Gradient barrier superlattice infrared detector and manufacturing method thereof

Abstract

This application discloses a gradient barrier superlattice infrared detector and its fabrication method. The gradient barrier superlattice infrared detector comprises, from bottom to top: a substrate; a buffer layer; a P-type contact layer; an absorption layer; a gradient transition barrier layer, which is an N-order M-structure superlattice where N≥2. Along the direction away from the absorption layer, the equivalent valence band top of the gradient transition barrier layer decreases in a stepwise manner, and its equivalent conduction band bottom is not higher than the equivalent conduction band bottom of the absorption layer; and an N-type contact layer. The traditional fixed-period M-barrier layer is improved into an N-order energy band height-stepped transition barrier layer. By making the equivalent energy band of the barrier layer smoothly transition, both the flat, barrier-free conduction band and the gradual decrease in valence band are ensured. This breaks through the technical bottleneck of the mutual constraint between dark current suppression and quantum efficiency improvement in traditional structures, and solves the problem of low quantum efficiency and large dark current coexisting in long-wavelength detectors.

Description

Technical Field

[0001] This application belongs to the field of semiconductor materials technology, and in particular relates to a gradient barrier superlattice infrared detector and its fabrication method. Background Technology

[0002] Antimonide III-V group type II superlattice materials have become the mainstream infrared detection material system. Long-wavelength type II superlattice infrared detectors have significant advantages in terms of fabrication difficulty, cost, and wavelength tunability. However, dark current in long-wavelength infrared detectors is one of the main factors limiting detector performance. Because long-wavelength detection requires narrow bandgap materials (typically between 0.103 eV and 0.155 eV), this narrow absorption region significantly enhances non-radiative recombination mechanisms such as Auger recombination and SRH recombination within the material, leading to a substantial reduction in minority carrier lifetime (photogenerated electrons) and diffusion length. If these carriers cannot be effectively extracted before recombination, the detector's photogenerated carrier extraction efficiency will be extremely low, severely impacting the device's quantum efficiency.

[0003] To overcome this problem and suppress the high dark current caused by the narrow bandgap, existing technologies typically introduce a unipolar barrier structure into the device. This structure intentionally blocks the migration of majority carriers (holes) to suppress the generation-recombination dark current and surface leakage current caused by the depletion region, while simultaneously improving the transport efficiency of a minority of photogenerated carriers (electrons) to successfully cross the barrier and reach the electrode.

[0004] Barrier-type long-wavelength InAs / GaSb type II superlattices typically include PπBN type (using InAs / AlSb superlattices as barriers), unipolar barrier XBn / XBp type, complementary barrier type (CBIRD), and PπMN type (using InAs / GaSb / AlSb / GaSb M-structure barriers). Among these, the PπMN type structure does not require ternary compounds such as InAsSb, is easier to grow via molecular beam epitaxy and adjust the barrier band structure, and the M-barrier structure can be strain-balanced by incorporating InSb at the interface. Specifically, the PπMN type structure is based on a PIN-type superlattice structure, where the absorber layer I is weakly p-type doped to become a π layer, and InAs / GaSb / AlSb / GaSb is added as a barrier. Its band structure is staggered, arranged in an "M" shape, hence it is usually called the M-barrier layer.

[0005] In a conventional PπMN structure, a long-wavelength, narrow-bandgap π-type absorber layer is directly connected to a wide-bandgap M-type barrier layer. To meet the hole blocking requirement, the equivalent valence band (first hole band HH1) of the M-type barrier needs to be much lower than that of the π-type absorber layer to form a sufficiently high hole barrier. However, due to the inherent difference in band structure between the materials on both sides of the heterojunction, when the M-type barrier is designed to meet the hole blocking requirement, its equivalent conduction band bottom is often inevitably higher than that of the π-type absorber layer, resulting in abrupt, spike-shaped conduction band breaks at the interface. This abrupt band break severely hinders the migration of photogenerated electrons to the N-type contact layer, causing carriers to accumulate and recombine at the heterojunction interface, significantly reducing the device's quantum efficiency. Simultaneously, the abrupt jump in valence band position is often accompanied by a strong interfacial electric field distribution, which easily induces interband tunneling dark currents in narrow-bandgap materials, offsetting the barrier layer's suppression effect on generation-recombination dark currents.

