Device for detecting infrared radiation

Abstract

A device for detecting infrared radiation comprises a superlattice, provided with an alternation of a first layer (4) and second layer (5) that are each of general formulation InAs1-xSbx. The antimony concentration is between 4% and 10% in the first layer (4) and between 12% and 24% in the second layer (5). Each of the first layer (4) and second layer (5) has an antimony concentration gradient over the entirety of the thickness. The superlattice has a period of 10 nm or less.

Description

INFRARED RADIATION DETECTION DEVICE

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

[0002] In many applications, 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, particularly infrared radiation, into an electrical signal by generating electric charge carriers.

[0004] To detect infrared radiation, it is known to use an absorbing layer with a superlattice, that is, a stack of several films representing an alternation between a compound A and a compound B, each with 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 in order to consider the quantum structure of the entire stack. This architecture allows charge carriers to be confined to discrete energy levels.

[0005] In a conventional manner, 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., “Anisotropic 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 affects 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 based on the level of detail of an object. The impact of anisotropy on the modulation transfer function was demonstrated 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 to separate each absorption zone from adjacent absorption zones. These trenches are created across the entire thickness of the absorbing layer. Creating deep trenches or mesas physically separates the pixels, bringing the modulation transfer function closer to its theoretical optimal value. However, this operation is not without drawbacks, as it generates parasitic currents and degrades operability at high operating temperatures. Such results were demonstrated 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 relatively low theoretical absorption, which implies 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).

[0011] It is known from the publication by Nicole Kotulak et al., "Three-dimensional visualization of sb segregation in InAs / InAsSb superlattices using atom probe tomography," Journal of Applied Physics, American Institute of Physics, 2 Huntington Quadrangle, Melville, NY 11747, vol. 128, no. 1, July 1, 2020 (2020-07-01), to form an InAsSb / InAsSb superlattice with a period approximately equal to 5 nm and with an antimony concentration that varies periodically. The antimony concentration varies between 40% and 4%.

[0012] 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 especially those with an InAs / InAsSb superlattice. Preferably, the aim is to improve at least one of the quantum absorption efficiency and the hole mobility.

[0013] These drawbacks are addressed by means of an infrared radiation detection device comprising an absorbing layer designed to absorb infrared radiation and generate electric charge carriers, the absorbing layer comprising a superlattice, the superlattice comprising an alternation of a first layer and a second layer, the first layer having the general formulation InAs 1-x Sb xwith a first concentration of antimony and a first thickness and the second layer being of general formulation InAs 1-x Sb 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 percent.

[0014] The infrared radiation detection device is notable 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 and second thicknesses; in that at least one of the first and second layers has an antimony concentration gradient; in which, when the first layer has a first antimony concentration gradient, the first antimony concentration represents a minimum value of antimony 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 wherein, 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.

[0015] 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%.

[0016] Preferably, the first antimony concentration is between 5% and 8% atomic and the second antimony concentration is between 12% and 24% atomic.

[0017] In one particular embodiment, the period is less than or equal to 10nm.

[0018] Advantageously, the second thickness is less than or equal to 90% of the first thickness.

[0019] In a particular embodiment, the second thickness is less than or equal to 50% of the first thickness.

[0020] Preferably, the first concentration gradient is a linear concentration gradient over the entire thickness of the first layer or a sublinear concentration gradient.

[0021] 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.

[0022] Preferably, the first layer and the second layer each possess an antimony gradient.

[0023] 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. The second layer has a constant antimony concentration over a thickness less than or equal to 20% of the second layer. Description of the drawings

[0024] 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:

[0025] : schematically illustrates an infrared radiation detection device equipped with a stack of several layers, including at least one super-array;

[0026] : schematically illustrates a variation in antimony concentration in the first and second layers of a superlattice;

[0027] : schematically illustrates an energy representation of the minibands of heavy holes, light holes and electrons. Detailed description

[0028] The detection device is a device configured to detect infrared radiation, that is, configured to capture infrared radiation and generate an electrical signal representative of the radiation captured.

[0029] The detection device schematically illustrated at lacomporte an absorbing layer 1 intended to absorb infrared radiation and generate electric charge carriers.

[0030] 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 layer 1. The contact areas 2e and 2c can advantageously be formed from one or more semiconductor materials. Preferably, the contact areas 2 are formed from doped semiconductor materials to reduce contact resistance. Advantageously, the contact areas 2 are coated with a metal. The contact areas are used to polarize the photodetector if necessary and to collect the generated charge carriers.

[0031] During operation, electric charge carriers are generated in the absorbing layer 1 when the light radiation to be detected is absorbed. These electric charge carriers are captured by the contact areas 2e / 2c to provide an electric current representative of the detected light radiation.

[0032] 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 thus 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.

[0033] In order to improve the transport performance of load carriers and / or absorption efficiency, it is advantageous to modify the structure of the absorbing layer 1.

[0034] As illustrated in Figure 1, the absorbing layer 1 has a superlattice consisting of alternating first layer 4 and second layer 5. Both the first layer 4 and the second layer 5 are single-crystal semiconductor layers. The first layer 4 has a different composition than the second layer 5, resulting in distinct band characteristics that define a barrier layer and a sink layer.

[0035] The first layer 4 is a general formulation InAs layer 1-x Sb x with a first antimony concentration X4 and a first thickness e4 which is non-zero. The second layer 5 is a layer of general formulation InAs 1-x Sb xThe second layer 5 has a second antimony concentration X5 strictly greater than the first concentration X4. The second layer 5 has a second non-zero thickness e5. The general formula is of the InAs type. 1-x Sb x corresponds to a crystal possessing one atom of indium and the equivalent of one atom of the mixture formed by arsenic and antimony.

