A long wavelength PIN photodiode with a composite intrinsic region and a preparation method thereof

Abstract

The application discloses a long-wavelength PIN photodiode with a composite intrinsic region and a preparation method thereof, and relates to the technical field of semiconductors. The long-wavelength PIN photodiode comprises a GaAs substrate, a DBR layer, a deformation growth layer and an absorption layer. The DBR layer, the deformation growth layer and the absorption layer jointly form a composite intrinsic region. The optical function of the composite intrinsic region is realized by reflecting light transmitted through the absorption layer by the DBR layer and cooperating with the absorption layer to achieve optical path multiplication. The electrical function of the composite intrinsic region is realized by jointly forming a wide depletion region by the DBR layer and the deformation growth layer to reduce junction capacitance. The composite intrinsic region provided by the application makes the two traditionally contradictory requirements of "expanding the depletion region" and "enhancing light absorption" be respectively optimized and synergistically improved in different physical layers, thereby fundamentally solving the long-term trade-off problem between bandwidth and responsivity in the physical layer of the device.

Description

Technical Field

[0001] This invention relates to the field of semiconductor technology, and in particular to a long-wavelength PIN photodiode with a composite intrinsic region and its fabrication method. Background Technology

[0002] As a core component of high-speed optical communication and detection systems, the performance of PIN photodiodes is determined by both responsivity and bandwidth. However, a fundamental contradiction exists in the design of the intrinsic absorption layer (I-layer) thickness for these two key indicators, constituting a classic performance bottleneck for this type of device. Specifically, the device's response speed is mainly limited by the RC time constant bandwidth and the carrier transit time bandwidth. On the one hand, to reduce junction capacitance and increase RC bandwidth, the depletion region width needs to be increased, requiring a thicker intrinsic absorption layer; on the other hand, to shorten the drift time of photogenerated carriers in the depletion region and increase transit time bandwidth, a thinner intrinsic absorption layer is required. This design conflict makes it difficult to simultaneously achieve high responsivity and high bandwidth in traditional single-absorption-layer PIN structures.

[0003] To alleviate the aforementioned contradiction, some journal articles have proposed introducing distributed Bragg reflector (DBR) structures into PIN or single-carrier photodetectors (UTC-PDs). This approach places the DBR below the absorption layer, achieving a "path multiplication" effect by reflecting light transmitted through the absorption layer back to the absorption region for secondary absorption. This improves quantum efficiency and responsivity without significantly increasing the physical thickness of the absorption layer (which is beneficial for transit time). However, the DBR in this approach is typically designed as a passive "optical mirror," with its design goal purely focused on high reflectivity. The doping state and interface electrical properties of its multilayer structure are not integrated with the intrinsic region of the PIN junction for optimization. This prevents the DBR structure from effectively participating in the formation and expansion of the depletion region, thus failing to fulfill the crucial electrical functions of reducing junction capacitance and increasing RC bandwidth. Therefore, such approaches can only improve responsivity to a limited extent and cannot fundamentally resolve the inherent contradiction between responsivity and bandwidth.

[0004] Furthermore, when applying the aforementioned DBR enhancement scheme to long wavelength bands such as 1310nm or 1550nm, even more severe material system and performance bottlenecks are encountered. To achieve efficient absorption of light in this band, narrow bandgap materials such as indium gallium arsenide (InGaAs) must be used as the intrinsic absorption layer. However, to obtain high-quality lattice-matched epitaxy, traditional techniques generally rely on indium phosphide (InP) substrates and their supporting material systems to construct the entire device, including the DBR. This brings new challenges: the refractive index difference between layers in InP-based material systems (such as InP / InGaAsP or InAlAs / InGaAs) is small. To achieve sufficiently high reflectivity, a very large number of period pairs (usually exceeding 40 pairs) need to be stacked. This results in an exceptionally complex epitaxial structure, extremely long growth time, and high cost. At the same time, the accumulated stress and interface defects introduced by the multilayer heterogeneous interfaces are difficult to control, severely restricting the uniformity, yield, and long-term reliability of the epitaxial materials. In other words, in the long-wavelength field, the InP-based DBR material system, which is forced to be chosen to achieve optical enhancement, has itself become a new bottleneck restricting device performance, reliability, and manufacturing cost.

[0005] In summary, the current technological development of high-performance long-wavelength PIN photodetectors faces a dual dilemma: firstly, existing DBR-incorporated solutions offer limited functionality at the device physics level, failing to achieve synergistic optimization of optoelectronic performance; secondly, at the materials and fabrication level, traditional InP-based DBRs suitable for long wavelengths are structurally complex, have limited performance, and are difficult to fabricate. Therefore, an innovative device architecture is urgently needed to break free from the constraints of material systems and achieve a novel solution that deeply integrates optical enhancement structures with electrical performance optimization mechanisms. Summary of the Invention

[0006] This invention provides a long-wavelength PIN photodiode with a composite intrinsic region and its fabrication method. It aims to systematically solve the inherent problem of the incompatibility between high bandwidth, high responsivity and low-cost fabrication in long-wavelength photodetectors by integrating a DBR layer and a deformable growth layer with synergistic optoelectronic functions on a GaAs substrate.

