2/3 of the particle melting point is reached. It is further believed that large shear stresses generated by elevated temperatures in neck regions of the nanoparticles tend to cause a plastic deformation between two proximately located nanoparticles. For a given nanoparticles material, smaller nanoparticles generally have a lower sintering temperature than that of larger nanoparticles.
• various heat sources may be used to sinter the nanoparticle, such as conventional contact thermal sources (e.g., resistive heaters, etc.), as well as radiative heat sources (e.g., lamps, lasers, microwave processing equipment, plasmas, tungsten-halogen, continuous arc lamps, flash lamps, etc.).
• conventional contact thermal sources e.g., resistive heaters, etc.
• radiative heat sources e.g., lamps, lasers, microwave processing equipment, plasmas, tungsten-halogen, continuous arc lamps, flash lamps, etc.
• a wavelength range of between about 0.3 microns and about 10 microns is generally optimal.
• a lower sintering temperature also allows the use of alternative materials in or near the junction (i.e., substrate, dielectric layer, etc.) that may have a melting point substantially below the Group IV melting temperature.
• polymides e.g., Kapton, Kaptrex, etc.
• a glass temperature of around 400°C may be used both as a dielectric and as a mask for production of electrical junctions. Consequently, by reducing the Group IV nanoparticle diameter sufficiently (to about 7 run in this example), a dense nanoparticle layer may be formed on a polymide layer.
• nanoparticles may be more readily suspended in a colloidal dispersion. Because of their small size, nanoparticles tend to be difficult to manipulate. Consequently, in an advantageous manner, assembled nanoparticles may be suspended in a colloidal dispersion or colloid, such as an ink, in order to transport and store the nanoparticles.
• colloidal dispersions of Group IV nanoparticles are possible because the interaction of the particle surface with the solvent is strong enough to overcome differences
• the Group IV nanoparticles are transferred into the colloidal dispersion under a vacuum, or else an inert substantially oxygen- free environment.
• particle dispersal methods and equipment such as sonication, high shear mixers, and high pressure/high shear homogenizers may be used to facilitate dispersion of the nanoparticles in a selected solvent or mixture of solvents.
• solvents examples include alcohols, aldehydes, ketones, carboxylic acids, esters, amines, organosiloxanes, halogenated hydrocarbons, and other hydrocarbon solvents.
• the solvents may be mixed in order to optimize physical characteristics such as viscosity, density, polarity, etc.
• nanoparticle capping groups may be formed with the addition of organic compounds, such as alcohols, aldehydes, ketones, carboxylic acids, esters, and amines, as well as organosiloxanes.
• organic compounds such as alcohols, aldehydes, ketones, carboxylic acids, esters, and amines, as well as organosiloxanes.
• capping groups may be added in-situ by the addition of gases into the plasma chamber. These capping groups may be subsequently removed during the sintering process, or in a lower temperature pre-heat just before the sintering process.
• bulky capping agents suitable for use in the preparation of capped Group IV semiconductor nanoparticles include C4-C8 branched alcohols, cyclic alcohols, aldehydes, and ketones, such as tertiary-butanol, isobutanol, , cyclohexanol, methyl- cyclohexanol, butanal, isobutanal, cyclohexanone, and oraganosiloxanes, such as methoxy(tris(trimethylsilyl)silane)(MTTMSS), tris(trimethylsilyl)silane (TTMSS), decamethyltetrasiloxane (DMTS), and trimethylmethoxysilane (TMOS).
• MTTMSS methoxy(tris(trimethylsilyl)silane)
• TTMSS tris(trimethylsilyl)silane
• DMTS decamethyltetrasiloxane
• TMOS trimethylmethoxysi
• the colloidal dispersion may be applied to a substrate and subjected to a heat treatment in order to sinter the Group IV nanoparticles into a densified conductive film.
• application methods include, but are not limited to, roll coating, slot die coating, gravure printing, flexographic drum printing, and ink jet printing methods, etc.
• the colloidal dispersion may be applied in patterned regions by an inkjet printer.
• InkJet printers generally are configured with a piezoelectric material in an ink-filled chamber behind each nozzle. When a voltage is applied, the crystal changes shape or size, which generates a pressure pulse in the fluid forcing a droplet of ink from the nozzle.
