US3585430A - Gallium arsenide phosphide camera tube target having a semi-insulating layer on the scanned surface - Google Patents

Gallium arsenide phosphide camera tube target having a semi-insulating layer on the scanned surface Download PDF

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US3585430A
US3585430A US754850A US3585430DA US3585430A US 3585430 A US3585430 A US 3585430A US 754850 A US754850 A US 754850A US 3585430D A US3585430D A US 3585430DA US 3585430 A US3585430 A US 3585430A
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target
region
semi
wafer
type
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US754850A
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Ralph E Simon
Robert L Rodgers
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RCA Corp
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RCA Corp
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    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01J—ELECTRIC DISCHARGE TUBES OR DISCHARGE LAMPS
    • H01J29/00—Details of cathode-ray tubes or of electron-beam tubes of the types covered by group H01J31/00
    • H01J29/02—Electrodes; Screens; Mounting, supporting, spacing or insulating thereof
    • H01J29/10—Screens on or from which an image or pattern is formed, picked up, converted or stored
    • H01J29/36—Photoelectric screens; Charge-storage screens
    • H01J29/39—Charge-storage screens
    • H01J29/45—Charge-storage screens exhibiting internal electric effects caused by electromagnetic radiation, e.g. photoconductive screen, photodielectric screen, photovoltaic screen
    • H01J29/451—Charge-storage screens exhibiting internal electric effects caused by electromagnetic radiation, e.g. photoconductive screen, photodielectric screen, photovoltaic screen with photosensitive junctions
    • H01J29/456—Charge-storage screens exhibiting internal electric effects caused by electromagnetic radiation, e.g. photoconductive screen, photodielectric screen, photovoltaic screen with photosensitive junctions exhibiting no discontinuities, e.g. consisting of uniform layers
    • H—ELECTRICITY
    • H10—SEMICONDUCTOR DEVICES; ELECTRIC SOLID-STATE DEVICES NOT OTHERWISE PROVIDED FOR
    • H10D—INORGANIC ELECTRIC SEMICONDUCTOR DEVICES
    • H10D99/00—Subject matter not provided for in other groups of this subclass

