Architecture of an absorption zone for an infrared detector

Abstract

The invention relates to a detection device configured to detect infrared radiation at a predetermined operating temperature, comprising at least one pixel made by stacking layers on a substrate along the first direction normal to said substrate, said pixel comprising an absorption heterostructure including at least: a first planar absorption structure having a first valence band maximum value; and a second planar absorption structure adjacent to the first planar absorption structure. Said second planar absorption structure having a second valence band maximum value distinct from the first valence band maximum value.The thickness of each of the first and second planar absorption structures is chosen so as to create at least one interface electric field at the interface between the second planar absorption structure and the first planar absorption structure. Said interface electric field is oriented along said first direction. Figure for the abbreviation: Fig. 2a.

Description

Title of the invention: Architecture of an absorption zone for an infrared detector. Field of the invention

[0001] 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 IILV type semiconductor materials. More specifically, the invention relates to an imaging device in the far-infrared (LWIR), mid-infrared (MWIR), and near-infrared (SWIR) regions.

[0002] Problem raised

[0003] Imagers operating in the infrared range are generally made up of an assembly of a matrix comprising a plurality of elementary pixels based on photodiodes transforming a flux of incident photons into photo-generated charge carriers, and a readout circuit commonly called ROIC for "Read Out Integrated Circuit" in English to process the electrical signal from the detector pixels.

[0004] The invention aims to solve a technical problem in this field consisting of designing a matrix detector operating in the infrared at cryogenic temperatures for MWIR and LWIR and non-cryogenic for SWIR by reducing the cross-talk phenomenon between the pixels of the matrix to a step of less than 15pm, without increasing the dark current noise compared to state-of-the-art solutions.

[0005] We will begin by physically explaining these two interdependent characteristics of an infrared matrix sensor.

[0006] By way of illustration, in a space (X,Y,Z) the axis A of each pixel is defined along the direction Z, and the plane having as its normal the axis of the pixel, called the normal plane, is the plane (X, Y).

[0007] Each infrared matrix detector is characterized by a cutoff wavelength Xc defined by the effective energy gap Egeff of the absorbing region of each pixel of the matrix detector according to the Planck-Einstein relation Xc = hc / Egeff, where h is Planck's constant and c is the speed of light in a vacuum. The cutoff wavelength then depends on the energy band structure of the materials used to create the absorbing region of the pixel.

[0008] The phenomenon of crosstalk arises from the interference between adjacent pixels, the photocharges generated by one pixel being able to scatter to a neighboring pixel along the plane perpendicular to the pixel axis. The amplitude of the phenomenon Crosstalk in an infrared array detector increases with the scattering length of minority charge carriers in the normal (X,Y) plane, denoted Ldx>y. The scattering length Ldx>y along the plane normal to the pixel increases with the scattering coefficient in the same plane. The scattering coefficient is inversely proportional to the effective masses mhx and mhy of minority charge carriers (holes in the case of an N-doped absorbing region) in the plane normal to the pixel. The crosstalk phenomenon constitutes a technical limitation for the proper functioning of pixel arrays with small pitches, particularly those smaller than 15 pm.

[0009] For example, for a detector in the mid-infrared, the scattering length is generally greater than 15 pm. Thus, for a pixel pitch less than 15 pm, the imager resolution is degraded compared to the theoretical resolution it can achieve. To quantify this degradation, the modulation transfer function (MTF) is measured at the Nyquist frequency. The value obtained for state-of-the-art solutions is less than 0.5 compared to a theoretical value of 0.64.

[0010] The dark current Jblack is the charge carrier current generated in the absence of incident radiation in the materials that make up the absorbing area of ​​a pixel of the detection matrix. The dark current can be expressed by the following formula:

[0011] T black

[0012] With nja the intrinsic charge carrier density in the absorption zone, r the minority charge carrier lifetime, N the doping, and d the thickness of the absorption zone. N and d are dimensional parameters; r depends on the manufacturing conditions.

[0013] In summary, the technical challenge is to find a solution that limits the degradation of resolution with the reduction of the pixel pitch due to the increase in crosstalk without increasing the dark current, and this for a given cutoff frequency at a given operating temperature.

[0014] The technical problem to be solved is then to develop infrared detectors with pixels comprising absorbing areas with an improvement of the following interdependent criteria: maximization of the modulation transfer function (MTF) of a detection system and simultaneous minimization of crosstalk and dark current noise constraints at a given cutoff frequency, at a given pixel pitch and at a given operating temperature.

[0015] Prior art / Restrictions of the state of art

[0016] The publication “Large format InSb infrared detector with lOpm pixels” by Gershon et al. presents an infrared detector with a pixel matrix with a pixel pitch of 15pm and lOpm at 150K. The described solution exhibits a transfer function of The modulation is less than 0.45 for a 15pm step size and less than 0.35 for a 1opm step size. This reflects a degradation in detector performance due to increased crosstalk effects between adjacent pixels.

[0017] Response to the problem and provision of a solution

[0018] To overcome the limitations of existing solutions regarding resolution improvement while minimizing crosstalk and dark current, the invention proposes several embodiments of a pixel structure comprising an absorption heterostructure having at least two adjacent planar structures with close energy gaps and staggered valence and / or conduction band levels. This energy band staggering creates a local electric field at the interface between the two adjacent planar structures. The local electric field is oriented along the pixel axis, axis A, so as to channel charge carriers along the axial direction of the pixel. This reduces charge carrier transport along the (X,Y) plane and thus limits crosstalk.The shift between the valence (and / or conduction) band levels is less than 4kT, where k is the Boltzmann constant and T is the predetermined operating temperature. This maintains a flat energy band structure within the planar heterostructure, thus preventing the increase in dark current due to the formation of a space charge region devoid of charge carriers.

[0019] Advantageously, the absorption heterostructure comprises a repetitive alternation of adjacent planar structures according to the invention to improve the channeling of charge carriers along the pixel axis.

[0020] Advantageously, the absorption heterostructure comprises a succession of several absorption structures with different materials according to the invention so as to form a descending step energy diagram along the axial direction of the pixel.

