US3278782A - Electron emitter comprising photoconductive and low work function layers - Google Patents

Electron emitter comprising photoconductive and low work function layers Download PDF

Info

Publication number
US3278782A
US3278782A US219022A US21902262A US3278782A US 3278782 A US3278782 A US 3278782A US 219022 A US219022 A US 219022A US 21902262 A US21902262 A US 21902262A US 3278782 A US3278782 A US 3278782A
Authority
US
United States
Prior art keywords
layer
photoconductive
work function
low work
electrons
Prior art date
Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
Expired - Lifetime
Application number
US219022A
Other languages
English (en)
Inventor
Kanter Helmut
Current Assignee (The listed assignees may be inaccurate. Google has not performed a legal analysis and makes no representation or warranty as to the accuracy of the list.)
Westinghouse Electric Corp
Original Assignee
Westinghouse Electric Corp
Priority date (The priority date is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the date listed.)
Filing date
Publication date
Application filed by Westinghouse Electric Corp filed Critical Westinghouse Electric Corp
Priority to US219022A priority Critical patent/US3278782A/en
Priority to JP4373063A priority patent/JPS402972B1/ja
Application granted granted Critical
Publication of US3278782A publication Critical patent/US3278782A/en
Anticipated expiration legal-status Critical
Expired - Lifetime legal-status Critical Current

Links

Images

Classifications

    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01J—ELECTRIC DISCHARGE TUBES OR DISCHARGE LAMPS
    • H01J1/00—Details of electrodes, of magnetic control means, of screens, or of the mounting or spacing thereof, common to two or more basic types of discharge tubes or lamps
    • H01J1/02—Main electrodes
    • H01J1/34—Photo-emissive cathodes
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01J—ELECTRIC DISCHARGE TUBES OR DISCHARGE LAMPS
    • H01J2201/00—Electrodes common to discharge tubes
    • H01J2201/34—Photoemissive electrodes
    • H01J2201/342—Cathodes
    • H01J2201/3421—Composition of the emitting surface
    • H01J2201/3425—Metals, metal alloys

