Infrared detector improved via engineering of the effective mass of charge carriers

Abstract

The subject of the invention is a device for detecting infrared radiation comprising at least one pixel having an axis in a Z-direction, said pixel comprising a first absorbent planar structure comprising at least one semiconductor layer. The composition of the materials used to produce the at least one layer of the first absorbent planar structure is chosen such that: The first absorbent planar structure has an effective valence band formed by a plurality of energy levels. Each energy level is occupied by one among: a first type of positive charge carriers denoted heavy holes having a first effective mass; and a second type of positive charge carriers denoted light holes having a second effective mass strictly lower than the first effective mass. The maximum energy level of the effective valence band is occupied by light holes along the axis of the pixel.

Description

DESCRIPTION Title of the invention: Infrared detector improved via effective mass engineering of charge carriers.

[0001] Scope

[0002] The present invention relates to the field of infrared (IR) imaging and in particular to a radiation detector or photodetector made with heterostructures based on type III-V semiconductor materials. More specifically, the invention relates to an imaging device in the short-wave infrared (SWIR) and mid-wave infrared (MWIR) at non-cryogenic temperatures.

[0003] Problem raised

[0004] Infrared imagers are generally made up of an assembly of a matrix comprising a plurality of elementary pixels based on photodiodes that transform a flow of incident photons into photo-generated charge carriers, and a readout circuit commonly called ROIC for "Read Out Integrated Circuit" to process the electrical signal from the detector pixels.

[0005] The invention aims to solve a technical problem in this field consisting of designing a matrix detector operating in the short-wave infrared (SWIR) and medium-wave infrared (MWIR) at non-cryogenic temperatures by improving the quantum efficiency of the detector while simultaneously minimizing the cross-talk phenomenon between the pixels of the matrix and further minimizing dark current noise compared to state-of-the-art solutions.

[0006] We will begin by physically explaining these three interdependent characteristics of an infrared matrix sensor.

[0007] As an illustration, in a space (X,Y,Z) we define the axis A of each pixel according to the direction Z, and the plane having as its normal the axis of the pixel, called the normal plane, is the plane (X, Y).

[0008] Each infrared array detector is characterized by a cutoff wavelength Δc defined by the effective energy gap Δg e ff of the absorbing zone of each pixel of the matrix detector according to the Planck-Einstein relation Δc=hc / Eg eff with h being Planck's constant and c the speed of light in a vacuum. The cutoff length then depends on the energy band structure of the materials used to create the pixel's absorbing region.

[0009] The "quantum efficiency" of a semiconductor-based IR detector is defined as the ratio of the number of electron / hole pairs generated by the photoelectric effect to the number of photons passing through the structure of a pixel belonging to the IR detector. Quantum efficiency depends on the absorption coefficient and the scattering wavelength L. dz in the pixel structure along the pixel axis. The absorption coefficient depends on the materials used to create the pixel structure. The scattering wavelength L dz along the pixel axis increases with the scattering coefficient along the pixel axis. The scattering coefficient is inversely proportional to the effective mass m hz minority charge carriers (holes in the case of an N-doped absorbing area) along the pixel axis.

[0010] Crosstalk arises from interference between adjacent pixels. The photocharges generated by one pixel can scatter to a neighboring pixel along the plane normal to the pixel axis. The amplitude of crosstalk in an infrared array detector increases with the scattering length of minority charge carriers in the normal (X,Y) plane, denoted L. dx , y The diffusion length L dx , y along the plane normal to the pixel increases with the diffusion coefficient in the same plane. The diffusion coefficient is inversely proportional to the effective masses m hx and m hy minority charge carriers (holes in the case of an N-doped absorbing region) in the plane normal to the pixel.

[0011] The dark current J nOir is the charge carrier current generated in the absence of incident radiation in the materials that make up the absorbing area of ​​a pixel in the detection matrix. The dark current can be expressed by the following formula: 2 îli Jnoir With rij the intrinsic charge carrier density in the absorption zone, T the minority charge carrier lifetime, N the doping level, and d the thickness of the absorption zone. N and d are dimensional parameters, and T depends on the manufacturing conditions. These three parameters must be optimized to find a compromise that minimizes the dark current while maintaining sufficient quantum efficiency for proper operation. ni is the most fundamental parameter and depends on the effective mass of the minority charge carriers along the pixel axis m. hz and according to the normal plan to the pixel mh X mh y- Engineering the composition of the materials in the absorption zone allows control of these effective masses in order to find the compromise between quantum efficiency, dark current and crosstalk, and this for a given cutoff frequency at a given operating temperature.

[0012] In summary, we have demonstrated that: firstly, quantum efficiency is a technical characteristic that determines the electro-optical performance of an infrared detector. Secondly, dark current noise and crosstalk present technical constraints that limit this performance.

[0013] The technical problem to be solved is then to develop infrared detectors in SWIR (1.4 pm to 3 pm) and MWIR (3 pm to 8 pm) with pixels including absorbing areas allowing with an improvement of the following interdependent criteria: maximization of quantum efficiency and minimization of crosstalk and dark current noise constraints at a given cutoff frequency.

[0014] Prior art / State of the art restrictions

[0015] European patent application EP3482421 B1 describes a matrix infrared image detector comprising a plurality of pixels. The planar absorption structure of each pixel, according to the solution proposed in this application, is implemented using a bulk InGaAsSb material on a GaSb substrate in a specific vertical architecture. Furthermore, European patent EP1642345B1 describes a matrix infrared radiation detector comprising a plurality of pixels. The planar absorption structure of each pixel, according to the proposed solution, is implemented using a bulk InGaAsSb material on a GaSb material substrate. by this patent is achieved by a bulk material InGaAsSb on a substrate of GaSb material.

[0016] The drawback of the solutions proposed in these two documents is that crosstalk is amplified when the pixel pitch reaches a distance of less than 15 pm. Furthermore, the solutions proposed in these two documents are unable to function at cutoff frequencies around 5 pm.

[0017] The publication "Strain-induced enhancement of near-infrared absorption in Ge epitaxial layers grown on Si substrate" by Ikishawa et al. presents an infrared detector with an absorption zone made of bulk germanium epitaxially deposited on silicon. The drawback of this solution is that the detector fabrication involves heat treatment of the epitaxial layers. This heat treatment, along with the magnitude of the lattice mismatch between the silicon and germanium, leads to dislocations caused by the relaxation of the material composing the absorption zone. Consequently, the infrared detector will exhibit mechanical fragility and degradation of the electro-optical performance of the pixels.

[0018] The publication "Infrared absorption enhancement in light and heavyhole inverted Gal λαναAs / λαναs quantum wells" by Xie et al. presents a constraint-compensated InGaAS / λαναs quantum well infrared detector. The drawback of the solution proposed in this paper is that it is not functional in the short-wave infrared (SWIR from 1.4 pm to 3 pm) and in the mid-wave infrared (MWIR from 3 pm to 8 pm).

[0019] Answer to the problem and provision of a solution

[0020] To overcome the limitations of existing solutions regarding the optimization of the trade-off point between quantum efficiency, crosstalk minimization, and dark current minimization in SWIR and MWIR, the invention proposes several embodiments of a pixel structure comprising a planar absorption structure exhibiting a valence band with a maximum energy level occupied by light holes higher than that occupied by heavy holes along the pixel axis. The planar absorption structure according to the invention can be implemented using a superlattice or a bulk material. The invention details embodiments with examples of material choices for the planar absorption structure, ranges of semiconductor alloy compositions, and The design ranges for the thicknesses of the layers of the planar absorption structure according to the invention are defined. The compositions (molar fractions of III-V alloys) of the materials used to create the layer(s) of the planar absorption structure according to the invention are chosen so as to reverse the heavy and light holes along the pixel axis while avoiding the occurrence of interface dislocations due to material relaxation. This simultaneously improves, compared to state-of-the-art solutions, the performance of the IR detector in terms of quantum efficiency, dark current reduction, and crosstalk reduction.

