Photodetector with coupled Fabry-Perot resonators

Abstract

The photodetector (100) incorporates Fabry-Perot cavities (FP1, FP2) coupled to focus the radiation to be detected onto a photoconductive material. It is then possible to use photoconductive nanocrystals with high photodetection sensitivity as they are precipitated from a colloidal solution of nanocrystals. This allows for the formation of a matrix array of such photodetectors into an image sensor readout circuit, while avoiding the need to add separate detection circuits to the readout circuit using intermediate solder balls. Additionally, each photodetector can be easily produced using a deposition and selective removal process and reconfigured to have a tunable detection sensitivity spectrum.

Description

[Technical Field]

[0001] The present specification relates to photodetectors as well as image sensors comprising such photodetectors. [Background technology]

[0002] Infrared photodetectors are usually based on semiconductors as light-absorbing materials. These semiconductors are manufactured by epitaxy. This growth method incurs high manufacturing costs due to the use of an ultra-high vacuum growth environment and also due to the constraints on mesh parameter adjustment between the substrate and the semiconductor.

[0003] Furthermore, the cost of an infrared imager is also due to the bonding step between the detection circuit, which includes the light absorption layer, and the readout circuit, which is generally implemented using CMOS technology. This bonding between the two circuits is performed by indium beads. Each of these beads connects the active layer to a pixel in the CMOS readout circuit. The efficiency of this step is limited, which generates additional costs. Furthermore, the smaller the pixel size, the more complex the procedure. Although a small pixel size is desirable to improve image quality, this bonding step between the two circuits limits it to current dimensions (10-15 μm).

[0004] Therefore, it is desirable to use alternative materials to reduce the cost of infrared components. In the spectral range of interest of the present invention, i.e., for wavelengths above 1 μm, conducting polymers are not a viable alternative due to the strong coupling between molecular excitons and vibrations. Other possible alternatives include semiconductor nanocrystals with low bandgaps, such as lead sulfide (PbS) or mercury telluride (HgTe), or two-dimensional materials like graphene.

[0005] In materials such as nanocrystals, a compromise is necessary. The granular nature of nanoparticles means that transport occurs via nearest-neighbor hops. This transport mechanism is associated with lower charge carrier mobility values ​​than in solid-state materials. The result is short carrier diffusion lengths, typically 50–100 nm. This diffusion length is shorter than the absorption length of the electromagnetic field, which is a few micrometers. Therefore, transport is only effective at small sizes, but thick films are required to absorb most of the incident light. One strategy to overcome this limitation is to introduce an optical cavity into the photodetector, whose role is to focus the incident light onto a thin film of semiconductor with an optimal thickness for charge collection.

[0006] Several strategies (metal-insulator-metal cavities, Fabry-Perot cavities, plasmon cavities, etc.) have been proposed to enhance the absorption of components by strengthening the light-matter coupling in nanoparticle films. In Non-Patent Document 1, the authors propose introducing mirrored surfaces into the component to allow double-pass of the incident light in the absorbing layer, which enhances the absorption by approximately a factor of two. In addition, the authors add a grating to generate optical modes in which the light propagates along the substrate, thus also creating multiple optical paths through the film.

[0007] This type of strategy based on periodic networks suffers from two limitations: the resulting detectors have a strong angular dependence, which is not favorable for integration into imagers. In addition, for optimal operation, the network must be quasi-infinite, which means that a large number of grating periods must be included in each pixel. This last point defeats the stated goal of reducing pixel size. Therefore, there is interest in developing new optical resonator geometries that are compatible with the pixel sizes used in imagers and also have a low angular dependence of response.

[0008] It is also known to form coupled radiation-absorbing nanostructures, each consisting of a pair of coupled Fabry-Perot cavities. Each pair of coupled cavities exhibits, in addition to the individual resonances of each resonator, a coupled resonance that results in a value close to unity for the absorption coefficient of the incident radiation. In such coupled Fabry-Perot cavities nanostructures, each of the two resonators in each pair can be formed by trenches in the surface of a metal substrate, as described in Non-Patent Document 2 or Non-Patent Document 3. In these structures, standing wave components formed inside the trenches propagate perpendicular to the substrate surface. For this reason, the corresponding Fabry-Perot cavities are said to have a vertical axis. However, it is also known, inter alia, from Patent Document 1, to form other nanostructured coupled Fabry-Perot cavities in which the standing wave components inside the resonators propagate parallel to the substrate surface. Consequently, such other Fabry-Perot cavities are said to have a horizontal axis.

[0009] Another important aspect of the present invention is the creation of components with reconfigurable spectral responses. Generally, the response of an infrared detector is determined by the properties of the active layer. In the case of nanoparticles, the size of the individual components determines the cutoff wavelength. Therefore, changing the cutoff wavelength requires modifying the active material. An alternative strategy is to influence the spectral response by the presence of an optical cavity. Non-Patent Document 1 demonstrated that the spectral response of a material can be adjusted by the lattice period while keeping the same active material. Adding a degree of reconfigurability allows the spectral response to be changed after the component has been fabricated. This type of active component is currently based on phase-change materials or MEMS technology. Recently, Non-Patent Document 4 demonstrated that it is possible to achieve a spectral response shift via voltage application. In this paper, the effect is still weak. One of the challenges of the present invention is to use this concept to obtain infrared detectors whose spectral response is highly reconfigurable after the component has been fabricated. [Prior art documents] [Patent documents]

[0010] [Patent Document 1] International Publication No. 2020 / 002330 Brochure [Non-patent literature]

[0011] [Non-Patent Document 1] Audrey Chu et al., "Near Unity Absorption in Nanocrystal-Based Short Wave Infrared Photodetectors Using Guided Mode Resonators," ACS Photonics 6, 2553 (2019) [Non-patent document 2] Ling Guo et al., "Cooperative optical trapping in asymmetric plasmon nanocavity arrays," Optics Express, 31324, Vol. 23, No. 24, November 2015. [Non-patent document 3] B. Fix et al., "High-quality-factor double Fabry-Perot plasmonic nanoresonator," Optics Letters, Vol. 42, No. 24, December 15, 2017, pp. 5062-5065 [Non-patent document 4] Dang et al., "Bias Tunable Spectral Response of Nanocrystal Array in a Plasmonic Cavity," Nano Letters 21, 6671 (2021) Summary of the Invention [Problem to be solved by the invention]

[0012] Based on this situation, one object of the present invention is to propose a new photodetector structure that provides high optical absorption and simplifies the manufacturing of each photodetector.

[0013] Specifically, one objective of the present invention may be that the photodetector structure is compatible with the use of layers of photoconductive nanocrystals deposited from colloidal solutions.

[0014] A secondary object of the present invention is that each photodetector has a small lateral dimension (typically less than 15 μm, preferably less than 5 μm) to enable the realization of high resolution image sensors.

[0015] A further subsidiary object of the present invention is to preserve the effectiveness of each photodetector in detecting radiation whose angle of incidence varies within a wide angular sector.

[0016] Finally, it is another object of the invention to provide a photodetector whose spectral detection characteristics can be easily modified and / or the photodetector can be reconfigured based on its application or between two consecutive use sequences of the photodetector. [Means for solving the problem]

[0017] To achieve at least one or another of these objectives, a first aspect of the present invention comprises: a substrate that is reflective to electromagnetic radiation incident on the photodetector; electrode portions supported by the substrate and facing away from the substrate, each having a surface referred to as an upper surface and spaced at a common level from the substrate; an electrically insulating material portion disposed between each electrode portion and the substrate so as to electrically insulate the electrode portion from the substrate; at least one photoconductive material portion disposed in electrical contact with two adjacent electrode portions; We propose a new photodetector equipped with the above.

[0018] When using this photodetector, at least two of the electrode portions and the substrate are designed to collect a photodetection current.

[0019] In the photodetector of the present invention, the first and second adjacent electrode portions define a space between them parallel to the substrate through which radiation penetrates and is reflected by the substrate when the photodetector is in use, forming a first Fabry-Perot cavity between the substrate and the level of the upper surface of the electrode portions. Similarly, the second electrode portion and a third electrode portion disposed on the side of the second electrode portion opposite the first electrode portion define a further space between them parallel to the substrate through which radiation also penetrates and is reflected by the substrate when the photodetector is in use, forming a second Fabry-Perot cavity between the substrate and the level of the upper surface of the electrode portions. In other words, the first and second Fabry-Perot cavities are designed to generate standing wave components that propagate perpendicular to the substrate when the photodetector is in use. Therefore, they are of the vertical axis type according to the terminology of those skilled in the art described above.