Definitions

  • the present invention relates to light sensitive electron emitting devices, and more particularly to electron emitting devices utilizing high gain photoconductors.
  • Photoconductors have a high sensitivity because of their, so-called, internal high gain. That is, if a photoconductor is placed between electrically conducting electrodes and an electric field is placed thereacross, an incident photon will cause a large number of majority carriers to flow between the electrodes. Except for the carriers produced by the incident photon, by far the largest number of carriers originate from the replenisher electrode.
  • the gain of the device is given by the ratio of minority carrier life time to the transit time of the majority carrier. Gains in the order of 1000 or more have been obtained. In this particular application the majority carriers are electrons, flowing towards a thin positive electrode.
  • the sensitivity and the gain of the photoconductive device in large part, depend upon the thickness and material of the positive electrode especially when emission into a vucuum is desired.
  • the present invention provides a photoconductive electron emissive device in which a layer of photoconductive material is sandwiched between a layer of light transparent electrically conductive material and a layer comprising a low work function material, so that, electrons, under the influence of an electric field, may be readily transmitted through the device into a vacuum to provide a source of electrons in response to light.
  • FIGURE 1 is a schematic diagram embodying the teachings of the present invention.
  • FIG. 2 is an energy versus distance diagram used in aid in the explanation of the operation of the present invention.
  • an electron discharge tube structure having an envelope T, which may be evacuated to form a vacuum v therein.
  • An anode electrode A having an external terminal a, is disposed at one end of the tube.
  • a grid electrode G having an external terminal g, is also disposed within the envelope T.
  • the photoconductive cathode is disposed at the other end of the tube envelope T to convert light energy into electrical energy.
  • a transparent electrically conducting layer M is evaporated adjacent the wall W of the envelope T.
  • the wall W may be glass and transmissive to light.
  • the layer M may for example comprise indium and be such a thickness to be transmissive to light and yet electrically conducting.
  • Deposited by evaporation onto the transparent metal layer M is a layer PC of photoconductive material, which for example may be cadium sulfide.
  • photoconductive layer PC may be of a thickness between 1 and microns.
  • an electrode L Onto the photoconductive layer PC is deposited an electrode L by, for example, evaporation.
  • the electrode L may comprise an alkali metal, such as potassium, or an earth alkali metal, such as barium.
  • the layer L should be of the order of Angstroms.
  • the layer L may comprise a metal layer that is oxidized at its surface to provide a low work function, such as barium oxidized to form barium oxide.
  • the layer L could be formed by alloying a metal layer with another material, for example, gold alloyed with barium.
  • Another method of providing the low work function layer L would be to deposit a monolayer of a low work function material on a metal surface, such as, a monolayer of cesium deposited on a layer of antimony.
  • a monolayer of cesium deposited on a layer of antimony there are, of course, other methods that could be used to provide the low work function layer L, such as disposing a mesh in a matrix pattern on the layer PC.
  • a source of direct potential V is connected with its positive terminal to the layer L and with its negative terminal connected to the transparent metal layer M.
  • an accelerating electric field is applied across the photoconductive layer PC.
  • the photoconductor With no light being supplied to the photoconductive layer PC the photoconductor is in its dark state, that is, only few electrons are emitted into the vacuum v corresponding to the dark current within the PC.
  • the Fermi energy level of the metal M is shown to be Efm.
  • the Fermi level of the layer L is substantially lower at a level Efl, with the Fermi level Efpc of the photoconductive layer PC being between that of the layer M and the layer L.
  • the vacuum barrier is substantially reduced to Efl to allow relatively low energy electrons from the conduction band of the photoconductive layer PC to penetrate the layer L and then be emitted into the vacuum v.
  • the photoconductor PC is illuminated by supplying photons through the transparent layer M to the photoconductive layer PC, electron-hole pairs will be created in the photoconductor PC, with electrons in the conduction band, at an energy above the forbidden region, flowing toward the positive electrode L and holes in the valence band of the photoconductor flowing toward the negative electrode M.
  • a current will exist across the photoconductor PC until the holes have diffused into the electrode M.
  • the electrons in the photoconductor will drift toward the low work function electrode L being accelerated in the conduction band by the electric field. Because the mean free path of low energy electrons in metals is quite large, up to several hundred angstroms, a portion of the electrons entering the layer L will be able to penetrate the film L and to escape from the surface into the vacuum v. Once electrons are in the vacuum v, they may be controlled by the operation of the grid electrode G and the anode electrode A in the usual manner. Furthermore, by using :a thin film L, with a low work function, a high transfer ratio would result, that, is, the number of electrons that escape from the layer L is a high percentage of those being introduced into the layer L from the photoconductor PC.
  • An electron emissive device including, a first layer comprising a light transparent electrically conducting material, a second layer comprising a photoconductive material disposed adjacent said first layer, a third layer disposed contiguous to said second layer and comprising an electrically conductive material having a low work function surface and having a thickness such that the transfer ratio of electrons passing through said third layer compared to the electrons entering the layer is high, and a potential source connected across said third layer and said first layer to :apply a potential to said device to accelerate electrons thereacross.
  • a photoconductive electron emissive device including, a first layer comprising a light transparent electrically conducting material, a second layer comprising a photoconductive material disposed adjacent said first layer, a third layer disposed contiguous said second layer, said third layer comprising a low work function electrically conductive alkali metal having a thickness such that the transfer ratio of electrons passing through said third layer compared to the electrons entering said third layer is high, and a potential source connected across said third layer and said first layer to apply a potential to said device to accelerate electrons thereacross.
  • An electron emissive device including, a first layer comprising a light transparent electrically conductive material, a second layer comprising a photoconductive material disposed adjacent said first layer, a third layer disposed contiguous said second layer, said third l-ayer comprising an electrically conductive metallic material coated with a monolayer of an alkali metal and having a low work function, and a potential source connected across said third layer :and said first layer to apply a potential to said device to accelerate electrons thereacross.
  • a photoconductive electron emissive device including, a first layer comprising a light transparent electrically conductive material, a second layer comprising a photoconductive material disposed adjacent said first layer, a third layer disposed contiguous said second layer, said third layer comprising a low work function electrically conductive alkali metal and having a thickness of less than 500 Angstroms, and a potential source con- 4 nected across said third layer and said first layer to apply a potential to said device to accelerate electrons thereacross.
  • a photoconductive electron emissive device including a first layer comprising a light transparent electrically conducting material, a second layer comprising a photoconductive material being disposed adjacent said first layer, and a third layer disposed adjacent said second layer, said third layer comprising a metallic electrically conductive material oxidized at its structure to have a low work function, and a potential source connected across said third layer and said first layer to apply a potential to said device to accelerate electrons thereacross.
  • An electron discharge device responsive to light including, an anode, a grid, and a photoconductive cathode, said cathode including a first layer comprising a light transparent electrically conductive material, a second layer comprising a photoconductive material disposed adjacent said first layer, a third layer disposed contiguous said second layer, said third layer comprising an electrically conductive material having a low work function surface and having a thickness such that the transfer ratio of electrons passing through the layer compared to electrons entering the layer is high, and a potential source connected across said third layer and said first layer to apply a potential to said device to accelerate electrons thereacross.
  • An electron discharge device responsive to light including, an anode, a grid and a photoconductive cathode, said cathode includiug a first layer comprising a light transparent electrically conducting material, a second layer comprising a photoconductive material disposed adjacent said first layer, a third layer disposed contiguous said second layer, said third layer comprising a low work function electrically conductive alkali metal having a thickness of less than 500 Angstroms, and :a potential source connected across said third layer and said first layer to apply a potential to said device to accelerate electrons thereacross.