[0021] The adjacent planar absorption structures according to the invention can be made from a superlattice or a bulk material. The invention details embodiments with examples of material choices for the planar absorption structures, composition ranges for the semiconductor alloys, and thickness ranges for the absorption heterostructure layers according to the invention. The compositions (mole fractions of III-V alloys) of the materials used to fabricate the absorption heterostructure layers according to the invention are chosen to obtain the energy band diagram according to the invention. 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.

[0022] Summary / Claims

[0023] The invention relates to a detection device configured to detect infrared radiation at a predetermined operating temperature, comprising at least one pixel made by a stacking of layers on a substrate along the first direction normal to said substrate, said pixel comprising an absorption heterostructure; said absorption heterostructure comprising at least: - a first planar absorption structure having a first valence band maximum value; - and a second planar absorption structure adjacent to the first planar absorption structure; said second planar absorption structure having a second valence band maximum value distinct from the first valence band maximum value; the thickness of each of the first and second planar absorption structures being chosen so as to create at least one interface electric field at the interface between the second planar absorption structure and the first planar absorption structure; said interface electric field being oriented along said first direction.

[0024] According to a particular aspect of the invention, the difference between the first valence band maximum value and the second valence band maximum value is less than four times the product of the Boltzmann constant by the operating temperature.

[0025] According to a particular aspect of the invention, the thickness of each of the first and second planar absorption structure is greater than or equal to 20 nm.

[0026] According to a particular aspect of the invention, the first planar absorption structure has a first energy gap and the second planar absorption structure has a second energy gap; the absolute difference between the first energy gap and the second energy gap is less than or equal to 20 meV.

[0027] According to a particular aspect of the invention, the first planar absorption structure has a first minimum conduction band value and the second planar absorption structure has a second minimum conduction band value distinct from the first minimum conduction band value with an energy difference of less than four times the product of the Boltzmann constant by the operating temperature.

[0028] According to a particular aspect of the invention, the absorption heterostructure comprises a periodic alternation of the first planar absorption structure and the second planar absorption structure.

[0029] According to a particular aspect of the invention, the absorption heterostructure is doped with N- or P-type dopants, the concentration of said dopants being asymmetric on either side of at least one interface between a first planar absorption structure and a second planar absorption structure.

[0030] According to a particular aspect of the invention, the absorption heterostructure is doped with N-type or P-type dopants, the concentration of said dopants having a decreasing gradient from the interface with the lower electrode to the interface with the upper electrode.

[0031] According to a particular aspect of the invention, the absorption zone comprises a stacking of a succession of several planar absorption structures of rank i=l to increasing N from the substrate along the first direction, with N a natural number strictly greater than 1, such that: - each planar absorption structure of rank i=l at Nl has a maximum valence band value strictly greater than the maximum valence band value of the planar absorption structure of rank i +1, so as to create at least one interface electric field directed along the first direction at each interface; said succession of several planar absorption structures comprising the set formed by the first planar absorption structure and the second planar absorption structure.

[0032] According to a particular aspect of the invention, the difference between, on the one hand, the maximum valence band value of a planar absorption structure of rank i=1 at Nl and, on the other hand, the maximum valence band value of an adjacent planar absorption structure of rank i+1 is less than four times the product of the Boltzmann constant by the operating temperature.

[0033] According to a particular aspect of the invention, the absolute gap between the energy gaps associated with two adjacent planar absorption structures is less than or equal to 20 meV.

[0034] According to a particular aspect of the invention, each planar absorption structure is made of type III-V semiconductor materials.

[0035] According to a particular aspect of the invention, the substrate is made of GaSb or InAs or InP or GaAs.

[0036] According to a particular aspect of the invention, the first planar absorption structure is made by a first massive layer of a first material or a first super-lattice and the second planar absorption structure is made by a second massive layer of a second material different from said first material or a second super-lattice.

[0037] According to a particular aspect of the invention, the first material is the InAsiySby alloy or the Gai_xInxAs alloy or the GaxIni_xAsiySby alloy or the GaxIni_xAsiyPy alloy.

[0038] According to a particular aspect of the invention, the second material is the GaxIni xAsi ySby alloy or the Gai_xInxAs alloy or the GaxIni xAsi yPy alloy.

[0039] According to a particular aspect of the invention, the first super-network and / or the second super-network is constituted by an alternation according to a predetermined spatial period of a pair of layers in InAsiySby / GaxIni_xAsiySby or in InxGai_xAs / InxGai_xAsi yPy or inlnx iGabx iAsby iSby i / Inx 2Gabx 2Asby 2Sby 2.

[0040] According to a particular aspect of the invention, the detection device further comprises a pixel matrix having a pixel pitch less than or equal to 15pm. Detailed description

[0041] In the context of the description of the invention, the term "planar absorption structure" defines a layer in a solid material or a stack of layers forming a super-lattice capable of converting an incident ray into charge carriers.

[0042] Other features and advantages of the present invention will become more apparent from the following description in relation to the following accompanying drawings.

[0043] Fig. 1 illustrates a perspective view of an example pixel belonging to a matrix detector in the infrared frequency range.

[0044] Figure [Fig. 2a] illustrates a cross-sectional view of an infrared detector pixel comprising an absorption heterostructure according to a first embodiment of the invention.

[0045] Fig. 2b illustrates a diagram of the band structure of the absorption heterostructure according to the first embodiment of the invention in the direction of the pixel axis.

[0046] Fig. 2c illustrates the distribution of the electric field in the absorption heterostructure according to the first embodiment of the invention in the direction of the pixel axis.

[0047] Figure 3a illustrates a cross-sectional view of an infrared detector pixel comprising an absorption heterostructure according to a second embodiment of the invention.

[0048] Fig. 3b illustrates the distribution of the electric field in the absorption heterostructure according to the second embodiment of the invention in the direction of the pixel axis.

[0049] Figure 4 illustrates a cross-sectional view of an infrared detector pixel comprising an absorption heterostructure according to a third embodiment of the invention.

