Back-incident high-speed photodetector based on sub-wavelength artificial microstructures

Abstract

The application relates to the technical field of optoelectronic design, in particular to a back-incident high-speed photodetector based on a subwavelength artificial microstructure, which comprises, from bottom to top, a polarization-independent super lens integrated on the back of a substrate, an indium phosphide substrate layer, an N-type epitaxial layer, a first annular metal electrode formed on an N-type ohmic contact, an intrinsic absorption layer, a P-type epitaxial layer, a second annular metal electrode formed on a P-type contact, a grating oxide layer and a high-contrast subwavelength grating layer integrated on the top of the substrate. Therefore, the contradiction between the response and the bandwidth of a traditional photodetector is solved.

Description

Technical Field

[0001] This invention relates to the field of optoelectronic design technology, and in particular to a back-incident high-speed photodetector based on a subwavelength artificial microstructure. Background Technology

[0002] Integrated optoelectronics technology has ushered in the era of digital communication, which relies on high-speed transmission, ultra-high bandwidth, and low interference. With the explosive growth of data, photodetectors, as a core component of information transmission and processing, are an indispensable link in integrated optoelectronic links. As mobile communication systems continue to evolve towards higher frequencies and wider bandwidths, these systems place higher demands on device performance. Therefore, high-performance photodetectors play a crucial role, requiring several superior characteristics, including high responsivity, low dark current, and large bandwidth.

[0003] Mesa-type photodetectors offer advantages such as good saturation performance and simple fabrication. Based on the incident light direction, mesa-type photodetectors can be divided into top-incident and back-incident types. In the back-incident structure, when light enters from the back of the device, it is reflected by the metal electrodes, passing through the absorption region twice. This improves responsivity without introducing complex structures (such as multi-layer Bragg reflectors, Distributed Bragg Reflectors, DBRs). Simultaneously, the photosensitive area in back-incident is located at the bottom, allowing heat to dissipate more easily to the surrounding environment, resulting in better stability and anti-interference capabilities. However, regardless of the incident direction, traditional PIN photodetectors still face the limitation of not being able to simultaneously improve responsivity and bandwidth. Since a thinner intrinsic region results in a shorter carrier transit time, and transit time directly affects the device's bandwidth, a larger bandwidth requires a smaller intrinsic region thickness, which inevitably leads to fewer absorbed photons and a lower responsivity. Therefore, traditional PIN photodetectors have a trade-off between responsivity and bandwidth.

[0004] To overcome the trade-offs, researchers have attempted to improve the coupling efficiency of small-sized, high-bandwidth photodetectors by fabricating microlenses on the back of the substrate. Microlens arrays are typically three-dimensional structures, usually formed by melting photoresist into a spherical shape using a hot-melt reflow method. This method, employing inductively coupled plasma etching (ICP), requires strict control over the etching ratio to 1, and the lenses are relatively thick, typically tens of micrometers, making integration difficult and the fabrication process complex.

[0005] On the other hand, current back-incidence photodetectors use a top P-electrode as a reflector to perform secondary reflection of light. This top P-electrode is typically made of titanium / platinum / gold (Ti / Pt / Au). The first layer of titanium is crucial for forming an ohmic contact; however, titanium has certain absorption losses, resulting in a reflectivity of approximately 65.9%. Furthermore, excessively thin or thick titanium layers increase contact resistivity. Therefore, the reflectivity of metal electrodes with good ohmic contacts is usually between 30% and 60%, further limiting the high responsivity of the device. To increase top reflectivity, various methods have been employed in surface-emitting lasers. The earliest approach was to use a multilayer DBR structure for high reflectivity, but this placed high demands on the epitaxial structure. Therefore, researchers proposed a subwavelength grating surrounded by low refractive indices, approximately several hundred nanometers thick, which exhibits high reflectivity over a wide bandwidth. However, the low-refractive-index region beneath the high-reflectivity grating is an air gap, requiring the fabrication of a suspended grating. This lack of structural support results in poor mechanical stability, limiting further semiconductor fabrication.

