EP3465725A2 - Nanowire photocathode and method for producing such a photocathode - Google Patents

Nanowire photocathode and method for producing such a photocathode

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Publication number
EP3465725A2
EP3465725A2 EP17731230.3A EP17731230A EP3465725A2 EP 3465725 A2 EP3465725 A2 EP 3465725A2 EP 17731230 A EP17731230 A EP 17731230A EP 3465725 A2 EP3465725 A2 EP 3465725A2
Authority
EP
European Patent Office
Prior art keywords
nanowires
photocathode
substrate
layer
growth
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.)
Granted
Application number
EP17731230.3A
Other languages
German (de)
French (fr)
Other versions
EP3465725B1 (en
Inventor
Claude ALIBERT
Moustapha CONDE
Jean-Christophe Harmand
Théo JEGOREL
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.)
Centre National de la Recherche Scientifique CNRS
Photonis France SAS
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Centre National de la Recherche Scientifique CNRS
Photonis France SAS
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Publication of EP3465725A2 publication Critical patent/EP3465725A2/en
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Publication of EP3465725B1 publication Critical patent/EP3465725B1/en
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Classifications

    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01J—ELECTRIC DISCHARGE TUBES OR DISCHARGE LAMPS
    • H01J9/00—Apparatus or processes specially adapted for the manufacture, installation, removal, maintenance of electric discharge tubes, discharge lamps, or parts thereof; Recovery of material from discharge tubes or lamps
    • H01J9/02—Manufacture of electrodes or electrode systems
    • H01J9/12—Manufacture of electrodes or electrode systems of photo-emissive cathodes; of secondary-emission electrodes
    • 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
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01J—ELECTRIC DISCHARGE TUBES OR DISCHARGE LAMPS
    • H01J40/00—Photoelectric discharge tubes not involving the ionisation of a gas
    • H01J40/02—Details
    • H01J40/04—Electrodes
    • H01J40/06—Photo-emissive cathodes

Definitions

  • the present invention relates to the field of photocathodes, in particular for electromagnetic radiation detectors such as image intensifiers or sensors of EBCMOS (Electron Bombarded CMOS) or EBCDD (Electron Bombarded CDD) type.
  • electromagnetic radiation detectors such as image intensifiers or sensors of EBCMOS (Electron Bombarded CMOS) or EBCDD (Electron Bombarded CDD) type.
  • Electromagnetic radiation detectors such as, for example, image intensifier tubes and photomultiplier tubes, make it possible to detect electromagnetic radiation by converting it into a light or electrical output signal. They usually comprise a photocathode for receiving the electromagnetic radiation and in response transmitting a photoelectron flux, an electron multiplier device for receiving said photoelectron flux and in response transmitting a flow of so-called secondary electrons, then an output device for receiving said secondary electron flow and in response transmitting the output signal.
  • Photocathodes convert an incident photon flux into a photoelectron flux. They are generally composed of a substrate that is transparent to the spectral band of interest and an electro-emissive layer deposited on the rear face of this substrate.
  • Photocathodes can be characterized by their quantum efficiency QE (Quantum Efficiency) defined as the average percentage of incident photons converted to photoelectrons or by their sensitivity defined as the photocathode current generated by a given luminous flux. There are two types of photocathodes.
  • QE Quantum Efficiency
  • the so-called second-generation photocathodes use an electro-emissive layer of multi-alkaline compound such as SbNaK or SbNa 2 KCs deposited by CVD (Chemical Vapor Deposition) on a glass substrate.
  • the thickness of the light emitting layer is usually between 50 and 200 nm.
  • the sensitivity of these photocathodes is generally 700 to 800 ⁇ ⁇ ⁇ and its quantum efficiency is relatively low (of the order of 15%).
  • the so-called third-generation photocathodes use an electro-emissive layer of GaAs, epitaxialized by MOCVD (Metal Organic Chemical Vapor Desposition) and reported on a glass substrate.
  • the thickness of the electro-emissive layer is generally of the order of 2 ⁇ m.
  • the sensitivity of such a photocathode is of the order of 1500 to 2000 ⁇ ⁇ Im.
  • the third-generation photocathodes have a high quantum efficiency, of the order of 30%, but their manufacture is complex and expensive.
  • nanostructured photocathodes As described in application WO-A-2003/043045. These photocathodes are obtained by etching a channel pattern in an alumina matrix and filling these channels, by an electroplating technique, with an electro-emissive material such as an alkaline compound or a III-V semiconductor.
  • photocathodes can reach high sensitivities but are complex to manufacture.
  • the transfer of the emissive layer on a transparent substrate to the spectral band of interest proves particularly difficult because of the fragility of the nanostructure.
  • the nanostructure is directly etched in a substrate constituting the input window of the photocathode, an important part of the conversion takes place in the solid part of the semiconductor layer so that the quantum yield is reduced by the recombinations. within it.
  • the object of the present invention is therefore to provide a photocathode structure that allows to obtain levels of sensitivity / high quantum efficiency (s) which is very simple to manufacture.
  • Another object of the present invention is to propose a method of manufacturing such a photocathode.
  • the present invention is defined by a photocathode comprising an amorphous substrate, transparent to the spectral working band of the photocathode and having a first face, said front face and a rear face opposite to the front face, characterized in that it comprises a nanowire mats made of at least one semiconductor material III-V, deposited on said rear face and extending from this face in a direction opposite to the front face.
  • the substrate is made of glass.
  • the semiconductor material is selected from GaAs, GaN, InGaAs, InGaAs, GaP, InGaP,
  • GaSb GaSb, GaAsSb, AIGaAS, AIGaASP, GaBiAs.
  • the composition of the nanowires has a radial variation in the ratio of the elements of the material III-V so as to obtain a band gap gradient directed from the core of the nanowires to their periphery.
  • the semiconductor material may be doped with a dopant selected from Zn, Be, C or an amphoteric material.
  • the nanowires are advantageously covered with a layer of activation material selected from LiO, CsO or N F3.
  • the nanowire mat can be electrically connected to a polarization electrode deposited on said substrate.
  • the photocathode may have a transparent contact layer in the working spectral band of the photocathode, connected to the polarization electrode, the contact layer being located between the nanowire mat and said substrate.
  • the contact layer may be a layer of ITO, graphene or a polycrystalline layer of highly doped III-V semiconductor material.
  • the photocathode may include an antireflection layer located between the contact layer and said substrate.
  • the diameter of the nanowires is typically between 50 to 300 nm, preferably between 50 to 150 min.
  • the density of nanowires can be 10 5 to 10 cm 2 and preferably 10 8 to 10 cm 2 .
  • the present invention also relates to a method for manufacturing a photocathode as defined above, wherein the nanowires are grown on said substrate by means of molecular beam epitaxy in an MBE frame.
  • a gold film Prior to the growth of nanowires, within the same frame of MBE, it is advantageous to deposit on said substrate a gold film at a temperature of 0 to 1200 ° C for a period of 1 to 30 min and then it is left to dewake to a temperature between 400 ° C and 700 ° C for 1 to 30 min so as to create gold particles of 5 to 50 nm in diameter.
  • a colloidal solution of gold particles 5 to 50 nm in diameter can be dispersed on the surface of the substrate, prior to the growth of nanowires.
