High-performance micro photodetector integrated with achromatic superlens and equipment

Abstract

The embodiment of the application provides a kind of integrated achromatic super-structure lens high-performance micro photoelectric detector and equipment, belong to the technical field of optoelectronic devices.The detector includes substrate support layer, bottom reflection layer, micro mesa photoelectric conversion structure, dielectric passivation layer, low refractive index spacer layer and achromatic super-lens layer.The bottom reflection layer has the function of back electrode and optical mirror, and forms a double-pass absorption light path with the photoelectric conversion structure.The dielectric passivation layer has high-density fixed negative charge, and suppresses the surface leakage current of mesa sidewall through field effect.The achromatic super-lens layer is composed of sub-wavelength nanocolumn array, which is used to focus wide-band incident light into the absorption area of micro mesa.The above-mentioned three structures are coordinated to simultaneously achieve wide-band achromatic high-efficiency light coupling, high-bandwidth response and extremely low dark current noise, which significantly improves the signal-to-noise ratio of micro photoelectric detector, and is suitable for high-speed optical communication, laser radar and weak light detection.

Description

Technical Field

[0001] This application relates to the field of optoelectronic device technology, and in particular to a high-performance miniature photodetector and device with integrated achromatic metalens. Background Technology

[0002] Photodetectors are core components of optical communication, lidar, and environmental sensing and imaging systems. In high-speed, low-light detection applications, the signal-to-noise ratio (SNR) is a key performance indicator. However, traditional photodetectors face an inherent contradiction between bandwidth and sensitivity: to improve response speed (bandwidth), the photosensitive area needs to be reduced to decrease junction capacitance, but this leads to decreased light collection efficiency and reduced sensitivity; conversely, increasing the photosensitive area can improve sensitivity, but it will increase capacitance and limit bandwidth.

[0003] In existing technologies, microlens arrays are commonly used to focus light to improve the optical coupling efficiency of small-area detectors. However, traditional refractive microlenses suffer from significant chromatic aberration. When operating over a wide wavelength range (such as the visible light band), the focal point differs for different wavelengths, leading to uneven reception efficiency of multi-wavelength signals and a decline in system performance. Furthermore, with the miniaturization of detector dimensions (e.g., mesa diameters reduced to the order of several micrometers), the ratio of sidewall surface area to volume increases significantly. Leakage current (dark current) caused by surface states becomes the main noise source, severely limiting the signal-to-noise ratio and detection limit of the detector.

[0004] Therefore, there is an urgent need for a miniature photodetector that can achieve efficient optical coupling over a wide spectral range while possessing low noise and high bandwidth characteristics, in order to meet the application requirements of high-speed, high-sensitivity optoelectronic systems. Summary of the Invention

[0005] The main objective of this application is to propose a high-performance micro photodetector and device with an integrated achromatic metalens. By integrating an achromatic metalens, the problem of small-area optical coupling and chromatic aberration is solved. The bottom reflection structure is used to solve the problem of thin-layer absorption efficiency. Combined with negative charge passivation technology, surface leakage current is suppressed, thus achieving a combination of high bandwidth, wide spectral response and high signal-to-noise ratio.

[0006] To achieve the above objectives, one aspect of this application proposes a high-performance miniature photodetector integrating an achromatic metalens, comprising: Base support layer; A bottom reflective layer located above the substrate support layer; A photoelectric conversion structure is located above the bottom reflective layer. The photoelectric conversion structure is etched into a micro mesa structure, and the bottom reflective layer and the bottom contact layer of the photoelectric conversion structure form an ohmic contact. A top electrode is located at the top edge of the micro-mesa, and the top electrode forms an ohmic contact with the top contact layer of the photoelectric conversion structure; A dielectric passivation layer covering the sidewalls of the micro-mesa structure, the dielectric passivation layer carrying a fixed negative charge; A low-refractive-index spacer layer covering the photoelectric conversion structure and the dielectric passivation layer; and An achromatic superlens layer located on top of the low-refractive-index spacer layer; The achromatic superlens layer is used to focus incident broadband light into the absorption layer of the micro-mesa structure, and the dielectric passivation layer is used to suppress surface leakage current on the sidewall of the micro-mesa structure through field effect.

