Photoelectric detector

Abstract

The utility model relates to a photoelectric detector which comprises a detector substrate, an active area is arranged on the detector substrate, a refraction inclined plane is corroded at the end part of the detector substrate, an upper reflection layer is epitaxially grown above the active area, a lower reflection layer is epitaxially grown below the active area, the lower reflection layer is grown on the detector substrate, and the refraction inclined plane is arranged on the upper reflection layer. The active region includes an absorption layer. Based on the upper reflecting layer and the lower reflecting layer, multiple times of absorption and conversion of photoelectricity are achieved, incident light can be completely converted into electric signals, the light absorption efficiency is higher, the photoelectric conversion efficiency is higher, and in other words, the responsivity of the photoelectric detector is higher. The photoelectric detector is of a waveguide-free edge incidence detector structure, and the problems that an edge incidence waveguide structure is large in coupling difficulty and low in responsivity can be effectively solved.

Description

Technical Field

[0001] This utility model relates to the technical field of optical communication, and in particular to a photodetector. Background Technology

[0002] As a core component of optical communication systems, the bandwidth performance and responsivity of photodetectors directly affect the signal transmission rate and system sensitivity. Traditional technologies to improve the bandwidth of photodetectors often involve reducing the active region area to decrease junction capacitance or optimizing carrier transport paths to shorten transit time. However, such approaches often lead to a significant decrease in optical coupling efficiency and responsivity, making it difficult to simultaneously meet the requirements of high-frequency response and high quantum efficiency.

[0003] Currently, mainstream high-bandwidth photodetectors mainly employ two types of structures: back-incident structures and side-incident waveguide structures. Back-incident structures effectively reduce junction capacitance and thus improve bandwidth by thinning the absorption layer and reducing the active region area. However, the reduced absorption region area makes it difficult for incident light to couple efficiently to the absorption layer. Even with back-etched lens technology to focus the incident light, insufficient responsivity remains due to the excessively thin absorption layer. Furthermore, the light incident direction of this structure is aligned with the carrier transport direction, easily leading to space charge accumulation, which limits the saturation output current and further restricts its application in high-power scenarios.

[0004] Side-entry waveguide structures can improve light absorption efficiency even with thin absorption layers by extending the light absorption layer along the waveguide direction. However, this structure faces two major bottlenecks: First, the coupling between the waveguide end face and the incident light requires extremely high alignment accuracy; even a small deviation can lead to significant light loss. While introducing a three-dimensional mode converter can improve coupling efficiency, it significantly increases process complexity and manufacturing costs. Second, the waveguide front face is prone to light saturation under strong light incidence, and there is an inherent contradiction in the matching design between the waveguide transmission mode and the absorption layer thickness, leading to a decrease in device reliability.

[0005] To address the aforementioned issues, there is an urgent need for a novel photodetector structure that can overcome the technical bottlenecks in optical coupling efficiency and responsivity while ensuring a large bandwidth. Utility Model Content

[0006] In order to improve responsivity while ensuring high bandwidth characteristics, this application provides a photodetector.

[0007] This application provides a photodetector, including a detector substrate, an active region on the detector substrate, a refractive bevel etched at the end of the detector substrate, an upper reflective layer epitaxially grown above the active region and a lower reflective layer epitaxially grown below the active region, the lower reflective layer being grown on the detector substrate, and the active region including an absorption layer.

[0008] The beneficial effects of this invention are as follows: the initial incident light enters the detector substrate through refraction via the refracting inclined plane, and then enters the absorption layer of the active region at a certain angle. After passing through the absorption layer, the unabsorbed light is reflected by the upper reflective layer at the top and can re-enter the absorption layer, achieving secondary photoelectric absorption and conversion. The light that is still not absorbed after the secondary photoelectric conversion is reflected again by the lower reflective layer at the bottom to the absorption layer, achieving a third photoelectric absorption and conversion. Through multiple reflections and absorptions, the incident light can be completely converted into an electrical signal, resulting in higher light absorption efficiency, higher photoelectric conversion efficiency, and thus higher responsivity of the photodetector. The photodetector is a waveguide-less edge-incident detector structure, which can effectively solve the problems of difficult coupling and low responsivity in edge-incident waveguide structures.

