US2426377A - Selenium rectifier and method of making - Google Patents

Selenium rectifier and method of making Download PDF

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US2426377A
US2426377A US513265A US51326543A US2426377A US 2426377 A US2426377 A US 2426377A US 513265 A US513265 A US 513265A US 51326543 A US51326543 A US 51326543A US 2426377 A US2426377 A US 2426377A
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selenium
metal
orifice
stream
boiler
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Jr Cleveland Scudder Smith
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    • C—CHEMISTRY; METALLURGY
    • C23—COATING METALLIC MATERIAL; COATING MATERIAL WITH METALLIC MATERIAL; CHEMICAL SURFACE TREATMENT; DIFFUSION TREATMENT OF METALLIC MATERIAL; COATING BY VACUUM EVAPORATION, BY SPUTTERING, BY ION IMPLANTATION OR BY CHEMICAL VAPOUR DEPOSITION, IN GENERAL; INHIBITING CORROSION OF METALLIC MATERIAL OR INCRUSTATION IN GENERAL
    • C23C—COATING METALLIC MATERIAL; COATING MATERIAL WITH METALLIC MATERIAL; SURFACE TREATMENT OF METALLIC MATERIAL BY DIFFUSION INTO THE SURFACE, BY CHEMICAL CONVERSION OR SUBSTITUTION; COATING BY VACUUM EVAPORATION, BY SPUTTERING, BY ION IMPLANTATION OR BY CHEMICAL VAPOUR DEPOSITION, IN GENERAL
    • C23C14/00—Coating by vacuum evaporation, by sputtering or by ion implantation of the coating forming material
    • C23C14/04—Coating on selected surface areas, e.g. using masks
    • C—CHEMISTRY; METALLURGY
    • C23—COATING METALLIC MATERIAL; COATING MATERIAL WITH METALLIC MATERIAL; CHEMICAL SURFACE TREATMENT; DIFFUSION TREATMENT OF METALLIC MATERIAL; COATING BY VACUUM EVAPORATION, BY SPUTTERING, BY ION IMPLANTATION OR BY CHEMICAL VAPOUR DEPOSITION, IN GENERAL; INHIBITING CORROSION OF METALLIC MATERIAL OR INCRUSTATION IN GENERAL
    • C23C—COATING METALLIC MATERIAL; COATING MATERIAL WITH METALLIC MATERIAL; SURFACE TREATMENT OF METALLIC MATERIAL BY DIFFUSION INTO THE SURFACE, BY CHEMICAL CONVERSION OR SUBSTITUTION; COATING BY VACUUM EVAPORATION, BY SPUTTERING, BY ION IMPLANTATION OR BY CHEMICAL VAPOUR DEPOSITION, IN GENERAL
    • C23C14/00—Coating by vacuum evaporation, by sputtering or by ion implantation of the coating forming material
    • C23C14/22—Coating by vacuum evaporation, by sputtering or by ion implantation of the coating forming material characterised by the process of coating
    • C23C14/24—Vacuum evaporation
    • C—CHEMISTRY; METALLURGY
    • C23—COATING METALLIC MATERIAL; COATING MATERIAL WITH METALLIC MATERIAL; CHEMICAL SURFACE TREATMENT; DIFFUSION TREATMENT OF METALLIC MATERIAL; COATING BY VACUUM EVAPORATION, BY SPUTTERING, BY ION IMPLANTATION OR BY CHEMICAL VAPOUR DEPOSITION, IN GENERAL; INHIBITING CORROSION OF METALLIC MATERIAL OR INCRUSTATION IN GENERAL
    • C23C—COATING METALLIC MATERIAL; COATING MATERIAL WITH METALLIC MATERIAL; SURFACE TREATMENT OF METALLIC MATERIAL BY DIFFUSION INTO THE SURFACE, BY CHEMICAL CONVERSION OR SUBSTITUTION; COATING BY VACUUM EVAPORATION, BY SPUTTERING, BY ION IMPLANTATION OR BY CHEMICAL VAPOUR DEPOSITION, IN GENERAL
    • C23C14/00—Coating by vacuum evaporation, by sputtering or by ion implantation of the coating forming material
    • C23C14/22—Coating by vacuum evaporation, by sputtering or by ion implantation of the coating forming material characterised by the process of coating
    • C23C14/24—Vacuum evaporation
    • C23C14/243—Crucibles for source material
    • C—CHEMISTRY; METALLURGY
    • C23—COATING METALLIC MATERIAL; COATING MATERIAL WITH METALLIC MATERIAL; CHEMICAL SURFACE TREATMENT; DIFFUSION TREATMENT OF METALLIC MATERIAL; COATING BY VACUUM EVAPORATION, BY SPUTTERING, BY ION IMPLANTATION OR BY CHEMICAL VAPOUR DEPOSITION, IN GENERAL; INHIBITING CORROSION OF METALLIC MATERIAL OR INCRUSTATION IN GENERAL
    • C23C—COATING METALLIC MATERIAL; COATING MATERIAL WITH METALLIC MATERIAL; SURFACE TREATMENT OF METALLIC MATERIAL BY DIFFUSION INTO THE SURFACE, BY CHEMICAL CONVERSION OR SUBSTITUTION; COATING BY VACUUM EVAPORATION, BY SPUTTERING, BY ION IMPLANTATION OR BY CHEMICAL VAPOUR DEPOSITION, IN GENERAL
    • C23C14/00—Coating by vacuum evaporation, by sputtering or by ion implantation of the coating forming material
    • C23C14/22—Coating by vacuum evaporation, by sputtering or by ion implantation of the coating forming material characterised by the process of coating
    • C23C14/56—Apparatus specially adapted for continuous coating; Arrangements for maintaining the vacuum, e.g. vacuum locks
    • C23C14/562—Apparatus specially adapted for continuous coating; Arrangements for maintaining the vacuum, e.g. vacuum locks for coating elongated substrates
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01L—SEMICONDUCTOR DEVICES NOT COVERED BY CLASS H10
    • 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
    • H01L21/02104—Forming layers
    • H01L21/02365—Forming inorganic semiconducting materials on a substrate
    • H01L21/02518—Deposited layers
    • H01L21/02521—Materials
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01L—SEMICONDUCTOR DEVICES NOT COVERED BY CLASS H10
    • 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
    • H01L21/02104—Forming layers
    • H01L21/02365—Forming inorganic semiconducting materials on a substrate
    • H01L21/02612—Formation types
    • H01L21/02617—Deposition types
    • H01L21/02631—Physical deposition at reduced pressure, e.g. MBE, sputtering, evaporation
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01L—SEMICONDUCTOR DEVICES NOT COVERED BY CLASS H10
    • 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 potential barriers, e.g. a PN junction, depletion layer or carrier concentration layer
    • H01L21/06—Manufacture or treatment of semiconductor devices or of parts thereof the devices having potential barriers, e.g. a PN junction, depletion layer or carrier concentration layer the devices having semiconductor bodies comprising selenium or tellurium in uncombined form other than as impurities in semiconductor bodies of other materials
