Enhanced ultraviolet avalanche photodiode based on grating super lens and preparation method of enhanced ultraviolet avalanche photodiode

Abstract

The invention discloses an enhanced ultraviolet avalanche photodiode based on a grating super lens and a preparation method thereof. The enhanced ultraviolet avalanche photodiode comprises an N-type SiC substrate, and an N-type drift layer, a P-type region and a P + contact layer which are sequentially positioned on the upper surface of the N-type SiC substrate, the grating super lens structure is positioned on the P + contact layer, so that the incident ultraviolet parallel light is focused in the P-type region through the grating super lens structure; wherein the grating super-lens structure is made of a transparent medium material; from an overlook direction, the grating super-lens structure is a one-dimensional linear chirp grating or a two-dimensional square nano-column array grating. The passivation layer is located on the grating super-lens structure; the two upper electrodes penetrate through the passivation layer and the grating super-lens structure close to the two ends of the device and are located on the P + contact layer; and the lower electrode is positioned on the lower surface of the N-type SiC substrate. Through the micro focusing element integrated on the chip, the photon utilization rate, the signal-to-noise ratio and the working stability of the device are remarkably improved.

Description

Technical Field

[0001] This invention belongs to the field of microelectronics technology, specifically relating to an enhanced ultraviolet avalanche photodiode based on a grating superlens and its fabrication method. Background Technology

[0002] Ultraviolet avalanche photodiodes (UV-APDs) are core devices for detecting weak ultraviolet signals. Their performance largely depends on the efficiency of photon absorption and conversion. Traditional avalanche photodiodes (APDs) mainly face the following challenges: Limited photon collection efficiency: First, due to the high refractive index difference between semiconductor materials (such as GaN and SiC) and air, more than 20% of the incident light is directly reflected, causing permanent loss. Second, in some high-density detector arrays, there are non-photosensitive passivation regions and electrode regions between the photosensitive area (active region), resulting in some incident photons being unusable, i.e., the fill factor is less than 100%.

[0003] Avalanche multiplication noise and inhomogeneity: The avalanche multiplication process of APDs is extremely sensitive to the electric field distribution. At the edges of the active region of the device or at locations with material defects, the electric field is prone to distortion. If photons are absorbed in these areas and trigger avalanches, unstable and excessively high multiplication noise can easily be generated, even leading to premature device breakdown. This seriously affects the signal-to-noise ratio and detection stability of the device.

[0004] While existing technologies combine microlens arrays with CMOS (Complementary Metal-Oxide-Semiconductor) image sensors to improve the fill factor, traditional refractive microlenses are large and have steep profiles. Their curved structures typically require significant vertical space, and their optical designs have poor compatibility with standard semiconductor planar processes, making integration with APD planar processes difficult. Furthermore, the steep sidewall angles easily cause light scattering and aberrations, especially in modern detector structures where pixel sizes are constantly shrinking, further reducing optical coupling efficiency and introducing crosstalk, thus limiting the overall performance improvement of APD devices. The emerging metasurface technology offers a new approach, but existing solutions are mostly focused on silicon-based detectors in the visible / infrared bands, or functionally limited to anti-reflection and light trapping, without specifically addressing the correlation between avalanche noise and photon incident position in APD devices.

[0005] Therefore, there is an urgent need for a new type of optical management structure that can not only guide more photons to the active region, but also accurately project photons to the highest quality and most stable active region, thereby improving the photoelectric response and signal-to-noise ratio performance of the device. Summary of the Invention

