Two-color infrared detector based on Sb chalcogenide superlattice and infrared focal plane array

Abstract

The application provides a dual-color infrared detector based on a bismuth antimonide second-type superlattice and an infrared focal plane array. The epitaxial structure of the dual-color infrared detector comprises: a bismuth antimonide substrate and an n-type lower electrode contact layer, a first superlattice absorption layer, a first barrier layer, a p-type middle electrode contact layer, an optical reflection structure layer, a second barrier layer, a second superlattice absorption layer and an n-type top cover contact layer which are sequentially stacked on the bismuth antimonide substrate; the optical signal is incident from the side of the n-type top cover contact layer, the first superlattice absorption layer is used for absorbing and detecting a first infrared optical signal of a first cut-off wavelength in the optical signal which is projected from the optical reflection structure layer to the first superlattice absorption layer; the second superlattice absorption layer is used for absorbing and detecting a second infrared optical signal of a second cut-off wavelength in the optical signal; and the optical reflection structure layer is also used for reflecting the second infrared optical signal which is not completely absorbed in the optical signal, so that the second superlattice absorption layer secondarily absorbs the reflected second infrared optical signal.

Description

Technical Field

[0001] This application relates to the field of epitaxial structure design and growth technology of infrared photodetectors, and in particular to a dual-color infrared detector based on antimony-based type II superlattice, an infrared focal plane array, and its fabrication method. Background Technology

[0002] With the development of infrared detection technology, multi-band infrared detectors have attracted widespread attention. By simultaneously acquiring information from different bands (such as two long-wave infrared bands) in the same device, target recognition and tracking capabilities can be significantly improved, and complex background noise can be effectively suppressed. Traditionally, HgCdTe (mercury cadmium telluride) materials can cover the mid-infrared to long-infrared bands, but they suffer from problems such as high material toxicity, high cost, and poor wafer uniformity. Summary of the Invention

[0003] In view of this, this application provides a dual-color infrared detector based on antimony-based type-two superlattice and an infrared focal plane array, which is used to at least solve the above-mentioned technical problems.

[0004] One embodiment of this application provides a dual-color infrared detector based on antimony compound superlattice. The epitaxial structure of the dual-color infrared detector includes: an antimony compound substrate and an n-type lower electrode contact layer, a first superlattice absorption layer, a first barrier layer, a p-type intermediate electrode contact layer, an optical reflection structure layer, a second barrier layer, a second superlattice absorption layer, and an n-type top cover contact layer, which are sequentially stacked on the antimony compound substrate. An optical signal is incident from the n-type top cover contact layer side. The first superlattice absorption layer absorbs and detects a first infrared light signal with a first cutoff wavelength projected from the optical reflection structure layer to the first superlattice absorption layer. The second superlattice absorption layer absorbs and detects a second infrared light signal with a second cutoff wavelength. The optical reflection structure layer also reflects the second infrared light signal that is not completely absorbed by the second superlattice absorption layer, so that the second superlattice absorption layer absorbs the reflected second infrared light signal a second time, and the first cutoff wavelength is less than the second cutoff wavelength.

[0005] According to an embodiment of this application, the optical reflection structure layer includes a distributed Bragg mirror or an equivalent multilayer reflection structure; the distributed Bragg mirror is formed by alternating superposition of a dielectric film layer with a first refractive index and a dielectric film layer with a second refractive index for multiple periods, and is used to enhance the reflection of the second infrared light signal, wherein the first refractive index is greater than the second refractive index.

[0006] According to embodiments of this application, the material of the dielectric film layer with the first refractive index includes one of GaSb, InAs, InAsSb, and GaInSb, or a short-period superlattice of GaSb, InAs, InAsSb, and GaInSb, or a digital alloy of GaSb, InAs, InAsSb, and GaInSb; the material of the dielectric film layer with the first refractive index includes AlSb and AlAs. x Sb 1-x One of AlGaAsSb, or AlSb, AlAs x Sb 1-x Short-period superlattices of AlGaAsSb, or AlSb and AlAs x Sb 1-x A digital alloy of AlGaAsSb, where x is 0.02 to 0.30; the material of the uppermost dielectric film of the distributed Bragg mirror is lattice-matched with the epitaxial material system.

[0007] According to an embodiment of this application, the thickness of the dielectric film is positively correlated with one-quarter of the target center wavelength of the distributed Bragg reflector, and negatively correlated with the refractive index of the dielectric film material at the target center wavelength; the target center wavelength of the distributed Bragg reflector is between the first cutoff wavelength and the second cutoff wavelength.

[0008] According to an embodiment of this application, the thickness of the dielectric film is the product of one-quarter of the target center wavelength and the reciprocal of the refractive index of the dielectric film material at the target center wavelength.