[0020] The photodetector of the present invention further has the following features (1) to (3). (1) The width of the first Fabry-Perot cavity measured between the first and second electrode portions parallel to the substrate is different from the width of the second Fabry-Perot cavity measured between the second and third electrode portions also parallel to the substrate, so that the first and second Fabry-Perot cavities have respective individual resonant wavelength values ​​that are effective for radiation incident on the photodetector, and these values ​​are different, and the respective individual resonant quality factor values ​​of these first and second Fabry-Perot cavities are determined on the wavelength axis of the incident radiation by the following individual resonant spacing: [λ ri ·(1-3 / Q i );λ ri (1+3 / Q i )] have an overlap, where i is equal to 1 or 2 to designate the first or second Fabry-Perot cavity, respectively, and λ ri and Qi are the wavelengths and quality factor values ​​of the individual resonances of Fabry-Perot cavity i, respectively. In other words, the two Fabry-Perot cavities have individual resonance wavelengths that are different but not too far apart. Additionally, the two cavities are distinguished by their respective cavity widths, which is particularly easy to achieve, especially using masking methods. (2) the sum of the width of the first and second Fabry-Perot cavities and the width of the second electrode portion measured parallel to the substrate between the spaces of the first and second Fabry-Perot cavities is - a first wave resulting from the reflection of the incident radiation on the substrate; a second wave emerging from the first Fabry-Perot cavity resulting from the superposition of several wave components, at least one of which makes at least one round trip in the space of the second Fabry-Perot cavity; a third wave emerging from the second Fabry-Perot cavity resulting from another superposition of several other wave components, at least one of which makes at least one round trip within the space of the first Fabry-Perot cavity; and adapted to provide coupling between the first and second Fabry-Perot cavities by being below a resonant wavelength value for coupling, known as a coupling resonant wavelength, that is effective for radiation incident on the photodetector, resulting from interference between at least three waves including (3) The optically conductive material is absorptive at the combined resonant wavelength, and a portion of this optically conductive material is disposed in or on at least one of the spaces of the first and second Fabry-Perot cavities.

[0021] Due to the coupling resonance that the photodetector of the present invention exhibits for the radiation to be detected, its light absorption is very high. This is because the coupling resonance focuses the radiation on at least a portion of the photoconductive material, significantly increasing the probability that a photon of the radiation will be absorbed. For this reason, the photoconductive material can be of a type that is compatible with deposition methods, particularly spin-coating methods, using colloidal solutions of nanocrystals of this material. Such methods reduce the manufacturing costs of the photodetector, firstly because the photoconductive material can be deposited on a substrate at low cost, and secondly because the readout circuit can be used as a substrate for depositing the photoconductive material. In this way, the step of integrating the detection circuit into the readout circuit can be avoided.

[0022] Furthermore, because the photodetector structure of the present invention can be limited to two Fabry-Perot cavities with dimensions smaller than the wavelength of the radiation to be detected, the photodetector can have very small lateral dimensions, and as a result, an image sensor based on the photodetector of the present invention can provide very fine spatial resolution and act as a high-resolution sensor.

[0023] Again, the structure of the photodetector of the present invention maintains its detection efficiency within a wide angular sector relative to the direction of incidence of the detected radiation.

[0024] The optically conductive material portion may be at least partially disposed in or on whichever of the spaces of the first and second Fabry-Perot cavities has a maximum or minimum width, also measured parallel to the substrate, and may also be at least partially disposed in or on each of the two spaces of the first and second Fabry-Perot cavities.

[0025] In embodiments of the invention that may be easier to manufacture, the portions of electrically insulating material may be part of a continuous layer of this insulating material that extends across the space between the first Fabry-Perot cavity and the second Fabry-Perot detector in addition to extending between the substrate and each electrode portion, eliminating the need to etch away layers of insulating material.

[0026] Alternatively, in addition to the first, second, and third electrode portions, the substrate may be in contact with the photoconductive material portions to form additional electrode portions. Specifically, the substrate may be in contact with the photoconductive material portions because a portion of the photoconductive material is contained within the volume of at least one of the first and second Fabry-Perot cavities. In this case, at least two of the first, second, and third electrode portions may be electrically shorted to form a first photodetection current collecting electrode, and the substrate may be used to form a second photodetection current collecting electrode. Alternatively, the photodetection current may be collected between two electrode portion subsets, which may be electrically shorted within each subset.

[0027] Generally speaking, the photodetector may further comprise a bias circuit adapted to apply a variable voltage between two electrode portions that collect a photodetection current during use of the photodetector, and to vary this voltage arbitrarily between two successive uses of the photodetector. Such a variable bias voltage allows the detection sensitivity, or more generally, the sensitivity spectrum, of the photodetector to be modified, making it particularly suitable for a variety of uses. The variable bias voltage increases the efficiency with which the electrode portions collect the charge generated by radiation in the photoconductive material. The bias voltage may vary between 0 V (volts) and 10 V, although advantageously a value of 1 V or less may be sufficient. Advantageously, such a photodetector may be adapted so that the radiation absorption value at at least one wavelength value varies by at least 30%, preferably at least 50%, and more preferably at least 90% between the two electrode portions, or between a first use of the photodetector in which no voltage is applied by the bias circuit while the voltage applied by the bias circuit is zero, and a second use of the same photodetector in which the voltage applied by the bias circuit is non-zero.

[0028] In one embodiment, the electric field applied to actuate the component is 100 kV.cm -1 less than 30 kV.cm -1 is less than.

[0029] Also generally, in accordance with the present invention, a photodetector may also include a reconfiguration circuit adapted to selectively electrically connect at least two electrode and substrate portions of the photodetector to collect a photodetection current through selected electrode and substrate portions. These may be changed between several photodetection current collection modes associated with different spectra of the photodetector's sensitivity to incident radiation. Indeed, each mode may prioritize collecting the photodetection current through a different portion of the photoconductive material than another mode, and each portion of the photoconductive material may be a focal point for detected radiation for different values ​​of radiation wavelength. In this manner, a photodetector of the present invention may be easily and quickly reconfigured between two successive uses. For example, a first photodetection current collection mode may collect current using the first and second electrode portions, while another mode may use the second and third electrode portions. Thus, a first collection mode may correspond to a coupled resonance generated by the photodetector structure of the present invention, while another collection mode may instead correspond to an individual resonance of a Fabry-Perot cavity, with the individual and coupled resonances corresponding to different wavelength values ​​of the detected radiation. Possibly, for at least one or each of the collection modes, each electrode portion not used to collect a photodetection current may be shorted by a reconfiguration circuit that includes a selected one of the electrode portions. Alternatively, the electrode portion not used to collect a photodetection current may be at floating potential.

[0030] Advantageously, the photodetector may have at least one of the following additional features, either separately or in some combination: The substrate may have a flat surface that extends continuously beneath the insulating material portion and beneath the space between the first and second Fabry-Perot cavities. The substrate may comprise read-out circuits for the photodetectors. Each portion of photoconductive material may be part of a layer of this photoconductive material that extends continuously over the spaces and over the electrode portions of the first and second Fabry-Perot cavities. The photodetector may comprise a plurality of pairs of coupled first and second Fabry-Perot resonators, with first, second and third electrode portions associated with each pair and electrically connected to accumulate a photodetection current resulting from each pair when the photodetector is in use. In the case of such a photodetector comprising several pairs of coupled Fabry-Perot resonators, the repeat pitch of the pattern of coupled Fabry-Perot resonator pairs on the substrate is smaller than the coupled resonant wavelength. The photodetector may have lateral dimensions, measured parallel to the substrate, between 1 μm (micrometer) and 1 cm (centimeter), preferably between 1 μm and 100 μm, in particular less than 15 μm. The spacing of the first and second Fabry-Perot cavities together with the width of the second electrode portion may be dimensioned so that the combined resonant wavelength is between 1 μm and 12 μm, preferably between 1 μm and 2.5 μm. The photoconductive material may be selected to have a band gap of less than 0.8 eV (electron volts). This limit corresponds to a photodetector that is effective for wavelength values ​​of the radiation to be detected that are greater than approximately 1 μm. In particular, the photoconductive material may be based on lead sulfide (PbS), mercury telluride (HgTe), or graphene. Each photoconductive material portion may consist of aggregated nanocrystals, which may be precipitated from a colloidal solution.

[0031] A second aspect of the invention proposes an image sensor comprising a matrix arrangement of photodetectors, each photodetector conforming to the first aspect of the invention presented above.