    • H01L21/10—Preliminary treatment of the selenium or tellurium, its application to the foundation plate, or the subsequent treatment of the combination
    • H01L21/101—Application of the selenium or tellurium to the foundation plate

Definitions

  • This invention relates to metalrectiflers and photocells, and to methods and apparatus for depositing a relatively thin layer or layers of a metal such as selenium upon a base composed of a different metal or alloy. It has long been recognized that When the surfaces of certain metals or metallic compounds are placed in contact with each other such combination possesses photoelectric characteristics and is also capable of rectifying an alternating electric current. While numerous combinations of metals and metallic compounds have been proposed for use as rectifying and photoelectric elements, one of the most satisfactory combinations is a layer or lm oi selenium deposited upon an aluminum, bronze, copper or ferrous metal base and having a counter-electrode deposited upon or in Contact with its exposed surface.
  • selenium due to its inherent chemical characteristics selenium is difcult to control and of its several known forms which exist at room temperature only one form appears to possess photoelectric and rectifying properties. To be suitable for use in a photoelectric or rectifying element, selenium must be present substantially or entirely in .the form cf a thin gray metallic'lm upon a suitable base metal. If the conditions for depositing the selenium are not carefully controlled, a useless deposit of the amorphous or crystalline form of selenium may result.
  • the present invention overcomes the numerous disadvantages inherent in prior processes and provides a method and apparatus for the economical and commercial production of selenium photocell and rectier elements.
  • the objects of this invention are: to provide an improved method in which selenium is deposited on a base plate under ordinary atmospheric conditions in the form of as many different layers of metallic selenium as may be desired; to provide a method in which the selenium deposition is uniform and the thickness of such deposit may be accurately controlled to any desired value; to provide a method which is adapted to the automatic, continuous and elllcient production of selenium photocell and rectifier elements; to provide apparatus of relatively simple design which is adapted to carry out the method of the invention.
  • Fig, 1 shows an elevational view, in cross-section, of one form of an apparatus embodying the principles of this invention
  • Fig. 2 is an enlarged sectional view taken from the left along the line 2-2 of Fig. 1;
  • Fig. 3 is an elevational View, partly in crosssection, of a modification of the apparatus of the invention
  • Fig. 4 is an enlarged sectional view of one of the several selenium vaporizing boilers or units illustrated generally in Fig. 3;
  • FIGs. 5 and 6 are elevational views of a further modification of the selenium vaporizing boilers or units embodying the principles of this invention.
  • Fig. '7 is an elevational view, partly in section of an apparatus adapted to coat a film or thin layer of selenium simultaneously on both sides of a metal plate;
  • Fig, 8 illustrates a method 0f applying a metal counter-electrode onto a metallic plate
  • Figs. 9 and 10 illustrate partially completed rectifier blanks.
  • the improved method of this invention is carried out by vaporizing selenium in a suitable boiler above and substantially at atmospheric pressure and impinging the resulting vapor against the surface of a suitable metal plate maintained either at or above room temperature.
  • the boiler is preferably provided, in one embodiment of the invention, with a slotted discharge orifice which has a length greater than or substantially equal to the width of the plate to be coated.
  • the metal plate to be coated is maintained at apreselected distance from the orifice of the boiler and when such plate is moved back and forth through the stream of selenium vapor issuing from such orifice, at a preselected rate and in a direction substantially transversely of the longitudinal direction of the slot orifice, an extremely smooth and uniform illm or layer of gray metallic selenium of desirable rectifier or photocell quality is deposited on the metal plate.
  • any desired thickness of selenium may be built up.
  • several boilers may be disposed in tandem relation, so that the metallic plate may pass successively through several streams of selenium and thereby quickly build-up a plurality of layers of selenium. In such an arrangement the boilers may be operated to discharge the same or different concentrations of vapors, and different impurities may be introduced into the several boilers to build up selenium of desirable composition for low forward resistance and high reverse resistance,
  • Figs. 1 and 2 illustrate an embodiment of the invention wherein a selenium 'boiler B comprising a cylindrical casing I2 is provided with an upper threaded portion I4 adapted to frlctionally engage a threaded portion I6 of a cap I8.
  • a slotted orifice 20 isv provided in cap I8, and has substantially uniform cross-section throughout its length.
  • the oriiice 20 has a length substantially equal to the inside diameter of the casing I2.
  • a circular ilange 22 is welded as at 23, or otherwise secured, to the cap I8 to support the boiler and to position the upper surface of the cap I8 substantially ilush with the upper surface of a suitable supporting base board 24', which may be composed of asbestos or other non-inflammable material.
  • Guides 26 are secured to the base board 24 along lines equidistant on either side of the boiler B. These guides 26 are adapted to support a slide 28 carrying the metal plates 30 to be coated with selenium.