[0007] In some embodiments, the bottom reflective layer is made of aluminum (Al), silver (Ag), or gold (Au), and has a thickness of 0.05 μm to 0.3 μm. This layer has both electrical and optical functions: electrically, it serves as the back electrode of the device; optically, it acts as a highly reflective mirror, forming a double-pass absorption optical path with the upper absorption layer, allowing incident light to pass through the absorption layer twice, thereby achieving high quantum efficiency with a relatively thin absorption layer thickness.

[0008] In some embodiments, the photoelectric conversion structure is a PIN junction photodiode, comprising, from bottom to top: The N-type contact layer has a thickness of less than 0.3 μm and a doping concentration greater than 1 × 10⁻⁶. 19 cm -3 ; The intrinsic absorption layer is made of silicon or germanium and has a thickness of 2.0 μm to 3.5 μm. The P-type contact layer has a thickness of less than 0.05 μm and a doping concentration greater than 5 × 10⁻⁶. 19 cm -3 .

[0009] The highly doped and ultra-thin design of the N-type contact layer is intended to achieve low contact resistance and high optical transmittance to facilitate bottom reflection.

[0010] In some embodiments, the material of the dielectric passivation layer is aluminum oxide (Al2O3) or hafnium dioxide (HfO2), and the fixed charge density at the interface between it and the sidewall of the micro-mesa is negative, with an absolute value greater than 1 × 10⁻⁶. 11 cm -2 This negative charge induces the formation of a hole accumulation layer or depletes electrons on the semiconductor surface, thereby effectively suppressing surface electron conduction channels and significantly reducing surface leakage current.

[0011] In some embodiments, the diameter of the micro-mesa structure is 3.0 μm to 4.0 μm, such that the junction capacitance of the photodetector is less than 1.0 fF, thereby obtaining an extremely high RC-limited bandwidth.

[0012] In some embodiments, the top electrode is a ring-shaped columnar structure, the material of which includes one or more combinations of titanium (Ti), chromium (Cr), gold (Au), and aluminum (Al). The inner diameter of the ring is less than or equal to the diameter of the micro-mesa structure, and an optical aperture is formed in the central region to allow the focused light spot to enter the absorption layer without obstruction.

[0013] In some embodiments, the achromatic superlens layer is composed of an array of subwavelength nanopillar units. By carefully designing the geometry (such as cylinders, square pillars, rings, etc.) and dimensions (diameter, side length) of the nanopillars, phase compensation and group delay modulation are simultaneously performed on incident light in the wavelength range of 520nm to 620nm, so that the focal point of all wavelengths in this band converges to the same focal plane, and the position deviation of the focal plane is less than 1.5μm.

[0014] In some embodiments, the characteristic dimensions (side length or diameter) of the achromatic superlens layer are 15 μm to 30 μm, and the focal plane is located 16 μm to 19 μm from the lower surface of the achromatic superlens layer, precisely matching the position of the underlying micro-mesa absorption layer.

[0015] In some embodiments, the nanopillar unit comprises at least two different structures selected from solid cylinders, solid square cylinders, and hollow cylinders, wherein the height of the nanopillar unit is 1.4 μm to 1.6 μm, and the arrangement period is 500 nm to 600 nm. The combination design of multiple structural units can provide richer degrees of freedom for phase and dispersion modulation, thereby achieving superior achromatic performance.

[0016] In some embodiments, the low-refractive-index spacer layer is made of silicon dioxide (SiO2), and its thickness is precisely designed to match the design focal length of the achromatic superlens layer, ensuring that the focal point falls accurately at the center of the absorption layer.

[0017] To achieve the above objectives, another aspect of the embodiments of this application proposes a photodetector array comprising multiple high-performance micro photodetectors with integrated achromatic metalenses as described above, arranged in an array on the same substrate support layer.

