High gain bandwidth avalanche photodiode, method of manufacture and use

Abstract

This invention belongs to the field of optoelectronic device technology, specifically relating to a high-gain, bandwidth avalanche photodiode, comprising: a P+ contact layer, multiple laterally parallel N+ regions, a P- epitaxial layer, an N+ type substrate layer, and metal electrodes. The P+ contact layer and multiple N+ regions are located on the device surface, the P- epitaxial layer is located in the middle as an absorption layer, and the N+ type substrate layer is located at the bottom, forming a multiplication layer together with the absorption layer. The metal electrodes are in contact with the P+ contact layer and the N+ regions respectively. This invention integrates multiple PN junctions laterally and a separated absorption-multiplication layer vertically. The vertical separation absorption and multiplication layer design ensures high gain and low noise; simultaneously, multiple PN junctions are integrated laterally. These PN junctions work together to not only effectively suppress edge electric field concentration, improve breakdown voltage uniformity and device reliability as a guard ring, but more importantly, to construct parallel carrier collection channels, significantly shortening the lateral transit time of carriers, thereby overcoming the inherent contradiction between gain and bandwidth in traditional APDs.

Description

Technical Field

[0001] This invention belongs to the field of optoelectronic device technology, specifically relating to a high-gain bandwidth avalanche photodiode. Background Technology

[0002] An avalanche diode, also known as a negative resistance diode, is a solid-state microwave device based on the semiconductor avalanche breakdown effect. Its name derives from the physical phenomenon of avalanche multiplication of charge carriers. This device generates negative resistance through impact ionization and transit time effects induced by reverse voltage, and is primarily used in microwave oscillation, radar, communication, and photoelectric detection. Its core principle is that when the reverse voltage reaches a threshold, charge carriers undergo avalanche breakdown under a strong electric field, forming a multiplied current and utilizing the transit phase delay to achieve high-frequency oscillation. Typical structures include single-drift-region (e.g., P+NN+) and dual-drift-region designs, manufactured using silicon or gallium arsenide materials to improve power efficiency. Operating modes include IMPATT (impact avalanche transit time) and TRAPATT (trapped plasma mode), covering frequencies from 3-400 GHz, with a maximum output power of 80 mW. This device features high breakdown voltage, fast response, and temperature stability, but is accompanied by significant avalanche noise.

[0003] Avalanche photodiodes (APDs), as core devices for high-sensitivity photodetectors, are widely used in high-speed optical communication, lidar, and quantum detection. With the continuous increase in system speed and performance requirements, traditional APD structures face two major technical bottlenecks: first, intrinsic limitations exist in device performance regarding gain and bandwidth, making it difficult to simultaneously achieve high gain and high-speed response; second, in terms of structural design, the edge electric field concentration effect of planar or mesa structures easily leads to premature device breakdown, limiting operating voltage and reliability. Existing technologies mainly suppress breakdown through guard rings or complex epitaxial layers, but these often fail to balance response speed.

[0004] The high-gain-bandwidth product avalanche photodiode (APD) structure provided by this invention is a novel device that integrates lateral multiple PN junctions and longitudinally separated absorption-multiplication layers, breaking through the inherent contradiction between gain and bandwidth in traditional APDs. Summary of the Invention

[0005] To address the aforementioned shortcomings in existing technologies, this invention provides a high-gain bandwidth avalanche photodiode. Structurally, it achieves simultaneous breakthroughs in high bandwidth and high gain by integrating multiple pn junctions laterally and employing a separated absorption-multiplication (SAM) design in the vertical direction. This design provides an effective solution to the performance trade-off between high gain and high speed in APDs.

[0006] To solve the above-mentioned technical problems, the present invention adopts the following technical solution:

[0007] One of the objectives of this invention is to provide a high-gain bandwidth avalanche photodiode that achieves both high bandwidth and high gain.

[0008] To achieve the above objective, the technical solution of the present invention is as follows: a high-gain bandwidth avalanche photodiode, comprising: a P+ contact layer, multiple horizontally parallel N+ regions, a P- epitaxial layer, an N+ type substrate layer, and a metal electrode. The P+ contact layer and the multiple N+ regions are located on the device surface, the P- epitaxial layer is located in the middle as an absorption layer, and the N+ type substrate layer is located at the bottom, working together with the absorption layer to form a multiplication layer. The metal electrode is in contact with the P+ contact layer and the N+ regions respectively, for the collection and output of charge carriers.

[0009] The design was further optimized so that the doping concentration of the P+ contact layer was greater than 1×10⁻⁶. 18 cm -3 The thickness is 0.2-0.4μm.