[0006] To address the aforementioned problems in the prior art, this invention provides an enhanced ultraviolet avalanche photodiode based on a grating superlens and its fabrication method. The technical problem to be solved by this invention is achieved through the following technical solution: In a first aspect, embodiments of the present invention provide an enhanced ultraviolet avalanche photodiode based on a grating superlens, the enhanced ultraviolet avalanche photodiode comprising: An N-type SiC substrate, and an N-type drift layer, a P-type region, and a P+ contact layer sequentially located on the upper surface of the N-type SiC substrate; A grating superlens structure is located on the P+ contact layer to focus incident ultraviolet parallel light into a P-type region; wherein, the grating superlens structure is a transparent dielectric material; from the top view, the grating superlens structure appears as a one-dimensional linear chirped grating or a two-dimensional square nanopillar array grating. The passivation layer is located on the grating superlens structure; Two upper electrodes penetrate the passivation layer and grating superlens structure near both ends of the device and are located on the P+ contact layer; The lower electrode is located on the lower surface of the N-type SiC substrate.

[0007] In one embodiment of the present invention, the transparent dielectric material includes at least one of silicon nitride, titanium dioxide, hafnium dioxide, aluminum oxide, or silicon dioxide.

[0008] In one embodiment of the present invention, when the grating superlens structure is a one-dimensional linear chirped grating, the grating height, grating duty cycle, and grating linewidth of the grating superlens structure are designed according to the total aperture of the lens of the grating superlens structure, so as to focus the incident ultraviolet parallel light into the P-type region through the grating superlens structure.

[0009] In one embodiment of the present invention, when the grating superlens structure is a one-dimensional linear chirped grating, the grating height is designed to be greater than the wavelength of the incident ultraviolet parallel light according to the total aperture of the lens of the grating superlens structure, the grating duty cycle remains unchanged, and the grating linewidth gradually narrows from the center to the edge of the grating superlens.

[0010] In one embodiment of the present invention, the total aperture of the grating superlens structure is 15μm×15μm, the wavelength of the incident ultraviolet parallel light is 280nm, the grating height is designed to be 350nm, the grating duty cycle is 50%, the grating linewidth at the center of the grating superlens is 220nm, and the grating linewidth at the edge of the grating superlens is 170nm, so that the incident ultraviolet parallel light is focused into a position with a depth of 1.2μm in the P-type region by the grating superlens structure.

[0011] In one embodiment of the present invention, when the grating superlens structure is a two-dimensional square nanopillar array grating, the grating height, grating period, and side length of the nanopillars of the grating superlens structure are designed according to the total aperture of the lens of the grating superlens structure, so as to focus the incident ultraviolet parallel light into the P-type region through the grating superlens structure.

[0012] In one embodiment of the present invention, when the grating superlens structure is a two-dimensional square nanopillar array grating, the grating height is designed to be greater than the wavelength of the incident ultraviolet parallel light according to the total aperture of the lens of the grating superlens structure, the grating period remains unchanged, and the side length of the nanopillars gradually decreases from the center to the edge of the grating superlens.

[0013] In one embodiment of the present invention, the total aperture of the grating superlens structure is 20μm×20μm, the wavelength of the incident ultraviolet parallel light is 360nm, the grating height is designed to be 500nm, the grating period is 250nm, the side length of the nanopillar at the center of the grating superlens is 180nm, and the side length of the nanopillar at the edge of the grating superlens is 80nm, so that the incident ultraviolet parallel light is focused into a position with a depth of 1.5μm in the P-type region by the grating superlens structure.

[0014] In a second aspect, embodiments of the present invention provide a method for fabricating an enhanced ultraviolet avalanche photodiode based on a grating superlens, used to fabricate any of the enhanced ultraviolet avalanche photodiodes based on a grating superlens described in the first aspect, the corresponding fabrication method comprising: An N-type SiC substrate was obtained, and an N-type drift layer, a P-type region, and a P+ contact layer were sequentially grown on the N-type SiC substrate. A grating superlens structure is grown on the P+ contact layer to focus incident ultraviolet parallel light into the P-type region; wherein, the grating superlens structure is a transparent dielectric material; from the top view, the grating superlens structure appears as a one-dimensional linear chirped grating or a two-dimensional square nanopillar array grating. A passivation layer is grown on the grating superlens structure; Etch the passivation layer near both ends of the device down to the upper surface of the P+ contact layer to form two upper electrodes on the exposed P+ contact layer. A lower electrode is formed on the lower surface of an N-type SiC substrate.