[0032] When each of the photodetectors of the image sensor comprises several pairs of coupled Fabry-Perot cavities, with an electrode portion associated with each pair and electrically connected to accumulate a photodetection current resulting from each pair when the photodetector is in use, the number of coupled Fabry-Perot cavities pairs in each photodetector may be 5 or less. Alternatively, or in combination, each photodetector may have an individual photodetector size, measured in the parallel direction of the coupled first and second Fabry-Perot cavities pairs, that is 10 times or less the value of the wavelength of radiation corresponding to the maximum detection sensitivity of the photodetector.

[0033] Finally, a third aspect of the invention proposes a method for manufacturing a photodetector according to the first aspect of the invention, according to which a photoconductive material part is obtained by precipitation of a colloidal solution containing nanocrystals of a photoconductive material, followed by drying of the precipitated colloidal solution. In particular, a spin-coating method may be used to obtain the photoconductive material part.

[0034] The features and advantages of the present invention will become apparent in the following detailed description of non-limiting embodiments, which proceeds with reference to the accompanying drawings, in which: FIG. [Brief explanation of the drawings]

[0035] [Figure 1a] 1 is a cross-sectional view of a photodetector according to the present invention; [Figure 1b] FIG. 1b is a view corresponding to FIG. 1a for an alternative embodiment of the photodetector. [Figure 1c] FIG. 1b is a view corresponding to FIG. 1a for another alternative embodiment of the photodetector. [Figure 1d] FIG. 1b is a view corresponding to FIG. 1a for yet another alternative embodiment of the photodetector. [Figure 2] FIG. 2 is a plan view of a photodetector according to any one of FIGS. 1a to 1d. [Figure 3a] FIG. 1b: Spectral absorption diagram for a photodetector according to FIG. [Figure 3b] FIG. 3 is a spectral detection response diagram for the photodetector according to FIGS. 1b and 2; [Figure 4a] FIG. 3 is a diagram corresponding to FIG. 2 for another electrode subgrouping mode. [Figure 4b] FIG. 3b corresponds to FIG. 3b for the photodetector of FIG. 4a. [Figure 5a] FIG. 10 is a diagram corresponding to FIG. 2 but for another electrode subgrouping mode. [Figure 5b] FIG. 3b corresponds to FIG. 3b for the photodetector of FIG. 5a. [Figure 6] FIG. 1a corresponds to FIG. 1a for an improvement of the present invention. [Figure 7]1 is a perspective view of an image sensor according to the present invention; DETAILED DESCRIPTION OF THE INVENTION

[0036] For clarity, the dimensions of the elements shown in these figures do not correspond to actual dimensions or to scale. In addition, some of these elements are shown symbolically only, and the same reference signs shown in different figures refer to elements that are identical or have the same function.

[0037] According to a particular embodiment shown in FIG. 1a, the substrate 1 of the photodetector 100 has a continuous, flat, reflective upper surface S on which radiation R incident on this surface is detected. For this purpose, the surface S of the substrate 1 may be formed by a continuous metal layer 11 supported on a base portion 10 of the substrate 1. This base portion 10 may be at least partly made of silica, quartz, calcium fluoride (CaF), undoped silicon (Si), undoped germanium (Ge), zinc selenide (ZnSe), zinc sulfide (ZnS), potassium bromide (KBr), lithium fluoride (LiF), alumina (AlO), potassium chloride (KCl), barium fluoride (BaF), cadmium telluride (CdTe), sodium chloride (NaCl), cesium bromide (CsBr), gallium arsenide (GaAs), magnesium fluoride (MgF), or, in particular, thallium bromoiodide (Br3- x I x Alternatively, the base portion 10 of the substrate 1 may incorporate a readout circuit for the photodetector 100, in particular a readout circuit implemented in CMOS technology. The metal layer 11 may consist of gold (Au), silver (Ag) or aluminium (Al), in particular, or an alloy, or may be a superposition of several simple metal layers.

[0038] On top of the metal layer 11, the substrate 1 is coated with a continuous insulating layer 2, for example a layer of silica (SiO2) or alumina (Al2O3). In particular, the insulating layer 2 may consist of alumina and have a thickness e2 of approximately 50 nm (nanometers) measured parallel to a direction D1 that is perpendicular to the surface S of the substrate 1.

[0039] The thickness of the insulating layer 2 can be between 10 nm and 10 μm, preferably between 30 nm and 5 μm.

[0040] Three electrode portions, labeled 3a, 3b, and 3c, are formed in the insulating layer 2. They may be formed from a continuous metal layer, such as a gold, silver, or aluminum layer, and then etched to form a separation gap between adjacent electrode portions. Alternatively, the electrode portions 3a, 3b, and 3c may be deposited using a lift-off method, in which a resin pattern is first formed in the insulating layer 2, followed by deposition of electrode material and subsequent dissolution of the resin, simultaneously removing the electrode material at the resin pattern locations. The common thickness es of the electrode portions 3a, 3b, and 3c may be approximately 100 nm in the direction D1. Each electrode portion 3a, 3b, and 3c is thus electrically insulated from the metal layer 11 by the insulating layer 2.

[0041] Finally, a layer 4 of photoconductive material is deposited in the electrode portions 3 a, 3 b, and 3 c so as to be in contact with the two electrode portions on either side of each of these separation gaps. In the embodiment shown in Figure 1 a, the layer of photoconductive material 4 also continuously covers the three electrode portions 3 a, 3 b, and 3 c.

[0042] In possible embodiments of photodetector 100, the photoconductive material of layer 4 can be a two-dimensional material such as graphene, or a transition metal chalcogenide such as molybdenum sulfide (MoS), molybdenum selenide (MoSe), molybdenum telluride (MoTe), tungsten sulfide (WS), tungsten selenide (WSe), tungsten telluride (WTe), or an alloy or heterostructure thereof. Aggregated nanocrystals of these transition metal chalcogenides can be deposited onto electrode portions 3a, 3b, and 3c from a colloidal solution of these nanocrystals using a spin-coating method to fill the inter-electrode separation gap.

[0043] In other possible embodiments of photodetector 100, the photoconductive material of layer 4 can be a conductive polymer such as a mixture of poly(3,4-ethylenedioxythiophene) and polysodium styrene sulfonate, denoted as PDOT-PSS, or poly(3-hexylthiophene-2,5), denoted as P3HT, which can also be deposited onto electrode portions 3a, 3b, and 3c using a spin-coating method to also fill the inter-electrode separation gap.

[0044] In yet another possible embodiment of the photodetector 100, the photoconductive material of the layer 4 is silicon (Si), germanium (Ge), cadmium sulfide (CdS), cadmium selenide (CdSe), cadmium telluride (CdTe), zinc sulfide (ZnS), zinc selenide (ZnSe), zinc telluride (ZnTe), mercury sulfide (HgS), mercury selenide (HgSe), mercury telluride (HgTe), lead sulfide (PbS), lead selenide (PbSe), lead telluride (PbTe), copper indium sulfide (CdS), copper indium sulfide (CdSe), copper indium sulfide (CdTe ...Te), copper indium sulfide (CdTe), copper indium sulfide (CdTe), copper indium sulfide Copper (CuInS2), copper indium selenide (CuInSe2), silver indium sulfide (AgInS2), silver indium selenide (AgInSe2), copper II sulfide (CuS), copper I sulfide (Cu2S), silver sulfide (Ag2S), silver selenide (Ag2Se), silver telluride (Ag2Te), indium nitride (InN), indium phosphide (InP), indium arsenide (InAs), indium antimonide (InSb), indium sulfide (In2S3), cadmium phosphide ( Cd3P2), zinc phosphide (Zn3P2), cadmium arsenide (Cd3As2), zinc arsenide (Zn3As2), zinc oxide (ZnO), aluminum nitride (AlN), aluminum phosphide (AlP), aluminum arsenide (AlAs), aluminum antimonide (AlSb), gallium nitride (GaN), gallium phosphide (GaP), gallium arsenide (GaAs), gallium antimonide (GaSb), iron sulfide (FeS2), titanium oxide (TiO2), bismuth sulfide (Bi2S Nanocrystals may be composed of bismuth selenide (BiSe), bismuth telluride (BiTe), molybdenum sulfide (MoS), tungsten sulfide (WS), vanadium oxide (VO), cesium lead chloride (CsPbCl), cesium lead bromide (CsPbBr), cesium lead iodide (CsPbI), methylammonium lead iodide or MAPI (CHNHPbI), formamidine lead iodide or FAPI (NHPbI), alloys or heterostructures thereof. Such nanocrystals may be spherical or tetrahedral in shape, or in the form of platelets, rods, wires, tripods, etc. Layer 4 may then be deposited by spin coating from a solution of the nanocrystals used. In this solution, the nanocrystals may be coated with ligands such as carboxylic acids, amines, thiols, or phosphines. Alternatively, S2- (sulfide), OH - (hydroxide), HS - (hydrosulfide), Se 2- (Selenide), NH2 - (amide), Te 2- (Tellurium), SCN - (thiocyanate), Cl - (chloride), Br - (Bromide), I - (iodide), Cd 2+ (Cadmium), NH4 + (ammonium), Hg 2+ (mercury), Zn 2+ (Zinc), and Pb 2+ It may be coated with an ionic ligand such as (lead).