• the colloidal dispersions should disperse well in the selected solvents and should easily filter though a 500 nm filter (more preferably through a 300 nm filter), in order to optimize printability.
• various configurations of doped Group IV nanoparticle colloidal dispersions can be formulated by the selective blending of doped, undoped, and/or differently doped Group IV nanoparticles.
• various formulations of blended Group IV nanoparticle colloidal dispersions can be prepared in which the dopant level for a specific layer of a junction is formulated by blending doped and undoped Group IV nanoparticles to achieve the requirements for that layer.
• the blended Group TV nanoparticle colloidal dispersions may be used to compensate for substrate defects, such as the passivation of oxygen atoms in order to reduce undesirable energy states.
• FIGS. 4A-C a set of schematic diagrams of a concentric flow- through plasma reactor is shown, in accordance with the present invention.
• FIG. 4A shows a side view.
• FIG. 4B shows a cross-sectional view.
• FIG. 4C shows the cross-sectional view of FIG. 4B with the addition of a coating on a first dielectric and a second dielectric.
• a Group TV precursor gas, a set of inert gases, as well as a dopant gas (if required), are generally flowed through the annular channel and ignited in a reaction zone between a set of electrodes.
• An RF (radiofrequency) signal is then applied to the powered electrode in order to strike a plasma and subsequently dissociate and form Group IV nanoparticles which are generally collected downstream of the reaction zone.
• the concentric flow-through plasma reactor is configured with an outer tube 3214 and an inner tube 3215 concentrically positioned along a longitudinal axis with respect outer tube 3214.
• outside inner tube 3215 may be sealed from the ambient atmosphere by inlet port flange 3218a and outlet port flange 3218b.
• a plasma reaction zone i.e., the zone in which the nanoparticles are created
• a plasma reaction zone is defined as an area inside annular channel 3227 between a tube-shaped outer electrode 3225 (positioned outside outer tube 3214) and a tube-shaped central electrode 3224 (central electrode tube), positioned concentrically along a longitudinal axis with respect to tube- shaped outer electrode 3225 (outer electrode tube), and further positioned inside inner tube 3215.
• the precursor gas or gases may be introduced into annular channel 3227 along flow path 3211 from a precursor gas source in fluid communication with an inlet port (not shown) on inlet port flange 3218a.
• nanoparticles produced within the plasma reactor chamber may exit through an exit port (not shown) on outlet port flange 3218b into a nanoparticle collection chamber (not shown).
• the nanoparticles may be collected on a substrate or grid housed in the plasma reactor chamber.
• tube-shaped central electrode 3224 is configured to extend along a substantial portion of the plasma reactor.
• tube-shaped central electrode 3224 and tube-shaped outer electrode 3225 may be made of any sufficiently electrically conductive materials, including metals, such as copper or stainless steel.
• Outer tube 3214 may be further shielded from the plasma by outer tube dielectric layer 3209 disposed on the inner surface of outer tube 3214.
• outer tube 3214 may be any material that does not substantially interfere with the generated plasma, such as a dielectric material.
• outer tube 3214 and outer tube dielectric layer 3209 are comprised of different materials, such as different dielectric materials.
• outer tube 3214 and outer tube dielectric layer 3209 are the same physical structure and material, such as quartz.
• inner tube 3215 may be further shielded from the plasma by inner tube dielectric layer 3213. Examples of dielectric materials include, but are not limited to, quartz, sapphire, fumed silica, polycarbonate alumina, silicon nitride, silicon carbide, and borosilicate.
• Group IV nanoparticles produced below a certain temperature will be amorphous, whereas particles produced such that they are hotter during synthesis are crystalline.
• particle temperature during synthesis will affect dopant activation.
• Doped nanoparticles that were exposed to higher temperature during synthesis will have dopants that are electrically active, as opposed to the electrically inactive dopants in the low-temperature produced particles.
• Group IV precursor gases include silane, disilane, germane, digermane, halide analogs, etc.
• n-type dopant gases include phosphine, arsine, etc.
• p-type dopant gases include boron diflouride, trimethyl borane, diborane, etc.
• the inert gases include argon, helium, neon, etc.