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  • the present invention relates to targets for camera tubes andparticularly concerns a target having a semi-insulating layer on its scanned side and an electrical barrier region.
  • One type ofcamera tube which is at present widely used and readily available commercially is the vidicon. Its basic structure is well known to those skilled in the art and usually comprises an elongated glass envelope having a transparent faceplate at one end. Inside the tube envelope is an electron gun device for producing a flne'electron beam. With the aid of magnetic or electrostatic deflection means, such as magnetic coils disposed just outside the envelope, this beam can be made to scan a target area on the inside faceplate surface.
  • the inside faceplate surface is coated first with a transparent, electrically conductive material, such as tin oxide, to form a signal plate.
  • a transparent, electrically conductive material such as tin oxide
  • the signal plate is then coated with a photoconductive substance to form a target.
  • the electron beam When the vidicon is in operation, the electron beam continually scans a well-defined area, or raster, of the target and tends to charge it uniformly to an equilibrium potential each time it scans the entire raster, or each frame time.
  • the signal plate is impressed with a voltage a few volts above equilibrium potential, and this results in a continual dark current of elec trons from the rastersurface of the higher voltage signal plate when the photoconductor is not exposed to light.
  • a light pattern incident on the photoconductor greatly increases current in the lighted areas. Areas on the raster which have lost charge through such current during the course ofa frame time are in the next scanning frame brought abruptly back to equilibrium potential by the beam.
  • the sudden change in voltage of those target areas that are returned to equilibrium potential results in a signal at the signal plate.
  • This signal is the video output of the tube.
  • the dark current of a vidicon target can be decreased by providing an electrical barrier between the scanned side of the target and the signal plate.
  • a barrier may be a Shottky barrier or a PN junction, for example.
  • the barrier in effect gives the target a higher dark resistance than it would have without the barrier.
  • barrier-type targets are relatively expensive.
  • the forming of PN junctions on the scanned side of the target usually involves a somewhat complex type of diffusion process or vapor phase growth, both of which are relatively slow processes requiring complex equipment.
  • Formation of a Shottky barrier target usually requires application of very precise masking techniques, and those masking techniques may impose a limitation on the resolution attainable by the target.
  • a barrier region target for a vidicon-type camera tube is provided with a thin semi-insulating layer on its scanned side.
  • the target comprises a target crystal wafer of photoconductive semiconducting material.
  • the wafer has a slightly N conductivity-type region in its bulk and a p conductivity-type region near and including at least a portion of one major surface of the wafer.
  • the semi-insulating layer acts to thermalize electrons impinging on it from the scanning means and to prevent those electrons from traveling through the wafer to the signal electrode as dark current.
  • FIG. 1 shows a sectional view ofa vidicon-type camera tube having therein a target according to a preferred embodiment of the invention
  • FIG. 2 shows a fragmentary sectional view of the charge storage target in the tube of FIG. 1.
  • a conventional vidicon-type camera tube 10 having an elongated envelope 12 with a transparent faceplate 14 at one end and electron beam forming and scanning means 16 disposed inside the envelope [2, is provided with a thin semiconducting target I8 attached to the inside surface of the faceplate l4. Scanning of the electron beam may also be effected by magnetic coils (not shown) situated outside the envelope l2.
  • the target 18 shown in FIG. 2 is photoconducting and comprises a single crystal wafer 19 having three regions 20, 22, 24 of different conductivity types and a semi-insulating coating 26 on the wafer 19.
  • the first region 20 of the wafer 19 is that nearest the faceplate l4 and is N type
  • the second region 22 is in the bulk ofthe wafer 19 and is N-type
  • the third region 24 is a very thin surface state region 24 in the wafer 19 surface which is opposite the N"-type region 20.
  • the surface state region 24 has a density of surface states such that this region 24 behaves like a P-type layer.
  • the semi-insulating material is the thin coating 26 on the P-region 24 surface of the wafer 19.
  • the voltages applied to its various elements may be on the order of those voltages used in vidicon-type tubes known to those skilled in the art.
  • the scanning means 16 which may include an electron gun device with electrostatic deflection, scans the semi-insulating material 26 with an electron beam whose electrons have various energies, the average energy of which is on the order ofa fraction of an electron volt.
  • the semi-insulating layer 26 ther malizes" these beam electrons by bringing them to energy states which are described by a Fermi energy function at the temperature of the target 18 and collects enough electrons to bring the semi-insulating layer 26 to equilibrium potential.
  • the N"-region 20 of the wafer 19 is a highly conductive accumulation region and is impressed with a potential a few volts positive with respect to equilibrium potential.
  • the equilibrium potential will remain on the semi-insulating layer 26 and on the portion of the P-region 24 near the wafer surface for some time because the very thin Pregion 24, where it joins the N-region 22, forms a depletion region which acts as a potential barrier to the passage of electrons through it in the direction of the N -region 20. This is due largely to the fact that, in the absence of light, the depletion region has a rather low carrier concentration and is highly resistive to electrons with energies near the Fermi level.
  • the wafer 19 may be of any semiconducting material which has a suitable band gap and satisfies other well-known requirements ofa vidicon-type target, such as resistivity and degree of transparency.
  • a single crystal comprised of a plurality of epitaxial layers of very high purity gallium arsenide phosphide (GaAs P whose composition has been regulated to make it responsive to visible light.
  • GaAs P gallium arsenide phosphide
  • a wafer 19 of GaAs P, where x 0.45, would be suitable.
  • Materials having a band gap of about 1.8 ev. are especially suitable for visible light television applications.
  • Fabrication of the wafer 19 may be accomplished by using well-known techniques such as liquid phase or vapor phase growth. In using methods such as vapor phase growth, a GaAs wafer on the order of 5 mil. thickness is used as a substrate for growth of the GaAs,,,P, wafer 19. It is preferred that the GaAs wafer be a single crystal. for in the epitaxial growth process the crystal structure of the substrate is continued in the growing crystal. However, it is not necessary that the substrate be a single crystal, as a target which is of several crystals, each continuous through the thickness of the wafer 19 would be acceptable, especially if the boundaries of the crystals are not resolvable. Thus, one could make a large area target out of several smaller area crystals.