Landscapes

  • Common Detailed Techniques For Electron Tubes Or Discharge Tubes (AREA)
  • Light Receiving Elements (AREA)
US219022A 1962-08-23 1962-08-23 Electron emitter comprising photoconductive and low work function layers Expired - Lifetime US3278782A (en)

Priority Applications (2)

Application Number Priority Date Filing Date Title
US219022A US3278782A (en) 1962-08-23 1962-08-23 Electron emitter comprising photoconductive and low work function layers
JP4373063A JPS402972B1 (cs) 1962-08-23 1963-08-21

Applications Claiming Priority (1)

Application Number Priority Date Filing Date Title
US219022A US3278782A (en) 1962-08-23 1962-08-23 Electron emitter comprising photoconductive and low work function layers

Publications (1)

Publication Number Publication Date
US3278782A true US3278782A (en) 1966-10-11

Family

ID=22817487

Family Applications (1)

Application Number Title Priority Date Filing Date
US219022A Expired - Lifetime US3278782A (en) 1962-08-23 1962-08-23 Electron emitter comprising photoconductive and low work function layers

Country Status (2)

Country Link
US (1) US3278782A (cs)
JP (1) JPS402972B1 (cs)

Cited By (3)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US3458748A (en) * 1967-04-17 1969-07-29 Us Army Field-enhanced thermionic emitter
US3619622A (en) * 1969-12-10 1971-11-09 Goodyear Aerospace Corp Brightness distribution electron storage tube
US4644221A (en) * 1981-05-06 1987-02-17 The United States Of America As Represented By The Secretary Of The Army Variable sensitivity transmission mode negative electron affinity photocathode

Citations (4)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US2850657A (en) * 1956-08-20 1958-09-02 Gen Dynamics Corp Cathode ray tube current amplifying means
US2970219A (en) * 1955-08-18 1961-01-31 Westinghouse Electric Corp Use of thin film field emitters in luminographs and image intensifiers
US3002101A (en) * 1954-03-17 1961-09-26 Westinghouse Electric Corp Image amplifier
US3184636A (en) * 1961-06-15 1965-05-18 Sylvania Electric Prod Cold cathode

Patent Citations (4)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US3002101A (en) * 1954-03-17 1961-09-26 Westinghouse Electric Corp Image amplifier
US2970219A (en) * 1955-08-18 1961-01-31 Westinghouse Electric Corp Use of thin film field emitters in luminographs and image intensifiers
US2850657A (en) * 1956-08-20 1958-09-02 Gen Dynamics Corp Cathode ray tube current amplifying means
US3184636A (en) * 1961-06-15 1965-05-18 Sylvania Electric Prod Cold cathode

Cited By (3)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US3458748A (en) * 1967-04-17 1969-07-29 Us Army Field-enhanced thermionic emitter
US3619622A (en) * 1969-12-10 1971-11-09 Goodyear Aerospace Corp Brightness distribution electron storage tube
US4644221A (en) * 1981-05-06 1987-02-17 The United States Of America As Represented By The Secretary Of The Army Variable sensitivity transmission mode negative electron affinity photocathode

Also Published As

Publication number Publication date
JPS402972B1 (cs) 1965-02-16

Similar Documents

Publication Publication Date Title
US2898499A (en) Transmission secondary emission dynode structure
US3657596A (en) Electron image device having target comprising porous region adjacent conductive layer and outer, denser region
US2945973A (en) Image device
US3585439A (en) A camera tube with porous switching layer
US3107303A (en) Positive or negative high gain image amplifier
US3246200A (en) Cathode including photoconductive and tunneling layers
US3213308A (en) Ultraviolet radiation detector
US2717971A (en) Device for storage of images of invisible radiation
US2928969A (en) Image device
US2212923A (en) Picture transmitter
US3278782A (en) Electron emitter comprising photoconductive and low work function layers
US3128406A (en) Radiation image pickup tube
US4293790A (en) Image converter having cylindrical housing and photocathode separated by spacing element from luminescent screen on frustrum
US2850657A (en) Cathode ray tube current amplifying means
US3986065A (en) Insulating nitride compounds as electron emitters
US2970219A (en) Use of thin film field emitters in luminographs and image intensifiers
US3213315A (en) High gain storage tube with bic target
US2896088A (en) Regenerating scintillation counter
US2818520A (en) Photocathode for a multiplier tube
US3368077A (en) Infra-red image intensifier having a tunnel-emission cathode having a conductive mosaic
US2175691A (en) Photovoltaic target
US2213173A (en) Television transmitting tube
US2617058A (en) Television transmitting tube
US3321659A (en) Radiation sensitive electron emissive device
US3268764A (en) Radiation sensitive device