[0009] Furthermore, the active region also includes an N-contact layer, a drift layer, and a P-contact layer, with the N-contact layer, the drift layer, the absorption layer, the P-contact layer, and the upper reflective layer epitaxially grown sequentially above the lower reflective layer.

[0010] The beneficial effects of adopting the above-mentioned further scheme are: through the vertical integration design of N-contact layer-drift layer-absorption layer-P-contact layer-upper reflective layer, this structure achieves synergistic optimization of carrier transport, optical field localization and process compatibility, and significantly surpasses traditional side-incident waveguide detectors in terms of responsivity, bandwidth and reliability, providing a high-performance solution for high-speed optoelectronic systems.

[0011] Furthermore, the detector substrate is an InP semi-insulating substrate.

[0012] The beneficial effect of adopting the above-mentioned further scheme is that the InP semi-insulating substrate is much lower than that of ordinary doped substrates, thus improving the bandwidth.

[0013] Furthermore, the length of the N-contact layer extending along the incident direction of the initial incident light before refraction by the refracting slope is greater than the lengths of the drift layer, the absorption layer, the P-contact layer, the upper reflective layer, and the lower reflective layer extending along the incident direction of the initial incident light, and the end of the lower reflective layer away from the refracting slope is aligned with the N-contact layer.

[0014] The advantages of adopting the above-mentioned further scheme are: the N-contact layer extends longer along the light incident direction, thus covering the potential carrier generation region after multiple reflections of light within the absorption layer, and providing additional absorption opportunities during multiple light reflections. Alignment between the lower reflective layer and the end of the N-contact layer eliminates the need for strict alignment of the absorption layer boundary during wet etching of the bevel; the N-contact layer can be used as the mask reference, reducing alignment errors in multi-step lithography and increasing process tolerance and product yield.

[0015] Furthermore, the drift layer, the absorption layer, the P-contact layer, and the upper reflective layer extend to the same length along the incident direction of the initial incident light.

[0016] The advantages of adopting the above-mentioned further scheme are: the length of the absorption layer is consistent with the lengths of the drift layer and the P-contact layer, ensuring that the propagation path of the incident light within the absorption layer can completely cover the depletion region. The upper reflective layer is the same length as the absorption layer, ensuring that the incident light reflected from the top can be confined within the absorption layer region, reducing the possibility of light leakage due to an excessively long reflective layer or insufficient reflection due to an excessively short reflective layer.

[0017] Furthermore, the detector substrate includes a first region and a second region, the refractive slope is located in the first region, the lower reflective layer is located above the second region, and the upper surface of the lower reflective layer is flush with the upper surface of the first region.

[0018] The beneficial effects of adopting the above-mentioned further scheme are as follows: the first region is dedicated to light incidence, and the incident light is efficiently guided into the thin absorption layer through refraction by the refracting slope. The lower reflective layer of the second region extends outward to form an extended reflective surface. After being refracted in the first region, the incident light enters the absorption layer at a low angle, extending the propagation path of the light within the absorption layer and improving the absorption efficiency.

[0019] Furthermore, the angle of the refractive bevel is 46 degrees to 68 degrees, the lateral etching depth corresponding to the refractive bevel is 20 μm to 35 μm, and the longitudinal etching depth corresponding to the refractive bevel is 25 μm to 40 μm.

[0020] The advantages of adopting the above-mentioned further scheme are as follows: By reserving the etching depth dimension of the refractive slope, the incident light can be refracted into the active region, facilitating the entry of a light spot of this size into the photodetector. The refractive slope allows for the refraction of light at a small angle, resulting in a larger light absorption area, reduced carrier density, decreased space charge accumulation effect, and increased saturation response current. The edge-incident structure formed by the refractive slope ensures that the transmission direction of the incident light and the transmission direction of the electrons after photoelectric conversion are at a certain angle, reducing charge accumulation.