  • the metal plates 30 may be bolted at 32 or otherwise secured to the carriage 28, and cooperate with suitable grooves 34 in the guides 26.
  • 28 is provided to slide the plates back and forth on the boiler.
  • the distance between the top of the cap I8 and the surface of the metal plate to be coated with selenium, is maintained at a Value such that when selenium vapor streams at the desired rate through the slotted perennial the lower surface of the metallic plate is uniformly coated.
  • a pair of gas burners 36 or other heating agents may be used to vaporize the selenium, and in order to prevent condensation of selenium vapor in the upper part of the bolier B, the heat is preferably applied to the upper regions of the boiler.
  • Boiler casing I2 is unscrewed from cap I8, and about 10 grams or more of selenium is deposited in the boiler; the casing is then screwed back into position in the cap I8, and suitably heated as by one or more gas burners to a temperature suflicient to cause a stream of selenium vapor to issue through the orifice 20. Heat is applied to the upper portion of the boiler to avoid condensation of selenium therein and is conducted downward by the boiler Walls to vaporize the selenium charge.
  • the slide or carriage 28 carrying the metal plates to be coated is inserted in the guides and a number of passes are made back and forth through the stream of selenium vapor thereby forcing a thin adherent coating of selenium upon the surface of the plates.
  • the interspersed iilms are so thin as to cause no adverse effects on the completed rectifier.
  • the iilms can be completely eliminated by conducting the deposition of selenium in an atmosphere of inert gas such as argon, a relatively inert gas such as nitrogen, or carbon dioxide, or a reducing gas such as household cooking gas.
  • the surrounding gas may be at any desired temperature, and should be above the boiling temperature of selenium if it is desired to avoid any condensation of selenium before the selenium vapor reaches the receiving plate.
  • the ratio of length to width of the orifice is somewhat critical to the deposition of the desired layer of selenium. For example, an orifice width of about 0.012 inch has been found to yield good results. A smaller width gives a greater proportion of selenium oxide to selenium. Slight variations in the width of the orifice slit are to be avoided because such variations cause striations to appear in the deposited selenium. A greater orifice width makes it diiiicult to build up sufficient pressure in the boiler to permit uniform vapor flow along the entire length of the perennial slit, and also causes a greater quantity of selenium vapor to emerge than is necessary or desirable. Hence, care in construction and choice of materials may dictate the use of smaller orifice widths.
  • the distance of the plate from the discharge orifice must be carefully selected to give the most desirable results. In general, the closer the plate is brought to the orifice, the more satisfactory is' the deposition of selenium. If the operation is carried out under conventional atmospheric conditions, some of the selenium oxidizes and some of the selenium condenses to ne red particles. The greater the plate distance, the greater is the ratio of oxidized and condensed selenium to selenium still in vapor form. Too large a proportion of selenium oxide and selenium condensed to the red particle form causes thc selenium to peel and crack from the base plate during later heat treatment and may also lead to high resistance in the forward direction.
  • the temperature of the plate or plates upon which selenium is to be deposited has not been found to be critical, but plates maintained at a temperature of between about 60 to 100 C. are satisfactory and yield a smooth black deposit of selenium, which is desirable in the manufacture of rectifier elements.
  • Figure 3 illustrates a modification in which a long or continuous band of metal 31 is led over a series of selenium boilers B', which may be heated in any manner, as with electric resistance heating coils 39.
  • the boilers may all be identical in construction or may differvas to width oi' orifice or other factors to superimposed layers of different thickness or other characteristics. After coating, the strip may be cut into rectifier elements of the desired dimensions.
  • Figure 4 shows a boiler modification wherein a gaseous atmosphere is introduced by a conduit 38 into a boiler B2, the upper portion of which is heated by a high frequency inductance coil 40. The heat travels downward to vaporize the selenium but the upper part of the boiler is kept hottest to prevent condensation.
  • the gaseous atmosphere entering through conduit 38 may comprise an inert gas such as argon, a relatively inert gas such as nitrogen or carbon dioxide, or a reducing gas.
  • the boiler may be alternatively heated by gas, by radiant heat from an electrical heater, by conducted heat from an electric heater, by electromagnetic induction, or by other convenient means.
  • Figure 5 illustrates a two compartment boiler, wherein compartment 44 is adapted to receive so. lidified selenium or melted selenium at low temperature and compartment 46 is adapted to vaporize molten selenium flowing from compartment 44.
  • a valve 48 is disposed in the base of the 'boiler to drain oiT the selenium or the accumulation of excessive amounts of impurities.
  • molten heated selenium may be introduced into a boiler 50 from a vessel 5l, through a needle valve 52. Suiiicient heat is applied to 50 to cause the selenium to vaporize and flow through a slotted oriiice 54.
  • the amount of selenium vaporized in this type of boiler can be accurately controlled by the setting of the needle valve 52 and the pressure behind the selenium in the vessel 5l.
  • Figure 8 shows a method for applying a metal counter-electrode on top of the selenium deposit 62 on a metal plate 6I.
  • a mask 63 having apertures or windows 64 is placed against the selenium surface and a soft, low-melting-point metal 68 is sprayed onto the exposed areas of selenium by the metal spray gun 65 supplied with com pressed air by air hose 66 and containing molten metal heated by an electric heating element supplied by wires 10.
  • Figure 9 shows a plate after spraying, comprising backing metal plate 6
  • Figure 10 shows an improved plate wherein the backing plate 19 is notched at intervals before the selenium. layer 18 is applied. After spraying of electrodes 'I2 the strip can be readily broken or cut at the notches.
  • the metal strips to be coated with selenium are grooved by means of a kick press or automatic power press.
  • Both sides of the metal strips are then sand-blasted, as for example, with Carborundum of a particle size of 240 to 280 mesh, the metal strips being driven between rollers at a linear speed of about 10 ft. per minute, one sand blast being directed against each side.