[0050] Figure [5a] illustrates a cross-sectional view of an infrared detector pixel comprising an absorption heterostructure according to a fourth embodiment of the invention.

[0051] Fig. 5b illustrates a diagram of the band structure of the absorption heterostructure according to the fourth embodiment of the invention in the direction of the pixel axis.

[0052] Fig. 5c illustrates the distribution of the electric field in the absorption heterostructure according to the fourth embodiment of the invention in the direction of the pixel axis.

[0053] Fig. 1 illustrates a perspective view of an example of several adjacent pixels belonging to a DI matrix detector in the infrared frequency range.

[0054] The illustration is limited to a single row of pixels Pxli to Pxl5 for the sake of simplification but it does not exclude the integration of the pixels into a matrix comprising a plurality of rows and columns of pixels.

[0055] A pixel Pxl (i=l to 5) of the infrared detector is made by stacking layers of semiconductor materials forming the pixel structure on a substrate SUB. The axis of pixel A is the axis perpendicular to the horizontal plane (x,y) formed by the upper surface of the substrate SUB. The substrate SUB is made of a bulk semiconductor material of type IILV, for example. The choice of the substrate material SUB 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 (or multilayers), starting from the substrate, along the direction of the axis of pixel A: a lower electrode EL_INF, an absorption zone SPA, and an upper electrode EL_SUP.

[0056] The lower electrode EL_INF is confined between the absorption zone SPA and the substrate SUB. The lower electrode EL_INF can be made of a bulk semiconductor material or an N+ doped superlattice material. Preferably, the material constituting the lower electrode EL_INF is of type IILV such as, by way of example, gallium arsenide, indium arsenide, gallium nitride, gallium antimonide, indium antimonide, indium phosphide, boron phosphide, as well as their ternary, quaternary, or quinary alloys.The lower electrode EL_INF can also be made with heterostructures obtained by stacking a plurality of thin layers of bulk or N, N+ doped superlattice semiconductor materials, preferably of type IILV such as, for example, gallium arsenide, indium arsenide, gallium nitride, gallium antimonide, indium antimonide, indium phosphide, boron phosphide, as well as their ternary, quaternary, or quinary alloys. Alternatively, the lower electrode EL_INF constitutes, for example, an N+ doped superlattice exhibiting a large energy gap value relative to the SPA absorption region.

[0057] The SPA absorption zone is formed by a stack of N-doped layers and has an energy gap value less than or equal to that of the upper electrode. The band diagram characteristics of the SPA absorption zone (valence band, conduction band, gap energy) are intrinsic in the case of a solid material, or effective layers resulting from the combination of different thin layers in the case of a super-lattice. For the purposes of describing the invention, the term "effective" has been omitted for super-lattices to simplify the description.

[0058] The SPA absorption zone converts the flux of incident photons with a wavelength X into negatively charged carriers, "electrons," in the conduction band and positively charged carriers, "holes," in the valence band of the SPA absorption zone. 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 by infrared radiation. The semiconductor materials used to create the SPA absorption zone (in bulk or superlattice form) can be of type IILV, such as, for example, gallium arsenide, indium arsenide, gallium nitride, gallium antimonide, indium antimonide, indium phosphide, boron phosphide, as well as their ternary, quaternary, or quinary alloys.The energy band structure in the SPA absorption region is crucial for increasing the cutoff frequency of the matrix detector comprising the pixel Pxl;. In the illustrated example, the SPA absorption region is N-doped.

[0059] The upper electrode EL_SUP is made, by way of non-limiting example, by a P+ doping zone on the upper face of the SPA absorption zone. Alternatively, the upper electrode EL_SUP can be made of materials generally having a large energy gap value relative to the SPA absorption zone. These materials are preferably of type III-V such as, by way of example, gallium arsenide, indium arsenide, gallium nitride, gallium antimonide, indium antimonide, indium phosphide, boron phosphide, as well as their ternary, quaternary, or quinary alloys.The upper electrode EL_SUP can also be fabricated with heterostructures obtained by stacking a plurality of thin layers of semiconductor materials, preferably of type IILV, such as, for example, gallium arsenide, indium arsenide, gallium nitride, gallium antimonide, indium antimonide, indium phosphide, boron phosphide, and their ternary, quaternary, or quinary alloys. The upper electrode EL_SUP, for example, constitutes a P+-doped superlattice exhibiting a large energy gap relative to the SPA absorption region. The upper electrode EL_SUP is designed to collect the charges generated by the SPA absorption region.

[0060] The different doping between the upper electrode EL_SUP and the absorption zone induces that the direction of migration of the photo-generated positive charges is from the lower electrode EL_INF to the upper electrode EL_SUP.

[0061] Fig. 2a illustrates a cross-sectional view of an infrared detector pixel Pxl comprising a SPA absorption heterostructure according to a first embodiment of the invention.

[0062] The SPA absorption zone is a heterostructure obtained by stacking along the axial Z direction. The SPA absorption heterostructure comprises N planar absorption structures (Cn, C2b, C3i, etc.) corresponding to bulk layers of a first material ml, where N is a non-zero natural number. The SPA absorption heterostructure further comprises N planar absorption structures (Ci2, C22, C32, etc.) corresponding to bulk layers of a second material m2, where N is a non-zero natural number. The planar structures are stacked alternately to obtain a heterostructure formed by adjacent bulk layers of different materials ml and m2. The first material ml is a semiconductor characterized by a first valence band maximum value Evb, a first conduction band minimum value Eci, and a first energy gap value Egi.The second material m2 is a semiconductor characterized by a second valence band maximum value Ev2, a second conduction band minimum value Ec2, and a second energy gap value Eg2. The second valence band maximum value Ev2 is distinct from the first valence band maximum value Evi by an energy gap (also called offset) of less than 4KbT, where Kb is the Boltzmann constant and T is the detector's operating temperature. The valence band level offset induces a local electric field E at each interface between a planar absorption structure of the first material ml and a planar absorption structure of the second material m2. The interface electric field E at each interface has a direction parallel to the Z direction of the pixel's A-axis.This allows the movement of photogenerated charge carriers to be channeled along the pixel axis, thus reducing the diffusion of charge carriers along the normal (X,Y) plane towards adjacent pixels. This results in a reduction of crosstalk between pixels at reduced pixel pitch values.