[0009] According to embodiments of this application, the number of alternating periods of the dielectric film layers is 6 to 30 pairs.

[0010] According to embodiments of this application, the thickness of the first superlattice absorption layer and the second superlattice absorption layer is 0.5 μm to 6 μm, and the number of superlattice periods is 10 to 200.

[0011] According to an embodiment of this application, the p-type intermediate electrode contact layer serves as a common electrode, forming two back-to-back photodiode structures with the n-type lower electrode contact layer and the n-type top cover contact layer. Selective readout of the first cutoff wavelength and the second cutoff wavelength is achieved by changing the bias polarity of the p-type intermediate electrode contact layer relative to the n-type lower electrode contact layer and the n-type top cover contact layer.

[0012] According to embodiments of this application, the first barrier layer and the second barrier layer are undoped M-structure barrier layers, the periodic structure of which includes InAs / GaSb / AlSb stacks, and the thicknesses of the first and second barrier layers are 0.1 μm to 1.5 μm; the first and second superlattice absorption layers are antimonide type II superlattice absorption layers; the first and second superlattice absorption layers are intrinsic absorption layers or lightly doped absorption layers, with a doping concentration of 1 × 10⁻⁶. 15 cm -3 ~1×10 17 cm -3 The p-type intermediate electrode contact layer is a heavily doped p-type GaSb layer with a doping concentration of 5 × 10⁻⁶. 17 cm -3 ~5×10 18 cm -3 The thickness of the n-type lower electrode contact layer is 0.5 μm to 1 μm, and the thickness of the n-type top cover contact layer is 20 nm to 50 nm; both the n-type lower electrode contact layer and the n-type top cover contact layer are heavily doped n-type layers with a doping concentration of 5 × 10⁻⁶. 17 cm -3 ~5×10 18 cm -3 The thickness is 20nm~50nm.

[0013] This application also provides an infrared focal plane array, comprising: a plurality of pixel units, each pixel unit including an epitaxial structure, the epitaxial structures of each pixel unit being interconnected; the epitaxial structure includes: an antimony substrate and an n-type lower electrode contact layer, a first superlattice absorption layer, a first barrier layer, a p-type intermediate electrode contact layer, an optical reflection structure layer, a second barrier layer, a second superlattice absorption layer, and an n-type top cover contact layer sequentially stacked on the antimony substrate; wherein, an optical signal is incident from the n-type top cover contact layer side, the first superlattice absorption layer is used to absorb and detect a first infrared light signal of a first cutoff wavelength projected from the optical reflection structure layer to the first superlattice absorption layer in the optical signal; the second superlattice absorption layer is used to absorb and detect a second infrared light signal of a second cutoff wavelength in the optical signal; the optical reflection structure layer is also used to reflect the second infrared light signal of the optical signal that is not completely absorbed by the second superlattice absorption layer, so that the second superlattice absorption layer absorbs the reflected second infrared light signal a second time, the first cutoff wavelength being less than the second cutoff wavelength.

[0014] The antimony-based type-II superlattice dual-color infrared detector and infrared focal plane array provided in this application have at least the following technical advantages:

[0015] By incorporating an optical reflection structure layer between the two absorption layers, the optical reflection structure layer reflects the second infrared light signal that is not completely absorbed by the second superlattice absorption layer. This allows the second superlattice absorption layer to absorb the second infrared light signal reflected back after secondary absorption, significantly enhancing the light absorption of the second infrared light signal and achieving high quantum efficiency without excessively increasing the thickness of the absorption layer. Simultaneously, the n-type lower electrode contact layer, the first barrier layer, the first superlattice absorption layer, the p-type intermediate electrode contact layer, the second superlattice absorption layer, the second barrier layer, and the n-type top cover contact layer constitute an N–M– –P– The –M–N dual-junction structure design improves response while suppressing dark current and crosstalk, enhances the optical field of the target wavelength channel, and reduces dependence on the ultra-thick absorption layer. Attached Figure Description

[0016] The above-mentioned contents, other objects, features and advantages of this application will become clearer from the following description of embodiments with reference to the accompanying drawings, in which:

[0017] Figure 1 The diagram schematically illustrates a cross-sectional view of the epitaxial structure of a type-II superlattice dual-color infrared detector based on antimony compounds according to an embodiment of this application.

[0018] Figure 2 The flowchart illustrating the fabrication method of an epitaxial structure based on an antimony compound type-two superlattice dual-color infrared detector according to an embodiment of this application is shown. Detailed Implementation

[0019] The embodiments of this application will now be described with reference to the accompanying drawings. However, it should be understood that these descriptions are exemplary only and are not intended to limit the scope of this application. In the following detailed description, numerous specific details are set forth to provide a thorough understanding of the embodiments of this application for ease of explanation. However, it will be apparent that one or more embodiments may be implemented without these specific details. Furthermore, descriptions of well-known structures and technologies are omitted in the following description to avoid unnecessarily obscuring the concepts of this application.