[0007] The present invention adopts the following technical solution:

[0008] A long-wavelength PIN photodiode with a composite intrinsic region includes, from bottom to top, a GaAs substrate, a DBR layer, a deformable growth layer, and an absorption layer; the DBR layer consists of multiple pairs of intrinsically undoped Al atoms. x Ga 1-x As / Al y Ga 1-yThe material is composed of alternating As layers; the absorption layer is lattice-matched with InP to absorb light of the target wavelength; the deformed growth layer is intrinsically undoped, and its lattice constant gradually changes along the growth direction to bridge the lattice mismatch between the DBR layer and the absorption layer; the DBR layer, the deformed growth layer, and the absorption layer together constitute a composite intrinsic region; the optical function of the composite intrinsic region is to reflect light transmitted through the absorption layer through the DBR layer, and to work in conjunction with the absorption layer to achieve optical path multiplication; the electrical function of the composite intrinsic region is to form a broad depletion region through the DBR layer and the deformed growth layer to reduce junction capacitance.

[0009] Furthermore, the DBR layer has a reflectivity of more than 60% for light of the target wavelength, and its periodicity is at least 9 pairs.

[0010] Furthermore, the DBR layer is composed of Al 0.9 Ga 0.1 The structure consists of alternating As / GaAs material layers, with the optical thickness of each layer being one-quarter of the wavelength of the target wavelength in the corresponding material.

[0011] Furthermore, the deformed growth layer is an InAlAs ternary alloy gradient layer or an InAlGaAs quaternary alloy gradient layer. By linearly controlling the In, Al and / or Ga components of the deformed growth layer, a synergistic gradient of the lattice constant and the bandgap width is achieved.

[0012] Furthermore, it also includes a dislocation filtering layer, which is disposed between the deformable growth layer and the absorption layer to block the transmission of dislocations generated in the deformable growth layer to the absorption layer.

[0013] Furthermore, the dislocation filtering layer is an InAlAs / InGaAs superlattice layer, and the dislocation filtering function can be precisely controlled by adjusting the composition, sublayer thickness, and / or periodic parameters.

[0014] Furthermore, the absorber layer is made of InGaAs material and has a thickness of 0.8-2.0 μm.

[0015] A method for fabricating a long-wavelength PIN photodiode with a composite intrinsic region, characterized by comprising the following steps:

[0016] Step S1: Provide a GaAs substrate;

[0017] Step S2: Grow a DBR layer on the GaAs substrate, the DBR layer consisting of multiple pairs of intrinsically undoped Al atoms. x Ga 1- x As / Al y Ga 1-yAs material layers are stacked alternately;

[0018] Step S3: An intrinsically undoped deformable growth layer is grown above the DBR layer, wherein the lattice constant of the deformable growth layer gradually changes along the growth direction;

[0019] Step S4: Grow an absorption layer on top of the deformed growth layer.

[0020] Furthermore, after step S2 and before step S3, a first growth interruption is performed: during a first preset duration, the supply of group V source and growth temperature are maintained, while the supply of group III source is interrupted; after step S3 and before step S4, a second growth interruption is performed: during a second preset duration, the supply of group V source and growth temperature are maintained, while the supply of group III source is interrupted.

[0021] Furthermore, the growth temperature range of the absorption layer is 600°C to 650°C.

[0022] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0023] 1. This invention, based on the design concept of a composite intrinsic region, expands the traditional single-function absorption layer into a functional whole consisting of a DBR layer, a deformable growth layer, and an absorption layer working synergistically. In the composite intrinsic region, both the DBR layer and the deformable growth layer remain intrinsically undoped, and together form an ultra-wide depletion region under reverse bias to minimize junction capacitance. Simultaneously, the DBR layer efficiently reflects unabsorbed light back to the absorption layer, effectively extending the optical path. This design allows the traditionally contradictory requirements of "extending the depletion region" and "enhancing light absorption" to be optimized and synergistically enhanced at different physical levels, thus fundamentally solving the long-standing trade-off between bandwidth and responsivity at the device physics level.

[0024] 2. This invention utilizes a deformable growth layer with a gradually varying lattice constant to successfully achieve monolithic heterogeneous integration of a high-quality long-wavelength absorption layer with InP lattice matching on a low-cost, large-size GaAs substrate. This approach completely eliminates the dependence of traditional technologies on expensive InP substrates and complex InP-based DBR structures. By leveraging the advantages of the GaAs material system, it achieves the required functions in fewer cycles while ensuring high performance, significantly reducing fabrication difficulty and cost, and laying a solid foundation for large-scale, high-yield device manufacturing.

[0025] 3. The fabrication method of this invention precisely controls the crystal quality of multiple heterojunction interfaces between the GaAs and InP systems by introducing key processes such as growth interruption, high-temperature thermal cleaning, and optional dislocation filtering layers. These processes effectively obtain atomically flat interfaces and suppress defect and dislocation propagation, thereby significantly reducing the dark current noise of the device. This not only ensures the full utilization of the electrical functions of the composite intrinsic region but also guarantees the high performance consistency and long-term operational reliability of the device. Attached Figure Description

[0026] Figure 1 This is a schematic diagram of the extensional structure of Embodiment 1 and Embodiment 2 of the present invention.

