Photodetector including coupled Fabry-Perot resonators

Abstract

A photodetector (100) includes Fabry-Perot resonators (FP1, FP2) that are coupled so that radiation to be detected is concentrated in a photoconductive material. In this way, photoconductive nanocrystals deposited from a colloidal solution of the nanocrystals can be used while having high photoelectric detection sensitivity. Thus, a matrix array of such photodetectors can be formed on an image sensor readout circuit while avoiding the need to use intermediate solder balls to connect separate detection circuits to the readout circuit. Moreover, each photodetector may be readily produced using deposition and selective removal processes, and may be reconfigurable to have a variable detection sensitivity spectrum.

Description

Technical Field

[0001] The present invention relates to a photodetector and an image sensor including the photodetector. Background Art

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

[0003] In addition, the cost of infrared imagers also stems from the coupling step between the detection circuit including the light absorbing layer and the readout circuit, which is usually implemented using CMOS technology. This coupling between the two circuits is done through 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 incurs additional costs. In addition, the smaller the pixel size, the more complicated the process. In order to improve image quality, it is desired that the pixel size is small, but the current size (10-15μm) is limited by the coupling step between the two circuits.

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

[0005] In materials such as nanocrystals, a compromise is necessary. The granular nature of nanoparticles means that transport occurs via nearest neighbor hopping. This transport mechanism is associated with lower charge carrier mobility values ​​than in solid materials. The result is a short carrier diffusion length, typically 50nm to 100nm. This diffusion length is shorter than the absorption length of the electromagnetic field, which is several microns. Therefore, transport is only efficient for 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 resonator in the photodetector, the role of which is to concentrate the incident light on a thin layer of the semiconductor, the thickness of which is optimal for charge collection.

[0006] A variety of strategies (metal-insulator-metal cavities, Fabry-Perot resonances, plasma resonators, etc.) have been proposed to enhance light-matter coupling in nanoparticle films, thereby enhancing the absorption of the component. In the paper "Near Unity Absorption in Nanocrystal Based Short Wave Infrared Photodetectors Using Guided Mode Resonators" by Audrey Chu et al., ACS Photonics 6, 2553 (2019), the authors proposed introducing mirrors into the component to allow the incident light to pass through the absorption layer in two ways. This almost doubles the absorption rate. In addition, the authors added gratings to generate optical modes for light propagation along the substrate, which also generates multiple light paths through the film.

[0007] This strategy based on periodic networks has two limitations. The resulting detectors have a strong angular dependence, which is not conducive to integration in imagers. Moreover, 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 is incompatible with the above-mentioned goal of reducing the pixel size. It is therefore of interest to develop new optical resonator geometries that are compatible with the pixel sizes used in imagers and whose angular dependence of response is also reduced.

[0008] It is also known to form radiation absorbing nanostructures, each consisting of a coupled pair of Fabry-Perot resonators. In addition to the individual resonances of each resonator, each pair of coupled resonators exhibits a coupled resonance that produces a value close to unity for the absorption coefficient of the incident radiation. In such coupled Fabry-Perot resonator nanostructures, the two resonators of each pair can each be formed by a groove in the surface of a metal substrate, as described in Ling Guo et al., “Cooperative optical trapping in asymmetric plasmon nanocavity arrays,” Optics Express 31324, Vol. 23, No. 24, November 2015, or in B. Fix et al., “High-quality-factor double Fabry-Perot plasmonic nanoresonator,” Optics Letters, Vol. 42, No. 24, December 15, 2017, pp. 5062-5065. 15, 2017, p. 5062-5065). In these structures, the standing wave component formed in the groove propagates perpendicular to the substrate surface. For this reason, the corresponding Fabry-Perot resonator is said to have a vertical axis. However, in particular from WO 2020 / 002330, other nanostructures that form coupled Fabry-Perot resonators are also known, in which the standing wave component in the resonator propagates parallel to the substrate surface. Therefore, such other Fabry-Perot resonators are said to have a horizontal axis.

[0009] Another important aspect of the present invention is to realize a component whose spectral response is reconfigurable. Typically, the response of an infrared detector is determined by the properties of its active layer. In the case of nanoparticles, the size of the individual building blocks determines the cut-off wavelength. Therefore, changing the cut-off wavelength requires changing the active material. An alternative strategy is to make the spectral response also affected by the presence of an optical resonator. Audrey Chu et al. have demonstrated in ACS Photonics 6, 2553 (2019) that the spectral response of the material can be adjusted by the grating period while keeping the same active material. An additional degree of reconfigurability would be the ability to change the spectral response after the component has been manufactured. This type of active component is currently based on phase change materials or MEMS technology. Recently, Dang et al. demonstrated in an article entitled "Bias Tunable Spectral Response of Nanocrystal Array in a Plasmonic Cavity" in Nano Letters 21, 6671 (2021) that a spectral response shift can be obtained via the application of a voltage. In this article, the effect remains weak.One of the challenges of the present invention is to use this concept to obtain an infrared detector whose spectral response is largely reconfigurable after the component is manufactured.

[0010] Technical issues

[0011] Based on this situation, an object of the present invention is to propose a new photodetector structure which provides high optical absorption and simplifies the manufacture of each photodetector.

[0012] In particular, it may be an object of the invention that the photodetector structure is compatible with the use of photoconductive nanocrystal layers deposited from colloidal solutions.

[0013] A subsidiary object of the invention is to enable each photodetector to have reduced lateral dimensions (typically less than 15 μm, preferably less than 5 μm) to enable high resolution image sensors.

[0014] It is another subsidiary object of the present invention that each photodetector remain effective in detecting radiation whose angle of incidence varies over a wide angular sector.

[0015] Finally, yet another object of the present invention is 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 sequences of use of the photodetector. Summary of the invention

[0016] In order to achieve at least one or another of these objectives, a first aspect of the present invention provides a novel photodetector, the photodetector comprising:

[0017] – a substrate which is reflective to electromagnetic radiation incident on the photodetector;

[0018] - electrode portions, which are supported by the substrate and which have respective surfaces facing away from the substrate, which surfaces are called upper surfaces and are located at a common level spaced from the substrate;

[0019] - portions of electrically insulating material located between the electrode portions and the substrate to electrically insulate each electrode portion from the substrate; and

[0020] - at least a portion of the photoconductive material, the at least a portion being arranged in electrical contact with two adjacent ones of the electrode portions.

[0021] When the photodetector is used, at least two of the electrode parts and the substrate are designed to collect a photodetection current.

[0022] In the photodetector of the present invention, the first electrode portion and the second electrode portion in the adjacent electrode portions define a volume between them, parallel to the substrate, and when the photodetector is in use, radiation penetrates into the volume so as to be reflected by the substrate, forming a first Fabry-Perot resonator between the level of the substrate and the upper surface of these electrode portions. Similarly, the second electrode portion in the electrode portion and the third electrode portion located on the side of the second electrode portion opposite to the first electrode portion define another volume between them, parallel to the substrate, and when the photodetector is in use, radiation also penetrates into the other volume so as to be reflected by the substrate, forming a second Fabry-Perot resonator between the level of the substrate and the upper surface of these electrode portions. In other words, the first Fabry-Perot resonator and the second Fabry-Perot resonator are designed to generate a standing wave component that propagates perpendicular to the substrate when the photodetector is in use. Therefore, according to the terminology of the technician as described above, they are of vertical axis type.

