ROF photodiode, manufacturing method thereof and optical receiver

Abstract

The embodiment of the invention provides an ROF photodiode, a manufacturing method thereof and an optical receiver, and belongs to the technical field of photoelectric detection. The ROF photodiode comprises: a wafer substrate; the intrinsic absorption layer is arranged on the upper surface of the wafer substrate; the light-transmitting flat layer is arranged outside the intrinsic absorption layer in a covering manner, and one surface of the light-transmitting flat layer, which is used for receiving the Gaussian light emitted into the ROF photodiode by the optical fiber, is provided with a flat surface; the micro lens is arranged on the flat surface of the light-transmitting flat layer, and the center of the micro lens is aligned with the center of Gaussian light emitted by the optical fiber; gaussian light emitted by the optical fiber is converged after passing through the micro lens, and after the converged Gaussian light passes through the light-transmitting flat layer, the power density peak value is dispersed and weakened, and the converged Gaussian light is converted into flat-topped light to be emitted into the intrinsic absorption layer. According to the ROF photodiode, Gaussian light emitted by the optical fiber is dispersed, weakened and converted into flat-topped light, the electric field suppression effect caused by light power peak value concentration is avoided, the good bandwidth characteristic is guaranteed, and the light response performance is improved.

Description

Technical Field

[0001] The invention belongs to the technical field of photoelectric detection, and in particular relates to a ROF photodiode and a manufacturing method thereof, and an optical receiver. Background Art

[0002] Radio-over-fiber (ROF) technology is a technology that combines wireless communication with optical fiber communication. This technology combines the high bandwidth of optical fiber with the high mobility of wireless communication to achieve long-distance, high-speed, and large-capacity wireless communication. At the same time, the rapid development of large-capacity ROF technology has brought higher challenges to the performance of photodetection diodes. The optical signal after direct modulation of the laser is transmitted through the optical fiber and detected by the ROF photodiode at the receiving end. Since the laser is Gaussian light distribution when it is emitted at the output end of the optical fiber, the optical power density of the Gaussian light beam at the center position is very high. When the optical signal with Gaussian light distribution is incident on the ROF photodiode, a large number of photogenerated carriers will be generated in the absorption zone of the ROF photodiode, and the photogenerated carriers corresponding to the center position are the most. The ultra-high density of photogenerated carriers will weaken the electric field strength, thereby increasing the transition time of the photocarriers, which will seriously reduce the effective bandwidth of the ROF photodiode, thereby affecting its detection performance.

[0003] The existing technology generally weakens the peak intensity of Gaussian light by adjusting the assembly method of the optical fiber and the ROF photodiode. For example, the optical fiber is raised a certain distance away from the ROF photodiode. At this time, the Gaussian light beam first radiates in this distance and then falls on the photosensitive surface of the ROF photodiode, thereby avoiding the problem of the high power density light in the center of the ROF photodiode producing an electric field shielding effect on it and suppressing its signal bandwidth. However, this method will cause part of the Gaussian light to fall outside the photosensitive surface of the ROF photodiode and cannot be effectively absorbed by it, resulting in waste and loss of optical power.

[0004] In view of this, it is necessary to propose a new type of ROF photodiode and a manufacturing method thereof for an optical receiver to solve the above problems. Summary of the invention

[0005] In order to solve at least one aspect of the above-mentioned problems and defects in the prior art, the embodiments of the present invention provide a ROF photodiode and a manufacturing method thereof, and an optical receiver, which disperses and weakens the peak intensity of the Gaussian light beam emitted from the optical fiber at the center position by setting a light-transmitting flat layer and a microlens above the intrinsic absorption layer, thereby converting it into a flat-top light, which is evenly incident on the photosensitive surface of the intrinsic absorption layer, avoiding the electric field suppression effect generated by high-intensity light, improving the detection responsiveness of the ROF photodiode to high-power optical signals and ensuring its good bandwidth characteristics. The technical solution is as follows:

[0006] According to one aspect of the present invention, a ROF photodiode is provided. The ROF photodiode comprises:

[0007] Wafer substrate;

[0008] An intrinsic absorption layer is disposed on the upper surface of the wafer substrate;

[0009] A light-transmitting flat layer, which is covered on the outside of the intrinsic absorption layer and has a flat surface on a side receiving Gaussian light emitted from the optical fiber to the ROF photodiode;

[0010] A micro lens is disposed on the flat surface of the light-transmitting flat layer and the center of the micro lens is aligned with the center of the Gaussian light emitted from the optical fiber;

[0011] Among them, the Gaussian light emitted from the optical fiber is converged after passing through the microlens. After the converged Gaussian light passes through the transparent flat layer, the power density peak is dispersed and weakened and converted into flat-top light to be emitted into the intrinsic absorption layer.

[0012] In some embodiments, the wafer substrate is an SOI wafer substrate, which includes: a base silicon layer with a thickness ranging from 600 to 900 μm and a resistance value ranging from 1 k to 10 kΩ·cm; an insulating silicon oxide layer, which is arranged on the upper surface of the base silicon layer and has a thickness ranging from 1 to 3 μm; and a top silicon layer, which is arranged on the upper surface of the insulating silicon oxide layer and has a thickness ranging from 0.1 to 0.5 μm.