[0063] The first material ml and the second material m2 are preferably type III-V semiconductor materials.

[0064] The first and second energy gap values ​​Egi and Eg2 are close to each other, with an absolute difference of less than 20 meV. This makes it possible to obtain a SPA absorption heterostructure suitable for converting radiation to the operating wavelength. Advantageously, the first and second energy gap values ​​Egi and Eg2 are equal.

[0065] Advantageously, the second minimum conduction band value Ec2 is distinct from the first minimum conduction band value Eci with an energy gap (also called offset) of less than 4.KbT with Kb the Boltzmann constant and T the operating temperature of the detector.

[0066] Limiting the phase shifts between the valence (and conduction) energy bands to 4 kBt allows for maintaining a nearly planar band configuration of the energy potential in the absorption region. This prevents the formation of space charge zones with charge carrier depletion, which can lead to a strong generation-recombination current in the SPA absorption heterostructure according to the invention. The result is a reduction in crosstalk without increasing the dark current.

[0067] In the illustrated example, the number of repetitions N is 4, by way of non-limiting indication. The technical effect relating to the invention is obtained from N=1, with a first planar absorption structure Cn and a second planar absorption structure Ci2. The SPA absorption heterostructure comprises at least one first planar absorption structure Cn and a second planar absorption structure Ci2 with the aforementioned band diagram characteristics. The first planar absorption structure Cn and the second planar absorption structure Ci2 are adjacent. The interface formed between the two planar structures exhibits a potential difference that induces an electric field E having a direction parallel to that of the axis A of the pixel Pxl.

[0068] A first planar absorption structure Cn, made of the first material ml and of rank i, has a thickness in the Z direction. A second planar absorption structure Ci2, made of the second material m2 and of rank i, has a thickness ei2 in the Z direction. The thickness in (and ei2) of each of the planar absorption structures Cn, i (and Ci2) is greater than or equal to 20 nm. Indeed, the alternating stacking forming the SPA absorption heterostructure is neither a superlattice nor a multi-quantum well. Recall the definition of a superlattice and a quantum well: In semiconductor physics, a superlattice is a periodic stacking of thin layers of a few nanometers. If these layers are sufficiently thin (generally less than 1 nm), quantum coupling is possible. The carriers (holes and electrons) then have access to an energy continuum along "mini-bands".In the case of a quantum well, the layer with the material that has the minimum of the lowest energy conduction band and / or the maximum of the highest energy valence band has a thickness of less than 20 nm, while the other layer(s) have a thickness greater than 20 nm. In this case, charge carriers access discrete energy levels. along the period axis. The thicknesses enet ei2s are chosen to avoid quantum coupling between the superimposed layers and thus remain within an energy band structure.

[0069] Figure 2b illustrates the band structure of the SPA absorption heterostructure along the axis of pixel Pxl in Figure 2a. An alternating band structure is observed, with variations in valence levels AEv and variations in conduction levels AEc corresponding to the interfaces between adjacent layers of different materials. For example, when positive charge carriers are collected for detection, the variations in valence levels AEv seen through the holes correspond to interface electric fields along the pixel axis. This results in charge channeling along the A-axis, thereby reducing crosstalk.

[0070] The direction of migration of the photogenerated charge carriers is directed from the lower electrode EL_INF to the upper electrode EL_SUP through the SPA absorption heterostructure. On the one hand, during the transition from a planar structure in said first material ml (Cn, C2i, C3i...) to a planar structure in said second material m2 (C12, C22, C32...), the interface electric field vector E is directed in the opposite direction to the migration direction. In this case, the interface electric field E is considered to be negative. On the other hand, during the transition from a planar structure in said second material m2 to a planar structure in said first material ml, the interface electric field E is directed in the direction of migration. In this case, the interface electric field E is considered to be positive. Figure 2c illustrates the distribution of the electric field in the SPA absorption heterostructure along the pixel axis.The alternation between negative and positive interface electric fields E is illustrated by this diagram. Negative interface electric fields E slow the movement of charge carriers towards the upper electrode EL_SUP, and positive interface electric fields E accelerate the movement of charge carriers towards the upper electrode EL_SUP. However, despite the opposing effect of these negative interface electric fields E, the photogenerated charges still propagate towards the upper electrode EL_SUP under the overall effect of the band structure.

[0071] In the case where the SPA absorption heterostructure consists of two planar structures Cn and Ci2 such that the first planar structure Cn is deposited on the lower electrode EL_INF and the second planar structure Ci2 is deposited on said first planar structure Cn. The first planar structure Cn exhibits a first valence band maximum value Evi greater than the valence band maximum value Ev2 of the second planar structure Ci2 with a difference (also called offset) with an energy less than 4KbT, where Kb is the Boltzmann constant and T is the operating temperature of the detector. This allows the creation of a positive interface electric field E.

[0072] By way of a non-limiting example of the first embodiment of the invention, the substrate SUB is GaSb; the first material ml is the InAsbyiSbyi alloy with the mole fraction of Sb in the InAsbyiSbyi alloy such that 0.05 <yl<0,15 ; le deuxième matériau m2 est l’alliage Gax 2Ini_x 2Asby 2Sby 2avec x2 la fraction molaire du Ga dans l’alliage Gax 2Inbx 2Asby 2Sby 2tel que 0<x2<0,5 et y2 la fraction molaire de Sb dans l’alliage Gax 2Inbx 2Asby 2Sby 2tel que y2=0,914.x2+z avec 0,05< z <0,15. L’hétérostructure d’absorption SPA est réalisée par une croissance épitaxiale sur le substrat SUB.