[0045] In another embodiment, the nanocrystals used to form the photoconductive film are coated with a mixture of organic and inorganic ligands, such as mercaptoethanol and mercuric chloride (HgCl2), solubilized in dimethylformamide.

[0046] Typically, the layer of photoconductive material 4, in addition to filling the inter-electrode separation gap, may have a thickness e4 of approximately 80 nm measured parallel to direction D1 over electrode portions 3a, 3b, and 3c. Depending on the photoconductive material used, the electrical carriers may be approximately 10 -4 cm 2 .V -1 .s -1 (square centimeter per volt per second) ~ approx. 50 cm 2 .V -1 .s -1 between about 10 -3 cm 2 .V -1 .s -1 ~about 10cm 2 .V -1 .S -1Its optical refractive index may be between 1 and 4, more particularly between 1.3 and 3. The layer 4 of photoconductive material may then have an absorption between 200 nm and 15 μm, preferably between 1 μm and 5 μm, and even more preferably between 1 μm and 2.5 μm, and a mobility of 100 cm -1 ~10,000cm -1 Between 1,000 cm and 1,000 cm -1 ~5,000cm -1 The absorption coefficient value per unit thickness of the layer 4 between

[0047] In the photodetector 100, the separation gap between the electrode portions 3a and 3b on the one hand and the electrode portions 3b and 3c on the other hand are of essential importance to the operation of the photodetector. Each is a Fabry-Perot cavity with a vertical axis, i.e., the propagation direction of its standing wave component is parallel to direction D1. In the figure, FP1 refers to the Fabry-Perot cavity located between electrode portions 3a and 3b, and FP2 refers to the Fabry-Perot cavity located between electrode portions 3b and 3c. In direction D1, each of the Fabry-Perot cavities FP1 and FP2 is bounded on the one hand by metal layer 11 and on the other hand by a linear extension between the upper surfaces of the electrode portions above the inter-electrode separation gap opposite substrate 1. Laterally, i.e., along direction D2, each of the Fabry-Perot cavities FP1 and FP2 is bounded by the edges of the electrode portions. 1a, the space of each Fabry-Perot cavity FP1, FP2 includes a portion of insulating layer 2 aligned with the corresponding inter-electrode separation gap along direction D1, and further includes an inter-electrode gap filling portion made of the photoconductive material used in layer 4. In this case, the phase matching relationship for each Fabry-Perot cavity FP1, FP2 established for two propagation directions parallel to direction D1 but with opposite orientations takes into account the overlap of insulating layer material 2 and the photoconductive material.

[0048] Additionally, the two Fabry-Perot cavities FP1 and FP2 have different widths measured parallel to the direction D2. For example, the width of the resonator FP1, designated W1, may be 400 nm, and the width of the resonator FP2, designated W2, may be 200 nm. However, because the width of each resonator contributes to the effective values ​​of the refractive indices involved in the phase-matching relationship for these resonators FP1 and FP2, the two resonators FP1 and FP2, when viewed separately, have their own resonant wavelength values, known as individual resonant wavelength values, which are different. The width of the electrode portion 3b between the two resonators FP1 and FP2 is designated r1. For the embodiment shown in FIG. 1a, r1 may be equal to 200 nm.

[0049] In the variant shown in FIG. 1b, the layer of photoconductive material 4 is discontinuous and has the same thickness where it is located in each of the resonators FP1 and FP2 and where it is located over the electrode portions 3a, 3b, and 3c. The insulating layer 2 is also continuous over the entire surface S of the photodetector 100 and has a thickness e2 that may also be equal to 50 nm. The thickness e3 of each electrode portion 3a, 3b, and 3c may also be equal to approximately 100 nm, and the thickness e4 of the layer of photoconductive material 4 may be equal to approximately 80 nm everywhere. The portions of the layer 4 disposed in each of the resonators FP1 and FP2 are also in contact with the adjacent electrode portions. The portions of the layer 4 disposed in the resonator FP1 are in contact with the electrode portions 3a and 3b, and the portions of the layer 4 disposed in the resonator FP2 are in contact with the electrode portions 3b and 3c. The values ​​of widths W1, W2, and r1 may remain the same as those cited with respect to FIG. 1a.

[0050] The embodiment of FIG. 1c corresponds to the embodiment of FIG. 1b by removing the insulating layer 2 inside each of the resonators FP1 and FP2. This selective removal of material from the insulating layer 2 can be performed by any method well known to those skilled in the art, and therefore need not be described here. The following values ​​can be used: e2 = 120 nm, e3 = 70 nm, and e4 = 140 nm. Meanwhile, the values ​​of W1, W2, and r1 remain the same as in the embodiments of FIGS. 1a and 1b. For the thickness values ​​just given, the portion of the layer 4 disposed in each of the resonators FP1 and FP2 is still in contact with the adjacent electrode portion. In the embodiment shown in FIG. 1c, the metal layer 11 of the substrate 1 is in contact with the portion of the photoconductive material 4 disposed in each of the resonators FP1 and FP2. As a result, in addition to the electrode portions 3a, 3b, and 3c, the metal layer 11 can be used as an additional electrode portion. The advantages of adding additional electrodes in this manner, in particular, will be explained later in this specification.

[0051] Finally, in the embodiment shown in FIG. 1d, the inter-electrode gap between electrode portions 3a and 3b of resonator FP1 and between electrode portions 3b and 3c of resonator FP2 is filled with a planarizing resin up to the upper surfaces of electrode portions 3a, 3b, and 3c. A layer of photoconductive material 4 has parallel surfaces and, together with resin portion 5, continuously covers electrode portions 3a, 3b, and 3c. Insulating layer 2 may also be continuous across the entire photodetector 100. For the embodiment of FIG. 1d, the following values ​​may be used: e2 = 50 nm, e3 = 130 nm, e4 = 140 nm, W1 = 400 nm, W2 = 1050 nm, and r1 = 725 nm. Layer 4 may be composed of a graphene sheet.

[0052] For the embodiment shown in FIG. 1b and associated figures, and when the photoconductive material of layer 4 is mercury telluride (HgTe), the Fabry-Perot cavity FP1 has an effective individual resonant wavelength value λ1 equal to 1650 nm (nanometers) and an individual resonant quality factor Q1 equal to approximately 5 for incident radiation R in the direction of surface S, and the Fabry-Perot cavity FP2 has an individual resonant wavelength value λ2 equal to approximately 1550 nm and an individual resonant quality factor Q2 equal to approximately 5. The individual resonant ranges of cavity FP1 [λr1·(1−3 / Q1);λr1·(1+3 / Q1)] are [660 nm; 2640 nm], and the individual resonant ranges of cavity FP2 [λr2·(1−3 / Q2);λr2·(1+3 / Q2)] are [620 nm; 2480 nm]. Therefore, these two intervals overlap between 660 nm and 2480 nm. Similar individual resonances exist for the embodiments of Figures 1a, 1c, and 1d.