[0023] The photodetector of the present invention also has the following features / 1 / to / 3 / :

[0024] / 1 / A width of the first Fabry-Perot resonator measured parallel to the substrate between the first electrode portion and the second electrode portion is different from a width of the second Fabry-Perot resonator measured between the second electrode portion and the third electrode portion, also measured parallel to the substrate, so that the first Fabry-Perot resonator and the second Fabry-Perot resonator have different respective individual resonant wavelength values ​​effective for radiation incident on the photodetector, and the individual resonance quality factors of these first Fabry-Perot resonators and the second Fabry-Perot resonators have such respective values ​​that on a wavelength axis of the incident radiation, the following individual resonant spacings: [λ ri ·(1-3 / Q i ); ri (1+3 / Q i )] have overlap, where i is equal to 1 or 2 to represent the first Fabry-Perot resonator or the second Fabry-Perot resonator, respectively, and λ ri and Q i are the wavelength and quality factor value of the individual resonance of Fabry-Perot resonator i, respectively. In other words, the two Fabry-Perot resonators have individual resonance wavelengths that are different, but not too far apart. Moreover, the two resonators are distinguished by their respective cavity widths, which is particularly easy to achieve, especially using a mask method;

[0025] / 2 / The sum of the width of the first Fabry-Perot resonator and the second Fabry-Perot resonator and the width of the second electrode portion measured parallel to the substrate between the volume of the first Fabry-Perot resonator and the volume of the second Fabry-Perot resonator is suitable for generating a coupling between the first Fabry-Perot resonator and the second Fabry-Perot resonator, which is achieved by the sum being less than a resonant wavelength value with respect to the coupling, called the coupling resonant wavelength, which is effective for the radiation incident on the photodetector and which is generated by interference between at least three waves, the at least three waves comprising:

[0026] – the first wave generated by the reflection of the incident radiation on the substrate;

[0027] a second wave emerging from the first Fabry-Perot resonator, which results from the superposition of a plurality of wave components, at least one of which has made at least one round trip within the volume of the second Fabry-Perot resonator; and

[0028] a third wave emerging from the second Fabry-Perot resonator, resulting from another superposition of a plurality of other wave components, at least one of which has made at least one round trip within the volume of the first Fabry-Perot resonator; and

[0029] / 3 / The photoconductive material is absorptive for the coupling resonance wavelength, and a portion of the photoconductive material is located within or on at least one of the volume of the first Fabry-Perot resonator and the volume of the second Fabry-Perot resonator.

[0030] Due to the coupled resonance exhibited by the photodetector of the present invention for the detected radiation, its light absorption rate is very high. This is because the coupled resonance concentrates the radiation within at least a portion of the photoconductive material, significantly increasing the probability that the radiated photons are absorbed. For this reason, the photoconductive material can be of a type that is compatible with the deposition method (particularly the spin coating method) of a colloidal solution of nanocrystals using the material. This method reduces the cost of manufacturing the photodetector, firstly because the photoconductive material can be deposited on the substrate inexpensively, and secondly because the readout circuit can be used as a substrate for depositing the photoconductive material. In this way, the step of assembling the detection circuit to the readout circuit can be avoided.

[0031] Furthermore, since the photodetector structure of the present invention can be limited to two Fabry-Perot resonators whose size is smaller than the wavelength of the radiation to be detected, the photodetector can have very small lateral dimensions. Therefore, an image sensor based on a photodetector according to the present invention is able to provide a very fine spatial resolution and act as a high-resolution sensor.

[0032] Also due to the structure of the photodetector of the invention, its detection efficiency is maintained over a wide angular sector of the direction of incidence of the radiation to be detected.

[0033] The portion of the photoconductive material may be at least partially located in or on the volume with the largest width or the smallest width in the volume of the first Fabry-Perot resonator and the volume of the second Fabry-Perot resonator, these widths being also measured parallel to the substrate. It may also be at least partially located in or on the two corresponding volumes of the first Fabry-Perot resonator and the second Fabry-Perot resonator.

[0034] In an embodiment of the invention that may be simpler to manufacture, the portion of electrically insulating material may be part of a continuous layer of that insulating material that extends across the volume of the first Fabry-Perot resonator and the volume of the second Fabry-Perot resonator in addition to extending between the substrate and each electrode portion. This obviates the need to etch the layer of insulating material.

[0035] Alternatively, in addition to the first electrode portion, the second electrode portion and the third electrode portion, the substrate may also be in contact with a portion of the photoconductive material so as to form an additional electrode portion. Specifically, the substrate may be in contact with a portion of the photoconductive material because one or more portions of the latter are contained within the volume of at least one of the first Fabry-Perot resonator and the second Fabry-Perot resonator. In this case, at least two of the first electrode portion, the second electrode portion and the third electrode portion may be electrically short-circuited 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 any two subsets of the electrode portions that are electrically short-circuited within each subset.

[0036] In general, the photodetector may also include a bias circuit adapted to apply a variable voltage between two electrode portions in the electrode portion collecting the photodetection current during use of the photodetector, and adapted to optionally change the voltage between two consecutive uses of the photodetector. Due to this variable bias voltage, the detection sensitivity of the photodetector can be modified, and more generally its sensitivity spectrum can be modified, and in particular it can be adapted for different uses. The variable bias voltage improves the efficiency of the electrode portion in collecting the charge generated by the radiation in the photoconductive material. The bias voltage can be varied between 0V (volts) and 10V, but a value of 1V or less may advantageously be sufficient. Advantageously, such a photodetector may be adapted to cause the radiation absorption value at least at one wavelength value to vary by at least 30%, preferably at least 50%, and even more preferably at least 90% between the first use of the photodetector and the second use of the same photodetector, during which the bias circuit does not apply a voltage between the two electrode portions or the voltage applied by the bias circuit is zero, and during the second use, the voltage applied by the bias circuit is not zero.

[0037] In one embodiment, the electric field applied to operate the assembly is less than 100 kV.cm -1 , preferably below 30 kV.cm -1 .

[0038] Also generally for the present invention, the photodetector may further include a reconstruction circuit adapted to select and electrically connect at least two of the electrodes and substrate portions of the photodetector so as to collect a photodetection current through those selected electrodes and substrate portions. These electrodes and substrate portions may be varied between a plurality of modes of photodetection current collection, which are associated with different corresponding spectra of sensitivity of the photodetector to incident radiation. In fact, each mode may preferentially collect a photodetection current through a portion of the photoconductive material different from other modes, and each portion of the photoconductive material may be a concentrated location for different wavelength values ​​of the radiation to be detected. In this way, the photodetector of the present invention can be simply and immediately reconstructed between two consecutive uses. For example, a first mode in the photodetection current collection mode may use a first electrode portion and a second electrode portion to collect current, while another mode may use a second electrode portion and a third electrode portion. 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 correspond to a separate resonance of one of the Fabry-Perot resonators, the separate resonance and the coupled resonance corresponding to different wavelength values ​​of the radiation to be detected. Possibly, for at least one or each collection mode, each electrode portion not used for collecting photodetection current may be short-circuited to one of the selected electrode portions by the reconstruction circuit.Alternatively, electrode portions not used for collecting photodetection current may be at floating potential.

[0039] Advantageously, the photodetector may have at least one of the following additional features, alone or in combination:

[0040] The substrate may have a flat surface which extends continuously under the portion of the insulating material and under the volume of the first Fabry-Perot resonator and the volume of the second Fabry-Perot resonator;

[0041] - the substrate may include readout circuitry for the photodetector;

[0042] - each portion of photoconductive material may be part of a layer of photoconductive material which extends continuously over the volume of the first Fabry-Perot resonator and the volume of the second Fabry-Perot resonator and over the electrode portion;

[0043] - the photodetector may include a plurality of pairs of coupled first and second Fabry-Perot resonators, wherein a first electrode portion, a second electrode portion and a third electrode portion are associated with each pair of Fabry-Perot resonators and are electrically connected to accumulate a photodetection current generated by each pair of Fabry-Perot resonators when the photodetector is in use. In the case of such a photodetector having a plurality of pairs of coupled Fabry-Perot resonators, a repetition pitch of a pattern of pairs of coupled Fabry-Perot resonators on a substrate is less than a coupling resonance wavelength;

[0044] - the photodetector may have lateral dimensions, measured parallel to the substrate, of 1 μm (micrometer) to 1 cm (centimeter), preferably 1 μm to 100 μm, in particular less than 15 μm;

[0045] - the volume of the first Fabry-Perot resonator and the volume of the second Fabry-Perot resonator and the width of the second electrode portion are dimensioned so that the coupling resonance wavelength is 1 μm to 12 μm, preferably 1 μm to 2.5 μm;

[0046] - the photoconductive material may be chosen to have a band gap of less than 0.8 eV (electron volts). This limit corresponds to photodetectors that are effective for wavelength values ​​of the radiation to be detected greater than about 1 μm. In particular, the photoconductive material may be based on lead sulfide (PbS), mercury telluride (HgTe) or graphene; and

[0047] -Each part of the photoconductive material can be composed of aggregated nanocrystals. Such nanocrystals can be deposited from a colloidal solution.

[0048] A second aspect of the invention proposes an image sensor comprising a matrix arrangement of photodetectors, each photodetector being in accordance with the above-mentioned first aspect of the invention.