[0006] Therefore, there is an urgent need for a new type of back-incident photodetector to break the constraints. Summary of the Invention

[0007] This invention provides a back-incidence high-speed photodetector based on a subwavelength artificial microstructure to solve the trade-off between bandwidth and responsivity.

[0008] A first aspect of the present invention provides a back-incident high-speed photodetector based on a subwavelength artificial microstructure, comprising: a polarization-independent metalens integrated on the back side of a substrate, an indium phosphide substrate layer, an N-type epitaxial layer, a first annular metal electrode formed on an N-type ohmic contact, an intrinsic absorption layer, a P-type epitaxial layer, a second annular metal electrode formed on a P-type contact, a grating oxide layer, and a high contrast subwavelength grating (HCG) layer, formed sequentially from bottom to top.

[0009] Optionally, the polarization-independent metalens is composed of multiple InP cylindrical nanopillars of equal height and different radii, wherein the multiple InP cylindrical nanopillars of equal height and different radii are integrated and arranged on the indium phosphide substrate.

[0010] Optionally, the phase distribution of the plurality of InP cylindrical nanopillars of equal height and different radii satisfies:

[0011]

[0012] Where φ(x,y) is the phase distribution, x is the abscissa of each nanopillar on the polarization-independent metalens, y is the ordinate of each nanopillar, λ is the working wavelength, f is the theoretical focal length of the lens design, and φ0 is the initial phase.

[0013] Optionally, the polarization-independent meta-lens has a focal length of 110 μm, a radius of 60 μm, and a numerical aperture (NA) of 0.968.

[0014] Optionally, the initial epitaxial material of the grating oxide layer is indium aluminum arsenide, which is converted into aluminum oxide after wet heat oxidation.

[0015] Optionally, the high-contrast diaphragm layer includes a one-dimensional oxide high-contrast grating, a ring-shaped high-contrast grating, and a two-dimensional oxide high-contrast grating.

[0016] Optionally, the spacer material used below the high-contrast, low-wavelength grating layer is indium aluminum arsenide, which is oxidized in an oxidation furnace to form a low-refractive-index oxide spacer layer.

[0017] A second aspect of this invention provides a method for fabricating a back-incident high-speed photodetector based on a subwavelength artificial microstructure, comprising the following steps:

[0018] Prepare an epitaxial layer wafer and clean the epitaxial layer wafer, wherein the epitaxial layer wafer includes a top grating region, an oxide region P+ region, an absorption region, a depletion region and an N+ region;

[0019] After electron beam exposure, the cleaned epitaxial wafer is subjected to the first ICP etching, which is performed down to the oxide stop layer to obtain the first device with a high-contrast low-wavelength grating.

[0020] The P-mesa and N-mesa are photolithographically etched onto the first device to obtain the second device;

[0021] The oxide stop layer is subjected to a wet oxidation process. The second device is placed in a mixture of water vapor and N2 gas and oxidized at 60 mbar pressure and 525°C for 1 hour. The water vapor flows through the gap of the high-diameter grating and oxidizes the oxide isolation layer, generating low-refractive-index Al2O3 below the high-diameter grating.

[0022] A P-electrode pattern and an N-electrode pattern are photolithographically etched onto the second device, and a P-electrode and an N-electrode are sputtered using a magnetron sputtering device to obtain a third device;

[0023] The third device is thinned and polished, and the thinned and polished part is then inverted and attached to the sapphire substrate.

[0024] A polarization-independent metalens pattern is exposed on the back side of the sapphire substrate by electron beam exposure, and then ICP etching is performed to integrate the polarization-independent metalens pattern on the back side of a preset substrate to obtain a fourth device.

[0025] The sapphire substrate of the fourth device is peeled off to obtain a back-incident high-speed photodetector.