  • the temperature of the substrate during the growth phase of the nanowires is advantageously between 400 ° C. and 700 ° C.
  • the atomic fluxes are advantageously calibrated so as to obtain a nanowires growth rate of between 0.5 ⁇ s and 10 ⁇ s.
  • the flows of the materials making up the semiconductor material III-V are varied in such a way as to increase a material having a wider band gap at the beginning of the growth phase than at the beginning of the growth phase. at the end of this same phase.
  • an activation layer is deposited in LiO, CsO or N F3, within the same MBE frame or without breaking the vacuum.
  • FIG. 1A schematically shows a nanowire photocathode structure according to a first embodiment of the invention
  • Fig. 1B schematically shows a nanowire photocathode structure according to a second embodiment of the invention
  • Fig. 1C schematically shows a nanowire photocathode structure according to a third embodiment of the invention
  • Fig. 2 represents an image obtained by scanning electron microscopy of a photocathode according to one embodiment of the invention.
  • the present invention is based on the surprising finding that it is possible, under certain conditions, to directly epitaxize semiconductor nanowires III-V with a high crystalline quality on an amorphous substrate such as a glass substrate.
  • the research carried out so far in nanowire growth involved either crystalline substrates or amorphous substrates undergoing a prior step of surface crystallization.
  • Cohin et al. entitled "Growth of vertical GaAs nanowires on an amorphous susbtrate via a fiber-textures Si platform” published in Nanoletters, 13 May 2013, 13, pp. 2743-2747.
  • Fig. 1A schematically shows the structure of a nanowire photocathode, according to a first embodiment of the invention.
  • the photocathode comprises an amorphous substrate such as a glass substrate, 110, constituting the input window of the image intensifier or the sensor.
  • the material of the amorphous substrate is chosen to be transparent in the spectral working band of the photocathode. If necessary, the amorphous substrate may be nano-structured to allow a more even distribution of the nanowires at the cost of greater complexity. The growth then starts in the wells of the nanostructure.
  • the substrate is covered with a nanowire mat of III-V semiconductor material, for example GaN, InGaN, InGaAs, GaP, InGaP, InAs, GaSb, GaAsSb, AIGaAS, AIGaASP, GaBiAs and more generally their ternary and quaternary alloys.
  • III-V semiconductor material for example GaN, InGaN, InGaAs, GaP, InGaP, InAs, GaSb, GaAsSb, AIGaAS, AIGaASP, GaBiAs and more generally their ternary and quaternary alloys.
  • the nanowires are doped with a P-type material, for example Zn, Be, C, or an amphoteric material such as Si.
  • a P-type material for example Zn, Be, C, or an amphoteric material such as Si.
  • the nanowire stack 120 is grown directly on the amorphous substrate by molecular beam epitaxy (MBE) as described below.
  • MBE molecular beam epitaxy
  • the nanowires have a diameter of from 20 to 500 nm, preferably from 50 to 150 nm.
  • the nanowire mat has a density of 10 5 to 10 cm 2 , preferably 10 8 to 10 9 cm -2 .
  • a metal layer, 130 serves as an electrode and makes it possible to apply a polarization to the nanowire mat.
  • This polarization is negative with respect to a remote anode (not shown), opposite to the photocathode.
  • the photons arriving on the input face of the substrate, transparent at the wavelength of interest generate electron-hole pairs within the nanowires.
  • the holes are removed by recombination with the electrons provided by the biasing electrode 130.
  • the electrons generated can be emitted along the length of the nanowires.
  • the nanowires are covered with a layer for lowering the output work, for example LiO, CsO or N F3 and thus to facilitate the extraction of electrons in a vacuum.
  • the electrons extracted from the nanowires can then be multiplied by an electron multiplier 140, such as a microchannel slab or a nanodiamond layer (NDs).
  • the secondary electrons thus generated can then form an image on a phosphorescent screen or on a matrix of CMOS transistors or even a CCD matrix (EBCCD), in a manner known per se.
  • the electrons extracted from the nanowires can directly impact the rear face of an EBCMOS (Electron Bombarded CMOS) sensor.
  • EBCMOS Electrode Bombarded CMOS
  • the phosphorescent screen, the CCD, CMOS or EBCMOS matrix constitute the output window of the detector.
  • FIG. 1B schematically shows the structure of a nanowire photocathode, according to a second embodiment of the invention.
  • the elements identical to those of FIG. 1A have the same reference numbers and will not be described again.
  • This second embodiment differs from the first by the presence of a contact layer 135 which is transparent in the spectral band of interest and which is conductive, for example an ITO layer, a graphene layer or even a thin polycrystalline layer. of heavily doped P-lll-V semiconductor material deposited on the substrate prior to growth of the nanowire mat.
  • the contact layer 135 is electrically connected to the bias electrode 130.
  • FIG. 1C schematically shows the structure of a nanowire photocathode, according to a third embodiment of the invention.
  • the elements identical to those of FIG. 1B bear the same reference numbers and will not be described again.
  • This second embodiment differs from the first by the presence of an antireflection layer, 125.
  • This antireflection layer is deposited on the surface of the substrate before the deposition of the contact layer, 135. It prevents the light in the the spectral band of the photocathode is reflected by the interface between the substrate 110 and the contact layer 135.
  • Figs. 1A-1C illustrate embodiments in which the photocathodes operate in transmission in the sense that they are located between the input window and the output window of the detector.
  • these photocathodes can operate in reflection. More precisely, the photon flux in this case is incident on the rear face of the photocathode (with an angle of incidence determined by an input optic) and the photoelectrons generated in the nanowires are emitted by this same rear face.
  • the detector input and output windows are therefore here on the same side of the photocathode.
  • nanowire growth method on amorphous substrate such as a glass substrate, where appropriate after deposition of an antireflection layer and a contact layer, will be described below.
  • the growth of the nanowires is carried out by molecular beam epitaxy (MBE) of the semiconductor material III-V on the amorphous substrate.
  • MBE molecular beam epitaxy
  • the gold is deposited beforehand on the substrate a gold film.
  • the gold is deposited at a temperature of between 800 and 1200 ° C. (temperature of the MBE cell) on the substrate at room temperature or warm, preferably between 400 ° C. and 700 ° C., for a period of 1 to 30 hours. min.
  • At the end of the deposition of the gold film one waits for a duration of 30s to 30mn, so that the gold de-wets on the substrate.
  • Gold particles 5 to 50 nm in diameter are then formed on the glass substrate.
  • the gold film is deposited or dispersed on the contact layer.
  • the dewetting and nucleation phenomenon is substantially the same as on the glass substrate.
  • the growth of the nanowires is then carried out in the same MBE frame, which avoids any contamination by the ambient air. It is carried out in a temperature range of 400 to 700 ° C. The temperature is measured by means of a pyrometer adapted to the wavelength of the materials III-V composing the nanowires.
  • Atomic fluxes are chosen to correspond to growth rates of between 0.5 ⁇ s and 10 ⁇ s.
  • the fluxes are calibrated by high-energy electron diffraction grazing incidence or RHEED (Reflecting High Energy Electron Diffraction) by observing the RHEED observations corresponding to the deposition of successive layers, in a manner known per se. After a few seconds of growth, the diffraction pattern reveals semicircles indicating the growth of monocrystalline nanowires in a multitude of directions.