[0006] It is evident that in existing long-wavelength superlattice infrared detectors, there is a technical bottleneck where dark current suppression and quantum efficiency improvement are mutually restrictive, and a new device structure that can break through this bottleneck is urgently needed. Summary of the Invention

[0007] This application provides a gradient barrier superlattice infrared detector and its fabrication method.

[0008] In a first aspect, embodiments of this application provide a gradient barrier superlattice infrared detector, comprising, from bottom to top, the following: Substrate; Buffer layer; P-type contact layer; Absorption layer; A gradient transition barrier layer, wherein the gradient transition barrier layer is an N-order M-structure superlattice, N≥2; along the direction away from the absorption layer, the equivalent valence band top of the gradient transition barrier layer decreases in a stepwise manner, and its equivalent conduction band bottom is not higher than the equivalent conduction band bottom of the absorption layer; and, N-type contact layer.

[0009] Optionally, the M-structure superlattice of the gradient transition barrier layer has a single period comprising stacked InAs layers, a first GaSb layer, an AlSb layer, and a second GaSb layer. Along the direction away from the absorption layer, in each order of M-structure superlattice, the thickness of the InAs layer increases or remains constant before increasing, the thickness of the first GaSb layer and / or the second GaSb layer decreases, and the thickness of the AlSb layer remains constant.

[0010] Optionally, the InAs layer has a thickness ranging from 11 to 18 atomic layers, the first GaSb layer and the second GaSb layer each have a thickness ranging from 1 to 3 atomic layers, and the AlSb layer has a thickness ranging from 4 to 6 atomic layers.

[0011] Optionally, the absorption layer is a π-type long-wavelength superlattice absorption layer.

[0012] Optionally, the P-type contact layer is a P-type mid-wave superlattice contact layer, used to absorb mid-wave photons.

[0013] Optionally, the substrate is a GaSb substrate or an InAs substrate; the absorption layer is an InAs / GaSb superlattice structure or an InAs / InAsSb superlattice structure.

[0014] Optionally, in the N-order M-structure superlattice, the value of N ranges from 3 to 5.

[0015] Optionally, the thickness of each step of the gradient transition barrier layer is 0.1µm to 0.2µm.

[0016] Secondly, embodiments of this application provide a method for fabricating a gradient barrier superlattice infrared detector, applicable to any of the embodiments of the first aspect of the gradient barrier superlattice infrared detector, the method comprising: Provide a substrate; An absorption layer is formed on the substrate; A gradient transition barrier layer is formed on the absorption layer. The gradient transition barrier layer is an N-order M-structure superlattice with N≥2. Along the direction away from the absorption layer, the equivalent valence band top of the gradient transition barrier layer decreases in a step-like manner, and its equivalent conduction band bottom is not higher than the equivalent conduction band bottom of the absorption layer. A contact layer is formed on the gradient transition barrier layer.

[0017] Optionally, the M-structure superlattice of the gradient transition barrier layer has a single period comprising stacked InAs layers, a first GaSb layer, an AlSb layer, and a second GaSb layer. When forming the gradient transition barrier layer, the thickness of the InAs layer is increased stepwise along the direction away from the absorption layer, and the thicknesses of the first GaSb layer and the second GaSb layer are decreased stepwise.

[0018] The gradient barrier type superlattice infrared detector and its fabrication method in this application improve the traditional fixed-period M-barrier layer into a transition barrier layer with N-order (N≥2) energy band height stepped change. By making the equivalent energy band of the barrier layer smoothly transition, it can ensure that the conduction band is flat and barrier-free, and achieve the gradual reduction of the valence band. This breaks through the technical bottleneck of mutual constraint between dark current suppression and quantum efficiency improvement in the traditional structure, and solves the problem of low quantum efficiency and large dark current coexisting in long-wavelength detectors. Attached Figure Description

[0019] To more clearly illustrate the technical solutions of the embodiments of this application, the accompanying drawings used in the embodiments of this application will be briefly introduced below. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0020] Figure 1 This is a schematic cross-sectional view of the epitaxial structure of a gradient barrier superlattice infrared detector provided in an embodiment of this application; Figure 2 This is a simulation calculation diagram of the overall band structure of a gradient barrier superlattice infrared detector provided in an embodiment of this application. Detailed Implementation

[0021] The features and exemplary embodiments of various aspects of this application will be described in detail below. To make the objectives, technical solutions, and advantages of this application clearer, the application will be further described in detail below with reference to the accompanying drawings and specific embodiments. It should be understood that the specific embodiments described herein are only intended to explain this application and not to limit it. For those skilled in the art, this application can be implemented without some of these specific details. The following description of the embodiments is merely to provide a better understanding of this application by illustrating examples.