[0010] The design was further optimized, and the doping concentration of the P-epitaxial layer was 1×10⁻⁶. 13 Up to 5×10 13 cm -3 The thickness is 10-15μm.

[0011] Further design optimization resulted in an N+ type substrate layer with a doping concentration greater than 5 × 10⁻⁶. 15 cm -3 The thickness is 0.5-2μm.

[0012] With further design optimization, the width of the metal electrode is 1-3 μm.

[0013] Further design optimization: the number of N+ regions is 1-4.

[0014] The design was further optimized so that the number of N+ regions is 3.

[0015] The second objective of this invention is to provide a method for fabricating a high-gain bandwidth avalanche photodiode, which is suitable for industrial production.

[0016] To achieve the above objective, the technical solution of the present invention is: a method for fabricating a high-gain bandwidth avalanche photodiode, comprising the following steps:

[0017] S1. Perform standard cleaning on the semiconductor epitaxial substrate and use a high-temperature thermal oxidation process to grow a uniform and dense silicon dioxide thin film on the wafer surface as the field oxygen isolation layer and surface passivation layer of the device.

[0018] S2. Fabrication of the key doped structure of the actuator, using photolithography, implantation and annealing processes to form the P+ region;

[0019] S3. A composite dielectric layer is grown in the photosensitive area of ​​the device, contact holes are etched, and metal electrodes are deposited. That is, aluminum or aluminum-copper alloy metal thin films are deposited on the entire substrate by magnetron sputtering technology to form interconnect electrodes and external bonding pads.

[0020] S4. After interconnecting the front circuit, prepare a photosensitive functional material layer and perform subsequent sensitization processes.

[0021] S5. Remove the dielectric layer in the pad area at the edge of the chip to expose the metal bonding pad.

[0022] Further optimizations are made, wherein the thickness of the silicon dioxide film grown on the wafer surface by the high-temperature thermal oxidation process is 200 nm to 500 nm, and the thickness of the aluminum-copper alloy metal film deposited by the magnetron sputtering technology is 500 nm to 1 μm.

[0023] The third objective of this invention is to provide a method for applying a high-gain bandwidth avalanche photodiode, which can be used for optical signal detection.

[0024] To achieve the above objective, the technical solution of the present invention is: a method for applying a high-gain bandwidth avalanche photodiode.

[0025] In high-speed optical communication systems, avalanche photodiodes are used for the detection of high-sensitivity and high-speed optical signals.

[0026] In lidar systems, avalanche photodiodes are used to achieve long-distance optical signal detection;

[0027] In quantum detection systems, avalanche photodiodes are used to improve detection sensitivity and accuracy.

[0028] Compared with the prior art, the present invention has the following beneficial effects:

[0029] 1. The present invention integrates multiple pn junctions laterally and employs a separated absorption-multiplication (SAM) design in the vertical direction to synergistically optimize device performance. The lateral multi-pn junction structure can not only effectively disperse the edge electric field and improve breakdown uniformity, but also significantly shorten the lateral transit time of charge carriers by constructing parallel conductive channels, thereby directly improving the response speed and gain-bandwidth product. The vertical absorption-multiplication separation structure can not only achieve decoupling and independent optimization of photoelectric conversion and signal amplification functions, but also significantly improve the carrier injection efficiency and avalanche controllability through the high-field localization of the multiplication region and the low-field broadband design of the absorption region, thereby synergistically achieving a simultaneous breakthrough in low noise, high bandwidth and high gain.

[0030] 2. This invention simultaneously improves speed gain and bandwidth: multiple N+ regions in the lateral direction serve as parallel local collection points, which physically shortens the carrier collection path and time, and reduces parasitic capacitance, enabling the device to significantly improve response speed and gain-bandwidth product while maintaining high gain.

[0031] 3. The avalanche photodiode of the present invention has higher reliability. The N+ region effectively smooths the electric field distribution at the edge of the device, fundamentally suppressing premature edge breakdown and improving the upper limit of operating voltage, stability and yield consistency.

[0032] 4. The avalanche photodiode of the present invention has better performance: the vertical separation absorption-multiplication structure ensures high quantum efficiency and low noise gain, while the lateral multi-channel design is dedicated to high-speed response. The combination of the two achieves a synergy of high sensitivity and high speed.

[0033] 5. The present invention has a simple and efficient structural design: it integrates the two major functions of "electric field management" and "high-speed collection" into multiple N+ regions in the horizontal direction, and achieves a significant improvement in the overall performance of the device with a relatively simple process, and has good manufacturability. Attached Figure Description

[0034] Figure 1 This invention provides a schematic diagram of the structure of a high-gain bandwidth avalanche photodiode.