[0015] The beneficial effects of this invention are: This invention proposes an enhanced ultraviolet avalanche photodiode based on a grating superlens. The grating superlens, integrally integrated with a layer of fully transparent dielectric material, has its surface etched into a nanograting structure with a specific geometric arrangement, such as a one-dimensional linear chirped grating or a two-dimensional square nanopillar array grating. By designing the nanograting structure, when plane-wave ultraviolet light is incident, the beam can be focused to a predetermined position within the semiconductor active region located at its focal plane through diffraction. The grating superlens designed in this invention brings the following unexpected technical effects: Increased effective light flux: This grating superlens concentrates the light that would otherwise illuminate the entire unit (including the non-photosensitive area) into the photosensitive area, increasing the light flux density per unit area. This effectively improves the device's fill factor and photon collection capability, thereby enhancing the device's response to weak point signals.

[0016] Optimizing the avalanche multiplication process and suppressing noise: By focusing the beam to the center region of the APD's active area, photogenerated carriers can be actively prevented from being multiplied at the device edges or defects where the electric field is unstable, thus ensuring that the avalanche process occurs in the most uniform and stable region. This not only guarantees the stability of the avalanche gain but also fundamentally suppresses excess noise related to edge effects, significantly improving the device's signal-to-noise ratio.

[0017] In summary, this invention creatively combines technologies from two different fields—superlens focusing and APD avalanche multiplication—by integrating a grating superlens. This not only allows more photons to be introduced into the device but also more accurately directs photons into the active region, improving the stability of avalanche multiplication, successfully enhancing responsivity and signal-to-noise ratio, and solving the noise optimization problem that cannot be addressed by simple anti-reflection or light-trapping schemes. This achieves a simultaneous improvement in the device's optoelectronic performance and signal quality.

[0018] The present invention will be further described in detail below with reference to the accompanying drawings and embodiments. Attached Figure Description

[0019] Figure 1 This is a schematic diagram of the structure of an enhanced ultraviolet avalanche photodiode based on a grating superlens provided in an embodiment of the present invention; Figure 2 This is a top view schematic diagram of a grating superlens structure provided in an embodiment of the present invention; Figure 3 This is another top view schematic diagram of the grating superlens structure provided in the embodiment of the present invention; Figure 4This is a schematic flowchart of a method for fabricating an enhanced ultraviolet avalanche photodiode based on a grating superlens provided in an embodiment of the present invention; Figures 5(a) to 5(g) This is a schematic diagram of the fabrication process of the enhanced ultraviolet avalanche photodiode based on a grating superlens provided in this embodiment of the invention.

[0020] Explanation of reference numerals in the attached figures: 101- N-type SiC substrate; 102- N-type drift layer; 103- P-type region; 104- P+ contact layer; 105- Grating superlens structure; 106- Diffraction grating pattern; 107- Upper electrode; 108- Lower electrode; 109- Passivation layer. Detailed Implementation

[0021] The present invention will be further described in detail below with reference to specific embodiments, but the implementation of the present invention is not limited thereto.

[0022] The inventors discovered that metasurface technology is mostly applied to photodiodes in the visible / infrared bands, with very little research in the ultraviolet (UV) band. Materials that work well in the infrared region (such as silicon and metals) become completely ineffective in the UV region; visible / infrared metasurface designs cannot be directly transferred to the UV band because of excessive material absorption losses, and UV devices require smaller dimensions (tens of nanometers). Furthermore, infrared detectors such as CCDs (Charge-Coupled Devices) / CMOS typically do not involve avalanche multiplication and edge breakdown problems; therefore, the designed structure can only increase the optical path, unable to control the spatial distribution of photons in the active region, and cannot solve the noise problem caused by edge electric field distortion in APD devices. Therefore, to address the needs of the UV band, this invention proposes an enhanced UV avalanche photodiode based on a grating metalens and its fabrication method.