[0049] When each of the photodetectors of the image sensor includes a plurality of pairs of coupled Fabry-Perot resonators, wherein an electrode portion is associated with each pair of Fabry-Perot resonators and is electrically connected to accumulate photodetection current originating from each pair of Fabry-Perot resonators when the photodetector is in use, within each photodetector, the number of coupled Fabry-Perot resonator pairs may be less than or equal to five. Alternatively or in combination, each photodetector may have an individual photodetector size measured along a juxtaposition direction of the pair of coupled first and second Fabry-Perot resonators, the individual photodetector size being less than or equal to ten times the value of the radiation wavelength corresponding to the maximum detection sensitivity of the photodetector.

[0050] Finally, the third aspect of the present invention proposes a method for manufacturing a photodetector according to the first aspect of the present invention, according to which a portion of the photoconductive material is obtained by depositing a colloidal solution containing nanocrystals of the photoconductive material and then drying the deposited colloidal solution. Specifically, the photoconductive material portion can be obtained using a spin coating method. BRIEF DESCRIPTION OF THE DRAWINGS

[0051] The features and advantages of the present invention will become more apparent from the following detailed description of non-limiting embodiments with reference to the accompanying drawings, in which:

[0052] [ Figure 1a ] is a cross-sectional view of a photodetector according to the present invention;

[0053] [ Figure 1b ] corresponds to [ Figure 1a ] alternative embodiments of the photodetector;

[0054] [ Figure 1c ] corresponds to [ Figure 1a ] another alternative embodiment of the photodetector;

[0055] [ Figure 1d ] corresponds to [ Figure 1a ] yet another alternative embodiment of the photodetector;

[0056] [ Figure 2 ] is based on [ Figure 1a ]to[ Figure 1d ] a plan view of a photodetector according to any one of the above;

[0057] [ Figure 3a ] is based on [ Figure 1b ] Spectral absorption diagram of the photodetector;

[0058] [ Figure 3b ] is based on [ Figure 1b ]and[ Figure 2 ] Spectral detection response diagram of the photodetector;

[0059] [ Figure 4a ] corresponds to [ Figure 2 ] another mode of grouping electrode portions;

[0060] [ Figure 4b ] corresponds to [ Figure 4a ] of the photodetector in Figure 3b ];

[0061] [ Figure 5a ] also corresponds to [ Figure 2 ] yet another mode of grouping electrode portions;

[0062] [ Figure 5b ] corresponds to [ Figure 5a ] of the photodetector [ Figure 3b ];

[0063] [ Figure 6 ] corresponds to the [ Figure 1a ]; and

[0064] [ Figure 7 ] is a stereoscopic diagram of an image sensor according to the present invention. DETAILED DESCRIPTION

[0065] For the sake of clarity, the sizes of the elements shown in these drawings do not correspond to the actual sizes or size ratios. In addition, some of these elements are only shown symbolically, and the same reference numerals shown in different drawings represent the same or functionally identical elements.

[0066] according to[ Figure 1a ], the substrate 1 of the photodetector 100 has a continuous, flat, reflective upper surface S for the radiation R to be detected incident on the surface. For this purpose, the surface S of the substrate 1 can be formed by a continuous metal layer 11, which is supported by a base portion 10 of the substrate 1. In particular, the base portion 10 can be at least partially silicon dioxide, quartz, calcium fluoride (CaF 2 ), undoped silicon (Si), undoped germanium (Ge), zinc selenide (ZnSe), zinc sulfide (ZnS), potassium bromide (KBr), lithium fluoride (LiF), aluminum oxide (Al 2 O 3 ), potassium chloride (KCl), barium fluoride (BaF 2 ), cadmium telluride (CdTe), sodium chloride (NaCl), cesium bromide (CsBr), gallium arsenide (GaAs), magnesium fluoride (MgF 2 ), or thallium iodide (Br 3-x I x T1). Alternatively, the base part 10 of the substrate 1 may incorporate a readout circuit for the photodetector 100, in particular such a readout circuit implemented in CMOS technology. The metal layer 11 may be made of gold (Au), silver (Ag) or aluminum (Al), in particular, or of an alloy, or it may be a superposition of several basic metal layers.

[0067] The substrate 1 consists of a continuous insulating layer 2 (e.g., silicon dioxide (SiO 2 ) or aluminum oxide (Al 2 O 3 Specifically, the insulating layer 2 may be made of aluminum oxide and has a direction D parallel to a direction perpendicular to the surface S of the substrate 1.1 The thickness e2 was measured to be approximately 50 nm (nanometers).

[0068] The thickness of the insulating layer 2 may be 10 nm to 10 μm, preferably 30 nm to 5 μm.

[0069] Three electrode portions are formed on the insulating layer 2, which are represented as 3a, 3b and 3c. They can be obtained by a continuous metal layer (such as a layer of gold, silver or aluminum), which is then etched to form a separation gap between adjacent electrode portions. Alternatively, a stripping method can be used to deposit the electrode portions 3a, 3b and 3c, wherein a resin pattern is first formed on the insulating layer 2, followed by deposition of electrode material and subsequent dissolution of the resin, while removing the electrode material at the position of the resin pattern. The common thickness es of the electrode portions 3a, 3b and 3c can be about 100nm in the direction Di. Therefore, each electrode portion 3a, 3b, 3c is electrically insulated from the metal layer 11 by the insulating layer 2.

[0070] Finally, a layer 4 of photoconductive material is deposited in the separation gaps between the electrode portions 3a, 3b and 3c so as to be in contact with the two electrode portions on either side of each of these separation gaps. Figure 1a ] In the embodiment shown in FIG. 1 , the layer 4 of photoconductive material also continuously covers the three electrode parts 3a, 3b and 3c.

[0071] In possible embodiments of the photodetector 100, the layer 4 of photoconductive material may be a two-dimensional material such as graphene, or a transition metal chalcogenide such as molybdenum sulfide (MoS 2 ), Molybdenum selenide (MoSe 2 ), molybdenum telluride (MoTe 2 ), tungsten sulfide (WS 2 ), tungsten selenide (WSe 2 ), tungsten telluride (WTe 2 ) or its alloy or heterostructure. The condensed nanocrystals of these transition metal chalcogenides can be deposited on the electrode parts 3a, 3b and 3c from the colloidal solution of these nanocrystals using spin coating to fill the separation gaps between the electrodes.

[0072] In other possible embodiments of the photodetector 100, the photoconductive material of layer 4 can be a conductive polymer, such as a mixture of poly(3,4-ethylenedioxythiophene) and sodium polystyrene sulfonate, named PDOT-PSS, or such as poly(3-hexylthiophene-2,5), named P3HT. These conductive polymers can also be deposited on the electrode portions 3a, 3b and 3c using a spin coating method to fill the inter-electrode separation gaps again.

[0073] In yet other possible embodiments of the photodetector 100, the photoconductive material of layer 4 may be composed of nanocrystals of 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 (CuS), or 2 )、Copper Indium Selenide (CulnSe 2 ), silver indium sulfide (AglnS 2 ), Silver Indium Selenide (AglnSe 2 ), copper sulfide II (CuS), copper sulfide I (Cu 2 S), silver sulfide (Ag 2 S), silver selenide (Ag 2 Se), silver telluride (Ag 2 Te), indium nitride (InN), indium phosphide (InP), indium arsenide (InAs), indium antimonide (InSb), indium sulfide (InSb), 2 S 3 ), cadmium phosphide (Cd 3 P 2 ), zinc phosphide (Zn 3 P 2 ), cadmium arsenide (Cd 3 As 2 ), zinc arsenide (Zn 3 As 2 ), 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 (FeS 2 ), titanium oxide (TiO 2 ), bismuth sulfide (Bi 2 S 3 ), Bismuth selenide (Bi 2 Se 3 ), Bismuth telluride (Bi 2 Te 3 ), molybdenum sulfide (MoS 2 ), tungsten sulfide (WS 2 ), vanadium oxide (VO 2 ), cesium lead chloride (CsPbCl 3 ), cesium lead bromide (CsPbBr 3 ), cesium lead iodide (CsPbl 3 ), methylammonium lead iodide or MAPI (CH 3 NH3 Pb 3 ), formamidinium lead iodide or FAPI (N 2 H 4 Pb 3 ), alloys thereof or heterostructures thereof. These nanocrystals may be spherical or tetrahedral in shape, or in the form of platelets, rods, wires, tripods, etc. The 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 phosphine compounds. Alternatively, they may be coated with ionic ligands such as S 2- (sulfide), OH - (hydroxide), HS - (hydrogen sulfide), Se 2- (Selenide), NH 2 - (amide), Te 2- (Tellurium), SCN - (Thiocyanate), Cl - (chloride), Br - (Bromide), I - (iodide), Cd 2+ (Cadmium), NH 4 + (ammonium), Hg 2+ (Mercury), Zn 2+ (Zinc) and Pb 2 + (lead).

