WO1994001882A1 - Photoemitteurs - Google Patents

Photoemitteurs Download PDF

Info

Publication number
WO1994001882A1
WO1994001882A1 PCT/GB1993/001326 GB9301326W WO9401882A1 WO 1994001882 A1 WO1994001882 A1 WO 1994001882A1 GB 9301326 W GB9301326 W GB 9301326W WO 9401882 A1 WO9401882 A1 WO 9401882A1
Authority
WO
WIPO (PCT)
Prior art keywords
iii
elements
photoemitter
layer
gaps
Prior art date
Application number
PCT/GB1993/001326
Other languages
English (en)
Inventor
Jonathan Ross Howorth
Original Assignee
Photek Limited
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 Photek Limited filed Critical Photek Limited
Publication of WO1994001882A1 publication Critical patent/WO1994001882A1/fr

Links

Classifications

    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01J—ELECTRIC DISCHARGE TUBES OR DISCHARGE LAMPS
    • H01J43/00—Secondary-emission tubes; Electron-multiplier tubes
    • H01J43/04—Electron multipliers
    • H01J43/06—Electrode arrangements
    • H01J43/08—Cathode arrangements
    • 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
    • H01J2201/3423—Semiconductors, e.g. GaAs, NEA emitters

Definitions

  • This invention relates to photoemit ters, and concerns in particular a novel form of Group III-V device having both photoemitter and electron multiplier properties.
  • photoemitters mounted within some suitable vacuum envelope with an appropriate input window, photoemit ters, usually in the form of photocathodes, are used in a wide variety of devices, such as image intensifiers and photomultipliers (utilised as photon counters), to convert received photons of light (or other electromagnetic radiation) into electrons. It is then common to employ an
  • associated electron multiplier to amplify the usually low electron flux into something usable by an imaging or a counting system, or whatever is appropriate.
  • dynode a 2 or 3 cm diameter metal plate electrode coated with a good secondary electron emitter such as magnesium oxide
  • the microchannel plate devices Because of the small size of the individual glass tubes, the microchannel plate devices have good imaging properties, so they are chosen for use with
  • the earliest approach was to grow a thin epitaxial layer of GaAs on a GaP substrate, forming a structure that allowed infrared (IR) light (from around 500 nanometre, being the band gap of GaP, to 900 nm, the band gap of GaAs) to pass through the GaP substrate and to be absorbed in the thin GaAs layer, where it is converted into electrons which are then emitted from the opposite - GaP-distant - surface of the GaAs (so the surface was acting in transmissive mode).
  • IR infrared
  • the large lattice mismatch between GaP and GaAs results in poor crystal quality, and this type of photocathode structure has low efficiency.
  • a more recent structure uses thin layers of AlAs and GaAs to provide a window and buffer between the GaAs and a glass support to which the crystal is bonded.
  • the bulk of the GaAs is etched away to leave a layer of optimum thickness for photoemission (as disclosed in our British Patent Specification
  • III-V materials may be relatively blue insensitive in transmissive mode, it turns out that they are much more sensitive to these shorter
  • the present invention seeks to solve this problem in another way, by providing a novel structure of III-V photoemitter such that, even though the photoemissive material is operating in reflective mode, where its blue sensitivity is highest, the device itself is operating in transmissive mode, so enabling the image properties of the exciting photons to be retained in the ejected electrons. More specifically, the invention proposes that the III-V photoemitter layer be in the form of an array of spaced III-V elements the front faces of which are angled towards the gaps between the elements (and the invention includes a method of making such an arrays .
  • the invention also proposes that to form a photocathode/photomult iplier device a plurality of these individual III-V layers be stacked (within some suitable windowed vacuum envelope) one above the next, with the elements of each succeeding layer aligned with the gaps in the preceding layer, so that electrons ejected from each layer and passing through the gaps will impact the next adjacent layer without losing their image-defining spatial resolution.
  • the invention provides a novel structure of III-V photoemitter material capable of operating in reflective mode but in a device itself operating in transmissive mode, in which structure the III-V photoemitter layer is in the form of an array of spaced III-V elements the front faces of which are angled towards the gaps between the elements.