[0020] In realizing this application, it was discovered that the dual-color infrared detector structure based on InAs / GaSb type II superlattice inserts an AlGaSb layer between the two absorption layers as a potential barrier to reduce inter-channel crosstalk, and introduces "M-structure" electron blocking layers on both sides of the absorption layers to suppress dark current. However, even with the above design, since the absorption coefficient of long-wavelength light in the narrow bandgap absorption layer is limited, it is usually necessary to increase the thickness of the absorption layer to achieve high quantum efficiency. This may lead to problems such as increased device structure complexity, longer growth time, and increased dark current.

[0021] Distributed Bragg reflectors (DBRs), as optical resonant cavity elements, can provide high reflectivity in specific wavelength bands, thereby increasing the effective optical path length of light in the absorption layer. Introducing DBRs into infrared detectors can improve photon utilization and enhance device response. However, integrating DBRs into traditional dual-color detectors faces several challenges, such as material refractive index matching, fabrication complexity, and maintaining the normal operation of the other wavelength channel. Currently, no detailed epitaxial growth method has been publicly disclosed for integrating DBRs between two absorption layers to improve the quantum efficiency of a particular channel in long-wavelength infrared dual-color detection devices.

[0022] In view of this, this application proposes a dual-color infrared detector based on antimony compound type-two superlattices and its fabrication process to improve the optical absorption efficiency of the second band in the dual-color detector. Specific embodiments are described below.

[0023] Figure 1 The diagram schematically illustrates a cross-sectional view of the epitaxial structure of a type-II superlattice dual-color infrared detector based on antimony compounds according to an embodiment of this application.

[0024] like Figure 1 As shown, the epitaxial structure of the antimony-based type II superlattice dual-color infrared detector in this embodiment may include an antimony substrate 1 and an n-type lower electrode contact layer 2, a first superlattice absorption layer 3, a first barrier layer 4, a p-type intermediate electrode contact layer 5, an optical reflection structure layer 6, a second barrier layer 7, a second superlattice absorption layer 8, and an n-type top cover contact layer 9, which are sequentially stacked on the antimony substrate 1.

[0025] Optical signal 1 is incident from the contact layer 9 side of the n-type top cover. The first superlattice absorption layer 3 is used to absorb and detect the first infrared light signal with a first cutoff wavelength projected from the optical reflective structure layer 6 to the first superlattice absorption layer 3. The second superlattice absorption layer 8 is used to absorb and detect the second infrared light signal with a second cutoff wavelength in the optical signal. The optical reflective structure layer 6 is also used to reflect the second infrared light signal in the optical signal that is not completely absorbed by the second superlattice absorption layer 8, so that the second superlattice absorption layer 8 absorbs the reflected second infrared light signal a second time, and the first cutoff wavelength is smaller than the second cutoff wavelength.

[0026] According to embodiments of this application, the n-type lower electrode contact layer 2, the first superlattice absorption layer 3, the first barrier layer 4, the p-type intermediate electrode contact layer 5, the second barrier layer 7, the second superlattice absorption layer 8, and the n-type top cover contact layer 9 constitute an N–M– –P– The –M–N double junction structure can improve the response and suppress dark current and crosstalk.

[0027] According to an embodiment of this application, an n-type lower electrode contact layer 2, a first superlattice absorption layer 3, a first barrier layer 4, and a p-type intermediate electrode contact layer 5 constitute an upper channel, while an optical reflection structure layer 6, a second barrier layer 7, a second superlattice absorption layer 8, and an n-type top cover contact layer 9 constitute a lower channel, thereby obtaining a bias-selectable dual-color epitaxial structure.

[0028] According to embodiments of this application, "dual-color" refers to obtaining infrared responses with two different center wavelengths or cutoff wavelengths in the same epitaxial structure / device. The combination of the two bands is not limited to long-wave–long-wave (LWIR–LWIR), but can also be mid-wave–long-wave (MWIR–LWIR), long-wave–very-long-wave (LWIR–VLWIR), or other combinations of the two bands. The relationship between the band sizes of the upper and lower channels is not limited.

[0029] In some embodiments, the antimonybide substrate 1 can be an n-type GaSb single crystal substrate (100). The n-type lower electrode contact layer 2 and the n-type top cover contact layer 9 can be heavily doped n-type layers with a doping concentration of 5 × 10⁻⁶. 17 cm -3 ~5×10 18 cm -3 The doping material can be Si or Te. The thickness of the n-type lower electrode contact layer 2 is 0.5 μm to 1 μm, and the thickness of the n-type top cover contact layer 9 is 20 nm to 50 nm.