[0074] 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 mercurous chloride (HgCl) dissolved in dimethylformamide. 2 ).

[0075] Typically, in addition to filling the inter-electrode separation gap, the layer 4 of photoconductive material may have a plurality of layers parallel to the direction D above the electrode portions 3a, 3b and 3c. 1 The measured thickness e4 is about 80 nm. Depending on the photoconductive material used, the mobility of the charge carriers can be about 10 -4 cm 2 .V -1 .s -1 (square centimeters per volt per second) to about 50 cm 2 .V -1 .s -1 , preferably about 10 -3 cm 2 .V -1 .s -1 To approximately 10cm 2 .V-1 .S -1 Its optical refractive index may be between 1 and 4, more particularly between 1.3 and 3. The layer 4 of photoconductive material may then be absorptive from 200 nm to 15 μm, preferably from 1 μm to 5 μm, and even more preferably from 1 μm to 2.5 μm, wherein the absorption coefficient per unit thickness of the layer 4 has a value of 100 cm -1 Up to 10,000cm -1 , and more particularly 1,000 cm -1 Up to 5,000cm -1 .

[0076] In the photodetector 100, the separation gap between the electrode portions 3a and 3b on the one hand, and between the electrode portions 3b and 3c on the other hand, is crucial for the operation of the photodetector. Each is a Fabry-Perot resonator with a vertical axis, i.e., the propagation direction of its standing wave component is parallel to the direction D i In the drawings, FP1 represents a Fabry-Perot resonator located between electrode portions 3a and 3b, and FP2 represents a Fabry-Perot resonator located between electrode portions 3b and 3c. 1 1 , each of the Fabry-Perot resonators FP1 and FP2 is delimited on the one hand by the metal layer 11 and on the other hand by a straight extension between the upper surfaces of the electrode portions, away from the substrate 1, above the inter-electrode separation gap. Each of the Fabry-Perot resonators FP1 and FP2 is delimited in the transverse direction, i.e., along the direction D 2 , defined by the edge of the electrode portion. Therefore, in [ Figure 1a In the embodiment shown in FIG. 1 , the volume of each Fabry-Perot resonator FP1, FP2 includes a portion of the insulating layer 2, which is along the direction D 1 is aligned with the corresponding inter-electrode separation gap. It also includes an inter-electrode gap filling portion made of the photoconductive material used for layer 4. In this case, for each Fabry-Perot resonator FP1, FP2, for a direction parallel to the direction D 1 However, the phase matching relationship established by the two propagation directions with opposite orientations takes into account the superposition of the insulating layer material 2 and the photoconductive material.

[0077] Furthermore, the two Fabry-Perot resonators FP1 and FP2 have a direction parallel to the direction D 2 For example, the width of resonator FP1 is denoted as W 1 The width of resonator FP2 may be 400 nm, and is denoted as W 2The width of the electrode portion 3b between the two resonators FP1 and FP2 may be 200 nm. However, the width of each resonator contributes to the effective value of each refractive index involved in the phase matching relationship of the resonators FP1 and FP2, so that the two resonators FP1 and FP2 have respective resonant wavelength values, called individual resonant wavelength values, which are different. The width of the electrode portion 3b between the two resonators FP1 and FP2 is represented by r i .for[ Figure 1a ] shown in the embodiment, r i It can be equal to 200nm.

[0078] exist[ Figure 1b ] In the variant shown in FIG. 1 , the layer 4 of photoconductive material is discontinuous and has the same thickness between the locations located in each of the resonators FP1, FP2 and the locations located above each of the electrode portions 3a, 3b and 3c. The insulating layer 2 is still continuous over the entire surface S in the photodetector 100, wherein the thickness e 2 The thickness e of each electrode portion 3a, 3b, 3c may still be equal to 50 nm. 3 can still be approximately equal to 100 nm, and the thickness e of the layer 4 of photoconductive material 4 The portion of layer 4 located in each of resonators FP1 and FP2 is still in contact with the adjacent electrode portion: the portion of layer 4 located in resonator FP1 is in contact with electrode portions 3a and 3b, and the portion of layer 4 located in resonator FP2 is in contact with electrode portions 3b and 3c. Width W 1 , W 2 and r i The value can be maintained and combined with [ Figure 1a ] refer to the same values.

[0079] [ Figure 1c ] corresponds to [ by removing the insulating layer 2 inside each of the resonators FP1 and FP2. Figure 1b ] This selective removal of material from the insulating layer 2 can be performed in any manner known to those skilled in the art, so it is not necessary to describe it here. The following values ​​can be used: e 2 =120nm, e 3 =70nm and e 4 =140nm, and W 1 , W 2 and r i The value can be kept the same as [ Figure 1a ]and[ Figure 1b ] is the same as in the embodiment of . For the thickness values ​​just given, the portion of layer 4 located in each of resonators FP1 and FP2 is still in contact with the adjacent electrode portion. Figure 1c] In the embodiment shown, the metal layer 11 of the substrate 1 is in contact with the portion of the photoconductive material 4 located in each of the resonators FP1 and FP2. Thus, the metal layer 11 can be used as a further electrode portion in addition to the electrode portions 3a, 3b and 3c. In particular, the advantages of adding further electrodes in this way will be explained later in this specification.

[0080] Finally, in [ Figure 1d In the embodiment shown in ], the inter-electrode gaps between the electrode portions 3a and 3b in the resonator FP1 and between the electrode portions 3b and 3c in the resonator FP2 are filled with a planarizing resin up to the top surfaces of the electrode portions 3a, 3b and 3c. Then, a layer 4 of photoconductive material has parallel faces and continuously covers the electrode portions 3a, 3b and 3c and the resin portion 5. The insulating layer 2 can again be continuous throughout the photodetector 100. For [ Figure 1d ], the following values ​​may be used: e 2 =50nm, e 3 =130nm, e 4 =140nm, W 1 =400nm,W 2 =1050nm, r 1 =725nm, and layer 4 may consist of graphene sheets.

[0081] for[ Figure 1b ] and the associated values, and when the photoconductive material of layer 4 is mercury telluride (HgTe), the Fabry-Perot resonator FP1 has a single resonant wavelength value λ effective for incident radiation R in the direction of the surface S 1 , which is approximately equal to 1650nm (nanometers), where the individual resonant quality factor value Q 1 is approximately equal to 5, and the Fabry-Perot resonator FP2 has a single resonance wavelength value λ approximately equal to 1550 nm 2 , where the individual resonant quality factor value Q 2 is approximately equal to 5. The individual resonance range of resonator FP1 [λ r1 ·(1-3 / Q 1 ); r1 (1+3 / Q 1 )]] is [660nm; 2640nm], and the individual resonance range of resonator FP2 is [λ r2 ·(1-3 / Q 2 ); r2 (1+3 / Q 2 )] is [620nm; 2480nm]. Therefore, these two intervals overlap between 660nm and 2480nm. Figure 1a ]、[ Figure 1c ]and[ Figure 1d ] embodiments, there is a similar separate resonance.