  • the selenium plated strips are next heat treated at a temperature of about 210 C. for a period ranging from 15 minutes to one hour.
  • a blocking layer is then applied to the plates, this consisting of a thin film of selenium oxide. This may be effected, for example, by exposing the plates to selenium oxide vapors in a closed chamber for a few seconds, or by any other suitable method.
  • (8) 'I'he final operation is the forming treatment, which consists in subjecting the plates to a suitable direct current, applied through contacts engaging the metal base plate and the sprayed metal layer in a direction in which the element tends to block current flow.
  • the method of depositing a layer of selenium of substantially uniform thickness upon a metal surface which comprises the steps of vaporizing selenium at substantially atmospheric pressure, causing the resulting vapors to assume the shape of a thin ribbon, surrounding said stream with an envelope of gas selected from the group consisting of reducing gases and inert gases, and establishing relative transverse movement between said ribbon of gas and said surface to effect the condensation and deposition of a gray, metallic layer of selenium upon said surface.
  • the improvement which comprises the steps of vaporizing selenium at substantially atmospheric pressure, forming the resulting vapors into a4 thin ribbon-like. stream in substantially unadulterated vaporized form, surropnding said stream with an envelope of gas selected from the group consisting of reducing gases and inert gases, moving said metal base so as to intersect said stream in a direction perpendicular to the widest dimension of said stream to form a thin, uniform and adherent coating of selenium in the gray, metallic state upon said surface, and repeating said movement back and forth through said stream to form a selenium layer of desired thickness.
  • Apparatus for depositing a relatively thin layer of selenium upon a metal base comprising, in combination, means for vaporizing and forming a thin ribbonlike stream of selenium vapor substantially at atmospheric pressure, means for supporting and bringing a base into contact with said stream of selenium vapor, and means for mixing a gas selected from the group consisting of vinert gases and reducing gases with said stream of selenium vapor.
  • Apparatus for depositing a relatively thin layer of selenium upon a metal base said apparatus including a selenium vaporizer operable substantially at atmospheric pressure having a relatively narrow slot-like orifice disposed in the upper portion thereof, means for externally heating said vaporizer to generate a stream of selenium vapor and to avoid condensation of said vapor in said orifice.
  • a method of depositing a layer of selenium upon a metal base which comprises vaporizing selenium at substantially atmospheric pressure, causing the resulting vapors to assume the shape of a stream, surrounding said stream with an envelope of gas selected from the group consisting of reducing gases and inert gases, and directing said stream against a metal base to form a uniform adherent coating of gray metallic selenium thereon.
  • Apparatus for depositing a layer of selenium upon a metal base which comprises a selenium vaporizing furnace having a narrow slotlike discharge orifice, means forapplying heat to said furnace adjacent said discharge orifice to prevent condensation of selenium vapors in the regions near said perennial, and a guide for supporting a metal base a preselected distance from said orifice.
  • Apparatus for depositing a layer of selenium upon a metal base which comprises a selenium vaporizing furnace having a narrow slotlike discharge orifice, a guide for movably supporting a metal base a preselected distance from said orifice, said guide being accessible for insertion of the base therein or removal of the base therefrom during the operation of said furnace,
  • Apparatus for depositing a layer of selenium upon arnetal base which comprises a selenium vaporizing furnace having a narrow slotlike discharge orifice, and a pair of slotted guide members at opposite respective sides of said orifice to slidably receive and support a metal base a preselected distance from said orifice, whereby said base may be moved along the slotted portions of said guides during operation of the furnace.
  • Apparatus for depositing a layer of selenium upon a metal base which comprises a plurality of selenium vaporizing furnaces each having a narrow slot-like discharge tone, and a guide common to all of said furnaces for passing a metal base, in succession, a preselected distance from the respective discharge orifices whereby a coating of selenium is applied to the base by the gases discharged from each furnace.
  • steps which comprise vaporizing selenium at substantially atmospheric pressure, forming the resulting vapors into a thin rbbonlike stream in substantially unadulterated vaporized form, directing said stream of gas against a metal base while eflecting relative transverse movement between said stream and said base to deposit a thin adherent coating of selenium on one surface of said base, and maintaining a protective gaseous envelope around said stream of selenium and said surface while the deposition is carried out to inhibit the formation of oxides of selenium, said envelope being formed by a gas selected from the group consisting of inert gases and reducing gases.
  • steps which comprise vaporizing selenium at substantially atmospheric pressure, forming the resulting vapors into a thin unadulterated stream of gas, moving a metal base transversely through said stream to deposit an adherent vselenium coating on at least one surface thereof, and surrounding said stream and said surface W'lth a gas selected from the group consisting of inert gases and reducing gases to prevent formation of oxides of selenium.

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Description

Aug. 26, 1947. c.'s. SMITH, JR 2,426,377
' SELENIUM RECTIFIER AND METHOD OF MAKING Filed Dec. 7, 1943 2 Sheets-Sheet 2 Patented Aug. 26, 1947 2,426,377 SELENIUM RECTIFIER AND METHOD MAKING Cleveland Scudder Smith, Jr., Indianapolis, Ind., assignor to Samuel Ruben, New Rochelle,
Application December 7, 1943, Serial No. 513,265
11 Claims.
This invention relates to metalrectiflers and photocells, and to methods and apparatus for depositing a relatively thin layer or layers of a metal such as selenium upon a base composed of a different metal or alloy. It has long been recognized that When the surfaces of certain metals or metallic compounds are placed in contact with each other such combination possesses photoelectric characteristics and is also capable of rectifying an alternating electric current. While numerous combinations of metals and metallic compounds have been proposed for use as rectifying and photoelectric elements, one of the most satisfactory combinations is a layer or lm oi selenium deposited upon an aluminum, bronze, copper or ferrous metal base and having a counter-electrode deposited upon or in Contact with its exposed surface. However, due to its inherent chemical characteristics selenium is difcult to control and of its several known forms which exist at room temperature only one form appears to possess photoelectric and rectifying properties. To be suitable for use in a photoelectric or rectifying element, selenium must be present substantially or entirely in .the form cf a thin gray metallic'lm upon a suitable base metal. If the conditions for depositing the selenium are not carefully controlled, a useless deposit of the amorphous or crystalline form of selenium may result.