[0021] Summary / Claims

[0022] The invention relates to an infrared radiation detection device comprising at least one pixel having an axis along a Z direction, said pixel comprising a first planar absorbing structure including at least one semiconductor layer. Each layer of the first planar absorbing structure is arranged in a crystalline lattice structure. The first planar absorbing structure is N-doped and fabricated by epitaxy on a substrate, and the composition of the materials used to fabricate at least one layer of the first planar absorbing structure is chosen such that: ■ The first planar absorbing structure exhibits an effective valence band formed by a plurality of energy levels. Each energy level is occupied by one of: o a first type of positive charge carrier called heavy holes having a first effective mass; or o a second type of positive charge carrier called light holes having a second effective mass strictly less than the first effective mass. The maximum energy level of the effective valence band is occupied by light holes along the pixel axis; The crystalline structure of the lattice of said layer does not exhibit dislocations resulting from mechanical relaxation of said lattice. The effective mass of the positive charge carriers along the pixel axis is less than half of the effective mass of positive charge carriers along directions defining a plane orthogonal to the pixel axis.

[0023] According to a particular aspect of the invention, the substrate is arranged according to a crystalline lattice structure and the composition of the materials used to create at least one layer of the first planar absorbing structure is chosen such that: ■ the meshes of at least one layer forming said planar absorbing structure undergo internal mechanical stresses to adapt to the meshes of the crystalline structure of the substrate; ■ and such that the resulting stress from the sum of internal mechanical stresses is a tensile stress.

[0024] According to a particular aspect of the invention, the effective mass of the holes carrying positive charges along the pixel axis is less than one tenth of the mass of a free electron.

[0025] According to a particular aspect of the invention, the difference between the maximum energy level occupied by light holes and the maximum energy level occupied by heavy holes is greater than the product of the Boltzmann constant by the operating temperature.

[0026] According to a particular aspect of the invention, the composition of the materials used to create at least one layer of the first planar absorbing structure is chosen such that the magnitude of the stress resulting from the sum of the internal mechanical stresses is less than a predetermined dislocation limit stress. The dislocation density in the first planar absorbing structure is strictly less than 10 4 dislocations / cm2.

[0027] According to a particular aspect of the invention, the first planar absorbing structure consists of a single layer of a solid semiconducting material of type III-V.

[0028] According to one particular aspect of the invention, the bulk semiconductor material is the quaternary alloy Ga x ilni-xiAs y iSbi-yi with x1 the mole fraction of gallium in the Gaxiln-ix-iASyiSbi.yi alloy and y1 the mole fraction of arsenic in the Ga alloy x lni.xiAs y iSbi.yi .

[0029] According to a particular aspect of the invention: ■ the substrate is made of gallium antimonide GaSb; ■ the mole fraction x1 of gallium Ga in the alloy Gaxln-i.xiASyiSbi.yi is between 0 and 1; ■ and the mole fraction y1 of arsenic As in the Ga alloy x lni-xiAs yiSbi-yi is between a minimum and a maximum value such that: o the minimum value is an affine function of the mole fraction x1 of gallium Ga in the alloy Gaxln-i.xiASyiSbi.yi characterized by a slope equal to -0.92 and a y-intercept equal to 0.93 o the maximum value of the mole fraction y1 of arsenic As in the alloy Ga x lni.xiAs y iSbi.yi is an affine function of the mole fraction x1 of gallium Ga in the Ga alloy x lni-xiAs y iSbi-yi characterized by a slope equal to -0.92 and a y-intercept equal to 0.97.

[0030] According to a particular aspect of the invention: ■ The substrate is made of indium antimonide InSb; ■ and the mole fraction x2 of gallium Ga in the bulk semiconductor material is between 0.02 and 0.05; ■ and the mole fraction y2 of arsenic As in the bulk semiconductor material is between 0.02 and 0.05.

[0031] According to a particular aspect of the invention, the first planar absorbing structure comprises a first super-lattice comprising a stacking along the pixel axis of an elementary group of semiconductor layers comprising: ■ a first layer in a first semiconductor material exhibiting o a first minimum conduction band value; o a first maximum valence band value; o a first energy gap value; ■ at least a second layer made of a second semiconductor material exhibiting: o a second minimum conduction band value strictly less than the first minimum conduction band value; o a second maximum valence band value strictly less than the first maximum valence band value; o and a second energy gap value. The meshes of the first layer are subjected to tensile stresses and the meshes of the second layer are subjected to compressive stresses.

[0032] According to a particular aspect of the invention, the first superlattice exhibits a first effective valence band maximum value, and the positive charge carriers in the first shell of an elementary group experience an energy barrier equal to the difference between: ■ the maximum energy level of the effective valence band occupied by heavy holes; ■ and a first value of maximum effective valence band. The product of said energy barrier and the thickness of the second layer is less than a predetermined value.

[0033] According to a particular aspect of the invention, the second semiconductor material is the ternary alloy lnAs y3 Sbi-y3 with y3 the mole fraction of arsenic in the alloy lnAs y 3Sbi- y 3.

[0034] According to a particular aspect of the invention, the first semiconductor material is the quaternary alloy Gax3ln-i.x3ASy4Sb1.y4 with x3 the mole fraction of gallium in the alloy Gax3ln-i.x3ASy4Sb1.y4 and y4 the mole fraction of arsenic in the alloy Gax3ln1.x2Asy4Sb1.y4.

[0035] According to a particular aspect of the invention: ■ the mole fraction y3 of arsenic in the alloy lnASy3Sbi- y 3 is between 0.6 and 0.88. ■ The mole fraction x3 of gallium in the alloy Gax3ln1.x3Asy4Sb1.y4 is between 0.2 and 0.5 ■ and the mole fraction y4 of arsenic in the alloy Gax3ln1.x3ASy4Sb1.y4 is between a minimum value and a maximum value such that: o The minimum value of the mole fraction y4 of arsenic in the alloy Gax3ln1.x3ASy4Sb1.y4 is an affine function of the mole fraction x3 of gallium in the alloy Gax3ln1.x3ASy4Sb1.y4, characterized by a slope of -0.92 and a y-intercept of 0.93. o The maximum value of the mole fraction y4 of arsenic in the alloy Ga X 3lni. X 3ASy4Sbi-y4 being an affine function of the mole fraction x3 of gallium in the Ga alloy X 3lni. X 3ASy4Sbi-y4 characterized by a slope equal to -0.66 and a y-intercept equal to 1.13.

[0036] According to a particular aspect of the invention, the first planar absorbing structure has a first effective valence band maximum value, a first effective conduction band minimum value, and a first effective energy gap value. The pixel comprises, along its axis in this order: ■ the substrate; ■ A lower contact structure in a third semiconductor material or in a lower contact superlattice, doped N+ and having: o a lower contact valence band maximum value strictly less than the effective valence band maximum value of the first planar absorbing structure; o and a lower contact energy gap value greater than or equal to the first effective energy gap value of the first planar absorbing structure. ■ An overall planar absorbing structure comprising: the first planar absorbing structure; the layers of said first planar absorbing structure being N-doped; ■ one or more transition structures; the transition structure in contact with the overall planar absorbing structure is called the initial transition structure. The initial transition structure is made of a fourth semiconductor material or a first N-doped superlattice of the transition structure and exhibiting: o a maximum valence band value of the initial transition structure strictly greater than the maximum effective valence band value of the first planar absorbing structure; o and an energy gap value of the initial transition structure strictly greater than the first effective energy gap value of the first planar absorbing structure. ■ A top contact structure in a fifth semiconductor material or in a top contact superlattice, doped P+ and having: o a top contact valence band maximum value strictly greater than the valence band maximum value of each transition structure; o and a top contact energy gap value strictly greater than the energy gap value of each transition structure.

[0037] According to a particular aspect of the invention, the pixel comprises several transition structures of rank i=1 to increasing N, starting from the overall absorbing planar structure to the upper contact structure, with N a non-zero natural number, such that: ■ Each transition structure of rank i=2 to N has a maximum valence band value strictly greater than the maximum valence band value of the transition structure of rank i-1.