[0082] Generally speaking, the electrode portion 3b separating the two Fabry-Perot resonators FP1 and FP2 has a 2 The width is measured and is denoted as r i , which is small enough to couple the two resonators. Figure 1b ], and also when the photoconductive material of layer 4 is lead sulfide (PbS), the two Fabry-Perot resonators FP1 and FP2 exhibit a coupled resonance having a resonance wavelength value of about 1.55 μm (called the coupled resonance wavelength), with an associated quality factor (called the coupled resonance quality factor) of about 15. For each monochromatic component of the radiation R, this coupled resonance is produced by the interference between the following three waves:

[0083] a portion of the radiation R reflected on the surface S of the substrate 1, i.e. a portion of the radiation R reflected by the metal layer 11. This portion of the radiation which is reflected only once is denoted in the figures by the reference OR0;

[0084] - a first further wave OR1 which emerges from the Fabry-Perot resonator FP1 and which results from the superposition of several wave components, at least one of which propagates back and forth within the Fabry-Perot resonator FP2. In other words, the amplitude of the further wave OR1 depends on the coupling between the resonator FP1 and the free space from which the radiation R originates. Additionally, at least one component of this further wave OR1 propagates in the resonator FP2, having been subjected to a direction parallel to the direction D 1 The further wave components that may further participate in constituting the further wave OR1 may make any combination of successive round trips in the two resonators FP1 and FP2 and then be re-emitted into free space by the resonator FP1, wherein the intermediate space between the two resonators FP1 and FP2 is crossed at each pass between a round trip in one of the resonators FP1 or FP2 and a round trip in the other resonator; and

[0085] - a second further wave OR2 which emerges from the Fabry-Perot resonator FP2 and which results from the superposition of several other wave components, at least one of which propagates back and forth within the Fabry-Perot resonator FP1. In other words, the amplitude of the further wave OR2 depends on the coupling between the resonator FP2 and the free space from which the radiation R originates. Additionally, at least one component of this further wave OR2 propagates in the resonator FP1, having been subjected to a rotation parallel to the direction D 1As in the case of the additional wave OR1, any combination of additional wave components that may further participate in constituting the additional wave OR2 may make at least one round trip in the two resonators FP1 and FP2 and then be re-transmitted into free space by the resonator FP2, wherein the intermediate space between the two resonators FP1 and FP2 is crossed at each pass between a round trip in one of the resonators FP1 or FP2 and a round trip in the other resonator.

[0086] The two additional waves OR1 and OR2 are derived from the 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 a constructive interference that contributes to the total reflected wave OR as a coupled resonance object. 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. For [ Figure 1a ]to[ Figure 1d ], the criterion for sufficient coupling between resonators FP1 and FP2 is the width W 1 +r 1 +W 2 The sum of is less than the value of the coupling resonance wavelength, expressed as λ c .

[0087] [ Figure 1a ]to[ Figure 1d Each of the photodetectors 100 in the embodiment of the present invention can be arranged in a direction D 2 is repeated several times to form a repeating pattern M with a repeating pitch represented by p. Thus, a new photodetector 101 is obtained, which is composed of a plurality of basic photodetectors 100 arranged in electrical parallel. Figure 2 ] shows such a photodetector 101, which is composed of five elementary photodetectors 100 connected by their electrode parts 3a / 3c. All electrode parts 3a / 3c and 3b are connected along the direction D 3 The electrode portions 3a / 3c belong to the electrode 3 of the obtained photodetector 101. 1 , and electrode portion 3b belongs to its electrode 3 2 As an example, the repetition pitch p inside the photodetector 101 may be equal to 1 μm, for example, when each electrode portion 3a / 3c is in the direction D 2 The width r 2 When W is equal to 200nm, or when W 1 =400nm,W 2 =200nm and r1 = 200nm. In this case, the photodetector 101 is in the direction D 2 and D 3 The photodetector 101 may have a lateral dimension L of about 6 μm. Such a photodetector 101 generates a photodetection current that is greater than the photodetection current of each elementary photodetector 100 , with a ratio that is substantially equal to the number of elementary photodetectors 100 grouped together in the photodetector 101 .

[0088] [ Figure 3a ] shows the spectral absorption of the photodetector 101 when the pattern M is [ Figure 1b The basic photodetector 100 of ] is composed of a large number of repetitions of this pattern. This example uses the following values: r 1 =r 2 =200nm,W 1 =400nm,W 2 =200nm, p=1μm, e 2 =50nm, e 3 = 100 nm, and e 4 =80nm. The value of the coupling resonance wavelength λ c remains substantially equal to 1.5 μm and with a value Q of the coupled resonance quality factor approximately equal to 15 c Related. Figure 3a ], the horizontal axis marks the wavelength value of the monochromatic radiation R, denoted by λ, and expressed in micrometers (μm), and the vertical axis marks the spectral absorption value, denoted by A, and expressed in percentage (%). The spectral absorption is greater than the value λ of the coupling resonance wavelength. c 80% and in the coupled resonance range [λ c ·(1-3 / Q c ); c (1+3 / Q c )] is less than 20%. In addition, when the radiation R is in the direction D 1 and D 2 The incident direction in the plane of 1 When the coupling resonance wavelength changes by ±25°, the value λ c The absolute value of the change is less than 0.1μm. At the same time, for the coupling resonance wavelength λ c The absorption value A(λ C ) changes by less than 10%. c and A(λ C ) provides the photodetector 101 with a large angular tolerance in its photodetection efficiency. Finally, the coupled resonant wavelength λ cThe variation with the number of elementary photodetectors 100 arranged in parallel to form the photodetector 101 is small: it varies by approximately 0.025 μm between five and an infinite number of elementary photodetectors 100 .

[0089] Generally, photodetectors consistent with the present invention may have the following additional features:

[0090] - for a wavelength λ of the radiation R, the photodetector may be effective from 200 nm to 15 μm, and more particularly from 1 μm to 5 μm, in particular from 1 μm to 2.5 μm, depending on the photoconductive material used;

[0091] -The photodetection current can be 1μA.W -1 (microamperes per watt) to 1kA.W -1 (kiloamperes per watt), and more specifically 1mA.W -1 (milliamperes per watt) to 5A.W -1 (microamperes per watt), preferably 100mA.W -1 To 2A.W -1 , expressed as R per unit radiated power;

[0092] - the photodetector response time may be less than 40 ms (milliseconds), more particularly less than 1 ms, and preferably less than 10 μs (microseconds);

[0093] -The specific detection rate of the photodetector can be greater than 10 8 cm·Hz 1 / 2 ·W -1 (centimeter times one-half hertz per watt: the unit is also called Jones), more specifically greater than 10 9 cm·Hz 1 / 2 ·W -1 , and preferably greater than 10 10 cm·Hz 1 / 2 ·W -1 ;as well as

[0094] The operating temperature of the photodetector may be above 80K (Kelvin), preferably above 150K, and even more preferably above 200K.

[0095] When the incident radiation R has a coupled resonance λ c At a wavelength value λ of λ, the photodetection efficiency of the photodetector according to the invention is provided by the two Fabry-Perot resonators FP1 and FP2 coupled to each other. For this wavelength value, the photodetector concentrates the radiation in the two resonators with a width W 1 or W 2 The larger portion of the photoconductive material. Figure 1b], the radiation is more precisely concentrated at the top of the part of the photoconductive material inside the resonator FP1 that is farthest from the substrate 1. Figure 1c ], the radiation is concentrated both at the top of the portion of photoconductive material in the resonator FP1 and also in the lower corners of that portion. In general, at those points of the photoconductive material portion of the widest resonator, the energy density of the radiation is multiplied by a factor greater than 10 or even greater than 15 compared to the energy density of the radiation on its optical path before reaching the photodetector. Due to this concentration of the radiation, a greater number of charges are generated in the photoconductive material, resulting in an improvement in the efficiency and sensitivity of the photodetection.

[0096] In accordance with [ Figure 1c ], the surface S of the substrate 1 is conductive and is in contact with a portion of the photoconductive material 4 contained in the resonators FP1 and FP2, and is also in contact with the electrode 3 1 and 3 2 Then, the photodetection current can be generated by electrode 3 1 、Electrode 3 2 When a photodetector is used, a reconstruction circuit can be used to select the two electrodes actually used to collect the photodetection current. This reconstruction circuit can select the two electrodes 3 and 11 as the other electrodes. 1 、Electrode 3 2 And the one of the conductive layers 11 that is not used to collect the photodetection current is connected to one of the other two, or is placed at a floating potential.

[0097] The photodetector may be further supplemented by a bias circuit arranged to apply an adjustable voltage between two electrodes for collecting the photodetection current. The use of such a bias circuit is well known to those skilled in the art, so it is not necessary to describe it in more detail here. In general, for the same pair of electrodes used, the efficiency of collecting the charges generated by the radiation R in the layer 4 of the photoconductive material increases with the absolute value of the bias voltage. Another advantage of the photodetector according to the invention is that the value of the bias voltage applied between the electrodes used can be less than 10V, or even less than 1V. Therefore, this voltage value can be transmitted by an integrated electronic circuit implemented using one of the prior art. Therefore, the electric field generated in the photoconductive material by the bias circuit can be between 0 and 100kV·cm -1 (kilovolts per centimeter), and more particularly less than 20 kV·cm -1 .