[0023] Firstly, please see Figure 1 This invention provides an enhanced ultraviolet avalanche photodiode based on a grating superlens, the enhanced ultraviolet avalanche photodiode comprising: An N-type SiC substrate 101, and an N-type drift layer 102, a P-type region 103, and a P+ contact layer 104 sequentially located on the upper surface of the N-type SiC substrate 101; A grating superlens structure 105 is located on the P+ contact layer 104 to focus incident ultraviolet parallel light into the P-type region 103; wherein, the grating superlens structure 105 is a transparent dielectric material; from the top view, the grating superlens structure 105 is a one-dimensional linear chirped grating or a two-dimensional square nanopillar array grating. A passivation layer is located on the grating superlens structure 105; Two upper electrodes penetrate the passivation layer and the grating superlens structure 105 near both ends of the device and are located on the P+ contact layer 104; The lower electrode is located on the lower surface of the N-type SiC substrate 101.

[0024] In this embodiment of the invention, the transparent dielectric material includes at least one of silicon nitride (Si3N4), titanium dioxide (TiO2), hafnium dioxide (HfO2), aluminum oxide (Al2O3), or silicon dioxide (SiO2). The transparent dielectric material is chosen instead of a metal material because metal materials exhibit significant ohmic losses in the ultraviolet band, causing photons to be thermally lost before entering the device. The selected transparent dielectric material is highly transparent in the target ultraviolet band, avoiding the parasitic absorption losses of metal materials.

[0025] In this embodiment of the invention, the N-type drift layer 102, the P-type region 103, and the P+ contact layer 104 are all made of SiC, but the doping type and doping concentration are different.

[0026] The enhanced ultraviolet avalanche photodiode of this invention can be applied to focus enhancement in the UVA (long-wave ultraviolet), UVB (medium-wave ultraviolet), and UVC (short-wave ultraviolet) bands.

[0027] In the embodiments of the present invention, the active region of the device is a homogeneous epitaxial pin structure of SiC substrate 101, namely, an N-type drift layer 102 and a P-type region 103 forming a pin structure, and a transparent dielectric material is directly integrated on the P+ contact layer 104 as a grating superlens structure 105.

[0028] In this embodiment of the invention, when the grating superlens structure 105 is a one-dimensional linear chirped grating, as shown... Figure 2 As shown, based on the total aperture of the grating superlens structure 105, the grating height, grating duty cycle, and grating linewidth of the grating superlens structure 105 are designed to focus incident ultraviolet parallel light into the P-type region 103. More specifically, when the grating superlens structure 105 is a one-dimensional linear chirped grating, based on the total aperture of the grating superlens structure 105, the grating height is designed to be greater than the wavelength of the incident ultraviolet parallel light, the grating duty cycle remains constant, and the grating linewidth gradually narrows from the center to the edge of the grating superlens. This gradual change in grating linewidth from the center to the edge of the grating superlens produces a focusing effect.

[0029] For example, taking the incident ultraviolet parallel light with a wavelength of 280nm (UVC) as an example: the total aperture of the grating superlens structure 105 is 15μm×15μm, covering the active area of ​​a single APD pixel. The wavelength of the incident ultraviolet parallel light is 280nm, and the grating height is designed to be 350nm. This grating height is sufficient to provide complete phase coverage from 0 to 2π. The grating duty cycle is fixed at 50%. The grating linewidth at the center of the grating superlens is 220nm, and the grating linewidth at the edge of the grating superlens is 170nm. This allows the grating superlens structure 105 to focus the incident ultraviolet parallel light at a depth of 1.2μm within the P-type region 103. Aluminum oxide is chosen to form the grating superlens structure 105, as it is transparent in the ultraviolet region and has good compatibility with SiC processes, with a refractive index of approximately 1.8.