[0036] The use of two layers of general InAs formulas 1-x Sb x and whose antimony concentrations are different allows us to define the band structure of the stack which allows us to adjust the cutoff length of the absorbing layer 1.

[0037] In a particular embodiment, the first concentration of antimony X4 is zero, but preferably, the first concentration of antimony X4 is non-zero.

[0038] 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 achieve good differentiation between the behavior of 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.

[0039] Even more advantageously, the first antimony concentration X4 is between 5% and 8 atomic percent, and the second antimony concentration X5 is between 12% and 24 atomic percent. These concentration ranges ensure good collection of infrared radiation while allowing acceptable compensation for variations in lattice parameters between the first layer 4 and the second layer 5.

[0040] Advantageously, the superlattice has a period e that is less than 15 nm. The period e corresponds to the 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 10 nm. The smaller the period e, the greater the effect on the wavefunctions of electrons and holes, and in particular, the more pronounced the out-of-shell effect.

[0041] The first layer e4 and the second layer e5 are chosen to form a stack where the mechanical stresses related to differences in lattice parameters are compensated. The superlattice 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.

[0042] 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.

[0043] 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 band gap energy Eg, which in turn defines the cutoff wavelength of the radiation captured by the superlattice. The band gap energy corresponds, or is very close to corresponds, to the energy difference between the heavy hole miniband (HH1 in the λ) and the electron miniband (E1 in the λ).

[0044] As illustrated in Figure 1, in order to improve the performance of the superlattice, and in particular to improve its absorption quantum efficiency, 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.

[0045] The presence of an antimony composition gradient allows for manipulation of the width of the heavy-hole and light-hole (HH1 and LH1) minibands. 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 15 meV.

[0046] 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.

[0047] It is particularly advantageous for the first concentration gradient to be either 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 antimony concentration between the two ends of the first layer 4. Advantageously, the first layer 4 exhibits 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 achieve a significant broadening 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.

[0048] 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.

[0049] It is particularly advantageous for the second concentration gradient to be either 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 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 achieve 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.

[0050] 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.

[0051] 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 10 nm and 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. It is particularly advantageous that the threshold value represents the energy of an optical longitudinal phonon, which can be expressed in the form E = ħω LO .

[0052] 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.

[0053] The use of an antimony concentration gradient in the first layer 4 and in the second layer 5 allows for the spreading of electron wave functions beyond the first layer 4 as well as a spreading of the wave functions of heavy holes and light holes outside the second layer 5. The spreading of the wave functions improves the absorption coefficient of the superlattice compared to an equivalent superlattice with steep surfaces.

[0054] 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 preferentially when the period e is less than 10nm.

[0055] The energy separation between the light hole miniband and the heavy hole miniband, below the threshold value (e.g., 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 in the heavy hole band can migrate to the light hole band. Since the phonons obey Bose-Einstein statistics, their characteristics change, resulting in increased mobility. The emission of optical longitudinal phonons is also enhanced. 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, in this case a hole, has characteristics represented by a mixture of the heavy hole and light hole characteristics.The effective mass of the holes representing the captured optical signal is reduced compared to a super-network using only heavy holes, for example a super-network with abrupt interfaces.

[0056] 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, allowing the superlattice to be considered as possessing an infinite or near-infinite reservoir of optical longitudinal phonons. The increased 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 photon absorption. The superlattice exhibits closer transport properties between the direction parallel to the layer interface and the perpendicular direction, i.e., the growth direction.

[0057] Preferably, the super-network comprises a stacking 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.

[0058] Stacking is preferentially achieved by molecular beam epitaxy (MBE) or by metal-organic chemical vapor deposition (MOCVD).

Claims

Infrared radiation detection device comprising: - an absorbing layer (1) intended to absorb infrared radiation and generate electric charge carriers, the absorbing layer (1) comprising a superlattice, the superlattice comprising an alternation of a first layer (4) and a second layer (5), the first layer (4) being of general formulation InAs 1-x Sb x with a first concentration of antimony (X4) and a first thickness (e4) and the second layer (5) being of general formulation InAs 1-x Sb xwith a second antimony concentration (X5) and having a second thickness (e5), the second antimony concentration (X5) being strictly greater than the first concentration (X4) by at least 2 atomic %; in which the first antimony concentration (X4) is greater than 4 atomic % and less than 10 atomic %; in which 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 which at least one of the first layer (4) and the second layer (5) has 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 value of antimony 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 value of antimony 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); characterized in that the second concentration (X5) is between 10% and 30% atomic. Infrared radiation detection device (1) according to claim 1 wherein the first antimony concentration (X4) is between 5% and 8% atomic and the second antimony concentration (X5) is between 12% and 24% atomic. Infrared radiation detection device (1) according to any one of claims 1 and 2 wherein the period (e) is less than or equal to 10nm. Infrared radiation detection device (1) according to any one of claims 1 to 3 wherein the second thickness (e5) is less than or equal to 90% of the first thickness (e4). Infrared radiation detection device (1) according to claim 4 wherein the second thickness (e5) is less than or equal to 50% of the first thickness (e4). Infrared radiation detection device (1) according to any one of claims 1 to 5 wherein the first concentration gradient is a linear concentration gradient over the entire thickness of the first layer (4) or a sublinear concentration gradient. Infrared radiation detection device (1) according to claim 6 wherein the second concentration gradient is a linear concentration gradient over the entire thickness of the second layer (5) or a superlinear concentration gradient. Infrared radiation detection device (1) according to any one of claims 1 to 7 in which the first layer (4) and the second layer (5) each have an antimony gradient. Infrared radiation detection device (1) according to claim 8 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). Infrared radiation detection device (1) according to claim 8 when it depends on claim 2 and claim 7 wherein the period (e) is less than or equal to 10nm.

Images