[0021] Furthermore, the thickness of the absorption layer is 60nm to 120nm, and the absorption layer has a PIN structure.

[0022] The beneficial effects of adopting the above-mentioned further scheme are: by reducing the thickness of the absorption layer, the carrier transport distance is reduced, the carrier transport time is decreased, and the bandwidth is increased.

[0023] Furthermore, an N electrode is provided above the N contact layer.

[0024] The beneficial effects of adopting the above-mentioned further scheme are: the N electrode is directly located above the N contact layer, forming a vertical conductive channel, and the transmission path of photogenerated electrons from the absorption layer → drift layer → N contact layer → N electrode can be shortened to the micrometer level, reducing the carrier transit time and increasing the bandwidth.

[0025] Furthermore, the detector substrate includes a first region and a second region, the refractive slope is located in the first region, the lower reflective layer is located above the second region, the surface of the refractive slope is covered with a first gradient refractive index coupling layer, a second gradient refractive index coupling layer is epitaxially grown on the upper surface of the first region, and the upper surface of the second gradient refractive index coupling layer is flush with the upper surface of the lower reflective layer.

[0026] The beneficial effects of adopting the above-mentioned further scheme are as follows: The first gradient refractive index coupling layer serves as an external coupling transition layer, connecting the lens and the detector substrate. This reduces light loss when light enters the high refractive index substrate from the low refractive index medium, thus improving optical coupling efficiency. The second gradient refractive index coupling layer matches the refractive index difference between the detector substrate and the N-contact layer, further enhancing coupling efficiency. Through the dual-interface refractive index gradient design, seamless light transmission from the external medium to the active region is achieved. Attached Figure Description

[0027] Figure 1 This is a schematic diagram of the structure of the photodetector in Embodiment 1 of this application;

[0028] Figure 2 This is a schematic diagram of the structure of the photodetector in Embodiment 2 of this application.

[0029] The attached diagram lists the components represented by each number as follows:

[0030] 1. Detector substrate; 11. Refractive slope; 12. First region; 13. Second region; 14. First gradient refractive index coupling layer; 15. Second gradient refractive index coupling layer; 2. Active region; 21. Absorption layer; 22. N contact layer; 23. Drift layer; 24. P contact layer; 3. Upper reflective layer; 4. Lower reflective layer; 5. N electrode. Detailed Implementation

[0031] The present application will be further described in detail below with reference to the accompanying drawings.

[0032] Example 1:

[0033] like Figure 1As shown, a photodetector includes a detector substrate 1, an active region 2 on the detector substrate 1, a refractive bevel 11 etched at the end of the detector substrate 1, an upper reflective layer 3 epitaxially grown above the active region 2 and a lower reflective layer 4 epitaxially grown below the active region 2, the lower reflective layer 4 being grown on the detector substrate 1, and the active region 2 including an absorption layer 21.

[0034] In this embodiment, the area of ​​the active region 2 can be designed as a rectangle of different sizes. The width of the active region 2 can be 3 to 6 μm, and the length of the active region 2 can be 8 to 20 μm. The spot size of the lens fiber or lens system that is matched and coupled with it can be less than 3 μm. Increasing the area of ​​the active region 2 can increase the coupling tolerance.

[0035] The detector substrate 1 can be an InP semi-insulating substrate. First, the detector substrate 1 is selectively etched by ICP dry etching. Then, an epitaxial layer such as the active region 2 is grown by MBE or MOCVD. Then, the fabrication process of the spot detector is carried out. Finally, a refractive slope 11 is etched on the detector substrate 1. Specifically, the refractive slope 11 can be selectively etched by wet etching on the detector substrate 1 corresponding to the position of the front vertical surface of the active region 2.