[0030] In this embodiment of the invention, when the grating superlens structure 105 is a two-dimensional square nanopillar array grating, such as... Figure 3 As shown, based on the total aperture of the grating superlens structure 105, the grating height, grating period, and side length of the nanopillars are designed to focus incident ultraviolet parallel light into the P-type region 103. More specifically, when the grating superlens structure 105 is a two-dimensional square nanopillar array grating, based on the total aperture of the grating superlens structure 105, the grating height is designed to be greater than the wavelength of the incident ultraviolet parallel light, the grating period remains unchanged, and the side length of the nanopillars gradually decreases from the center to the edge of the grating superlens. Using a two-dimensional square nanopillar array as the phase modulation unit, the side length of the nanopillars gradually changes from the center to the edge of the grating superlens to achieve finer point focusing and polarization independence. Furthermore, this two-dimensional square nanopillar array has rotational symmetry and is insensitive to the polarization state of the incident light, making it suitable for detecting natural light.

[0031] For example, taking the incident ultraviolet parallel light with a wavelength of 360 nm (UVA) as an example: the total aperture of the grating superlens structure 105 is 20 μm × 20 μm, covering the active area of ​​a single APD pixel. The wavelength of the incident ultraviolet parallel light is 360 nm. The grating height is designed to be 500 nm, which is sufficient to provide complete phase coverage from 0 to 2π. The grating period is 250 nm, which is less than the wavelength of the incident ultraviolet parallel light, ensuring that no high-order diffraction is generated and only phase modulation is performed. The side length of the nanopillar at the center of the grating superlens is 180 nm, and the side length of the nanopillar at the edge of the grating superlens is 80 nm, so that the incident ultraviolet parallel light is focused by the grating superlens structure 105 at a position with a depth of 1.5 μm within the P-type region 103. Silicon nitride (Si3N4) was chosen to form the grating superlens structure 105. Si3N4 has a high refractive index (n ≈ 2.0 - 2.1) and extremely low absorption loss, making it an ideal dielectric material.

[0032] The nano-unit arrangement (such as a one-dimensional linear chirped grating or a two-dimensional square nanopillar array grating) designed in this invention is not only for light focusing, but also to solve the problem of "excessive noise caused by uneven edge electric field" unique to APDs. This invention introduces a specific phase gradient through the designed nano-unit arrangement, focusing the incident light to the geometric center of the active region of the device. This reduces the incident light at the edge of the active region, thereby reducing edge leakage current. In other words, it actively avoids the high-noise edge region of the device in physical space, achieving a noise reduction effect.

[0033] The embodiments of this invention also tested the proposed enhanced ultraviolet avalanche photodiode based on a grating superlens, including IV characteristics, spectral response, avalanche gain, and noise tests, all of which verified the effectiveness of its design. Finally, chip-level or module-level packaging was performed according to application requirements to ensure efficient and stable operation of the device in the ultraviolet band.

[0034] In summary, the enhanced ultraviolet avalanche photodiode based on a grating superlens proposed in this invention integrates a layer of fully transparent dielectric material into a grating superlens. The surface of this grating superlens is etched into a nanograting structure with a specific geometric arrangement, such as a one-dimensional linear chirped grating or a two-dimensional square nanopillar array grating. By designing the nanograting structure, when plane-wave ultraviolet light is incident, the beam can be focused to a predetermined position within the semiconductor active region located at its focal plane through diffraction. The grating superlens designed in this invention brings the following unexpected technical effects: Increased effective light flux: This grating superlens concentrates the light that would otherwise illuminate the entire unit (including the non-photosensitive area) into the photosensitive area, increasing the light flux density per unit area. This effectively improves the device's fill factor and photon collection capability, thereby enhancing the device's response to weak point signals.