Various methods for the deposition of a layer of selenium on a base metal for the manufacture of rectiers and photocells have been proposed. In general, such processes involve the application of selenium, either in paste or powder form, to a previously prepared base plate while the latter is maintained at an elevated temperature. Another suitably heated metal plate is then brought in contact with the paste, and the assembly is subjected to a hot pressing operation to form a structure having an inner layer of metallic selenium. This method possesses several inherent disadvantages which render it impractical for commercial use. For instance, a layer cf selenium cannot easily be formed which has controlled variation in chemical or electrical characteristics throughout the body of the selenium, furthermore, several successive layers cannot readily be built up to form a homogeneous larger layer. In addition, such known process is not only costly in time required for carrying out the numerous steps, but it is impractical for thecommercial manufacture'of large plate rectiflers oecause of unavoidable variations in plate thickness, the random orientation of the resulting crystalline deposit, and the erratic and poor rectifying characteristics of such surface. t
Another process has been proposed in which the plates to be coated with selenium are passed the discharge orices of one or more selenium boilers or are mounted at xed distances from stationary selenium boilers, the plates and boiler or boilers being disposed in an evacuated chamber maintained at a pressure of the order of 1 micron of mercury or less. Such, process is necessarily a batch process and is not adapted to the rapid and continuous production of photocell and rectifier elements. Also, because of the long pumping time required to obtain the desired vacuum, and because of practical limitations on the size of the vacuum system, such process is highly uneconomical for the manufacture of large size elements or for the deposition of more than one layer of selenium both in first cost, operating cost and maintenance cost.
The present invention overcomes the numerous disadvantages inherent in prior processes and provides a method and apparatus for the economical and commercial production of selenium photocell and rectier elements.
Accordingly, among the objects of this invention are: to provide an improved method in which selenium is deposited on a base plate under ordinary atmospheric conditions in the form of as many different layers of metallic selenium as may be desired; to provide a method in which the selenium deposition is uniform and the thickness of such deposit may be accurately controlled to any desired value; to provide a method which is adapted to the automatic, continuous and elllcient production of selenium photocell and rectifier elements; to provide apparatus of relatively simple design which is adapted to carry out the method of the invention.
The above and other objects, advantages and novel features of the invention will become apparent from the following description and accompanying drawings, in which:
Fig, 1 shows an elevational view, in cross-section, of one form of an apparatus embodying the principles of this invention;
Fig. 2 is an enlarged sectional view taken from the left along the line 2-2 of Fig. 1;
Fig. 3 is an elevational View, partly in crosssection, of a modification of the apparatus of the invention,
Fig. 4 is an enlarged sectional view of one of the several selenium vaporizing boilers or units illustrated generally in Fig. 3;
Figs. 5 and 6 are elevational views of a further modification of the selenium vaporizing boilers or units embodying the principles of this invention;
Fig. '7 is an elevational view, partly in section of an apparatus adapted to coat a film or thin layer of selenium simultaneously on both sides of a metal plate;
Fig, 8 illustrates a method 0f applying a metal counter-electrode onto a metallic plate; and
Figs. 9 and 10 illustrate partially completed rectifier blanks.
In general, the improved method of this invention is carried out by vaporizing selenium in a suitable boiler above and substantially at atmospheric pressure and impinging the resulting vapor against the surface of a suitable metal plate maintained either at or above room temperature. The boiler is preferably provided, in one embodiment of the invention, with a slotted discharge orifice which has a length greater than or substantially equal to the width of the plate to be coated. The metal plate to be coated is maintained at apreselected distance from the orifice of the boiler and when such plate is moved back and forth through the stream of selenium vapor issuing from such orifice, at a preselected rate and in a direction substantially transversely of the longitudinal direction of the slot orifice, an extremely smooth and uniform illm or layer of gray metallic selenium of desirable rectifier or photocell quality is deposited on the metal plate. By making several passes back and forth through the stream of vapors issuing from the oriiice, any desired thickness of selenium may be built up. If desired, several boilers may be disposed in tandem relation, so that the metallic plate may pass successively through several streams of selenium and thereby quickly build-up a plurality of layers of selenium. In such an arrangement the boilers may be operated to discharge the same or different concentrations of vapors, and different impurities may be introduced into the several boilers to build up selenium of desirable composition for low forward resistance and high reverse resistance,
Referring to the drawings, Figs. 1 and 2 illustrate an embodiment of the invention wherein a selenium 'boiler B comprising a cylindrical casing I2 is provided with an upper threaded portion I4 adapted to frlctionally engage a threaded portion I6 of a cap I8. A slotted orifice 20 isv provided in cap I8, and has substantially uniform cross-section throughout its length. The oriiice 20 has a length substantially equal to the inside diameter of the casing I2. A circular ilange 22 is welded as at 23, or otherwise secured, to the cap I8 to support the boiler and to position the upper surface of the cap I8 substantially ilush with the upper surface of a suitable supporting base board 24', which may be composed of asbestos or other non-inflammable material. Guides 26 are secured to the base board 24 along lines equidistant on either side of the boiler B. These guides 26 are adapted to support a slide 28 carrying the metal plates 30 to be coated with selenium. The metal plates 30 may be bolted at 32 or otherwise secured to the carriage 28, and cooperate with suitable grooves 34 in the guides 26. A knob or handle |28 is provided to slide the plates back and forth on the boiler. The distance between the top of the cap I8 and the surface of the metal plate to be coated with selenium, is maintained at a Value such that when selenium vapor streams at the desired rate through the slotted orice the lower surface of the metallic plate is uniformly coated. A pair of gas burners 36 or other heating agents may be used to vaporize the selenium, and in order to prevent condensation of selenium vapor in the upper part of the bolier B, the heat is preferably applied to the upper regions of the boiler.