[0030] The first barrier layer 4 and the second barrier layer 7 can be undoped M-structure barrier layers, nBn barrier layers, CBIRD / DBIRD type barrier layers, or equivalent barrier structures. The periodic structure of the M-structure barrier layer includes InAs / GaSb / AlSb stacks, for example, 18MLInAs / 3MLGaSb / 5MLAlSb / 3MLGaSb forming one period. The thickness of the first barrier layer 4 and the second barrier layer 7 is 0.1μm~1.5μm to provide a barrier effect against majority carriers (electrons) in the device depletion region, thereby suppressing dark current.

[0031] The first superlattice absorption layer 3 and the second superlattice absorption layer 8 are antimony-based type II superlattice absorption layers, for example, composed of InAs / GaSb type II superlattices. The first superlattice absorption layer 3 and the second superlattice absorption layer 8 are intrinsic absorption layers or lightly doped absorption layers, with a doping concentration of 1×10⁻⁶. 15 cm -3 ~1×10 17 cm -3 For example, p-type impurities (such as Be) can be slightly doped, with a doping concentration of approximately (4~6)×10⁻⁶. 16 cm -3 In order to control the carrier concentration.

[0032] The thickness of the first superlattice absorption layer 3 and the second superlattice absorption layer 8 is 0.5–6 μm, and the number of superlattice periods is 10–200. For example, the thickness of the first superlattice absorption layer 3 and the second superlattice absorption layer 8 is 2 μm, and the number of superlattice periods is 50.

[0033] In some embodiments, the p-type intermediate electrode contact layer 5 is a p-type GaSb heavily doped layer with a doping concentration of 5 × 10⁻⁶. 17 cm -3 ~5×10 18 cm -3 The thickness is 0.2μm~0.5μm. For example, Be can be used as the dopant, and the doping concentration is approximately (5×10⁻⁶). 17 ~1×10 18 )cm -3 This makes it a low-resistivity P-type barrier layer.

[0034] In some embodiments, the optical reflection structure layer 6 includes a distributed Bragg mirror or an equivalent multilayer reflection structure. The distributed Bragg mirror is formed by alternating multiple periods of a dielectric film layer with a first refractive index and a dielectric film layer with a second refractive index, and is used to enhance the reflection of the second infrared light signal, wherein the first refractive index is greater than the second refractive index.

[0035] Furthermore, the material of the dielectric film layer with the first refractive index includes one of GaSb, InAs, InAsSb, GaInSb, or a short-period superlattice of GaSb, InAs, InAsSb, GaInSb, or a digital alloy of GaSb, InAs, InAsSb, GaInSb.

[0036] Materials for dielectric films with the first refractive index include AlSb and AlAs. x Sb 1-x One of AlGaAsSb, or AlSb, AlAs x Sb 1-x Short-period superlattices of AlGaAsSb, or AlSb and AlAs x Sb 1-x Digital alloys of AlGaAsSb, where x is 0.02 to 0.30;

[0037] The material of the uppermost dielectric film layer of the distributed Bragg mirror is lattice-matched with the epitaxial material system.

[0038] In some embodiments, the thickness of the dielectric film is positively correlated with one-quarter of the target center wavelength of the distributed Bragg reflector and negatively correlated with the refractive index of the dielectric film material at the target center wavelength; the target center wavelength of the distributed Bragg reflector is between the first cutoff wavelength and the second cutoff wavelength.

[0039] Furthermore, the thickness of the dielectric film is the product of one-quarter of the target center wavelength and the reciprocal of the refractive index of the dielectric film material at the target center wavelength.

[0040] For example, the DBR is designed with a thickness of one-quarter of the target center wavelength λ0, and the thickness of each layer satisfies t=λ0 / (4n), where n is the refractive index of the corresponding material at λ0; the number of period pairs in the DBR is 6 to 30, preferably 8 to 20. The number of DBR periods is crucial to the reflection effect: it has been estimated that selecting a GaSb / AlAsSb stack of about 8–12 periods can achieve high reflectivity in the target band. The DBR structure designed in this application can achieve a reflectivity of over 90% in the λc 2 band. Using a GaSb-based DBR with about 12 periods, the peak quantum efficiency of the detector has been increased from 45% to about 80% in the mid-infrared band.

[0041] In some embodiments, the p-type intermediate electrode contact layer 5 serves as a common electrode, forming two back-to-back photodiode structures with the n-type lower electrode contact layer 2 and the n-type top cover contact layer 9. By changing the bias polarity of the p-type intermediate electrode contact layer 5 relative to the n-type lower electrode contact layer 2 and the n-type top cover contact layer 9, selective readout of the first cutoff wavelength and the second cutoff wavelength can be achieved.