[0073] By way of a non-limiting example of the first embodiment of the invention, the substrate SUB is made of InAs; the first material ml is the InAsby 3Sby 3 alloy with y3 the mole fraction of Sb in the InAsby 3Sby 3 alloy such that 0 <y3<0,07 ; le deuxième matériau m2 est l’alliage Ga^In^Asi^Sb^avec x4 la fraction molaire du Ga dans l’alliage GaX4lni.X4Asi.y4Sby4tel que 0<x4<0,5 et y4 la fraction molaire de Sb dans l’alliage GaX4lni.X4Asi.y4Sby4tel que yl=0,914.xl+z avec 0< z <0,07. L’hétérostructure d’absorption SPA est réalisée par une croissance épitaxiale sur le substrat SUB.

[0074] By way of a non-limiting example of the first embodiment of the invention, the substrate SUB is made of InP; the first material ml is the alloy Gai y 5Iny 5As with y5 the mole fraction of In in the alloy Gai y 5Iny 5As such that 0.46 <y5<0,6 ; le deuxième matériau m2 est l’alliage Inx6Gabx6Asi_y 6Py 6 avec x6 la fraction molaire du Ga dans l’alliage Inx6Gai.x6Asi.y 6Py 6tel que 0,55<x6<0,85 et y6 la fraction molaire de P dans l’alliage Inx6Gai.x6Asi.y 6Py 6tel que y6=2.x5-z avec 1,13< z <1,37. L’hétérostructure d’absorption SPA est réalisée par une croissance épitaxiale sur le substrat SUB.

[0075] By way of a non-limiting example of the first embodiment of the invention, the substrate SUB is made of InP; the first material ml is the alloy Gax 7Inbx 7Asby 7Sby 7 with x7 the mole fraction of Ga in the alloy Gax 7Inbx 7Asby 7Sby 7 such that 0 <x7<0,3 et avec y 7 la fraction molaire du Sb dans l’alliage Gax 7Inbx 7Asi y 7Sby 7 tel que y7=-0,9.x7+z avec 0,46< z < 0,5 ; le deuxième matériau m2 est l’alliage Gax 8Inb x 8Asby 8Sby 8 avecx8 la fraction molaire du Ga dans l’alliage Gax 8Inbx 8Asby 8Sby 8 tel que 0<x8<0,3 et avec y8 la fraction molaire du Sb dans l’alliage Gax 8In[ x 8Asb y 8Sby 8 tel que y8=-0,9.x8+z avec 0,46< z < 0,5. La fraction molaire x7 du Ga dans l’alliage Gax 7Inbx 7Asi y 7Sby 7 du premier matériau ml est différente de la fraction molaire x8 du Ga dans l’alliage Gax 8Inbx 8Asby 8Sby 8 du deuxième matériau m2.The mole fraction y 7 of Sb in the alloy Gax 7Inbx 7Asby 7Sby 7 of the first material ml is different from the mole fraction y8 of Sb in the alloy Gax 8Inbx 8Asi y 8Sby . 8 of the second material m2. The SPA absorption heterostructure is achieved by epitaxial growth on the SUB substrate.

[0076] By way of a non-limiting example of the first embodiment of the invention, the substrate SUB is made of GaAs; the first material ml is the alloy In[x 9Gax 9Asi_ y 9Py 9 with x9 the mole fraction of Ga in the alloy Inbx 9Gax 9Asi y 9Py 9 such that 0 <x9<0,3 et y9 la fraction molaire de P dans l’alliage In[ x 9Gax 9Asi y 9Py 9tel que y9=0,2.x9+z avec 0< z <0,05; le deuxième matériau m2 est l’alliage Gabx i0Inx i0As avecxlO la fraction molaire du In dans l’alliage Gabx i0Inx i0As tel que 0<xl0<0,03. L’hétérostructure d’absorption SPA est réalisée par une croissance épitaxiale sur le substrat SUB.

[0077] Figure 3a illustrates a cross-sectional view of an infrared detector pixel Pxl comprising an SPA absorption heterostructure according to a second embodiment of the invention. The SPA absorption heterostructure retains the structural characteristics detailed in the first embodiment. The difference between the first and second embodiments lies in the distribution of the doping profile of the planar absorption structures Cü and Ci2, with i = 1 at N.

[0078] Consider an example where the minority charge carriers are holes. Thus, the stacked layers of the SPA absorption heterostructure are N-doped according to a predetermined impurity concentration. It has been established that when holes migrate from a planar structure in the first material ml to an adjacent planar structure in the second material m2 along the migration direction, the holes encounter a negative interface electric field E. In this embodiment, at each interface exhibiting a negative electric field E, a doping asymmetry is integrated on both sides of said interface. More specifically, the second planar absorption structure in the second material m2 has an interface doping zone N extending from said interface into the volume of said second planar absorption structure in the second material ml.The N-type interface doping zone has a second impurity concentration lower than the first predetermined impurity concentration. For example, each N-type interface doping zone is doped with a concentration of 2 x 10¹⁴ cm³ and the rest of the volume of the SPA absorption heterostructure is N-type doped with a concentration of 1 x 10¹⁵ cm³. The N-type interface doping zone has a penetration depth into the volume of the second planar absorption structure greater than 1 onm.

[0079] This creates a doping asymmetry at the interfaces, which have interface electric fields that slow the movement of charge carriers towards the upper collection electrode EL_SUP. The doping asymmetry at the Interfaces allow for a reduction in the amplitude of the negative interface electric fields E, thereby improving the mobility of photogenerated charges along the pixel axis Pxl. Figure 3b illustrates the electric field distribution in the SPA absorption heterostructure along the pixel axis Pxl with the doping asymmetry described previously.

[0080] Alternatively, the N-type doping profile of the SPA absorption heterostructure exhibits a decreasing gradient from the lower electrode EL_INF to the upper electrode EL_SUP. This results in more intense interface electric fields E at the base of the pixel Pxl compared to the apex next to the upper electrode EL_SUP. Thus, the channeling effect according to the invention is accentuated at the base of the pixel Pxl where the risk of crosstalk is greater.