[0027] Figure 2 This is a schematic diagram of the lattice adaptation and bandgap variation of the InAlAs ternary alloy gradient layer in Embodiment 1 of the present invention.

[0028] Figure 3 This is a growth structure diagram of the InAlAs / InGaAs strained superlattice in Example 1 of this invention.

[0029] Figure 4 This is a schematic diagram of the lattice adaptation and bandgap variation of the InAlGaAs quaternary alloy gradient layer in Embodiment 2 of the present invention.

[0030] Figure 5 This is a growth structure diagram of the InAlAs / InGaAs unstrained superlattice in Example 2 of this invention.

[0031] In the figure: 1-GaAs substrate; 2-n-type contact layer; 3-n-type buffer layer; 4-DBR layer; 5-deformation growth layer; 6-dislocation filter layer; 7-absorption layer; 8-window layer; 9-p-type contact layer. Detailed Implementation

[0032] Specific embodiments of the present invention will now be described with reference to the accompanying drawings. Many details are described below to provide a comprehensive understanding of the invention; however, those skilled in the art will be able to implement the invention without these details.

[0033] Reference Figure 1The core concept of this invention lies in constructing an ideal crystal platform for epitaxially growing long-wavelength InP-based absorption layers on a low-cost, large-size GaAs substrate by introducing a high-quality deformable growth layer. Based on this, an innovative DBR layer (GaAs-based distributed Bragg mirror) with optoelectronic synergy is integrated. This DBR layer, together with the intrinsically undoped deformable growth layer and the absorption layer above, constitutes a "composite intrinsic region." This region ensures high responsivity through "optical path multiplication" and actively reduces junction capacitance through "extended depletion region," thus systematically solving multiple bottlenecks in performance, cost, and reliability of long-wavelength high-speed PIN photodiodes at both the material system and device physics levels.

[0034] Based on the above concept, the following two embodiments, combining two typical material systems and designs, will be described in detail. The device architecture of each embodiment is the same as the inventive concept; the main difference lies in the specific technical path for achieving lattice gradient and defect control.

[0035] Example 1: Scheme based on InAlAs ternary alloy gradient layer

[0036] Reference Figure 1 This embodiment provides a long-wavelength PIN photodiode with a composite intrinsic region. Its epitaxial structure, from bottom to top, mainly includes: a GaAs substrate 1, an n-type contact layer 2, an n-type buffer layer 3, a DBR layer 4, a deformable growth layer 5, an optional dislocation filter layer 6, an absorption layer 7, a window layer 8, and a p-type contact layer 9. The DBR layer 4, the deformable growth layer 5, and the absorption layer 7 together constitute the composite intrinsic region that realizes the core function of this invention. The dislocation filter layer 6, as a preferred additional layer located within this composite intrinsic region and between the deformable growth layer 5 and the absorption layer 7, is used to further improve crystal quality, but it is not a necessary component defining the photoelectric function of the composite intrinsic region.

[0037] Reference Figures 1 to 3 The functions, material design, and beneficial effects of each epitaxial layer are described in detail below:

[0038] GaAs substrate 1: Serves as the epitaxial growth foundation and mechanical support for the entire device. This invention preferably uses a 6-inch semi-insulating GaAs substrate, whose core advantages are significantly lower cost than traditional InP substrates, the ability to obtain larger wafers, and superior mechanical strength and thermal conductivity. This provides fundamental conditions for significantly reducing manufacturing costs, improving production yield and capacity, and enhancing heat dissipation under high-frequency operation.

[0039] n-type contact layer 2: grown on GaAs substrate 1, typically composed of highly doped n-type contact layers. + - It is made of GaAs material and is used to form a low-resistance ohmic contact with the cathode metal to ensure efficient longitudinal current conduction.

[0040] n-type buffer layer 3: Typically composed of n-type AlGaAs material. This layer mainly serves as a transition and buffer between the substrate and the subsequent DBR layer 4 in terms of lattice and energy band; its moderate doping concentration helps to optimize the longitudinal electric field distribution and provides a smooth surface for the growth of high-quality DBR layer 4.

[0041] DBR layer 4: One of the core innovative structures of this invention for achieving synergistic optoelectronic functions. This layer is lattice-matched with GaAs and consists of multiple pairs of intrinsically undoped Al atoms. x Ga 1-x As / Al y Ga 1-y The DBR layer is composed of alternating layers of As material. Preferably, the DBR layer 4 is made of Al. 0.9 Ga 0.1 The design consists of alternating As / GaAs material layers. By precisely designing the optical thickness of each layer to be one-quarter (λ / 4n) of the wavelength of the target wavelength (e.g., 1550nm) in the corresponding material, and employing a sufficient number of periodic pairs (at least 9 pairs), it can be ensured that the reflectivity to the target wavelength is greater than 60%. This specific reflectivity threshold is the result of systematic optimization: it firstly meets the minimum performance requirement for effective optical synergy with the upper absorption layer 7 to achieve a significant "optical path multiplication" effect; at the same time, it is based on profound considerations for the industrial manufacturing of large-size substrates: setting the reflectivity target above 60% rather than higher (e.g., >90%) can significantly reduce the demanding requirement for the extreme uniformity of the thickness and composition of each material layer of DBR layer 4 across the entire wafer, thereby achieving higher epitaxial growth yield and a wider process window on the 6-inch GaAs substrate 1, ensuring the feasibility and cost advantage of this high-performance design for large-scale production. The revolutionary significance of DBR layer 4 lies in the fact that its intrinsic undoped nature allows it to be completely depleted under reverse bias, contributing the overall thickness of its dozens of layers of material to the main body of the PIN junction depletion region. This significantly expands the width of the depletion region without increasing the physical thickness of the absorption layer 7, directly leading to a significant reduction in intrinsic junction capacitance and realizing the transformation from a "passive optical mirror" to an "active electrical functional layer".