[0013] In some embodiments, the wafer substrate is a high-resistance silicon wafer substrate.

[0014] In some embodiments, the intrinsic absorption layer is a germanium-based photosensitive intrinsic absorption layer, and the thickness of the intrinsic absorption layer in the direction of Gaussian light emitted from the optical fiber is in the range of 0.5 to 2 μm.

[0015] In some embodiments, the thickness of the light-transmitting flat layer in the direction of Gaussian light emitted from the optical fiber is in the range of 5 to 30 μm.

[0016] In some embodiments, the light-transmitting planar layer is made of a light-transmitting material, and the light-transmitting material is any one of polymethyl methacrylate (PMMA), polydimethylsiloxane (PDMS), photoresist, and silicon dioxide.

[0017] In some embodiments, the microlens is a convex lens, which is an aspherical lens; the curvature radius of the microlens ranges from 3 to 8 μm, and the height of the microlens in the direction of Gaussian light emitted from the optical fiber ranges from 5 to 10 μm.

[0018] In some embodiments, the microlenses are made of the same material as the light-transmitting planar layer, which is polymethyl methacrylate (PMMA).

[0019] According to another aspect of the present invention, an optical receiver is provided, in which the ROF photodiode described in the above aspect is arranged to detect and receive a high-speed optical signal with Gaussian distribution emitted from an optical fiber.

[0020] According to another aspect of the present invention, a method for manufacturing a ROF photodiode is provided, for manufacturing the ROF photodiode described in the above aspect. The steps of the manufacturing method include:

[0021] preparing a wafer substrate;

[0022] Forming a P-type heavily doped region or an N-type heavily doped region on the upper surface of the wafer substrate through photolithography, ion implantation and annealing processes;

[0023] Growing a germanium-based intrinsic absorption layer on the P-type heavily doped region or the N-type heavily doped region by selective epitaxial growth;

[0024] By photolithography, ion implantation and annealing processes, a local N-type heavily doped region or a local P-type heavily doped region with a preset doping depth is formed on the upper surface of the intrinsic absorption layer;

[0025] An anti-reflection film of the detection wavelength is covered on the upper surface of the intrinsic absorption layer;

[0026] After the passivation layer is grown and the electrode contact hole is etched, a metal layer is grown to form a first electrode lead metal on the upper surface of the wafer substrate, and a second electrode lead metal is formed on the upper surface of a local N-type heavily doped region or a local P-type heavily doped region of the intrinsic absorption layer;

[0027] A light-transmitting flat layer is grown by metal surrounding the intrinsic absorption layer and the first electrode on the wafer substrate, and a flat surface is formed on one side of the light-transmitting flat layer that receives Gaussian light emitted from the optical fiber into the ROF photodiode;

[0028] A microlens is grown on the flat surface of the light-transmitting flat layer with the central direction of the Gaussian light emitted from the optical fiber as the central axis.

[0029] In some embodiments, the peak doping concentration of the P-type heavily doped region or the N-type heavily doped region is in the range of 5×10 18 ~5×10 20 / cm 3 The intrinsic absorption layer uses an in-situ doping process, and the in-situ doping P-type doping concentration or N-type doping concentration ranges from 1×10 14 ~1×10 17 / cm 3 ; The preset doping depth of the local N-type heavily doped region or the local P-type heavily doped region is in the range of 0.1 to 0.3 μm.

[0030] In some embodiments, the thickness of the light-transmitting flat layer in the direction of Gaussian light emitted from the optical fiber is in the range of 5 to 30 μm.

[0031] In some embodiments, the height of the microlens in the direction of the Gaussian light emitted from the optical fiber is in the range of 5 to 10 μm, and the radius of curvature is in the range of 3 to 8 μm.

[0032] The ROF photodiode and the manufacturing method thereof, and the optical receiver provided by the embodiments of the present invention have at least one or part of the following advantages:

[0033] (1) The ROF photodiode and its manufacturing method, and the optical receiver provided by the embodiments of the present invention provide a light-transmitting flat layer and a microlens above the intrinsic absorption layer to weaken the peak intensity of the Gaussian light beam output from the optical fiber at the center position, thereby avoiding the electric field suppression effect generated by the high-intensity light at the center position of the Gaussian light beam, and ensuring the normal working bandwidth of the ROF photodiode;

[0034] (2) The ROF photodiode and its manufacturing method, and the optical receiver provided by the embodiments of the present invention effectively disperse the Gaussian light beam output from the optical fiber by setting a thick transparent flat layer above the intrinsic absorption layer, so that the Gaussian light is converted into a flat-top light and uniformly incident on the photosensitive surface of the intrinsic absorption layer, thereby improving the detection response of the ROF photodiode to high-power input light and ensuring its good bandwidth characteristics;