  • the invention provides a method of making such an element array photoemitter structure, in which a corresponding sheet of photoemitter material is etched away, through a suitable mask, in the central area thereof to form the desired element array supported within a peripheral area of unmodified sheet material.
  • the invention provides a
  • photocathode/photomult iplier device comprising a
  • photoemitter structures stacked as layers one above the next, with the elements of each succeeding layer aligned with the gaps in the preceding layer, so that light passing through the gaps in the first layer, or
  • III-V photoemitter material may be any of those III-V materials used or suggested for use, typically GaAs or GaP, or the mixed materials like InGaAsP and GaAsP (which exhibit longer wavelength response or higher quantum efficiency in the spectrum green region), any of which may be caesium activated (GaP is easier to activate, and is for that reason generally preferred as a secondary emitter).
  • the novel structure of the invention is one wherein the III-V photoemitter layer is in the form of an array of spaced III-V elements the front faces of which are angled towards the gaps between the elements.
  • the idea of this is that when the layer is built into a
  • transmissive mode and so has good imaging properties.
  • the elements and the gaps therebetween may take any of a wide variety of geometrical forms.
  • the elements may be parallel spaced bars (the sizes mentioned above are then the bar width and depth, and intet—bar widths), or the elements may be a foraminous mesh-like structure with the spaces the actual "island” holes therein.
  • a mesh can be a reticulated, square mesh, effectively formed from two orthogonal sets of "bars", with correspondingly square holes, or it can be a hexagonal mesh, with three crossed sets of bars and hexagonal holes; it can even be a mesh of circular holes, with no definable bars.
  • each element t hus has a generally isosceles t riangular cross-section.
  • the angle - the triangle's base angle - can be of any significant value; 45* is generally satisfactory, though the actual angle may, as explained hereinafter, depend upon the method employed to form the spaces and shape the elements.
  • the photoemitter structure is an array of elements, and these elements need to be supported.
  • a support substrate, on which all the elements are individually mounted, would be suitable were it possible to use a material for the substrate that was transparent to photons and electrons, but in the absence of such a material it is acceptable to provide the array with a peripheral support across which the element array extends.
  • the array could, either before or after formation, be attached to and mounted on a separate "hoop" support, or it could be provided during its formation with an integral peripheral support formed as an "unholed" boundary area of the III-V material.
  • a typical array is a disc around 10 cm (4 in) diameter, the outer 1.25 cm (0.5 in) of which is the supporting boundary area.
  • the photoemitter structure of the invention may be made in any convenient way, even by cutting away material from a sheet of photoemitter material. This cutting is best effected by a through-mask etching process, and thus in its second aspect the invention provides a method of making the element array structure in which a corresponding sheet of photoemitter material is etched away through a suitable mask (if the etched area is a central area of the sheet, then the formed array is supported within a peripheral area of
  • the sheet of photoemitter material is first provided with a layer of photoresist, this is then exposed to light radiation, through a photographic mask, to generate the mask pattern thereon, the unwanted areas of photoresist are then dissolved away to leave the mask pattern covering the wanted areas of material sheet (those areas defining the array elements), and then the exposed, unwanted sheet areas (those defining the "spaces" between array elements) are etched away using some appropriate etchant, and finally the remaining
  • photoresist is removed to leave the finished array.
  • Liquid-phase etchants are commonly aqueous mixtures (1 pbv water) of sulphuric acid (5 pbv) and hydrogen peroxide (1 pbv), whilst vapour-phase etching involves a glow discharge in a mixture of an inert gas or halogen.
  • Shaping a photoemitter sheet by etching results in the etchant "cutting" down into the material through the exposed surface where the material is unprotected by the remaining photoresist.
  • the etchant will cut slightly sideways as well, undercutting the photoresist, with the result that the exposed side surface of the cut will be at an angle rather than normal to the sheet surface, so giving the cut the cross-section of an inverted triangle (and the remaining material defining the bars that of a right-way-up triangle).