[0022] It should be noted that, in this document, relational terms such as "first" and "second" are used merely to distinguish one entity or operation from another, and do not necessarily require or imply any such actual relationship or order between these entities or operations. Furthermore, the terms "comprising," "including," or any other variations thereof are intended to cover non-exclusive inclusion, such that a process, method, article, or apparatus that comprises a list of elements includes not only those elements but also other elements not expressly listed, or elements inherent to such a process, method, article, or apparatus. Without further limitations, an element defined by the phrase "comprising..." does not exclude the presence of additional identical elements in the process, method, article, or apparatus that includes said element.

[0023] Antimonide III-V group type II superlattice materials have become the mainstream infrared detection material system. Long-wavelength type II superlattice infrared detectors have significant advantages in terms of fabrication difficulty, cost, and wavelength tunability. However, dark current in long-wavelength infrared detectors is one of the main factors limiting detector performance. This is typically addressed by intentionally blocking carrier migration and suppressing different types of dark current by adding electron and hole barriers to the long-wavelength molecular beam epitaxial material structure. Therefore, the matching of the barrier layer material system and its band structure with the long-wavelength absorption layer material and its band structure becomes crucial. The selection of the barrier layer material must meet at least two conditions: first, the epitaxial barrier layer material must have a lattice match with the substrate material, or a low lattice mismatch, without introducing additional stress; second, the band structure of the epitaxial barrier layer material must match the absorption layer band structure, avoiding situations where electron barriers block hole migration or hole barriers block electron migration.

[0024] Barrier-type long-wavelength InAs / GaSb class II superlattices typically include the PπBN type (using InAs / AlSb superlattice as the barrier), the unipolar barrier XBn and XBp types, the complementary barrier type (CBIRD), and the PπMN type (using the M-structure barrier of InAs / GaSb / AlSb / GaSb). The PπMN type structure does not require ternary compounds such as InAsSb, making it easier for molecular beam epitaxy growth and barrier band adjustment. Furthermore, the M-barrier structure allows for strain balancing by incorporating InSb at the interface. The PπMN type structure is based on a PIN-type superlattice structure, with the absorber layer I weakly doped with p-type to become a π layer, and InAs / GaSb / AlSb / GaSb added as a barrier. Its band structure is staggered, arranged in an "M" shape, hence the name M-barrier layer. The P-layer is an InAs / GaSb mid-wavelength superlattice layer designed to absorb photons at mid-wavelength frequencies, allowing photons at longer wavelengths to reach the absorption region and reducing interference from mid-wavelength photogenerated carrier signals. The N-layer typically uses an InAs / GaSb / AlSb / GaSb structure similar to the M-barrier layer, with high N-type doping used to establish the electrical contact layer. For long-wavelength superlattice absorption layers with different cutoff wavelengths, the corresponding optimized M-barrier band structure also needs to be adjusted according to the absorption layer's band structure.

[0025] Matching a single M-structure barrier to a long-wavelength superlattice absorber layer results in a conduction band Cb of the M-structure barrier being higher than the equivalent conduction band Cb of the π absorber layer, forming a conduction band step. However, the M-barrier in the PπMN structure primarily functions as a hole barrier, meaning the equivalent valence band (first hole band HH1) of the M-barrier structure needs to be significantly lower than the equivalent valence band of the π absorber layer to form a barrier. To reduce superlattice dark current and improve device quantum efficiency, the following two conditions should ideally be met: first, the barrier should act as a hole barrier, without a prominent band step in the conduction band to form an electron barrier; second, the hole barrier band step in the M-layer valence band should gradually decrease towards the N-layer valence band. However, the typical PπMN structure struggles to meet this gradual hole barrier condition, necessitating a specially designed gradient barrier layer to satisfy this gradient and improve carrier mobility.

[0026] To achieve long-wavelength infrared detection, the cutoff wavelength of the detector is controlled between 8 and 12 µm, based on the different wavelength requirements of the infrared detection target characteristics. The wavelength modulation principle of long-wavelength superlattices mainly involves designing the long-wavelength absorption region as a narrow-bandgap superlattice material, with a bandgap between 0.103 eV and 0.155 eV. This narrow-bandgap absorption region significantly enhances non-radiative recombination mechanisms such as Auger recombination and SRH (Shockley-Reed-Hall) recombination within the material, resulting in a substantial reduction in minority carrier lifetime (photogenerated electrons) and diffusion length. If these carriers cannot be effectively extracted before recombination, the photogenerated carrier extraction efficiency of the detector will be extremely low, severely impacting the device's quantum efficiency.