[0042] The deformed growth layer 5 is crucial for achieving heterogeneous integration from the underlying GaAs-based DBR layer 4 to the upper InP-based absorber layer 7. In this embodiment, an InAlAs ternary alloy graded layer is preferred. By linearly increasing the In composition while simultaneously linearly decreasing the Al composition along the growth direction, the lattice constant smoothly transitions from matched GaAs (~5.65 Å) to matched InP (~5.87 Å). This design not only effectively relaxes the lattice mismatch stress, which is as high as approximately 4%, avoiding the high-density dislocations generated by direct epitaxy, but the natural band slope formed by the compositional gradient also facilitates the directional transport of photogenerated carriers. Similar to the DBR layer 4, this deformed growth layer is intrinsically undoped. Under reverse bias, its entire graded structure is also completely depleted, thus forming a depletion region with a very large total thickness together with the underlying DBR layer 4. This is another key electrical contribution source for achieving low junction capacitance and high RC bandwidth.

[0043] Dislocation filtering layer 6 (optional): Located above the deformed growth layer 5, its main function is to further capture and block residual penetrating dislocations that may be generated during strain relaxation of the deformed growth layer from propagating to the upper core absorption layer 7, thereby optimizing crystal quality and reducing dark current. In this embodiment, this layer is preferably an InAlAs / InGaAs strained superlattice (made of InP) that matches the InP lattice. 0.58 Al 0.42 As tensile strain layer and In x Ga 1-x This is achieved by alternating layers of compressive strain. It should be clarified that the role of this layer is purely for material quality optimization and does not directly participate in defining the core optoelectronic (optical path multiplication and extended depletion region) functions of the composite intrinsic region.

[0044] Absorption layer 7: The core region of the device that responds to long-wavelength light. It is composed of intrinsic InGaAs material that matches the InP lattice and adopts a thin-layer design with a thickness optimized between 0.8 and 2.0 μm to minimize carrier transit time.

[0045] Window layer 8: Typically composed of wide-bandgap p-type InP or InAlAs materials. Its function is to form a barrier to minority carriers (electrons) in the absorption layer, preventing them from diffusing to the surface and undergoing nonradiative recombination, thereby significantly reducing surface leakage current and improving the internal quantum efficiency of the device.

[0046] p-type contact layer 9: Located on the top layer of the device, typically composed of heavily doped p-type contact layers. + It is made of InGaAs material, and its function is to form a low-resistance ohmic contact with the anode metal to complete the photoelectric signal output of the device.

[0047] Reference Figures 1 to 3The first design focus of this invention is the synergistic effect of the deformable growth layer and the dislocation filtering layer. The design premise for both is to ensure that the bandgap of the deformable growth layer 5 and the dislocation filtering layer 6 is greater than the energy of the target photon, making them "transparent windows." This ensures that light energy travels efficiently between the absorption layer 7 and the DBR layer 4, supporting the optical and electrical synergistic function described later. The structural design and working principle are analyzed in detail below:

[0048] (1) Structural design and working principle of the deformable growth layer

[0049] Reference Figure 1 The deformed growth layer 5 is the core for achieving high-quality heterogeneous integration from the GaAs-based DBR layer 4 to the InP-based absorber layer 7. In this embodiment, this layer is preferably an InAlAs ternary alloy gradient layer, which achieves a synergistic gradient of lattice constant and bandgap width through linear control of the In and Al compositions.

[0050] Specifically, a metal-organic chemical vapor deposition (MOCVD) process was employed, with the flow rates of trimethylindium (TMIn) and trimethylaluminum (TMAl) linearly adjusted during growth. This resulted in a linear increase in the In composition from 0.01 to 0.52 along the growth direction, and a linear decrease in the Al composition from 0.99 to 0.48. This linear gradient process, within a thickness of 1–3 μm, allowed the lattice constant of the material to smoothly and continuously transition from a value close to GaAs (~5.65 Å) at the bottom to a value matching InP (~5.87 Å) at the top. This effectively relaxed approximately 4% of the lattice mismatch strain, forming a "virtual InP" surface suitable for epitaxy at the top.

[0051] The key synergistic benefit of this design lies in the fact that, with the increase of the In composition, the bandgap of InAlAs changes from a wide bandgap (~2.24 eV) to a narrow bandgap (~1.54 eV), naturally forming an energy band slope from the substrate to the active region. This built-in electric field facilitates the directional and rapid transport of photogenerated carriers generated in the absorption layer 7, providing a physical basis for improving the device response speed.