[0081] Figure 4 illustrates a cross-sectional view of an infrared detector pixel Pxl comprisingA SPA absorption heterostructure according to a third embodiment of the invention. The SPA absorption heterostructure comprises a first group of N planar absorption structures. Each structure in the first group is realized by a first superlattice SRi, where N is a non-zero natural number. The SPA absorption heterostructure further comprises a second group of N planar absorption structures. Each structure in the second group is realized by a second superlattice SR2, where N is a non-zero natural number. The SRi and SR2 superlattices are stacked alternately to obtain a heterostructure formed by different adjacent superlattices. It should be noted that the invention discloses an alternating stacking of at least two different superlattices. It is not a single, unique superlattice.The first superlattice SRi is characterized by a first valence band maximum value Evb, a first conduction band minimum value Eci, and a first energy gap value Egb. The second superlattice SR2 is characterized by a second valence band maximum value Ev2, a second conduction band minimum value Ec2, and a second energy gap value Eg2. The second valence band maximum value Ev2 is distinct from the first valence band maximum value Evi by an energy difference (also called a band shift) of less than 4KbT, where Kb is the Boltzmann constant and T is the detector's operating temperature. The band shift induces the creation of a local electric field E at each interface between a planar absorption structure produced by the first superlattice SRi and a planar absorption structure produced by the second superlattice SR2.This gives us the same alternating energy band diagram described in the first one. an embodiment allowing the charge carriers to be channeled along the A-axis of the pixel and thus reducing the crosstalk phenomenon between adjacent pixels.

[0082] The first superlattice SRie and second superlattice SR2 are made with semiconductor materials preferably of type III-V. In this embodiment, the absorption zone SPA is an alternating stacking of at least two different superlattices, which does not correspond to a superlattice as such.

[0083] Generally speaking, the design choices for a superlattice according to the invention cover the choice of materials used (materials engineering), the thickness of the layers composing the superlattice, the period of the superlattice (here π and π²), and the mole fractions in the case of using alloys. According to a particular aspect of the invention, the second superlattice SR2 is composed of a stack of layers made of materials different from those forming the first superlattice SRi. Alternatively, the second superlattice SR2 is composed of a stack of layers of the same materials as those forming the first superlattice SRi but with different layer thicknesses. Alternatively, the second superlattice SR2 is composed of a stack of layers of the same materials as those forming the first superlattice SRi but with different periods π².Alternatively, the second SR2 superlattice is composed of a stack of layers of the same alloys as those that form the first SRi superlattice but with different mole fractions, layers of different thicknesses and different periods pi^p2. .

[0084] By way of a non-limiting example of the third embodiment of the invention, the SUB substrate is GaSb. The first SRi superlattice is InAsiy i iSby ii / Gaxi 2Inb xi 2Asi y 12Sby 12with0.084 <y 11<0.4 pour l’alliage ternaire et la plage en composition pour l’alliage quaternaire est un quadrilatère tel que 0,1 < xl2 <0,5 et en xl2=0,l : 0< yl2 <0,25 et en xl2=0,5 : 0,2< yl2 <0,4. Les épaisseurs du ternaire elnAsSb et du quaternaire eGa in ASsb sont comprises entre 0,9nm<elnAsSb <2nm et 0,9nm<eGalnAsSb <5nm. Le deuxième super-réseau SR2 est InAsi y i iSby i i / Gax i 2Ini x i 2Asby- i2Sby- i 2avec0,084<y’ 11<0,4 pour l’alliage ternaire et la plage en composition pour l’alliage quaternaire est un quadrilatère tel que 0,1 < x’ 12 <0,5 et en x’ 12=0,1 : 0< y’ 12 <0,25 et en x’ 12=0,5 : 0,2< y’ 12 <0,4. Les épaisseurs du ternaire elnAsSb et du quaternaire e’Ga in ASsb sont comprises entre 0,9nm<e’lnAsSb <2nm et 0,9nm<e’GalnAsSb <5nm.The second SR2 superlattice has a p2 period different from the pi period of the first SRi superlattice and / or different alloy mole fractions than the alloy mole fractions constituting the first SRi superlattice. The SPA absorption heterostructure is produced by epitaxial growth on the SUB substrate.

[0085] By way of a non-limiting example of the third embodiment of the invention, the SUB substrate is in InAs. The first SRi supernetwork is InAsPyi 3Sbyi 3 / Gaxi 4InP xi 4AsPy i4Sby i4avec0 <yl3<0,4 pour l’alliage ternaire et la plage en composition pour l’alliage quaternaire est un quadrilatère tel que 0,1 < xl4 <0,5 et en xl4=0,l : 0< yl4 <0,25 et en xl4=0,5 : 0,l< yl4 <0,4. Les épaisseurs du ternaire elnAsSb et du quaternaire eGa in ASsb sont comprises entre 0,9nm<elnAsSb <2nm et 0,9nm<eGalnAsSb <5nm. Le deuxième super-réseau SR2 est InAsi y i 3Sby i 3 / Gax i 4InPx-i 4AsPy- 14Sby’ 14avec0<y’ 13<0,4 pour l’alliage ternaire et la plage en composition pour l’alliage quaternaire est un quadrilatère tel que 0,1 < x’ 14 <0,5 et en x’ 14=0,1 : 0< y’ 14 <0,25 et en x’ 14=0,5 : 0,l< y’ 14 <0,4. Les épaisseurs du ternaire elnAsSb et du quaternaire e’Ga in ASsb sont comprises entre 0,9nm<e’lnAsSb <2nm et 0,9nm<e’GalnAsSb <5nm.The second SR2 superlattice has a p2 period different from the pi period of the first SRi superlattice and / or different alloy mole fractions than the alloy mole fractions constituting the first SRi superlattice. The SPA absorption heterostructure is produced by epitaxial growth on the SUB substrate.