[0018] To achieve the above objectives, another aspect of the embodiments of this application proposes a communication device or optical sensing device, including a high-performance miniature photodetector with an integrated achromatic metalens as described above, or a photodetector array as described above.

[0019] Compared with the prior art, the technical solution provided in this application has the following significant advantages: 1) Wideband high-efficiency achromatic focusing: By integrating achromatic superlens based on metasurface, the dispersion problem of traditional microlenses is successfully solved, enabling light energy in the 520nm-620nm wideband to be accurately and uniformly focused onto the micron-scale photosensitive surface, which greatly improves the coupling efficiency and detection uniformity of wide spectrum or white light signals.

[0020] 2) The unity of high bandwidth and high quantum efficiency: The micro-mesa structure (3-4 μm in diameter) reduces the junction capacitance to the fF level, achieving high-speed response; at the same time, the dual-pass optical path formed by the bottom reflective layer allows light to undergo two absorptions in the absorption layer. Even if the absorption layer thickness is only 2-3.5 μm, it can achieve a quantum efficiency close to that of a single-pass thick absorption layer, thus breaking the traditional trade-off between "bandwidth" and "sensitivity".

[0021] 3) Extremely low dark current noise: The sidewalls of the micrometastases are passivated using a dielectric layer with a high fixed negative charge density (such as Al2O3), which physically suppresses surface leakage channels through the field effect. Experiments show that this technique can reduce the dark current of the microdetector by more than an order of magnitude compared to unoptimized devices, resulting in a qualitative improvement in core noise performance.

[0022] 4) High Signal-to-Noise Ratio and System Integration Advantages: The synergistic effect of the aforementioned advantages in optical focusing, electrical speed, and noise suppression results in a several-fold improvement in the overall signal-to-noise ratio (SNR) of the device under low-light conditions. Furthermore, the device employs a vertically stacked planar structure, offering good compatibility with CMOS processes and facilitating large-scale integration to form high-density focal plane arrays (FPAs). This has significant application value in areas such as on-chip optical interconnects, miniature spectrometers, and quantum chip readout. Attached Figure Description

[0023] Figure 1 This is a three-dimensional structural schematic diagram of a miniature photodetector unit according to an embodiment of this application.

[0024] Figure 2 yes Figure 1 A top view of the nanopillar array arrangement of the achromatic superlens layer in the embodiment.

[0025] Figure 3 This is a cross-sectional structural diagram of a preferred embodiment of this application.

[0026] Figure 4 yes Figure 3 The schematic diagram shows the structure of several typical nanopillar units used in the achromatic superlens layer in the embodiment.

[0027] Figure 5The image shows the light field focusing intensity distribution of the detector in this application at multiple wavelengths from 520nm to 620nm, obtained through simulation.

[0028] Figure 6 This is a spectral response curve of the device in the embodiment of this application over a wide wavelength range.

[0029] Figure 7 This is a comparison chart of the dark current-voltage characteristics of the device in the embodiment of this application and a traditional large-scale device.

[0030] Explanation of the labels in the diagram: 101: Achromatic Superlens Layer 102: Low-refractive-index spacer layer 103: Top Electrode 104: P-type contact layer (top contact layer) 105: Intrinsic Absorbing Layer 106: N-type contact layer (bottom contact layer) 107: Bottom reflective layer / back electrode 108: Base support layer 201, 202, 203: Different types of nanopillar units Detailed Implementation The embodiments of the present invention are described in detail below. Examples of these embodiments are shown in the accompanying drawings, wherein the same or similar reference numerals denote the same or similar elements or elements having the same or similar functions throughout. The embodiments described below with reference to the accompanying drawings are exemplary and are only used to explain the present invention, and should not be construed as limiting the present invention. The step numbers in the following embodiments are set only for ease of explanation, and there is no limitation on the order between the steps. The execution order of each step in the embodiments can be adaptively adjusted according to the understanding of those skilled in the art.

