US3571646A - Photoconductive target with n-type layer of cadmium selenide including cadmium chloride and cuprous chloride - Google Patents

Photoconductive target with n-type layer of cadmium selenide including cadmium chloride and cuprous chloride Download PDF

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Publication number
US3571646A
US3571646A US744743A US74474368A US3571646A US 3571646 A US3571646 A US 3571646A US 744743 A US744743 A US 744743A US 74474368 A US74474368 A US 74474368A US 3571646 A US3571646 A US 3571646A
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United States
Prior art keywords
layer
target
photoconductive
cadmium
chloride
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Expired - Lifetime
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US744743A
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English (en)
Inventor
Yuji Kiuchi
Kazuo Shimizu
Okio Yoshida
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Toshiba Corp
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Tokyo Shibaura Electric Co Ltd
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Publication of US3571646A publication Critical patent/US3571646A/en
Priority to US34348973 priority Critical patent/USRE28156E/en
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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

Definitions

  • This photoconductive target comprises a photoconductive member consisting of two layers: a first layer 0.5 micron minimum thick formed on a transparent electrode and a second layer 0.6 micron maximum thick superposed on the first layer so as to be disposed on the side electron gun.
  • the first layer is solely or mainly made of cadmium selenide, and the second layer is formed from a high resistance semiconductor material.
  • the present invention relates to a photoconductive target, more particularly to the high sensitivity and high resistance photoconductive target of a photoelectric amplifier or photoconductive image pickup tube (having the same construction as the one commercially known as Vidicon, Plumbicon, etc.) used in the television and other fields.
  • the conventional photoconductive target of a photoconductive image pickup tube is prepared by depositing a photoconductive layer on a transparent faceplate disposed at one end of a vacuum vessel and constituting a light input plane, with a transparent signal electrode inserted therebetween. While an image pickup tube provided with, for example, such a photoconductive target is in operation, the signal electrode is impressed with a positive voltage (for example, 30 volts), and the surface of the photoconductive layer is scanned by low velocity electron beams emitted from an electron gun similarly enclosed in the vacuum vessel in an op posite relation to said target.
  • a positive voltage for example, 30 volts
  • the electric resistance of the photoconductive layer varies with the intensity of light entering the image pickup tube from the outside thorough the faceplate, so that when scanned by the electron beam, a signal current is produced through a load resistance connected to the transparent electrode in proportion to the intensity of the incident light.
  • the photoconductive layer consists of a porous P-type material such as antimony trisulfide, lead monoxide, etc.
  • antimony trisulfide for example, to prepare the target from three layers of the sulfide, namely, a so-called continuous solid layera so-called porous layera continuous solid layer arranged in the order mentioned in the direction of the thickness of the photoconductive layer thus formed.
  • porous layer means a loose aggregate of relatively large particles of the photoconductive material vapor deposited in low vacuum, for example torr
  • continuous solid layer means a compact or vitreous layer of minutely fine particles of said material vapor deposited in high vacuum, for example 10 torr. lt may be generalized that where the same material is used, a porous layer thereof has a relatively high apparent resistance to the introduced electrons, whereas a continuous solid layer thereof has a relatively low apparent resistance thereto.
  • the quality of an image regenerated by an image pickup tube using such material is determined by a combination of resistivity measured in the direction of the thickness of the photoconductive layer and resistivity measured in a direction perpendicular thereto, namely, a direction parallel with the surface of said layer.
  • the inventors previously developed a photoconductive target using cadmium selenide as a photoconductive layer, and disclosed that an image pickup tube comprising this target had as high a photosensitivity as more than ten times that of an image pickup tube consisting of the conventional photoconductive target.
  • This photoconducn've target was distinct from the one in common use not only in respect of the use of a different material as a photoconductive layer, but also in the fact that cadmium selenide used as said layer possessed an N-type electronic conductivity.
  • the operational difference between such N-type photoconductive target and the previously known P-type target lies in the fact that in case of N-type conductivity, scanning electron beams can be freely introduced into a photoconductive layer to reach the signal electrode.
  • the high photosensitivity of the N-type target originates with the fact that photoexcited holes in the layer are immediately caught in the recombination centers within the layer and that a secondary photocurrent can continue to flow due to the influx of electron beams until the captured hole is recombined with a free electron.