[0026] The back-incidence high-speed photodetector based on subwavelength artificial microstructures proposed in this invention solves the contradiction between responsivity and bandwidth in traditional photodetectors by utilizing subwavelength artificial microstructures integrated on the back and top of the substrate. It has high efficiency and high speed. At the same time, the thickness of the designed microstructures is less than 1 μm, which has the characteristics of small size, easy integration, polarization independence, and simple process, and has high practical value.

[0027] Additional aspects and advantages of the invention will be set forth in part in the description which follows, and in part will be obvious from the description, or may be learned by practice of the invention. Attached Figure Description

[0028] The above and / or additional aspects and advantages of the present invention will become apparent and readily understood from the following description of the embodiments taken in conjunction with the accompanying drawings, wherein:

[0029] Figure 1 This is a schematic diagram of a back-incidence high-speed photodetector based on a subwavelength artificial microstructure provided in an embodiment of the present invention.

[0030] Figure 2 This is a structural diagram of a single InP nanopillar provided in an embodiment of the present invention;

[0031] Figure 3 This is a top view of the polarization-independent metalens provided in an embodiment of the present invention;

[0032] Figure 4 This is a schematic diagram of the transverse and longitudinal field distribution after the metasurface modulates the incident light according to an embodiment of the present invention, wherein (a) is a simulated normalized longitudinal intensity distribution diagram, (b) is a normalized transverse distribution field at the focal point, and (c) is the full width at half maximum (FWHM) at the focal point.

[0033] Figure 5 The diagram shows the structure of the high contrast low wavelength grating layer provided in the embodiment of the present invention, wherein (a) is a schematic diagram of an oxide high contrast grating, (b) is a top view of a one-dimensional oxide high contrast grating, and (c) is a top view of an annular high contrast grating.

[0034] Figure 6 The high-contrast, low-wavelength grating layer provided in this embodiment of the invention exhibits grating reflectivity at different wavelengths and different duty cycles;

[0035] Figure 7 The HCG reflectance over 10 cycles is simulated using a high-contrast, low-wavelength grating layer with a duty cycle of 0.55, as provided in this embodiment of the invention.

[0036] Figure 8This is a flowchart illustrating the fabrication method of a back-incident high-speed photodetector based on a subwavelength artificial microstructure, as provided in an embodiment of the present invention.

[0037] Explanation of reference numerals in the attached figures:

[0038] 1-Polarization-independent metalens, 2-Indium phosphide substrate, 3-N-type epitaxial layer, 4-First annular metal electrode, 5-Intrinsic absorption layer, 6-P-type epitaxial layer, 7-Second annular metal electrode, 8-Grate oxide layer, 9-High-contrast-di-wavelength grating layer and 10-Unoxidized indium aluminum arsenide layer. Detailed Implementation

[0039] Embodiments of the present invention are described in detail below, examples of which are illustrated 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 intended to explain the present invention, and should not be construed as limiting the present invention.

[0040] The following describes an embodiment of the present invention, a high-speed back-incidence photodetector based on a subwavelength artificial microstructure, with reference to the accompanying drawings.

[0041] Figure 1 This is a flowchart of a back-incident high-speed photodetector based on a subwavelength artificial microstructure proposed in an embodiment of the present invention.

[0042] like Figure 1 As shown, this back-incident high-speed photodetector based on subwavelength artificial microstructures includes: a polarization-independent metalens 1, an indium phosphide substrate 2, an N-type epitaxial layer 3, a first annular metal electrode 4, an intrinsic absorption layer 5, a P-type epitaxial layer 6, a second annular metal electrode 7, a grating oxide layer 8, and a high-contrast subwavelength grating layer 9. This back-incident high-speed photodetector integrates subwavelength micro / nano structures at the bottom and top, increasing both the optical coupling efficiency and the reflectivity of the incident light. This reconciles the trade-off between responsivity and bandwidth, and the detector is simple to fabricate, has high tolerance, high efficiency, and is easy to integrate.