[0035] Figure 2 This invention provides simulation test results for different numbers of N+ regions in a high-gain bandwidth avalanche photodiode, as shown in the following figure.

[0036] Figure 3 A comparison diagram of the dark-state current of a high-gain bandwidth avalanche photodiode and a conventional avalanche photodiode with a similar structure is provided for an embodiment of the present invention.

[0037] The reference numerals in the accompanying drawings include: 1. P+ contact layer, 2. N+ region, 3. P- epitaxial layer, 4. N+ type substrate layer, 5. multiplication layer, and 6. metal electrode. Detailed Implementation

[0038] The present invention will be further described below with reference to specific embodiments. It should be understood that these embodiments are for illustrative purposes only and are not intended to limit the scope of the invention. Furthermore, it should be understood that after reading the teachings of this invention, those skilled in the art can make various alterations or modifications to the invention, and these equivalent forms also fall within the scope defined by the appended claims.

[0039] To better explain the technical solution, the following technical terms are explained:

[0040] Avalanche photodiode (APD): A type of highly sensitive photodetector. An APD operates under reverse bias; when photocurrent passes through it, an avalanche effect occurs, amplifying the photocurrent and thus increasing the detection sensitivity of the optical signal.

[0041] P+ Contact Layer 1: In avalanche photodiodes, the P+ contact layer is a highly doped P-type semiconductor region used to connect to external circuits, reduce contact resistance, and improve carrier collection efficiency.

[0042] N+ Region 2: In avalanche photodiodes, the N+ region is a highly doped N-type semiconductor region, which is typically used to improve carrier collection efficiency and reduce lateral transit time.

[0043] P-Epitaxial Layer 3: In avalanche photodiodes, the P-epitaxy layer is a light-doped P-type semiconductor layer that serves as a light-absorbing layer, used to absorb photons and generate electron-hole pairs.

[0044] N+ Substrate Layer 4: In avalanche photodiodes, the N+ substrate layer is a highly doped N-type semiconductor layer that acts as a multiplication layer to amplify the generated photocurrent.

[0045] Metal Electrode 6: In an avalanche photodiode, the metal electrode is a conductive layer used to connect to external circuits. It is usually made of materials such as aluminum-copper alloys and is used for the collection and output of charge carriers.

[0046] High-Temperature Oxidation: In semiconductor manufacturing, high-temperature thermal oxidation refers to the process of growing a silicon dioxide thin film on the surface of a silicon substrate at high temperatures, which is used to form the field oxygen isolation layer and surface passivation layer of the device.

[0047] Magnetron sputtering: In semiconductor manufacturing, magnetron sputtering is a physical vapor deposition process that uses high-energy plasma in a magnetic field to bombard a target material, causing the target atoms to be deposited on a substrate to form a metal electrode layer.

[0048] Photosensitive functional material layer: In avalanche photodiodes, the photosensitive functional material layer is a key material layer used for light absorption and photoelectric conversion. It typically includes specific semiconductor materials such as silicon and gallium arsenide.

[0049] Separate Absorption and Multiplication (SAM) Structure: In avalanche photodiodes, the SAM structure refers to a design in which the absorption layer and the multiplication layer are spatially separated. The absorption layer is used to absorb photons and generate electron-hole pairs, while the multiplication layer is used to amplify these electron-hole pairs to achieve high gain and high bandwidth.

[0050] These technical terms are key to understanding the design and manufacturing process of avalanche photodiodes, defining the device's structure, characteristics, and manufacturing process.

[0051] This application provides a high-gain, bandwidth avalanche photodiode, a novel device integrating multiple PN junctions laterally and a vertically separated absorption-multiplication layer. The structure employs a vertically separated absorption and multiplication layer design to ensure high gain and low noise; simultaneously, it integrates multiple PN junctions laterally. These PN junctions work synergistically, not only acting as a guard ring to effectively suppress edge electric field concentration, improve breakdown voltage uniformity and device reliability, but also, crucially, constructing parallel carrier collection channels, significantly shortening the carrier lateral transit time, thus overcoming the inherent contradiction between gain and bandwidth in traditional APDs. This invention significantly improves response speed and gain-bandwidth product while maintaining high sensitivity, exhibits good process compatibility, and provides a high-performance detector solution for cutting-edge fields such as high-speed optical communication, lidar, and quantum detection.