[0027] To overcome this problem and suppress the high dark current caused by the narrow bandgap, specific barrier structures, such as unipolar barriers, must be introduced into the device to intentionally block the migration of majority carriers (holes), suppress the generation-recombination (GR) dark current and surface leakage current caused by the depletion region, and at the same time improve the transport efficiency of a minority of photogenerated carriers (electrons) to successfully cross the barrier and reach the electrode.

[0028] However, traditional unipolar barrier structures such as PπBN, PπMN, and nBn have significant limitations in long-wavelength detector applications. In a conventional PπMN structure, the long-wavelength narrow-bandgap π-type absorber layer is directly connected to the wide-bandgap M barrier layer. Due to the inherent difference in band structure between the materials on both sides of the heterojunction, when the M barrier is designed to block holes (i.e., its equivalent valence band is much lower than that of the absorber layer), its equivalent conduction band bottom (Cb) is often inevitably higher than that of the π absorber layer, resulting in abrupt, spike-shaped conduction band gradient at the interface. This abrupt band gradient acts like a wall, severely hindering the migration of photogenerated electrons to the N-type contact layer, leading to carrier accumulation and recombination at the heterojunction interface. Simultaneously, to achieve sufficient hole blocking capability, the barrier layer requires a high equivalent valence band barrier. However, in conventional structures, the abrupt change in the valence band position is often accompanied by a strong interfacial electric field distribution, which can easily induce interband tunneling (TAT) dark current in narrow bandgap materials, thus negating the effect of the barrier layer on suppressing the generation-recombination (GR) dark current.

[0029] Therefore, this application aims to solve the problem of how to design a gradient structure that can dynamically match and take into account both "unobstructed conduction band" and "deep barrier in valence band" for narrow bandgap absorption layers with different cutoff wavelengths in the range of 8-12µm, which can effectively solve the above-mentioned problems of interface band mismatch and carrier transport obstruction.

[0030] To address the problems in the related technologies, this application provides a gradient barrier superlattice infrared detector and its fabrication method, which can achieve synergistic optimization of conduction band flush barrier-free and valence band deep barrier, thereby simultaneously improving quantum efficiency and suppressing dark current.

[0031] It should be noted that the embodiments of this application are intended to cover long-wave infrared detector applications with wavelengths of 8-12µm, and therefore have a certain adjustable range in parameter design.

[0032] The gradient barrier superlattice infrared detector provided in this application will be described in detail below with reference to the accompanying drawings, through specific embodiments and application scenarios.

[0033] In this embodiment of the application, the gradient barrier superlattice infrared detector includes, from bottom to top, the following: Substrate; Buffer layer; P-type contact layer; Absorption layer; A gradient transition barrier layer, wherein the gradient transition barrier layer is an N-order M-structure superlattice, N≥2; along the direction away from the absorption layer, the equivalent valence band top of the gradient transition barrier layer decreases in a stepwise manner, and its equivalent conduction band bottom is not higher than the equivalent conduction band bottom of the absorption layer; and, N-type contact layer.

[0034] refer to Figure 1 This is a schematic cross-sectional view of the epitaxial structure of a gradient barrier superlattice infrared detector according to an embodiment of this application. Figure 1 As shown, the gradient barrier type long-wavelength superlattice infrared detector comprises, from bottom to top: a GaSb substrate, a GaSb buffer layer, a P-type mid-wavelength superlattice contact layer, a π-type long-wavelength superlattice absorption layer, a gradient transition barrier layer, an N-type wide-bandgap superlattice base layer, and a capping layer.

[0035] In some embodiments, other lattice-matching materials such as GaSb or InAs are used as semiconductor substrates, and buffer layers are epitaxially grown on them to release lattice mismatch stress and provide a basis for low defect density epitaxial growth.

[0036] In some embodiments, the contact layer (P-layer) adopts a highly p-type doped InAs / GaSb mid-wave superlattice structure. On the one hand, it serves as a p-type ohmic contact layer at the bottom of the device; on the other hand, it utilizes the mid-wave absorption characteristics to act as a filter layer to absorb mid-wave high-frequency photons in the incident light, thereby reducing the crosstalk of mid-wave photogenerated carriers to long-wave target signals.