[0053] Generally speaking, the electrode portion 3b separating the two Fabry-Perot cavities FP1 and FP2 has a width, measured along the direction D2, denoted r1, which is small enough for these two cavities to be coupled. Under the conditions just described with respect to FIG. 1b, and again when the photoconductive material of layer 4 is lead sulfide (PbS), the two Fabry-Perot cavities FP1 and FP2 exhibit a coupled resonance with a resonance wavelength value of approximately 1.55 μm, referred to as the coupled resonance wavelength, and with an associated quality factor of approximately 15, referred to as the coupled resonance quality factor. This coupled resonance occurs due to interference between the following three waves for each monochromatic component of the radiation R: a portion of the radiation R that is reflected at the surface S of the substrate 1, i.e. reflected by the metal layer 11. This portion of the radiation that is reflected only once is marked in the figure with the reference OR0. a first additional wave OR1 resulting from the superposition of several wave components emerging from the Fabry-Perot cavity FP1, at least one of which has traveled back and forth inside the Fabry-Perot cavity FP2. In other words, the amplitude of the additional wave OR1 depends on the coupling between the cavity FP1 and the free space from which the radiation R originates. Additionally, at least one component of this additional wave OR1 propagates in the cavity FP2, making at least one round trip parallel to the direction D1, and then passing through the intermediate space between the two cavity resonators FP1 and FP2 before being retransmitted from free space by the cavity FP1. Additional wave components that may further participate in the formation of the additional wave OR1 may make any combination of successive round trips in the two cavity resonators FP1 and FP2, crossing the intermediate space between the two cavity resonators FP1 and FP2 with each pass between a round trip in one cavity FP1 or FP2 and a round trip in the other cavity before being retransmitted back to free space by the cavity FP1. - a second additional wave OR2 emerging from the Fabry-Perot cavity FP2 and resulting from the superposition of several other wave components, at least one of which has traveled back and forth inside the Fabry-Perot cavity FP1. In other words, the amplitude of the additional wave OR2 depends on the coupling between the cavity FP2 and the free space from which the radiation R originates. Additionally, at least one component of the additional wave OR2 propagates in the cavity FP1, making at least one round trip parallel to the direction D1, and then passing through the intermediate space between the two cavity resonators FP1 and FP2 before being retransmitted by the cavity FP2 to free space. As in the case of the additional wave OR1, other additional wave components that may further participate in the formation of the additional wave OR2 may make any combination of round trips in the two cavity resonators FP1 and FP2, crossing the intermediate space between the two cavity resonators FP1 and FP2 with each pass between a round trip in one of the cavity resonators FP1 or FP2 and a round trip in the other cavity, before being retransmitted by the cavity FP2 to free space.

[0054] The two additional waves OR1 and OR2 result from coupling between the two Fabry-Perot structures FP1 and FP2. Then, for a specific value of the radiation wavelength R, the reflected wave OR0, the first additional wave OR1, and the second additional wave OR2 form constructive interference that serves to constitute the overall reflected wave OR, which is the purpose of the coupled resonance. When the wavelength of the radiation R is equal to the wavelength value of the coupled resonance, the absorption coefficient of the photodetector 100 is substantially equal to 1, and is less than 0.2 outside the coupled resonance range. The criterion for sufficient coupling between the resonators FP1 and FP2 for the photodetector 100 of Figures 1a-1d is that the sum of the widths W1 + r1 + W2 is less than λ c The wavelength is below the value of the combined resonant wavelength, denoted as

[0055] Each of the photodetectors 100 in FIGS. 1a-1d can be repeated several times in direction D2 to form a repeating pattern M with a repeating pitch denoted p. This results in a new photodetector 101 consisting of several elementary photodetectors 100 arranged electrically parallel. FIG. 2 shows such a photodetector 101 consisting of five elementary photodetectors 100 associated with electrode portions 3a / 3c. All of the electrode portions 3a / 3c and 3b extend longitudinally in direction D3. The electrode portions 3a / 3c belong to electrode 31 of the resulting photodetector 101, and the electrode portion 3b belongs to electrode 32. By way of example, the repeating pitch p inside the photodetector 101 can be equal to 1 μm when the width r2 of each electrode portion 3a / 3c in direction D2 is equal to 200 nm, or when W1=400 nm, W2=200 nm, and r1=200 nm. In this case, the photodetector 101 may have a lateral dimension L of the order of 6 μm in directions D2 and D3. Such a photodetector 101 generates a photodetection current that is larger than that of each of the elementary photodetectors 100, in a ratio substantially equal to the number of elementary photodetectors 100 grouped together in the photodetector 101.

[0056] The diagram in Figure 3a shows the spectral absorption of a photodetector 101 composed of a large number of repeating patterns M when this pattern is the basic photodetector 100 of Figure 1b. For this example, the following values ​​were adopted: r1 = r2 = 200 nm, W1 = 400 nm, W2 = 200 nm, p = 1 μm, e2 = 50 nm, e3 = 100 nm, and e4 = 80 nm. The value of the combined resonant wavelength λ c remains substantially equal to 1.5 μm, resulting in a value of the coupled resonance quality factor Q equal to approximately 15 c In the diagram of FIG. 3a, the horizontal axis displays wavelength values ​​for monochromatic radiation R, labeled λ and expressed in micrometers (μm), and the vertical axis displays spectral absorption values, labeled A and expressed in percent (%). The spectral absorption is determined by the value of the combined resonance wavelength λ c is higher than 80%, and the coupling resonance range [λ c ·(1-3 / Q c );λ c (1+3 / Q c ) is lower than 20%. In addition, when the incidence of radiation R on the plane of directions D1 and D2 changes by ±25° (degrees) with respect to direction D1, the value of the combined resonant wavelength λ c shows a change of less than 0.1 μm in absolute value. At the same time, the coupled resonant wavelength λ c The absorption value A(λ c ) indicates a change of less than 10%. c and A(λ c Such small changes in the value of λ ) give the photodetector 101 a large angular tolerance in light detection efficiency. Finally, the combined resonant wavelength λ c varies only slightly with the number of elementary photodetectors 100 arranged in parallel to form the photodetector 101. Between five and an infinite number of elementary photodetectors 100 it varies by approximately 0.025 μm.

[0057] Generally, a photodetector compatible with the present invention may have the following additional features: The photodetector may be effective for a wavelength λ of radiation R between 200 nm and 15 μm, more particularly between 1 μm and 5 μm, and especially between 1 μm and 2.5 μm, depending on the photoconductive material used. - The photodetection current is 1μA.W when expressed per unit of radiation output R. -1 (microamperes per watt) ~ 1kA.W -1 (kiloamperes per watt), more specifically 1mA.W -1 (milliamperes per watt) ~5A.W -1 (microamperes per watt), preferably 100mA.W -1 ~2A.W -1 It can be between. The photodetector response time may be less than 40 ms (milliseconds), more particularly less than 1 ms, preferably less than 10 μs (microseconds). - The specific detectivity of the photodetector is 10 8 cm Hz 1 / 2 ·W -1 (centimeter times hertz to the power of one-half per watt, also known as Jones) 9 cm Hz 1 / 2 ·W -1 Higher, preferably 10 10 cm Hz 1 / 2 ·W -1 Higher. The operating temperature of the photodetector may be higher than 80K (Kelvin), preferably higher than 150K, and even more preferably higher than 200K.

[0058] The photodetection efficiency of the photodetector according to the invention is such that the incident radiation R is cWhen the wavelength λ is 1000 s, the photodetector is provided by two Fabry-Perot cavities EP1 and EP2 coupled to each other. For this wavelength, the photodetector focuses radiation on whichever of the two cavities has the larger width W1 or W2. For the photodetector of FIG. 1b, the radiation is more precisely focused on the top of the photoconductive material portion inside the resonator FP1 that is farthest from the substrate 1. For the photodetector of FIG. 1c, the radiation is focused both on the top of the photoconductive material portion of the resonator FP1 and on the lower corners of this portion. Generally speaking, the energy density of the radiation is multiplied by a factor of more than 10, or even more than 15, at these points in the photoconductive material portion of the resonator that are the widest, relative to the energy density of the radiation in the optical path before reaching the photodetector. This focusing of the radiation generates a much larger number of charges in the photoconductive material, thereby increasing the efficiency and sensitivity of photodetection.

[0059] In the photodetector according to FIG. 1c, the surface S of the substrate 1 is electrically conductive and in contact with the photoconductive material portions 4 housed in the resonators FP1 and FP2, while being electrically insulated from the electrodes 31 and 32. A photodetection current can then be collected by any two of the electrodes 31, 32, and the conductive layer 11, which acts as an additional electrode. A reconfiguration circuit can be used to select the two electrodes actually used to collect the photodetection current when the photodetector is in use. Such a reconfiguration circuit can connect the electrode 31, electrode 32, or conductive layer 11 that is not used to collect the photodetection current to one of the other two, or leave it at a floating potential.

[0060] The photodetector can further be complemented by a biasing circuit arranged to apply an adjustable voltage between the two electrodes used to collect the photodetection current. The use of such a biasing circuit is well known to those skilled in the art and therefore does not need to be described in more detail here. Generally speaking, for the same electrode pair used, the efficiency of collecting the charge generated by the radiation R in the photoconductive material layer 4 increases with the absolute value of the biasing voltage. A further advantage of the photodetector according to the invention lies in the fact that the biasing voltage value applied between the electrodes used can be less than 10 V, or even less than 1 V. Such a voltage value can therefore be transmitted by an integrated electronic circuit implemented using one of the existing technologies. The electric field generated by the biasing circuit in the photoconductive material is in the range of 0 to 100 kV cm. -1 (kilovolts per centimeter), more specifically 20 kV cm -1 It may be less than.

