Silicon-based germanium runway type micro-ring photoelectric detector

Abstract

The invention discloses a silicon-based germanium runway type micro-ring photoelectric detector which comprises a silicon waveguide layer (012), a ridge-shaped silicon bus waveguide (001) and a runway type silicon micro-ring (006) are arranged on the upper surface of the silicon waveguide layer (012), the long axis of the runway type silicon micro-ring (006) is perpendicular to the silicon bus waveguide (001), and the partial arc section, close to the silicon bus waveguide (001), of the runway type silicon micro-ring (006) is a coupling area (020). Germanium absorption layers (004) are arranged on the upper surfaces of two straight line sections of the runway type outer silicon micro ring (006). Compared with a circular Ge-on-Si micro-ring structure, the runway type micro-ring has the advantages that the Ge-on-Si structure is only prepared on a straight line section, the problems that annular germanium is difficult to grow, the quality of a germanium layer is poor and the yield is low due to lattice mismatch of germanium and silicon are solved, and the resonance intensity, the light intensity multiplication factor and the like of the runway ring in simulation are higher than those of a circular ring in the performance aspect.

Description

Technical Field

[0001] The invention belongs to the field of photoelectric detectors, and in particular relates to a silicon-based germanium photoelectric detector comprising a racetrack-shaped micro-ring. Background Art

[0002] Photodetectors are devices that convert light signals into electrical signals, and they play a very important role in the optical communication technology of modern communications. The signal detection principle of photodetectors is mainly based on the photoconductivity effect, which is to use the free carrier concentration of semiconductor materials to change under the illumination of a certain range of wavelengths, causing the conductivity of the semiconductor to change, that is, the conductivity to change. By detecting the change of the current flowing through the semiconductor before and after illumination, the optical signal can be detected, and it is widely used in various signal receiving equipment, sensors, biological information detection and other fields.

[0003] With the rapid development of optical communication systems, traditional communication bands may face a "capacity crunch". However, devices such as low-loss hollow-core photonic bandgap fiber (<0.2dB / km) and high-gain thulium-doped fiber amplifiers (gain up to 30dB) that exhibit excellent performance in the 2-micron band make the 2-micron band have the potential to become a new communication band.

[0004] With the development of electronic information technology, especially the improvement of semiconductor manufacturing technology, the performance of commercial photodetection devices is also constantly improving, including performance parameters such as the responsivity and working bandwidth of photodetectors. In terms of production cost, due to the relatively mature development of complementary metal oxide semiconductor technology, the production cost of integrated circuits can now be very low, while ordinary optical waveguide technology is relatively difficult to achieve high integration at low cost. Researchers have extended the production process of integrated circuits to optical devices, bringing about the development of silicon photonics, that is, making optical devices on silicon substrates. The biggest feature of silicon-based photodetectors is that they are compatible with mature complementary metal oxide semiconductor semiconductor processes, have low production costs, and have high product yields, which is conducive to large-scale production, especially for the realization of highly integrated optical information systems. Based on the above advantages, in the past decade, silicon photonics has been promoted as a platform that provides revolutionary progress in data communications, medical technology, sensing technology and other fields.

[0005] Since silicon is an indirect bandgap material, its bandgap width is 1.12eV, that is, the cutoff wavelength of the photoelectric effect for silicon is 1.1μm, and light signals with wavelengths exceeding 1.1μm are hardly absorbed in silicon, so it is impossible to directly detect 2μm light signals through silicon. At present, the solution for 2μm wavelength light detection mainly relies on III-V materials with tunable bandgaps, such as InGaAs / InP photodetectors, but the manufacturing process of III-V material system devices is relatively complex and the manufacturing cost is also high, which is not conducive to promoting commercial detection equipment based on such devices to ordinary individual users.

[0006] Germanium and silicon both belong to Group VI materials, but the band gap width of germanium is 0.66eV, which has advantages such as large absorption coefficient, high carrier mobility, and compatibility with complementary metal oxide semiconductor technology; in addition, based on strain engineering and doping engineering, its affected wavelength can be extended to the 2μm band. Therefore, silicon-based germanium photodetectors are regarded as one of the most promising photonic devices in the field of silicon-based photodetector integration. For example, a silicon-based microring photodetector disclosed in Chinese patent CN115939231A utilizes the two-photon absorption effect of semiconductor materials, and utilizes silicon-based platforms and microring resonant cavity structures to achieve low-cost, highly integrated 2μm band photodetectors, and optimizes the structure of the photodetector, changing the single-layer silicon microring to a Ge-on-Si double-layer microring, and partially etching the germanium microring in the coupling area. However, the photodetector still faces difficulties such as high lattice mismatch, difficulty in preparing n-type high-doped junctions of germanium materials, and large dark current during preparation.

