INFRARED RADIATION DETECTION DEVICE

Abstract

INFRARED RADIATION DETECTION DEVICE An infrared radiation detection device comprises a super-lattice, equipped with alternating first layers (4) and second layers (5), each of the general formulation InAs1-xSbx. The antimony concentrations are between 4% and 10% for the first layer (4) and between 12% and 24% for the second layer (5). Each of the first layer (4) and the second layer (5) exhibits an antimony concentration gradient throughout its thickness. The super-lattice has a period less than or equal to 10 nm. Figure for the abstract: Figure 1

Description

Title of the invention: INFRARED RADIATION DETECTION DEVICE technical field

[0001] The invention relates to an infrared radiation detection device. State of the art

[0002] In many activities, a scene is observed by a detection device that includes a photodetector. The photodetector receives a light signal which it transforms into an electrical signal representative of the observed scene.

[0003] Conventionally, the photodetector includes an absorbing layer which transforms received electromagnetic radiation, in particular infrared radiation, into an electrical signal by generating electric charge carriers.

[0004] To detect infrared radiation, it is known to use an absorbing layer having a superlattice, that is, a stack of several films representing an alternation between a compound A and a compound B that have different band structures. One of the two materials used forms a "barrier" layer while the other forms a "sink" layer. The thicknesses of the different layers are small so as to consider the quantum structure of the entire stack. This architecture makes it possible to confine the charge carriers to discrete energy levels.

[0005] Conventionally, to capture infrared radiation, an InAs / GaSb, InAs / AlSb or InAs / InAsSb superlattice is created. During the formation of the superlattice, the multiple layers of the stack are deposited one after the other in a growth direction.

[0006] It is known that this type of stacking exhibits a significant transport anisotropy between the perpendicular direction, which corresponds to the growth direction of the stacking of the layers, and the parallel direction, which is the direction contained in the interface between the layers.

[0007] This transport anisotropy has an important consequence on the diffusion length of charge carriers in the MWIR and LWIR ranges, as shown by Arounassalame et al., “Anisotropy transport investigation through different etching depths in InAs / InAsSb T2SL barrier midwave infrared detector”, Infrared Physics & Technology, vol. 126, p. 104315, Nov. 2022, and by Liu et al., “Short-period InAsSb-based strained layer superlattices for high quantum efficiency long-wave infrared detectors”, Appl. Phys. Lett. 4 April 2022; 120 (14): 141101.

[0008] It is also known that transport anisotropy has an effect on the modulation transfer function (MTF), which is similar to the optical transfer function. This function characterizes the ability of an optical system to restore contrast as a function of the fineness of the details of an object. An impact of anisotropy on the modulation transfer function was shown by Berthoz et al., "Range infrared detector issues in the SWAPc and pitch reduction context," Proc. SPIE 11407, Infrared Technology and Applications XLVI, 1140715 (5 May 2020). It can be observed that transport anisotropy leads to a significant decrease in the performance of an infrared detection system.

[0009] To limit anisotropy by restricting scattering along the parallel direction, it is known to create trenches within the absorbing layer so as to separate each absorption zone from adjacent absorption zones. The trenches are made throughout the entire thickness of the absorbing layer. Creating deep trenches or mesas allows the pixels to be physically separated in order to bring the modulation transfer function value closer to its theoretical optimal value. However, this operation is not neutral because it generates parasitic currents as well as a degradation of operability at high operating temperatures. Such results were shown by Ting et al., "InAs / InAsSb Type-II Superlattice Mid-Wavelength Infrared Focal Plane Array With Significantly Higher Operating Temperature Than InSb," in IEEE Photonics Journal, vol. 10, no. 6, pp. 1-6, Dec. 2018, Art. no. 6804106, and by Delmas et al.“Type-II superlattice detectors for high-performance SWaP detectors and HOT HD applications at IRnova”, Proc. SPIE 12534, Infrared Technology and Applications XLIX, 125340H (13 June 2023). .

[0010] It is also known that T2SL InAs / InAsSb superlattices exhibit a relatively low theoretical absorption which implies a lower quantum efficiency than other known detectors as shown by Klipstein "Physics and technology of antimonide heterostructure devices at SCD", Proc. SPIE 9370, Quantum Sensing and Nanophotonic Devices XII, 937020 (8 February 2015). Description of the invention

[0011] One object of the invention is to overcome these drawbacks, and more particularly to provide an infrared radiation detection device that performs better than prior art detection devices equipped with an absorbing layer formed by a superlattice, and in particular those with an InAs / InAsSb superlattice. Preferably, the aim is to improve at least one of the quantum absorption efficiency and the hole mobility.