  • the target comprising a cadmium selenide photoconductive layer still had the drawbacks that it was impossible to obtain a signal current, unless an appreciably high target voltage was applied and that there was a limit to the latitude in which the target could be operated.
  • the photoconductive target of the present invention consists of a first photoconductive layer solely or mainly composed of cadmium selenide formed on a transparent electrode to a thickness of 0.5 micron minimum and a second layer made of a high resistance semiconductor material superposed on the first layer to a thickness of 0.6 micron maximum so as to broaden the potential gradient in that part of the second layer which faces the first layer, and ease the electron influx from the second layer. Accordingly, the present photoconductive target produces a signal current at a low target voltage and is operable over a broad range of voltage.
  • H6. 1 is a schematic sectional view of an image pickup tube fitted with the photoconductive target according to the present invention
  • FIG. 2 is a schematic sectional view of an embodiment of the photoconductive target according to the invention.
  • H6. 3 is a curve diagram offered by way of comparing the prior photoconductive target only provided with a photoconductive layer mainly consisting of cadmium selenide and the photoconductive target according to the present invention provided with a photoconductive layer prepared in the manner shown in F'lG. 2, regarding the capacity of generating a signal current at a given target voltage, with the target illumination as a parameter, the currents and voltages of the present invention being the dashed lines.
  • the tube 10 as illustrated comprises a vacuum vessel 11 containing an electron gun section l2 and a photoconductive target assembly 13.
  • the electron gun assembly 12 comprises a heater 14, a cathode l5 surrounding the heater, and a control grid electrode 16 and an accelerating electrode 17 both disposed coaxially with the cathode 15.
  • An electrode 18 is mounted coaxially with said accelerating electrode 17, and a mesh electrode 19 is disposed so as to face said cathode at one end of the electrode 18 opposite to the accelerating electrode 17.
  • the photoconductive target section l3 comprises a transparent glass substrate 20, a transparent conductive layer 21 deposited on said substrate 20, and a photoconductive target 22 according to the invention, said target 22 being deposited on the conductive layer 2R to face the mesh electrode 19.
  • the photoconductive target of the present invention consists of a first layer 23 mainly composed of cadmium selenide formed on a transparent electrode 21 and a second layer 24 made of high resistance semiconductive material such as antimony trisulfide superposed on the first layer 23.
  • the arrow 0 denotes the direction from which light is projected and the arrow )8 shows the direction in which electron beams are introduced.
  • a transparent electrode 21 on a transparent substrate is vapor deposited in as high vacuum as l or 2X10 mm. Hg a layer of cadmium selenide about 1 micron thick. Prior to vapor deposition, there are added in advance to cadmium selenide, for example, 20 percent by weight of cadmium chloride and 0.05 percent by weight of cuprous chloride. The layer thus laminated by vapor deposition is further sintered, for example, by heating minutes at a temperature of 600 C. in a nitrogen atmosphere.
  • the mass is then subjected to heat treatment in a selenium atmosphere, for example, 30 minutes at a temperature of 500 C., to obtain a high resistivity photoconductive layer.
  • This layer is named a first layer 23 for convenience.
  • On the first layer 23 is vapor deposited in the aforesaid high vacuum of 10 mm.
  • Hg a layer of antimony trisulfide 24 having a thickness of 0.4 micron to form the photoconductive target of the present invention.
  • Addition of cuprous chloride in this process is intended to elevate the photoconductivity of the layer obtained.
  • inclusion of cadmium chloride in heat treatment after vapor deposition aims at the acceleration of growth' of cadmium selenide crystals.
  • the cadmium selenide component may consist of a solid solution or mixture containing a proper amount of cadmium sulfide (for example, weight ratio of cadmium sulfide to cadmium selenide lz2).
  • the added impurities may include in addition to copper one or more of silver, gold, thallium, indium, gallium, aluminum, halogens, tellurium, antimony, bismuth, lead, tin, alkali metals, and alkali earth metals.
  • FIG. 3 compares the present and prior targets with the signal current value (logarithmic scale) represented by the ordinate and the target voltage value (logarithmic scale) denoted by the abscissa, using the target illuminations (0.8 lux, 0.3 lux and nonillumination) as a parameter.
  • the solid curves of FIG. 3 indicate the properties of the prior target and the dashed curves denote those of the present target.
  • the present target uses a far lower voltage than the prior one in obtaining the same signal current. This is particularly prominent where there is only required a minute signal current. Moreover, the application of such a low target voltage does not affect the dark current value.
  • the photoconductive target according to the invention permits the target voltage to be chosen over a broader range than in the prior art device. For example, based on 0.8 lux illumination, the prior art ranges in target voltage between about 40 volts and about 25 volts, whereas the present invention ranges from about 45 volts to about 8 volts.