[0007] Germanium and silicon have a 4.2% lattice mismatch, which means that it is difficult to heteroepitaxially grow germanium films on silicon. If a Ge film is grown on a Si substrate and the film thickness is below the critical thickness, the top film will undergo compressive strain on the film plane, and the lattice mismatch will introduce vertical tensile strain, causing the lattice to undergo tetragonal distortion. Usually, lattice mismatch can be compensated by biaxial strain, but the ring structure will cause a mismatch between internal and external stresses, which makes it difficult to heteroepitaxially grow germanium on a ring-shaped silicon waveguide. If the film thickness exceeds the critical value, the rising strain will no longer accommodate the lattice of the substrate, and dislocation defects may form at the interface, resulting in relaxed epitaxy.

[0008] For double-layer silicon-based micro-ring photodetectors based on the two-photon effect, although people have proposed a method of transitioning from low-temperature germanium to high-temperature germanium to reduce the influence of lattice mismatch based on the characteristics of germanium, this also limits the growth shape of the germanium layer. Due to the compact characteristics of the micro-ring structure, it is more difficult to grow annular germanium, and even if it is produced, it faces problems such as poor yield and large performance gap. Therefore, how to reduce the difficulty of preparing silicon-based germanium micro-rings and improve the yield by designing the micro-ring structure, especially the active area, is the key to making silicon-based germanium racetrack-type micro-ring photodetectors. Summary of the invention

[0009] In view of the problems that silicon-based photodetectors are difficult to effectively detect optical signals in the 2μm band and that ring-shaped germanium is difficult to industrially prepare, the present invention utilizes two-photon absorption in nonlinear absorption to enable silicon-based detectors to detect light in the 2μm band, and adopts a racetrack-type straight active area design to reduce the difficulty of industrial preparation and improve the yield rate.

[0010] The technical solution of the present invention:

[0011] A silicon-based germanium racetrack microring photodetector comprises a silicon waveguide layer 012, a ridge-shaped silicon busbar waveguide 001 and a racetrack-shaped silicon microring 006 are provided on the upper surface of the silicon waveguide layer 012, the long axis of the racetrack-shaped silicon microring 006 is perpendicular to the silicon busbar waveguide 001, a partial arc section of the racetrack-shaped silicon microring 006 close to the silicon busbar waveguide 001 is a coupling region 020, and a germanium absorption layer 004 is provided on the upper surface of two straight line sections of the racetrack-shaped outer silicon microring 006.

[0012] A straight middle electrode 005 is installed above the two germanium absorption layers 004 , an inner racetrack electrode 007 is arranged inside the racetrack-shaped silicon microring 006 , and an outer racetrack electrode 003 is arranged outside. The outer racetrack electrode 003 has a notch near the coupling region 020 .

[0013] The silicon waveguide layer 012 below the racetrack-shaped silicon microring 006 is lightly doped with phosphorus, and the silicon waveguide layer 012 region below the outer racetrack electrode 003 and the inner racetrack electrode 007 is heavily doped with phosphorus.

[0014] The upper surface of the silicon waveguide layer 012 is lightly doped with phosphorus to form a racetrack-shaped lightly doped region, and phosphorus is heavily doped on both sides of the lightly doped region to form two racetrack-shaped heavily doped regions; the silicon busbar waveguide 001 and the racetrack-shaped silicon microring 006 are obtained by etching, and a germanium absorption layer 004 is epitaxially grown on the upper surface of the two straight segments of the racetrack-shaped silicon microring 006.

[0015] Boron is doped in the germanium absorption layer 004, the area near the bottom is lightly doped, and the area near the upper surface is heavily doped.

[0016] The inner track electrode 007, the middle track electrode 005 and the outer track electrode 003 are placed in the corresponding doping areas in sequence, and a silicon dioxide filling layer 009 is injected on the silicon waveguide layer 012 to cover the inner track electrode 007, the middle track electrode 005 and the outer track electrode 003, leaving only the electrode plate 022 on the upper surface exposed.

[0017] The shortest distance between the silicon busbar waveguide 001 and the silicon microring 006 is 310nm. A 2μm wavelength optical signal is re-input into the silicon busbar waveguide 001. The attenuation factor γ in the ring is equal to the transmission coefficient t in the coupling region 020. The microring is in a critical coupling state, and the resonant light intensity in the ring reaches a maximum.

[0018] The length of the germanium absorption layer 004 is an odd multiple of the directional coupling length of light between the silicon microring 006 and the germanium absorption layer 004 .

[0019] There are a buried oxide layer 013 and a silicon substrate 014 below the silicon waveguide layer 012 .

[0020] Silicon-based germanium racetrack microring photodetector for biological detection.

[0021] The beneficial effects of the present invention are:

[0022] The present invention utilizes the two-photon absorption effect of semiconductor materials, and utilizes a silicon-based platform and a microring resonant cavity structure to realize a 2μm band photoelectric detector with low cost, low preparation difficulty, high integration, and high yield, and optimizes the structure of the photoelectric detector, changing the double-layer microring into a Ge-on-Si direct absorption zone racetrack-type microring. The processed microring detector retains the characteristics of compatibility with mature complementary metal oxide semiconductor technology. In numerical simulation, the racetrack-type microring structure achieves good simulation effects in terms of resonance intensity, light intensity multiplication factor, etc., which provides a new idea for the design of future 2μm band and its corresponding infrared band photoelectric detectors.