[0052] (2) Structural design and working principle of dislocation filter layer

[0053] To ensure extremely high crystal quality in the upper absorption layer 7, this embodiment preferably incorporates an optimized dislocation filtering layer 6 on top of the deformed growth layer 5. This layer employs an InAlAs / InGaAs strained superlattice structure, its main function being to trap and block residual penetrating dislocations in the deformed growth layer. Similarly, the bandgap of each sublayer material in this superlattice is designed to be greater than the target photon energy, thereby ensuring that it does not absorb light of the working wavelength and maintains high transmittance of the optical path.

[0054] To achieve efficient filtration, this superlattice requires precise design. Taking 10 cycles as an example, each cycle has a total thickness of 10 nm, constructed from In... 0.58 Al 0.42 As tensile strain layer and In x Ga 1-x As is composed of alternating compressive strain layers. Along the growth direction, by making In... x Ga 1-x The thickness of the As layer and its In composition x increase progressively, while adjusting the In content... 0.58 Al 0.42 The thickness of the As layer enables "dynamic strain compensation" between cycles. This spatially gradual distribution of a strong strain field can efficiently bend and annihilate dislocations, thus providing a nearly defect-free growth interface for the absorption layer with a relatively thin overall thickness.

[0055] Reference Figure 1 The second design focus of this invention lies in the synergistic design of the composite intrinsic region, which systematically solves the contradiction between responsivity and bandwidth in existing long-wavelength PIN photodiodes through structural innovation:

[0056] (1) Optical path multiplication principle: The incident light is first partially absorbed in the thinner absorption layer 7, and the transmitted part passes through the transparent deformable growth layer 5 and dislocation filter layer 6 in sequence, and continues to propagate to the lower DBR layer 4. The DBR layer 4 acts as a highly efficient reflector, reflecting this part of the transmitted light, which then passes back through the transparent intermediate layer and returns to the absorption layer 7 for secondary or even multiple absorptions. This "optical path multiplication" effect is equivalent to greatly increasing the effective path of light in the absorption layer, enabling the device to maintain high quantum efficiency and responsivity while using a thin absorption layer (to optimize transit time bandwidth).

[0057] (2) Principle of reducing junction capacitance: Under reverse bias, both the intrinsically undoped DBR layer 4 and the deformed growth layer 5 are completely depleted, and their huge total thickness together constitutes an exceptionally wide depletion region. According to the planar capacitance formula (C=εA / d), the junction capacitance is inversely proportional to the width of the depletion region (d). Therefore, this composite structure directly and effectively reduces the intrinsic junction capacitance of the device by physically increasing the width of the depletion region d, thereby improving the high-frequency bandwidth determined by the RC constant.

[0058] (3) System-level synergy with low-cost large substrates: This invention combines the above-mentioned high-performance device structure with a 6-inch GaAs substrate platform. This is not merely a material replacement, but a system-level innovation from the perspective of manufacturability and commercial competitiveness. The cost and size advantages of GaAs substrate 1 provide a solid foundation for the large-scale industrialization and market competitiveness of this high-performance long-wavelength detector solution.

[0059] Reference Figures 1 to 3This embodiment further provides a method for fabricating this long-wavelength PIN photodiode. The method first fabricates a high-quality photoelectric co-growing DBR layer 4 on a GaAs substrate 1, and then constructs a crystal platform that can be used to extend the wavelength absorption layer 7 through the synergistic growth of a deformable growth layer 5 and a dislocation filtering layer 6. The key steps of this fabrication process are described in detail below:

[0060] Step S1: Provide and process the GaAs substrate.

[0061] A 6-inch semi-insulating GaAs substrate 1 with (100) crystal orientation is provided, and standard chemical cleaning and high-temperature thermal deoxidation are performed in sequence to obtain a clean, atomically flat substrate surface, laying the foundation for subsequent high-quality epitaxial growth.

[0062] Step S2: Grow n-type contact layer 2, n-type buffer layer 3 and DBR layer 4.

[0063] Step S21: Growth of n-type contact layer and buffer layer: Using metal-organic chemical vapor deposition (MOCVD) process, highly doped n-type contact layers are sequentially grown at optimized temperature. + -GaAs layer as n-type contact layer 2, and n-type AlGaAs layer as n-type buffer layer 3.

[0064] Step S22: Growing DBR layer 4: An intrinsically undoped DBR layer 4 is grown above the n-type buffer layer 3. Al is grown alternately by precisely controlling the flow rates of trimethylaluminum (TMAl) and trimethylgallium (TMGa). 0.9 Ga 0.1 As and GaAs layers. The optical thickness of each layer is controlled to be one-quarter of the wavelength of the target wavelength in the corresponding material (λ / 4n), and the number of periodic pairs is at least 9 to ensure that the reflectivity is greater than 60%.

[0065] Step S23: Perform the first growth interruption: After completing the growth of DBR layer 4 and before starting the growth of deformable layer 5, perform the first growth interruption. Specifically, for a first preset duration (e.g., 30 to 60 seconds), maintain the arsine (AsH3) atmosphere and growth temperature (600-650℃), and interrupt the supply of all group III metal-organic sources. This step allows the atoms on the newly grown AlGaAs surface sufficient migration time to achieve atomic-level flatness, providing an ideal interface for subsequent heteroepitaxial growth.