[0038] Other features and advantages of the present invention will become more apparent from the following description in relation to the following attached drawings.

[0039] [Fig. 1 a] Figure 1 a illustrates a perspective view of a first example of a pixel belonging to a matrix detector in the infrared frequency range.

[0040] [Fig. 1 b] Figure 1 b illustrates a perspective view of a second example of a pixel belonging to a matrix detector in the infrared frequency range.

[0041] [Fig. 2a] Figure 2a illustrates a cross-sectional view of an infrared detector pixel comprising a planar absorption structure according to a first embodiment of the invention.

[0042] [Fig. 2b] Figure 2b illustrates ranges of mole fraction values ​​for the selection of material compositions for the planar absorption structure according to the first embodiment of the invention.

[0043] [Fig. 2c] Figure 2c illustrates a simulated band diagram of the absorbing planar structure according to the first embodiment of the invention in the three directions of the reciprocal vector space.

[0044] [Fig. 2d] Figure 2d illustrates a schematic of the band structure of the planar absorbing structure according to the first embodiment of the invention in the direction of the pixel axis at k z =0.

[0045] [Fig. 3a] Figure 3a illustrates a cross-sectional view of an infrared detector pixel comprising a planar absorption structure according to a second embodiment of the invention.

[0046] [Fig. 3b] Figure 3b illustrates ranges of mole fraction values ​​for the selection of material compositions for the planar absorption structure according to the second embodiment of the invention.

[0047] [Fig. 3c] Figure 3c illustrates a simulated mini-band diagram of the planar absorbing structure according to the second embodiment of the invention in the three directions of the reciprocal vector space at k z =0.

[0048] [Fig. 3d] Figure 3d illustrates a diagram of the band structure of the planar absorbing structure according to the second embodiment of the invention in the direction of the pixel axis.

[0049] [Fig. 4a] Figure 4a illustrates a cross-sectional view of a first example of a pixel comprising a planar absorbing structure according to any one of the embodiments of the invention.

[0050] [Fig. 4b] Figure 4b illustrates a diagram of the band structure along the axis of the pixel of Figure 4a.

[0051] [Fig. 5] Figure 5 illustrates a cross-sectional view of an infrared radiation detection device comprising a plurality of pixels according to the invention.

[0052] Figure 1a illustrates a perspective view of an example pixel belonging to an infrared radiation matrix detector. The illustration is limited to a single pixel Pxl for the sake of simplicity, but it does not preclude the integration of the pixel into a matrix comprising a plurality of juxtaposed pixels.

[0053] The pixel Pxl of an infrared detector is created by stacking layers of semiconductor materials that form the pixel structure on a substrate SUB. The pixel axis A is perpendicular to the horizontal (x,y) plane formed by the top surface of the substrate SUB. The substrate SUB is made of a bulk semiconductor material, such as type III-V. The choice of substrate material is important because it determines the technology of the manufacturing process steps of the device, as well as the technical characteristics (optical, electrical, mechanical, etc.) of the matrix detector. The pixel Pxl comprises the following layers, starting from the substrate and along the direction of the pixel axis A: a lower contact structure CONTJNF, a planar absorbing structure SPA, and an upper contact structure CONT_SUP.

[0054] The lower contact structure CONTJNF can be made of N+-doped solid semiconductor material and has a lower maximum valence band energy than the maximum valence band energy of the planar absorbing SPA structure. Preferably, the material constituting the lower contact structure is of type III-V such as, for example, gallium arsenide, indium arsenide, gallium nitride, gallium antimonide, boron phosphide, and their ternary, quaternary, or quinary alloys. The lower contact CONTJNF can also be achieved with heterostructures obtained by stacking a plurality of thin layers of semiconductor materials preferably of type III-V such as, for example, gallium arsenide, indium arsenide, gallium nitride, gallium antimonide, boron phosphide, as well as their ternary or quaternary or quinary alloys.The lower contact structure CONTJNF is an example of an N+-doped superlattice with a large energy gap. Examples include the N+-doped InAS / lnAsSb superlattice and the N+-doped InAs / InGaAsSb superlattice.

[0055] The planar absorbing structure SPA acts as the absorbing zone. It is made of N-doped semiconductor bulk material (or a superlattice heterostructure) with an energy gap value less than or equal to that of the lower contact structure. The band diagram characteristics of the planar absorbing SPA structure (valence band, conduction band, band gap energy) are intrinsic in the case of a bulk material, or effective, resulting from the combination of different thin layers in the case of a superlattice. The planar absorbing SPA structure converts the flux of incident photons with a wavelength λ into negatively charged carriers "electrons" in the conduction band (intrinsic or effective) of the SPA structure and positively charged carriers "holes" in the valence band (intrinsic or effective) of the SPA structure. For the devices covered by the invention, this is a photoelectric effect where the minority charge carriers (holes for N-type doping) are used to generate the readout signal following stimulation of the planar absorbing SPA structure by infrared radiation.The semiconductor materials used to fabricate the planar absorbing SPA structure (in bulk or superlattice form) can be of type III-V, such as gallium arsenide, indium arsenide, gallium nitride, gallium antimonide, boron phosphide, and their ternary, quaternary, or quinary alloys. The energy band structure within the planar absorbing SPA structure is crucial for increasing the cutoff frequency of the matrix detector comprising the pixel Pxl.

[0056] The upper contact structure CONT_SUP is made of P+ doped semiconductor bulk materials, generally exhibiting a large energy gap. These materials are preferably of type III-V, such as, for example, gallium arsenide, indium arsenide, gallium nitride, gallium antimonide, boron phosphide, and their ternary, quaternary, or quinary alloys. The upper contact CONT_SUP can also be made with heterostructures obtained by stacking a plurality of thin layers of semiconductor materials, preferably of type III-V, such as, for example, gallium arsenide, indium arsenide, gallium nitride, gallium antimonide, boron phosphide, and their ternary, quaternary, or quinary alloys. The upper contact structure CONT_SUP constitutes, as an example, a P+ doped superlattice exhibiting a large energy gap value.

[0057] Figure 1a illustrates a pixel exhibiting a structure obtained through successive deposition and etching operations. A pixel is thus delimited along the (x,y) plane by its three-dimensional structure obtained through the etching operations.

[0058] Alternatively, it is possible to achieve the same pixel architecture along the axis of pixel A but delimited along the (x,y) plane with doping zones and not a structure resulting from etching.

[0059] Figure 1b illustrates a perspective view of a plurality of pixels belonging to a matrix detector in the infrared frequency range, delimited by the P+ doped areas of the upper contact CONT_SUP. The characteristics of the different parts of each pixel along its axis A remain the same as in Figure 1a. The major difference lies in the method of pixel delimitation within the matrix, resulting from the manufacturing process used for delimitation (etching in 1a and doping of the upper contact in 1b).

[0060] As previously mentioned, the choice of compositions of the semiconductor alloys used to create the planar absorption structure is crucial to achieving the desired optimal point in terms of quantum efficiency, crosstalk reduction, and dark current reduction.

[0061] To understand the invention, it is essential to understand the growth mechanism of a lattice-matched thin film on a substrate. Generally, a bulk material in the solid state is organized according to a crystalline structure obtained by the spatially periodic repetition of a unit cell composed of the atoms of said material. For a given material, the set of mechanical, physical, and electrical characteristics is determined, among other things, by the structure of the crystalline lattice. In the case of an alloy of semiconductor materials, the choice of mole fractions of the different materials that compose the alloy defines the crystalline structure and the geometric parameters of the crystalline lattice of the resulting alloy.

[0062] In the case of infrared detectors based on thin semiconductor films, the fabrication of the layers that form the planar absorbing structure is carried out via the epitaxy process on a substrate. Molecular beam epitaxy or metal-organic vapor deposition can be used. In the case of a semiconductor alloy, the choice of fractions The molar fractions used in the epitaxial step of each alloy component allow control over the lattice parameters of the deposited layer. Thus, with a judicious choice of mole fractions, it is possible to achieve epitaxial deposition of a thin film whose lattice matches the crystalline structure of the substrate. This is referred to as heteroepitaxy.