[0035] Optimizing the avalanche multiplication process and suppressing noise: By focusing the beam to the center region of the APD's active area, photogenerated carriers can be actively prevented from being multiplied at the device edges or defects where the electric field is unstable, thus ensuring that the avalanche process occurs in the most uniform and stable region. This not only guarantees the stability of the avalanche gain but also fundamentally suppresses excess noise related to edge effects, significantly improving the device's signal-to-noise ratio.

[0036] In summary, this invention creatively combines technologies from two different fields—superlens focusing and APD avalanche multiplication—by integrating a grating superlens. This not only allows more photons to be introduced into the device but also more accurately directs photons into the active region, improving the stability of avalanche multiplication, successfully enhancing responsivity and signal-to-noise ratio, and solving the noise optimization problem that cannot be addressed by simple anti-reflection or light-trapping schemes. This achieves a simultaneous improvement in the device's optoelectronic performance and signal quality.

[0037] Secondly, please see Figure 4 This invention provides a method for fabricating an enhanced ultraviolet avalanche photodiode based on a grating superlens, used to fabricate any of the enhanced ultraviolet avalanche photodiodes based on a grating superlens described in the first aspect. The corresponding fabrication method includes: S10. Obtain an N-type SiC substrate, and sequentially grow an N-type drift layer, a P-type region, and a P+ contact layer on the N-type SiC substrate.

[0038] In this embodiment of the invention, an N-type SiC substrate 101 is obtained. An active region of an avalanche photodiode with a pin structure composed of SiC is formed on the N-type SiC substrate 101 using epitaxial growth technology. Ion implantation, annealing, and etching processes are then performed to sequentially form an N-type drift layer 102, a P-type region 103, and a P+ contact layer 104 from bottom to top, as shown in Figure 5(a). That is, the N-type drift layer 102, P-type region 103, and P+ contact layer 104 are all SiC, but with different doping types and concentrations. For example, the thickness of the N-type drift layer 102, P-type region 103, and P+ contact layer 104 is 0.4 mm, and the doping concentration is 5e⁻¹. 18 cm -3 5e 17 cm -3 3e 15 cm -3 5e 18 cm -3 .

[0039] S20. A grating superlens structure is grown on the P+ contact layer to focus incident ultraviolet parallel light into the P-type region through the grating superlens structure; wherein, the grating superlens structure is a transparent dielectric material; from the top view, the grating superlens structure is a one-dimensional linear chirped grating or a two-dimensional square nanopillar array grating.

[0040] In this embodiment of the invention, an atomic layer deposition (ALD) technique is used to grow a high-purity, high-transparency transparent dielectric material on the P+ contact layer 104, as shown in Figure 5(b). This transparent dielectric material can be at least one of silicon nitride (Si3N4), titanium dioxide (TiO2), hafnium dioxide (HfO2), aluminum oxide (Al2O3), or silicon dioxide (SiO2). The deposition thickness needs to meet the grating height of the grating superlens structure 105, such as 350 nm or 500 nm. The ALD process used in this embodiment of the invention enables atomic-level thickness control and high step coverage, ensuring film uniformity and density.

[0041] In this embodiment of the invention, electron beam lithography (EBL) or extreme ultraviolet lithography (EUVL) is used to define a diffraction grating pattern 106 on a transparent dielectric material, as shown in Figure 5(c). The diffraction grating pattern 106 can be a one-dimensional linear chirped grating or a two-dimensional nanopillar array grating, depending on the design requirements. During the patterning of a one-dimensional linear chirped grating, the grating height, grating duty cycle, and grating linewidth must be strictly controlled. During the patterning of a two-dimensional square nanopillar array grating, the grating height, grating period, and the side length of the nanopillars must be strictly controlled to ensure its focusing performance.