[0031] In the description of this invention, it should be understood that the orientation descriptions, such as up, down, front, back, left, right, etc., are based on the orientation or positional relationship shown in the accompanying drawings. They are only for the convenience of describing this invention and simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, or be constructed and operated in a specific orientation. Therefore, they should not be construed as limiting this invention.

[0032] In the description of this invention, "several" means one or more, "more than" means two or more, "greater than," "less than," and "exceeding" are understood to exclude the stated number, while "above," "below," and "within" are understood to include the stated number. The use of "first" and "second" in the description is merely for distinguishing technical features and should not be construed as indicating or implying relative importance, or implicitly indicating the number of indicated technical features, or implicitly indicating the order of the indicated technical features.

[0033] In the description of this invention, unless otherwise explicitly defined, terms such as "set up," "install," and "connect" should be interpreted broadly, and those skilled in the art can reasonably determine the specific meaning of the above terms in this invention in conjunction with the specific content of the technical solution.

[0034] In this embodiment, the photoelectric conversion structure is etched into a micro mesa structure, and the photoelectric conversion structure is described in detail using a PIN junction photodiode as an example.

[0035] Figure 1 The overall three-dimensional structure of the miniature photodetector unit provided in the embodiment of the present invention is shown.

[0036] like Figure 1 As shown, the detector unit has an overall square columnar structure, a design that facilitates high-density, seamless stitching in a focal plane array (FPA). The device comprises, from bottom to top: Substrate support layer: Located at the bottom, it provides mechanical support for the entire device (e.g., Figure 1 (As shown in the medium gray base) Miniature mesa structure: A cylindrical structure located in the center of the base (such as...) Figure 1 (As shown in the dark-colored cylinder), this area contains the core functional layer of the PIN junction photodiode. It can be seen that the top electrode surrounds the top edge of the micro-mesa, leaving a light-incident window in the center; Low-refractive-index spacer layer: fills and covers the micro-mesa and substrate (e.g.) Figure 1 (As shown in the transparent square area), it provides the optical path distance required for the superlens to focus; Achromatic superlens layer: located on the topmost surface of the spacer layer (e.g.) Figure 1 (As shown in the black array at the top), its horizontal cross-section is square, completely covering the photosensitive area below.

[0037] Figure 2 Further demonstration Figure 1 The specific microscopic arrangement of the top achromatic superlens layer (top view).

[0038] like Figure 2 As shown, this superlens is composed of a large number of subwavelength-scale nanopillars arranged according to a specific phase distribution pattern. To achieve achromatic focusing over a wide wavelength range (e.g., 520nm-620nm), this embodiment does not use a single structural design but rather employs a library of multiple geometric structures. Specifically, Figure 2The nanopillar units include, but are not limited to, various cross-sectional shapes such as cylinders, square pillars, rings, or square rings (as shown by dots of different gray levels and shapes in the figure). The dimensions (such as radius and side length) and spatial positions of these nanopillars are calculated using a rigorous global optimization algorithm. Through this non-periodic, complex spatial arrangement, the superlens can simultaneously control the phase and group delay of incident light of different wavelengths, thereby ensuring that light of different wavelengths can be precisely focused onto the photosensitive surface of the underlying micro-mesa.

[0039] like Figure 3 As shown, this embodiment provides a high signal-to-noise ratio micro photodetector with an integrated achromatic superlens. Its main structure includes: a substrate support layer 108, a bottom reflective layer (back electrode) 107, a micro mesa structure PIN junction photodiode composed of an N-type contact layer 106, an intrinsic absorption layer 105 and a P-type contact layer 104, a top electrode 103, a negative charge dielectric passivation layer (not shown in the figure), a low refractive index spacer layer 102, and an achromatic superlens layer 101 located at the top.