[0036] Due to the difference in refractive index between air and the InP semi-insulating substrate, the initial incident light enters the detector substrate 1 through refraction from the refracting slope 11, and then enters the absorption layer 21 of the active region 2 at a certain angle. After passing through the absorption layer 21, the unabsorbed light is reflected by the upper reflective layer 3 at the top and can re-enter the absorption layer 21, achieving a secondary photoelectric absorption conversion. The light that is still not absorbed after the secondary photoelectric conversion is reflected again by the lower reflective layer 4 at the bottom to the absorption layer 21, achieving a third photoelectric absorption conversion. Through multiple reflections and absorptions, the incident light can be completely converted into an electrical signal.

[0037] The combination of the upper reflective layer 3 at the top of the absorption layer 21 and the lower reflective layer 4 at the bottom results in higher light absorption efficiency and higher photoelectric conversion efficiency, meaning a higher responsivity of the photodetector. The photodetector is a waveguide-less edge-incident detector structure, which effectively solves the problems of difficult coupling and low responsivity in edge-incident waveguide structures.

[0038] like Figure 1 As shown, in this embodiment, the active region 2 further includes an N-contact layer 22, a drift layer 23, and a P-contact layer 24. The N-contact layer 22, the drift layer 23, the absorption layer 21, the P-contact layer 24, and the upper reflective layer 3 are epitaxially grown sequentially above the lower reflective layer 4. An N-electrode 5 may be disposed above the N-contact layer 22.

[0039] like Figure 1As shown in the diagram, the arrows indicate the initial incident light direction. The incident light strikes the refractive inclined surface 11 from the left end and enters the detector substrate 1 after refraction by the refractive inclined surface 11. This causes the incident light to be refracted at a small angle onto the active region 2, forming an angled refractive surface. Specifically, the incident light sequentially strikes the N-contact layer 22, the drift layer 23, the absorption layer 21, and the P-contact layer 24. Unabsorbed light is reflected by the upper reflective layer 3 at the top and can re-enter the absorption layer 21. Unabsorbed light then sequentially strikes the drift layer 23 and the N-contact layer 22, and after reflection by the lower reflective layer 4, it re-striks the drift layer 23, the absorption layer 21, and the P-contact layer 24 until the incident light can be completely converted into an electrical signal. This significantly improves the incident light absorption efficiency and increases the responsivity.

[0040] like Figure 1 As shown, in this embodiment, the symbol θ represents the etching angle of the refractive bevel 11. The angle of the refractive bevel 11 is 46 degrees to 68 degrees, the lateral etching depth corresponding to the refractive bevel 11 is 20 μm to 35 μm, and the longitudinal etching depth corresponding to the refractive bevel 11 is 25 μm to 40 μm.

[0041] Since the incident light is light that has passed through the lens, by reserving the etching depth size of the refractive slope 11, the incident light can be refracted into the active region 2, which makes it easy for a light spot of this size to enter the photodetector.

[0042] The refracting inclined plane 11 refracts incident light at a small angle, resulting in a larger light absorption area, reduced carrier density, decreased space charge accumulation effect, and increased saturation response current. The edge-incident structure formed by the refracting inclined plane 11 creates an angle between the incident light's transmission direction and the electron transmission direction after photoelectric conversion, further reducing charge accumulation.

[0043] In this embodiment, the thickness of the absorption layer 21 can be from 60 nm to 120 nm, and the absorption layer 21 has a PIN structure. By reducing the thickness of the absorption layer 21, the carrier transport distance is reduced, the carrier transport time is decreased, and the bandwidth is increased.

[0044] like Figure 1 As shown, in this embodiment, the length of the N-contact layer 22 extending along the incident direction of the initial incident light before refraction by the refracting slope 11 is greater than the lengths of the drift layer 23, the absorption layer 21, the P-contact layer 24, the upper reflective layer 3, and the lower reflective layer 4 extending along the incident direction of the initial incident light. The end of the lower reflective layer 4 away from the refracting slope 11 is aligned with the N-contact layer 22.