[0042] The embodiments of this application also provide a preparation method for preparing an epitaxial structure based on an antimonyide type-two superlattice dual-color infrared detector.

[0043] Figure 2 The flowchart illustrating the fabrication method of an epitaxial structure based on an antimony compound type-two superlattice dual-color infrared detector according to an embodiment of this application is shown.

[0044] like Figure 2 As shown, the preparation method of this embodiment may include operations S210 to S260.

[0045] In operation S210, an antimonide single crystal substrate is provided, and an n-type doped buffer layer is grown on the substrate by molecular beam epitaxy to form an n-type lower electrode contact layer.

[0046] In operation S220, a first superlattice absorption layer (corresponding to the first cutoff wavelength λc1) and its corresponding first barrier layer are epitaxially grown on the n-type lower electrode contact layer.

[0047] The first superlattice absorption layer is a type II superlattice absorption layer of antimony compound system or an equivalent bandgap engineered absorption layer. The first barrier layer is disposed on the first superlattice absorption layer to block majority carriers and suppress dark current.

[0048] In operation S230, a P-type intermediate electrode contact layer is epitaxially grown on the first barrier layer.

[0049] In operation S240, epitaxy is stopped and the sample is removed from the epitaxial growth equipment. An optical reflection structure layer is constructed on the surface of the P-type intermediate electrode contact layer.

[0050] The optical reflection structure layer is a distributed Bragg reflector (DBR) or an equivalent multilayer reflection structure. The DBR is composed of alternating high-refractive-index layers and low-refractive-index layers for several periods. It is used to enhance the reflection of the working band of at least one target channel in the dual-color detector, so as to improve the effective optical path in the absorption region of the corresponding channel.

[0051] In operation S250, the sample with the integrated optical reflective structure layer is sent back to the epitaxial growth equipment. After the surface of the optical reflective structure layer is pre-treated by the epitaxial interface, a second superlattice absorption layer (corresponding to the second cutoff wavelength λc2), a second barrier layer, and an N-type top cover contact layer are epitaxially grown on it to form the final epitaxial structure of the dual-color infrared detector.

[0052] In operation S260, an N–M–P–M–N type double junction structure is formed, and selective readout of the dual-color channel is achieved through electrode bias.

[0053] The preparation process will be described in more detail below.

[0054] Substrate preparation and growth of the n-type lower electrode contact layer: A double-sided polished n-type GaSb single crystal substrate (100) is provided. The substrate is pretreated for deoxidation in an MBE system (e.g., heated to ~580°C to remove the surface oxide layer). Subsequently, a GaSb buffer layer is epitaxially grown on the substrate to optimize lattice matching and surface flatness. The buffer layer thickness is approximately 0.5 μm to 1 μm, preferably approximately 900 nm, and is doped with an appropriate amount of n-type impurities (such as Te or Si, at a concentration of approximately 1 × 10⁻⁶). 18 cm -3 To form an n-type lower electrode contact layer.

[0055] Growth of the first superlattice absorption layer and the first barrier layer: A first superlattice absorption layer λc1 is grown on the GaSb buffer layer. This absorption layer is composed of an InAs / GaSb type II superlattice, for example, a stacked structure containing 11 monolayers (ML) InAs and 7ML GaSb per period. The thickness of this absorption layer is approximately 2 μm (e.g., approximately 50 periods), and it can be slightly doped with p-type impurities (e.g., Be), with a doping concentration of approximately (4~6)×10⁻⁶. 16 cm -3To control the carrier concentration, a corresponding barrier layer is then grown on top of the absorber layer. This barrier layer employs an "M-structure" superlattice barrier, for example, a periodic structure of InAs / GaSb / AlSb multilayer stacks (e.g., 18MLInAs / 3MLGaSb / 5MLAlSb / 3MLGaSb) forming one period. This M-structure barrier is approximately 0.5 μm thick and is preferably undoped to provide a barrier against majority carriers (electrons) in the device depletion region, thereby suppressing dark current.

[0056] Growth of the p-type intermediate electrode contact layer: After completing the first absorber layer and its barrier layer, a p-type heavily doped GaSb layer is epitaxially grown as an intermediate contact transition layer. The thickness of this layer is, for example, 0.2 μm to 0.5 μm, and Be can be used as the dopant with a doping concentration of approximately (5 × 10⁻⁶). 17 ~1×10 18 )cm -3 This makes it a low-resistivity P-type barrier layer.