[0086] By way of a non-limiting example of the third embodiment of the invention, the SUB substrate is InP. The first SRi superlattice is Inxi5Gai_xi5As / Inxi6Gai_xi6Asl yl6Pyl6avec0.45 <xl5<0,8 pour l’alliage ternaire et la plage en composition pour l’alliage quaternaire est un quadrilatère tel que 0,4 < xl6 <0,8 et en xl6=0,4 : 0< yl6 <0,2 et en xl6=0,8 : 0,55< yl6 <1. Les épaisseurs du ternaire elnGaAs et du quaternaire elnGaAsP sont comprises entre 0,9nm<elnGaAs <5nm et 0,9nm<elnGaAsP <5nm. Le deuxième super-réseau SR2 est Inx i5Gai x i5As / Inx i6Gai_x i6Asi_y i6Py i6avec0,45<x’ 15<0,8 pour l’alliage ternaire et la plage en composition pour l’alliage quaternaire est un quadrilatère tel que 0,4 < x’ 16 <0,8 et en x’ 16=0,4 : 0< y’ 16 <0,2 et en x’ 16=0,8 : 0,55< y’ 16 <1. Les épaisseurs du ternaire e’InGaAs et du quaternaire e’lnGaAsP sont comprises entre 0,9nm<e’lnGaAs <5nm et 0,9nm<e’lnGaAsP <5nm.The second SR2 superlattice has a p2 period different from the pi period of the first SRi superlattice and / or different alloy mole fractions than the alloy mole fractions constituting the first SRi superlattice. The SPA absorption heterostructure is produced by epitaxial growth on the SUB substrate.

[0087] By way of a non-limiting example of the third embodiment of the invention, the SUB substrate is made of InP. The first super-lattice SRi is Inxl 7GaPxl 7AsPyl 7Sbyl 7 / Inx i8GaPx i8Asi.y 18Sby 18 and the second super-lattice SR2 is made of the same materials but with a different period and / or different stoichiometric coefficients.

[0088] By way of a non-limiting example of the third embodiment of the invention, the SUB substrate is GaAs. The first SRi superlattice is InxiQGai_xiQAs / Inx2oGai_ x2oAsby2oPy2oavecO <xl9<O,2 pour l’alliage ternaire et la plage en composition pour The quaternary alloy is a quadrilateral such that 0 < x20 < 0.3 and at x20=0: 0 < y20 < 0.4 and at x20=0.3: 0.6 < y20 < 1. The thicknesses of the ternary elnGaAs and the quaternary elnGaAsP are between 0.9 nm <elnGaAs <5nm et 0,9nm<elnGaAsp <5nm. Le deuxième superréseau SR2 est InX’i9Gai_X’i9As / InX’2oGai.X’2oAsiy2oPy’2oavecO<x’ 19<0,2 pour l’alliage ternaire et la plage en composition pour l’alliage quaternaire est un quadrilatère tel que 0 < x’20 <0,3 et en x’20=0 : 0< y’20 <0,4 et en x’20=0,3 : 0,6< y’20 <1. Les épaisseurs du ternaire e’lnGaAs et du quaternaire e’lnGaAsp sont comprises entre 0,9nm <e’lnGaAs <5nm et 0,9nm<e’lnGaAsP <5nm. Le deuxième super réseau SR2 présente une période p2 différente de celle pi du premier réseau SRi et / ou des fractions molaires d’alliages différentes des fractions molaires des alliages constituant le premier super réseau SRi. L’hétéro structure d’absorption SPA est réalisée par une croissance épitaxiale sur le substrat SUB.

[0089] Alternatively, it is possible to implement a SPA absorption heterostructure according to the invention in which the alternating energy diagram is obtained by the alternating stacking of bulk layers with superlattices. This is a hybrid mode between the first embodiment and the third embodiment.

[0090] Figure 5a illustrates a cross-sectional view of an infrared detector pixel Pxl comprising an absorption heterostructure SPA according to a fourth embodiment of the invention. The absorption heterostructure SPA comprises a stacking of a plurality of planar structures C, of ​​rank i=1 to N, where N is a natural number greater than or equal to 2. The first planar structure Ci is made of a layer of a first bulk material ml or of a first superlattice SRI. The second planar structure C2 is made of a layer of a second bulk material m2 or of a second superlattice SR2, and so on.In the direction of minority charge carrier migration, each planar absorption structure Ci of rank i=l to Nl exhibits a maximum valence band value Ev strictly greater than the maximum valence band value Ev + i of the planar absorption structure Ci + i of rank i+1, with an energy gap less than four times the product of the Boltzmann constant and the operating temperature. A descending step-like energy diagram is obtained from the lower electrode ELINF to the upper electrode ELSUP. The absolute difference between the energy gap Eg of the planar absorption structure Ci of rank i=l to Nl and the planar absorption structure Ci + i is less than or equal to 20 meV.

[0091] Advantageously, each planar absorption structure Cdc rank i=l to Nl has a minimum conduction band value Ec; strictly greater than the minimum conduction band value Ec; + i of the planar structure absorption of rank i+1, with an energy gap less than four times the product of the Boltzmann constant by the operating temperature.

[0092] This results in a succession of several layers C, of ​​rank i=l to N, starting from EL_INF along the first direction Z, with an energy band diagram in the form of a descending staircase. [Fig. 5b] illustrates a schematic of the band structure of the SPA absorption heterostructure according to the fourth embodiment of the invention in the direction of the pixel axis Pxl.

[0093] The materials used to create the absorption heterostructure are preferably III-V type semiconductor materials.

[0094] The choice of valence and conduction levels of the planar absorption structures Ci allows for obtaining an energy diagram in the form of a descending staircase. Each energy step corresponds to the interface between two planar absorption structures. Each energy difference at the interface induces an interface electric field E directed along the Z-axis, the direction of the A-axis of the pixel Pxl.

[0095] The advantage of this embodiment is that the energy variation is always in the same direction, making it possible to induce positive interface electric fields E as illustrated in [Fig. 5c]. The direction of E is thus always identical to the direction of migration of minority charge carriers.