  • Fig. 2 is a scanning electron microscope (SEM) image of a GaAs nanowire carpet grown by MBE epitaxy on a glass substrate (Corning TM 7056).
  • the ratio of the flows of the materials III-V during the growth can be varied so that the nanowires have a wider band gap. at their base (and at their periphery) than at their summit (and in their heart). More precisely, for a material 11 lV of the type X " 1 ⁇ 1 " Y where ⁇ '", ..., X'" are the materials II I and y the material V, it will be possible to vary the flows of the materials X '", ..., X ! " With respect to the material flow V during the epitaxy so as to obtain a bandgap gradient directed from the core of the nanowires to their periphery.
  • the concentration x can be varied during epitaxy.
  • composition that is to say the variation of the flows of II I materials during epitaxy
  • the variation of composition can be carried out in stages in time. Alternatively, it may be gradual so as to obtain a positive gradient bandgap directed from the heart of the nanowires to their periphery. Whatever the law of composition variation envisaged, this variant will absorb a wider spectral band with a simple homogeneous composition.
  • the diameter of the nanowires is substantially less than the average free path length of the electrons in the II-V material, the electrons generated in the nanowires have a high probability of being emitted into vacuum before being recombined.
  • the emission of photoelectrons can take place all along the nanowires.
  • the high electric field due to the peak effect also increases the probability of emission compared with a conventional planar photocathode configuration.

Abstract

The invention relates to a photocathode comprising an amorphous substrate, such as a glass substrate (110), having an input face for receiving incident photons and a rear face opposite the input face. Nanowires (120) made from at least one III-V semiconductor material are deposited on the rear face of the substrate and extend from said face away from the input face. The invention also relates to a method for the MBE production of such a photocathode.

Description

PHOTOCATHODE À NANOFILS ET MÉTHODE DE FABRICATION D'UNE TELLE  NANO-THIN PHOTOCATHODE AND METHOD OF MANUFACTURING SUCH
PHOTOCATHODE  PHOTOCATHODE
DESCRIPTION DESCRIPTION
DOMAINE TECHNIQUE TECHNICAL AREA
La présente invention concerne le domaine des photocathodes, en particulier pour des détecteurs de rayonnement électromagnétique tels que des intensificateurs d'image ou des capteurs de type EBCMOS (Electron Bombarded CMOS) ou EBCDD (Electron Bombarded CDD). The present invention relates to the field of photocathodes, in particular for electromagnetic radiation detectors such as image intensifiers or sensors of EBCMOS (Electron Bombarded CMOS) or EBCDD (Electron Bombarded CDD) type.
ÉTAT DE LA TECHNIQUE ANTÉRIEURE Les détecteurs de rayonnement électromagnétique, tels que, par exemple, les tubes intensificateurs d'image et les tubes photomultiplicateurs, permettent de détecter un rayonnement électromagnétique en le convertissant en un signal de sortie lumineux ou électrique. Ils comportent habituellement une photocathode pour recevoir le rayonnement électromagnétique et émettre en réponse un flux de photoélectrons, un dispositif multiplicateur d'électrons pour recevoir ledit flux de photoélectrons et émettre en réponse un flux d'électrons dits secondaires, puis un dispositif de sortie pour recevoir ledit flux d'électrons secondaires et émettre en réponse le signal de sortie. STATE OF THE PRIOR ART Electromagnetic radiation detectors, such as, for example, image intensifier tubes and photomultiplier tubes, make it possible to detect electromagnetic radiation by converting it into a light or electrical output signal. They usually comprise a photocathode for receiving the electromagnetic radiation and in response transmitting a photoelectron flux, an electron multiplier device for receiving said photoelectron flux and in response transmitting a flow of so-called secondary electrons, then an output device for receiving said secondary electron flow and in response transmitting the output signal.
Les photocathodes assurent la conversion d'un flux de photons incidents en un flux de photoélectrons. Elles sont généralement composées d'un substrat transparent à la bande spectrale d'intérêt et d'une couche électro-émissive déposée sur la face arrière de ce substrat.  Photocathodes convert an incident photon flux into a photoelectron flux. They are generally composed of a substrate that is transparent to the spectral band of interest and an electro-emissive layer deposited on the rear face of this substrate.
Les photocathodes peuvent être caractérisées par leur rendement quantique QE (Quantum Efficiency) défini comme le pourcentage moyen de photons incidents convertis en photoélectrons ou bien par leur sensibilité définie comme le courant de photocathode engendré par un flux lumineux donné. On peut distinguer deux types de photocathodes. Photocathodes can be characterized by their quantum efficiency QE (Quantum Efficiency) defined as the average percentage of incident photons converted to photoelectrons or by their sensitivity defined as the photocathode current generated by a given luminous flux. There are two types of photocathodes.
Les photocathodes dites de seconde génération, utilisent une couche électro- émissive en composé multi-alcalin tel que SbNaK ou SbNa2KCs, déposée par CVD (Chemical Vapor Déposition) sur un substrat de verre. L'épaisseur de la couche photoémissive est habituellement entre 50 et 200 nm. La sensibilité de ces photocathodes est généralement de 700 à 800 μΑ Ι Ιτη et son rendement quantique est relativement faible (de l'ordre de 15%). The so-called second-generation photocathodes use an electro-emissive layer of multi-alkaline compound such as SbNaK or SbNa 2 KCs deposited by CVD (Chemical Vapor Deposition) on a glass substrate. The thickness of the light emitting layer is usually between 50 and 200 nm. The sensitivity of these photocathodes is generally 700 to 800 μΑ Ι Ιτη and its quantum efficiency is relatively low (of the order of 15%).
Les photocathodes dites de troisième génération utilisent quant à elles une couche électro-émissive en GaAs, épitaxiée par MOCVD (Métal Organic Chemical Vapor Desposition) et reportée sur un substrat de verre. L'épaisseur de la couche électro-émissive est généralement de l'ordre de 2 flm . La sensibilité d'une telle photocathode est de l'ordre de 1500 à 2000 μΑ Ι Im .  The so-called third-generation photocathodes use an electro-emissive layer of GaAs, epitaxialized by MOCVD (Metal Organic Chemical Vapor Desposition) and reported on a glass substrate. The thickness of the electro-emissive layer is generally of the order of 2 μm. The sensitivity of such a photocathode is of the order of 1500 to 2000 μΑ Ι Im.
Les photocathodes de troisième génération présentent une efficacité quantique élevée, de l'ordre de 30%, mais leur fabrication est complexe et coûteuse.  The third-generation photocathodes have a high quantum efficiency, of the order of 30%, but their manufacture is complex and expensive.
II a été proposé plus récemment d'utiliser des photocathodes nanostructurées, comme décrit dans la demande WO-A-2003/043045. Ces photocathodes sont obtenues en gravant un motif de canaux dans une matrice en alumine et en remplissant ces canaux, par une technique d'électrodéposition, avec un matériau électro-émissif tel qu'un composé alcalin ou un semi-conducteur lll-V.  It has been proposed more recently to use nanostructured photocathodes, as described in application WO-A-2003/043045. These photocathodes are obtained by etching a channel pattern in an alumina matrix and filling these channels, by an electroplating technique, with an electro-emissive material such as an alkaline compound or a III-V semiconductor.