[0057] Fabrication of the DBR mirror: The sample with the lower channel structure grown above was removed from the MBE cavity, and a distributed Bragg reflector (DBR) structure made of GaSb was fabricated on its surface. This DBR is used to enhance the reflection of the upper channel (λc2 band) optical signal, thereby increasing the effective optical path of light in the upper absorption layer. Preferably, the DBR consists of a high-refractive-index layer GaSb and a low-refractive-index layer AlAs. 0.08 Sb 0.92 Alternating layers are used to form the multi-period DBR mirror, with each layer having a thickness equivalent to a quarter-wavelength optical thickness for the center wavelength of λc2. The GaSb layer can be deposited using vacuum evaporation or molecular beam deposition, while the AlAsSb layer can be deposited through co-evaporation of Al, As, and Sb elements, or using other compatible processes. The number of DBR cycles is crucial for reflectivity: it is estimated that approximately 8-12 cycles of GaSb / AlAsSb stacks can achieve high reflectivity in the target wavelength band. The DBR structure designed in this invention achieves over 90% reflectivity in the λc2 band. Studies have shown that using a GaSb-based DBR with approximately 12 cycles has increased the detector's peak quantum efficiency from 45% to approximately 80% in the mid-infrared band. After this step, the top layer of the DBR is preferably made of GaSb material to facilitate lattice matching and surface compatibility during subsequent epitaxial growth.

[0058] MBE growth of the second superlattice absorber layer λc2, the second barrier layer, and the n-type top cap contact layer: The sample with integrated DBR is reloaded into the MBE system, and the second superlattice absorber layer λc2 and the corresponding structure are grown on top of the DBR. Before growth, the sample surface can be gently treated in situ, such as short-term baking at a temperature not exceeding 400°C and introducing a small amount of Group V elements to remove the extremely thin oxide layer formed in the air and protect the DBR surface. Subsequently, the λc2 absorber layer is grown, also using an InAs / GaSb type II superlattice, but the periodic structure can be slightly adjusted to achieve a longer cutoff wavelength. For example, each period consists of 14 mL InAs / 7 mL GaSb, with a total thickness of approximately 2 μm. The λc2 absorber layer can be lightly doped with Be (p-type, ~5 × 10⁻⁶) similar to λc1. 16 cm -3 After the λc2 absorber layer is grown, the corresponding M-structure barrier layer (approximately 0.55 μm thick, undoped) is grown to block the dark current of the upper-layer device. Finally, an N-type capping layer is epitaxially grown on top as the top electrode contact layer. The capping layer can be made of GaSb or InAs material, with a thickness of approximately 20–50 nm, and doped with Si or Te at a concentration of approximately 2 × 10⁻⁶. 18 cm -3 The use of InAs as the capping material helps reduce surface oxidation and form good ohmic contacts. At this point, the complete epitaxial structure of the dual-color infrared detector is grown.

[0059] After the epitaxial wafer is removed from the MBE system, it can be used to fabricate devices using conventional processes. For example, detector island arrays or pixels can be formed using photolithography and dry etching, with the etching depth penetrating from the top layer to the lower N-type GaSb contact layer; the sidewalls are passivated with sulfides and covered with a dielectric protective layer; subsequently, metal electrodes are evaporated to contact the top N-type InAs capping layer and the intermediate P-type GaSb layer, respectively, to bring out the upper and lower electrodes. After device packaging, spectral response and electrical performance testing can be performed.

[0060] Through the above steps, the obtained device structure, from bottom to top, is as follows: GaSb substrate, N-type buffer layer (bottom electrode), λc1 superlattice absorber layer (lightly P-doped), λc1 barrier M layer, P-type GaSb intermediate contact layer, GaSb / AlAsSb DBR reflective layer, λc2 superlattice absorber layer (lightly P-doped), λc2 barrier M layer, and N-type top cap contact layer (top electrode). This structure corresponds to N–M– –P– The M–N type double-junction structure achieves high optical response with a moderate thickness of each absorption layer (~2μm). The embedded DBR provides resonance enhancement for the longer wavelength λc2 channel: when incident light in the λc2 band enters from the top surface of the device, light not completely absorbed by the upper absorption layer is reflected back to the absorption layer at the DBR, achieving secondary absorption and effectively improving the quantum efficiency of the absorption layer for this band. For the shorter wavelength λc1 channel, due to the low reflectivity of the DBR in this band, most light can pass through the DBR to reach the lower absorption layer and be detected. Therefore, this invention achieves efficient detection of dual-color infrared signals without increasing the thickness of the absorption layer. Simultaneously, the use of the M-structure barrier layer effectively reduces the device's dark current, and the central P-layer structure and material selection ensure good electrical isolation between the two channels, avoiding excessive carrier crosstalk. Furthermore, the middle electrode, in conjunction with the upper and lower electrodes, forms two back-to-back photodiodes, enabling bias-selectable dual-color readout.

[0061] The fabrication method has clear process steps and the functional layers in the resulting device structure are well-defined, making it suitable for fabricating high-performance dual-color infrared focal plane detector chips.