[0066] Step S3: Grow the deformable growth layer and the dislocation filtering layer sequentially, and optimize the interface.

[0067] Step S31: Growing a deformable growth layer: On the flat surface of the DBR layer 4, an InAlAs ternary alloy gradient layer is grown as a deformable growth layer 5. By linearly controlling the flow rates of trimethylindium (TMIn) and trimethylaluminum (TMAl) through a program, the In composition increases linearly and the Al composition decreases linearly, thereby achieving a smooth gradient of the lattice constant from matched GaAs to matched InP.

[0068] Step S32: Perform a second growth interruption: After the growth of deformed growth layer 5 is completed and before the growth of dislocation filter layer 6 begins, perform a second growth interruption. During a second preset duration (e.g., 60 to 180 seconds), maintain the group V source supply and growth temperature, and interrupt the group III source supply. This step aims to optimize the surface of deformed growth layer 5, providing an atomically flat interface for subsequent high-quality epitaxy of the superlattice.

[0069] Step S33: Growth of a dislocation filter layer: An InAlAs / InGaAs strained superlattice is grown on the optimized surface as a dislocation filter layer 6. By designing the sublayer thickness and composition of the superlattice, dynamic strain compensation is achieved to efficiently filter penetrating dislocations.

[0070] Step S34, High-Temperature Thermal Cleaning: After the growth of the dislocation filter layer 6 is completed and before the epitaxial growth of the absorption layer 7, the surface of the dislocation filter layer 6 must be thermally cleaned at high temperature. Specifically, the surface of the newly grown InAlAs / InGaAs strained superlattice is briefly treated at high temperature under a continuous phosphine (PH3) or arsine (AsH3) protective atmosphere and at a growth temperature (600-650℃). This step aims to completely remove the surface oxide layer (such as aluminum oxide, indium oxide) that may form due to environmental exposure or impure atmosphere, providing a clean, activated, and atomically ordered crystal surface, laying a decisive foundation for the subsequent growth of a high-quality, low-defect-density intrinsic InGaAs absorption layer.

[0071] Step S4: Grow the absorption layer 7 and the upper structure.

[0072] Step S41, Absorption Layer: On the surface of the high-quality dislocation filter layer 6, an intrinsic InGaAs layer is grown as the absorption layer 7, with a thickness controlled between 0.8 and 2.0 μm and a growth temperature range of 600℃ to 650℃. Strictly controlling the growth temperature of the absorption layer 7 within the range of 600℃ to 650℃ is a systematic optimization from three core dimensions: ensuring the intrinsic quality of the material, optimizing the heterogeneous interface, and ensuring process repeatability. This is an indispensable key process condition for ultimately achieving high device performance (high responsivity, low dark current, and high reliability).

[0073] Step S42, Upper Structure: Continue growing p-type window layer 8 and heavily doped p + Contact layer 9 completes the growth of all epitaxial layers.

[0074] Step S5: Subsequent processes.

[0075] After epitaxy is completed, standard device fabrication processes are performed: the device mesa is defined by photolithography and etching; a passivation layer is deposited for surface passivation and contact holes are drilled; ohmic contact electrodes on the p-side and n-side are fabricated respectively; finally, dicing, packaging and performance testing are performed.

[0076] The combination of InAlAs ternary alloy graded layer, strained superlattice, and optoelectronic synergistic DBR technology employed in this embodiment represents a technological path that pursues ultimate material quality and optoelectronic performance. Its DBR design, while achieving optical path multiplication, deeply participates in the formation of the depletion region, fundamentally and synergistically improving the device's responsivity and bandwidth.

[0077] Example 2: Scheme based on InAlGaAs quaternary alloy graded layer

[0078] Reference Figure 1 , Figure 4 and Figure 5 This embodiment provides another specific implementation scheme for a long-wavelength PIN photodiode with a composite intrinsic region. It completely adopts the core device architecture and inventive concept of Embodiment 1, with the DBR layer 4, deformed growth layer 5, and absorption layer 7 together constituting the composite intrinsic region that achieves photoelectric synergy. The main difference between this embodiment and Embodiment 1 is that the deformed growth layer 5 uses an InAlGaAs quaternary alloy gradient layer and is compatible with it, while the dislocation filtering layer 6 adopts a non-strained superlattice design. The technical approach of this embodiment focuses on optimizing process robustness, large-scale production yield, and long-term device reliability.

[0079] Reference Figure 1 , Figure 4 and Figure 5 The following section will focus on the differences between this embodiment and Embodiment 1:

[0080] (1) Material design and growth strategy of deformable growth layer 5

[0081] In this embodiment, the deformed growth layer 5 is an InAlGaAs quaternary alloy gradient layer. Its core design is to adopt a "fixed Al composition" strategy: during the growth process, the aluminum (Al) composition is fixed at a constant value (e.g., 0.47), while the indium (In) and gallium (Ga) compositions are linearly gradient along the growth direction.