[0043] The back-incident high-speed photodetector 100 based on a subwavelength artificial microstructure comprises, from bottom to top, a polarization-independent metalens 1, an indium phosphide substrate layer 2, an N-type epitaxial layer 3, a first annular metal electrode 4 formed on an N-type ohmic contact, an intrinsic absorption layer 5, a P-type epitaxial layer 6, a second annular metal electrode 7 formed on a P-type contact, a grating oxide layer 8, and a high-contrast subwavelength grating layer 9 integrated on the back side of the substrate. The polarization-independent metalens 1 and the high-contrast subwavelength grating layer 9 are both composed of indium phosphide material integrated above and below the device, collectively constituting the back-incident high-speed photodetector 100. The initial epitaxial material of the grating oxide layer 8 is indium aluminum arsenide (In4α) lattice-matched to indium phosphide. 0.52Al 0.48 As), after being subjected to wet heat oxidation, it becomes aluminum oxide 8 with a refractive index of 1.78.

[0044] In some embodiments, such as Figure 2 and 3 As shown, the bottom subwavelength polarization-independent metalens 1 is a dielectric metasurface. A metasurface is a functional film device based on a subwavelength structure. It mainly consists of subwavelength unit structures that interact with electromagnetic waves. By changing the geometric parameters, rotation angles, and arrangement of the microstructures, the polarization state, phase, amplitude, and spectral information of light can be controlled. This embodiment of the invention proposes a polarization-independent metalens with a focal length of 110 μm, a radius of 60 μm, and a numerical aperture (NA) of 0.968. This polarization-independent metalens is composed of multiple InP cylindrical nanopillars of equal height and different radii. By changing the corresponding radii, they are integrated and arranged on an indium phosphide substrate to form a metalens. Each metalens has several thousand nanopillar units.

[0045] It should be noted that, Figure 2 In this context, D represents the diameter of the nanopillar, and P... x P y The periods are 750 nm in the x and y directions, respectively, and H is the height of the nanopillar, which is 800 nm.

[0046] In some embodiments, starting with the desired optical field, the incident optical field is modulated using the transmission phase principle. Multiple InP cylindrical nanopillars of equal height and different radii exhibit the following focusing phase distribution:

[0047]

[0048] Wherein, φ(x,y) is the phase distribution, x is the abscissa of each nanopillar on the polarization-independent metalens, y is the ordinate of each nanopillar, λ is the working wavelength, the working wavelength of this embodiment is 1550nm, f is the theoretical focal length of the lens design, and φ0 is the initial phase.

[0049] It should be noted that the phase library selected in this embodiment is based on 49 screened InP nanocircular structures. The transmittance of these InP nanocircular structures is maintained above 90%. As basic building elements, their phase distribution covers 0 to 2π, which can be used to control diffraction at each level.

[0050] like Figure 4As shown, the transverse and longitudinal field distributions of the polarization-independent metalens surface after the incident light is modulated are displayed. (a) is the simulated normalized longitudinal intensity distribution diagram, which shows that the incident light converges at 110 μm to form a relatively clear focal spot. (b) is the normalized transverse distribution field at the focal point. (c) is the full width at half maximum (FWHM) at the focal point.

[0051] As can be seen, the light converges in the intrinsic absorption layer 5, which enhances the device's light absorption capability and improves the device's responsivity without sacrificing transit time bandwidth. According to Mie scattering theory, surface microstructures can reduce the reflection of incident light. The designed polarization-independent metalens 1 has unit nanopillars with dimensions on the subwavelength order, smaller than the incident light wavelength. Therefore, the equivalent refractive index of the microstructure can be considered to be gradually changing, thereby achieving the purpose of reducing reflection.