[0035] (3) The ROF photodiode and its manufacturing method, and the optical receiver provided by the embodiments of the present invention can reduce the distance between the ROF photodiode and the output end of the optical fiber to receive the optical signal emitted by the optical fiber to the maximum extent by setting a microlens to pre-focus the Gaussian light beam output from the optical fiber, thereby reducing the loss of optical power;

[0036] (4) The ROF photodiode and its manufacturing method, and the optical receiver provided by the embodiments of the present invention can realize the conversion of Gaussian light into flat-top light through conventional and mature processes such as etching, ion implantation, epitaxial growth, and mature lens processing technology, which has high feasibility and reliability and is conducive to integrated manufacturing;

[0037] (5) The ROF photodiode and its manufacturing method, and the optical receiver provided by the embodiments of the present invention can uniformly optimize the design of the optical fiber size, the photosensitive surface size of the intrinsic absorption layer, the structure of the light-transmitting flat layer and the microlens, thereby improving the flexibility and adaptability of the ROF photodiode design;

[0038] (6) The ROF photodiode and its manufacturing method and optical receiver provided in the embodiments of the present invention set the intrinsic absorption layer on the SOI wafer or the high-resistance silicon wafer, and use the high thermal conductivity of silicon to improve the thermal diffusion efficiency of the intrinsic absorption layer of the ROF photodiode when high-power light is incident on it, thereby avoiding the burning of the ROF photodiode. BRIEF DESCRIPTION OF THE DRAWINGS

[0039] These and / or other aspects and advantages of the present invention will become apparent and readily understood from the following description of the preferred embodiments in conjunction with the accompanying drawings, in which:

[0040] Figure 1 A schematic diagram of a cross-sectional structure of a ROF photodiode package structure according to an embodiment of the present invention;

[0041] Figure 2 for Figure 1 The light intensity distribution curves of the ROF photodiode and the conventional ROF photodiode on the photosensitive surface of the intrinsic absorption layer after receiving Gaussian light emitted by the optical fiber. DETAILED DESCRIPTION

[0042] The technical solution of the present invention is further specifically described below by examples and in conjunction with the accompanying drawings. In the specification, the same or similar reference numerals indicate the same or similar components. The following description of the embodiments of the present invention with reference to the accompanying drawings is intended to explain the overall inventive concept of the present invention and should not be construed as a limitation of the present invention.

[0043] In the Radio-Over-Fiber (ROF) technology, the performance requirements for photodetectors are relatively high. On the one hand, the photodetector needs to have a high response sensitivity, that is, a high optical signal-to-electrical signal conversion efficiency. On the other hand, the photodetector also needs to have a fast response speed to ensure that the photodetector can respond quickly when the incident optical signal is modulated at a high frequency.

[0044] The response speed of existing photodetectors, such as common photodiodes, is mainly determined by the time constant and the transit time effect of photogenerated carriers. For a Gaussian-distributed optical signal from an optical fiber (hereinafter referred to as Gaussian light), the optical power density in the center area of ​​the optical path is very high. When this Gaussian light is incident on the photosensitive surface of the absorption layer of the photodetector, the density of photogenerated carriers generated in the corresponding center area will be very high. Too high a density of photogenerated carriers will weaken the electric field strength and increase the transit time, thereby reducing the effective bandwidth of the photodetector and reducing the response speed.

[0045] Therefore, in order to improve the distribution of the optical signal output by the optical fiber, avoid the excessive concentration of the optical power density of Gaussian light, reduce the loss of the optical signal, and ensure the effective working bandwidth and response performance of the photodetector, an embodiment of the present invention provides a new ROF photodiode structure and a manufacturing method thereof for a high-speed optical receiver.

[0046] See also Figure 1 , shows the structure of the ROF photodiode 100 of an embodiment of the present invention. The ROF photodiode 100 includes several functional layers inside its packaging structure, which include, from the substrate layer to the receiving surface of the optical signal emitted by the optical fiber 200: a wafer substrate 10; an intrinsic absorption layer 20 is arranged on the upper surface of the wafer substrate 10, for receiving the optical signal (i.e., Gaussian light) emitted from the optical fiber 200 and having a Gaussian distribution; a light-transmitting flat layer 30 is arranged outside the intrinsic absorption layer 20 and has a flat surface 31, for receiving the Gaussian light emitted from the optical fiber 200 into the ROF photodiode 100; a microlens 40 is arranged on the flat surface 31 of the light-transmitting flat layer 30 and the center of the microlens 40 is aligned with the center of the Gaussian light emitted by the optical fiber 200; wherein the Gaussian light emitted by the optical fiber 200 first passes through the microlens 40 and then converges inside it, and the converged Gaussian light then passes through the light-transmitting flat layer 30. Since the power density peak of the Gaussian light is dispersed and weakened by the flat surface 31 of the transparent flat layer 30, the Gaussian light is converted into flat-top light and then emitted into the intrinsic absorption layer 20 to complete the detection of the optical signal and convert the optical signal into an electrical signal.