[0037] In some embodiments, the π-type long-wavelength superlattice absorption layer (π layer) adopts a narrow bandgap InAs / GaSb or InAs / InAsSb superlattice structure with weak p-type (π-type) doping. This layer serves as the main infrared photoelectric conversion region, generating photogenerated electron-hole pairs, and its bandgap structure determines the cutoff wavelength of the device.

[0038] In some embodiments, a gradient transition barrier layer is located between the π layer and the N layer. This layer consists of a multi-period M-type superlattice structure (InAs / GaSb / AlSb / GaSb). Unlike traditional barrier layers, this layer is not a uniform structure with a fixed period. By changing the physical thickness of each InAs, GaSb, and AlSb material layer within a single period along the epitaxial growth direction, either periodically or stepwise, such as gradually decreasing the thickness of the InAs layer along the growth direction and correspondingly increasing the thickness of the AlSb and GaSb layers, continuous control of the equivalent microscopic energy band in this region can be achieved.

[0039] Optionally, the M-structure superlattice of the gradient transition barrier layer comprises, in a single period, a stacked InAs layer, a first GaSb layer, an AlSb layer, and a second GaSb layer. Along the direction away from the absorption layer, in each order of the M-structure superlattice, the thickness of the InAs layer either increases or remains constant before increasing, the thickness of the first GaSb layer and / or the second GaSb layer decreases, and the thickness of the AlSb layer remains constant. That is, at least one of the first GaSb layer and the second GaSb layer, or the sum of their thicknesses, decreases.

[0040] It should be noted that in this embodiment, by designing a gradient in the thickness of the superlattice layer, the transition layer simultaneously follows the following principles in terms of energy bands: First, conduction band alignment. Starting from the first step near the absorption layer, the thickness of the InAs monolayer within the barrier layer is designed to be no less than the thickness of the InAs within the absorption layer, and increases stepwise along the growth direction (thickness range 11-18ML). This design ensures that the equivalent conduction band bottom of the barrier layer is always flush with or slightly lower than the conduction band bottom of the absorption layer, eliminating conduction band steps at the interface and establishing an "unobstructed downhill" channel for photogenerated electrons; Second, The valence band gradient sinks, and within each step of the barrier layer, the thickness of the GaSb monolayer decreases step by step along the growth direction (thickness range 3-1ML). Utilizing the characteristic that the valence band energy decreases due to the reduction in GaSb thickness, combined with the support of the wide bandgap AlSb layer, the equivalent valence band top (Vb) exhibits a step-like continuous decline, forming a deep hole barrier with adjustable thickness; thirdly, stress compensation and thickness control, the thickness of each step is controlled at 0.1-0.2µm, the total thickness is optimized according to wavelength requirements, and the AlSb layer thickness is maintained at 4-6ML to maintain structural stability.

[0041] In some embodiments, the equivalent valence band top (first hole band HH1) of the gradient barrier layer starts near the π-layer interface, gradually and continuously decreasing along the direction of epitaxial growth, and finally perfectly connects with the valence band top of the upper wide-bandgap N-layer. This forms a thick hole-blocking slope without abrupt changes.

[0042] It should be noted that the barrier layer in this embodiment has extremely strong band coverage. For the 8-9µm band, a lower initial InAs ratio, such as 14ML, is used as the first step of the gradient barrier; for the 10-12µm band, the InAs thickness of each step of the barrier layer is increased simultaneously, such as increasing the first step to 15ML or 16ML, to dynamically offset the effect of the absorption layer's conduction band shift.

[0043] In this way, the traditional fixed-period M barrier layer is improved into a transition barrier layer with N-order (N≥2) band height stepped variation. By microscopically adjusting the proportion of single-atom layers (ML) of each component within the M structure period, fine control of the band space can be achieved.

[0044] In some embodiments, the N-type wide bandgap superlattice base layer (N layer) is made of a highly N-type doped wide bandgap M-structure superlattice material. As the ohmic contact layer at the top of the device, it has an extremely low valence band position, which works in conjunction with the end of the gradient barrier layer to completely block holes and extract photogenerated electrons.