[0052] It should be noted that the surface of the bottom polarization-independent metalens 1 provided in this embodiment is not unique, and the working wavelength is not limited to 1550nm. Any one-dimensional or two-dimensional subwavelength structure or microlens integrated at the bottom of the detector can be used. Those skilled in the art can choose according to the actual situation, which will not be specifically described here.

[0053] In some embodiments, for the top high-reflectivity structure, to further enhance absorption by secondary reflection of incident light at the top, a high-reflectivity oxide subwavelength grating (i.e., a high-contrast subwavelength grating layer) is designed, with the specific structure as follows: Figure 5 As shown in (a), unlike the use of selective etchants to remove the layer beneath HCG to create an air spacer layer, the spacer layer material used beneath HCG is indium aluminum arsenide (In). 0.52 Al 0.48 As), is oxidized in an oxidation furnace to form a low-refractive-index oxide spacer layer. This technique can obtain gratings with high reflectivity using a relatively simple oxidation step, increasing the flexibility of HCG process design. Figure 5 As shown in (b) and (c), the top grating layer in the figure can be one-dimensional (i.e., one-dimensional oxide high-contrast grating), annular (i.e., annular high-contrast grating), or two-dimensional. Since the grating is surrounded by low-refractive-index materials (the upper air layer has a refractive index of 1, the lower oxide layer has a refractive index of 1.78, and the indium phosphide grating layer has a refractive index of 3.17), a high-contrast sub-wavelength grating integrated on the surface of the device can be obtained. By utilizing the high reflectivity of the grating, a high reflectivity can be obtained in a wide wavelength range.

[0054] The design scheme presented in this embodiment has an oxide layer thickness of 150 nm and a grating layer thickness of 460 nm. The thicknesses of the oxide layer and the grating layer can be adjusted as needed. Figure 6The grating reflectivity at different wavelengths and duty cycles is presented, showing that it has a broadband reflectivity between 0.5 and 0.7 duty cycles. Figure 7 The subwavelength grating reflectivity over 10 cycles with a duty cycle of 0.55 was simulated. It can be seen that the structure has a high reflectivity of over 90% in the 1400nm to 1660nm band, which efficiently reflects incident light and enhances light absorption and improves device responsivity without increasing the thickness of the intrinsic absorption region.

[0055] It should be noted that the high contrast medium wavelength grating HCG given in this embodiment is not unique. Any one-dimensional or two-dimensional grating structure with high reflectivity can be used. Those skilled in the art can choose according to the actual situation, and it will not be specifically described here.

[0056] In summary, the back-incidence high-speed photodetector based on subwavelength artificial microstructures proposed in this invention has the following beneficial effects:

[0057] For the bottom metasurface:

[0058] By employing the concept of phase transmission and utilizing metasurface design, a metalens integrated on the back side of a substrate was realized. This design features a high numerical aperture and high focusing efficiency, converging incident light onto the absorption layer. This largely solves the limitations of responsivity and bandwidth in mesa-type photodetectors, enabling high-speed, high-responsivity photodetectors. It is polarization-independent, allowing for incident light of any polarization. Using InP-based materials, it can be directly integrated on the back side of the substrate. Compared to existing bonded gratings or bonded metasurface structures, it offers advantages such as good thermal conductivity and reduced device damage. The metalens unit structure is made of all-dielectric materials, resulting in low loss and transmittance exceeding 90%. The surface microstructure reduces incident light reflection, eliminating the need for secondary anti-reflection coating deposition.

[0059] For the top subwavelength grating:

[0060] Compared to traditional metal electrodes which suffer from significant optical loss, this device utilizes an oxide subwavelength grating to achieve a high reflectivity of over 90% in the 1400nm–1660nm wavelength range. This allows for greater light absorption within the absorption region without sacrificing transit time bandwidth. Furthermore, its thickness is only a few hundred nanometers, resulting in high integration.