[0012] These drawbacks are addressed by means of an infrared radiation detection device comprising an absorbing layer designed to absorb a infrared radiation and to generate electric charge carriers, the absorbing layer comprising a super-lattice, the super-lattice comprising an alternation of a first layer and a second layer, the first layer being of general formulation InAsixSbx with a first concentration of antimony and a first thickness and the second layer being of general formulation InAsi xSb x with a second concentration of antimony and having a second thickness, the second concentration of antimony being strictly greater than the first concentration by at least 2 atomic%.

[0013] The infrared radiation detection device is remarkable in that the first antimony concentration is greater than 4 atomic%; in that the super-lattice has a period of less than 15nm, the period corresponding to an average value of a sum of the first thickness and the second thickness; in that at least one of the first and second layers exhibits an antimony concentration gradient; wherein, when the first layer exhibits a first antimony concentration gradient, the first antimony concentration represents a minimum antimony value in the first layer, and the first concentration gradient is monotonic from the second concentration to the first concentration, the first concentration gradient extending over at least 33% of the first thickness; and / or in which, when the second layer exhibits a second antimony concentration gradient, the second antimony concentration represents a maximum antimony value in the second layer and the second concentration gradient is monotonic from the first concentration to the second concentration, the second concentration gradient extending over at least 33% of the second thickness.

[0014] According to one aspect of the invention, the first concentration of antimony is less than 10 atomic% and the second concentration is between 10% and 30 atomic%.

[0015] Preferably, the first antimony concentration is between 5% and 8% atomic and the second antimony concentration is between 12% and 24% atomic.

[0016] In a particular embodiment, the period is less than or equal to lOnm.

[0017] Advantageously, the second thickness is less than or equal to 90% of the first thickness.

[0018] In a particular embodiment, the second thickness is less than or equal to 50% of the first thickness.

[0019] Preferably, the first concentration gradient is a linear concentration gradient over the entire thickness of the first layer or a sublinear concentration gradient.

[0020] In another development, the second concentration gradient is a linear concentration gradient over the entire thickness of the second layer or a superlinear concentration gradient.

[0021] Preferably, the first layer and the second layer each have an antimony gradient.

[0022] In an advantageous embodiment, the first layer has a constant antimony concentration over a thickness less than or equal to 20% of the first layer's thickness. The second layer has a constant antimony concentration over a thickness less than or equal to 20% of the second layer's thickness. Drawing description

[0023] Other advantages and features will become clearer from the following description of particular embodiments and implementations of the invention given by way of non-limiting examples and shown in the accompanying drawings, in which:

[0024] [Fig.l]: schematically illustrates an infrared radiation detection device equipped with a stack of several layers, including at least one super-array;

[0025] [Fig.2]: schematically illustrates a variation in the concentration of antimony in the first layer and in the second layer of a super-lattice;

[0026] [Fig.3]: schematically illustrates an energy representation of the minibands of heavy holes, light holes and electrons. Detailed description

[0027] The detection device is a device configured to detect infrared radiation, i.e. configured to capture infrared radiation and generate an electrical signal representative of the radiation captured.

[0028] The detection device illustrated schematically in [Fig.1] includes an absorbing layer 1 intended to absorb infrared radiation and to generate electric charge carriers.

[0029] The absorbing layer 1 is connected on one side to an emitter contact 2e and on the other side to a collector contact 2c. In other words, the emitter contact 2e and the collector contact 2c are separated by the absorbing zone 1. The contact zones 2e and 2c can advantageously be formed from one or more semiconductor materials. Preferably, the contact zones 2 are formed from semiconductor materials doped to reduce contact resistance. Advantageously, the The two contact zones are coated with a metal. These contact zones are used to polarize the photodetector if necessary and to collect the charge carriers that have been generated.

[0030] During operation, electric charge carriers are generated in the absorbing layer 1 during the absorption of the light radiation to be detected. The electric charge carriers are captured by the contact areas 2e / 2c to provide an electric current representative of the detected light radiation.

[0031] Between the absorbing layer 1 and at least one of the contacts 2e, 2c, it is advantageous to have a blocking zone 3 that prevents the passage of majority charge carriers between the contact zone 2 and the absorbing layer 1. This blocking zone 3 will reduce or even eliminate the dark current component associated with electrically active faults in the structure and will therefore increase the signal-to-noise ratio of the photodetector. During operation, the photodetector also generates minority charge carriers, and these minority carriers are measured to determine the detected luminous flux. Other architectures are possible.