[0045] The N-contact layer 22 extends further along the light incident direction, thus covering the potential carrier generation region after multiple reflections of light within the absorption layer 21, and providing additional absorption opportunities during multiple reflections. Photogenerated carriers (electrons) generated in the drift layer 23 and absorption layer 21 can be rapidly collected by the N-contact layer 22, reducing lateral diffusion paths and preventing recombination losses of carriers in areas not covered by the P-contact layer 24.

[0046] The lower reflective layer 4 is aligned with the end of the N contact layer 22, so that the boundary of the absorption layer 21 does not need to be strictly aligned when wet etching the bevel. Only the N contact layer 22 needs to be used as the mask reference, which reduces the alignment error of multi-step lithography and increases the process tolerance and product yield.

[0047] like Figure 1 As shown, in this embodiment, the drift layer 23, the absorption layer 21, the P contact layer 24, and the upper reflective layer 3 extend to the same length along the incident direction of the initial incident light.

[0048] When all layers have the same length, the lateral boundaries of the PIN junction are aligned, and the depletion region formed under reverse bias exhibits a uniform longitudinal electric field distribution within the drift layer 23, reducing the possibility of electric field distortion caused by interlayer misalignment. The length of the absorption layer 21 is consistent with the lengths of the drift layer 23 and the P-contact layer 24, ensuring that the propagation path of incident light within the absorption layer 21 can completely cover the depletion region. The upper reflective layer 3 has the same length as the absorption layer 21, ensuring that incident light reflected from the top can be confined within the absorption layer 21 region, reducing the possibility of light leakage due to an excessively long reflective layer or insufficient reflection due to an excessively short reflective layer.

[0049] The N-contact layer 22 and the lower reflective layer 4 extend outward from the other layers, ensuring that unabsorbed light is still confined within the absorption layer 21 when reflected at the bottom, reducing the possibility of light leakage to the non-active region 2.

[0050] like Figure 1 As shown, in this embodiment, the detector substrate 1 includes a first region 12 and a second region 13. The refractive inclined surface 11 is located in the first region 12, and the lower reflective layer 4 is located above the second region 13. The upper surface of the lower reflective layer 4 is flush with the upper surface of the first region 12.

[0051] The first region 12 is dedicated to light incidence. Through refraction by the refracting slope 11, the incident light is efficiently guided into the thin absorption layer 21. The lower reflective layer 4 of the second region 13 extends outward to form an extended reflective surface. After being refracted by the first region 12, the incident light enters the absorption layer 21 at a low angle, extending the propagation path of the light within the absorption layer 21 and improving the absorption efficiency.

[0052] Example 2:

[0053] like Figure 1 and Figure 2 As shown, the surface of the refracting inclined plane 11 (light incident plane) is covered with a first gradient refractive index coupling layer 14 (GRIN layer). The first gradient refractive index coupling layer 14 serves as an external coupling transition layer, used to connect the lens and the detector substrate 1. This reduces the light loss when light enters the high refractive index substrate from the low refractive index medium, thereby improving the optical coupling efficiency.

[0054] A second gradient refractive index coupling layer 15 (GRIN layer) can be provided between the N-contact layer 22 and the surface of the first region 12. Specifically, the second gradient refractive index coupling layer 15 is epitaxially grown on the upper surface of the first region 12, with its upper surface flush with the upper surface of the lower reflective layer 4. Outside the second gradient refractive index coupling layer 15 and the lower reflective layer 4, the N-contact layer 22, drift layer 23, absorption layer 21, P-contact layer 24, and upper reflective layer 3 are then grown sequentially. This matches the refractive index difference between the detector substrate 1 and the N-contact layer 22, improving coupling efficiency. Through this dual-interface refractive index gradient design, seamless light transmission from the external medium to the active region 2 is achieved.

[0055] 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 process, method, article, or apparatus.