  • the rate of etching/undercutting will depend upon the III-V material and its crystal structure and orientation, upon the etchant, and upon the physical conditions. In any given case it will be relatively easy to work out what is required, and no further comments are needed at this time.
  • the photoemitter structure of the invention is a III-V photoemitter layer in the form of an array of spaced III-V elements the front faces of which are angled towards the gaps between the elements.
  • a suitably-windowed vacuum envelope such a structure can in fact be used as a photoemitter device, for photons or electrons impacting the front face of the structure will indeed result in electron emission, and these electrons, suitably directed by an applied electrical field, can be directed through the gaps between the elements for subsequent use either to form an image or to feed a counter.
  • the efficiency of a single layer device such as this is poor, much of the original photon or electron flux passing straight through the gaps in the array rather than impacting the elements to cause electron emission, and it is very much preferred to employ at least two layers stacked on on the other, with the elements of the second "blocking" the gaps in the first. Accordingly, the third aspect the invention provides a
  • photocathode/photomult iplier device comprising a
  • an electric field is applied to turn the electrons emitted from the elements in a layer towards and through the adjacent gaps. It is one of the characteristics of negative electron affinity emitters of the III-V type that the electrons are ejected both normal to the surface and with a fairly precise electron energy (the negative affinity). Knowing this, and knowing also the mechanical dimensions of the array of elements, it is possible to calculate the optimum field needed to ensure that all the emitted electrons are indeed swept into and through the gaps. By way of example, with element bars 0.2 mm thick the field would be about 50 volts/mm.
  • An electric field is also employed to drive the electrons emitted from one layer though to the next, where they impinge to cause many more electrons to be emitted.
  • the minimum energy required to achieve this is perhaps 10 to 20 volts, so for an applied field of
  • the device can be optimised for either opacity (and thus imaging capability) or counting efficiency - the closer the layers the better the second blocks the gaps in the first, and higher the opacity, while the more distant the layers the higher the voltage between the two, and the greater the secondary emission and thus the counting efficiency.
  • the photoemitter device of the invention employs one or more array structure suitably mounted within an appropriately windowed vacuum envelope. This may take any form used or suggested for use in the Art, and needs no further comment here.
  • the invention enables the construction of a III-V photoemitter device having a good short wavelength response limited only by the cut-off of the vacuum window.
  • the device has excellent potential as a
  • Figures 1A & B show respectively plan and cross- section views of a photoemitter structure according to the
  • Figure 2 shows a stage in the manufacture of a structure of Figure 1
  • Figure 3 shows a photoemitter device made from a stacked pair of structures as in Figure 1.
  • the photoemitter structure of Figure 1 is a
  • FIG. 1B The sectional view of Figure 1B (taken on the line A-A in Figure 1A) helps to show the general layout, shape and relative size of the various parts; the bars 13 in particular are shown with a triangular cross-section, apex to the front (the top as viewed).
  • the photoemitter structure of Figure 1 can best be made by masking and etching a plane sheet of III-V material, and this is represented in Figure 2.
  • the sheet is provided (on both sides) with a protective layer of photoresist, which is exposed to light through an appropriate mask (not shown) and then selectively removed to leave on one side the required pattern of bar and peripheral portions (as 23 and 24 respectively).
  • a stacked pair of structures as in Figure 1 is shown very diagrammat ically in the device of Figure 3, which also shows the way in which the pair are staggered laterally so that the bars 13 of the lower sheet (lll.) are aligned with the spaces between the bars of the upper sheet (11u), thus rendering the device as a whole more or less opaque.
  • Photons (ho) impacting the front (upper as viewed) face of the device strike either a bar 13 in the upper sheet llu or a bar in the lower one 11l, while electrons emitted by either strike are turned by the applied field E towards and through the adjacent space.
  • Electrons (e-) emitted from the upper sheet 11u and driven through the gaps therein are accelerated towards the lower sheet 11l, striking the bars 13 therein to cause multiple secondary emission.