The method of carrying out the invention to obtain a coating of selenium upon a metal plate is as follows: Boiler casing I2 is unscrewed from cap I8, and about 10 grams or more of selenium is deposited in the boiler; the casing is then screwed back into position in the cap I8, and suitably heated as by one or more gas burners to a temperature suflicient to cause a stream of selenium vapor to issue through the orifice 20. Heat is applied to the upper portion of the boiler to avoid condensation of selenium therein and is conducted downward by the boiler Walls to vaporize the selenium charge. When selenium vapor is issuing at the desired rate from the orifice, the slide or carriage 28, carrying the metal plates to be coated, is inserted in the guides and a number of passes are made back and forth through the stream of selenium vapor thereby forcing a thin adherent coating of selenium upon the surface of the plates.
It has been found that during each deposition of selenium thin iilms are formed on the previous surface and on the new selenium surface, which iilms are composed of a mixture of selenium oxides, water and condensed particles of' selenium in forms unsuitable for rectifiers. These lms may cause the selenium to peel or crack, and they may produce high forward resistance in the completed rectifier.
Usually the interspersed iilms are so thin as to cause no adverse effects on the completed rectifier. The iilms can be completely eliminated by conducting the deposition of selenium in an atmosphere of inert gas such as argon, a relatively inert gas such as nitrogen, or carbon dioxide, or a reducing gas such as household cooking gas. The surrounding gas may be at any desired temperature, and should be above the boiling temperature of selenium if it is desired to avoid any condensation of selenium before the selenium vapor reaches the receiving plate.
The ratio of length to width of the orifice is somewhat critical to the deposition of the desired layer of selenium. For example, an orifice width of about 0.012 inch has been found to yield good results. A smaller width gives a greater proportion of selenium oxide to selenium. Slight variations in the width of the orifice slit are to be avoided because such variations cause striations to appear in the deposited selenium. A greater orifice width makes it diiiicult to build up sufficient pressure in the boiler to permit uniform vapor flow along the entire length of the orice slit, and also causes a greater quantity of selenium vapor to emerge than is necessary or desirable. Hence, care in construction and choice of materials may dictate the use of smaller orifice widths.
The distance of the plate from the discharge orifice must be carefully selected to give the most desirable results. In general, the closer the plate is brought to the orifice, the more satisfactory is' the deposition of selenium. If the operation is carried out under conventional atmospheric conditions, some of the selenium oxidizes and some of the selenium condenses to ne red particles. The greater the plate distance, the greater is the ratio of oxidized and condensed selenium to selenium still in vapor form. Too large a proportion of selenium oxide and selenium condensed to the red particle form causes thc selenium to peel and crack from the base plate during later heat treatment and may also lead to high resistance in the forward direction.
Other factors which influence the characteristics of the deposited selenium are: speed of the plate past the boiler orifice, rate of selenium iiow and number of passes made by the plate past the orifice. All of the above factors must be correlated to give the most desirable type of selenium deposition.
The temperature of the plate or plates upon which selenium is to be deposited has not been found to be critical, but plates maintained at a temperature of between about 60 to 100 C. are satisfactory and yield a smooth black deposit of selenium, which is desirable in the manufacture of rectifier elements.
Figure 3 illustrates a modification in which a long or continuous band of metal 31 is led over a series of selenium boilers B', which may be heated in any manner, as with electric resistance heating coils 39. The boilers may all be identical in construction or may differvas to width oi' orifice or other factors to superimposed layers of different thickness or other characteristics. After coating, the strip may be cut into rectifier elements of the desired dimensions.
Figure 4 shows a boiler modification wherein a gaseous atmosphere is introduced by a conduit 38 into a boiler B2, the upper portion of which is heated by a high frequency inductance coil 40. The heat travels downward to vaporize the selenium but the upper part of the boiler is kept hottest to prevent condensation. The gaseous atmosphere entering through conduit 38 may comprise an inert gas such as argon, a relatively inert gas such as nitrogen or carbon dioxide, or a reducing gas. The boiler may be alternatively heated by gas, by radiant heat from an electrical heater, by conducted heat from an electric heater, by electromagnetic induction, or by other convenient means.
Figure 5 illustrates a two compartment boiler, wherein compartment 44 is adapted to receive so. lidified selenium or melted selenium at low temperature and compartment 46 is adapted to vaporize molten selenium flowing from compartment 44. A valve 48 is disposed in the base of the 'boiler to drain oiT the selenium or the accumulation of excessive amounts of impurities.
In the embodiment shown in Figure 6, molten heated selenium may be introduced into a boiler 50 from a vessel 5l, through a needle valve 52. Suiiicient heat is applied to 50 to cause the selenium to vaporize and flow through a slotted oriiice 54. The amount of selenium vaporized in this type of boiler can be accurately controlled by the setting of the needle valve 52 and the pressure behind the selenium in the vessel 5l. In
slide 60. When the selenium vapor issues at the desired rate from each orifice the plate 56 is moved past the orifices in a manner similar to that described in connection with Figure 1.
Figure 8 shows a method for applying a metal counter-electrode on top of the selenium deposit 62 on a metal plate 6I. A mask 63 having apertures or windows 64 is placed against the selenium surface and a soft, low-melting-point metal 68 is sprayed onto the exposed areas of selenium by the metal spray gun 65 supplied with com pressed air by air hose 66 and containing molten metal heated by an electric heating element supplied by wires 10.
Figure 9 shows a plate after spraying, comprising backing metal plate 6| with selenium coating 62, and several sprayed metal electrodes 12 on the selenium surface. This plate may 'be cut into individual rectifier units.