[0040] The achromatic superlens layer 101, under the excitation of broadband incident light, modulates the phase of light fields of different wavelengths and uses group delay for phase compensation, converging the light fields onto the same focal plane. This, combined with the micro mesa PIN junction photodiode below, achieves efficient coupling of broadband signals. The micro mesa PIN junction photodiode employs a miniaturized design to reduce junction capacitance, and its sidewalls are wrapped by the negatively charged dielectric passivation layer 301. The field effect is used to suppress surface leakage current, achieving low-noise detection. The bottom reflective layer 107 serves as both the back electrode of the device and an optical mirror, reflecting the light transmitted through the diode back to the intrinsic absorption layer 105, forming a double-pass absorption optical path, further enhancing the absorption of incident light of the target wavelength.

[0041] The substrate support layer 108 can be made of semiconductor materials such as Si, Ge, and GaAs, or insulating materials such as sapphire and quartz. In this embodiment, a high-resistivity Si substrate is preferred.

[0042] The bottom reflective layer 107 is made of Au, Ag, or Al, with Al being preferred in this embodiment. Its thickness is 0.05 μm to 0.3 μm, but in other embodiments, Ag, Au, or a distributed Bragg reflector (DBR) can also be used. This layer is deposited directly on the substrate support layer 108, or transferred to the substrate support layer 108 via wafer bonding, and is used to provide mechanical support and extract photoelectric signals.

[0043] The PIN junction photodiode is an etched cylindrical or polygonal micromesa structure with a diameter or feature size of 3.0 μm to 4.0 μm. The diode includes, from bottom to top, an N-type ohmic contact layer 106, an intrinsic absorption layer 105, and a P-type ohmic contact layer 104. One surface of the N-type ohmic contact layer 106 forms an ohmic contact with the bottom reflective layer 107; the upper surface of the P-type ohmic contact layer 104 is connected to the low-refractive-index spacer layer 102, and its edge region is connected to the annular top electrode 103.

[0044] To achieve "dual-pass absorption" and reduce contact resistance, the N-type ohmic contact layer 106 is made of highly doped n-type Si with a doping concentration on the order of 10¹. 9 / cm³, its thickness is designed to be 0.1μm to 0.3μm. This thickness design is extremely thin and has a high doping concentration, which not only ensures good electrical contact with the bottom reflective layer 107, but also allows the layer to maintain high optical transmittance in the operating wavelength range, allowing light to pass through and be reflected by the bottom.

[0045] The intrinsic absorption layer 105 is undoped i-type Si or lightly doped p-type Si, with a thickness of 2.0 μm to 3.5 μm. This thickness is optimized based on a trade-off between the absorption depth and carrier transit time at the operating wavelength (e.g., 550 nm). The p-type ohmic contact layer 104 is ultrathin, highly doped p-type Si, with a doping concentration on the order of 10¹⁰. 9 / cm³, with a thickness of 0.02μm to 0.05μm. The ultra-thin design is to reduce parasitic absorption of short-wavelength incident light by the dead layer and improve quantum efficiency.

[0046] The top electrode 103 is located at the top edge of the micro-mesa structure, forming an ohmic contact with the upper surface of the P-type ohmic contact layer 104. The top electrode 103 is a centrally hollowed-out annular columnar structure with an inner diameter slightly smaller than or equal to the diameter of the micro-mesa to expose the photosensitive area, allowing incident light to pass through and enter the underlying intrinsic absorption layer 105; its outer diameter is designed to match the size of wire bonding or extension electrodes. Specifically, the material of the top electrode 103 is preferably a low-contact-resistance metal combination such as Ti / Au, Cr / Au, or Al, with a thickness of 0.1 μm to 0.3 μm. This annular electrode not only collects photogenerated holes and extracts electrical signals but also physically defines the effective optical aperture of the device.

[0047] The negatively charged dielectric passivation layer covers the sidewall surfaces of the intrinsic absorption layer 105 and the P-type ohmic contact layer 104 of the micro-mesa PIN junction photodiode. The passivation layer is made of materials including, but not limited to, Al₂O₃ or HfO₂, and has a fixed negative interface charge with an absolute charge density greater than 1 × 10¹¹ cm⁻¹. - ². The presence of this negative charge layer induces hole accumulation or depletes electrons on the N-type and intrinsic silicon surfaces, thereby cutting off the electron conduction channels on the sidewalls and significantly reducing the surface dark current of the device.