  • the wafer 19 can be any one of a variety of flat shapes.
  • the reason for using a discoid is simply that it is more adaptable to vidicon tubes.
  • Another purpose of using a GaAs substrate is that, since the GaAs R wafer 19 after the growth process is very thin, it is desirable to have a supporting structure under it to prevent breakage.
  • the substrate be GaAs, for many substrate crystals having the right crystal structure can be used. For instance, a sapphire crystal could be used as a substrate.
  • the doping levels can be varied in such a way as to make the resulting wafer 19 a multilayered epitaxial structure.
  • the GaAs PBx Nearest the GaAs surface the GaAs PBx has surface states, for this occurs naturally when one forms a crystal of GaAs P, with a light N-type doping level in the bulk central portion. The fact of the existence of these surface states is well known to those skilled in the art.
  • the N-doping in the bulk central portion of the GaAs P should be light enough for the depletion region to extend from the P-region 24 throughout most of the N-region 22.
  • silicon dopant to a level on the order of donors/cm. in the bulk for a resistivity there which will give optimum characteristics for operation in a vidicon.
  • the N -region of the GaAs R wafer 19 is on the order of a fraction of a micron thick and is farthest from the GaAs substrate. This portion is made N by, for instance, either adding the dopant, which may be silicon, during the growth of the wafer 18 or by diffusion after growing the wafer 18. N type doping should be heavy enough to give a high conductivity to the N-region 20 so that it is suitable as a signal plate.
  • the thickness of the wafer 19 should be determined to keep the capacitive lag to a desirable level and yet to have enough thickness for the three regions 20, 22, 24 of conductivity to be defined in the wafer 19.
  • the thickness can be on the order of from 3 microns to 10 microns, although we prefer to use a thickness of about 5 microns.
  • the N,-region 20 of the GaAs P may be attached to the inside surface of the faceplate 14 such as by adhering the two surfaces with transparent epoxycement.
  • the attachment of the N*-surface 20 to the faceplate 14 surface lends sufficient support to the GaAs ,P, wafer 19 that the GaAs substrate may now be removed, such as by polishing or by preferential etching, thereby exposing the GaAs P, surface.
  • lt is because the gallium arsenide is removed in this step that it is advantageous to make the substrate just thick enough to lend the necessary support, so that it can be readily removed.
  • the semi-insulating layer 26 is deposited on the exposed P region 24 surface which remains after the GaAs substrate has been removed from the wafer 19.
  • the word semi-insulating is used to indicate a material having a resistivity on the order of 10" or 10 ohm-cm. Many materials naturally have a resistivity in this range and some other materials may be adjusted by proper doping to have such a resistivity. Several materials such as resistive glasses can be used to form this layer 26. We prefer to use antimony trisulfide which has a resistivity of about 10 ohm-cm, is easily obtainable and can be readily evaporated to a P-type GaAs P surface.
  • antimony trisulfide is commonly used as a photoconductor in vidicon tubes, its function in the present invention is not as a photoconductor, nor is it intended to function in a mechanical manner on the photoconducting wafer.
  • the function of the semi-insulating layer 26 is rather to decrease dark current by thermalizing beam electrons as they impinge on that layer 26 so that electrons from the beam will not directly travel through the N-region 22 of the wafer 19 to the signal electrode N"-region 20.
  • the average thermalized beam electron does not have sufficient energy to be injected from the P-region 24 into the N-region 22.
  • a barrier layer target 18 is formed using the natural surface states of the P-region 24 without the necessity of a diffusion, an array of islands or other complex structures on the scanned side of the target 18.
  • a target for a vidicon-type camera tube having an envelope at one end of which is a transparent faceplate and having means for directing an electron beam toward said target, said target comprising:
  • said semi-insulating layer having a resistivity on the order of from about 10 ohm-cm to about 10 ohm-cm and acting to thermalize electrons impinging on it from the electron beam to prevent those electrons from traveling through said wafer as dark current.
  • a target as claimed in claim 1 and wherein said wafer consists essentially of gallium arsenide phosphide semiconductor alloy having a donor density of about 10 donors per cubic centimeter.
  • a target as claimed in claim 1 and wherein said wafer consists essentially of gallium arsenide phosphide semiconductor alloy having a band gap between one and 3 electron volts.
  • a target as claimed in claim 1 and wherein said semi-insulating material is antimony trisulfide.
  • an epitaxial single crystal wafer of gallium arsenide phosphide semiconductor material having:
  • a first continuous region including at least a portion of said second face of said target and extending through a portion of the thickness of said wafer, said first region being heavily doped N*to be electrically conducting;
  • a second continuous region including at least a portion of said first face of said target, said second region being doped lightly N-type and exhibiting P-type surface state properties at said first face of said target;
  • said semi-insulating layer acting to thermalize electrons impinging on it when scanned by said electron beam and preventing said electrons from traveling through said second region to said first region as dark current.
  • a semiconductor vidicon-type camera tube target comprising a single crystal target electrode of N-conductivity-type gallium arsenide phosphide, said target electrode having at its scanned face a continuous P-conductivity-type surface state region and having on said scanned surface a thin layer of semiinsulating material with a resistivity of between about 10 ohm-cm and 10 ohm-cm which acts to thermalize electrons impinging on said face and to prevent those electrons from traveling through said target as dark current.
  • a target for a vidicon-type camera tube comprising:
  • a photoconductive single crystal wafer of gallium arsenide phosphide semiconductor material being lightly doped N-conductivity type in its bulk to a doping level of less than 10 donors/cm and being from about 3 microns to about 10 microns thick, said wafer having,
  • a layer of semi-insulating material on the P-conductivitytype region surface said layer having a thickness of less than about 2 microns and a resistivity on the order of from about 10 ohm-cm to about 10 ohm-cm.