[0042] This invention employs reactive ion etching (RIE) or inductively coupled plasma etching (ICP) techniques to transfer the diffraction grating pattern 106 on the photoresist into a transparent dielectric material, forming a grating superlens structure 105 as shown in Figure 5(d). The etching gas can be selected according to the transparent dielectric material, such as CF4 / Ar for Si3N4 or Al2O3, and Cl2 / BCl3 for TiO2. After etching, the grating sidewalls must be as steep as possible and the surface smooth to minimize optical scattering loss. For example, in this embodiment, the sidewall tilt angle is greater than 85°; the larger the tilt angle, the smaller the optical scattering loss.

[0043] In this embodiment of the invention, oxygen plasma or wet cleaning is used to remove residual photoresist and etching byproducts. Finally, annealing is performed to repair surface damage that may have been introduced during the etching process, thereby improving the optical quality of the transparent dielectric material.

[0044] S30. A passivation layer is grown on the grating superlens structure.

[0045] In this embodiment of the invention, a passivation layer 109 with a thickness of, for example, 40 nm is grown on the grating superlens structure 105 using PECVD (Plasma-Enhanced Chemical Vapor Deposition) technology, as shown in Figure 5(e), to protect the device structure and improve environmental stability. The passivation layer material can be, for example, SiO2 or Si3N4.

[0046] S40. Etch the passivation layer near both ends of the device until the upper surface of the P+ contact layer, forming two upper electrodes on the exposed P+ contact layer.

[0047] In this embodiment of the invention, the passivation layer near both ends of the device is etched using RIE or ICP etching technology until the upper surface of the P+ contact layer 104 is reached. Then, Ni / Ti / Al is deposited on the exposed P+ contact layer 104 using electron beam evaporation technology to form two upper electrodes 107 as shown in Figure 5(f).

[0048] S50. A lower electrode is formed on the lower surface of an N-type SiC substrate.

[0049] In this embodiment of the invention, electron beam evaporation technology is used to deposit Ni as the lower electrode 108 on the lower surface of an N-type SiC substrate 101, as shown in Figure 5(g).

[0050] As for the second aspect of the preparation method embodiment, since it is basically similar to the first aspect of the device structure embodiment, the description is relatively simple. For relevant details, please refer to the description of the first aspect of the device structure embodiment.

[0051] In the description of this invention, it should be understood that 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. Therefore, a feature defined as "first" or "second" may explicitly or implicitly include one or more of that feature. In the description of this invention, "a plurality of" means two or more, unless otherwise explicitly specified.

[0052] Although the invention has been described herein in conjunction with various embodiments, those skilled in the art, by reviewing the specification and accompanying drawings, will understand and implement other variations of the disclosed embodiments in carrying out the claimed invention. In the specification, the word "comprising" does not exclude other components or steps, and "a" or "an" does not exclude a plurality. While certain measures are described in different embodiments, this does not mean that these measures cannot be combined to produce good results.

[0053] The above description, in conjunction with specific preferred embodiments, provides a further detailed explanation of the present invention. It should not be construed that the specific implementation of the present invention is limited to these descriptions. For those skilled in the art, various simple deductions or substitutions can be made without departing from the concept of the present invention, and all such modifications and substitutions should be considered within the scope of protection of the present invention.

Claims

1. An enhanced ultraviolet avalanche photodiode based on a grating superlens, characterized in that, The enhanced ultraviolet avalanche photodiode includes: An N-type SiC substrate, and an N-type drift layer, a P-type region, and a P+ contact layer sequentially located on the upper surface of the N-type SiC substrate; A grating superlens structure is located on the P+ contact layer to focus incident ultraviolet parallel light into a P-type region; wherein, the grating superlens structure is a transparent dielectric material; from the top view, the grating superlens structure appears as a one-dimensional linear chirped grating or a two-dimensional square nanopillar array grating. The passivation layer is located on the grating superlens structure; Two upper electrodes penetrate the passivation layer and grating superlens structure near both ends of the device and are located on the P+ contact layer; The lower electrode is located on the lower surface of the N-type SiC substrate.