[0063] If the mole fractions used in the alloy deposited on the substrate differ from the values ​​corresponding to a lattice match, it is possible to grow semiconductor alloy layers a few nanometers thick on the substrate. Indeed, the crystalline lattices of a deposited layer will adapt to the crystalline lattice of the substrate during the epitaxial process by undergoing internal mechanical stresses. These internal mechanical stresses can be tensile or compressive, depending on the chosen mole fractions of the alloy. At the scale of the crystal lattice, the internal mechanical stresses experienced by the crystalline lattices of the deposited layer generate asymmetries within these lattices and modify the electromagnetic forces between atoms. From an electrical perspective, this leads to a modification of the energy band structure in the deposited layer.

[0064] In general, in a stack of layers deposited on a substrate by epitaxy, two types of dislocations can appear in the crystal lattice of the deposited layers: substrate dislocations and relaxation dislocations.

[0065] Substrate dislocations originate from intrinsic dislocations within the substrate's crystal lattice, with a dislocation volume density that depends on the substrate fabrication process. Substrate dislocations include those characterized by their Burgers vector being inclined at an angle of 60° to the interface. These 60° dislocations can propagate through the stack volume to the surface of the epitaxially deposited layer. These are referred to as emergent dislocations or threading dislocations. Substrate dislocations exhibit a volume density on the order of 1 to 10 4dislocations / cm² depending on the maturity of the technological process. For example, the volumetric density of substrate dislocations present in an InP substrate is less than 5 x 10⁻³ 3 dislocations / cm2.

[0066] Relaxation dislocations are dislocations related to lattice mismatch between an epitaxially deposited layer and the substrate (SUB). Indeed, when the internal stresses applied to the lattice of the deposited layer exceed a threshold value, a mechanical relaxation phenomenon occurs in some of the lattice cells. The elastic energy of the lattice in the layer stack is no longer sufficient to withstand the stress, and a plurality of emergent and non-emergent relaxation dislocations appear within the volume of the crystal lattice. This phenomenon is then indirectly determined by the composition of the epitaxially deposited alloys relative to the substrate. In the case of exceeding the limiting relaxation stress, the volume density of dislocations becomes on the order of 10 7 at 1 O 10dislocations / cm2. In the case of the infrared detector made by epitaxy, mechanical relaxation generates dislocations which propagate in the volume of the absorption structure, mechanically weakening the entire structure of the pixel and degrading the electro-optical performance of the pixel.

[0067] In the following paragraphs we will describe the different embodiments of the invention.

[0068] Figure 2a illustrates a cross-sectional view of an infrared detector pixel comprising a planar absorption structure according to a first embodiment of the invention. In this case, the planar absorption structure is made with a layer of bulk material C m m ■

[0069] The solid material layer C m m is deposited by epitaxy on the SUB substrate with a mismatch in lattice parameters generating internal stresses on the lattice of the absorbing layer Cm m as represented by the arrows in Figure 2a. The layer of solid material C m m is N-doped and it is the minority charge carriers that constitute the photogenerated electrical signal. In addition, the internal stresses experienced by the lattice generate a quantum phenomenon known as "lifting of degeneracy".

[0070] The "lifting of degeneracy" consists of separating the energy level of the so-called "heavy hole" valence band from the so-called "light hole" valence band at k=0. A valence band is called a "heavy hole" band when its dispersion relation is weak. A valence band is called a "light hole" band when its dispersion relation is strong. A so-called "heavy hole" valence band is thus occupied by heavy holes, and a valence band known as the "light hole" band is occupied by light holes. In a semiconductor material, light holes have an effective mass mi h significantly lower than that of heavy holes, noted m h h- We thus obtain in the layer of solid material C m The distinction between a maximum energy level in the valence band occupied by heavy holes and a maximum energy level in the valence band occupied by light holes is made at k=0. Furthermore, the positions of the conduction and valence bands are modified under stress. Under tensile stress, the energy gap decreases (the minimum of the conduction band decreases and the maximum of the valence band increases). Under compressive stress, the energy gap increases (the minimum of the conduction band increases and the maximum of the valence band decreases).

[0071] The solid material layer C m The N-doped layer is made from an alloy of type III-V semiconductor materials, and the mole fractions are chosen such that the resulting stress from the sum of the internal mechanical stresses is a tensile stress. This overall tensile stress on the entire bulk material layer leads to the formation of a valence band known as the "light hole" band with the highest energy along the pixel axis and a valence band known as the "heavy hole" band with the highest energy along the normal (x,y) plane. This generates an asymmetry between: on the one hand, the effective mass of the holes along the pixel axis m z mostly light holes and on the other hand the effective mass of the holes along the plane normal to pixel m x , ymostly heavy holes. The asymmetry of effective masses (and therefore of mobility) results in greater hole mobility along the pixel axis than in the normal (x,y) plane.

[0072] The low effective mass m z Minority charge carriers in the planar absorption structure along the axis of pixel A ensure better quantum efficiency of the detector pixel Pxl. The mobility of positive charge carriers along the pixel axis in the absorption structure of the first embodiment is multiplied by 20 compared to a structure where there is no inverse relationship between the energy levels of heavy and light holes.

[0073] The large effective mass m x , y Minority charge carriers in the planar absorption structure in the normal (x,y) plane reduce crosstalk between adjacent pixels. The asymmetry between the effective masses of holes allows crosstalk to be reduced for distances between pixels less than 15pm.

[0074] Figure 2b illustrates ranges of mole fraction values ​​used for the selection of material compositions for the planar absorption structure according to the first embodiment of the invention.

[0075] The planar SPA absorption structure exhibiting the characteristics detailed above can be obtained by depositing a C layer m m is produced with the alloy Ga-xIn^xAsySb^y on a GaSb substrate. x1 denotes the mole fraction of gallium Ga in the Ga-xIn^xAsySb^y alloy and y1 the mole fraction y of arsenic As in the Ga alloy. x ln 1-x As y Sb 1-yThe set of mole fraction pairs (x1, y1) defines the surface P1 described in the diagram in Figure 2b, corresponding to the range of compositions that allow obtaining a planar SPA absorption structure with: ■ The overall stress on the meshes of layer C m m is a tensile stress. ■ An asymmetry between the valence band along the pixel axis having a maximum energy level occupied by light holes and the valence band along the (x,y) plane having a maximum energy level occupied by heavy holes. ■ A low density of dislocations due to the absence of relaxation dislocations.

[0076] The composition range P1 is defined by the following rules: ■ the mole fraction x1 of gallium Ga in the alloy Ga x ilni. xiAs y iSbi-yi is between 0 and 1; 0 < xl < 1 ■ and the mole fraction y1 of arsenic As in the alloy Gaxiln-i-xiASyiSb-i- y i is between a minimum value y1 m and a maximum value y1 max such that: y^-min — yl — y^-max • the minimum value y1 min of the mole fraction y1 of arsenic As in the Ga alloy xi lni-xiAs y iSbi-yi is an affine function of the mole fraction x1 of gallium Ga in the Ga alloy x ilni. x iASyiSbi. y i characterized by a slope equal to -0.92 and a y-intercept equal to 0.93; y^-min = -0.92x1 + 0.93 • the maximum value y1 ma x of the mole fraction y1 of arsenic As in the alloy Ga xi lni. x iASyiSbi-yi is an affine function of the mole fraction x1 of gallium Ga in the Ga alloy x ilni. x iASyiSbi. y icharacterized by a slope of -0.92 and a y-intercept of 0.97; y max = -0.92x1 + 0.97

[0077] Alternatively, the planar SPA absorption structure exhibiting the characteristics detailed above can be obtained by depositing a Cmm layer made with the Ga alloy x \n -x As y Sb -y on an InSb substrate. The set of mole fraction pairs (x2,y2) defines the disk arc P2 described in the diagram in Figure 2b, corresponding to the range of compositions that allow obtaining a planar SPA absorption structure on an InSb substrate with: ■ The overall stress on the meshes of layer C m m is a tensile stress. ■ An asymmetry between the valence band along the pixel axis having a maximum energy level occupied by light holes and the valence band along the (x,y) plane having a maximum energy level occupied by heavy holes. ■ A low density of dislocations due to the absence of relaxation dislocations.