[0047] In one example, alternatively, the wafer substrate 10 can be a SOI wafer substrate or a high-resistance silicon wafer substrate. Since silicon material has a large thermal conductivity coefficient, when a high-power optical signal is injected into the intrinsic absorption layer 20 of the ROF photodiode 100, good heat diffusion can be generated through the SOI wafer substrate or the high-resistance silicon wafer substrate to prevent the ROF photodiode 100 from overheating and burning. Preferably, the wafer substrate 10 in this embodiment uses an SOI wafer substrate. This example is only an illustrative example for the selection of a specific wafer substrate, and those skilled in the art should not be understood as a limitation of the present invention.

[0048] In one example, specifically, the wafer substrate 10 (SOI wafer substrate) is as follows Figure 1 As shown, from bottom to top, it includes a base silicon layer 11, an insulating silicon oxide layer 12 and a top silicon layer 13. The top silicon layer 13 can be connected to the base silicon layer 11 by conventional processes such as trench etching and silicon epitaxial growth.

[0049] In one example, the thickness, doping conditions and resistance of the base silicon layer 11, the insulating silicon oxide layer 12 and the top silicon layer 13 are further set. Among them, the thickness range of the base silicon layer 11 is 600-900μm, the preferred thickness range is 700-800μm, and the further preferred thickness is 750μm; at the same time, P-type doping is performed to make the resistance value range of the base silicon layer 11 reach 1k-10kΩ·cm. The insulating silicon oxide layer 12 is formed on the upper surface of the base silicon layer 11, and its thickness range is 1-3μm, the preferred thickness range is 1.5-2.5μm, and the further preferred thickness is 2μm. The top silicon layer 13 is formed on the upper surface of the insulating silicon oxide layer 12, and its preferred thickness range is 0.1-0.5μm.

[0050] In one example, further, a first electrode lead metal 14 is formed on the upper surface of the top silicon layer 13 and in an area outside the intrinsic absorption layer 20. Specifically, a passivation layer is first grown in the area outside the intrinsic absorption layer 20, and then an electrode contact hole is etched on the grown passivation layer and a metal layer is grown, thereby forming a first electrode lead metal 14 for electrode connection. The formation process of the electrode lead metal is not limited to the process described above, and this example is only an illustrative example, and those skilled in the art should not be understood as a limitation of the present invention.

[0051] In one example, if Figure 1 As shown, an intrinsic absorption layer 20 is further formed on the upper surface of the top silicon layer 13 of the wafer substrate 10. Since the optical fiber 200 usually aligns with the center of the ROF photodiode 100 to emit Gaussian light, it is preferred that the area where the intrinsic absorption layer 20 is formed is located within the central radiation range of the top silicon layer 13 so as to uniformly receive the optical signal emitted from the optical fiber 200. The area of ​​the intrinsic absorption layer 20 is positively correlated with the coverage range of the optical signal emitted by the optical fiber 200, and can be matched and designed according to the actual structure and performance requirements of the ROF photodiode 100.

[0052] In one example, preferably, the intrinsic absorption layer 20 is a photosensitive intrinsic absorption layer based on germanium. Specifically, P-type ion implantation is continued to be used within the central radiation range on the surface of the top silicon layer 13 to form a local P-type heavily doped region (the interface between the top silicon layer 13 and the intrinsic absorption layer 20 in the figure). Then, a layer of germanium structure is formed as the intrinsic absorption layer 20 on the local P-type heavily doped region by a selective epitaxial growth process. Finally, N-type ion implantation is used on the upper surface of this layer of germanium structure to form a local N-type heavily doped region 21 and cover the anti-reflection film structure used to detect the wavelength of the optical signal to form a photosensitive surface.

[0053] In one example, further, similar to the formation method of the first electrode lead metal 14 on the top silicon layer 13, a second electrode lead metal 22 is formed on the local N-type heavily doped region 21 of the intrinsic absorption layer 20. The second electrode lead metal 22 and the first electrode lead metal 14 form the anode structure and cathode structure (PN junction) of the ROF photodiode 100.

[0054] In one example, further, the peak value of the P-type doping concentration of the local P-type heavily doped region formed on the upper surface of the top silicon layer 13 is in the range of 5×10 18 ~5×10 20 / cm 3 The germanium structure of the intrinsic absorption layer 20 adopts an in-situ doping process to form a P-type doped germanium-based photosensitive intrinsic absorption layer, and the peak value range of the in-situ doped P-type doping concentration is 1×10 14 ~1×10 17 / cm 3 The thickness of the germanium structure is in the range of 0.5 to 2 μm, and the preferred thickness is 1.5 μm. The peak value of the N-type doping concentration of the local N-type heavily doped region formed on the upper surface of the intrinsic absorption layer 20 (germanium structure) is in the range of 5×10 18 ~5×10 20 / cm 3 The doping depth ranges from 0.1 to 0.3 μm, and the preferred doping depth is 0.2 μm. The above-mentioned optimization setting of doping concentration and germanium structure generation parameters helps to ensure that the intrinsic absorption layer 20 and the ROF photodiode 100 can achieve their optimal working bandwidth and light receiving and detection performance when receiving optical signals.