[0032] In order to improve the transport performance of the load carriers and / or the absorption efficiency, it is advantageous to modify the structure of the absorbing layer 1.

[0033] As illustrated in [Fig. 1], the absorbing layer 1 has a superlattice comprising an alternation of a first layer 4 and a second layer 5. The first layer 4 and the second layer 5 are semiconductor layers in a single-crystal form. The first layer 4 has a different composition from the second layer 5 in order to have different band characteristics and define a barrier layer and a sink layer.

[0034] The first layer 4 is a layer of general formulation InAS|XSbx with a first antimony concentration X4 and a first non-zero thickness e4. The second layer 5 is a layer of general formulation InAsi xSbx. The second layer 5 has a second antimony concentration X5 strictly greater than the first concentration X4. The second layer 5 has a non-zero second thickness e5. The general formula of the type InAsi xSbx corresponds to a crystal possessing one indium atom and the equivalent of one atom of the mixture formed by arsenic and antimony.

[0035] The use of two layers of general formulas InAsi xSbxet whose antimony concentrations are different allows the band structure of the stack to be defined, which allows the cutoff length of the absorbing layer 1 to be adjusted.

[0036] In a particular embodiment, the first concentration of antimony X4 is zero, but preferably, the first concentration of antimony X4 is non-zero.

[0037] Advantageously, the first antimony concentration X4 is greater than or equal to 4 atomic percent and preferably less than or equal to 10 atomic percent, and the second concentration X5 is between 10% and 30 atomic percent. It is particularly advantageous for the difference between the first concentration X4 and the second concentration X5 to be at least 2 atomic percent, or even at least 5 atomic percent, in order to have a good differentiation of behavior between the barrier layer and the sink layer. It is preferable that the second layer X5 forms a sink and that the first layer X5 forms a barrier.

[0038] Even more advantageously, the first antimony concentration X4 is between 5% and 8% atomic, and the second antimony concentration X5 is between 12% and 24% atomic. These concentration ranges ensure good collection of infrared radiation while allowing acceptable compensation of variations in lattice parameters between the first layers 4 and the second layers 5.

[0039] Advantageously, the superlattice has a period e that is less than 15 nm. The period e corresponds to an average value of the sum of the first thickness e4 and the second thickness e5. The period e corresponds to the repetition rate of the stacking that forms the superlattice. Preferably, the repetition rate or period e is less than 1 nm. The smaller the period e, the greater the effect on the wavefunctions of the electrons and holes, and in particular, the more significant the out-of-shell effect.

[0040] The first layer e4 and the second layer e5 are chosen to form a stack where the mechanical stresses related to the differences in lattice parameters are compensated. The super-lattice is formed on a support substrate 6, and the first layer e4 and the second layer e5 are chosen to form a stack where the stresses are compensated. For example, the stack is deposited on a GaSb substrate 6 or on a buffer layer that has a lattice parameter identical or substantially identical to that of GaSb.

[0041] In a preferred embodiment, the first thickness e4 is less than the second thickness e5 and more preferably, the first thickness e4 is less than or equal to 50% of the second thickness e5. This configuration allows for a better compromise between the mechanical constraints related to the differences in lattice parameters and the electro-optical performance of the absorbing layer 1. This facilitates the formation of an absorbing layer 1 whose performance is more stable over time.

[0042] The values ​​of the first thickness e4 and the second thickness e5, in conjunction with the values ​​of the first antimony concentration X4 and the second antimony concentration X5, allow us to define the value of the band gap energy Eg, which in turn allows us to define the cutoff wavelength of the radiation captured by the super-lattice. The value of the band gap energy corresponds to, or is approximately equivalent to, the energy difference between the heavy hole miniband (HH1 in [Fig. 3]) and the electron miniband (E1 in [Fig. 3]).

[0043] As illustrated in [Fig. 2], in order to improve the performance of the superlattice and in particular to improve the quantum absorption efficiency of the superlattice, at least one of the first layer 4 and the second layer 5 exhibits an antimony concentration gradient (as well as an opposing arsenic gradient). Most advantageously, the first layer 4 and the second layer 5 each exhibit an antimony concentration gradient and a complementary arsenic gradient.

[0044] The presence of an antimony composition gradient allows for influencing the width of the heavy hole and light hole minibands (HH1 and LH1). When the superlattice exhibits abrupt interfaces for antimony concentration, and therefore for arsenic concentration, the heavy hole miniband is estimated to have a width on the order of 4 meV. By using concentration gradients for antimony and arsenic, it is possible to achieve a heavy hole miniband width greater than 10 meV, or even at least equal to 15 meV.