[0061] The diagram of Figure 3b shows the spectral detection response of the photodetector 101 according to Figures 1b and 2. The horizontal axis of this diagram is marked σ and is expressed in cm -1 The wave number is plotted on the vertical axis, which is equal to the reciprocal of the wavelength λ, expressed as ph The photodetector current value expressed in arbitrary units (au) is displayed as ". The two electrodes used to collect this photodetection current are electrodes 31 and 32 shown in FIG. 2, and the conductive layer 11 is placed at a floating potential. A variable bias voltage is further applied between the two electrodes 31 and 32, and its value can be seen to be between 10 mV (millivolts) and 1000 mV by referring to the curves in the figure. When this bias voltage is zero or a low value, the photodetector has a detection efficiency resulting from the coupling resonance described above, which is approximately 6500 cm -1 The wavenumber σ value of 1000 mV is included as the detection maximum. This detection maximum corresponds to the focusing of the radiation in the widest Fabry-Perot cavity, i.e., cavity FP1 in Figures 1b and 2. As the bias voltage is increased, an additional detection contribution is observed, the maximum of which is approximately 5800 cm -1At values ​​of 10 mV to 1000 mV for the bias voltage, the axis system of the diagram in Figure 3b is 5800 cm -1 This additional contribution, which varies from 0.12 to 1.0 at 1000 mV, corresponds to a more efficient charge collection in the photoconductive material portion 4 disposed in the narrowest Fabry-Perot cavity, i.e., cavity FP2 in Figs. 1b and 2. -1 The spectral positions of correspond substantially to the individual resonances of the Fabry-Perot cavity FP2 that generate the focusing of the radiation.

[0062] In the photodetector 101 of Fig. 4a, the electrode portions intermediate the Fabry-Perot cavities FP1 and FP2 are connected to the electrodes 31 and 32, so that for each resonator FP2, the two electrode portions 3b and 3c closest to this resonator are short-circuited to each other and connected alternately between the two successive resonators FP2 to either the electrode 31 or the electrode 32. The coupled resonators again have the structure shown in Fig. 1b, where the width W2 of the resonator FP2 is smaller than the width W1 of the resonator FP1. The photodetection current is again collected between the two electrodes 31 and 32, and a variable bias voltage is applied between them. Under these conditions for the collection of the photodetection current, its spectral change is as shown in the diagram of Fig. 4b. Due to the electrode configuration, the charge generated by radiation R in the (widest) resonator FP1 is approximately 6500 cm -1 The peak detected at approximately 6000 cm is efficiently collected. -1 The detected peak at corresponds to the photoconductive material 4 outside the resonator FP1. Both peaks are strongly amplified by the bias voltage.

[0063] Conversely, in the photodetector 101 of FIG. 5A, which also has the configuration of pattern M shown in FIG. 1b, it is the electrode portions 3a and 3b adjacent to each resonator FP1 that are shorted to each other and connected to one of the two electrodes 31 and 32 alternately between the two successive resonators FP1. As in the previous example, the resonator FP1 has a width W1 that is larger than the width W2 of the resonator FP2. The photodetection current is still collected between the two electrodes 31 and 32, and a variable electrical bias voltage is also applied between them. Under these new collection conditions for the photodetection current, its spectral change is that shown in the diagram of FIG. 5b. Due to the electrode configuration, only the charge generated by the radiation R in the (narrowest) resonator FP2 is collected. The detection peak is then mainly at approximately 6000 cm. -1 and is strongly amplified by the bias voltage.

[0064] FIG. 6 is a cross-sectional view of another photodetector according to the present invention. One pattern of this other photodetector is composed of more than two, for example, three, juxtaposed Fabry-Perot cavities with different cavity widths within each pair. These three Fabry-Perot cavities are labeled FP1, FP2, and FP3, with respective cavity widths W1, W2, and W3. For example, width W3 is larger than width W2, which in turn is larger than width W1. The electrode portions are labeled 3a, 3b, 3c, and 3d, with the other reference numerals having the same meanings as above. On the one hand, the width of electrode portion 3b is small enough to allow Fabry-Perot cavities FP1 and FP2 to be coupled according to the present invention, and on the other hand, the width of electrode portion 3c is similarly small enough to allow Fabry-Perot cavities FP2 and FP3 to be coupled. Thus, a first photodetection current that can be collected between electrode portions 3a and 3b has a sensitivity spectrum based on the wavelength of the radiation to be detected resulting from coupling between Fabry-Perot cavities FP1 and FP2, and a second photodetection current that can be collected between electrode portions 3c and 3d has a different sensitivity spectrum resulting from coupling between Fabry-Perot cavities FP2 and FP3. A third photodetection current, additional to the two previously mentioned, can be collected between electrode portions 3b and 3c, with its sensitivity spectrum resulting from coupling between Fabry-Perot cavities FP2 and each of the other two Fabry-Perot cavities FP1 and FP3. It may then be advantageous to adjust the electrical bias voltage applied between the two electrode portions 3b and 3c to adjust the sensitivity spectrum of the third photodetection current. Because the first, second, and third photodetection currents are collected simultaneously, three separate pieces of information about the spectral composition of the detected radiation are obtained.

[0065] In fact, as can be seen from the above description, the numerous electrical connection modes of the electrode parts, the various possibilities for selecting the electrode pairs used to collect the photodetection current, and the bias voltages allow the photodetector to be reconfigured to modify its spectral sensitivity characteristics, so that the photodetector can be adapted based on its application or can measure the same radiation in several detection modes.

[0066] FIG. 7 shows an image sensor according to the present invention. This image sensor, generally designated 110, comprises a matrix array of photodetectors 100 or 101, all of the same model, e.g., one of the models described above. Specifically, this photodetector matrix array can be between 4x4 and 16384x12288 photodetectors, more specifically between 320x200 and 16384x12288 photodetectors. The pitch of the photodetectors in this matrix array can be between 1 μm and 1 cm, preferably less than 100 μm. When the photoconductive material is deposited using a spin-coating deposition method, the photodetectors can be directly formed in the readout circuit of the image sensor 110. For example, this readout circuit can be fabricated using CMOS technology. This readout circuit, designated 102 in FIG. 7, forms the base substrate 10 of all the photodetectors 100 / 101. In this case, a set of electrical connection layers 103 may be interposed between the photodetectors 100 / 101 and the readout circuit 102. These electrical connections connect the electrode portions of each photodetector to a readout cell dedicated to that photodetector and housed in the readout circuit 102. Additionally, as introduced above, a reconstruction circuit and an electrical biasing circuit may advantageously be integrated into the readout circuit 102. These are marked in Figure 7 with reference numeral 104 for the reconstruction circuit and reference numeral 105 for the electrical biasing circuit.

[0067] The method for fabricating a photodetector according to the present invention will now be described in detail by way of example. First, a method for obtaining a colloidal solution precursor is presented along with three examples of photoconductive nanocrystal colloidal solutions. [Example]

[0068] TOP: Te precursor molar solution (1M) In a first tricol flask, 6.35 g (grams) of tellurium (Te) powder was mixed with 50 mL (milliliters) of TOP, or trioctylphosphine. The flask was placed under vacuum at room temperature for 5 minutes, then heated to 100°C. Degassing was continued at this temperature for an additional 20 minutes. The atmosphere was replaced with nitrogen (N2), and the temperature was adjusted to 275°C. The solution was stirred until a clear orange color was obtained. The flask was then cooled to room temperature, and the color changed to yellow. Finally, the solution was transferred to a nitrogen-filled glove box for storage.

[0069] Example 1: 6000 cm -1 Synthesis of HgTe nanocrystals with a band gap of 1000 Å In a 100 mL tricol flask, 540 mg (milligrams) of mercuric chloride (HgCl2) and 50 mL of oleylamine were degassed under vacuum at 110 °C. At this stage, the solution was yellow and transparent. Meanwhile, 2 mL of TOP:Te precursor molar solution (1 M) was extracted from the glovebox and mixed with 8 mL of oleylamine. The atmosphere was replaced with nitrogen, and the temperature was set to 57 °C. The TOP:Te solution was rapidly injected into the tricol flask and thickened after 1 minute. After 3 minutes, 10 mL of a DDT or dodecanethiol solution in toluene (10% by volume of DDT) was further injected into the tricol flask, and a cold water bath was used to rapidly reduce the temperature. The contents of the second tricol flask were divided into four tubes, to which methanol was added. After centrifugation, the formed precipitate was redispersed in a single tube with 10 mL of toluene. The solution was precipitated twice with ethanol. Again, the precipitate formed was redispersed in 8 mL of toluene. In this step, the nanocrystals were centrifuged in pure toluene to remove the lamellar phase. The solid phase was removed, and the supernatant was filtered using a 0.2 μm polytetrafluoroethylene (PTFE) filter.