Ces photocathodes peuvent atteindre des sensibilités élevées mais sont complexes à fabriquer. En particulier, le report de la couche émissive sur un substrat transparent à la bande spectrale d'intérêt s'avère particulièrement délicat en raison de la fragilité de la nanostructure. Alternativement, lorsque la nanostructure est directement gravée dans un substrat constituant la fenêtre d'entrée de la photocathode, une partie importante de la conversion a lieu dans la partie massive de la couche semi-conductrice de sorte que le rendement quantique est réduit par les recombinaisons en son sein.  These photocathodes can reach high sensitivities but are complex to manufacture. In particular, the transfer of the emissive layer on a transparent substrate to the spectral band of interest proves particularly difficult because of the fragility of the nanostructure. Alternatively, when the nanostructure is directly etched in a substrate constituting the input window of the photocathode, an important part of the conversion takes place in the solid part of the semiconductor layer so that the quantum yield is reduced by the recombinations. within it.
Le but de la présente invention est par conséquent de proposer une structure de photocathode qui permette d'obtenir des niveaux de sensibilité/ un rendement quantique élevé(s) qui soit très simple à fabriquer. Un autre but de la présente invention est de proposer une méthode de fabrication d'une telle photocathode. EXPOSÉ DE L'INVENTION The object of the present invention is therefore to provide a photocathode structure that allows to obtain levels of sensitivity / high quantum efficiency (s) which is very simple to manufacture. Another object of the present invention is to propose a method of manufacturing such a photocathode. STATEMENT OF THE INVENTION
La présente invention est définie par une photocathode comprenant un substrat amorphe, transparent à la bande spectrale de travail de la photocathode et présentant une première face, dite face avant et une face arrière opposée à la face avant, caractérisée en ce qu'elle comprend un tapis de nanofils réalisés en au moins un matériau semi-conducteur lll-V, déposés sur ladite face arrière et s'étendant à partir de cette face dans une direction opposée à la face avant. The present invention is defined by a photocathode comprising an amorphous substrate, transparent to the spectral working band of the photocathode and having a first face, said front face and a rear face opposite to the front face, characterized in that it comprises a nanowire mats made of at least one semiconductor material III-V, deposited on said rear face and extending from this face in a direction opposite to the front face.
Avantageusement, le substrat est en verre.  Advantageously, the substrate is made of glass.
Le matériau semi-conducteur est choisi parmi GaAs, GaN,lnGaN InGaAs, GaP, InGaP, The semiconductor material is selected from GaAs, GaN, InGaAs, InGaAs, GaP, InGaP,
InAs, GaSb, GaAsSb, AIGaAS, AIGaASP, GaBiAs. InAs, GaSb, GaAsSb, AIGaAS, AIGaASP, GaBiAs.
Avantageusement, la composition des nanofils présente une variation radiale du rapport des éléments du matériau lll-V de manière à obtenir un gradient de bande interdite dirigé du cœur des nanofils vers leur périphérie.  Advantageously, the composition of the nanowires has a radial variation in the ratio of the elements of the material III-V so as to obtain a band gap gradient directed from the core of the nanowires to their periphery.
Le matériau semi-conducteur peut être dopé par un dopant choisi parmi Zn, Be, C ou un matériau amphotère.  The semiconductor material may be doped with a dopant selected from Zn, Be, C or an amphoteric material.
Les nanofils sont avantageusement recouverts d'une couche de matériau d'activation choisi parmi LiO, CsO ou N F3.  The nanowires are advantageously covered with a layer of activation material selected from LiO, CsO or N F3.
Le tapis de nanofils peut être relié électriquement à une électrode de polarisation déposée sur ledit substrat.  The nanowire mat can be electrically connected to a polarization electrode deposited on said substrate.
Alternativement, la photocathode peut présenter une couche de contact transparente dans la bande spectrale de travail de la photocathode, reliée à l'électrode de polarisation, la couche de contact étant située entre le tapis de nanofils et ledit substrat. La couche de contact peut être une couche d'ITO, de graphène ou encore une couche polycristalline de matériau semiconducteur lll-V fortement dopé P.  Alternatively, the photocathode may have a transparent contact layer in the working spectral band of the photocathode, connected to the polarization electrode, the contact layer being located between the nanowire mat and said substrate. The contact layer may be a layer of ITO, graphene or a polycrystalline layer of highly doped III-V semiconductor material.
En outre, la photocathode peut comporter une couche antireflet située entre la couche de contact et ledit substrat. Le diamètre des nanofils est typiquement compris entre 50 à 300 nm, de préférence entre 50 à 150 mn. La densité de nanofils peut être de 105 à 1010 cm 2 et de préférence de 108 à 1010 cm 2. In addition, the photocathode may include an antireflection layer located between the contact layer and said substrate. The diameter of the nanowires is typically between 50 to 300 nm, preferably between 50 to 150 min. The density of nanowires can be 10 5 to 10 cm 2 and preferably 10 8 to 10 cm 2 .
La présente invention concerne également une méthode de fabrication d'une photocathode comme défini précédemment, selon laquelle on fait croître les nanofils sur ledit substrat au moyen d'une épitaxie par jets moléculaires dans un bâti de MBE.  The present invention also relates to a method for manufacturing a photocathode as defined above, wherein the nanowires are grown on said substrate by means of molecular beam epitaxy in an MBE frame.
Préalablement à la croissance de nanofils, au sein du même bâti de MBE, on peut avantageusement déposer sur ledit substrat un film d'or à une température de 0 à 1200°C pendant une durée de 1 à 30 min puis on le laisse démouiller à une température entre 400°C et 700°C pendant 1 à 30 min de manière à créer des particules d'or de 5 à 50 nm de diamètre. Alternativement, on peut disperser à la surface du substrat, préalablement à la croissance de nanofils, une solution colloïdale de particules d'or de 5 à 50 nm de diamètre.  Prior to the growth of nanowires, within the same frame of MBE, it is advantageous to deposit on said substrate a gold film at a temperature of 0 to 1200 ° C for a period of 1 to 30 min and then it is left to dewake to a temperature between 400 ° C and 700 ° C for 1 to 30 min so as to create gold particles of 5 to 50 nm in diameter. Alternatively, a colloidal solution of gold particles 5 to 50 nm in diameter can be dispersed on the surface of the substrate, prior to the growth of nanowires.
La température du substrat lors de la phase de croissance des nanofils est avantageusement comprise entre 400°C et 700°C.  The temperature of the substrate during the growth phase of the nanowires is advantageously between 400 ° C. and 700 ° C.
Les flux atomiques sont avantageusement calibrés de manière à obtenir une vitesse de croissance des nanofils comprise entre 0.5 Â/s et 10 Â/s.  The atomic fluxes are advantageously calibrated so as to obtain a nanowires growth rate of between 0.5 Ås and 10 Ås.
Selon une variante, pendant la phase de croissance des nanofils, on fait varier les flux des matériaux composant le matériau semi-conducteur lll-V de manière à faire croître un matériau présentant une bande interdite plus large au début de la phase de croissance qu'à la fin de cette même phase.  According to one variant, during the growth phase of the nanowires, the flows of the materials making up the semiconductor material III-V are varied in such a way as to increase a material having a wider band gap at the beginning of the growth phase than at the beginning of the growth phase. at the end of this same phase.