[0048] like Figure 4 As shown, the achromatic superlens layer 101 is composed of three periodically arranged nanopillar units 201, 202, and 203 with different structures. The side length of the entire superlens layer is 15 μm to 30 μm. The material of the structure above the nanopillar unit can be a high-refractive-index medium such as TiO2, GaN, or SiN, and the substrate below is a partial low-refractive-index spacer layer 102. The height of the structure above the nanopillar unit is uniform and designed to be 1.4 μm to 1.6 μm, with a period of 500 nm to 600 nm. Among them, the structure above nanopillar unit 201 is a solid cylinder, the structure above nanopillar unit 202 is a solid square prism, and the structure above nanopillar unit 201 is a hollow cylinder with a fixed difference between its inner and outer diameters of 40 nm to 60 nm. By changing the diameter of the nanopillars, a propagation phase is introduced into the incident light. Specifically, for the 520nm to 620nm operating band, dispersion compensation design is carried out by adjusting the phase delay and group delay of different unit structures, so that the light in this band can be focused onto the same focal plane at a distance of 16μm to 19μm from the lens.

[0049] The focusing of the plane wave after passing through the achromatic superlens layer 101 is as follows: Figure 5 As shown in the figure, the two dashed lines correspond to the intrinsic absorption layer 105 region of the micro mesa PIN junction photodiode.

[0050] The specific working principle of the high signal-to-noise ratio micro photodetector in this embodiment is as follows: Incident light (e.g., broadband light in the 520-620nm band) illuminates the achromatic superlens layer 101. The superlens performs phase compensation for light of different wavelengths, eliminates chromatic aberration, and efficiently focuses the light beam through the low refractive index spacer layer 102 and the ultrathin P-type ohmic contact layer 104, entering the intrinsic absorption layer 105. In the intrinsic absorption layer 105, most photons are absorbed, generating electron-hole pairs; a small portion of the unabsorbed photons continue downward through the transparent N-type ohmic contact layer 106, reach the bottom reflective layer 107 and are reflected, then pass through the intrinsic absorption layer 105 again for secondary absorption. This dual-pass structure enables high light absorption even with a relatively thin absorption layer thickness (e.g., 3μm). Simultaneously, under reverse bias, photogenerated carriers drift to form a photocurrent. Due to the micro-mesa design (approximately 3.5μm in diameter), the junction capacitance is extremely small (<1fF), thus achieving an extremely high RC bandwidth. More importantly, addressing the surface leakage problem commonly faced by micro-mesa structures, this embodiment introduces a negatively charged dielectric passivation layer that utilizes the field effect to repel electrons on the sidewall surface, significantly suppressing surface dark current. In summary, this device combines the optical gain of a superlens, the high-speed characteristics of a micro-mesa, and the low-noise characteristics of negatively charged passivation, achieving high signal-to-noise ratio weak light detection.

[0051] The photodetector described above will be described in detail below with reference to the accompanying drawings and specific embodiments.