[0055] In one example, alternatively, P-type doping or N-type doping can be replaced in the functional layer of the ROF photodiode 100. That is, the functional layer using P-type doping can also use N-type doping, then correspondingly, the functional layer using N-type doping needs to be replaced with P-type doping, and the PN junction finally formed is just a positive and negative pole swap.

[0056] In one example, after the intrinsic absorption layer 20 is formed, Figure 1The upper surface of the local N-type heavily doped region on the upper surface of the germanium structure shown is a photosensitive surface, which is used to receive the optical signal emitted from the optical fiber 200 above it. At this time, a light-transmitting flat layer 30 and a microlens 40 are sequentially arranged between the upper surface of the local N-type heavily doped region and the emission port of the optical fiber 200. Specifically, the light-transmitting flat layer 30 is first grown by wrapping the entire wafer substrate 10 and the intrinsic absorption layer 20, and then a flat surface 31 is formed on the surface of the light-transmitting flat layer 30 close to the optical fiber 200 through a polishing process (such as chemical mechanical polishing CMP technology), and finally a microlens 40 is grown on the flat surface 31. After the above arrangement, when the optical fiber 200 emits a Gaussian distributed optical signal, the microlens 40 first receives the optical signal, and the optical signal enters the light-transmitting flat layer 30 after being converged in the microlens 40. At this time, the Gaussian distributed optical signal is transformed into a uniform flat top light through convergence and refraction, and finally enters the intrinsic absorption layer 20 to realize the reception and detection of the optical signal.

[0057] In one example, specifically, both the light-transmitting flat layer 30 and the microlens 40 need to be made of light-transmitting materials. In order to ensure the effective transmission of optical signals and avoid light loss as much as possible, alternatively, the light-transmitting material can use polymethyl methacrylate (PMMA), polydimethylsiloxane (PDMS), photoresist, silicon dioxide, etc. Alternatively, the light-transmitting flat layer 30 and the microlens 40 can be made of the same light-transmitting material, or different types of light-transmitting materials can be selected to be made separately. Preferably, the present embodiment uses the same light-transmitting material to make the light-transmitting flat layer 30 and the microlens 40. Further preferably, the light-transmitting material uses polymethyl methacrylate (PMMA). Although the above-listed materials or other materials of the same category or nature are suitable for making the light-transmitting flat layer 30 and the microlens 40, there are usually subtle differences in characteristic parameters between different materials. Therefore, using the same material for processing and manufacturing can, on the one hand, further simplify the manufacturing process and reduce production costs, and on the other hand, it is more helpful to maintain the consistency of the light receiving, convergence, refraction, scattering and other processes during the light transmission process, thereby ensuring that the ROF photodiode 100 has stable light receiving performance. The skilled person in the art can select the light-transmitting material according to the material properties and the actual product manufacturing requirements. This example only provides some illustrative examples, and the skilled person in the art should not understand it as a limitation of the present invention.

[0058] In one example, specifically, the thickness of the light-transmitting flat layer 30 in the direction of the Gaussian light emitted by the optical fiber 200 is in the range of 5 to 30 μm. The preferred thickness range is 15 to 25 μm. After the complete light-transmitting flat layer 30 is formed, the positions of the first electrode lead metal 14 in the wafer substrate 10 and the second electrode lead metal 22 in the intrinsic absorption layer 20 are first etched out, and then the upper surface of the receiving optical fiber 200 that emits the Gaussian light is polished to form a flat surface 31.

[0059] In one example, specifically, Figure 1 As shown, the microlens 40 uses a convex lens structure, which is used to pre-receive Gaussian light emitted from the optical fiber 200 before the intrinsic absorption layer 20 and converge the Gaussian light and then inject it onto the light-transmitting flat layer 30 disposed below the microlens 40. Alternatively, the convex lens structure of the microlens 40 can be an aspherical lens or a spherical lens. Preferably, the present embodiment uses an aspherical convex lens.

[0060] In one example, further, the curvature radius of the microlens 40 (aspherical convex lens) is in the range of 3 to 8 μm, and the height of the microlens 40 in the direction in which the optical fiber 200 emits Gaussian light is in the range of 5 to 10 μm.

[0061] In one example, the specific values ​​of the thickness of the light-transmitting flat layer 30, the height of the microlens 40 and the curvature radius thereof need to be designed based on the overall design of the ROF photodiode 100, the structure of the optical receiver and the performance of the optical fiber 200. The design principle is to receive the Gaussian light emitted by the optical fiber 200 to the maximum extent to avoid light leakage, and at the same time to the maximum extent to converge the Gaussian light in the microlens 40 and to the maximum extent to convert the Gaussian light into flat top light in the light-transmitting flat layer 30 and inject it into the intrinsic absorption layer 20 for efficient light detection.

[0062] In one example, further, in order to ensure that the intrinsic absorption layer 20 can uniformly receive the optical signal emitted from the optical fiber 200 and to avoid light loss caused by the optical signal incident on the area outside the intrinsic absorption layer 20 as much as possible, the center of the microlens 40 is aligned with the center of the optical fiber 200 and the center of the upper surface of the intrinsic absorption layer 20.