  • the present invention has such good effect as may be understandable from FIG. 3, it has a further advantage of reducing the afterimage.
  • a photoconductive image pickup tube containing the target of the present invention does not substantially present any afterimage when it undergoes the same operation.
  • this image pickup tube not only possesses the high sensitivity and panchromatism of the prior image pickup tube simply provided with cadmium selenide as a first layer, but also is more improved in various undesirable transitory properties associated with an image produced, thus offering a greater practical use.
  • the vital point of a composite .target according to the present invention is that its first layer consists of cadmium selenide which itself possesses a sufiicient photosensitivity. If the first layer has a poor photosensitivity, a composite target, though prepared pursuant to the invention, would ofier no ad vantage. It will be apparent that the method of manufacturing this first layer is not limited to the aforementioned embodiment. For instance, prior to heat treatment in a selenium atmosphere, it is possible to carry out the vapor deposition of the required layer in an inert atmosphere in as low vacuum as l0 mm. Hg instead of l0 mm. Hg as previously described.
  • the first layer be 0.5 micron minimum thick. The reason is that if the first layer is too thin, it will result in the reduction of photosensitivity and increase of a dark current and failure to produce high quality television pictures.
  • antimony trisulfide forms a continuous solid layer 0.4 micron thick. If the thickness increases over 0.6 micron, there will only be obtained an instantaneous regenerated picture at the time of pickup. Thus the regenerated picture at the time of pickup. Thus the regenerated image will disappear at once, rendering the image pickup tube quite useless. From the aforementioned operating principle of the first layer, this is considered due to the fact that such a thick second layer will obstruct the inflow of electron beams to stop the flow of a secondaryphotocurrent.
  • the second layer fonned on the first layer should not be so thick as appreciably to prevent the inflow of scanning electron beams.
  • the materials of the second layer may include in addition to the aforesaid antimony trisulfide other high resistance semiconductor materials such as antimony triselenide, arsenic trisulfide, arsenic triselenide,
  • the second layer consisted of any of the above-listed materials the same results were obtained as in the preceding embodiment. Since these materials have different specific resistances, the upper limit to the thickness of a layer prepared therefrom varies according to whether it is formed into a continuous solid layer or porous one. For instance, where arsenic trisulfide having a relatively high specific resistivity is used as a second layer, it is preferably formed into a continuous solid layer in consideration of the ease' of controlling the layer thickness in vapor deposition.
  • the second layer may of course consist of one or more layers, the total thickness thereof should not exceed 0.6 micron in any case.
  • Thespectroscopic photosensitivity of the first layer mainly consisting of cadmium selenide prevails all over the visible ray region from the blue to the red.
  • the layer has a great absorption coefficient over the entire region of visible light beams. Accordingly the light which has been transmitted through the first layer is considerably reduced in the power of exciting the second layer.
  • the second layer used in the present invention is only prepared by vapor deposition, requiring no further special treatment.
  • the above-listed second layer materials include P-type materials, it may be imagined that there will be formed a backbiased PN junction between the first layer (N-type layer) and the second layer (P-type layer).
  • the characteristics of the composite target according to the present invention are such that while the whole range of the operating voltage of the target rather shifts toward the low voltage side, the target displays substantially analogous current-voltage properties to those of a target only provided with a first layer. Therefore the composite target does not display a current saturated condition due to the presence of a PN junction as generally supposed. This fact proves that the photoelectric converting properties of the target according to the present invention are quite independent of the problem of special contact between the first and second layers.
  • the second layer is only intended to ease the inflow of electron beams by locally providing a sharp potential gradient on the scanned surface of the first layer.
  • the second layer acts to reduce a large number of levels present on the surface of the first layer, which behave traps to charge carriers. This effect comes from the fact that the transitory properties of the target, for example, the undesirable afterimage originates with the trapping of a charge carrier by these surface levels.
  • a photoconductive target comprising a first N-type layer made of cadmium selenide containing cadmium chloride and cuprous chloride formed on a substrate of transparent electrically conductive material to a thickness of about 0.5 micron minimum and a second P-type layer made of at least one high resistance semiconductor material selected from the group consisting of zinc sulfide and zinc selenide to a thickness of about 0.6 micron maximum.

