Stauffer Chemical Company

American Cyanamid Company

John A Baumann

Rozalie Schachter

Christian G Michel

Mark A Kuck

Paul M Raccah

David G Brock

William E Spicer

Diego J Olego

Robert W Parry

Henry S Marek

Marcello Viscogliosi

Harvey B Serreze

Pnictide thin films, particularly phosphorus, grown on III-V semiconductors, particularly InP, GaP, and GaAs, are amorphous and have a novel layer-like, puckered sheet-like local order. The thin films are typically 400 Angstroms thick and grown preferably by molecular beam deposition, although other processes such as vacuum evaporation, sputtering, chemical vapor deposition, and deposition from a liquid melt may be used. The layers are grown on the &lt;100&gt; &lt;110&gt;, and surfaces of the III-V crystals. The pnictide layer reduces the density of surface states, and allows the depletion layer to be modulated, the surface barrier reduced, the electron concentration at the surface increased, and there is a decrease in the surface recombination velocity and an increase in the photoluminescence intensity. The layers may be utilized in MIS and Metal-semiconductor (Schottky) devices for example to insulate and passivate MISFETS, to passivate MESFETS, to reduce the surface current component of the reverse bias dark current in P-I-N and avalanche diodes, and to improve performance of opto-electronic devices such as light emitting diodes, lasers, solar cells, photo cathodes and photo detectors. The pnictide layer may be applied to intermetallic and compound semiconductors having a pnictide component. The pnictides may be phosphorus, arsenic, antimony or bismuth, or combinations thereof.

Passivation and insulation of III-V devices with pnictides, particularly

High phosphorus polyphosphides, namely MP.sub.x, where M is an alkali metal (Li, Na, K, Rb, and Cs) or metals mimicking the bonding behavior of an alkali metal, and x=7 to 15 or very much greater than 15 (new forms of phosphorus) are useful semiconductors in their crystalline, polycrystalline and amorphous forms (boules and films). MP.sub.15 appears to have the best properties and KP.sub.15 is the easier to synthesize. P may include other pnictides as well as other trivalent atomic species. Resistance lowering may be accomplished by doping with Ni, Fe, Cr, and other metals having occupied d or f outer electronic levels; or by incorporation of As and other pnictides. Top contacts forming junction devices doped with Ni and employing Ni as a back contact comprise Cu, Al, Mg, Ni, Au, Ag, and Ti. Photovoltaic, photoresistive, and photoluminescent devices are also disclosed. All semiconductor applications appear feasible. These semiconductors belong to the class of polymer forming, trivalent atomic species forming homatomic, covalent bonds having a coordination number slightly less than 3. The predominant local order appears to be all parallel pentagonal tubes in all forms, including amorphous, except for the monoclinic and twisted fiber allotropes of phosphorus. Large crystal monoclinic phosphorus (a birefringent material) in two habits, a twisted fiber phosphorus allotrope and a star shaped fibrous high phosphorus material are also disclosed. Single and multiple source vapor transport, condensed phase, melt quench, flash evaporation, chemical vapor deposition, and molecular flow deposition may be employed in synthesizing these materials. Vapor transport may be employed to purify phosphorus.

Films of catenated phosphorus materials, their preparation and use, and

Effluent process gases, particularly those employed in the production and processing of solid state electronic components, are cracked to form products having a condensed phase, which may be separated from the flowing process gas. A plasma trap comprises a high frequency coil for producing a plasma therein. The walls of the trap may be cooled and the trap may employ a removable wall on which the cracked product collects. Particular gases that may be treated are arsine, phosphine, disilane, silane, germane, organometallics and gases containing beryllium and boron.