[0063] The ROF photodiode 100 is obtained by setting the wafer substrate 10, the intrinsic absorption layer 20, the light-transmitting flat layer 30 and the microlens 40 as described above. Figure 1 As shown, the optical fiber 200 is placed at the center position above the ROF photodiode 100. At this time, due to the arrangement of the light-transmitting flat layer 30 and the microlens 40, the distance between the optical fiber 200 and the upper surface of the ROF photodiode 100 (the surface of the microlens 40) can be very close. For example, the distance between the optical fiber 200 and the surface of the microlens 40 can be adjusted by moving the optical fiber 200 up and down in the vertical direction to ensure that the Gaussian light emitted by the optical fiber 200 completely enters the microlens 40.

[0064] After the Gaussian light enters the microlens 40 , the microlens 40 has a very small radius of curvature (eg, a radius of curvature in the range of 3 to 8 μm), so the Gaussian light incident therein can be quickly converged.

[0065] Since the thickness of the light-transmitting flat layer 30 is very large (for example, the thickness ranges from 5 to 30 μm), when the converged Gaussian light passes through the light-transmitting flat layer 30 and then enters the upper surface (photosensitive surface) of the intrinsic absorption layer 20, the peak value of the optical power density of the optical signal at its center position has been dispersed and weakened. At this time, the optical signal has been transformed from Gaussian light to flat-top light with more uniform optical power density.

[0066] The flat-top light received by the ROF photodiode 100 will no longer produce an electric field suppression effect due to excessive concentration of local light power, which causes excessive local photogenerated carrier density. Therefore, the working bandwidth of the ROF photodiode 100 can be effectively guaranteed, thereby improving the light detection responsivity, response sensitivity and other performances of the ROF photodiode 100.

[0067] See also Figure 2 , shows the distribution curve of the light intensity on the photosensitive surface of the intrinsic absorption layer 20 after the light signal from the optical fiber 200 is injected into the ROF photodiode 100. The two curves in the figure are respectively the light intensity distribution curve of the ROF photodiode 100 of the present embodiment (a light-transmitting flat layer 30 and a microlens 40 are arranged above the photosensitive surface of the intrinsic absorption layer 20) and the light intensity distribution curve of the conventional ROF photodiode (no light-transmitting flat layer 30 and microlens 40 are arranged above the photosensitive surface of the intrinsic absorption layer 20).

[0068] like Figure 2 As shown, the conventional ROF photodiode receives the maximum light intensity at the center of its photosensitive surface and the peak of the light intensity is very concentrated. Therefore, the electric field shielding effect is very likely to occur in the center area, thereby reducing the working bandwidth of the ROF photodiode and affecting the response performance of optical signal reception and detection. Relatively speaking, the ROF photodiode 100 of this embodiment, due to the structure of the light-transmitting flat layer 30 and the microlens 40, can convert the Gaussian light emitted from the optical fiber 200 into a flat-top light with uniform optical power density before it is incident on the photosensitive surface of the intrinsic absorption layer 20. At this time, the peak of the light intensity received at the center of the photosensitive surface is weakened and averaged, achieving a flat-top effect. Since the light intensity peak is no longer concentrated, the probability of the electric field shielding effect occurring in the center area of ​​the photosensitive surface will be greatly reduced, thereby ensuring the bandwidth characteristics and optical signal response performance of the ROF photodiode 100.

[0069] According to another aspect of the present invention, an optical receiver is provided for receiving high-rate optical signals. The optical receiver (not shown) is provided with the ROF photodiode 100 described in the above aspect for detecting and receiving high-intensity Gaussian light emitted from the optical fiber 200 .

[0070] According to another aspect of the present invention, a method for manufacturing a ROF photodiode is provided, which is used to manufacture the ROF photodiode 100 described in the above aspect. The steps of the manufacturing method include:

[0071] preparing a wafer substrate 10;

[0072] A P-type heavily doped region (an N-type heavily doped region when the polarity of the PN junction is reversed) is formed on the upper surface of the wafer substrate 10 through photolithography, ion implantation and annealing processes;

[0073] Growing a germanium-based intrinsic absorption layer 20 on the P-type heavily doped region or the N-type heavily doped region by selective epitaxial growth;

[0074] Through photolithography, ion implantation and annealing processes, a local N-type heavily doped region 21 (a local P-type heavily doped region when the polarity of the PN junction is reversed) with a preset doping depth is formed on the upper surface of the intrinsic absorption layer 20;

[0075] The upper surface of the intrinsic absorption layer 20 is covered with an anti-reflection film of the detection wavelength to form a photosensitive surface;

[0076] After the passivation layer is grown and the electrode contact hole is etched, a metal layer is grown to form a first electrode lead metal 14 on the upper surface of the wafer substrate 10, and a second electrode lead metal 22 is formed in a local N-type heavily doped region 21 (a local P-type heavily doped region when the polarity of the PN junction is reversed) of the intrinsic absorption layer 20;

[0077] A light-transmitting flat layer 30 is grown around the intrinsic absorption layer 20 and the first electrode lead metal 14 on the wafer substrate 10, and a flat surface 31 is formed by polishing on a side of the light-transmitting flat layer 30 that receives Gaussian light emitted from the optical fiber 200 into the ROF photodiode 100;

[0078] The microlens 40 is grown on the flat surface 31 of the light-transmitting flat layer 30 with the central direction of the Gaussian light emitted from the optical fiber 200 as the central axis.