2. The enhanced ultraviolet avalanche photodiode based on a grating superlens according to claim 1, characterized in that, The transparent dielectric material includes at least one of silicon nitride, titanium dioxide, hafnium dioxide, aluminum oxide, or silicon dioxide.

3. The enhanced ultraviolet avalanche photodiode based on a grating superlens according to claim 1, characterized in that, When the grating superlens structure is a one-dimensional linear chirped grating, the grating height, grating duty cycle, and grating linewidth of the grating superlens structure are designed according to the total aperture of the lens in the grating superlens structure, so as to focus the incident ultraviolet parallel light into the P-type region through the grating superlens structure.

4. The enhanced ultraviolet avalanche photodiode based on a grating superlens according to claim 3, characterized in that, When the grating superlens structure is a one-dimensional linear chirped grating, the grating height is designed to be greater than the wavelength of the incident ultraviolet parallel light, based on the total aperture of the lens in the grating superlens structure. The grating duty cycle remains unchanged, and the grating linewidth gradually narrows from the center to the edge of the grating superlens.

5. The enhanced ultraviolet avalanche photodiode based on a grating superlens according to claim 4, characterized in that, The total aperture of the grating superlens structure is 15μm×15μm, the wavelength of the incident ultraviolet parallel light is 280nm, the grating height is designed to be 350nm, the grating duty cycle is 50%, the grating linewidth at the center of the grating superlens is 220nm, and the grating linewidth at the edge of the grating superlens is 170nm, so that the incident ultraviolet parallel light can be focused into a P-type region at a depth of 1.2μm through the grating superlens structure.

6. The enhanced ultraviolet avalanche photodiode based on a grating superlens according to claim 1, characterized in that, When the grating superlens structure is a two-dimensional square nanopillar array grating, the grating height, grating period, and side length of the nanopillars of the grating superlens structure are designed according to the total aperture of the lens in the grating superlens structure, so as to focus the incident ultraviolet parallel light into the P-type region through the grating superlens structure.

7. The enhanced ultraviolet avalanche photodiode based on a grating superlens according to claim 6, characterized in that, When the grating superlens structure is a two-dimensional square nanopillar array grating, the grating height is designed to be greater than the wavelength of the incident ultraviolet parallel light, based on the total aperture of the lens in the grating superlens structure. The grating period remains unchanged, and the side length of the nanopillars gradually decreases from the center to the edge of the grating superlens.

8. The enhanced ultraviolet avalanche photodiode based on a grating superlens according to claim 7, characterized in that, The total aperture of the grating superlens structure is 20μm×20μm, the wavelength of the incident ultraviolet parallel light is 360nm, the grating height is designed to be 500nm, the grating period is 250nm, the side length of the nanopillar at the center of the grating superlens is 180nm, and the side length of the nanopillar at the edge of the grating superlens is 80nm, so that the incident ultraviolet parallel light can be focused into a P-type region at a depth of 1.5μm through the grating superlens structure.

9. A method for fabricating an enhanced ultraviolet avalanche photodiode based on a grating superlens, characterized in that, The method for fabricating the enhanced ultraviolet avalanche photodiode based on a grating superlens as described in any one of claims 1 to 8 includes: An N-type SiC substrate was obtained, and an N-type drift layer, a P-type region, and a P+ contact layer were sequentially grown on the N-type SiC substrate. A grating superlens structure is grown on the P+ contact layer to focus incident ultraviolet parallel light into the P-type region; wherein, the grating superlens structure is a transparent dielectric material; from the top view, the grating superlens structure appears as a one-dimensional linear chirped grating or a two-dimensional square nanopillar array grating. A passivation layer is grown on the grating superlens structure; Etch the passivation layer near both ends of the device down to the upper surface of the P+ contact layer to form two upper electrodes on the exposed P+ contact layer. A lower electrode is formed on the lower surface of an N-type SiC substrate.

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