[0078] The composition range P2 is defined by the following rules: the mole fraction x2 of gallium Ga in the alloy Gax2ln1.x2ASy2Sb1.y2 is between 0.02 and 0.05; 0.02 < x2 < 0.05 ■ and the mole fraction y2 of arsenic As in the Ga alloy x lni-xiAs y iSbi-yi is between 0.02 and 0.05; 0.02 < y2 < 0.05

[0079] The choice of mole fractions in the P1 or P2 ranges, depending on the substrate used, allows obtaining a planar absorbing SPA structure under a tensile stress denoted c tot without exceeding the limit of 4000 ppm which could cause relaxation of the C-layer material m Mr.

[0080] c tot < 4000 ppm

[0081] The tensile strength for alloys in the P1 range on a GaSb substrate is between 800 ppm and 4000 ppm. The tensile strength for alloys in the P2 range on an InSb substrate is between 500 ppm and 4000 ppm.

[0082] Figure 2c illustrates a simulated band diagram of an example of the planar absorbing structure according to the first embodiment of the invention in the three directions of the reciprocal vector space defined by k, the wave vector in a semiconductor material. More specifically, the simulated diagram in Figure 2c illustrates the band diagram of a C layer m m en on a GaSb substrate.

[0083] Under these conditions, the planar absorbing structure SPA experiences a tensile stress on the order of 1000ppm. The dislocation density in the absorbing structure SPA according to the first embodiment is on the order of 10 3 dislocations / cm² because there is no relaxation of the materials. The planar absorbing SPA structure with this composition example allows a cutoff wavelength of Åc = 4.2 pm to be achieved at an operating temperature of T = 150 K with an effective hole mass along the pixel axis m z =0.02 m0 and an effective mass of holes in the normal plane of the pixel m x , y =0.4 m o with m o the effective mass of a free electron.

[0084] For each energy level in the valence band, the effective mass of holes in the band diagram is inversely proportional to the slope of the energy level variation in the reciprocal vector space. Thus, we observe on the diagram that along the z-direction (pixel axis), the maximum energy level of the valence band is occupied by light holes (Evih). The energy gap A| b -hh between the maximum energy level B1 occupied by light holes Evih and the level of heavy holes Ev h h is on the order of k b T with k b the Boltzmann constant and T the operating temperature. The set of combinations of compositions included in the surface P1 or P2 (depending on the substrate) allows obtaining values ​​of A| b -hh of the order of k b T or more depending on the operating temperature and the target cutoff frequency.

[0085] When we look at the band diagram along the kx and ky directions corresponding to the normal plane of the pixel, we obtain an inverse distribution of holes. Indeed, the maximum energy level B1 of the valence band along the plane normal to the pixel (x,y) is occupied by heavy holes (with a flatter slope).

[0086] This gives us the asymmetry between the mobility of minority charge carriers (holes in this case) between the pixel axis and the plane normal to the pixel, allowing us to reduce the crosstalk phenomenon without reducing the quantum efficiency of the absorbing area.

[0087] Figure 2d illustrates in general terms a schematic of the band structure of the planar absorbing structure SPA according to the first embodiment of the invention along the direction of the pixel axis with k z =0.

[0088] Layer C mm is under tension stress and the degeneracy lifting phenomenon is observed by the distinction between the maximum energy level of heavy holes Evhh and the maximum energy level of light holes Evih with a difference of k b T. This distribution favors the circulation of light holes because the creation of electron-hole pairs by photoelectric effect by photonic stimulation requires less energy for light holes.

[0089] In the following paragraph we will give examples of preferred compositions according to the first embodiment on a GaSb substrate according to the target cutoff frequency and operating temperature: ■ For AC = 1.9 pm and T between 250 K and 300 K: C m m is made in Ga x lni- xAs y Sbi- y with 0.95 <x<0,98 et 0,04<y<0,08 ; ■ For AC = 2.5 pm and T between 250 K and 300 K: C m m is made in Ga x ln-|. xAs y Sbi-y with 0.78 <x<0,84 et 0,17<y<0,22 ; ■ For Ac=4.2pm and T=150K: C m m is made in Ga x lni- x As y Sbi- y with 0.03 <x<0,07 et 0,86<y<0,9.

[0090] In the following section we will describe the second embodiment of the invention based on a planar absorption structure made by a supernetwork.

[0091] Figure 3a illustrates a cross-sectional view of an infrared detector pixel comprising a planar absorption structure according to a second embodiment of the invention based on an SR super-array.

[0092] The planar absorption structure (SAP) is realized in this illustration via a periodic heterostructure that forms the SR superlattice. Generally speaking, the SR superlattice is a periodic stacking of an elementary group G1 formed by a plurality of thin layers of semiconductor materials. In this example, the elementary group is formed by the first layer C1 with a thickness of e1 and the second layer C2 with a thickness of e2. Thus, the period of the superlattice is equal to e1 + e2. From a quantum perspective, if the C1 and C2 layers are sufficiently thin (between 0.3 nm for an atomic monolayer and 10 nm), a quantum coupling phenomenon occurs at the various junctions at the layer interfaces. This quantum coupling allows charge carriers to access new mini-energy bands. This results in a different energy band diagram than that of the bulk materials constituting the SR superlattice.In the remainder of the text of this application, the energy band diagram resulting from the association of the thin films G1 = (C1, C1) forming the SR superlattice is designated by the "effective band diagram".

[0093] The effective band diagram is defined by: ■ an effective conduction band, BC e ff having a minimum energy value Ec e tf. ■ an effective valence band, BV e ff having a maximum energy value Ev e tf. ■ an effective energy gap Eg ef f. equal to the difference between the minimum energy value of the conduction band Ec e tf and the maximum energy value Ev e tf.

[0094] In general, the use of superlattices in planar absorbing pixel structures allows for cutoff frequencies unattainable with bulk-material absorption areas. Design choices for the planar absorbing SPA structure include, but are not limited to, the composition of the materials used (materials engineering), the use of a bulk-material or superlattice structure, and the layer thicknesses (structural design of the device). These design choices open up possibilities for improving the pixel's quantum efficiency and limiting crosstalk noise between adjacent pixels.

[0095] To implement the second embodiment of the invention, for each elementary group G1 of the super-lattice SR: ■ The C1 layer is made of a first semiconductor material SC1 having a first value of minimum conduction band Ec1; a first value of maximum valence band Ev1 and a first value of energy gap Eg1. ■ The second layer C2 is made of a second semiconductor material SC2 having a second minimum conduction band value Ec2 strictly less than the first minimum conduction band value Ec1; a second maximum valence band value Ev2 strictly less than the first maximum valence band value Ev1 and a second energy gap value Eg2.

[0096] The meshes of each layer C1 are subject to tensile stresses, the meshes of each layer C2 are subject to compressive stresses, the resulting stress from the sum of the internal mechanical stresses for each elementary group G1 is a tensile stress.

[0097] In general, the same electrical and mechanical characteristics as the first embodiment with a C layer m m in solid material are obtained with the second embodiment with a super SR network.

[0098] Figure 3b illustrates ranges of mole fraction values ​​used for the selection of material compositions for layers C1 and C2 of the SPA planar absorption structure according to the second embodiment of the invention.

[0099] The planar SPA absorption structure exhibiting the characteristics detailed above can be obtained by fabricating an SR superlattice on a GaSb substrate with an elemental group G1 = (C1, C2) such that the second layer C2 is made with the lnAs alloy y 3Sbi- y 3 with y3 the mole fraction of arsenic in the alloy lnAs y3 Sbi- y3 between 0.6 and 0.88 (range P4 on the composition diagram). 0.6 < y3 < 0.88

[0100] Furthermore, the first layer C1 is made with the Ga alloy x3 ln 1-x3 As y4 Sb 1-y4 We denote x3 the mole fraction of gallium Ga in the alloy Ga x3 ln 1-x3 As y4 Sb 1-y4 and y4 the mole fraction y of arsenic As in the Ga alloy x3 In 1-x3 As y4 Sb 1-y4 .. The set of pairs of mole fractions (x3, y4) define the surface P3 described in the diagram in Figure 3b.