[0098] [ Figure 3b ] shows the figure according to [ Figure 1b ]and[ Figure 2] is the spectral detection response of the photodetector 101. The horizontal axis of the figure marks the wavenumber value, which is equal to the inverse of the wavelength λ, denoted as σ and is expressed in cm -1 Indicates, and its vertical axis marks the value of the photodetection current, recorded as l ph and are expressed in arbitrary units (au), these values ​​are for radiation R with constant intensity and propagating in a direction parallel to direction D 1 The two electrodes used to collect the photodetection current are as follows [ Figure 2 ] Electrode 3 shown 1 and 3 2 , and the conductive layer 11 maintains a floating potential. 1 and 3 2 A variable bias voltage is also applied between the two electrodes, and its value is represented by each curve in the reference figure from 10 mV (millivolt) to 1000 mV. When the bias voltage is zero or low, the photodetector has a detection efficiency resulting from the coupled resonance as described above, wherein the detection maximum value is about 6500 cm at the wave number σ. -1 The detection maximum corresponds to the widest Fabry-Perot resonator (i.e., [ Figure 1b ]and[ Figure 2 ] in the resonator FP1). When the bias voltage is increased, an additional detection contribution appears, with a maximum at 5800 cm -1 This additional contribution corresponds to the photoconductive material 4 being located in the narrowest Fabry-Perot resonator (i.e., [ Figure 1b ]and[ Figure 2 ] of the resonator FP2) in the more efficient collection of charges in the part, the additional contribution in [ Figure 3b ] in the axis system of the figure at 5800cm -1 The bias voltage varies from 10mV to 1000mV. The spectral position is at 5800cm -1 Nearby, substantially corresponds to a single resonance of the Fabry-Perot resonator FP2, which single resonance produces a concentration of the radiation therein.

[0099] exist[ Figure 4a In the photodetector 101 of the present invention, the middle electrode portion between the Fabry-Perot resonators FP1 and FP2 is connected to the electrode 3 1 and 3 2 , so that for each resonator FP2, the two electrode portions 3b and 3c adjacent to this resonator are short-circuited relative to each other, and between two consecutive resonators FP2 are alternately connected to the electrode 3 1 or electrode 3 2 . The coupled resonators still have [ Figure 1b], wherein the width W of the resonator FP2 2 Smaller than the width W of the resonator FP1 1 . At two electrodes 3 1 and 3 2 The photodetection current is collected again between , and a variable bias voltage is applied during the period. Under these conditions of collecting the photodetection current, its spectral change becomes [ Figure 4b Due to the configuration of the electrodes, the charge generated by the radiation R in the (broadest) resonator FP1 is efficiently collected, corresponding to the peak at 6500 cm -1 The detection peak near 6000cm -1 The detection peak in the vicinity corresponds to the photoconductive material 4 outside the resonator FP1. Both peaks are strongly intensified by the bias voltage.

[0100] On the contrary, in [ Figure 5a ] in the photodetector 101, which also has [ Figure 1b ], the electrode portions 3a and 3b adjacent to each resonator FP1 are short-circuited relative to each other, and are alternately connected to the two electrodes 3 between two consecutive resonators FP1. 1 and 3 2 As mentioned above, the width W of the resonator FP1 is 1 Greater than the width W of the resonator FP2 2 . At two electrodes 3 1 and 3 2 The photodetection current is still collected between the two electrodes, and a variable electrical bias voltage is also applied between them. Under these new collection conditions of the photodetection current, its spectrum changes to [ Figure 5b Due to the configuration of the electrodes, only the charges generated by the radiation R in the (narrowest) resonator FP2 are collected. The detection peak is then mainly located at 6000 cm -1 nearby and is strongly exacerbated by the bias voltage.

[0101] [ Figure 6 ] is a cross-sectional view of another photodetector according to the present invention. One pattern of the other photodetector is composed of two or more (for example, three) Fabry-Perot resonators, which are juxtaposed and each pair has a different resonator width. The three Fabry-Perot resonators are designated as FP1, FP2 and FP3, and they have respective resonator widths W 1 , W 2 and W 3 For example, the width W 3 Greater than width W 2 , and the width W 2 Greater than the width W1 . The electrode portions are designated as 3a, 3b, 3c and 3d, and the other reference numerals have the same meanings as above. On the one hand, the width of the electrode portion 3b is small enough for the Fabry-Perot resonators FP1 and FP2 to be coupled according to the present invention, and on the other hand, the width of the electrode portion 3c is also small enough for the Fabry-Perot resonators FP2 and FP3 to be coupled. Therefore, the first photodetection current that can be collected between the electrode portions 3a and 3b has a sensitivity spectrum generated by the coupling between the Fabry-Perot resonators FP1 and FP2 based on the wavelength of the radiation to be detected, and the second photodetection current that can be collected between the electrode portions 3c and 3d has another sensitivity spectrum generated by the coupling between the Fabry-Perot resonators FP2 and FP3. In addition to the first two photodetection currents, a third photodetection current can be collected between the electrode portions 3b and 3c, and the sensitivity spectrum of the third photodetection current is generated by the coupling of the Fabry-Perot resonator FP2 with each of the other two (i.e., the two Fabry-Perot resonators FP1 and FP3). Then, the electrical bias voltage applied between the two electrode portions 3b and 3c can be advantageously adjusted to adjust the sensitivity spectrum of the third photodetection current. The first photodetection current, the second photodetection current and the third photodetection current are collected simultaneously so that they provide three different pieces of information about the spectral composition of the detected radiation.

[0102] In fact, as can be seen from the above description, a variety of electrical connection modes of the electrode parts, different possibilities for selecting the electrode pairs to be used for collecting the photodetection current, and the bias voltage simultaneously enable the photodetector to be reconfigured to modify its spectral sensitivity characteristics. Thus, the photodetector can be adjusted based on its application or provide the measurement of the same radiation in several detection modes.

[0103] [ Figure 7 ] shows an image sensor according to the present invention. The image sensor is generally represented by the reference numeral 110, which includes a matrix array of photodetectors 100 or 101, which have the same model, such as one of the above-mentioned models. Specifically, the photodetector matrix array can be 4×4 to 16384×12288 photodetectors, more specifically 320×200 to 16384×12288 photodetectors. The pitch of the photodetectors in the matrix array can be 1μm to 1cm, preferably less than 100μm. When a spin coating deposition method is used to deposit the photoconductive material, the photodetector can be directly formed on the readout circuit of the image sensor 110. For example, the readout circuit can be manufactured using CMOS technology. Figure 7This readout circuit, indicated by reference numeral 102 in the figure, then forms the base substrate 10 of all the photodetectors 100 / 101. In this case, a set 103 of electrical connection layers can be inserted between the photodetectors 100 / 101 and the readout circuit 102. These electrical connections link the electrode portions of each photodetector to a readout unit dedicated to this photodetector and contained in the readout circuit 102. Additionally, the readout circuit 102 can advantageously combine the reconstruction circuit and the electrical bias circuit as described above. Figure 7 In the figure, a reconstruction circuit is denoted by reference numeral 104, and an electrical bias circuit is denoted by reference numeral 105.

[0104] Now, the method for manufacturing a photodetector according to the present invention is described in detail by way of example. First, a method for obtaining a colloidal solution precursor and three embodiments of a photoconductive nanocrystal colloidal solution are provided.

[0105] Molar solution of TOP:Te precursor (1M)

[0106] 6.35 g of tellurium (Te) powder was mixed with 50 mL of TOP (trioctylphosphine) in a first triol flask. The flask was kept at room temperature under vacuum for 5 minutes, and then the temperature was raised to 100°C. Degassing was carried out at this temperature for another 20 minutes. The mixture was heated with nitrogen (N 2 ) replaced the atmosphere and adjusted the temperature to 275°C. Stir the solution until a clear orange color was obtained. The flask was then cooled to room temperature and the color turned yellow. Finally, the solution was transferred to a nitrogen-filled glove box for storage.