[0045] As an optional embodiment, to accommodate detection requirements for different cutoff wavelengths within the 8-12µm range, the bandgap of the π-type long-wavelength superlattice absorption layer (typically an InAs / GaSb structure) is adjusted accordingly, primarily by changing the thickness of the InAs layer, typically ranging from 11ML to 18ML. Furthermore, it should be understood that since the reduction in the absorption layer's bandgap causes its conduction band bottom to shift downwards, the gradient transition barrier layer must be dynamically matched and gradient-designed according to the specific band structure of the absorption layer.

[0046] Specifically, the gradient transition barrier layer is composed of an N-order M-structure superlattice (InAs / GaSb / AlSb / GaSb), where N≥2, preferably 3-5 order. Along the epitaxial growth direction, the thickness of the monolayer near the π-structure period follows the following variation law: the InAs layer thickness increases or remains constant before increasing, ranging from 11-18ML, to ensure that the conduction band bottom of the barrier layer is never higher than the conduction band bottom of the absorption layer, thus eliminating conduction band spikes; the GaSb layer thickness decreases, gradually decreasing from 3ML to 1ML, to achieve a significant step-like decrease in the valence band top; the AlSb layer thickness remains basically constant, typically 4-6ML, preferably 5ML, serving as a fixed barrier framework to maintain overall structural stress balance and wide bandgap characteristics.

[0047] Therefore, the gradient barrier superlattice infrared detector of this application has at least the following beneficial technical effects: At the physical mechanism level, it breaks the limitation of the coupling relationship between the conduction band and valence band in the traditional PπMN structure. Through the asymmetric control of the four degrees of freedom of the M structure, a perfect unity of conduction band smoothing (ensuring quantum efficiency) and deep valence band blocking (suppressing dark current) is achieved, eliminating band spikes that affect performance. In terms of process feasibility and high yield, the use of N-order step-gradient discontinuous composition gradient greatly reduces the risk of composition runaway caused by frequent fluctuations in source furnace temperature during MBE growth. A smooth band transition can be achieved through precise shutter action, which has high engineering application prospects. In terms of extended band application, the design concept provided by this application can cover the full spectrum detection needs from long wavelength to very long wavelength. By changing the starting point of the gradient step parameters, the optimal electron transport channel and hole blocking barrier can be customized for any narrow bandgap absorption layer in the range of 8-12µm.

[0048] Example 1 This embodiment is for a long-wavelength detector with a cutoff wavelength of 8-9µm. Figure 2 The diagram shows the overall band structure simulation of the gradient barrier type long-wavelength superlattice infrared detector in this embodiment. The upper gray solid line represents the equivalent conduction band bottom Cb, the lower red solid line represents the equivalent valence band top Vb, the horizontal axis represents the epitaxial growth thickness direction, and the vertical axis represents the energy level height.

[0049] from Figure 2 As can be seen from this, the band structure corresponding to this embodiment has the following specific epitaxial growth parameters: (1) Buffer layer: A highly p-type doped GaSb buffer layer with a thickness of 0.6µm is grown on a GaSb substrate.

[0050] (2) P layer: A medium-wave superlattice with a thickness of 0.5µm is grown, with a periodic structure of 8ML InAs / 8ML GaSb.

[0051] (3) π layer (absorption layer): grow a weakly p-type doped long-wavelength absorption layer with a periodic structure of 12ML InAs / 7MLGaSb.

[0052] (4) Gradient transition barrier layer (4th order): First stage: Closely attached to the absorption layer, grow M structures with a thickness of 0.1µm, consisting of 14 / 3 / 5 / 3 ML (corresponding to the atomic layer number ML of InAs / GaSb / AlSb / GaSb respectively); Second stage: Growth of 14 / 2 / 5 / 2 ML M structures with a thickness of 0.1µm; Third stage: Growth of 14 / 1 / 5 / 1 ML M structures with a thickness of 0.1µm; Fourth stage: Growth of 16 / 1 / 5 / 1 M-structures with a thickness of 0.2µm.

[0053] (5) N layer and capping layer: A heavily N-type doped 16 / 1 / 5 / 1 M structure layer with a thickness of 0.5µm is grown and covered with a 0.02µm InAs capping layer on top.

[0054] Combination Figure 2 Simulation results show that the first-stage 14ML InAs perfectly connects to the conduction band of the 12ML absorption layer. Subsequently, by decreasing the GaSb and increasing the InAs thickness, a smooth, stepped hole blocking barrier was successfully formed.

[0055] Example 2 This embodiment is for a very long wave detector with a cutoff wavelength of 10-11µm.