[0101] The composition range P3 is defined by the following inequalities: ■ the mole fraction x3 of gallium Ga in the alloy Ga X 3lni- x3As y 4Sbi- y 4 is between 0.2 and 0.5; 0.2 < x3 < 0.5 ■ and the mole fraction y4 of arsenic As in the alloy GaxsIn-i-xsAs^Sb-i- y4 is between a minimum value y4 minand a maximum value y4max such that: • the minimum value y4 m the in of the mole fraction y4 of arsenic As in the alloy Gax3ln-i.x3ASy4Sb1.y4 is an affine function of the mole fraction x3 of gallium Ga in the alloy Gax3ln-i.x3ASy4Sb1.y4 characterized by a slope equal to -0.92 and a y-intercept equal to 0.93; y^min = -0.92x3 + 0.93 • the maximum value y4 ma x of the mole fraction y3 of arsenic As in the alloy Gax3ln1.x3Asy4Sb1.y4 is an affine function of the mole fraction x3 of gallium Ga in the alloy Ga X 3ln 1.X 3ASy4Sbi. y4 characterized by a slope of -0.66 and a y-intercept of 1.13; y^max = -0.66x1 + 1.13

[0102] For layers C1 and C2, the composition ranges (x3,y4) for C1 and y3 for C2, taken from ranges P3 and P4, allow us to obtain a planar SPA absorption structure with: ■ The overall stress on the meshes of the elementary group G1 = (C1 , C2) is a tensile stress. ■ An asymmetry between the valence band along the pixel axis having a maximum energy level occupied by light holes and the valence band along the (x,y) plane having a maximum energy level occupied by heavy holes. ■ A low density of dislocations due to the absence of relaxation dislocations.

[0103] The choice of mole fractions in the P3 and P4 ranges for the SR superlattice allows for a planar absorbing SPA structure formed by the repetition of G1 elementary groups. Each group is subjected to a tensile stress without exceeding the limit of 4000 ppm, which could lead to relaxation of the materials in the C1 and C2 layers. The stresses and thicknesses of each C1 and C2 layer of the G1 elementary group must respect the following inequality to avoid relaxation dislocation phenomena: < 4000 ppm P ec e, the thickness of the i eme layer Ci of the elementary group G1, and the stress experienced by the meshes of the i eme layer Ci of the elementary group G1. The density of Dislocations in the absorbing SPA structure according to the second embodiment are on the order of 10 3 dislocations / cm2 because there is no relaxation of the materials.

[0104] To account for this inequality with the composition ranges detailed in Figure 3b, it is possible to choose the thickness e1 of the first layer C1 between 3 nm and 6 nm and the thickness e2 of the second layer C2 between 0.9 nm and 2 nm. These small thickness values ​​allow for stresses of up to 20,000 ppm for each layer Ci of the G1 element group.

[0105] Figure 3c illustrates a simulated band diagram of an example of the planar absorbing structure according to the second embodiment of the invention in the three directions of the reciprocal vector space defined by k as the wave vector in a semiconductor material. More specifically, the simulated diagram in Figure 3c illustrates the band diagram of the SR superlattice with C1 in Gao,26lno,74Aso,72Sbo,28 and C2 in lnAso,85Sbo,15 in In on a GaSb substrate.

[0106] Under these conditions, the planar absorbing SPA structure experiences a tensile stress on the order of 1000ppm. The planar absorbing SPA structure with this composition example allows a cutoff wavelength of Δc = 5pm to be achieved at an operating temperature of T = 150K with an effective hole mass along the pixel axis of m z =0.02 m o and an effective mass of holes in the normal plane of the pixel m x , y =0.4 m o with m o the effective mass of a free electron.

[0107] For each energy level in the valence band, the effective mass of holes in the band diagram is inversely proportional to the slope of the energy level variation in the reciprocal vector space. Similar to Figure 2c, the diagram shows that along the z-direction (pixel axis), the maximum energy level of the valence band is occupied by light holes. The energy difference Aih-hh between the maximum energy level B'1 occupied by light holes and the level of heavy holes is on the order of kbT, where kb is the Boltzmann constant and T is the operating temperature. All composition combinations taken from the intervals P3 for C1 and P4 for C2 allow Aih-hh values ​​to be obtained on the order of kbT, depending on the target operating temperature and cutoff frequency.

[0108] Similarly, when viewing the band diagram along the kx and ky directions corresponding to the pixel normal plane, an inverse hole distribution is obtained. Indeed, the maximum energy level B'1 of the valence band along the plane normal to the pixel (x,y) is occupied by heavy holes (with a flatter slope).

[0109] This gives us the asymmetry between the mobility of minority charge carriers (holes in this case) between the pixel axis and the plane normal to the pixel, allowing us to reduce the crosstalk phenomenon without reducing the quantum efficiency of the absorbing area.

[0110] Figure 3d illustrates a schematic of the band structure of the planar absorbing structure SPA according to the second embodiment of the invention along the direction of the pixel axis with k z =0.

[0111] The materials composing the superlattice are chosen such that Ec1 > Ec2 and Ev1 > Ev2 to obtain a type 2 potential diagram. This involves an alternation of potential barriers in the second C2 layers and potential sinks in the first C1 layers, as seen by positively charged carriers. Furthermore, it involves an alternation of potential barriers in the first C1 layers and potential sinks in the second C2 layers, as seen by negatively charged carriers.

[0112] As previously mentioned, the quantum coupling between the different layers of the superlattice generates the creation of an effective conduction band with a minimum effective energy level Ec e tf and an effective valence band with a maximum effective energy level Ev eff The effective energy gap of the supergrid is defined by Eg eff = Ec e tf - Ev eff .

[0113] The potential barrier BAR seen by holes confined in a potential well in a type 2 band heterostructure is defined by the difference between the maximum effective energy level Ev e ff of the mini-valence band of the SR superlattice and the maximum energy of the valence band occupied by heavy holes in the C2 layer, denoted Ev2 h h ;

[0114] BAR = Ev eff - EV2 hfl

[0115] We define [3 the product of the potential barrier BAR by the thickness e2 of the layer C2 corresponding to the barrier thickness seen through a hole in the volume of the superlattice according to SR.

[0116] ? = e2 . Bar

[0117] The product [3] constitutes a criterion for ensuring good quantum efficiency of the planar absorbing structure with a superlattice according to the invention. The optical efficiency increases as the product [3] decreases. The materials composing the SR superlattice are chosen such that [3] is less than the limiting value of 250 nm.meV.

[0118] The low effective mass m z Minority charge carriers along the axis of pixel A in the planar absorption structure with a superlattice SR as described ensures a better quantum efficiency of the detector pixel Pxl. The effective mass of positive charge carriers along the pixel axis in the absorption structure of the first embodiment is multiplied by 50 compared to a structure where there is no inverse relationship between the energy levels of heavy and light holes.

[0119] The large effective mass m x , yMinority charge carriers in the planar absorption structure in the normal (x,y) plane reduce crosstalk between adjacent pixels. The asymmetry between the effective masses of the holes further reduces crosstalk for pixel distances less than 15 pm.

[0120] The different embodiments of the planar SPA absorption structure are compatible with global pixel architectures enabling the implementation of quantum efficiency improvement and crosstalk reduction, as well as dark current reduction.

[0121] Figure 4a illustrates a cross-sectional view of a first example of a pixel comprising a planar absorbing structure according to any one of the embodiments of the invention. Figure 4b illustrates a schematic of the banding structure along the axis of the pixel of Figure 4a.