Avantageusement, au terme de la phase de croissance des nanofils, on dépose une couche d'activation en LiO, CsO ou N F3, au sein du même bâti de MBE ou sans rupture du vide.  Advantageously, at the end of the growth phase of the nanowires, an activation layer is deposited in LiO, CsO or N F3, within the same MBE frame or without breaking the vacuum.
BRÈVE DESCRIPTION DES DESSINS BRIEF DESCRIPTION OF THE DRAWINGS
D'autres caractéristiques et avantages de l'invention apparaîtront à la lecture d'un mode de réalisation préférentiel de l'invention, en faisant référence aux figures jointes parmi lesquelles : La Fig. 1A représente de manière schématique une structure de photocathode à nanofils selon un premier mode de réalisation de l'invention ; Other features and advantages of the invention will appear on reading a preferred embodiment of the invention, with reference to the attached figures among which: Fig. 1A schematically shows a nanowire photocathode structure according to a first embodiment of the invention;
La Fig. 1B représente de manière schématique une structure de photocathode à nanofils selon un second mode de réalisation de l'invention ;  Fig. 1B schematically shows a nanowire photocathode structure according to a second embodiment of the invention;
La Fig. 1C représente de manière schématique une structure de photocathode à nanofils selon un troisième mode de réalisation de l'invention ;  Fig. 1C schematically shows a nanowire photocathode structure according to a third embodiment of the invention;
La Fig. 2 représente une image obtenue par microscopie électronique à balayage d'une photocathode selon un mode de réalisation de l'invention.  Fig. 2 represents an image obtained by scanning electron microscopy of a photocathode according to one embodiment of the invention.
EXPOSÉ DÉTAILLÉ DE MODES DE RÉALISATION PARTICULIERS DETAILED PRESENTATION OF PARTICULAR EMBODIMENTS
La présente invention est basée sur le constat surprenant qu'il est possible, dans certaines conditions, d'épitaxier directement des nanofils de semi-conducteur lll-V avec une grande qualité cristalline sur un substrat amorphe tel qu'un substrat en verre. En effet, les recherches menées jusqu'à présent en matière de croissance de nanofils portaient soit sur des substrats cristallins, soit sur des substrats amorphes subissant une étape préalable de cristallisation en surface. On trouvera notamment une description d'une méthode de croissance de nanofils en GaAs sur un substrat amorphe en silicium avec étape préalable de cristallisation en surface dans l'article de Y. Cohin et al. intitulé « Growth of vertical GaAs nanowires on an amorphous susbtrate via a fiber-textures Si platform » publié dans Nanoletters, 13 mai 2013, 13, pp. 2743-2747. The present invention is based on the surprising finding that it is possible, under certain conditions, to directly epitaxize semiconductor nanowires III-V with a high crystalline quality on an amorphous substrate such as a glass substrate. Indeed, the research carried out so far in nanowire growth involved either crystalline substrates or amorphous substrates undergoing a prior step of surface crystallization. In particular, a description of a method for growing GaAs nanowires on an amorphous silicon substrate with a prior step of surface crystallization in the article by Y. Cohin et al. entitled "Growth of vertical GaAs nanowires on an amorphous susbtrate via a fiber-textures Si platform" published in Nanoletters, 13 May 2013, 13, pp. 2743-2747.
La Fig. 1A représente de manière schématique la structure d'une photocathode à nanofils, selon un premier mode de réalisation de l'invention.  Fig. 1A schematically shows the structure of a nanowire photocathode, according to a first embodiment of the invention.
La photocathode comprend un substrat amorphe tel qu'un substrat en verre, 110, constituant la fenêtre d'entrée de l'intensificateur d'image ou du capteur. Le matériau du substrat amorphe est choisi pour être transparent dans la bande spectrale de travail de la photocathode. Le cas échéant, le substrat amorphe peut être nano-structuré pour permettre une répartition plus régulière des nanofils au prix d'une plus grande complexité. La croissance démarre alors dans les puits de la nanostructure. Le substrat est recouvert d'un tapis de nanofils en matériau semiconducteur lll-V par exemple en GaN, InGaN, InGaAs, GaP, InGaP, InAs, GaSb, GaAsSb, AIGaAS, AIGaASP, GaBiAs et plus généralement leurs alliages ternaires et quaternaires. The photocathode comprises an amorphous substrate such as a glass substrate, 110, constituting the input window of the image intensifier or the sensor. The material of the amorphous substrate is chosen to be transparent in the spectral working band of the photocathode. If necessary, the amorphous substrate may be nano-structured to allow a more even distribution of the nanowires at the cost of greater complexity. The growth then starts in the wells of the nanostructure. The substrate is covered with a nanowire mat of III-V semiconductor material, for example GaN, InGaN, InGaAs, GaP, InGaP, InAs, GaSb, GaAsSb, AIGaAS, AIGaASP, GaBiAs and more generally their ternary and quaternary alloys.
Les nanofils sont dopés avec un matériau de type P par exemple Zn, Be, C, ou un matériau amphotère comme le Si.  The nanowires are doped with a P-type material, for example Zn, Be, C, or an amphoteric material such as Si.
On fait croître le tapis de nanofils, 120, directement sur le substrat amorphe par épitaxie à jets moléculaires (MBE), comme décrit plus loin.  The nanowire stack 120 is grown directly on the amorphous substrate by molecular beam epitaxy (MBE) as described below.
De préférence, les nanofils ont un diamètre de 20 à 500 nm, de préférence entre 50 à 150 nm Le tapis de nanofils présente une densité de 105 à 1010 cm 2, de préférence de 108 à l09 cm"2. Preferably, the nanowires have a diameter of from 20 to 500 nm, preferably from 50 to 150 nm. The nanowire mat has a density of 10 5 to 10 cm 2 , preferably 10 8 to 10 9 cm -2 .
Une couche métallique, 130, par exemple une couche de chrome, fait office d'électrode et permet d'appliquer une polarisation au tapis de nanofils. Cette polarisation est négative par rapport à une anode distante (non représentée), opposée à la photocathode. Les photons arrivant sur la face d'entrée du substrat, transparent à la longueur d'onde d'intérêt, génèrent des paires électrons-trous au sein des nanofils. Les trous sont éliminés par recombinaison avec les électrons apportés par l'électrode de polarisation, 130. Les électrons générés peuvent être émis sur toute la longueur des nanofils. Avantageusement, les nanofils sont recouverts d'une couche destinée à abaisser le travail de sortie, par exemple en LiO, CsO ou N F3 et donc à faciliter l'extraction des électrons dans le vide.  A metal layer, 130, for example a chromium layer, serves as an electrode and makes it possible to apply a polarization to the nanowire mat. This polarization is negative with respect to a remote anode (not shown), opposite to the photocathode. The photons arriving on the input face of the substrate, transparent at the wavelength of interest, generate electron-hole pairs within the nanowires. The holes are removed by recombination with the electrons provided by the biasing electrode 130. The electrons generated can be emitted along the length of the nanowires. Advantageously, the nanowires are covered with a layer for lowering the output work, for example LiO, CsO or N F3 and thus to facilitate the extraction of electrons in a vacuum.