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  • Physics & Mathematics (AREA)
  • Electromagnetism (AREA)
  • Light Receiving Elements (AREA)
  • Formation Of Various Coating Films On Cathode Ray Tubes And Lamps (AREA)
  • Image-Pickup Tubes, Image-Amplification Tubes, And Storage Tubes (AREA)
US744743A 1967-07-17 1968-07-15 Photoconductive target with n-type layer of cadmium selenide including cadmium chloride and cuprous chloride Expired - Lifetime US3571646A (en)

Priority Applications (1)

Application Number Priority Date Filing Date Title
US34348973 USRE28156E (en) 1967-07-17 1973-03-21 Photoconductive target with n-type layer of cadmium selenide including cadmium chloride and cuprous chloride

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Application Number Priority Date Filing Date Title
JP4564067 1967-07-17

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US3571646A true US3571646A (en) 1971-03-23

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US744743A Expired - Lifetime US3571646A (en) 1967-07-17 1968-07-15 Photoconductive target with n-type layer of cadmium selenide including cadmium chloride and cuprous chloride
US34348973 Expired USRE28156E (en) 1967-07-17 1973-03-21 Photoconductive target with n-type layer of cadmium selenide including cadmium chloride and cuprous chloride

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US (2) US3571646A (en, 2012)
DE (1) DE1764682A1 (en, 2012)
FR (1) FR1582561A (en, 2012)
GB (1) GB1198570A (en, 2012)
NL (1) NL157745B (en, 2012)

Cited By (5)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US3783324A (en) * 1972-09-11 1974-01-01 Rca Corp Photosensitive charge storage electrode having a selectively conducting protective layer of matching valence band on its surface
US3870921A (en) * 1973-09-24 1975-03-11 Xerox Corp Image intensifier tube with improved photoemitter surface
US3984722A (en) * 1973-05-21 1976-10-05 Hitachi, Ltd. Photoconductive target of an image pickup tube and method for manufacturing the same
US3985918A (en) * 1972-10-12 1976-10-12 Matsushita Electric Industrial Co., Ltd. Method for manufacturing a target for an image pickup tube
EP0345086A1 (en) * 1988-06-03 1989-12-06 Varian Associates, Inc. Single crystal output screen

Families Citing this family (5)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
JPS4830193B1 (en, 2012) * 1970-08-17 1973-09-18
BE791077A (fr) * 1971-11-09 1973-03-01 Matsushita Electric Ind Co Ltd Element transducteur photoelectrique
US3872344A (en) * 1972-09-15 1975-03-18 Tokyo Shibaura Electric Co Image pickup tube
JPS60140636A (ja) 1983-12-28 1985-07-25 Toshiba Corp 撮像管の光導電タ−ゲツトおよびその製造方法
RU2145454C1 (ru) * 1998-04-14 2000-02-10 Государственное малое межотраслевое предприятие "Диаконт" Мишень видикона

Citations (5)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US2997630A (en) * 1956-08-30 1961-08-22 Itt Holding switch
US3315108A (en) * 1963-12-17 1967-04-18 Rca Corp High lag, high sensitivity target having solid antimony oxysulphide and porous antimony trisulphide layers
US3346755A (en) * 1966-03-31 1967-10-10 Rca Corp Dark current reduction in photoconductive target by barrier junction between opposite conductivity type materials
GB1086603A (en) * 1966-03-08 1967-10-11 Gen Precision Inc Photoconductive thin film cell responding to a broad spectral range of light input
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

Patent Citations (5)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US2997630A (en) * 1956-08-30 1961-08-22 Itt Holding switch
US3315108A (en) * 1963-12-17 1967-04-18 Rca Corp High lag, high sensitivity target having solid antimony oxysulphide and porous antimony trisulphide layers
GB1086603A (en) * 1966-03-08 1967-10-11 Gen Precision Inc Photoconductive thin film cell responding to a broad spectral range of light input
US3346755A (en) * 1966-03-31 1967-10-10 Rca Corp Dark current reduction in photoconductive target by barrier junction between opposite conductivity type materials
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

Cited By (6)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US3783324A (en) * 1972-09-11 1974-01-01 Rca Corp Photosensitive charge storage electrode having a selectively conducting protective layer of matching valence band on its surface
US3985918A (en) * 1972-10-12 1976-10-12 Matsushita Electric Industrial Co., Ltd. Method for manufacturing a target for an image pickup tube
US3984722A (en) * 1973-05-21 1976-10-05 Hitachi, Ltd. Photoconductive target of an image pickup tube and method for manufacturing the same
US3870921A (en) * 1973-09-24 1975-03-11 Xerox Corp Image intensifier tube with improved photoemitter surface
EP0345086A1 (en) * 1988-06-03 1989-12-06 Varian Associates, Inc. Single crystal output screen
US4929867A (en) * 1988-06-03 1990-05-29 Varian Associates, Inc. Two stage light converting vacuum tube

Also Published As

Publication number Publication date
FR1582561A (en, 2012) 1969-10-03
NL6810017A (en, 2012) 1969-01-21
USRE28156E (en) 1974-09-10
GB1198570A (en) 1970-07-15
DE1764682A1 (de) 1971-03-04
NL157745B (nl) 1978-08-15

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