[0082] Specifically, through metal-organic chemical vapor deposition (MOCVD), the flow rates of trimethylindium (TMIn) and trimethylgallium (TMGa) are precisely controlled within a thickness of approximately 1.5–3.0 micrometers, causing the In composition to linearly increase from approximately 0.01 at the bottom to approximately 0.52 at the top, while the Ga composition linearly decreases from approximately 0.52 to approximately 0.01. Therefore, the material composition changes from the initial In... 0.01 Al 0.47 Ga 0.52 As (with a lattice similar to GaAs) gradually transitions to the final In. 0.52 Al 0.47 Ga 0.01 As (lattice constant matching InP).

[0083] The strategy of fixing the Al composition offers significant process advantages: it simplifies growth control from a complex dynamic adjustment requiring real-time coordination of the flow rates of three Group III metal-organic sources (TMIn, TMAl, and TMGa) to a set of synchronous, inverse linear controls primarily applied to TMIn and TMGa. This simplification greatly reduces the difficulty of controlling composition and thickness uniformity on large-area epitaxial wafers (especially 6-inch or larger), thereby significantly improving the repeatability, consistency, and yield of epitaxial processes, providing crucial technical support for the low-cost manufacturing of high-performance devices.

[0084] In terms of electrical function, the InAlGaAs quaternary alloy graded layer is completely identical to the InAlAs ternary alloy graded layer in Example 1, both being intrinsically undoped. When a reverse bias is applied to the device, its entire graded structure is also completely depleted, working together with the underlying DBR layer 4, becoming a key component in expanding the depletion region width and reducing the junction capacitance.

[0085] (2) Adaptability optimization of dislocation filter layer 6

[0086] To achieve optimal synergy with the aforementioned InAlGaAs quaternary alloy gradient layer and further pursue process robustness, in this embodiment, if a dislocation filter layer 6 is used, it can preferably be designed as an InP lattice perfectly matched with In... 0.52 Al 0.48 As sublayer and In 0.53 Ga 0.47 An InAlAs / InGaAs unstrained superlattice composed of alternating As sublayers.

[0087] Specifically, the superlattice is designed with 13 periods, each 10 nm thick, for a total thickness of 130 nm. Both sublayers perfectly match the InP lattice constant. Along the growth direction, In... 0.52 Al 0.48The thickness of the As sublayer decreases linearly from 8 nm in the first period to 2 nm in the thirteenth period; correspondingly, the In... 0.53 Ga 0.47 The thickness of the As sublayer increases linearly from 2 nm to 8 nm. This linear gradient design of the sublayer thickness allows the overall average lattice constant and stress state of the superlattice to be smoothly adapted to the top of the gradient layer below.

[0088] This unstrained superlattice bends and annihilates penetrating dislocations by abruptly changing the elastic modulus of the material at periodic interfaces. Its core advantage lies in achieving efficient dislocation filtering without introducing macroscopic tensile or compressive strain. This effectively avoids wafer warpage or reliability risks in subsequent processes that may result from strain accumulation, ensuring the flatness and long-term stability of the epitaxial wafer, making it particularly suitable for large-scale industrial manufacturing.

[0089] In summary, the "InAlGaAs quaternary graded layer + unstrained superlattice + optoelectronic synergistic DBR" technology combination employed in this embodiment represents a technological path that pursues superior process robustness and manufacturing friendliness. While fully retaining and utilizing the core advantage of synergistic enhancement of optoelectronic performance through "composite intrinsic regions," it elevates the manufacturability, yield, and reliability of high-performance long-wavelength detectors to new heights through ingenious optimization of the material system and growth strategy. This path is an ideal solution for commercial applications requiring large-scale, high-consistency, and high-reliability applications such as telecommunications equipment and data center optical interconnects.

[0090] The above are merely specific embodiments of the present invention, but the design concept of the present invention is not limited thereto. Any non-substantial modifications made to the present invention using this concept shall be considered as infringing upon the protection scope of the present invention.