Les électrons extraits des nanofils peuvent ensuite être multipliés par un multiplicateur d'électrons, 140, tel qu'une galette de microcanaux ou une couche de nanodiamants (NDs). Les électrons secondaires ainsi générés peuvent alors former une image sur un écran phosphorescent ou bien sur une matrice de transistors CMOS voire une matrice CCD (EBCCD), de manière connue en soi. Le cas échéant, les électrons extraits des nanofils peuvent directement impacter la face arrière d'un capteur EBCMOS (Electron Bombarded CMOS). L'écran phosphorescent, la matrice CCD, CMOS ou EBCMOS constituent la fenêtre de sortie du détecteur.  The electrons extracted from the nanowires can then be multiplied by an electron multiplier 140, such as a microchannel slab or a nanodiamond layer (NDs). The secondary electrons thus generated can then form an image on a phosphorescent screen or on a matrix of CMOS transistors or even a CCD matrix (EBCCD), in a manner known per se. If necessary, the electrons extracted from the nanowires can directly impact the rear face of an EBCMOS (Electron Bombarded CMOS) sensor. The phosphorescent screen, the CCD, CMOS or EBCMOS matrix constitute the output window of the detector.
La Fig. 1B représente de manière schématique la structure d'une photocathode à nanofils, selon un second mode de réalisation de l'invention. Les éléments identiques à ceux de la Fig. 1A portent les mêmes numéros de référence et ne seront pas décrits à nouveau. Fig. 1B schematically shows the structure of a nanowire photocathode, according to a second embodiment of the invention. The elements identical to those of FIG. 1A have the same reference numbers and will not be described again.
Ce second mode de réalisation diffère du premier par la présence d'une couche de contact, 135, transparente dans la bande spectrale d'intérêt et conductrice, par exemple, une couche d'ITO, une couche de graphène, voire une mince couche polycristalline de matériau semiconducteur lll-V fortement dopé P, déposée sur le substrat avant la croissance du tapis de nanofils. La couche de contact, 135, est reliée électriquement à l'électrode de polarisation, 130.  This second embodiment differs from the first by the presence of a contact layer 135 which is transparent in the spectral band of interest and which is conductive, for example an ITO layer, a graphene layer or even a thin polycrystalline layer. of heavily doped P-lll-V semiconductor material deposited on the substrate prior to growth of the nanowire mat. The contact layer 135 is electrically connected to the bias electrode 130.
La Fig. 1C représente de manière schématique la structure d'une photocathode à nanofils, selon un troisième mode de réalisation de l'invention. Les éléments identiques à ceux de la Fig. 1B portent les mêmes numéros de référence et ne seront pas décrits à nouveau.  Fig. 1C schematically shows the structure of a nanowire photocathode, according to a third embodiment of the invention. The elements identical to those of FIG. 1B bear the same reference numbers and will not be described again.
Ce second mode de réalisation diffère du premier par la présence d'une couche antireflet, 125. Cette couche antireflet est déposée sur la surface du substrat avant le dépôt de la couche de contact, 135. Elle permet d'éviter que la lumière dans la bande spectrale de travail de la photocathode ne soit réfléchie par l'interface entre le substrat, 110, et la couche de contact, 135.  This second embodiment differs from the first by the presence of an antireflection layer, 125. This antireflection layer is deposited on the surface of the substrate before the deposition of the contact layer, 135. It prevents the light in the the spectral band of the photocathode is reflected by the interface between the substrate 110 and the contact layer 135.
Les Figs. 1A à 1C illustrent des modes de réalisation dans lesquels les photocathodes opèrent en transmission dans le sens où elles sont situées entre la fenêtre d'entrée et la fenêtre de sortie du détecteur. Selon une variante, ces photocathodes peuvent opérer en réflexion. Plus précisément, le flux de photons est dans ce cas incident sur la face arrière de la photocathode (avec un angle d'incidence déterminé par une optique d'entrée) et les photoélectrons générés dans les nanofils sont émis par cette même face arrière. Les fenêtres d'entrée et de sortie du détecteur sont par conséquent ici situées du même côté de la photocathode.  Figs. 1A-1C illustrate embodiments in which the photocathodes operate in transmission in the sense that they are located between the input window and the output window of the detector. According to one variant, these photocathodes can operate in reflection. More precisely, the photon flux in this case is incident on the rear face of the photocathode (with an angle of incidence determined by an input optic) and the photoelectrons generated in the nanowires are emitted by this same rear face. The detector input and output windows are therefore here on the same side of the photocathode.
La méthode de croissance des nanofils sur substrat amorphe, tel qu'un substrat en verre, le cas échéant après dépôt d'une couche antireflet et d'une couche de contact, sera décrite ci-après.  The nanowire growth method on amorphous substrate, such as a glass substrate, where appropriate after deposition of an antireflection layer and a contact layer, will be described below.
De manière originale, la croissance des nanofils est réalisée par épitaxie à jets moléculaires (MBE) du matériau semi-conducteur lll-V sur le substrat amorphe. Pour ce faire, on dépose préalablement sur le substrat un film d'or. L'or est déposé à une température située entre 800 et 1200°C (température de la cellule de MBE) sur le substrat à l'ambiante ou chaud, préférentiellement entre 400°C et 700°C, pendant une durée de 1 à 30 mn. Au terme du dépôt du film d'or, on attend pendant une durée de 30s à 30mn, afin que l'or démouille sur le substrat. Des particules d'or de 5 à 50nm de diamètre se forment alors sur le substrat de verre. Alternativement, on pourra disperser à la surface du substrat une solution colloïdale de particules d'or ayant la taille précitée. Dans tous les cas, les particules d'or jouent le rôle de précurseurs pour la croissance des nanofils de matériau III- V. In an original manner, the growth of the nanowires is carried out by molecular beam epitaxy (MBE) of the semiconductor material III-V on the amorphous substrate. For this to do, is deposited beforehand on the substrate a gold film. The gold is deposited at a temperature of between 800 and 1200 ° C. (temperature of the MBE cell) on the substrate at room temperature or warm, preferably between 400 ° C. and 700 ° C., for a period of 1 to 30 hours. min. At the end of the deposition of the gold film, one waits for a duration of 30s to 30mn, so that the gold de-wets on the substrate. Gold particles 5 to 50 nm in diameter are then formed on the glass substrate. Alternatively, it will be possible to disperse on the surface of the substrate a colloidal solution of gold particles having the aforementioned size. In all cases, the gold particles act as precursors for the growth of nanowires of III-V material.
Dans les second et troisième modes de réalisation, le film d'or est déposé ou dispersé sur la couche de contact. Le phénomène de démouillage et de nucléation est sensiblement le même que sur le substrat de verre.  In the second and third embodiments, the gold film is deposited or dispersed on the contact layer. The dewetting and nucleation phenomenon is substantially the same as on the glass substrate.