Figure 10 shows an improved plate wherein the backing plate 19 is notched at intervals before the selenium. layer 18 is applied. After spraying of electrodes 'I2 the strip can be readily broken or cut at the notches.
The sequence of steps or operations in the production of rectifier elements according to this invention is substantially as follows:
(1) The metal strips to be coated with selenium are grooved by means of a kick press or automatic power press.
(2) They are then cleansed in any suitable manner, e. g. by immersion in a cleaning solution, a cleaning vapor, or wiping with a rag.
(3) Both sides of the metal strips are then sand-blasted, as for example, with Carborundum of a particle size of 240 to 280 mesh, the metal strips being driven between rollers at a linear speed of about 10 ft. per minute, one sand blast being directed against each side.
(4) The next step is the selenium deposition substantially as described above.
(5) The selenium plated strips are next heat treated at a temperature of about 210 C. for a period ranging from 15 minutes to one hour.
(6) A blocking layer is then applied to the plates, this consisting of a thin film of selenium oxide. This may be effected, for example, by exposing the plates to selenium oxide vapors in a closed chamber for a few seconds, or by any other suitable method.
('7) The plates are next sprayed with a metal or alloy having a melting point below the melting point of selenium.
(8) 'I'he final operation is the forming treatment, which consists in subjecting the plates to a suitable direct current, applied through contacts engaging the metal base plate and the sprayed metal layer in a direction in which the element tends to block current flow. This inverse: current is applied for a period of about 2 to hours, at a current density of, for example, about 300 milliamperes per sq. inch of active area.
While certain embodiments of the invention have been specifically illustrated and described, it is understood that the invention may be otherwise embodied and practiced without departing from the principles or scope of the invention as set forth in the appended claims.
What is claimed is:
1. The method of depositing a layer of selenium of substantially uniform thickness upon a metal surface which comprises the steps of vaporizing selenium at substantially atmospheric pressure, causing the resulting vapors to assume the shape of a thin ribbon, surrounding said stream with an envelope of gas selected from the group consisting of reducing gases and inert gases, and establishing relative transverse movement between said ribbon of gas and said surface to effect the condensation and deposition of a gray, metallic layer of selenium upon said surface. f
2. In the art of depositing a selenium layer of substantially uniform thickness upon at least one surface of a metal base, the improvement which comprises the steps of vaporizing selenium at substantially atmospheric pressure, forming the resulting vapors into a4 thin ribbon-like. stream in substantially unadulterated vaporized form, surropnding said stream with an envelope of gas selected from the group consisting of reducing gases and inert gases, moving said metal base so as to intersect said stream in a direction perpendicular to the widest dimension of said stream to form a thin, uniform and adherent coating of selenium in the gray, metallic state upon said surface, and repeating said movement back and forth through said stream to form a selenium layer of desired thickness.
3. Apparatus for depositing a relatively thin layer of selenium upon a metal base comprising, in combination, means for vaporizing and forming a thin ribbonlike stream of selenium vapor substantially at atmospheric pressure, means for supporting and bringing a base into contact with said stream of selenium vapor, and means for mixing a gas selected from the group consisting of vinert gases and reducing gases with said stream of selenium vapor.
4. Apparatus for depositing a relatively thin layer of selenium upon a metal base, said apparatus including a selenium vaporizer operable substantially at atmospheric pressure having a relatively narrow slot-like orifice disposed in the upper portion thereof, means for externally heating said vaporizer to generate a stream of selenium vapor and to avoid condensation of said vapor in said orifice.
5. A method of depositing a layer of selenium upon a metal base which comprises vaporizing selenium at substantially atmospheric pressure, causing the resulting vapors to assume the shape of a stream, surrounding said stream with an envelope of gas selected from the group consisting of reducing gases and inert gases, and directing said stream against a metal base to form a uniform adherent coating of gray metallic selenium thereon.
6. Apparatus for depositing a layer of selenium upon a metal base which comprises a selenium vaporizing furnace having a narrow slotlike discharge orifice, means forapplying heat to said furnace adjacent said discharge orifice to prevent condensation of selenium vapors in the regions near said orice, and a guide for supporting a metal base a preselected distance from said orifice.
7. Apparatus for depositing a layer of selenium upon a metal base which comprises a selenium vaporizing furnace having a narrow slotlike discharge orifice, a guide for movably supporting a metal base a preselected distance from said orifice, said guide being accessible for insertion of the base therein or removal of the base therefrom during the operation of said furnace,
and means for reciprocating said base to apply successive coatings of selenium thereto.
8. Apparatus for depositing a layer of selenium upon arnetal base which comprises a selenium vaporizing furnace having a narrow slotlike discharge orifice, and a pair of slotted guide members at opposite respective sides of said orifice to slidably receive and support a metal base a preselected distance from said orifice, whereby said base may be moved along the slotted portions of said guides during operation of the furnace.
9. Apparatus for depositing a layer of selenium upon a metal base which comprises a plurality of selenium vaporizing furnaces each having a narrow slot-like discharge orice, and a guide common to all of said furnaces for passing a metal base, in succession, a preselected distance from the respective discharge orifices whereby a coating of selenium is applied to the base by the gases discharged from each furnace.
10. In the art of depositing a selenium layer of substantially uniform thickness upon at least one surface of a metal base, the steps which comprise vaporizing selenium at substantially atmospheric pressure, forming the resulting vapors into a thin rbbonlike stream in substantially unadulterated vaporized form, directing said stream of gas against a metal base while eflecting relative transverse movement between said stream and said base to deposit a thin adherent coating of selenium on one surface of said base, and maintaining a protective gaseous envelope around said stream of selenium and said surface while the deposition is carried out to inhibit the formation of oxides of selenium, said envelope being formed by a gas selected from the group consisting of inert gases and reducing gases.