[0045] Preferably, when the first layer 4 exhibits an antimony concentration gradient, the first antimony concentration represents a minimum antimony value in the first layer 4. The first layer 4 has a first concentration gradient that is decreasing and monotonic from the second concentration value X5 to the first concentration value X4. In order to avoid a significant abrupt change in antimony concentration, the first concentration gradient extends over at least 33% of the first thickness to significantly increase the broadening of the heavy hole miniband.

[0046] It is particularly advantageous for the first concentration gradient to be a linear concentration gradient over the entire thickness of the first layer 4 or a sublinear concentration gradient. By sublinear gradient, we mean an antimony content that is always less than or equal to the content corresponding to a linear variation in the antimony concentration between the two ends of the first layer 4. Advantageously, the first layer 4 has a constant antimony concentration over a thickness less than or equal to 20% of the first thickness e4, or even over a thickness less than 10% to have a significant widening of the heavy hole miniband. Advantageously, the antimony concentration gradient extends over the entire first thickness e4. Preferably, the antimony concentration in the first layer 4 exhibits a logarithmic variation.

[0047] In an advantageous embodiment, the second antimony concentration X5 represents a maximum antimony value in the second layer 5, and the second layer 5 exhibits a second concentration gradient that is increasing monotonically from the first concentration value X4 to the second concentration value X5. Preferably, the second concentration gradient extends over at least 33% of the second thickness e5 to increase the broadening of the heavy hole miniband. Advantageously, the antimony concentration gradient extends over the entire second thickness e5. Preferably, the antimony concentration in the second layer 5 exhibits a logarithmic variation.

[0048] It is particularly advantageous for the second concentration gradient to be a linear concentration gradient over the entire thickness of the second layer 5 or a superlinear concentration gradient. By superlinear gradient, we mean an antimony content that is always greater than or equal to the content corresponding to a linear variation in the antimony concentration between the two ends of the second layer. Advantageously, the second layer 5 has a constant antimony concentration over a thickness less than or equal to 20% of the second thickness e5, or even over a thickness less than 10% to obtain a significant broadening of the heavy hole miniband. Advantageously, the antimony concentration gradient extends over the entire second thickness e5. Preferably, the antimony concentration in the second layer 5 exhibits a logarithmic variation.

[0049] The use of an antimony concentration gradient in the first layer 4 and in the second layer 5 makes it easier to broaden the heavy hole miniband up to 10meV or even up to 15meV or beyond.

[0050] The effect of the antimony concentration gradient on the broadening of the hole miniband becomes more pronounced when the period e is less than or equal to lOnm and when the concentration gradients extend over the entire first layer 4 and the entire second layer 5. This makes it easier to form a heavy hole miniband whose energy maximum is separated from the minimum of a light hole miniband by a value below a threshold value. It is particularly advantageous that the threshold value represents the energy of an optical longitudinal phonon, which can be expressed in the form E = h.coLO.

[0051] The adjustment of the position of the heavy hole band and the light hole band can be achieved by adjusting the value of the first antimony concentration X4 and / or the first thickness e4.

[0052] The use of an antimony concentration gradient in the first layer 4 and in the second layer 5 makes it possible to achieve a spreading of the wave functions of the electrons beyond the first layer 4 as well as a spreading of the wave functions of the heavy holes and the light holes outside the second layer 5. The spreading of the wave functions makes it possible to improve the absorption coefficient of the superlattice compared to an equivalent superlattice with abrupt surfaces.

[0053] More advantageously, when the first concentration of antimony X4 is between 5% and 8% atomic and the second concentration of antimony X5 is between 12% and 24% atomic, it is easier to obtain an energy separation between the heavy hole miniband and the light hole miniband which is lower than the energy of an optical longitudinal phonon while ensuring the presence of the minibands and more preferably when the period e is less than lOnm.

[0054] The energy separation between the light hole miniband and the heavy hole miniband, with a value below the threshold, for example below 35 meV, promotes the absorption of optical longitudinal phonons (LO phonons). For example, when the superlattice is at a temperature above 100 K, holes present in the heavy hole band can migrate into the light hole band. Since the phonons obey Bose-Einstein statistics, their characteristics are modified, resulting in a gain in mobility. The emission of optical longitudinal phonons is also promoted. Following the absorption of a phonon, photocarriers are generated, followed by a succession of absorptions and emissions of optical longitudinal phonons. The generated electric charge carrier, here a hole, has characteristics represented by a mixture of the characteristics of a heavy hole and those of a light hole.The effective mass of the holes representing the captured optical signal is reduced compared to a super-array using only heavy holes, for example a super-array with abrupt interfaces.