Cracking traps for process gas components having a condensed phase

High phosphorus polyphosphides, namely MP.sub.x, where M is an alkali metal (Li, Na, K, Rb, and Cs) or metals mimicking the bonding behavior of an alkali metal, and x=7 to 15 or very much greater than 15 (new forms of phosphorus) are useful semiconducutors in their crystalline, polycrystalline and amorphous forms (boules and films). MP.sub.15 appears to have the best properties and KP.sub.15 is the easier to synthesize. P may include other pnictides as well as other trivalent atomic species. Resistance lowering may be accomplished by doping with Ni, Fe, Cr, and other metals having occupied d or f outer electronic levels; or by incorporation of As and other pnictides. Top contacts forming junction devices doped with Ni and employing Ni as a back contact comprise Cu, Al, Mg, Ni, Au, Ag, and Ti. Photovoltaic, photoresistive, and photoluminescent devices are also disclosed. All semiconductor applications appear feasible. These semiconductors belong to the class of polymer forming, trivalent atomic species forming homatomic, covalent bonds having a coordination number slightly less than 3. The predominant local order appears to be all parallel pentagonal tubes in all forms, including amorphous, except for the monoclinic and twisted fiber allotropes of phosphorus. Large crystal monoclinic phosphorus (a birefringent material) in two habits, a twisted fiber phosphorus allotrope and a star shaped fibrous high phosphorus material are also disclosed. Single and multiple source vapor transport, condensed phase, melt quench, flash evaporation, chemical vapor deposition, and molecular flow deposition may be employed in synthesizing these materials. Vapor transport may be employed to purify phosphorus. The materials may be employed as protective coatings, optical coatings, fire retardants, fillers and reinforcing fillers for plastics and glasses, antireflection coatings for infrared optics, infrated transmitting windows, and optical rotators.

Catenated phosphorus materials and their preparation

High phosphorus polyphosphides, namely MP.sub.x, where M is an alkali metal (Li, Na, K, Rb, and Cs) or metals mimicking the bonding behavior of an alkali metal, and x=7 to 15 or very much greater than 15 (new forms of phosphorus) are useful semiconductors in their crystalline, polycrystalline and amorphous forms (boules and films). MP.sub.15 appears to have the best properties and KP.sub.15 is the easier to synthesize. P may include other pnictides as well as other trivalent atomic species. Resistance lowering may be accomplished by doping with Ni, Fe, Cr, and other metals having occupied d or f outer electronic levels; or by incorporation of As and other pnictides. Top contacts forming junction devices doped with Ni and employing Ni as a back contact comprise Cu, Al, Mg, Ni, Au, Ag, and Ti. Photovoltaic, photoresistive, and photoluminescent devices are also disclosed. All semiconductor applications appear feasible. These semiconductors belong to the class of polymer forming, trivalent atomic species forming homatomic, covalent bonds having a coordination number slightly less than 3. The predominant local order appears to be all parallel pentagonal tubes in all forms, including amorphous, except for the monoclinic and twisted fiber allotropes of phosphorus. Large crystal monoclinic phosphorus (a birefringent material) in two habits, a twisted fiber phosphorus allotrope and a star shaped fibrous high phosphorus material are also disclosed. Single and multiple source vapor transport, condensed phase, melt quench, flash evaporation, chemical vapor deposition, and molecular flow deposition may be employed in synthesizing these materials. Vapor transport may be employed to purify phosphorus. The materials may be employed as protective coatings, optical coatings, fire retardants, fillers and reinforcing fillers for plastics and glasses, antireflection coatings for infrared optics, infrared transmitting windows, and optical rotators.

A fore line trap is located before the forepump in a vacuum system. The trap utilizes a cracker, which may be a heated filament or a plasma, and cold walls. The cracker cracks pnictide gas species such as P.sub.4 into other species such as P.sub.2 which have a higher sticking co-efficient. The pnictides are deposited on the cold walls. The cold walls preferably comprise a sleeve which may be removed from the trap and replaced by a clean one.

Pnictide trap for vacuum systems

High phosphorus polyphosphides, namely MP.sub.x, where M is an alkali metal (Li, Na, K, Rb, and Cs) or metals mimicking the bonding behavior of an alkali metal, and where x=7 to 15 or very much greater than 15 (new forms of phosphorus) are useful semiconductors in their crystalline, polycrystalline and amorphous forms (boules and films). MP.sub.15 appears to have the best properties and KP.sub.15 is the easier to synthesize. P may include other pnictides as well as other trivalent atomic species. Resistance lowering may be accomplished by doping with Ni, Fe, Cr, and other metals having occupied d or f outer electronic levels; or by incorporation of As and other pnictides. Rectifying Schottky junction devices doped with Ni and employing Ni as a back contact comprise Cu, Al, Mg, Ni, Au, Ag, and Ti as junction forming top contacts. Photovoltaic, photoresistive, and photoluminescent devices are also disclosed. All semiconductor applications appear feasible. Single and multiple source vapor transport, condensed phase, melt quench, flash evaporation, chemical vapor deposition, and molecular flow deposition may be employed in synthesizing these materials. Vapor transport may be employed to purify phosphorus.