11. In the art of depositing a selenium layer of substantially uniform thickness upon a surface of a metal base, the steps which comprise vaporizing selenium at substantially atmospheric pressure, forming the resulting vapors into a thin unadulterated stream of gas, moving a metal base transversely through said stream to deposit an adherent vselenium coating on at least one surface thereof, and surrounding said stream and said surface W'lth a gas selected from the group consisting of inert gases and reducing gases to prevent formation of oxides of selenium.
C. SCUDDER SMITH.
REFERENCES CITED The following references are of record in the file of this patent:
UNITED STATES PATENTS France Nov. 10, 1936
US513265A 1943-12-07 1943-12-07 Selenium rectifier and method of making Expired - Lifetime US2426377A (en)

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US2476042A (en) * 1946-12-26 1949-07-12 Gen Electric Selenium rectifier and process of fabrication
US2503571A (en) * 1947-05-02 1950-04-11 Bell Telephone Labor Inc Apparatus for coating surfaces by thermal vaporization at atmospheric pressure
US2562120A (en) * 1948-08-26 1951-07-24 Bell Telephone Labor Inc Magnetic field strength meter
US2635579A (en) * 1949-12-01 1953-04-21 Nat Res Corp Coating by evaporating metal under vacuum
US2702760A (en) * 1951-04-25 1955-02-22 Western Electric Co Method of applying metallic stripes to a web of paper
US2704992A (en) * 1951-12-28 1955-03-29 Erie Resistor Corp Gas plating apparatus
US2753278A (en) * 1951-04-14 1956-07-03 Haloid Co Method for the production of a xerographic plate
US2767682A (en) * 1951-03-22 1956-10-23 Syntron Co Vaporizing apparatus for producing selenium rectifiers
US2789064A (en) * 1953-03-02 1957-04-16 Schladitz Hermann Process and apparatus for the metallisation of continuously travelling organic and inorganic foils by thermal decomposition of metal compounds
US2804396A (en) * 1952-08-19 1957-08-27 Battelle Development Corp Process of preparing an X-ray sensitive member
US2910039A (en) * 1956-06-21 1959-10-27 Nat Res Corp Apparatus for coating metal onto metal by vaporizing the coating
DE976803C (en) * 1950-09-12 1964-05-21 Siemens Ag Apparatus for manufacturing dry rectifier plates
US3989862A (en) * 1970-10-13 1976-11-02 Jones & Laughlin Steel Corporation Method and apparatus for vapor-depositing coatings on substrates
US4482622A (en) * 1983-03-31 1984-11-13 Xerox Corporation Multistage deposition process
FR2562099A1 (en) * 1984-03-30 1985-10-04 Commissariat Energie Atomique EVAPORATION CELL OF A LIQUID COMPOUND SUITABLE FOR MOLECULAR JET EPITAXY
WO1996035822A1 (en) * 1995-05-10 1996-11-14 Centre De Recherches Metallurgiques - Centrum Voor Research In De Metallurgie Device and plant for coating a steel band
US6444043B1 (en) * 1999-03-29 2002-09-03 Antec Solar Gmbh Apparatus for depositing CdS and CdTe layers on substrates by means of a CSS process
TWI555864B (en) * 2007-09-11 2016-11-01 中心熱光電股份公司 Method and arrangement for providing chalcogens

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Publication number Priority date Publication date Assignee Title
US2476042A (en) * 1946-12-26 1949-07-12 Gen Electric Selenium rectifier and process of fabrication
US2503571A (en) * 1947-05-02 1950-04-11 Bell Telephone Labor Inc Apparatus for coating surfaces by thermal vaporization at atmospheric pressure
US2562120A (en) * 1948-08-26 1951-07-24 Bell Telephone Labor Inc Magnetic field strength meter
US2635579A (en) * 1949-12-01 1953-04-21 Nat Res Corp Coating by evaporating metal under vacuum
DE976803C (en) * 1950-09-12 1964-05-21 Siemens Ag Apparatus for manufacturing dry rectifier plates
US2767682A (en) * 1951-03-22 1956-10-23 Syntron Co Vaporizing apparatus for producing selenium rectifiers
US2753278A (en) * 1951-04-14 1956-07-03 Haloid Co Method for the production of a xerographic plate
US2702760A (en) * 1951-04-25 1955-02-22 Western Electric Co Method of applying metallic stripes to a web of paper
US2704992A (en) * 1951-12-28 1955-03-29 Erie Resistor Corp Gas plating apparatus
US2804396A (en) * 1952-08-19 1957-08-27 Battelle Development Corp Process of preparing an X-ray sensitive member
US2789064A (en) * 1953-03-02 1957-04-16 Schladitz Hermann Process and apparatus for the metallisation of continuously travelling organic and inorganic foils by thermal decomposition of metal compounds
US2910039A (en) * 1956-06-21 1959-10-27 Nat Res Corp Apparatus for coating metal onto metal by vaporizing the coating
US3989862A (en) * 1970-10-13 1976-11-02 Jones & Laughlin Steel Corporation Method and apparatus for vapor-depositing coatings on substrates
US4482622A (en) * 1983-03-31 1984-11-13 Xerox Corporation Multistage deposition process
FR2562099A1 (en) * 1984-03-30 1985-10-04 Commissariat Energie Atomique EVAPORATION CELL OF A LIQUID COMPOUND SUITABLE FOR MOLECULAR JET EPITAXY
US4606296A (en) * 1984-03-30 1986-08-19 Commissariat A L'energie Atomique Evaporation cell for a liquid compound suitable for epitaxy by molecular jets
WO1996035822A1 (en) * 1995-05-10 1996-11-14 Centre De Recherches Metallurgiques - Centrum Voor Research In De Metallurgie Device and plant for coating a steel band
US6444043B1 (en) * 1999-03-29 2002-09-03 Antec Solar Gmbh Apparatus for depositing CdS and CdTe layers on substrates by means of a CSS process
TWI555864B (en) * 2007-09-11 2016-11-01 中心熱光電股份公司 Method and arrangement for providing chalcogens

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