[0052] like Figure 3 As shown, this embodiment provides a high signal-to-noise ratio miniature photodetector with an integrated achromatic superlens, and the device has a vertical incidence structure. The specific structural parameters used in this embodiment are as follows: the bottom reflective layer 107 is Al with a thickness of 0.3 μm; the N-type ohmic contact layer 106 has a doping concentration of 1 × 10¹. 9 The n-type Si layer has a density of 1 / cm³ and a thickness of 0.3 μm; the intrinsic absorber layer 105 is i-type Si with a thickness of 3.0 μm; the p-type ohmic contact layer 104 has a doping concentration of 5 × 10¹⁸. 9 The micro-mesa structure has a density of 0.03 μm / cm³ and a thickness of 0.03 μm; the micro-mesa structure has a diameter of 3.5 μm; the negatively charged dielectric passivation layer 301 is Al₂O₃ deposited by ALD, and the interface fixed charge density is set to -1.0 × 10¹¹ cm⁻¹. - ²; The low-refractive-index spacer layer 102 is made of SiO2 with a thickness of 19μm; The achromatic superlens layer 101 is designed to operate in the 520-620nm wavelength range. Figure 6This paper demonstrates the photocurrent response characteristics of the device according to an embodiment of the present invention over a wide visible light wavelength range. The simulation light source selected five typical wavelength points: 520nm, 550nm, 580nm, 600nm, and 620nm, with the test voltage fixed at -2V. Test data shows that, thanks to the phase compensation effect of the achromatic superlens integrated in the top layer for different wavelength light fields, and the dual-pass absorption optical path constructed by the bottom reflective layer, the device maintains a high photocurrent response throughout the wide wavelength range of 520nm to 620nm. The peak photocurrent occurs near 600nm, reaching approximately 2.75 × 10⁻⁶. -7 A; Within the range of 520nm to 620nm, the photocurrent fluctuation is small, consistently remaining within 1.5×10⁻⁶. -7 The achromatic superlens achieves a high level of A or above. This indicates that the achromatic superlens successfully eliminates the influence of chromatic aberration, enabling incident light of different wavelengths to be precisely focused within the absorption layer of the micro-mesa, thus verifying the device's excellent broadband detection capability. Figure 7 The dark current characteristics of the miniature mesa photodetector fabricated according to an embodiment of the present invention are compared with those of an unoptimized conventional large mesa detector (the mesa diameter is set to match the radius of the superlens). The test voltage range is -2.0V to 1.0V, and the absolute values ​​of the current results are taken using logarithmic coordinates. The sharp drop in the curve at the zero voltage point represents the positive and negative changes in the absolute current near this point, producing a 10... -31 The minimum value is on the order of magnitude (not shown in the figure because this point is outside the normal operating range of the detector). The curve comparison results show that, within the reverse bias operating region, the dark current of the device in this embodiment (square dot curve) is significantly lower than that of the conventional large-area detector (dot curve). Specifically, at a bias of -2.0V, the dark current of the conventional device is approximately 4.14 × 10⁻⁶. -13 A, while the dark current of the device of the present invention is reduced to approximately 2.05 × 10⁻⁶. -14 A. This order-of-magnitude reduction (approximately 20-fold) strongly demonstrates that the micro-mesa structure employed in this invention significantly reduces the junction area of ​​the device, while the negatively charged dielectric passivation layer effectively suppresses surface leakage current channels on the sidewalls through the field effect. The substantial reduction in dark current directly improves the signal-to-noise ratio of the device under weak light detection.

[0053] Although embodiments of the invention have been shown and described, those skilled in the art will understand that various changes, modifications, substitutions and alterations can be made to these embodiments without departing from the principles and spirit of the invention, the scope of which is defined by the claims and their equivalents.

[0054] Furthermore, those skilled in the art should understand that the core structure of this invention (i.e., the architecture combining an achromatic superlens with a micro-mesa) is not limited to a PIN junction. In other alternative embodiments, the photoelectric conversion structure can also be replaced with an avalanche photodiode (APD), a single-photon avalanche photodiode (SPAD), or a Schottky photodiode.

[0055] When using an APD structure, simply adding a charge multiplication layer between the N-type ohmic contact layer and the intrinsic absorption layer (or between the P-layer and the intrinsic layer) allows for internal gain detection without altering the focusing principle of the superlens of this invention. Such modifications should be included within the scope of protection of this invention.

[0056] The above is a detailed description of the preferred embodiments of the present invention. However, the present invention is not limited to the above embodiments. Those skilled in the art can make various equivalent modifications or substitutions without departing from the spirit of the present invention. All such equivalent modifications or substitutions are included within the scope defined by the claims of this application.