[0056] As the target wavelength extends to 10-11 µm, the absorption layer band gap narrows further, and the conduction band bottom becomes even lower. To avoid the formation of conduction band spikes at the heterojunction interface, the overall InAs composition of the barrier layer needs to be increased accordingly. The specific epitaxial growth parameters are as follows: (1) π layer (absorption layer): adjusted to 14ML InAs / 7ML GaSb or 13.5ML InAs / 7GaSb to achieve a longer cutoff wavelength.

[0057] (2) Gradient transition barrier layer (3rd order): First stage: grow a 15 / 3 / 5 / 3 M structure with a thickness of 0.1µm to match the lower conduction band of the absorption layer; Second stage: Growth of 16 / 2 / 5 / 2 M structures with a thickness of 0.1µm; Third stage: Growth of an 18 / 1 / 5 / 1M structure with a thickness of 0.2µm, further reducing the valence band.

[0058] (3) N layer and capping layer: a heavily N-type doped 18 / 1 / 5 / 1 M structure layer with a thickness of 0.5µm was grown.

[0059] Furthermore, this application also provides a method for fabricating a gradient barrier superlattice infrared detector. It should be noted that this method for fabricating a gradient barrier superlattice infrared detector can be applied to gradient barrier superlattice infrared detectors as described in any of the above embodiments.

[0060] Specifically, the fabrication method of this gradient barrier superlattice infrared detector may include the following steps: S101, Provide a substrate; S102, An absorption layer is formed on the substrate; S103. A gradient transition barrier layer is formed on the absorption layer. The gradient transition barrier layer is an N-order M-structure superlattice with N≥2. Along the direction away from the absorption layer, the equivalent valence band top of the gradient transition barrier layer decreases in a step-like manner, and its equivalent conduction band bottom is not higher than the equivalent conduction band bottom of the absorption layer. S104. A contact layer is formed on the gradient transition barrier layer.

[0061] In some embodiments, the M-structure superlattice of the gradient transition barrier layer has a single period comprising a stacked InAs layer, a first GaSb layer, an AlSb layer, and a second GaSb layer.

[0062] In some embodiments, when forming the gradient transition barrier layer, the thickness of the InAs layer is increased stepwise along the direction away from the absorption layer, and the thickness of the first GaSb layer and / or the second GaSb layer is decreased stepwise.

[0063] Thus, the stepped gradient design in the above embodiments perfectly matches the characteristic of molecular beam epitaxy (MBE) in which the thickness of a single atomic layer can be precisely controlled by the shutter opening and closing time. Compared with continuous stepless gradients, it is easier to implement and has higher repeatability and yield. At the same time, although the composition of each period inside the superlattice changes, by retaining the AlSb layer and cooperating with the specific strain compensation design of the interface, the entire gradient barrier layer still maintains good lattice matching with the GaSb substrate on a macroscopic scale, effectively preventing stress relaxation and the generation of mismatch dislocations.

[0064] It should be noted that the above description describes some embodiments of this application. Other embodiments are within the scope of the appended claims. In some cases, the actions or steps recorded in the claims can be performed in a different order than that shown in the above embodiments and still achieve the desired result. Furthermore, the processes depicted in the drawings do not necessarily require a specific or sequential order to achieve the desired result. In some embodiments, multitasking and parallel processing are also possible or may be advantageous.

[0065] In this application, the reference to "embodiment" means that a particular feature, structure, or characteristic described in connection with an embodiment may be included in at least one embodiment of this application. The appearance of this phrase in various places in the specification does not necessarily refer to the same embodiment, nor is it a separate or alternative embodiment that is mutually exclusive with other embodiments.

[0066] In the description of this application, it should be noted that, unless otherwise expressly specified and limited, the terms "installation," "connection," "linking," and "attachment" should be interpreted broadly. For example, they can refer to a fixed connection, a detachable connection, or an integral connection; they can refer to a direct connection or an indirect connection through an intermediate medium; and they can refer to the internal communication between two components. Those skilled in the art can understand the specific meaning of the above terms in this application according to the specific circumstances.

[0067] In the embodiments of this application, the same reference numerals denote the same components, and for the sake of brevity, detailed descriptions of the same components are omitted in different embodiments. It should be understood that the thickness, length, width, and other dimensions of various components in the embodiments of this application shown in the accompanying drawings, as well as the overall thickness, length, width, and other dimensions of the integrated device, are merely illustrative and should not constitute any limitation on this application.