[0061] Next, referring to the accompanying drawings, a method for fabricating a back-incidence high-speed photodetector based on a subwavelength artificial microstructure according to an embodiment of the present invention is described.

[0062] Figure 8 This is a schematic flowchart illustrating a method for fabricating a back-incident high-speed photodetector based on a subwavelength artificial microstructure, as provided in an embodiment of the present invention.

[0063] like Figure 8 As shown, the fabrication method of this back-incident high-speed photodetector based on subwavelength artificial microstructures includes the following steps:

[0064] In step S801, an epitaxial wafer is prepared and cleaned. The epitaxial wafer includes a top grating region, an oxide P+ region, an absorption region, a depletion region, and an N+ region.

[0065] In step S802, after electron beam exposure, the cleaned epitaxial wafer is subjected to the first ICP etching, which is performed down to the oxide stop layer to obtain the first device with a high-contrast low-wavelength grating.

[0066] In step S803, P-mesa and N-mesa are photolithographically etched on the first device to obtain the second device.

[0067] In step S804, a wet oxidation process is performed on the oxide stop layer. The second device is placed in a mixture of water vapor and N2 gas and oxidized at 60 mbar pressure and 525°C for 1 hour. Water vapor flows through the gap of the high-diameter grating and oxidizes the oxide isolation layer, generating low-refractive-index Al2O3 below the high-diameter grating.

[0068] In step S805, P electrode patterns and N electrode patterns are photolithographically patterned on the second device, and P electrode and N electrode are sputtered using a magnetron sputtering device to obtain the third device.

[0069] It should be noted that, for ease of subsequent use, after this step, the third device needs to be passivated and filled with SiO2, the electrode window is opened, and the P and N electrodes are led out by sputtering coplanar waveguides, followed by electroplating to thicken the electrode.

[0070] In step S806, the third device is thinned and polished, and the thinned and polished part is then inverted and attached to the sapphire substrate.

[0071] In step S807, a polarization-independent metalens pattern is electron-beam exposed on the back side of the sapphire substrate, and ICP etching is performed to integrate the polarization-independent metalens pattern on the back side of the preset substrate to obtain the fourth device.

[0072] In step S808, the sapphire substrate of the fourth device is peeled off to obtain a back-incident high-speed photodetector.

[0073] The fabrication method of the back-incidence high-speed photodetector based on subwavelength artificial microstructure proposed in the embodiments of the present invention has the following beneficial effects:

[0074] For the bottom metasurface:

[0075] By employing the concept of phase transmission and utilizing metasurface design, a metalens integrated on the back side of a substrate was realized. This design features a high numerical aperture and high focusing efficiency, converging incident light onto the absorption layer. This largely solves the limitations of responsivity and bandwidth in mesa-type photodetectors, enabling high-speed, high-responsivity photodetectors. It is polarization-independent, allowing for incident light of any polarization. Using InP-based materials, it can be directly integrated on the back side of the substrate. Compared to existing bonded gratings or bonded metasurface structures, it offers advantages such as good thermal conductivity and reduced device damage. The metalens unit structure is made of all-dielectric materials, resulting in low loss and transmittance exceeding 90%. The surface microstructure reduces incident light reflection, eliminating the need for secondary anti-reflection coating deposition.

[0076] For the top subwavelength grating:

[0077] Compared to traditional metal electrodes which suffer from significant optical loss, this device utilizes an oxide subwavelength grating to achieve a high reflectivity of over 90% in the 1400nm–1660nm wavelength range. This allows for greater light absorption within the absorption region without sacrificing transit time bandwidth. Furthermore, its thickness is only a few hundred nanometers, resulting in high integration.

[0078] In the description of this specification, the references to terms such as "one embodiment," "some embodiments," "example," "specific example," or "some examples," etc., refer to specific features, structures, materials, or characteristics described in connection with that embodiment or example, which are 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.

[0079] 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 invention, "N" means at least two, such as two, three, etc., unless otherwise explicitly specified.