[0052] Figure 1 This application provides a schematic diagram of a high-gain bandwidth avalanche photodiode. Figure 1 As shown, this high-gain bandwidth avalanche photodiode specifically includes the following structure:

[0053] The device surface consists of a P+ contact layer 1 and multiple horizontally parallel N+ regions 2, which constitute the N+ contact layer. A metal electrode 6 is deposited on top of each contact layer. The thicker middle part is the P- epitaxial layer 3, which has a low doping concentration and serves as the absorption layer of the entire device. The bottom of the device is an N+ type substrate layer 4, and the PN junction region formed between the N+ type substrate layer 4 and the P- epitaxial layer 3 is the multiplication layer. A metal bottom electrode is deposited below the substrate.

[0054] The P+ contact layer 1 is formed by doping monocrystalline silicon with a high concentration of boron ions, with a doping concentration greater than 1 × 10⁻⁶. 18 cm -3 The thickness is 0.2-0.4μm.

[0055] N+ region 2 is formed by doping single-crystal silicon with a high concentration of phosphorus ions, with a doping concentration greater than 1 × 10⁻⁶. 18 cm -3The thickness is 0.2-0.4μm.

[0056] P-epitaxial layer 3 is formed by doping single-crystal silicon with a high concentration of phosphorus ions, with a doping concentration of 1×10⁻⁶. 13 Up to 5×10 13 cm -3 The thickness is 10-15μm.

[0057] N+ type substrate layer 4, a silicon wafer doped with phosphorus ions, with a doping concentration greater than 5 × 10⁻⁶. 15 cm -3 The thickness is 0.5-2μm.

[0058] The metal electrode 6 is usually made of aluminum-copper alloy and has a width of 1-3 μm.

[0059] Specifically, different numbers of N+ regions were doped into the high-gain bandwidth avalanche photodiode of this application, and its response speed was simulated and tested, revealing an optimal value. For example... Figure 2 As shown, the number of options is set to 1-4, and the number of optimal solutions is 3.

[0060] This application provides a method for fabricating a high-gain bandwidth avalanche photodiode, comprising the following steps:

[0061] S1. Perform standard cleaning on the semiconductor epitaxial substrate and use a high-temperature thermal oxidation process to grow a uniform and dense silicon dioxide thin film on the wafer surface as the field oxygen isolation layer and surface passivation layer of the device. The thickness of the silicon dioxide thin film grown on the wafer surface by the high-temperature thermal oxidation process is 200 nm to 500 nm.

[0062] S2. Fabrication of the key doped structure of the actuator, using photolithography, implantation and annealing processes to form the P+ region;

[0063] S3. A composite dielectric layer is grown in the photosensitive area of ​​the device, contact holes are etched, and metal electrodes are deposited. That is, aluminum or aluminum-copper alloy metal thin films are deposited on the entire substrate by magnetron sputtering technology to form interconnect electrodes and external bonding pads. The thickness of the aluminum-copper alloy metal thin film deposited by magnetron sputtering technology is 500 nm to 1 μm.

[0064] S4. After interconnecting the front circuit, prepare a photosensitive functional material layer and perform subsequent sensitization processes.

[0065] S5. Remove the dielectric layer in the pad area at the edge of the chip to expose the metal bonding pad.

[0066] Specifically, firstly, the semiconductor epitaxial substrate undergoes standard cleaning to remove organic matter, metal ions, and particulate contaminants, providing a clean surface for subsequent processes. Subsequently, a high-temperature thermal oxidation process is used to grow a uniform and dense silicon dioxide film on the wafer surface, serving as the field oxygen isolation layer and surface passivation layer for the device.

[0067] After completing the basic isolation layer fabrication, the key doped structures of the device are fabricated. Using a photolithography process involving spin coating, soft baking, alignment exposure, and development, the pattern of the P-type guard ring is transferred to the wafer. Silicon dioxide at the window is removed using wet or reactive ion etching, and boron ions are implanted to form heavily doped P+ regions. Rapid thermal annealing is then immediately performed to repair lattice damage and activate impurities. Based on the same photolithography-implantation-annealing cycle, the active region is defined, and doped structures such as P-wells are fabricated, thereby precisely constructing the vertical electrical distribution of the device.

[0068] Next, using plasma-enhanced chemical vapor deposition (PECVD), silicon dioxide and silicon nitride films are sequentially grown on the surface of the photosensitive region of the device, forming a composite dielectric layer that combines passivation protection and optical anti-reflection. Then, contact hole patterns are defined using photolithography, and the dielectric layer is etched to the silicon surface using dry etching to form ohmic contact windows. Subsequently, aluminum or aluminum-copper alloy metal films are deposited on the entire substrate using magnetron sputtering, and the films are again patterned using photolithography and wet etching processes to form interconnect electrodes and external bonding pads.