[0068] In this application, "multiple" means two or more (including two).

[0069] Although this application has been described with reference to preferred embodiments, various modifications can be made thereto and components can be replaced with equivalents without departing from the scope of this application. In particular, the technical features mentioned in the various embodiments can be combined in any manner, provided there is no structural conflict. This application is not limited to the specific embodiments disclosed herein, but includes all technical solutions falling within the scope of the claims.

[0070] It should also be noted that the exemplary embodiments mentioned in this application describe methods or systems based on a series of steps or apparatus. However, this application is not limited to the order of the above steps; that is, the steps can be performed in the order mentioned in the embodiments, or in a different order, or several steps can be performed simultaneously.

[0071] The above description is merely a specific implementation of this application. Those skilled in the art will clearly understand that, for the sake of convenience and brevity, the specific working processes of the systems, modules, and units described above can be referred to the corresponding processes in the foregoing method embodiments, and will not be repeated here. It should be understood that the protection scope of this application is not limited thereto. Any person skilled in the art can easily conceive of various equivalent modifications or substitutions within the technical scope disclosed in this application, and these modifications or substitutions should all be covered within the protection scope of this application.

Claims

1. A gradient barrier superlattice infrared detector, characterized in that, Including the following, arranged from bottom to top: Substrate; Buffer layer; P-type contact layer; Absorption layer; A gradient transition barrier layer, wherein the gradient transition barrier layer is an N-order M-structure superlattice, N≥2; along the direction away from the absorption layer, the equivalent valence band top of the gradient transition barrier layer decreases in a stepwise manner, and its equivalent conduction band bottom is not higher than the equivalent conduction band bottom of the absorption layer; and, N-type contact layer.

2. The gradient barrier superlattice infrared detector according to claim 1, characterized in that, The M-structure superlattice of the gradient transition barrier layer has a single period comprising stacked InAs layer, first GaSb layer, AlSb layer and second GaSb layer. Along the direction away from the absorption layer, in each order of M-structure superlattice, the thickness of the InAs layer increases or remains constant before increasing, the thickness of the first GaSb layer and / or the second GaSb layer decreases, and the thickness of the AlSb layer remains constant.

3. The gradient barrier superlattice infrared detector according to claim 2, characterized in that, The InAs layer has a thickness ranging from 11 to 18 atomic layers, the first GaSb layer and the second GaSb layer each have a thickness ranging from 1 to 3 atomic layers, and the AlSb layer has a thickness ranging from 4 to 6 atomic layers.

4. The gradient barrier superlattice infrared detector according to claim 1, characterized in that, The absorption layer is a π-type long-wavelength superlattice absorption layer.

5. The gradient barrier superlattice infrared detector according to claim 1, characterized in that, The P-type contact layer is a P-type mid-wave superlattice contact layer used to absorb mid-wave photons.

6. The gradient barrier superlattice infrared detector according to claim 1, characterized in that, The substrate is a GaSb substrate or an InAs substrate; the absorption layer is an InAs / GaSb superlattice structure or an InAs / InAsSb superlattice structure.

7. The gradient barrier superlattice infrared detector according to claim 1, characterized in that, In the N-order M-structure superlattice, the value of N ranges from 3 to 5.

8. The gradient barrier superlattice infrared detector according to claim 1, characterized in that, The thickness of each step of the gradient transition barrier layer is 0.1µm to 0.2µm.

9. A method for fabricating a gradient barrier superlattice infrared detector, characterized in that, Applied to any one of the gradient barrier superlattice infrared detectors as described in claims 1-8, the method comprises: Provide a substrate; An absorption layer is formed on the substrate; A gradient transition barrier layer is formed on the absorption layer. The gradient transition barrier layer is an N-order M-structure superlattice with N≥2. Along the direction away from the absorption layer, the equivalent valence band top of the gradient transition barrier layer decreases in a step-like manner, and its equivalent conduction band bottom is not higher than the equivalent conduction band bottom of the absorption layer. A contact layer is formed on the gradient transition barrier layer.

10. The manufacturing method according to claim 9, characterized in that, The M-structure superlattice of the gradient transition barrier layer has a single period comprising stacked InAs layer, first GaSb layer, AlSb layer and second GaSb layer. When forming the gradient transition barrier layer, the thickness of the InAs layer is increased stepwise along the direction away from the absorption layer, and the thickness of the first GaSb layer and / or the second GaSb layer is decreased stepwise.

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