Claims

1. A back-incidence high-speed photodetector based on a subwavelength artificial microstructure, characterized in that, include: The polarization-independent meta-lens integrated on the back side of the substrate from bottom to top consists of an indium phosphide substrate layer, an N-type epitaxial layer, a first annular metal electrode formed on an N-type ohmic contact, an intrinsic absorption layer, a P-type epitaxial layer, a second annular metal electrode formed on a P-type contact, a grating oxide layer, and a high-contrast, low-wavelength grating layer.

2. The high-speed back-incidence photodetector based on subwavelength artificial microstructures according to claim 1, characterized in that, The polarization-independent metalens is composed of multiple InP cylindrical nanopillars of equal height and different radii, wherein the multiple InP cylindrical nanopillars of equal height and different radii are integrated and arranged on the indium phosphide substrate.

3. The high-speed back-incidence photodetector based on subwavelength artificial microstructures according to claim 2, characterized in that, The phase distribution of the multiple InP cylindrical nanopillars of equal height and different radii satisfies: Where φ(x,y) is the phase distribution, x is the abscissa of each nanopillar on the polarization-independent metalens, y is the ordinate of each nanopillar, λ is the working wavelength, f is the theoretical focal length of the lens design, and φ0 is the initial phase.

4. The high-speed back-incidence photodetector based on subwavelength artificial microstructures according to claim 2, characterized in that, The polarization-independent meta-lens has a focal length of 110 μm, a radius of 60 μm, and a numerical aperture (NA) of 0.

968.

5. The high-speed back-incidence photodetector based on subwavelength artificial microstructures according to claim 1, characterized in that, The initial epitaxial material of the grating oxide layer is indium aluminum arsenide, which becomes aluminum oxide after wet heat oxidation.

6. The high-speed back-incidence photodetector based on subwavelength artificial microstructures according to claim 1, characterized in that, The high-contrast diaphragm layer includes a one-dimensional oxide high-contrast grating, a ring-shaped high-contrast grating, and a two-dimensional oxide high-contrast grating.

7. The high-speed back-incidence photodetector based on subwavelength artificial microstructures according to claim 6, characterized in that, The spacer layer material used below the high-contrast, low-wavelength grating layer is indium aluminum arsenide, which is oxidized in an oxidation furnace to form a low-refractive-index oxide spacer layer.

8. A method for fabricating a back-incident high-speed photodetector based on a subwavelength artificial microstructure, characterized in that, Includes the following steps: Prepare an epitaxial layer wafer and clean the epitaxial layer wafer, wherein the epitaxial layer wafer includes a top grating region, an oxide region P+ region, an absorption region, a depletion region and an N+ region; After electron beam exposure, the cleaned epitaxial wafer is subjected to the first ICP etching, which is performed down to the oxide stop layer to obtain the first device with a high-contrast low-wavelength grating. The P-mesa and N-mesa are photolithographically etched onto the first device to obtain the second device; The oxide stop layer is subjected to a wet oxidation process. The second device is placed in a mixture of water vapor and N2 gas and oxidized at 60 mbar pressure and 525°C for 1 hour. The water vapor flows through the gap of the high-diameter grating and oxidizes the oxide isolation layer, generating low-refractive-index Al2O3 below the high-diameter grating. A P-electrode pattern and an N-electrode pattern are photolithographically etched onto the second device, and a P-electrode and an N-electrode are sputtered using a magnetron sputtering device to obtain a third device; The third device is thinned and polished, and the thinned and polished part is then inverted and attached to the sapphire substrate. A polarization-independent metalens pattern is exposed on the back side of the sapphire substrate by electron beam exposure, and then ICP etching is performed to integrate the polarization-independent metalens pattern on the back side of a preset substrate to obtain a fourth device. The sapphire substrate of the fourth device is peeled off to obtain a back-incident high-speed photodetector.

Images