Claims

1. A high-performance miniature photodetector integrating an achromatic metalens, characterized in that, include: Base support layer; A bottom reflective layer located above the substrate support layer; A photoelectric conversion structure is located above the bottom reflective layer. The photoelectric conversion structure is etched into a micro mesa structure, and the bottom reflective layer and the bottom contact layer of the photoelectric conversion structure form an ohmic contact. A top electrode is located at the top edge of the micro-mesa, and the top electrode forms an ohmic contact with the top contact layer of the photoelectric conversion structure; A dielectric passivation layer covering the sidewalls of the micro-mesa structure, the dielectric passivation layer carrying a fixed negative charge; A low-refractive-index spacer layer covering the photoelectric conversion structure and the dielectric passivation layer; as well as An achromatic superlens layer located on top of the low-refractive-index spacer layer; The achromatic superlens layer is used to focus incident broadband light into the absorption layer of the micro-mesa structure, and the dielectric passivation layer is used to suppress surface leakage current on the sidewall of the micro-mesa structure through field effect.

2. The miniature photodetector according to claim 1, characterized in that, The bottom reflective layer is made of aluminum, silver, or gold, and has a thickness of 0.05 μm to 0.3 μm. It also serves as the back electrode of the photodetector and an optical reflector that forms a dual-pass absorption optical path.

3. The miniature photodetector according to claim 1, characterized in that, The photoelectric conversion structure is a PIN junction photodiode, which includes, from bottom to top: The N-type contact layer has a thickness of less than 0.3 μm and a doping concentration greater than 1 × 10⁻⁶. 19 cm -3 ; The intrinsic absorption layer is made of silicon or germanium and has a thickness of 2.0 μm to 3.5 μm. The P-type contact layer has a thickness of less than 0.05 μm and a doping concentration greater than 5 × 10⁻⁶. 19 cm -3 .

4. The miniature photodetector according to claim 1, characterized in that, The dielectric passivation layer is made of Al2O3 or HfO2, and the fixed charge density at its interface with the sidewall of the micro-mesa is negative, with an absolute value greater than 1 × 10⁻⁶. 11 cm -2 .

5. The miniature photodetector according to claim 1, characterized in that, The diameter of the micro-mesa structure is 3.0 μm to 4.0 μm, and the junction capacitance of the photodetector is less than 1.0 fF; The top electrode is a ring-shaped columnar structure, and its material includes one or more combinations of titanium, chromium, gold, and aluminum. The inner diameter of the ring-shaped columnar structure is less than or equal to the diameter of the micro-mesa structure.

6. The miniature photodetector according to claim 1, characterized in that, The achromatic superlens layer is composed of an array of subwavelength nanopillar units. The nanopillar units introduce phase compensation and group delay modulation for incident light in the wavelength range of 520nm to 620nm through the modulation of their geometry and size, so that the incident light in this range is focused on the same focal plane and the position deviation of the focal plane is less than 1.5μm.

7. The miniature photodetector according to claim 6, characterized in that, The achromatic superlens layer has a feature size of 15 μm to 30 μm, and the focal plane is located at a distance of 16 μm to 19 μm from the lower surface of the achromatic superlens layer. The nanopillar unit includes at least two different structures selected from solid cylinders, solid square cylinders, and hollow cylinders. The height of the nanopillar unit is 1.4 μm to 1.6 μm, and the arrangement period is 500 nm to 600 nm.

8. The miniature photodetector according to claim 1, characterized in that, The low-refractive-index spacer layer is made of SiO2, and its thickness is configured to match the design focal length of the achromatic superlens layer.

9. A photodetector array, characterized in that, A high-performance micro photodetector comprising multiple integrated achromatic metalenses as described in any one of claims 1 to 8 is arranged in an array on the same substrate support layer.

10. A communication device or optical sensing device, characterized in that, It includes a high-performance micro photodetector with an integrated achromatic metalens as described in any one of claims 1 to 8, or a photodetector array as described in claim 9.

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