[0122] The pixel Pxl comprises, along the Z stacking direction (or pixel axis), in this order: the SUB substrate exhibiting the detailed characteristics Previously, a lower contact structure CONTJNF in a third N+-doped semiconductor material SC3, a planar absorbing structure SPA according to the invention with the C layer m m Or the N-doped C1, C2 layers; a series of two C transition structures tr ani and C tr an2 each made of a semiconductor material SC4; and a top contact structure CONT_SUP made of a fifth P-doped semiconductor material SC5.

[0123] The lower contact structure CONTJNF exhibits a maximum lower contact valence band value Ev inf strictly less than the maximum effective valence band value Ev etf of the planar absorbing structure SPA. The lower contact structure CONTJNF also exhibits an energy gap value Eg inf lower contact greater than or equal to the first effective energy gap value Eg eff of the first planar absorbing structure SPA. By way of non-limiting examples, the following materials can be used to create the lower contact: N+-doped InAsSb, N+-doped GaSb, N+-doped InGaAsSb, N+-doped InAIAsSb. Alternatively, the lower contact CONTJNF can be created with an SRJNF superlattice using a stack of N+-doped layers such as N+-doped InAs / InAsSb and N+-doped InAsSb / InGaAsSb.

[0124] The first Ctram transition structure exhibits a maximum valence band value Ev tr ani strictly greater than the maximum value of the effective valence band Ev eff of the first planar absorbing SPA structure. The first Ct transition structurera m also presents an energy gap value for the first transition structure (Eg tr ani strictly greater than the first value of ga of effective energy Eg eff of the planar absorbing SPA structure. By way of non-limiting examples, the following materials can be used for the first transition structure: N-doped InAIAsSb, N-doped InGaAsSb. Alternatively, the first transition structure can be realized with an SRtram superlattice with a stack of N-doped layers such as Al x iGa i- X1 As y1 Sb 1 -y1 / Alx2Ga i.x2ASy2Sbl.y2 ■

[0125] The second transition structure C tr an2 exhibits a maximum valence band value Ev tr ani strictly superior to that of the first Ctram transition structure - The second C transition structure tr an2 also exhibits a minimum conduction band value of Ec tran2 strictly greater than that of the first transition structure C tra nor - By way of non-limiting examples, it is The following materials can be used for the first transition structure: N-doped InAIAsSb, N-doped InGaAsSb. Alternatively, the first transition structure can be realized with an SR superlattice. tr an2 with a stacking of N-doped layers such as A^Ga 1-X2AS y2 Sb i- y2 / Alx3Ga 1.x3ASy3Sb1.y3.

[0126] More generally, it is possible to realize the series of transition structures Ctranj confined between the upper contact structure CONT_SUP and the global absorbing planar structure SPAG with a plurality of transition structures C tra nj of rank i=1 to N, starting from the global absorbing planar SPAG structure, where N is a non-zero natural number. Each transition structure Ctranj of rank i has a maximum valence band value Evtra nj strictly greater than that of the previous transition structure C tra nj-i of rank i-1. This is then a step transition with respect to the maximum values ​​of the valence band Ev tra nj as illustrated in figure 4b.

[0127] Alternatively, it is possible to limit oneself to a single transition structure C tra nor between the upper contact structure CONT_SUP and the overall absorbing planar structure SPAG.

[0128] The upper contact structure CONT_SUP exhibits a maximum upper contact valence band value Ev sup strictly greater than the maximum valence band value of each of the Evtrani, Ev transition structures tr an2 ■ In a preferred embodiment, the upper contact structure CONT_SUP also has an energy gap value Eg supof contact greater than strictly greater than the energy gap value of each of the transition structures Eg tra nor, Eg tr year 2

[0129] As non-limiting examples, the following materials can be used to make the upper contact: P+ doped GaSb, P+ doped AIGaSb, P+ doped InGaAsSb.

[0130] The implementation of the planar absorption structure Pxl according to the invention in the pixel described in Figure 4a is a non-limiting illustration. The invention is compatible with other variants of pixel architectures that also allow for the reduction of dark current.

[0131] We emphasize that it is possible to realize the overall planar absorption structure (SPAG) of the pixel with a plurality of planar absorption structures. superimposed one on top of the other. Thus, the SPAG global planar absorption structure can contain a first SPA global planar absorption structure according to any of the embodiments of the invention with a thickness of 0.5 µm to 5 µm. In addition, the SPAG global planar absorption structure can contain a second SPA global planar absorption structure arranged on top of the first SPA global planar absorption structure made of a solid material with a mesh matching the substrate and therefore not exhibiting degeneration. The second SPAG global planar absorption structure has a thickness of between 0.5 µm and 3 µm. This avoids putting the entire SPAG global planar absorption structure under mechanical stress.

[0132] Figure 5 illustrates a cross-sectional view of an infrared radiation detection device D1 comprising a plurality of pixels Pxl according to the invention.

[0133] The infrared radiation detection device D1 is mounted on the SUB substrate. It is a hybrid optoelectronic system, comprising: an optical (OPT) component based on a matrix formed by a plurality of pixels arranged in rows and columns, and an electronic component consisting of an integrated ROIC readout circuit on a semiconductor substrate, allowing the signal from each pixel of the optical (OPT) component to be read individually. A pixel belonging to the optoelectronic system can contain a single photosensitive element or a plurality of interconnected photosensitive elements. Alternatively, for specific applications, it is possible to implement the optical (OPT) component with a single pixel (Pxl).The ROIC readout integrated circuit is implemented using a plurality of transistors and thin films of conductive, semiconductor, or dielectric materials, based on CMOS (Complementary Metal-Oxide-Semiconductor) technology, on a silicon substrate. For each pixel Pxl, a buried electrode is associated to read the signals generated by the charge carriers photogenerated by the photodetector structure of a pixel Pxl.

Claims

32 DEMANDS 1. Infrared radiation detection device (D1) comprising at least one pixel (Pxl) having an axis (A) along a direction Z, said pixel comprising a first planar absorbing structure (SPA) comprising at least one semiconductor layer (C mm , C1 , C2); each layer (C m m, C1, C2) of the first planar absorbing structure (SPA) being arranged in a crystalline lattice structure; the first planar absorbing structure (SPA) being N-doped and being produced by epitaxy on a substrate (Sub) and the composition of the materials used to produce at least one layer (C m m, C1, C2) of the first planar absorbing structure (SPA) being chosen such that: ■ The first planar absorbing structure (SPA) exhibits an effective valence band (BV e ff) formed by a plurality of energy levels (Evhh, Evih); each energy level (Ev h h, Evih ) being occupied by one of: o a first type of positive charge carrier called heavy holes (hh) having a first effective mass (nrihh); o or a second type of positive charge carrier called light holes (Ih) having a second effective mass (mi h ) strictly less than the first effective mass (m h h) ; the maximum energy level of the effective valence band (BV eff ) being occupied by light holes (Ih) along the axis (A) of the pixel; the crystalline structure of the lattice of said layer does not exhibit dislocations resulting from a mechanical relaxation of said lattice; the effective mass of the positive charge carriers along the axis of the pixel (A) being less than half the effective mass of the positive charge carriers along directions defining a plane orthogonal to the axis of the pixel (A).