Doping of catenated phosphorus materials

MP.sub.15, where M is an alkali metal is used in a generator of P.sub.4 gas. KP.sub.15 is preferred. The generator is heated to produce the P.sub.4 gas. The generator may be used in various deposition processes such as chemical vapor deposition, vacuum evaporation, and molecular beam deposition. It is particularly useful in high vacuum processes below 10.sup.-3 Torr, particularly below 10.sup.-4 Torr such as vacuum evaporation and molecular beam deposition, for example vapor phase epitaxy and molecular beam epitaxy.

P.sub.4 gas generator using the alkali metal polyphosphide MP.sub.15

A method and apparatus are provided for producing fine quality pnictide films by vacuum evaporation and molecular beam deposition. A pnictide source, preferably phosphorous, is heated to produce a continuous supply of vapor species, preferably P.sub.4. The vapor species is cracked by a heated tungsten wire positioned adjacent the pnictide source to produce P.sub.2 molecules. A second tungsten wire cracker is located adjacent a substrate to prevent the recombination of P.sub.2 molecules into P.sub.4 molecules. The P.sub.2 molecules are deposited on the substrate and condense into amorphous pure phosphorous shiny red films. A separate source of alkali metal intercalate, preferably KC.sub.8, may also be heated to provide an alkali metal vapor for producing films of alkali metal polypnictide films, preferably KP.sub.x where x is equal to or greater than 15, to be deposited on the substrate. Fine quality films may also be deposited on a substrate by a molecular beam apparatus providing a continuous source of pnictide vapor species and a cracker disposed between the exit of a pnictide collimator and the substrate.

Method for forming evaporated pnictide and alkali metal polypnictide

Monoclinic phosphorus is produced in a single source vapor transport apparatus comprising a sealed evacuated ampoule containing a mixture or compound of phosphorus and an alkali metal with the phosphorus to alkali metal ratio being 11 or greater. The charge is heated to 550.degree.-560.degree. C. and the monoclinic phosphorus crystals are formed on the cooler surface at the top of the ampoule over the temperature range of 500.degree.-560.degree. C. The preferred heating temperature is in the neighborhood of 555.degree. C. and the preferred deposition temperature is in the neighborhood of 539.degree. C. Alkali metals that may be employed include sodium, potassium, rubidium and cesium. The monoclinic phosphorus crystals form in two habits. Those formed in the presence of sodium and cesium are in the form of flat square platelets up to 4 mm on a side and 2 mm thick. These platelets may be easily cleaved into thinner platelets, like mica. The other habit formed in the presence of potassium and rubidium is in the form of a truncated pyramid up to 4 mm.times.3 mm.times.2 mm high. This habit is hard to cleave. The crystals are semiconductors with a band gap, indicated by photoluminescence, of about 2.1 eV at room temperature. Powder X-ray diffraction, and differential thermal analysis are consistent with that reported for Hittorf's phosphorus prepared according to the prior art. The crystals are a deep red on transmission and birefringent, rotating the plane of polarization in a polarizing microscope. They contain from 50 to 2000 parts per million of alkali metal and therefore may be utilized as a form of very pure phosphorus as well as for their semiconducting and birefringent qualities and as phosphors.

Monoclinic phosphorus formed from vapor in the presence of an alkali

The present invention provides a trap for a vapor species, particularly a pnictide.sub.4 vapor species, for a vacuum system of the type including a vacuum chamber communicating with a forepump through a vacuum line. The trap may be positioned within the vacuum chamber itself, or in the alternative, the trap may be located between the vacuum chamber and the forepump. The trap includes a housing for a cracker, which may be a heated filament or a plasma, which cracks the pnictide vapor species into pnictide.sub.2. The walls of the housing are cooled so that the trapped pnictide species readily forms a film and adheres to the walls of the housing. The pnictide.sub.4 vapor species, which may be harmful to the operation of a forepump, is prevented from entering the forepump. A removable sleeve can be positioned in the housing so that the cracked species adheres to it. The sleeve may be removed from the housing for maintenance and replacement purposes. When the trap is located within the vacuum chamber itself, it also functions to reduce background pnictide.sub.4 pressure in that chamber.