[0079] In one example, specifically, the peak value of the doping concentration of the P-type heavily doped region (the N-type heavily doped region when the polarity of the PN junction is reversed) formed on the upper surface of the wafer substrate 10 is in the range of 5×10 18 ~5×10 20 / cm 3 The intrinsic absorption layer 20 uses an in-situ doping process, and the P-type doping concentration or N-type doping concentration of the in-situ doping is in the range of 1×10 14 ~1×10 17 / cm 3 The preset doping depth of the local N-type heavily doped region 21 (local P-type heavily doped region when the polarity of the PN junction is reversed) of the intrinsic absorption layer 20 is in the range of 0.1 to 0.3 μm.

[0080] In one example, specifically, the thickness of the light-transmitting flat layer 30 in the direction in which the optical fiber 200 emits Gaussian light is in a range of 5 to 30 μm.

[0081] In one example, specifically, the height of the microlens 40 in the direction in which the optical fiber 200 emits Gaussian light is in the range of 5 to 10 μm, and the radius of curvature is in the range of 3 to 8 μm.

[0082] In one example, alternatively, the size of the photosensitive surface of the intrinsic absorption layer 20 in the ROF photodiode 100, the thickness of the light-transmitting flat layer 30, and the structure of the microlens 40 can be designed in accordance with the structural size of the optical fiber 200, and the materials used in the light-transmitting flat layer 30 and / or the microlens 40 can also be adjusted. Through multi-parameter coupling optimization, the incident light signal is effectively collected and the electric field suppression caused by the peak intensity concentration of Gaussian light is avoided, thereby ensuring the effective working bandwidth of the ROF photodiode 100 and improving its light response performance.

[0083] The ROF photodiode and the manufacturing method thereof, and the optical receiver provided by the embodiments of the present invention have at least one or part of the following advantages:

[0084] (1) The ROF photodiode and its manufacturing method, and the optical receiver provided by the embodiments of the present invention provide a light-transmitting flat layer and a microlens above the intrinsic absorption layer to weaken the peak intensity of the Gaussian light beam output from the optical fiber at the center position, thereby avoiding the electric field suppression effect generated by the high-intensity light at the center position of the Gaussian light beam, and ensuring the normal working bandwidth of the ROF photodiode;

[0085] (2) The ROF photodiode and its manufacturing method, and the optical receiver provided by the embodiments of the present invention effectively disperse the Gaussian light beam output from the optical fiber by setting a thick transparent flat layer above the intrinsic absorption layer, so that the Gaussian light is converted into a flat-top light and uniformly incident on the photosensitive surface of the intrinsic absorption layer, thereby improving the detection response of the ROF photodiode to high-power input light and ensuring its good bandwidth characteristics;

[0086] (3) The ROF photodiode and its manufacturing method, and the optical receiver provided by the embodiments of the present invention can reduce the distance between the ROF photodiode and the output end of the optical fiber to receive the optical signal emitted by the optical fiber to the maximum extent by setting a microlens to pre-focus the Gaussian light beam output from the optical fiber, thereby reducing the loss of optical power;

[0087] (4) The ROF photodiode and its manufacturing method, and the optical receiver provided by the embodiments of the present invention can realize the conversion of Gaussian light into flat-top light through conventional and mature processes such as etching, ion implantation, epitaxial growth, and mature lens processing technology, which has high feasibility and reliability and is conducive to integrated manufacturing;

[0088] (5) The ROF photodiode and its manufacturing method, and the optical receiver provided by the embodiments of the present invention can uniformly optimize the design of the optical fiber size, the photosensitive surface size of the intrinsic absorption layer, the structure of the light-transmitting flat layer and the microlens, thereby improving the flexibility and adaptability of the ROF photodiode design;

[0089] (6) The ROF photodiode and its manufacturing method and optical receiver provided in the embodiments of the present invention set the intrinsic absorption layer on the SOI wafer or the high-resistance silicon wafer, and use the high thermal conductivity of silicon to improve the thermal diffusion efficiency of the intrinsic absorption layer of the ROF photodiode when high-power light is incident on it, thereby avoiding the burning of the ROF photodiode.

[0090] Although some embodiments of the present general inventive concept have been shown and described, it will be appreciated by those skilled in the art that changes may be made to these embodiments without departing from the principles and spirit of the present general inventive concept, the scope of which is defined by the claims and their equivalents.