Landscapes

  • Common Detailed Techniques For Electron Tubes Or Discharge Tubes (AREA)

Abstract

Des photoémetteurs sont utilisés pour convertir les photons de lumière reçus (ou d'autres rayonnements électromagnétiques) en électrons. Il est courant d'utiliser un multiplicateur d'électrons pour amplifier le faible flux d'électrons destiné à être utilisé par un système d'imagerie ou de comptage. Au cours des dernières années, on a manifesté un grand intérêt pour les dispositifs photoémetteurs à semi-conducteurs et de multiplication d'électrons à base de mélanges d'éléments de groupe III et V tels que gallium et arsenic ou phosphore, mais ces derniers ne sont pas faciles à utiliser dans un tube photoélectrique. En mode transmittif, ces matériaux de groupe III-V présentent une sensibilité élevée aux infrarouges mais une sensibilité plus faible au bleu et aux ultraviolets. On a découvert récemment que les matériaux de groupe III-IV étaient plus sensibles au bleu en mode réflectif. De plus, ils sont efficaces en tant que multiplicateurs d'électrons, dans ce mode, le problème étant d'obtenir un dispositif fonctionnant dans ce mode réflectif avec de bonnes capacités d'imagerie (les électrons éjectés s'éparpillent). Il est possible de résoudre ce problème grâce à une structure photoémettrice de groupe III-V dans laquelle le dispositif lui-même fonctionne en mode transmittif retenant les images bien que le matériau photoémetteur fonctionne en mode réflectif sensible au bleu. Plus précisément, dans les photoémetteurs selon l'invention la couche photoémettrice de groupe III-V (11) se présente sous la forme d'un groupement d'éléments de groupe III-V espacés (13) dont les faces sont angulaires et orientées vers les interstices entre les éléments. Les électrons (e1) éjectés de la face des éléments (par l'impact avec les photons ou les électrons) sont, sous l'influence d'un champ électrique approprié (E), balayés latéralement vers et à travers les interstices entre les éléments, de façon que le dispositif lui-même fonctionne en mode transmittif et présente de bonnes propriétés d'imagerie bien que le matériau de groupe III-V agisse en mode réflectif et présente une bonne sensibilité au bleu. Pour former un dispositif photomultiplicateur/ou à photocathode on peut empiler une pluralité de ces couches de groupe III-V individuelles les unes sur les autres, les éléments de chaque couche étant alignés avec les interstices de la couche précédente, de façon que les électrons de chaque couche éjectés à travers les interstices viennent percuter la couche immédiatement adjacente sans perdre leur résolution spatiale définissant l'image.
PCT/GB1993/001326 1992-07-03 1993-06-24 Photoemitteurs WO1994001882A1 (fr)

Applications Claiming Priority (2)

Application Number Priority Date Filing Date Title
GB9214125A GB2269048B (en) 1992-07-03 1992-07-03 Photoemitters
GB9214125.8 1992-07-03

Publications (1)

Publication Number Publication Date
WO1994001882A1 true WO1994001882A1 (fr) 1994-01-20

Family

ID=10718126

Family Applications (1)

Application Number Title Priority Date Filing Date
PCT/GB1993/001326 WO1994001882A1 (fr) 1992-07-03 1993-06-24 Photoemitteurs

Country Status (2)

Country Link
GB (1) GB2269048B (fr)
WO (1) WO1994001882A1 (fr)

Cited By (2)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
WO2013036576A1 (fr) * 2011-09-07 2013-03-14 Kla-Tencor Corporation Photocathode transmissive-réfléchissante
RU2646527C2 (ru) * 2016-08-29 2018-03-05 Федеральное государственное казённое военное образовательное учреждение высшего образования "Рязанское высшее воздушно-десантное ордена Суворова дважды Краснознаменное командное училище имени генерала армии В.Ф. Маргелова "Министерства обороны Российской Федерации Эмиттер с отрицательным электронным сродством