[0107] Example 1: At 6000cm -1 Synthesis of HgTe Nanocrystals with Band Gap at

[0108] In a 100 mL triol flask, 540 mg (milligrams) of mercuric chloride (HgCl 2) and 50mL of oleylamine were vacuum degassed at 110°C. At this stage, the solution was yellow and clear. At the same time, 2mL of TOP:Te precursor molar solution (1M) was extracted from the glove box and mixed with 8mL of oleylamine. The atmosphere was replaced with nitrogen and the temperature was set to 57°C. The TOP:Te solution was quickly injected into the triol flask and darkened after 1 minute. After 3 minutes, 10mL of DDT (dodecyl mercaptan) toluene solution (10% DDT by volume) was further injected into the triol flask, and the temperature was quickly reduced using a cold water bath. The contents of the second triol flask were divided into four tubes, and methanol was added to the tubes. After centrifugation, the precipitate formed was redispersed in a single tube with 10mL of toluene. The solution was precipitated a second time with ethanol. Again, the precipitate formed was redispersed in 8mL 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 or PTFE filter.

[0109] Example 2: At 4000cm -1 Synthesis of HgTe Nanocrystals with Band Gap at

[0110] In a 100 mL triol flask, 540 mg of mercuric chloride (HgCl 2 ) and 50mL of oleylamine were vacuum degassed at 110°C. At this stage, the solution was yellow and clear. At the same time, 2mL of TOP:Te precursor molar solution (1M) was extracted from the glove box and mixed with 8mL of oleylamine. The atmosphere was replaced with nitrogen and the temperature was set to 86°C. The TOP:Te solution was quickly injected into the triol flask and darkened after 1 minute. After 3 minutes, 10mL of DDT (dodecyl mercaptan) toluene solution (10% DDT by volume) was further injected into the triol flask, and the temperature was quickly reduced using a cold water bath. The contents of the triol flask were divided into four tubes, and methanol was added to the tubes. After centrifugation, the precipitate formed was redispersed in a single tube with 10mL of toluene. The solution was precipitated a second time with ethanol. Again, the precipitate formed was redispersed in 8mL 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 or PTFE filter.

[0111] Example 3: At 6000cm -1 Synthesis of PbS Nanocrystals with Band Gap

[0112] In a triol flask, 300 mg of lead chloride (PbCh) and 7.5 mL of oleylamine were degassed at room temperature and then at 110° C. for 30 minutes. At the same time, 30 mg of sulfur powder (S) was mixed with 7.5 mL of oleylamine by stirring in the presence of ultrasound until completely dissolved to obtain a clear orange solution. Then, under a nitrogen atmosphere of 160° C., the sulfur solution was quickly added to the triol flask. After 15 minutes, the reaction was quickly stopped by adding 1 mL of oleic acid and 9 mL of hexane. The nanocrystals were precipitated with ethanol, centrifuged and redispersed in toluene. The washing step was repeated once more. The toluene solution of the nanocrystals was then centrifuged to remove the unstable phase. The supernatant was precipitated with methanol and then redispersed in toluene. Finally, the toluene solution of the PbS nanocrystals was filtered using a 0.2 μm polytetrafluoroethylene or PTFE filtrate.

[0113] The fabrication of a coupled Fabry-Perot resonator photodetector according to the present invention is now described and comprises the following steps 1 to 5:

[0114] Step 1: Form a mirror surface to form a reflective layer

[0115] A silicon substrate coated with silicon dioxide of 12 mm x 14 mm in size was cleaned with acetone and isopropanol. The substrate was placed in an acetone bath and subjected to ultrasound for 5 minutes. It was then rinsed with acetone and isopropanol and dried under a nitrogen stream. The substrate was then heated to 40 ℃ and then heated to 30 ℃. The substrate was heated to 40 ℃ and then heated to 30 ℃. 2 ) plasma cleaned these substrates for 5 minutes. The adhesion promoter (e.g., made of Supply TI ), and baked at 120°C for 2 minutes. Then a resin (e.g., AZ 5214) is deposited by spin coating (e.g., at 4000rpm for 30 seconds), followed by annealing at 110°C for 90 seconds. The substrate is then exposed to ultraviolet (UV) radiation for 1.5 seconds through a mask, followed by annealing at 125°C for 2 minutes. Then a second ultraviolet radiation exposure is performed without a mask, for example, for 40 seconds. The resin is developed in a developer such as AZ 726MIF model for 30 seconds, and then rinsed with deionized water for 15 seconds. Each substrate is then cleaned with oxygen plasma for 5 minutes. A first titanium (Ti) layer of 3 nm thick is deposited using a thermal evaporator, preferably using sample spin, followed by a second gold (Au) layer of 80 nm thick. Finally, a third aluminum (Al) layer of 5 nm thick is deposited again using a thermal evaporator. The resin is then removed by soaking each sample in acetone for 1 hour. The substrate is then rinsed with acetone and isopropanol, and dried under a nitrogen stream. The mirror surface obtained on each silicon-based substrate is used to form a bond [ Figure 1a ]to[ Figure 1d ]The reflecting layer 11 mentioned.

[0116] Step 2: Deposit the insulating layer

[0117] A 50 nm thick aluminum oxide (Al2O3) was deposited on each substrate using the ALD (atomic layer deposition) method. 2 O 3 ) layer. This layer is used to form a bond [ Figure 1a ]to[ Figure 1d ]The insulating layer 2 mentioned.

[0118] Step 3: Forming Macroscopic Electrical Contact Areas

[0119] The substrate is rinsed with acetone and isopropanol and dried under a stream of nitrogen. The adhesion promoter (e.g., made of Supply TI ), then baked at 120°C for 2 minutes. AZ 5214 resin is then deposited by spin coating (e.g., at 4000rpm for 30 seconds), followed by annealing at 110°C for 90 seconds. Each substrate is then exposed to ultraviolet radiation for 1.5 seconds through a mask, followed by annealing at 125°C for 2 minutes. A second ultraviolet radiation exposure is then performed without a mask for 40 seconds. The resin is developed in AZ 726MIF developer for 30 seconds, followed by rinsing with deionized water for 15 seconds. Each substrate is then cleaned with oxygen plasma for 5 minutes. A 3nm thick titanium layer is deposited by thermal evaporation, preferably by substrate spin deposition, followed by another 150nm thick gold layer. The resin is then removed by soaking the sample in acetone for 1 hour. The substrate is then rinsed with acetone and isopropanol, and dried under a stream of nitrogen.

[0120] Step 4: Electron Beam Lithography

[0121] The substrate was rinsed with isopropanol and then dried under a stream of nitrogen. A layer of pure A6 grade polymethyl methacrylate or PMMA was deposited by spin coating at 400 rpm for 5 seconds and then at 4000 rpm for 30 seconds, and baking at 180 °C for 2 minutes. A 10 nm layer of aluminum was then deposited using an electron beam evaporator. The aluminum deposition rate was set to 0.1 nm·s -1 (nanometers per second), and sample rotation is activated in the evaporator.

[0122] Each substrate was then transferred to an electron lithography apparatus. Using a current of 12 pA (picoampere) and 200 μC.cm -2Electron lithography was performed with a total dose of 100 μC (microcoulombs per square centimeter). The substrate was then immersed in a 100 mL aqueous solution of 40 g potassium hydroxide or KOH for 15 seconds, rinsed with water and dried under a stream of nitrogen. This eliminated the aluminum layer. The PMMA resin was developed using a 1:3 volume ratio of methyl isobutyl ketone or MIBK:isopropanol or IPA solution for 45 seconds, followed by a rinse in pure isopropanol for 20 seconds. Each substrate was then cleaned with oxygen plasma for 2 minutes. It was then transferred to an electron evaporator. The substrates were then etched at 0.1 nm·s -1 and 0.2 nm·s -1 A 3 nm thick titanium layer was deposited at a deposition rate of 1.5 Å, followed by an 80 nm thick gold layer. The resin was then removed by immersing each substrate in acetone at 40 °C for at least 2 hours. The metal portion thus formed on each substrate was a combination of [ Figure 2 ]、[ Figure 4a ]and[ Figure 5a ] mentioned electrode 3 1 and 3 2 The substrate was then observed under a scanning electron microscope, where the parameters were 8 mm and 5 kV, and the electrodes were electrically controlled.