[0056] Furthermore, the terms "first" and "second" are used for descriptive purposes only and should not be construed as indicating or implying relative importance or implicitly specifying the number of indicated technical features. Thus, a feature defined as "first" or "second" may explicitly or implicitly include at least one of that feature. In the description of this utility model, "a plurality of" means at least two, such as two, three, etc., unless otherwise explicitly specified.

[0057] In the description of this specification, the references to terms such as "one embodiment," "some embodiments," "example," "specific example," or "some examples," etc., indicate that a specific feature, structure, material, or characteristic described in connection with that embodiment or example is included in at least one embodiment or example of the present invention. In this specification, the illustrative expressions of the above terms do not necessarily refer to the same embodiment or example. Furthermore, the specific features, structures, materials, or characteristics described may be combined in any suitable manner in one or more embodiments or examples. Moreover, without contradiction, those skilled in the art can combine and integrate the different embodiments or examples described in this specification, as well as the features of different embodiments or examples.

[0058] Although embodiments of the present invention have been shown and described above, it is understood that the above embodiments are exemplary and should not be construed as limiting the present invention. Those skilled in the art can make changes, modifications, substitutions and variations to the above embodiments within the scope of the present invention.

Claims

1. A photodetector, comprising: The detector includes a detector substrate (1), an active region (2) is provided on the detector substrate (1), a refractive bevel (11) is etched at the end of the detector substrate (1), an upper reflective layer (3) is epitaxially grown above the active region (2), a lower reflective layer (4) is epitaxially grown below the active region (2), the lower reflective layer (4) is grown on the detector substrate (1), and the active region (2) includes an absorption layer (21).

2. The photodetector of claim 1, wherein, The active region (2) further includes an N-contact layer (22), a drift layer (23), and a P-contact layer (24). The N-contact layer (22), the drift layer (23), the absorption layer (21), the P-contact layer (24), and the upper reflective layer (3) are epitaxially grown sequentially above the lower reflective layer (4).

3. The photodetector of claim 1, wherein, The detector substrate (1) is an InP semi-insulating substrate.

4. The photodetector of claim 2, wherein, The length of the N-contact layer (22) extending along the incident direction of the initial incident light before refraction by the refracting slope (11) is greater than the lengths of the drift layer (23), the absorption layer (21), the P-contact layer (24), the upper reflective layer (3), and the lower reflective layer (4) extending along the incident direction of the initial incident light. The end of the lower reflective layer (4) away from the refracting slope (11) is aligned with the N-contact layer (22).

5. The photodetector of claim 4, wherein, The drift layer (23), the absorption layer (21), the P contact layer (24), and the upper reflective layer (3) extend for the same length along the incident direction of the initial incident light.

6. The photodetector of claim 4, wherein, The detector substrate (1) includes a first region (12) and a second region (13). The refractive slope (11) is located in the first region (12). The lower reflective layer (4) is located above the second region (13). The upper surface of the lower reflective layer (4) is flush with the upper surface of the first region (12).

7. The photodetector of claim 4, wherein, The angle of the refracting slope (11) is 46 degrees to 68 degrees, the lateral etching depth of the refracting slope (11) is 20 μm to 35 μm, and the longitudinal etching depth of the refracting slope (11) is 25 μm to 40 μm.

8. The photodetector of claim 1, wherein, The thickness of the absorption layer (21) is 60 nm to 120 nm, and the absorption layer (21) has a PIN structure.

9. The photodetector of claim 2, wherein, An N electrode (5) is provided above the N contact layer (22).

10. The photodetector of claim 4, wherein, The detector substrate (1) includes a first region (12) and a second region (13). The refractive slope (11) is located in the first region (12), and the lower reflective layer (4) is located above the second region (13). The surface of the refractive slope (11) is covered with a first gradient refractive index coupling layer (14). A second gradient refractive index coupling layer (15) is epitaxially grown on the upper surface of the first region (12). The upper surface of the second gradient refractive index coupling layer (15) is flush with the upper surface of the lower reflective layer (4).

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