• Group FV nanoparticles may be produced in an RF plasma at a total pressure of no greater than about 25 Torr (e.g., about 3 Torr to about 25 Torr).
• Typical flow rates for the semiconductor precursor gas may be about 2 standard cubic centimeters (seem) to about 30 seem, while the flow rate for a dopant gas may be about 60 seem to about 150 seem (e.g., about 0.1% of dopant in inert buffer gas such as Ar).
• the ratio of semiconductor precursor gas molecules to dopant gas molecules in the plasma reaction is from about 25:1 to about 1000:1.
• the frequency of the RF power source used to ignite and/or sustain the RF plasma may vary within the RF range from 300 kHz to 300 GHz. Typically, however, a frequency of 13.56 MHz will be employed because this is the major frequency used in the radiofrequency plasma processing industry. Typical radiofrequency powers range from about 30 W to about 300 W.
• the concentration of dopants in the Group FV nanoparticles may vary depending on factors such as dopant gas concentration and flow rate.
• silane or germane may be used as dopant gas concentration and flow rate.
• the present radiofrequency plasma-based methods are capable of producing Group IV nanoparticles having dopant concentrations approaching the solubility limit of the dopant in a crystalline semiconductor.
• the present methods can provide p-type (e.g., phosphorous or arsenic) doping levels of at least about 2%.
• p-type dopant level in the silicon nanoparticles is between about 0.01% and about 5%.
• the present methods can provide n-type silicon nanoparticles with doping levels of at least about 1%. This includes embodiments wherein the n-type dopant level is between about 0.01% and about 5%.
• doped Group IV nanoparticles may be formed as crystalline nanoparticles with activated dopants. This configuration is advantageous because it may eliminate the need for a high-temperature dopant activation step, thereby rendering the method less expensive, less time-consuming and more efficient.
• a set of p-type and intrinsic nanoparticles were prepared in an RF reactor substantially similar to that described for FIGS. 4A-C.
• a 10% silane gas in argon was used at a flow rate of 22.5 seem.
• a dopant gas of diborane was used at a concentration of 100 ppm at flow rate of 75 seem, providing a ratio of boron to silicon in the reactor of about 0.66%.
• the pressure in the RF plasma reactor chamber was maintained at about 10 Torr.
• a 10% silane gas in argon was used at a flow rate of 22.5 seem.
• the pressure in the RF plasma reactor chamber was maintained at about 10 Torr.
• the resulting nanoparticle size distribution for the p-type silicon nanoparticles was 5.2 nm +/- 1.0 nm, while the size distribution for the intrinsic silicon nanoparticles was 5.7 nm +/- 1.2 nm.
• Colloidal dispersions made form the p-type and intrinsic nanoparticles of Example 1, were each deposited on a 1" x l"x 0.04" quartz substrates. Prior to deposition, the quartz substrate was cleaned using an argon plasma.
• colloidal dispersions were formulated as a 20 mg/ml solution in chloroform/chlorobenzene (4:1 v/v), which was sonicated using a sonication horn at 35% power for 15 minutes. A sufficient volume of each colloidal dispersion was delivered to each substrate respectively in order to effectively cover the quartz substrate surface. Porous compacts of between about 650 nm to about 700 nm thick were then formed by spin casting the colloidal dispersions on each substrate at 1000 rpm for 60 seconds.
• the substrates were then subjected to a conditioning step at 100 °C for 15 minutes at a pressure of between about 5 x 10 "6 to about 7 x 10 "6 Torr using a 15 minute ramp. This was followed by a heat treatment at a temperature of 765 0 C, and a pressure of between about 5 x 10 "6 Torr to about 7 x 10 "6 Torr for 6 minutes, after a 15 -minute ramp to the targeted fabrication temperature. Consequently, densified films formed were between about 300 nm to about 350 nm thick.
• FIG. 5 A a set of secondary ion mass spectroscopy (SIMS) results for an intrinsic densified film 506 and a p-type densified film 508.
• Horizontal axis 504 shows depth in micrometers ( ⁇ m), while vertical axis 502 shows concentration in atoms/cm 3 .