[0123] Step 5: Nanocrystal Deposition

[0124] 1 mL of HgTe nanocrystals (6000 cm -1 , with a band gap of 720 meV (millielectron volts) and an optical density of 0.9 at 400 nm) in toluene was mixed with 1 mL of a ligand exchange solution consisting of 9 mL of dimethylformamide, 1 mL of mercaptoethanol, and 15 mg of HgCl 2 . Three consecutive washing steps were performed using hexane. The nanocrystals were then precipitated with toluene. After centrifugation, the supernatant was removed and the precipitate was dried under vacuum for 15 minutes. The precipitate was redispersed in 170 μL (microliters) of pure dimethylformamide. The ink was then deposited on each substrate by spin coating at 2000 rpm (acceleration 200 rpm / s, rotation time 120 s). Prior to this, the substrates had been exposed to oxygen plasma for 4 minutes.

[0125] It should be understood that the invention can be repeated by modifying minor aspects of the embodiments described in detail above, while retaining at least some of the cited advantages. In particular, all numerical values ​​provided are for illustrative purposes only and may vary depending on the application in question.

Claims

1. A photodetector (100, 101), comprising: - a substrate (1), said substrate (1) being reflective to electromagnetic radiation incident on said photodetector (100, 101); - electrode portions (3a, 3b, 3c) supported by the substrate (1) and having respective surfaces facing away from the substrate, referred to as upper surfaces, located at a common level spaced from the substrate; - portions of electrically insulating material, said portions of electrically insulating material being located between said electrode portions (3a, 3b, 3c) and said substrate (1) so as to electrically insulate each electrode portion from said substrate; as well as - at least a portion of a photoconductive material, said at least a portion of the photoconductive material being arranged in electrical contact with two adjacent electrode portions of said electrode portions (3a, 3b, 3c), said at least two electrode portions of said electrode portions (3a, 3b, 3c) and said substrate (1) being used to collect a photodetection current when said photodetector (100, 101) is in use, characterised in that a first electrode portion (3a) and a second electrode portion (3b) adjacent to said electrode portions (3a, 3b, 3c) define between them, parallel to said substrate (1), a volume into which said radiation penetrates in order to be reflected by said substrate, forming a first Fabry-Perot resonator (FP1) between said substrate and the level of an upper surface of said electrode portions when said photodetector (100, 101) is in use, and in that the second electrode portion (3b) of the electrode portions (3a, 3b, 3c) and a third electrode portion (3c) located on the side of the second electrode portion opposite to the first electrode portion define between them, parallel to the substrate (1), another volume into which the radiation also penetrates to be reflected by the substrate when the photodetector (100, 101) is in use, forming a second Fabry-Perot resonator (FP2) between the substrate and the level of the upper surface of the electrode portions, The first Fabry-Perot resonator (FP1) and the second Fabry-Perot resonator (FP2) are designed to generate a standing wave component propagating perpendicularly to the substrate (1) when the photodetector (100, 101) is in use, And the photodetector (100, 101) has the following features / 1 / to / 3 / : / 1 / Between the first electrode portion and the second electrode portion, the width of the first Fabry-Perot resonator (FP1) measured parallel to the substrate (1) is different from the width of the second Fabry-Perot resonator (FP2) measured between the second electrode portion and the third electrode portion, also parallel to the substrate, so that the first Fabry-Perot resonator and the second Fabry-Perot resonator have different respective individual resonance wavelength values ​​effective for radiation incident on the photodetector (100, 101), and the individual resonance quality factors of the first Fabry-Perot resonator and the second Fabry-Perot resonator have such respective values ​​that on a wavelength axis of the incident radiation, the following individual resonance intervals: [λ ri ·(1-3 / Q i ); ri (1+3 / Q i )] have overlap, wherein i is equal to 1 or 2 to represent the first Fabry-Perot resonator or the second Fabry-Perot resonator, respectively, and λri and Qi are the wavelength and quality factor value of the individual resonance of the Fabry-Perot resonator i, respectively; / 2 / The sum of the width of the first Fabry-Perot resonator (FP1) and the second Fabry-Perot resonator (FP2) and the width of the second electrode portion (3b) measured parallel to the substrate (1) between the volumes of the first Fabry-Perot resonator and the second Fabry-Perot resonator is suitable for generating a coupling between the first Fabry-Perot resonator and the second Fabry-Perot resonator, which is achieved by the sum being less than a resonant wavelength value for the coupling, called a coupling resonant wavelength, which is effective for the radiation incident on the photodetector (100, 101), and the coupling resonant wavelength is generated by interference between at least three waves, the at least three waves comprising: - a first wave generated by said reflection of incident radiation on said substrate (1); a second wave emitted from the first Fabry-Perot resonator (FP1), which is generated by the superposition of a plurality of wave components, wherein at least one of the wave components has made at least one round trip in the volume of the second Fabry-Perot resonator (FP2); and a third wave emerging from the second Fabry-Perot resonator (FP2), which is generated by another superposition of a plurality of other wave components, wherein at least one of the other wave components has made at least one round trip within the volume of the first Fabry-Perot resonator (FP1); and / 3 / The photoconductive material is absorptive for the coupling resonance wavelength, and a portion of the photoconductive material is located within or on at least one of the volumes of the first Fabry-Perot resonator (FP1) and the second Fabry-Perot resonator (FP2).

2. The photodetector (100, 101) according to claim 1, wherein: The substrate (1) includes a photodetector readout circuit (102).

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

4. The photodetector (100, 101) according to claim 1 or 2, wherein: In addition to the first electrode portion (3a), the second electrode portion (3b) and the third electrode portion (3c), the substrate (1) is also in contact with a portion of the photoconductive material to form a further electrode portion.

5. The photodetector (100, 101) according to any one of the preceding claims, further comprising: A bias circuit (105) is adapted to apply a voltage between two of the electrode parts (3a, 3b, 3c) that collect the photodetection current during use of the photodetector, and is also adapted to change the voltage between two consecutive uses of the photodetector so as to modify the sensitivity spectrum of the photodetector, in particular the detection sensitivity.

6. The photodetector (100, 101) according to claim 5 is suitable for making the radiation absorption value at least at one wavelength value change by at least 30%, preferably at least 50%, and even more preferably at least 90% between the first use of the photodetector and the second use of the photodetector, during which the bias circuit (105) does not apply a voltage between the two electrode parts or the applied voltage is zero, and during the second use the applied voltage is not zero.

7. The photodetector (100, 101) according to any one of the preceding claims, further comprising: A reconstruction circuit (104) is adapted to select and electrically connect at least two of the electrode portions (3a, 3b, 3c) and substrate (1) of the photodetector so as to collect a photodetection current through the selected electrode portions and substrate, the selected electrode portions and substrate varying between a plurality of modes of photodetection current collection associated with different corresponding spectra of the sensitivity of the photodetector to incident radiation.

8. The photodetector (100, 101) according to any one of the preceding claims, wherein Each portion of the photoconductive material is part of a layer (4) of the photoconductive material, and the layer (4) of the photoconductive material extends continuously over the volume of the first Fabry-Perot resonator (FP1) and the volume of the second Fabry-Perot resonator (FP2) and over the electrode portions (3a, 3b, 3c).

9. The photodetector (100, 101) according to any one of the preceding claims, comprising: A plurality of pairs of coupled first Fabry-Perot resonators (FP1) and second Fabry-Perot resonators (FP2), wherein the first electrode portion (3a), the second electrode portion (3b) and the third electrode portion (3c) are associated with each pair of Fabry-Perot resonators and are electrically connected to accumulate a photodetection current generated by each pair of Fabry-Perot resonators when the photodetector is in use.

10. The photodetector (100, 101) according to any of the preceding claims, having lateral dimensions measured parallel to the substrate (1) of 1 μm to 1 cm, preferably 1 μm to 100 μm.

11. The photodetector (100, 101) according to any one of the preceding claims, wherein The volume of the first Fabry-Perot resonator (FP1) and the volume of the second Fabry-Perot resonator (FP2) and the width of the second electrode portion are sized so that the coupling resonance wavelength is 1 μm to 12 μm.

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

13. The photodetector (100, 101) according to any one of the preceding claims, wherein The portions of photoconductive material are each composed of aggregated nanocrystals.

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

15. The image sensor (110) according to claim 14, wherein: Each photodetector (100, 101) is an individual photodetector (100, 101) according to claim 9 and has an individual photodetector size measured along the juxtaposition direction of the pair of coupled first Fabry-Perot resonators (FP1) and second Fabry-Perot resonators (FP2), the individual photodetector size being less than or equal to ten times the value of the radiation wavelength corresponding to the maximum detection sensitivity of the photodetector.

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

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