[0069] After completing the front-side circuit interconnects, a photosensitive functional material layer is fabricated and patterned using deposition, photolithography, and etching processes to form precise light absorption or photoelectric conversion channels. Subsequent sensitization processes are then used to optimize its quantum efficiency and response speed. Finally, after completing all front-side processes, selective dry etching is performed on the pad area located at the chip edge to completely remove all the overlying dielectric layer, fully exposing the metal bonding pads and providing a complete electrical and mechanical interface for subsequent probe testing, wire bonding, and chip packaging.

[0070] This application provides a method for applying a high-gain bandwidth avalanche photodiode: in high-speed optical communication systems, avalanche photodiodes are used for high-sensitivity and high-speed optical signal detection; in lidar systems, avalanche photodiodes are used for long-distance optical signal detection; and in quantum detection systems, avalanche photodiodes are used to improve detection sensitivity and accuracy.

[0071] The above description is merely a preferred embodiment of the present invention and does not limit the patent scope of the present invention. Any equivalent structural or procedural transformations made based on the content of the present invention's specification and drawings, or direct or indirect applications in other related technical fields, are similarly included within the patent protection scope of the present invention.

Claims

1. A high-gain, bandwidth avalanche photodiode, characterized in that, include: The device comprises a P+ contact layer, multiple horizontally parallel N+ regions, a P- epitaxial layer, an N+ type substrate layer, and metal electrodes. The P+ contact layer and multiple N+ regions are located on the device surface. The P- epitaxial layer is located in the middle as an absorption layer. The N+ type substrate layer is located at the bottom and works together with the absorption layer to form a multiplication layer. The metal electrodes are in contact with the P+ contact layer and the N+ regions respectively, and are used for carrier collection and output.

2. The high-gain bandwidth avalanche photodiode as described in claim 1, characterized in that: The doping concentration of the P+ contact layer is greater than 1×10⁻⁶. 18 cm -3 The thickness is 0.2-0.4μm.

3. The high-gain bandwidth avalanche photodiode as described in claim 2, characterized in that: The doping concentration of the P-epitaxial layer is 1×10⁻⁶. 13 Up to 5×10 13 cm -3 The thickness is 10-15μm.

4. A high-gain bandwidth avalanche photodiode as described in claim 3. Its characteristics are: The doping concentration of the N+ type substrate layer is greater than 5 × 10⁻⁶. 15 cm -3 The thickness is 0.5-2μm.

5. A high-gain bandwidth avalanche photodiode as described in claim 4, characterized in that: The width of the metal electrode is 1-3 μm.

6. A high-gain bandwidth avalanche photodiode as described in claim 5, characterized in that: The number of N+ regions is 1-4.

7. A high-gain bandwidth avalanche photodiode as described in claim 6, characterized in that: The number of N+ regions is 3.

8. A method for fabricating a high-gain bandwidth avalanche photodiode, characterized in that: Includes the following steps: S1. Perform standard cleaning on the semiconductor epitaxial substrate and use a high-temperature thermal oxidation process to grow a uniform and dense silicon dioxide thin film on the wafer surface as the field oxygen isolation layer and surface passivation layer of the device. S2. Fabrication of the key doped structure of the actuator, using photolithography, implantation and annealing processes to form the P+ region; S3. A composite dielectric layer is grown in the photosensitive area of ​​the device, contact holes are etched, and metal electrodes are deposited. That is, aluminum or aluminum-copper alloy metal thin films are deposited on the entire substrate by magnetron sputtering technology to form interconnect electrodes and external bonding pads. S4. After interconnecting the front circuit, prepare a photosensitive functional material layer and perform subsequent sensitization processes. S5. Remove the dielectric layer in the pad area at the edge of the chip to expose the metal bonding pad.

9. The method for fabricating a high-gain bandwidth avalanche photodiode as described in claim 8, characterized in that: The silicon dioxide film grown on the wafer surface by the high-temperature thermal oxidation process has a thickness of 200 nm to 500 nm, and the aluminum-copper alloy metal film deposited by the magnetron sputtering technology has a thickness of 500 nm to 1 μm.

10. A method for applying a high-gain bandwidth avalanche photodiode, characterized in that: Avalanche photodiodes are used for optical signal detection in high-speed optical communication, lidar, and quantum detection systems.

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