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  • Physics & Mathematics (AREA)
  • Electromagnetism (AREA)
  • Image-Pickup Tubes, Image-Amplification Tubes, And Storage Tubes (AREA)
  • Light Receiving Elements (AREA)
  • Common Detailed Techniques For Electron Tubes Or Discharge Tubes (AREA)
  • Formation Of Various Coating Films On Cathode Ray Tubes And Lamps (AREA)
US754850A 1968-08-23 1968-08-23 Gallium arsenide phosphide camera tube target having a semi-insulating layer on the scanned surface Expired - Lifetime US3585430A (en)

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US75485068A 1968-08-23 1968-08-23

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US (1) US3585430A (enrdf_load_stackoverflow)
JP (1) JPS4741047B1 (enrdf_load_stackoverflow)
DE (1) DE1942897A1 (enrdf_load_stackoverflow)
FR (1) FR2016269A1 (enrdf_load_stackoverflow)
GB (1) GB1279276A (enrdf_load_stackoverflow)
NL (1) NL6912847A (enrdf_load_stackoverflow)

Cited By (2)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US3786294A (en) * 1971-02-22 1974-01-15 Gen Electric Protective coating for diode array targets
US3965385A (en) * 1974-01-28 1976-06-22 Raytheon Company Semiconductor heterojunction television imaging tube

Families Citing this family (1)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US4103203A (en) * 1974-09-09 1978-07-25 Rca Corporation Wafer mounting structure for pickup tube

Citations (4)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US3403278A (en) * 1967-02-07 1968-09-24 Bell Telephone Labor Inc Camera tube target including n-type semiconductor having higher concentration of deep donors than shallow donors
US3444412A (en) * 1963-03-12 1969-05-13 Edward Fokko De Haan Photo-responsive device having photo-sensitive pbo layer with portions of different conductivity types
US3458782A (en) * 1967-10-18 1969-07-29 Bell Telephone Labor Inc Electron beam charge storage device employing diode array and establishing an impurity gradient in order to reduce the surface recombination velocity in a region of electron-hole pair production
US3474285A (en) * 1968-03-27 1969-10-21 Bell Telephone Labor Inc Information storage devices

Patent Citations (4)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US3444412A (en) * 1963-03-12 1969-05-13 Edward Fokko De Haan Photo-responsive device having photo-sensitive pbo layer with portions of different conductivity types
US3403278A (en) * 1967-02-07 1968-09-24 Bell Telephone Labor Inc Camera tube target including n-type semiconductor having higher concentration of deep donors than shallow donors
US3458782A (en) * 1967-10-18 1969-07-29 Bell Telephone Labor Inc Electron beam charge storage device employing diode array and establishing an impurity gradient in order to reduce the surface recombination velocity in a region of electron-hole pair production
US3474285A (en) * 1968-03-27 1969-10-21 Bell Telephone Labor Inc Information storage devices

Non-Patent Citations (2)

* Cited by examiner, † Cited by third party
Title
ELECTRONICS March 4, 1968 - p. 109 Article Lighting Up In a Group by L. A. Murray, S. Caplan & R. Klein. (complete article pp. 104 110) *
SCIENTIFIC AMERICAN May 1967 p. 110 Article Light Emitting Semiconductors by Frederick F. Morehead, Jr. (complete article pp. 108 122) *

Cited By (2)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US3786294A (en) * 1971-02-22 1974-01-15 Gen Electric Protective coating for diode array targets
US3965385A (en) * 1974-01-28 1976-06-22 Raytheon Company Semiconductor heterojunction television imaging tube

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JPS4741047B1 (enrdf_load_stackoverflow) 1972-10-17
DE1942897A1 (de) 1970-02-26
GB1279276A (en) 1972-06-28
FR2016269A1 (enrdf_load_stackoverflow) 1970-05-08
NL6912847A (enrdf_load_stackoverflow) 1970-02-25

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