La croissance des nanofils est ensuite réalisée dans le même bâti de MBE, ce qui évite toute contamination par l'air ambiant. Elle est réalisée dans une gamme de température de 400 à 700°C. La température est mesurée au moyen d'un pyromètre adapté à la longueur d'onde des matériaux lll-V composant les nanofils. Les flux atomiques sont choisis pour correspondre à des vitesses de croissance comprises entre 0.5 Â/s et 10 Â/s. Avantageusement, les flux sont calibrés par diffraction d'électrons de haute énergie en incidence rasante ou RHEED (Reflection High Energy Electron Diffraction) en observant les observations RHEED correspondant au dépôt de couches successives, de manière connue en soi. Au bout de quelques secondes de croissance, le diagramme de diffraction fait apparaître des demi-cercles indiquant la croissance de nanofils monocristallins dans une multitude de directions.  The growth of the nanowires is then carried out in the same MBE frame, which avoids any contamination by the ambient air. It is carried out in a temperature range of 400 to 700 ° C. The temperature is measured by means of a pyrometer adapted to the wavelength of the materials III-V composing the nanowires. Atomic fluxes are chosen to correspond to growth rates of between 0.5 Ås and 10 Ås. Advantageously, the fluxes are calibrated by high-energy electron diffraction grazing incidence or RHEED (Reflecting High Energy Electron Diffraction) by observing the RHEED observations corresponding to the deposition of successive layers, in a manner known per se. After a few seconds of growth, the diffraction pattern reveals semicircles indicating the growth of monocrystalline nanowires in a multitude of directions.
Cette croissance multidirectionnelle a été confirmée par microscopie électronique à balayage.  This multidirectional growth was confirmed by scanning electron microscopy.
La Fig. 2 représente un cliché obtenu par microscopie électronique à balayage (MEB) d'un tapis de nanofils de GaAs ayant crû par épitaxie MBE sur un substrat de verre (Corning™ 7056).  Fig. 2 is a scanning electron microscope (SEM) image of a GaAs nanowire carpet grown by MBE epitaxy on a glass substrate (Corning ™ 7056).
Selon une variante, on pourra faire varier le rapport des flux des matériaux lll-V lors de la croissance de manière à ce que les nanofils présentent une bande interdite plus large à leur base (et à leur périphérie) qu'à leur sommet (et en leur cœur). Plus précisément, pour un matériau ll l-V du type X "1..X 1" Y où Χ '" , ..., X '" sont les matériaux II I et y le matériau V, on pourra faire varier les flux des matériaux X '" , ..., X !" par rapport au flux du matériau V lors de l'épitaxie de sorte à obtenir un gradient de bande interdite dirigé du cœur des nanofils vers leur périphérie. A titre d'exemple pour un matériau ll l-V tel que le composé ternaire l nxGai-xAs ou AlxGai-xAs, on pourra varier la concentration x lors de l'épitaxie. According to one variant, the ratio of the flows of the materials III-V during the growth can be varied so that the nanowires have a wider band gap. at their base (and at their periphery) than at their summit (and in their heart). More precisely, for a material 11 lV of the type X " 1 × 1 " Y where Χ '", ..., X'" are the materials II I and y the material V, it will be possible to vary the flows of the materials X '", ..., X ! " With respect to the material flow V during the epitaxy so as to obtain a bandgap gradient directed from the core of the nanowires to their periphery. By way of example, for a material such as the ternary compound In x Ga 1 -x As or Al x Ga 1- x As, the concentration x can be varied during epitaxy.
La variation de composition, c'est-à-dire la variation des flux des matériaux II I lors de l'épitaxie, pourra être réalisée par paliers dans le tem ps. Alternativement, elle pourra être graduelle de manière à obtenir un gradient positif de bande interdite dirigé du cœur des nanofils vers leur périphérie. Quelle que soit la loi de variation de composition envisagée, cette variante permettra d'absorber une bande spectrale plus large qu'avec une simple composition homogène.  The variation of composition, that is to say the variation of the flows of II I materials during epitaxy, can be carried out in stages in time. Alternatively, it may be gradual so as to obtain a positive gradient bandgap directed from the heart of the nanowires to their periphery. Whatever the law of composition variation envisaged, this variant will absorb a wider spectral band with a simple homogeneous composition.
Au terme de la croissance des nanofils, dans le même bâti ou sans rupture de l'ultra vide, on pourra avantageusement déposer une couche d'activation en LiO, CsO ou N F3.  At the end of the growth of the nanowires, in the same frame or without breaking the ultra-vacuum, it will advantageously be able to deposit an activation layer in LiO, CsO or N F3.
Le diamètre des nanofils étant sensiblement inférieur à la longueur de libre parcours moyen des électrons dans le matériau l ll-V, les électrons générés dans les nanofils ont une probabilité élevée d'être émis dans le vide avant d'être recombinés. L'émission des photoélectrons peut avoir lieu tout le long des nanofils. Qui plus est, le champ électrique élevé dû à l'effet de pointe augmente également la probabilité d'émission par rapport à une configuration de photocathode plane conventionnelle.  Since the diameter of the nanowires is substantially less than the average free path length of the electrons in the II-V material, the electrons generated in the nanowires have a high probability of being emitted into vacuum before being recombined. The emission of photoelectrons can take place all along the nanowires. Moreover, the high electric field due to the peak effect also increases the probability of emission compared with a conventional planar photocathode configuration.
La densité élevée de nanofils conjuguée au faible taux de recombinaison en leur sein conduit à une efficacité quantique et donc une sensibilité élevée de la photocathode.  The high density of nanowires conjugated to the low rate of recombination within them leads to a quantum efficiency and therefore a high sensitivity of the photocathode.

Claims

REVENDICATIONS
1. Photocathode comprenant un substrat en verre (110), transparent à la bande spectrale de travail de la photocathode et présentant une première face, dite face avant et une face arrière opposée à la face avant, caractérisée en ce qu'elle comprend un tapis de nanofils (120) réalisés en au moins un matériau semi-conducteur lll-V, déposés sur ladite face arrière et s' étendant à partir de cette face dans une direction opposée à la face avant, la composition des nanofils présentant une variation radiale du rapport des éléments du matériau l ll-V de manière à obtenir un gradient de bande interdite dirigé du cœur des nanofils vers leur périphérie. 1. Photocathode comprising a glass substrate (110), transparent to the working spectral band of the photocathode and having a first face, called the front face and a rear face opposite the front face, characterized in that it comprises a mat nanowires (120) made of at least one III-V semiconductor material, deposited on said rear face and extending from this face in a direction opposite to the front face, the composition of the nanowires exhibiting a radial variation of the ratio of the elements of the material l ll-V so as to obtain a band gap gradient directed from the core of the nanowires towards their periphery.
2. Photocathode selon la revendication 1, caractérisée en ce que le matériau semi-conducteur est choisi parmi I nGaN, InGaAs, I nGaP, GaAsSb, AIGaAs, AIGaAsP, GaBiAs. 2. Photocathode according to claim 1, characterized in that the semiconductor material is chosen from I nGaN, InGaAs, I nGaP, GaAsSb, AIGaAs, AIGaAsP, GaBiAs.
3. Photocathode selon la revendication 1 ou 2, caractérisée en ce que le matériau semi-conducteur est dopé par un dopant choisi parmi Zn, Be, C ou un matériau am photère. 3. Photocathode according to claim 1 or 2, characterized in that the semiconductor material is doped with a dopant chosen from Zn, Be, C or an amphoteric material.
4. Photocathode selon l'une des revendications précédentes, caractérisée en ce que les nanofils sont recouverts d'une couche de matériau d'activation choisi parmi LiO, CsO ou N F3. 4. Photocathode according to one of the preceding claims, characterized in that the nanowires are covered with a layer of activation material chosen from LiO, CsO or NF 3 .