[0062] Because a high-reflectivity DBR is integrated into the λc2 channel, the light field intensity in this band is increased, enabling enhanced detection of the λc2 channel signal. Meanwhile, the λc1 channel is largely unaffected by the DBR and can still independently acquire its response signal by adjusting the bias voltage. Testing at 77K showed that both channels exhibited significant optical responses in their respective target bands, improving the overall performance of the dual-color detector.

[0063] It should be noted that λc1 and λc2 are not limited to specific band combinations. λc1 and λc2 can each correspond to any two target infrared channels (e.g., MW–MW, MW–LW, LW–LW, LW–VLW, etc.), and typically λc2 > λc1. The core of this invention lies in: first, completing the epitaxy of the lower channel and forming an intermediate electrode contact layer; then, constructing an optical reflection structure on the surface of this intermediate electrode contact layer and performing a re-epitaxy interface pretreatment; subsequently, growing the upper channel to achieve optical field enhancement and effective optical path extension for at least one target channel, while maintaining the suppression effect of the N–M–P–M–N structure on dark current and electrical crosstalk. For different channel combinations, λc1 and λc2 can be set by adjusting the superlattice periodic structure, thickness, and doping of the two absorption layers, and the design center wavelength λ0 and period logarithm of the DBR can be selected accordingly to achieve high reflectivity in the target band of the enhanced channel. All the above variations do not depart from the spirit of this invention and should fall within the scope of protection of this invention. Equivalent substitutions or adjustments can be made to adapt to different design requirements. These modifications and variations should all be covered within the scope of protection of this invention.

[0064] An embodiment of this application also provides an infrared focal plane array, comprising: a plurality of pixel units, each pixel unit including an epitaxial structure, and the epitaxial structures of each pixel unit being interconnected.

[0065] The epitaxial structure of the dual-color infrared detector includes: an n-type lower electrode contact layer 2, a first barrier layer 3, a first superlattice absorption layer 4, a p-type intermediate electrode contact layer 5, an optical reflection structure layer 6, a second superlattice absorption layer 7, a second barrier layer 8, and an n-type top cover contact layer 9 on an antimony substrate 1.

[0066] Optical signal 1 is incident from the contact layer 9 side of the n-type top cover. The first superlattice absorption layer 4 is used to absorb and detect the first infrared light signal with a first cutoff wavelength projected from the optical reflective structure layer 6 to the first superlattice absorption layer 4. The second superlattice absorption layer 7 is used to absorb and detect the second infrared light signal with a second cutoff wavelength in the optical signal. The optical reflective structure layer 6 is also used to reflect the second infrared light signal in the optical signal that is not completely absorbed by the second superlattice absorption layer 7, so that the second superlattice absorption layer 7 absorbs the reflected second infrared light signal a second time, and the first cutoff wavelength is smaller than the second cutoff wavelength.

[0067] It should be noted that for details not covered in the infrared focal plane array embodiment section, please refer to the embodiment section on antimony-based type II superlattice dual-color infrared detector; specific details will not be repeated here.

[0068] The embodiments of this application have been described above. However, these embodiments are merely illustrative and not intended to limit the scope of this application. Although various embodiments have been described above, this does not mean that the measures in the various embodiments cannot be used advantageously in combination. The scope of this application is defined by the appended claims and their equivalents. Various substitutions and modifications can be made by those skilled in the art without departing from the scope of this application, and all such substitutions and modifications should fall within the scope of this application.

Claims

1. A dual-color infrared detector based on antimony compound type-two superlattice, characterized in that, The epitaxial structure of the dual-color infrared detector includes: An antimony substrate and an n-type lower electrode contact layer, a first superlattice absorption layer, a first barrier layer, a p-type intermediate electrode contact layer, an optical reflection structure layer, a second barrier layer, a second superlattice absorption layer, and an n-type top cover contact layer are sequentially stacked on the antimony substrate. In this configuration, the optical signal is incident from the contact layer side of the n-type top cover. The first superlattice absorption layer is used to absorb and detect the first infrared light signal with a first cutoff wavelength projected from the optical reflection structure layer to the first superlattice absorption layer in the optical signal. The second superlattice absorption layer is used to absorb and detect the second infrared light signal with a second cutoff wavelength in the optical signal. The optical reflection structure layer is also used to reflect the second infrared light signal in the optical signal that is not completely absorbed by the second superlattice absorption layer, so that the second superlattice absorption layer absorbs the reflected second infrared light signal a second time, and the first cutoff wavelength is smaller than the second cutoff wavelength.

2. The antimony-based type-two superlattice dual-color infrared detector according to claim 1, characterized in that, The optical reflection structure layer includes a distributed Bragg mirror or an equivalent multilayer reflection structure. The distributed Bragg reflector is formed by alternating superposition of a dielectric film layer with a first refractive index and a dielectric film layer with a second refractive index over multiple periods, and is used to enhance the reflection of the second infrared light signal. The first refractive index is greater than the second refractive index.