[0096] By way of a non-limiting example of the fourth embodiment of the invention, the SPA absorption heterostructure comprises the following series of super-lattices SRistashed in this order InAsi_yiSbyi / GaxIni.xAsi.y • ;Sby • ;withi=[l,2,3,4] and 0.2 < x <0.5 and such that 0.7< yl,y 1 ' <0.8 and 0.65< y2,y2' <0.75 and 0.6< y3,y3' <0.7 and 0.55< y4,y4' <0.65.

Claims

Demands

1. A detection device (Dl) configured to detect infrared radiation at a predetermined operating temperature, comprising at least one pixel (Pxl) made by a stacking of layers on a substrate (SUB) along the first direction (Z) normal to said substrate (SUB), said pixel comprising an absorption heterostructure (SPA); said absorption heterostructure (SPA) comprising at least: - a first planar absorption structure (Cn, SRJ) having a first valence band maximum value (Evi); - and a second planar absorption structure (Ci2, SR2) adjacent to the first planar absorption structure (Cn, SRJ); said second planar absorption structure (Ci2, SR2) having a second valence band maximum value (Ev2) distinct from the first valence band maximum value (EvJ;the thickness (en, ei2 , eSRi, eSR2) of each of the first and second planar absorption structures (Cn, SRi Ci2, SR2) being greater than or equal to 20 nm; the thickness (en, ei2 , eSRi, eSR2) of each of the first and second planar absorption structures being chosen so as to create at least one interface electric field (E) at the interface between the second planar absorption structure (Ci2, SR2) and the first planar absorption structure (Cn, SRi); said interface electric field (E) being oriented along said first direction (Z).;

2. Detection device (Dl) according to claim 1 wherein the difference between the first valence band maximum value (Evi) and the second valence band maximum value (Ev2) is less than four times the product of the Boltzmann constant by the operating temperature.

3. A detection device (Dl) according to any one of the preceding claims, wherein the first planar absorption structure (Cn, SRi) has a first energy gap (Egi) and the second planar absorption structure (Cn, SRi) has a second energy gap (Eg2); the absolute difference between the first gap energy (Egi) and the second energy gap (Eg2) is less than or equal to 20 meV.

4. A detection device (Dl) according to any one of the preceding claims wherein the first planar absorption structure (Cn, SRi) has a first conduction band minimum value (Eci) and the second planar absorption structure (Ci2, SR2) has a second conduction band minimum value (Ec2) distinct from the first conduction band minimum value (Eci) with an energy difference of less than four times the product of the Boltzmann constant by the operating temperature.

5. Detection device (Dl) according to any one of the preceding claims wherein the absorption heterostructure (SPA) comprises a periodic alternation of the first planar absorption structure (Cn, SRi) and the second planar absorption structure (C2b SR2).

6. Detection device (Dl) according to any one of claims 1 to 5 wherein the absorption heterostructure (SPA) is doped with N-type or P-type dopants, the concentration of said dopants being asymmetric on either side of at least one interface between a first planar absorption structure (Cn, SRi) and a second planar absorption structure (Ci2, SR2).

7. Detection device (Dl) according to any one of claims 1 to 5 wherein the absorption heterostructure (SPA) is doped with N-type or P-type dopants, the concentration of said dopants having a decreasing gradient from the interface with the lower electrode to the interface with the upper electrode.

8. A detection device (Dl) according to any one of the preceding claims, wherein the absorption zone (SPA) comprises a stacking of a succession of several planar absorption structures (Ci, C2, C3, C4, C5) of rank i=l to increasing N from the substrate (SUB) along the first direction (Z), with N a natural number strictly greater than 1, such that: - each planar absorption structure (Ci, C2, C3, C4) of rank i=l to Nl has a maximum valence band value (Ev;) strictly greater than the maximum valence band value of the planar absorption structure (Evi+i) of rank i+1, so as to create at least one interface electric field (E) directed along the first direction (Z) at each interface; said succession of several planar absorption structures (Ci, C2, C3, C4, C5) comprising the set formed by the first planar absorption structure (Cn, SRi) and the second planar absorption structure (Ci2, SR2).

9. Detection device (Dl) according to claim 8 wherein the difference between on the one hand the maximum valence band value (Ev;) of a planar absorption structure (Ci, C2, C3, C4) of rank i=l at Nl and on the other hand the maximum valence band value (Ev;) of an adjacent planar absorption structure (C2, C3, C4, C5) of rank i+1 is less than four times the product of the Boltzmann constant by the operating temperature.

10. Detection device (Dl) according to any one of claims 8 or 9 wherein the absolute gap between the energy gaps associated with two adjacent planar absorption structures (Ci, C2, C3, C4, C5) is less than or equal to 20 meV.

11. Detection device (Dl) according to any one of the preceding claims wherein each planar absorption structure is made of type III-V semiconductor materials.

12. Detection device (Dl) according to any one of the preceding claims wherein the substrate is GaSb or InAs or InP or GaAs.

13. A detection device (Dl) according to any one of the preceding claims, wherein: - the first planar absorption structure (Cn, SRi) is made by a first massive layer (Cn) in a first material (ml) or a first super-lattice (SRi); - the second planar absorption structure (Cn, SRj) is made by a second massive layer (Ci2) in a second material (m2) different from said first material or a second super-lattice (SR2).

14. Detection device (Dl) according to claim 13 in which the first material (ml) is the InAsiySby alloy or the Gai_xInxAs alloy or the GaxIni_xAsiySby alloy or the GaxIni_xAsiyPy alloy.

15. Detection device (Dl) according to any one of claims 13 or 14 wherein the second material (m2) is the GaxIni_xAsiySby alloy or the GabxInxAs alloy or the GaxIni xAsnyPy alloy.

16. A detection device (Dl) according to claim 15, wherein the first super-lattice and / or the second super-lattice is constituted by an alternation, according to a predetermined spatial period (pl, p2), of a pair of layers in InAsi ySby / GaxIni_xAsi ySby; or in InxGai_xAs / InxGai_xAsi_yPy; or inln^Ga^iAsi-yiSbyi / In^Gai^Asi^Sb^

17. Detection device (Dl) according to any one of the preceding claims comprising a pixel matrix (Pxl) having a pixel pitch less than or equal to 15pm.