Claims

1. A ROF photodiode, characterized in that: The ROF photodiode comprises: Wafer substrate; An intrinsic absorption layer, wherein the intrinsic absorption layer is disposed on the upper surface of the wafer substrate; A light-transmitting flat layer, wherein the light-transmitting flat layer is covered on the outside of the intrinsic absorption layer and has a flat surface on a side receiving Gaussian light emitted by the optical fiber into the ROF photodiode; A microlens, wherein the microlens is disposed on the flat surface of the light-transmitting flat layer and the center of the microlens is aligned with the center of the Gaussian light emitted from the optical fiber; The Gaussian light emitted from the optical fiber is converged after passing through the microlens, and the power density peak of the converged Gaussian light is dispersed and weakened after passing through the light-transmitting flat layer and is converted into flat-top light and emitted into the intrinsic absorption layer.

2. The ROF photodiode according to claim 1, characterized in that: The wafer substrate is an SOI wafer substrate, and the SOI wafer substrate comprises: A base silicon layer, wherein the base silicon layer has a thickness ranging from 600 to 900 μm and a resistance value ranging from 1 k to 10 kΩ·cm; An insulating silicon oxide layer, wherein the insulating silicon oxide layer is disposed on the upper surface of the base silicon layer, and the thickness of the insulating silicon oxide layer is in the range of 1 to 3 μm; A top silicon layer, wherein the top silicon layer is disposed on the upper surface of the insulating silicon oxide layer, and the thickness of the top silicon layer is in the range of 0.1 to 0.5 μm; or The wafer substrate is a high-resistance silicon wafer substrate.

3. The ROF photodiode according to claim 1, characterized in that: The intrinsic absorption layer is a photosensitive intrinsic absorption layer based on germanium, and the thickness of the intrinsic absorption layer in the direction of Gaussian light emitted from the optical fiber is in the range of 0.5 to 2 μm.

4. The ROF photodiode according to claim 1, characterized in that: The thickness of the light-transmitting flat layer in the direction of Gaussian light emitted from the optical fiber is in the range of 5 to 30 μm.

5. The ROF photodiode according to claim 4, characterized in that: The light-transmitting flat layer is made of a light-transmitting material, and the light-transmitting material is any one of polymethyl methacrylate (PMMA), polydimethylsiloxane (PDMS), photoresist and silicon dioxide.

6. The ROF photodiode according to any one of claims 1 to 5, characterized in that: The microlens is a convex lens, and the convex lens is an aspherical lens; The curvature radius of the microlens is in the range of 3 to 8 μm, and the height of the microlens in the direction in which the optical fiber emits Gaussian light is in the range of 5 to 10 μm.

7. The ROF photodiode according to claim 6, characterized in that: The micro lens is made of the same material as the light-transmitting flat layer, and the same material is polymethyl methacrylate (PMMA).

8. An optical receiver, characterized in that: A ROF photodiode according to any one of claims 1 to 7 is arranged in the optical receiver for detecting and receiving a high-speed optical signal with Gaussian distribution emitted from an optical fiber.

9. A method for manufacturing a ROF photodiode, for manufacturing a ROF photodiode according to any one of claims 1 to 7, characterized in that: The steps of the manufacturing method include: preparing a wafer substrate; Forming a P-type heavily doped region or an N-type heavily doped region on the upper surface of the wafer substrate through photolithography, ion implantation and annealing processes; Growing a germanium-based intrinsic absorption layer on the P-type heavily doped region or the N-type heavily doped region by selective epitaxial growth; By photolithography, ion implantation and annealing processes, a local N-type heavily doped region or a local P-type heavily doped region with a preset doping depth is formed on the upper surface of the intrinsic absorption layer; The upper surface of the intrinsic absorption layer is covered with an anti-reflection film of the detection wavelength to form a photosensitive surface; After the passivation layer is grown and the electrode contact hole is etched, a metal layer is grown to form a first electrode lead metal on the upper surface of the wafer substrate, and a second electrode lead metal is formed on the upper surface of a local N-type heavily doped region or a local P-type heavily doped region of the intrinsic absorption layer; A light-transmitting flat layer is grown by metal surrounding the intrinsic absorption layer and the first electrode on the wafer substrate, and a flat surface is formed on one side of the light-transmitting flat layer that receives Gaussian light emitted from the optical fiber into the ROF photodiode; A microlens is grown on the flat surface of the light-transmitting flat layer with the central direction of the Gaussian light emitted from the optical fiber as the central axis.

10. The manufacturing method according to claim 9, characterized in that: The peak value range of the doping concentration of the P-type heavily doped region or the N-type heavily doped region is 5×10 18 ~5×10 20 / cm 3 ; The intrinsic absorption layer uses an in-situ doping process, and the range of the in-situ doping P-type doping concentration or N-type doping concentration is 1×10 14 ~1×10 17 / cm 3 ; The preset doping depth of the local N-type heavily doped region or the local P-type heavily doped region is in the range of 0.1 to 0.3 μm; The thickness of the light-transmitting flat layer in the direction of Gaussian light emitted from the optical fiber is in the range of 5 to 30 μm; The height of the microlens in the direction of Gaussian light emitted from the optical fiber is in the range of 5 to 10 μm, and the radius of curvature is in the range of 3 to 8 μm.

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