Claims

1. A long-wavelength PIN photodiode with a composite intrinsic region, characterized in that: a GaAs substrate, a DBR layer, a metamorphic growth layer and an absorption layer are sequentially stacked from bottom to top; the absorption layer is lattice-matched with InP and is used for absorbing light of a target wavelength; the metamorphic growth layer is intrinsic and undoped, and its lattice constant gradually changes along the growth direction, and is used for bridging the lattice mismatch between the DBR layer and the absorption layer; the DBR layer, the metamorphic growth layer and the absorption layer together form a composite intrinsic region; the optical function of the composite intrinsic region is achieved by the DBR layer reflecting light transmitted through the absorption layer, and the absorption layer cooperates with the DBR layer to achieve optical path multiplication; the electrical function of the composite intrinsic region is achieved by the DBR layer and the metamorphic growth layer together forming a wide depletion region to reduce junction capacitance; the reflectivity of the DBR layer for light of the target wavelength is greater than 60%, and the period logarithm of the DBR layer is at least 9 pairs; the metamorphic growth layer is an InAlAs ternary alloy graded layer or an InAlGaAs quaternary alloy graded layer, and the linear regulation of the In, Al and / or Ga components of the metamorphic growth layer achieves the coordinated grading of the lattice constant and the band gap; a dislocation filter layer is further included, which is arranged between the metamorphic growth layer and the absorption layer and is used to block the transmission of dislocations generated by the metamorphic growth layer to the absorption layer; the dislocation filter layer is an InAlAs / InGaAs superlattice layer, and the component regulation, sublayer thickness regulation and / or period parameter regulation are used to achieve precise regulation of the dislocation filtering function; the absorption layer is an InGaAs material, and its thickness is 0.8-2.0 μm. 1.A long-wavelength PIN photodiode with a composite intrinsic region, characterized in that: a GaAs substrate, a DBR layer, a metamorphic growth layer and an absorption layer are sequentially stacked from bottom to top; the absorption layer is lattice-matched with InP and is used for absorbing light of a target wavelength; the metamorphic growth layer is intrinsic and undoped, and its lattice constant gradually changes along the growth direction, and is used for bridging the lattice mismatch between the DBR layer and the absorption layer; the DBR layer, the metamorphic growth layer and the absorption layer together form a composite intrinsic region; the optical function of the composite intrinsic region is achieved by the DBR layer reflecting light transmitted through the absorption layer, and the absorption layer cooperates with the DBR layer to achieve optical path multiplication; the electrical function of the composite intrinsic region is achieved by the DBR layer and the metamorphic growth layer together forming a wide depletion region to reduce junction capacitance; the reflectivity of the DBR layer for light of the target wavelength is greater than 60%, and the period logarithm of the DBR layer is at least 9 pairs; the metamorphic growth layer is an InAlAs ternary alloy graded layer or an InAlGaAs quaternary alloy graded layer, and the linear regulation of the In, Al and / or Ga components of the metamorphic growth layer achieves the coordinated grading of the lattice constant and the band gap; a dislocation filter layer is further included, which is arranged between the metamorphic growth layer and the absorption layer and is used to block the transmission of dislocations generated by the metamorphic growth layer to the absorption layer; the dislocation filter layer is an InAlAs / InGaAs superlattice layer, and the component regulation, sublayer thickness regulation and / or period parameter regulation are used to achieve precise regulation of the dislocation filtering function; the absorption layer is an InGaAs material, and its thickness is 0.8-2.0 μm. The DBR layers are formed by a plurality of pairs of intrinsically undoped Al x Ga 1-x As / Al y Ga 1-y As material layers stacked alternately. 1.A long-wavelength PIN photodiode with a composite intrinsic region, characterized in that: a GaAs substrate, a DBR layer, a metamorphic growth layer and an absorption layer are sequentially stacked from bottom to top; the absorption layer is lattice-matched with InP and is used for absorbing light of a target wavelength; the metamorphic growth layer is intrinsic and undoped, and its lattice constant gradually changes along the growth direction, and is used for bridging the lattice mismatch between the DBR layer and the absorption layer; the DBR layer, the metamorphic growth layer and the absorption layer together form a composite intrinsic region; the optical function of the composite intrinsic region is achieved by the DBR layer reflecting light transmitted through the absorption layer, and the absorption layer cooperates with the DBR layer to achieve optical path multiplication; the electrical function of the composite intrinsic region is achieved by the DBR layer and the metamorphic growth layer together forming a wide depletion region to reduce junction capacitance; the reflectivity of the DBR layer for light of the target wavelength is greater than 60%, and the period logarithm of the DBR layer is at least 9 pairs; the metamorphic growth layer is an InAlAs ternary alloy graded layer or an InAlGaAs quaternary alloy graded layer, and the linear regulation of the In, Al and / or Ga components of the metamorphic growth layer achieves the coordinated grading of the lattice constant and the band gap; a dislocation filter layer is further included, which is arranged between the metamorphic growth layer and the absorption layer and is used to block the transmission of dislocations generated by the metamorphic growth layer to the absorption layer; the dislocation filter layer is an InAlAs / InGaAs superlattice layer, and the component regulation, sublayer thickness regulation and / or period parameter regulation are used to achieve precise regulation of the dislocation filtering function; the absorption layer is an InGaAs material, and its thickness is 0.8-2.0 μm. ​ ​ 2. A long wavelength PIN photodiode with a composite intrinsic region as claimed in claim 1, wherein: ​ 3. A long-wavelength PIN photodiode with a composite intrinsic region as described in claim 1, characterized in that: The DBR layer is composed of Al 0.9 Ga 0.1 As / GaAs material layers are alternately stacked, and the optical thickness of each material layer is one quarter of the wavelength of the target wavelength in the corresponding material.

4. A long wavelength PIN photodiode having a composite intrinsic region as defined in claim 1, wherein: ​ 5. A long-wavelength PIN photodiode with a composite intrinsic region as described in claim 1, characterized in that: ​ 6. A long wavelength PIN photodiode having a composite intrinsic region as defined in claim 5, wherein: ​ 7. A long-wavelength PIN photodiode with a composite intrinsic region as described in claim 1, characterized in that: ​ 8. A method of fabricating a long-wavelength PIN photodiode having a composite intrinsic region as claimed in any one of claims 1 to 7, characterized by: ​ ​ Step S2, growing a DBR layer on the GaAs substrate, the DBR layer being composed of a plurality of pairs of intrinsic undoped Al x Ga 1-x As / Al y Ga 1-y material layers are alternately stacked; ​ ​ ​ ​ ​ 10. The method of claim 8, wherein the long wavelength PIN photodiode with a composite intrinsic region is prepared by the steps of: ​ ​

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