3. The antimony-based type-two superlattice dual-color infrared detector according to claim 2, characterized in that, The material of the dielectric film layer with the first refractive index includes one of GaSb, InAs, InAsSb, and GaInSb, or a short-period superlattice of GaSb, InAs, InAsSb, and GaInSb, or a digital alloy of GaSb, InAs, InAsSb, and GaInSb. The materials of the dielectric film layer with the second refractive index include AlSb and AlAs. x Sb 1-x One of AlGaAsSb, or AlSb, AlAs x Sb 1-x Short-period superlattices of AlGaAsSb, or AlSb and AlAs x Sb 1-x Digital alloys of AlGaAsSb, where x is 0.02 to 0.30; The material of the uppermost dielectric film layer of the distributed Bragg reflector is lattice-matched with the epitaxial material system.

4. The antimony-based type-two superlattice dual-color infrared detector according to claim 2 or 3, characterized in that, The thickness of the dielectric film is positively correlated with one-quarter of the target center wavelength of the distributed Bragg reflector, and negatively correlated with the refractive index of the dielectric film material at the target center wavelength; the target center wavelength of the distributed Bragg reflector is between the first cutoff wavelength and the second cutoff wavelength.

5. The antimony-based type-two superlattice dual-color infrared detector according to claim 4, characterized in that, The thickness of the dielectric film is the product of one-quarter of the target center wavelength and the reciprocal of the refractive index of the dielectric film material at the target center wavelength.

6. The antimony-based type-two superlattice dual-color infrared detector according to claim 5, characterized in that, The number of alternating stacked dielectric film layers is 6 to 30 pairs.

7. The antimony-based type-two superlattice dual-color infrared detector according to claim 1, characterized in that, The thickness of the first superlattice absorption layer and the second superlattice absorption layer is 0.5 μm to 6 μm, and the number of superlattice periods is 10 to 200.

8. The antimony-based type-two superlattice dual-color infrared detector according to claim 1, characterized in that, The p-type intermediate electrode contact layer serves as a common electrode, forming two back-to-back photodiode structures with the n-type lower electrode contact layer and the n-type top cover contact layer. By changing the bias polarity of the p-type intermediate electrode contact layer relative to the n-type lower electrode contact layer and the n-type top cover contact layer, selective readout of the first cutoff wavelength and the second cutoff wavelength can be achieved.

9. The antimony-based type-two superlattice dual-color infrared detector according to claim 1, characterized in that, The first barrier layer and the second barrier layer are undoped M-structure barrier layers, and the periodic structure of the M-structure barrier layer includes an InAs / GaSb / AlSb stack. The thickness of the first barrier layer and the second barrier layer is 0.1 μm to 1.5 μm. The first and second superlattice absorption layers are antimonide type II superlattice absorption layers; the first and second superlattice absorption layers are intrinsic absorption layers or lightly doped absorption layers with a doping concentration of 1×10⁻⁶. 15 cm -3 ~1×10 17 cm -3 ; The p-type intermediate electrode contact layer is a heavily doped p-type GaSb layer with a doping concentration of 5 × 10⁻⁶. 17 cm -3 ~5×10 18 cm -3 ; The n-type lower electrode contact layer and the n-type top cover contact layer are heavily doped n-type layers with a doping concentration of 5 × 10⁻⁶. 17 cm -3 ~5×10 18 cm -3 The thickness of the n-type lower electrode contact layer is 0.5μm~1μm, and the thickness of the n-type top cover contact layer is 20nm~50nm.

10. An infrared focal plane array, characterized in that, include: Multiple pixel units, each pixel unit contains an extensional structure, and the extensional structures of each pixel unit are interconnected; The epitaxial structure includes: an antimony substrate and an n-type lower electrode contact layer, a first superlattice absorption layer, a first barrier layer, a p-type intermediate electrode contact layer, an optical reflection structure layer, a second barrier layer, a second superlattice absorption layer, and an n-type top cover contact layer, which are sequentially stacked on the antimony substrate. In this configuration, the optical signal is incident from the contact layer side of the n-type top cover. The first superlattice absorption layer is used to absorb and detect the first infrared light signal with a first cutoff wavelength projected from the optical reflection structure layer to the first superlattice absorption layer in the optical signal. The second superlattice absorption layer is used to absorb and detect the second infrared light signal with a second cutoff wavelength in the optical signal. The optical reflection structure layer is also used to reflect the second infrared light signal in the optical signal that is not completely absorbed by the second superlattice absorption layer, so that the second superlattice absorption layer absorbs the reflected second infrared light signal a second time, and the first cutoff wavelength is smaller than the second cutoff wavelength.

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