Fine quality catenated phosphorus thin films are produced in a high vacuum evaporator. Heated tungsten wire crackers are provided above the phosphorus boat and below the substrates. Amorphous pure phosphorus shiny red films have been deposited on glass, metallized glass and GaP and exhibit an optical edge at 2.0 eV. Films of KP.sub.x where x is equal to 15 or greater than 15 are produced by utilizing a second baffled boat source containing the potassium graphite intercalate, KC.sub.8. Addition of a nickel evaporation source provides nickel-doped polyphosphide films.

Vacuum evaporating films of alkali metal polyphosphide

Polycrystalline and monocrystalline potassium polyphosphide, KP.sub.15, has been grown from the liquid phase at a temperature range of 600.degree.-700.degree. C. Massive crystallization of KP.sub.15 whiskers and platelets is observed. Crystalline KP.sub.15 films have been grown on gallium arsenide (110) and gallium phosphide (111) polished wafers, silicon (110) polished wafers, quartz, on a nickel evaporated 2000 angstrom nickel layer on quartz, and on nickel foil. Microcrystalline KP.sub.15 formed by a condensed phase process is incorporated into a sealed ampule evacuate 10.sup.-4 torr. The temperature is raised to 655.degree. C. and the furnace tilted to bring the melt in contact with the substrates. The temperature is then reduced to 640.degree. C. and the furnace is tilted back to the original position. Large KP.sub.15 whiskers several millimeters in size are grown from the melt and crystalline films of KP.sub.15 are grown topotaxially on gallium arsenide and gallium phosphide. Crystalline platelets of KP.sub.15 3.times.3 mm have been obtained by cleaving the grown film from a gallium phosphide substrate.

Liquid phase growth of crystalline polyphosphide

Metal-insulator-semiconductor devices are formed on III-V semiconductors utilizing a pnictide rich insulating layer. The layer may be applied by vacuum evaporation, sputtering, chemical vapor deposition, and from a liquid melt. Gallium arsenide, indium phosphide, and gallium phosphide substrates are insulated with an alkali metal high pnictide polypnictide, preferably a polyphosphide, having the formula MP.sub.x where x is equal to or greater than 15, including new forms of phosphorus grown in the presence of an alkali metal where x is much greater than 15. A KP.sub.15 layer is preferred. They may also be insulated with a layer of a solid elemental pnictide, namely phosphorus, arsenic, antimony or bismuth applied by one of the above named processes. An elemental phosphorus layer is preferred. A silicon nitride, Si.sub.3 N.sub.4, layer may be added on top of the pnictide layer to increase the breakdown voltage of the insulating layer.

MIS Device employing elemental pnictide or polyphosphide insulating

High phosphorus polyphosphides, namely MP.sub.x, where M is an alkali metal (Li, Na, K, Rb, and Cs) or metals mimicking the bonding behavior of an alkali metal, and where x=7 to 15 or very much greater than 15 (new forms of phosphorus) are useful semiconductors in their crystalline, polycrystalline and amorphous forms (boules and films). MP.sub.15 appears to have the best properties and KP.sub.15 is the easier to synthesize. P may include other pnictides as well as other trivalent atomic species. Resistance lowering may be accomplished by doping with Ni, Fe, Cr, and other metals having occupied d or f outer electronic levels; or by incorporation of As and other pnictides. Rectifying Schottky junction devices doped with Ni and employing Ni as a back contact comprise Cu, Al, Mg, Ni, Au, Ag, and Ti as junction forming top contacts. Photovoltaic, photoresistive, and photoluminescent devices are also disclosed. All semiconductor applications appear feasible. Single and multiple source vapor transport, condensed phase, melt quench, flash evaporation, chemical vapor deposition, and molecular flow deposition may be employed in synthesizing these materials. Vapor transport may be employed to purify phosphorus. The materials may be employed as protective coatings, optical coatings, fire retardants, fillers and reinforcing fillers for plastics and glasses, antireflection coatings for infrared optics, infrared transmitting windows, and optical rotators.

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Ossining, NY, United States of America

John A Baumann