[0070] Example 2: 4000 cm -1 Synthesis of HgTe nanocrystals with a band gap of 1000 Å In a 100 mL tricol flask, 540 mg of mercuric chloride (HgCl2) and 50 mL of oleylamine were degassed under vacuum at 110 °C. At this stage, the solution was yellow and transparent. Meanwhile, 2 mL of TOP:Te precursor molar solution (1 M) was extracted from the glovebox and mixed with 8 mL of oleylamine. The atmosphere was replaced with nitrogen, and the temperature was set to 86 °C. The TOP:Te solution was rapidly injected into the tricol flask and thickened after 1 minute. After 3 minutes, 10 mL of a solution of DDT, or dodecanethiol, in toluene (10% by volume of DDT) was further injected into the tricol flask, and a cold water bath was used to rapidly reduce the temperature. The contents of the tricol flask were divided into four tubes, to which methanol was added. After centrifugation, the formed precipitate was redispersed in a single tube with 10 mL of toluene. The solution was precipitated twice with ethanol. Again, the formed precipitate was redispersed in 8 mL of toluene. In this step, the nanocrystals were centrifuged in pure toluene to remove the lamellar phase, the solid phase was removed, and the supernatant was filtered using a 0.2 μm polytetrafluoroethylene (PTFE) filter.

[0071] Example 3: 6000 cm -1 Synthesis of PbS nanocrystals with a band gap of 1000 Å In a tricol flask, 300 mg of lead chloride (PbCl2) and 7.5 mL of oleylamine are degassed at room temperature and then placed at 110 °C for 30 minutes. Meanwhile, 30 mg of sulfur powder (S) is mixed with 7.5 mL of oleylamine by stirring under ultrasound until completely dissolved, resulting in a clear orange solution. This sulfur solution is then rapidly added to the tricol flask at 160 °C under a nitrogen atmosphere. After 15 minutes, the reaction is quickly stopped by adding 1 mL of oleic acid and 9 mL of hexane. The nanocrystals are precipitated with ethanol, centrifuged, and redispersed in toluene. This washing step is repeated several times. The nanocrystal solution in toluene is then centrifuged to remove any unstable phases. The supernatant is precipitated with methanol and then redispersed in toluene. Finally, the solution of PbS nanocrystals in toluene is filtered using a 0.2 μm polytetrafluoroethylene (PTFE) filter.

[0072] The fabrication of a coupled Fabry-Perot cavity photodetector according to the present invention will now be described and includes the following steps 1-5.

[0073] Step 1: Forming a reflective layer Silica-coated silicon substrates measuring 12 mm x 14 mm are cleaned with acetone and isopropanol. They are then placed in an acetone bath and ultrasonically exposed for 5 minutes. They are then rinsed with acetone and isopropanol and dried with a nitrogen flow. These substrates are then cleaned with oxygen (O2) plasma for 5 minutes. An adhesion promoter, such as TI Prime® supplied by MicroChemicals®, is applied by spin coating at 4000 revolutions per minute (rpm) for 30 seconds and baked at 120°C for 2 minutes. A resin, such as AZ 5214, is then applied by spin coating at 4000 rpm for 30 seconds and annealed at 110°C for 90 seconds. The substrates are then exposed to ultraviolet (UV) radiation through a mask for 1.5 seconds, followed by annealing at 125°C for 2 minutes. A second UV radiation exposure is then performed without a mask, for example, for 40 seconds. The resin is developed in a developer such as AZ 726 MIF for 30 seconds, followed by a 15-second rinse in deionized water. Each substrate is then cleaned with oxygen plasma for 5 minutes. A first layer of 3 nm thick titanium (Ti) is deposited, followed by a second layer of 80 nm thick gold (Au), preferably with sample rotation, using a vacuum evaporator. Finally, a third layer of 5 nm thick aluminum (Al) is deposited, again using a vacuum evaporator. The resin is then removed by immersing each sample in acetone for 1 hour. The substrate is then rinsed with acetone and isopropanol and dried in a nitrogen flow. The resulting mirror surface on each silicon-based substrate is intended to form the reflective layer 11 mentioned in connection with Figures 1a-1d.

[0074] Step 2: Depositing an insulating layer Using ALD (atomic layer deposition) methods, a 50 nm thick layer of alumina (Al2O3) is deposited on each substrate, which is intended to form the insulating layer 2 mentioned with reference to Figures 1a-1d.

[0075] Step 3: Formation of the microscopic electrical contact zone The substrates are rinsed with acetone and isopropanol and dried with a nitrogen flow. An adhesion promoter, such as TI Prime® from MicroChemicals®, is applied by spin coating at 4000 rpm for 30 seconds and baked at 120°C for 2 minutes. AZ 5214 resin is then applied by spin coating at 4000 rpm for 30 seconds and annealed at 110°C for 90 seconds. Each substrate is then exposed to UV radiation through a mask for 1.5 seconds and annealed at 125°C for 2 minutes. A second exposure to UV radiation is then performed without a mask for 40 seconds. The resin is developed in AZ 726 MIF developer for 30 seconds and rinsed with deionized water for 15 seconds. Each substrate is then cleaned in an oxygen plasma for 5 minutes. A 3 nm thick layer of titanium, followed by another 150 nm thick layer of gold, is deposited by thermal evaporation, preferably with substrate rotation. The resin is then removed by rinsing the sample with acetone for 1 hour. The substrate is then rinsed with acetone and isopropanol and dried under nitrogen flow.

[0076] Step 4: Electron beam lithography The substrate is rinsed with isopropanol and then dried under nitrogen flow. A layer of A6 purity polymethyl methacrylate (PMMA) is applied by spin coating at 400 rpm for 5 seconds, then 4000 rpm for 30 seconds, and baked at 180 °C for 2 minutes. A 10 nm layer of aluminum is then evaporated using an electron beam evaporator. The aluminum evaporation rate is 0.1 nm s -1 (nanometers per second) and sample rotation is started in the deposition system.

[0077] Each substrate is then transferred to an electron lithography tool using a current of 12 pA (picoamperes) and a density of 200 μC.cm -2Electron lithography is performed with a total dose of 0.1 nm·s (microcoulombs per square centimeter). The substrates are then immersed in a solution of 40 g of potassium hydroxide (KOH) in 100 mL of water for 15 seconds, rinsed with water, and dried in a nitrogen stream, thus removing the aluminum layer. The PMMA resin is developed for 45 seconds using a solution of 1:3 by volume of methyl isobutyl ketone (MIBK):isopropanol (IPA), and rinsed with pure isopropanol for 20 seconds. Each substrate is then cleaned in an oxygen plasma for 2 minutes. They are then transferred to an electron deposition system, each with a dose of 0.1 nm·s. -1 and 0.2 nm·s -1 A 3 nm thick titanium layer was deposited, followed by an 80 nm thick gold layer, at a deposition rate of 1000 sq. m / s. The resin was then removed by immersing each substrate in acetone at 40°C for at least 2 hours. The metal portions thus formed on each substrate are the electrodes 31 and 32 mentioned in relation to Figures 2, 4a, and 5a. The substrates were then observed under a scanning electron microscope with parameters of 8 mm and 5 kV, and the electrodes were electrically controlled.

[0078] Step 5: Nanocrystal precipitation 6000cm -1 A 1 mL solution of HgTe nanocrystals in toluene with a band gap of 720 meV (millielectronvolts) and an optical density of 0.9 at 400 nm was mixed with 1 mL of the ligand exchange solution, which consisted of 9 mL of dimethylformamide, 1 mL of mercaptoethanol, and 15 mg of HgCl2. These successive washing steps were performed using hexane. The nanocrystals were then precipitated with toluene. After centrifugation, the supernatant was removed and the pellet was dried under vacuum for 15 minutes. The pellet was then redispersed in 170 μL of pure dimethylformamide. The ink was then applied to each substrate by spin coating at 2000 rpm (acceleration 200 rpm / s, spin time 120 seconds). The substrates were previously exposed to oxygen plasma for 4 minutes.