[0055] The superlattice is particularly advantageous when used in the temperature range between 50 K and 250 K, preferably between 100 K and 200 K, because the optical longitudinal phonons are present in very large numbers, such that the superlattice can be considered to have an infinite or nearly infinite reservoir of optical longitudinal phonons. The gain in hole mobility along the growth direction of the superlattice layers improves the quantum efficiency of the superlattice by enhancing the collection of photocarriers generated following the absorption of a photon. The superlattice is thus able to exhibit transport properties. closer between the direction parallel to the interface of the layers and the perpendicular direction, that is to say the direction of growth.

[0056] Preferably, the super-network comprises a stack containing at least 10 pairs of a first layer 4 and a second layer 5, preferably at least 20 pairs, even more preferably at least 50 pairs or 100 pairs or even 200 pairs.

[0057] The stacking is preferably carried out by molecular beam epitaxy (MBE) or by metal-organic chemical vapor deposition (MOCVD).

Claims

1.

2. Demands Infrared radiation detection device comprising: - an absorbing layer (1) intended to absorb infrared radiation and to generate electric charge carriers, the absorbing layer (1) comprising a super-lattice, the super-lattice comprising an alternation of a first layer (4) and a second layer (5), the first layer (4) being of general formulation InAsixSbx with a first concentration of antimony (X4) and a first thickness (e4) and the second layer (5) being of general formulation InAsi xSbx with a second concentration of antimony (X5) and having a second thickness (e5), the second concentration of antimony (X5) being strictly greater than the first concentration (X4) by at least 2 atomic %; characterized in that the first concentration of antimony (X4) is greater than 4 atomic%; in that the super-lattice has a period (e) less than 15nm, the period (e) corresponding to an average value of a sum of the first thickness (e4) and the second thickness (e5); in that at least one of the first layer (4) and of the second layer (5) exhibits an antimony concentration gradient; in which, when the first layer (4) has a first antimony concentration gradient, the first antimony concentration (X4) represents a minimum antimony value in the first layer (3) and the first concentration gradient is monotonic from the second concentration (X5) to the first concentration (X4), the first concentration gradient extending over at least 33% of the first thickness (e4); and / or in which, when the second layer (5) has a second antimony concentration gradient, the second antimony concentration (X5) represents a maximum antimony value in the second layer (5) and the second concentration gradient is monotonic from the first concentration (X4) to the second concentration (X5), the second concentration gradient extending over at least 33% of the second thickness (e5). Infrared radiation detection device (1) according to claim 1 in which the first antimony concentration (X4) is less than 10% atomic and the second concentration (X5) is between 10% and 30% atomic.

3. Infrared radiation detection device (1) according to claim 2 wherein the first antimony concentration (X4) is between 5% and 8% atomic and the second antimony concentration (X5) is between 12% and 24% atomic.

4. Infrared radiation detection device (1) according to any one of claims 1 to 3 wherein the period (e) is less than or equal to lOnm.

5. Infrared radiation detection device (1) according to any one of claims 1 to 4 wherein the second thickness (e5) is less than or equal to 90% of the first thickness (e4).

6. Infrared radiation detection device (1) according to claim 5 wherein the second thickness (e5) is less than or equal to 50% of the first thickness (e4).

7. Infrared radiation detection device (1) according to any one of claims 1 to 6 wherein the first concentration gradient is a linear concentration gradient over the entire thickness of the first layer (4) or a sublinear concentration gradient.

8. Infrared radiation detection device (1) according to claim 7 wherein the second concentration gradient is a linear concentration gradient over the entire thickness of the second layer (5) or a superlinear concentration gradient.

9. Infrared radiation detection device (1) according to any one of claims 1 to 8 wherein the first layer (4) and the second layer (5) each have an antimony gradient.

10. Infrared radiation detection device (1) according to claim 9 wherein the first layer (4) has a constant concentration of antimony over a thickness less than or equal to 20% of the first thickness (e4) and wherein the second layer (5) has a constant concentration of antimony over a thickness less than or equal to 20% of the second thickness (e5).

11. Infrared radiation detection device (1) according to claim 9 when it depends on claim 3 and the claim 8 wherein the period (e) is less than or equal to lOnm.

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