• level of boron in the p-type nanoparticle densified film is about 5 x 10 19 atoms/cc, while the level of boron in the intrinsic nanoparticle
• densified film is about 5 x 10 17 atoms/cc.
• the substantial difference in order of magnitude (about 2x) between levels for the p-type densified film versus the instrinsic densified film demonstrates that the boron atoms were generally incorporated into the p-type nanoparticles. That is, the boron atoms were substantially retained during the thermal processing of the p-type nanoparticles.
• FIG. 5B a set of dark current versus voltage curves are shown, in accordance with the invention.
• Horizontal axis 510 shows voltage (V), while vertical axis 512 shows current (mA).
• p-type nanoparticle film 518 was able to conduct substantially more of dark current as voltage 510 was increased. Consequently, a conducting p-type Group IV nanoparticle film can be successfully fabricated from a p-type Group IV nanoparticle colloidal dispersion.
• a set of n-type nanoparticle colloidal dispersions were used in the fabrication of n- type nanoparticle films.
• the steps for the preparation of each 1" x l"x 0.04" quartz substrate through the preparation of the film were the same as for the preparation of the intrinsic nanoparticle film and p-type film of Example 2, above.
• both quartz substrates were baked in a conditioning step at 100°C for 30 minutes in an inert atmosphere.
• a set of densified films formed were between about 215 nm to about 250 nm thick.
• FIG. 6 a comparison of the conductivity of an amorphous n-type nanoparticle film (608) to a crystalline n-type nanoparticle film (606) is shown, in accordance with the present invention.
• Horizontal axis 602 shows rapid thermal processing (RTP) apparatus sintering temperature ( 0 C), while vertical axis 604 shows conductivity (S/cm).
• RTP rapid thermal processing
• S/cm conductivity
• the amorphous n-type nanoparticles (608) and the crystalline n-type nanoparticles were first manufactured, and then dispersed in chloroform/chlorobenzene solution (4:1 v/v ratio) with a concentration of 20 mg of powder per one mL of solvent. Each solution was then agitated using an ultrasonic horn for 15 minutes using a power setting of 35%.
• a set of eight films (four amorphous n-type nanoparticle films and four crystalline n-type nanoparticle films) was then created by depositing approximately 300-350 ⁇ L of each solution onto eight 1 x 1 inch square quartz substrates (each substrate corresponding to a particular conductivity reading for either amorphous or crystalline n-type nanoparticles) and spun at 1000 rpm for 60 seconds. Additional solvent drying was performed by placing all the substrates on a hotplate held at 100 0 C for 30 minutes.
• the substrates were then placed face down on a silicon carrier wafer and heated to temperatures (700 0 C, 800 0 C, 900 0 C, 1000 0 C) for 30 seconds in a rapid thermal processor (RTP), in an Ar ambient environment at about 30°C/second. 1500A thick aluminum lines were then evaporated onto the substrates with variable spacing.
• RTP rapid thermal processor
• the conductivity of the film was then measured by applying a voltage between the aluminum lines and measuring the current carried by the Si film across the gap between the two aluminum lines.
• amorphous n-type nanoparticle film (608) and the crystalline n-type nanoparticle film (606) are electrically substantially the same.
• FIG. 7 a particle size distribution for crystalline n-type Si nanoparticles is shown, in accordance with the present invention.
• Horizontal axis 702 shows Si nanoparticle size in nanometers (nm), while vertical axis 704 shows particle count.
• particle sizes are measured by comparing the diameter of individual particles from transmission electron microscopy (TEM) images.
• the average particle size and size distribution may then be calculated by using histograms and standard data processing algorithms. Consequently, a narrow distribution of nanoparticle sizes (here about 13 nm) may be obtained using a process as described in FIGS. 4A-C.
• FIG. 8 a comparison is shown of the degree of crystallinity of a crystalline n-type Si nanoparticle to an amorphous n-type Si nanoparticle using selected area diffraction (SAD), in accordance with the present invention.
• Horizontal axis 802 shows diffraction angle in arbitrary units, while vertical axis 804 shows intensity in arbitrary units.
• SAD is generally a crystallographic experimental technique that can be performed inside a transmission electron microscope (TEM).