Families Citing this family (3)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
FR2786024B1 (fr) * 1998-11-16 2001-06-08 Commissariat Energie Atomique Detecteur de localisation de photons, a remplissage gazeux
SE514471C2 (sv) * 1999-04-30 2001-02-26 Xcounter Ab Röntgendetektorenhet med omvandlare av fast typ
DE10014311C2 (de) * 2000-03-23 2003-08-14 Siemens Ag Strahlungswandler

Citations (1)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
GB2213634A (en) * 1987-12-08 1989-08-16 Third Generation Technology Li Photocathode structures

Family Cites Families (2)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US3814968A (en) * 1972-02-11 1974-06-04 Lucas Industries Ltd Solid state radiation sensitive field electron emitter and methods of fabrication thereof
GB1535061A (en) * 1975-12-16 1978-12-06 Standard Telephones Cables Ltd Gallium arsenide photocathode

Patent Citations (1)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
GB2213634A (en) * 1987-12-08 1989-08-16 Third Generation Technology Li Photocathode structures

Cited By (3)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
WO2013036576A1 (fr) * 2011-09-07 2013-03-14 Kla-Tencor Corporation Photocathode transmissive-réfléchissante
US9076639B2 (en) 2011-09-07 2015-07-07 Kla-Tencor Corporation Transmissive-reflective photocathode
RU2646527C2 (ru) * 2016-08-29 2018-03-05 Федеральное государственное казённое военное образовательное учреждение высшего образования "Рязанское высшее воздушно-десантное ордена Суворова дважды Краснознаменное командное училище имени генерала армии В.Ф. Маргелова "Министерства обороны Российской Федерации Эмиттер с отрицательным электронным сродством

Also Published As

Publication number Publication date
GB2269048B (en) 1995-10-04
GB9214125D0 (en) 1992-08-12
GB2269048A (en) 1994-01-26

Similar Documents

Publication Publication Date Title
JP4939033B2 (ja) 光電陰極
US5914491A (en) Detector for detecting photons or particles, method for fabricating the detector, and measuring method
EP0642147B1 (fr) Photo-émetteur, tube à électrons, et photodétecteur
GB1417032A (en) Cold cathode field electron emitting devices
JP2012516023A (ja) コーナーキューブにより改善された光電陰極
CN101101840A (zh) 光电阴极、电子管及电场辅助型光电阴极、阵列、电子管
CN107681465A (zh) 半导体光放大器及其制作方法
WO1994001882A1 (fr) Photoemitteurs
JPH02177244A (ja) 電子倍増器
JP2500209B2 (ja) 反射型光電面および光電子増倍管
WO1999040600A9 (fr) Structure d'electrode de grille pour dispositifs d'emission par effet de champ et son procede de fabrication
JP4995660B2 (ja) 光電陰極
JP2516995B2 (ja) 光電子増倍管
JP4607866B2 (ja) 画像増強装置及びそのための電子増倍装置
US4691099A (en) Secondary cathode microchannel plate tube
JPH0750587B2 (ja) 半導体光電子放出体
US3668388A (en) Multi-channel photomultiplier tube
US4963113A (en) Method for producing photomultiplier tube
JP3762535B2 (ja) 光電陰極及び電子管
GB1571551A (en) Electron discharge tube having an electron emissive electrode
JPS6258536A (ja) 電子増倍素子
JPH08255580A (ja) 光電陰極および電子管
JPH03147240A (ja) 光電子増倍管
JPS58184250A (ja) 二次電子増倍管
JPH0883561A (ja) 二次電子増倍電極および光電子増倍管

Legal Events

Date Code Title Description
AK Designated states

Kind code of ref document: A1

Designated state(s): JP US

AL Designated countries for regional patents

Kind code of ref document: A1

Designated state(s): AT BE CH DE DK ES FR GB GR IE IT LU MC NL PT SE

121 Ep: the epo has been informed by wipo that ep was designated in this application
DFPE Request for preliminary examination filed prior to expiration of 19th month from priority date (pct application filed before 20040101)
122 Ep: pct application non-entry in european phase