[0079] It goes without saying that the invention may be reproduced by modifying the second aspect of the embodiment detailed above while retaining at least some of the cited advantages. In particular, all numerical values ​​given are for illustrative purposes only and may be varied depending on the application in question. [Explanation of symbols]

[0080] 1 board 2. Insulation layer 3a, 3b, 3c electrode part 31, 32 electrodes 4. Photoconductive materials 5 Resin part 10 Base part 11 Metal layer 100, 101 Photodetector 102 readout circuit 103 Electrical Connection Layer Set 104 Reconfigurable circuit 105 Bias Electrical Circuit 110 Photodetector D1, D2, D3 direction e2 Insulation layer thickness e3 Electrode thickness e4 photoconductive material layer thickness FP1, FP2 Fabry-Perot resonators L horizontal dimension M Repeating Pattern OR0 reflected wave OR1 1st additional wave OR2 2nd additional wave p Repeated pitch R Radiation r1 Width of electrode portion 3b Width of r2 electrode part 3a / 3c S top surface W1 Width of resonator FP1 W2 Width of resonator FP2

Claims

1. A photodetector (100, 101), a substrate (1) that is reflective to the electromagnetic radiation incident on the photodetectors (100, 101); - electrode portions (3a, 3b, 3c) supported by said substrate (1) and arranged at a common distance from said substrate, referred to as upper surfaces, and each having a surface facing away from said substrate; - portions of electrically insulating material arranged between the electrode portions (3a, 3b, 3c) and the substrate (1) so as to electrically insulate each electrode from the substrate; at least one photoconductive material portion arranged in electrical contact with two of the adjacent electrode portions (3 a, 3 b, 3 c), wherein it is envisaged that at least two of the electrode portions (3 a, 3 b, 3 c) and the substrate (1) will collect a photodetection current when the photodetector (100, 101) is in use; Equipped with a first (3a) and a second (3b) of the adjacent electrode portions (3a, 3b, 3c) defining a space therebetween, parallel to the substrate (1), through which the radiation passes so as to be reflected by the substrate when the photodetector (100, 101) is in use, forming a first Fabry-Perot cavity (FP1) between the level of the substrate and the upper surface of the electrode portions; the second electrode portion (3b) and a third (3c) of the electrode portions (3a, 3b, 3c) arranged on the side of the second electrode portion opposite the first electrode portion define another space therebetween, parallel to the substrate (1), through which the radiation also passes to be reflected by the substrate when the photodetector (100, 101) is in use, forming a second Fabry-Perot cavity (FP2) between the substrate and the level of the upper surfaces of the electrode portions, the first and second Fabry-Perot cavities (FP1, FP2) are designed to generate standing wave components that propagate perpendicular to the substrate (1) when the photodetector (100, 101) is in use; The photodetector (100, 101) has the following features (1) to (3): (1) The width of the first Fabry-Perot cavity (FP1) measured between the first and second electrode portions parallel to the substrate (1) is different from the width of the second Fabry-Perot cavity (FP2) measured between the second and third electrode portions parallel to the substrate, so that the first and second Fabry-Perot cavities have respective individual resonant wavelength values ​​that are effective for radiation incident on a photodetector (100, 101), and the respective individual resonant wavelength values ​​are different, and the respective individual resonant quality factor values ​​of the first and second Fabry-Perot cavities are each spaced apart by the following individual resonant spacing: [λ ｒｉ ・(1-3 / Q ｉ ) ; λ ｒｉ ・(1+3 / Q ｉ ) )] have overlapping portions, where i is equal to 1 or 2 and refers to the first or second Fabry-Perot cavity, respectively; ｒｉ and Q １ are the wavelength and quality factor values ​​of individual resonances of the Fabry-Perot cavity i, respectively; (2) the sum of the width of the first and second Fabry-Perot cavities (FP1, FP2) and the width of the second electrode portion (3b) measured parallel to the substrate (1) between the spaces of the first and second Fabry-Perot cavities is a first wave resulting from reflection of incident radiation on said substrate (1); a second wave emerging from the first Fabry-Perot cavity (FP1) resulting from the superposition of several wave components, at least one of which makes at least one round trip within the space of the second Fabry-Perot cavity (FP2); a third wave emerging from the second Fabry-Perot cavity (FP2) resulting from another superposition of several other wave components, at least one of which makes at least one round trip within the space of the first Fabry-Perot cavity (FP1); and adapted to provide coupling between the first and second Fabry-Perot cavities by being below a resonant wavelength value for coupling known as a coupling resonant wavelength that is effective for radiation incident on the photodetector (100, 101) resulting from interference between at least three waves including (3) the photoconductive material is absorptive at the combined resonant wavelength, and the photoconductive material portion is disposed in or on at least one of the spaces of the first and second Fabry-Perot cavities (FP1, FP2); characterized by: Photodetector (100, 101).

2. The photodetector (100, 101) of claim 1, wherein the substrate (1) comprises a photodetector readout circuit (102).

3. 3. A photodetector (100, 101) according to claim 1 or 2, wherein the electrically insulating material portion is part of a continuous layer (2) of insulating material that extends across the space of the first and second Fabry-Perot cavities (FP1, FP2) in addition to extending between the substrate (1) and each electrode portion (3a, 3b, 3c).

4. 3. A photodetector (100, 101) according to claim 1 or 2, wherein the substrate (1) is also in contact with the photoconductive material portions in addition to the first, second and third electrode portions (3a, 3b, 3c) so as to form additional electrode portions.

5. 5. A photodetector (100, 101) according to any one of claims 1 to 4, further comprising a biasing electric circuit (105) adapted to apply a voltage between two of the electrode portions (3 a, 3 b, 3 c) collecting the photodetection current during use of the photodetector, the biasing electric circuit being further adapted to vary the voltage between two successive uses of the photodetector so as to modify the sensitivity spectrum, in particular the detection sensitivity, of the photodetector.

6. 6. A photodetector (100, 101) according to claim 5, adapted such that the radiation absorption value at at least one wavelength value changes by at least 30%, preferably at least 50%, more preferably at least 90% between a first use of the photodetector in which no voltage is applied between the two electrode portions by the bias electric circuit (105) or the applied voltage is zero, and a second use of the photodetector in which the applied voltage is non-zero.

7. 7. A photodetector (100, 101) according to any one of claims 1 to 6, further comprising a reconfiguration circuit (104) adapted to selectively electrically connect at least two of the electrode portions (3 a, 3 b, 3 c) of the photodetector to the substrate (1) to collect a photodetection current by selected said electrode and substrate portions, wherein selected said electrode and substrate portions are varied between several photodetection current collection modes associated with respective different spectra of photodetector sensitivity to incident radiation.

8. 8. A photodetector (100, 101) according to any one of claims 1 to 7, wherein each portion of the photoconductive material is part of a layer (4) of photoconductive material that extends continuously across the space of the first and second Fabry-Perot cavities (FP1, FP2) and across the electrode portions (3a, 3b, 3c).

9. 9. A photodetector (100, 101) according to any one of claims 1 to 8, comprising a plurality of pairs of coupled first and second Fabry-Perot cavities (FP1, FP2), with first, second and third electrode portions (3a, 3b, 3c) associated with each pair and electrically connected to accumulate a photodetection current arising from each pair when the photodetector is in use.

10. The photodetector (100, 101) according to any one of claims 1 to 9, having lateral dimensions measured parallel to the substrate (1) that are between 1 μm and 1 cm, preferably between 1 μm and 100 μm.

11. 11. The photodetector (100, 101) according to any one of claims 1 to 10, wherein the spacing between the first and second Fabry-Perot cavities (FP1, FP2) together with the width of the second electrode portion are dimensioned such that the combined resonant wavelength is between 1 μm and 12 μm.

12. 12. A photodetector (100, 101) according to any one of the preceding claims, wherein the photoconductive material is selected to have a bandgap that is less than 0.8 eV.

13. 13. A photodetector (100, 101) according to any one of claims 1 to 12, wherein each portion of the photoconductive material is composed of aggregated nanocrystals.

14. An image sensor (110) comprising a matrix arrangement of photodetectors, each photodetector (100, 101) being according to any one of claims 1 to 13.

15. 15. An image sensor (110) as claimed in claim 14, wherein each photodetector (100, 101) is according to claim 9 and has an individual photodetector size, measured in the juxtaposition direction of the pair by the coupled first and second Fabry-Perot cavities (FP1, FP2), that is less than or equal to 10 times the wavelength value of the radiation corresponding to the maximum detection sensitivity of the photodetector.

16. 14. A method for manufacturing a photodetector (100, 101), wherein the photodetector is according to any one of claims 1 to 13, and wherein the photoconductive material portion is obtained by precipitation of a colloidal solution containing nanocrystals of the photoconductive material, followed by drying of the precipitated colloidal solution.

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