2. Infrared radiation detection device (D1) according to claim 1, wherein the substrate (Sub) is arranged in a crystalline lattice structure and wherein the composition of the materials used to make the 33 minus one layer (C m m, C1, C2) of the first planar absorbing structure (SPA) is chosen such that ■ the meshes of at least one layer (C mm , C1 , C2) forming said planar absorbing structure (SPA) undergo internal mechanical stresses to adapt to the lattices of the substrate crystalline structure (SUB); ■ and such that the resulting stress from the sum of the internal mechanical stresses is a tensile stress. Infrared radiation detection device (D1) according to any one of the preceding claims, wherein the effective mass of the positively charged holes along the pixel axis (A) is less than one-tenth of the mass of a free electron. Infrared radiation detection device (D1) according to any one of the preceding claims, wherein the difference between the maximum energy level occupied by light holes (Evi h ) and the maximum energy level occupied by heavy holes (Evhh) is greater than the product of the Boltzmann constant and the operating temperature. Infrared radiation detection device (D1) according to any one of claims 2 to 4, wherein the composition of the materials used to make at least one layer (C mm, C1, C2) of the first planar absorbing structure (SPA) is chosen such that the magnitude of the resulting stress from the sum of the internal mechanical stresses is less than a predetermined dislocation limit stress; the dislocation density in the first planar absorbing structure being strictly less than 10 4 dislocations / cm2 Infrared radiation detection device (D1) according to any one of the preceding claims, wherein the first planar absorbing structure (PAS) consists of a single layer (C m m) in a bulk semiconducting material of type III-V. Infrared radiation detection device (D1) according to the preceding claim, wherein the bulk semiconductor material is the quaternary alloy Gaxiln-i.xiASyiSbi.yi with x1 the mole fraction of gallium in the Ga alloy xi lni-xiAs yiSbi-yi and y1 the mole fraction of arsenic in the alloy Gaxln-i.xiASyiSbi.yi. Infrared radiation detection device (D1) according to the preceding claim, wherein: ■ the substrate is made of gallium antimonide GaSb; ■ the mole fraction x1 of gallium Ga in the Ga alloy x lni. x iASyiSbi.yi is between 0 and 1; ■ and the mole fraction y1 of arsenic As in the Ga alloy x lni-xiAs y iSbi-yi is between a minimum value (y1 min) and a maximum value (y"l max) such that . o the minimum value (y1 min ) is an affine function of the mole fraction x1 of gallium Ga in the Ga alloy x lni- x iAs y iSbi- yi characterized by a slope equal to -0.92 and a y-intercept equal to 0.93 where the maximum value (y1 ma x) of the mole fraction y1 of arsenic As in the Ga alloy x lni-x iAs y iSbi- yi is an affine function of the mole fraction x1 of gallium Ga in the alloy Ga x lni- x iAs y iSbi- yi characterized by a slope of -0.92 and a y-intercept of 0.

97. Infrared radiation detection device (D1) according to claim 7, wherein: ■ The substrate is made of indium antimonide InSb; ■ and the mole fraction x2 of gallium Ga in the bulk semiconductor material is between 0.02 and 0.05; ■ and the mole fraction y2 of arsenic As in the bulk semiconductor material is between 0.02 and 0.

05. Infrared radiation detection device (D1) according to any one of claims 2 to 5, wherein the first planar structure absorbing (SPA) comprises a first superlattice (SR) comprising a stacking along the pixel axis (A) of an elementary group of semiconductor layers (G1) comprising: ■ a first layer (C1) in a first semiconductor material (SC1) exhibiting o a first minimum conduction band value (Ec1); o a first maximum valence band value (Ev1); o a first energy gap value (Eg1); ■ at least a second layer (C2) in a second semiconductor material (SC2) having: o a second minimum conduction band value (Ec2) strictly less than the first minimum conduction band value (Ec1); o a second maximum valence band value (Ev2) strictly less than the first maximum valence band value (Ev1); o and a second energy gap value (Eg2); the lattices of the first layer (C1) undergoing tensile stresses and the lattices of the second layer (C2) undergoing compressive stresses.

11. Infrared radiation detection device (D1) according to the preceding claim, wherein the first super-array has a first effective valence band maximum value (Ev etf), and in which the positive charge carriers in the first shell (C1) of an elementary group (G1) see an energy barrier (BE) equal to the difference between: ■ the maximum energy level (Evhh) of the effective valence band (BV e ff) occupied by heavy holes (hh); ■ and a first maximum value of the effective valence band (Ev eff ) ; 36 the product of said energy barrier (BE) by the thickness (e m 2) of the second layer (O2) being less than a predetermined value. Infrared radiation detection device (D1) according to any one of claims 10 or 11 wherein the second semiconductor material (SC2) is the ternary alloy lnAs y 3Sbi- y 3 with y3 the mole fraction of arsenic in the alloy lnAs y3 Sbi- y3 Infrared radiation detection device (D1) according to claim 12 wherein the first semiconductor material (SC1) is the quaternary alloy Gax3ln-i.x3ASy4Sb1.y4 with x3 the mole fraction of gallium in the alloy Gax3ln-i.x3ASy4Sb1.y4 and y4 the mole fraction of arsenic in the alloy Gax3ln1.x2Asy4Sb1.y4. Infrared radiation detection device (D1) according to claim 13 in which: ■ the mole fraction y3 of arsenic in the alloy lnASy3Sbi- y 3 is between 0.6 and 0.

88. ■ The mole fraction x3 of gallium in the alloy Gax3ln1.x3Asy4Sb1.y4 is between 0.2 and 0.5 ■ and the mole fraction y4 of arsenic in the alloy Gax3ln1.x3ASy4Sb1.y4 is between a minimum value (y4 m in) and a maximum value (y4 ma x) such that: o the minimum value (y4 min) of the mole fraction y4 of arsenic in the alloy Gax3ln1.x3ASy4Sb1.y4 being an affine function of the mole fraction x3 of gallium in the alloy Gax3ln1.x3ASy4Sb1.y4 characterized by a slope equal to -0.92 and a y-intercept equal to 0.

93. o the maximum value (y4 max ) of the mole fraction y4 of arsenic in the Ga alloy X 3lni. X 3ASy4Sbi.y4being an affine function of the mole fraction x3 of gallium in the alloy Gax3lni-x3As y 4Sbi-y4 characterized by a slope equal to -0.66 and a y-intercept equal to 1.

13.

37. Detection device (D1) according to any one of claims 1 to 14, wherein the first planar absorbing structure (PAS) has a first effective valence band maximum value (Ev). eff ), a first minimum value of the effective conduction band (Ec e tf) and a first effective energy gap value (Ege ff); the pixel includes along its axis (A) in this order: ■ the substrate (SUB); ■ A lower contact structure (CONTJNF) made of a third semiconductor material (SC3) or a lower contact superlattice (SRH), doped N+ and exhibiting: o a lower contact valence band maximum value (Ev inf ) strictly less than the maximum effective valence band value (Ev e tf) of the first planar absorbing structure (PAS); and a lower contact energy gap value (Eginf) greater than or equal to the first effective energy gap value (Eg eff ) of the first planar absorbing structure (SPA); ■ A global planar absorbing structure (SPAG) comprising: the first planar absorbing structure (SPA); the layers (C1, C2, Cmm) of said first planar absorbing structure (SPA) being N-doped; ■ one or more transition structures (Ctram, Ct ran 2, Ctranj); the transition structure (Ctrani) in contact with the overall absorbing planar structure (SPAG) being called the initial transition structure; the initial transition structure being made of a fourth semiconductor material (SC4) or a first superlattice of the transition structure (SR tra ni), N-doped and exhibiting: o a maximum valence band value of the initial transition structure (Ev tran i) strictly greater than the maximum effective valence band value (Ev e tf) of the first planar absorbing structure (SPA); o and an energy gap value of the initial transition structure (Egtrani) strictly greater than the first effective energy gap value (Eg eff ) of the first planar absorbing structure (SPA); 38 ■ A top contact structure (CONT_SUP) in a fifth semiconductor material (SC5) or in a top contact superlattice (SR) sup ), doped P+ and exhibiting: o a higher contact valence band maximum value (Ev sup ) strictly greater than the maximum valence band value of each transition structure (Ev tran i, Ev tr ani); o and an energy gap value (Eg sup ) of upper contact strictly greater than the energy gap value of each transition structure (Eg tra nor, Eg tr ani). Detection device (D1) according to the preceding claim in which the pixel comprises several transition structures (C tra nor, Ct ran 2, C tr anj) of rank i=1 to increasing N from the global absorbing planar structure (SPAG) to the upper contact structure (CONT_SUP), with N a non-zero natural number, such that: ■ each transition structure (C tr year 2 C tr anj) of rank i=2 at N exhibits a maximum valence band value (Ev tr an2) strictly greater than the maximum valence band value of the i-1 rank (Evtrani) transition structure.