• TEM transmission electron microscope
• a thin crystalline specimen here a Si nanoparticle
• TEM transmission electron microscope
• the wavelength of high-energy electrons is a fraction of a nanometer, and the spacings between atoms in a solid is only slightly larger, the atoms act as a diffraction grating to the electrons, a portion of which are diffracted to particular angles, determined by the crystal structure of the sample.
• FWHM Full Width at Half Maximum
• the crystalline Si n-type nanoparticle has a FWHM of about 1.8. That is, about 3x greater. Therefore, in an advantageous manner, by using the process as described in FIG. 4, a substantially crystalline Group IV nanoparticle may be produced.
• Horizontal axis 902 shows particle agglomerate size in a logarithmic nanometer (nm) scale, while vertical axis 904 shows % channel (e.g., the percentage of particles in a size range in each count).
• % channel e.g., the percentage of particles in a size range in each count.
• the particles tend to form lose agglomerates in order to reduce their surface energy.
• Agglomerates typically comprise very weak bonds between the nanoparticles, and can be easily disassociated with the addition of small mechanical or thermal energy.
• the larger the size of underlying nanoparticle the larger the corresponding size of the agglomerate.
• a first colloidal dispersion 906 is loaded with intrinsic Si nanoparticles.
• a second colloidal dispersion 908 is loaded with n-type Si nanoparticles.
• a third colloidal dispersion 910 is loaded with p-type Si nanoparticles.
• the ratio of silicon nanoparticles to solvent for all three colloidal dispersions was 20 mg/ml.
• the colloidal dispersions were prepared using pure IBA (iso-butanol) solvent. Particles and solvent were mixed and the mixture was stirred for 30 min by stirring at about 100 0 C followed by about a 15 min ultrasonic horn sonication at about 15% power. The colloidal dispersions were further filtered through 5 micron Nylon filter.
• IBA iso-butanol
• the second colloidal dispersion 908 with n-type Si nanoparticles and the third colloidal dispersion 910 with p-type Si nanoparticles each have agglomerate size centering at much smaller colloidal dispersions. That is, the second colloidal dispersion 908 has agglomerate size centering at about 200 nm, while the third colloidal dispersion 910 has agglomerate size centering at about 100 nm.
• FIG. 10 a set of n-type Si nanoparticle colloidal dispersions of varying viscosity is shown, in accordance with the present invention.
• Horizontal axis 1002 shows RPM (revolutions per minute corresponding to shearing force), while vertical axis 1004 shows measured viscosity at 40° C in Cp (centipoise).
• a Newtonian fluid is generally a fluid that flows like water. That is, its viscosity is substantially the same at a given temperature and pressure regardless of the forces acting on it.
• a set of amorphous n-type Si nanoparticle colloidal dispersions were produced, in accordance with the present invention.
• a first colloidal dispersion was made at 30 mg of amorphous Si nanoparticles per ml of solvent.
• a second colloidal dispersion was made of amorphous Si nanoparticles at 40 mg of Si nanoparticles per ml of solvent.
• a third colloidal dispersion was made of amorphous Si nanoparticles at 50 mg of nanoparticles per ml of solvent.
• the solvent used was cyclohexanol/ cyclohexanone mixtures (CHOH/CHO 1 :1).
• the colloidal dispersions were then prepared inside an N 2 glove box. About 1205 mg of the n-type type amorphous Si nanoparticles was first dispersed in 12 mL of the dispersant/primary solvent, and then distilled cyclohexanol (CHOH), by heating in 40 mL glass vial for 30 min at 82C with magnetic stirring (DCA hotplate setting lOOC, stir setting 1000, 1/8" stir bar).
• This suspension (100 mg Si/mL) was processed on a high shear mixer (15,000 RPM, 5 min, 10mm probe). 7.9 mL of the lOOmg Si/mL suspension was then combined with 7.9 mL of the co-solvent, distilled cyclohexanone (CHO), to form the third colloidal dispersion of 50 mg/mL, CHOH/CHO 1 :1.
• This third colloidal dispersion was processed on the high-shear mixed at 1000 RPM for 5 min. to complete the mixing, then filtered through 41 um Nylon mesh (25 mm diameter, Millipore), followed by filtration through 11 um Nylon and 5 um Nylon 25 mm syringe-type filters.

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