5. Photocathode selon l'une des revendications précédentes, caractérisée en ce que le tapis de nanofils est relié électriquement à une électrode de polarisation (130) déposée sur ledit substrat. 5. Photocathode according to one of the preceding claims, characterized in that the mat of nanowires is electrically connected to a polarization electrode (130) deposited on said substrate.
6. Photocathode selon la revendication 5, caractérisée en ce qu'elle présente une couche de contact transparente (135) dans la bande spectrale de travail de la photocathode, reliée à l'électrode de polarisation, la couche de contact étant située entre le tapis de nanofils et ledit substrat. 6. Photocathode according to claim 5, characterized in that it has a transparent contact layer (135) in the working spectral band of the photocathode, connected to the polarization electrode, the contact layer being located between the mat of nanowires and said substrate.
7. Photocathode selon la revendication 6, caractérisée en ce que le matériau de la couche de contact est une couche d'ITO, de graphène ou encore une couche polycristalline de matériau semiconducteur lll-V fortement dopé P. 7. Photocathode according to claim 6, characterized in that the material of the contact layer is a layer of ITO, of graphene or even a polycrystalline layer of heavily P-doped III-V semiconductor material.
8. Photocathode selon la revendication 6 ou 7, caractérisée en ce qu'elle comporte une couche antireflet (125) située entre la couche de contact et ledit substrat. 8. Photocathode according to claim 6 or 7, characterized in that it comprises an anti-reflection layer (125) located between the contact layer and said substrate.
9. Photocathode selon l'une des revendications précédentes, caractérisée en ce que le diamètre des nanofils est compris entre 50 à 300 nm, de préférence entre 50 à9. Photocathode according to one of the preceding claims, characterized in that the diameter of the nanowires is between 50 to 300 nm, preferably between 50 to
150 nm. 150nm.
10. Photocathode selon l'une des revendications précédentes, caractérisée en ce que la densité de nanofils est de 105 à 1010 cm 2, de préférence de 108 à 1010 cm 2. 10. Photocathode according to one of the preceding claims, characterized in that the density of nanowires is 10 5 to 10 10 cm 2 , preferably 10 8 to 10 10 cm 2 .
11. Méthode de fabrication d'une photocathode selon l'une des revendications précédentes, caractérisée en ce que l'on fait croître les nanofils sur ledit substrat au moyen d'une épitaxie par jets moléculaires dans un bâti de MBE, en faisant varier, pendant la phase de croissance des nanofils, les flux des matériaux composant le matériau semi- conducteur lll-V de manière à obtenir un matériau présentant une bande interdite plus large au début de la phase de croissance qu'à la fin de cette même phase. 11. Method for manufacturing a photocathode according to one of the preceding claims, characterized in that the nanowires are grown on said substrate by means of molecular beam epitaxy in an MBE frame, by varying, during the growth phase of the nanowires, the flows of the materials composing the semiconductor material III-V so as to obtain a material having a wider bandgap at the start of the growth phase than at the end of this same phase.
12. Méthode de fabrication de photocathode selon la revendication 11, caractérisée en ce que préalablement à la croissance de nanofils, au sein du même bâti de MBE, on dépose sur ledit substrat un film d'or à une température de 0 à 1200°C pendant une durée de 1 à 30 min puis on le laisse démouiller à une température entre 400°C et 700°C pendant 1 à 30 min de manière à créer des particules d'or de 5 à 50 nm de diamètre. 12. Photocathode manufacturing method according to claim 11, characterized in that prior to the growth of nanowires, within the same MBE frame, a gold film is deposited on said substrate at a temperature of 0 to 1200°C for a period of 1 to 30 min then it is left to dewet at a temperature between 400°C and 700°C for 1 to 30 min so as to create gold particles of 5 to 50 nm in diameter.
13. Méthode de fabrication de photocathode selon la revendication 12, caractérisée en ce que préalablement à la croissance de nanofils, on disperse à la surface du substrat une solution colloïdale de particules d'or de 5 à 50 nm de diamètre. 13. Photocathode manufacturing method according to claim 12, characterized in that prior to the growth of nanowires, a colloidal solution of gold particles of 5 to 50 nm in diameter is dispersed on the surface of the substrate.
14. Méthode de fabrication de photocathode selon l'une des revendications 11 à 13, caractérisée en ce que la température du substrat lors de la phase de croissance des nanofils est comprise entre 400°C et 700°C et que les flux atomiques sont calibrés de manière à obtenir une vitesse de croissance des nanofils comprise entre 0.5 Â/s et 10 Â/s. 14. Photocathode manufacturing method according to one of claims 11 to 13, characterized in that the temperature of the substrate during the growth phase of the nanowires is between 400°C and 700°C and that the atomic flows are calibrated so as to obtain a growth speed of the nanowires of between 0.5 Â/s and 10 Â/s.
15. Méthode de fabrication de photocathode selon l'une des revendications 11 à 14, caractérisée en ce qu'au terme de la phase de croissance des nanofils, on dépose une couche d'activation en LiO, CsO ou N F3, au sein du même bâti de MBE ou sans rupture du vide. 15. Photocathode manufacturing method according to one of claims 11 to 14, characterized in that at the end of the growth phase of the nanowires, an activation layer of LiO, CsO or N F3 is deposited within the same MBE frame or without vacuum break.
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JP2001143648A (en) 1999-11-17 2001-05-25 Hitachi Ltd Photoexcited electron beam source and apparatus for applying electron beam
WO2003043045A2 (en) 2001-11-13 2003-05-22 Nanosciences Corporation Photocathode
JP2006302610A (en) 2005-04-19 2006-11-02 Hamamatsu Photonics Kk Semiconductor photocathode
JP2008135350A (en) 2006-11-29 2008-06-12 Hamamatsu Photonics Kk Semiconductor photocathode
US20100180950A1 (en) * 2008-11-14 2010-07-22 University Of Connecticut Low-temperature surface doping/alloying/coating of large scale semiconductor nanowire arrays
WO2011152459A1 (en) * 2010-06-03 2011-12-08 株式会社Si-Nano Optical electricity storage device
US9478699B2 (en) 2010-08-26 2016-10-25 The Ohio State University Nanoscale emitters with polarization grading
WO2013126432A1 (en) * 2012-02-21 2013-08-29 California Institute Of Technology Axially-integrated epitaxially-grown tandem wire arrays
CN103594302B (en) * 2013-11-19 2016-03-23 东华理工大学 A kind of GaAs nano-wire array photocathode and preparation method thereof
US9478385B2 (en) * 2013-11-26 2016-10-25 Electronics And Telecommunications Research Institute Field emission device having field emitter including photoelectric material and method of manufacturing the same
CN104752117B (en) * 2015-03-03 2017-04-26 东华理工大学 NEA electron source for vertically emitting AlGaAs/GaAs nanowires
CA2923897C (en) * 2015-03-16 2023-08-29 Zetian Mi Photocathodes and dual photoelectrodes for nanowire photonic devices
FR3034908B1 (en) 2015-04-08 2017-05-05 Photonis France MULTIBAND PHOTOCATHODE AND ASSOCIATED DETECTOR
US9818894B2 (en) * 2015-09-02 2017-11-14 Physical Optics Corporation Photodetector with nanowire photocathode

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