[0023] Compared with the circular Ge-on-Si microring structure, the racetrack-type microring only prepares the Ge-on-Si structure in the straight segment, which solves the problem of difficulty in growing ring-shaped germanium, poor quality of the germanium layer, and low yield rate caused by the lattice mismatch between germanium and silicon. In terms of performance, the resonance intensity and light intensity multiplication factor of the racetrack ring in the simulation are higher than those of the circular ring. BRIEF DESCRIPTION OF THE DRAWINGS

[0024] Figure 1 A top view of the silicon-based racetrack-type micro-ring photodetector of the present invention;

[0025] Figure 2 for Figure 1 Cross-sectional view of the active area of ​​the micro-ring 010;

[0026] Figure 3 for Figure 1 Cross-sectional view of the micro-ring coupling region 011;

[0027] Figure 4 Schematic diagram of the coupling region between the busbar waveguide and the silicon racetrack microring;

[0028] Figure numerals: 001 silicon busbar waveguide; 003, 005, 007 metal electrode columns; 004 germanium absorption layer; 006 silicon racetrack-type microring; 008 phosphorus heavily doped region; 009 silicon dioxide protection layer; 010 microring active region cross section; 011 microring coupling region cross section; 012 silicon waveguide layer; 013 buried oxide layer; 014 silicon substrate; 015 germanium absorption layer height; 016 silicon microring width; 017 silicon busbar waveguide width; 018 microring coupling region Gap width; 019 busbar waveguide optical input end; 020 coupling region; 022 electrode plate. DETAILED DESCRIPTION

[0029] Embodiment 1:

[0030] like Figure 2 The silicon-based germanium racetrack-type micro-ring photodetector of the present invention comprises, from bottom to top, a silicon substrate 014, a buried oxide layer 013, a silicon waveguide layer 012 and a silicon dioxide filling layer 009.

[0031] The upper surface of the silicon waveguide layer 012 has a ridge-shaped straight silicon bus waveguide 001 and a racetrack-shaped silicon microring 006. The long axis of the racetrack-shaped silicon microring 006 is perpendicular to the silicon bus waveguide 001. The arc section of the racetrack-shaped silicon microring 006 close to the silicon bus waveguide 001 is the coupling region 020. The upper surface of the two straight sections of the racetrack-shaped silicon microring 006 has a germanium absorption layer 004. The closest distance between the silicon bus waveguide 001 and the silicon microring 006 is 310nm. When a 2μm wavelength optical signal is re-input into the silicon bus waveguide 001, the attenuation factor γ in the ring is equal to the transmission coefficient t in the coupling region 020. The microring is in a critical coupling state, and the resonant light intensity in the ring reaches the maximum. The length of a single germanium absorption layer 004 is an odd multiple of the directional coupling length of light between the silicon microring 006 and the germanium absorption layer 004.

[0032] The area below the silicon microring 006 is the phosphorus lightly doped area 021. On both sides of the phosphorus lightly doped area 021 are the phosphorus heavily doped areas 002 and phosphorus heavily doped areas 008. The specific concentration is generally related to the process and dopant type used by the wafer factory when manufacturing the device. The lightly doped dopant is generally in the order of 1 part per billion of the doped semiconductor atom, and the heavily doped dopant is in the order of 1 part per thousand. The germanium absorption layer 004 is a pure metal germanium layer, which is doped with boron. The lower half of the germanium absorption layer 004 is lightly doped with boron, and the upper half is heavily doped with boron.

[0033] The middle electrode 005 is installed above the germanium absorption layer 004, the inner racetrack electrode 007 is arranged inside the silicon microring 006, and the outer racetrack electrode 003 is arranged outside. The outer racetrack electrode ring 003 has a gap near the coupling region 020. The inner racetrack electrode 007 and the outer racetrack electrode 003 are respectively located on the upper surfaces of the phosphorus heavily doped region 002 and the phosphorus heavily doped region 008. The inner racetrack electrode 007 and the outer racetrack electrode 003 are both cylindrical structures with a racetrack-shaped cross section, and an electrode plate 022 is provided on the upper end surface of the cylinder wall.

[0034] The manufacturing process is as follows: lightly doping with phosphorus is performed on the upper surface of the silicon waveguide layer 012 to form a ring-shaped lightly doped area, and heavily doping with phosphorus is performed on both sides of the lightly doped area to form two ring-shaped heavily doped areas; silicon busbar waveguide 001 and racetrack-shaped silicon microring 006 are obtained by etching, and a germanium absorption layer 004 is epitaxially grown on the upper surface of the straight section of the racetrack-shaped silicon microring 006. The inner racetrack electrode 007, the middle electrode 005 and the outer racetrack electrode ring 03 are placed in the corresponding doping areas in sequence, and a silicon dioxide filling layer 009 is injected on the silicon waveguide layer 012 to cover the inner racetrack electrode 007, the middle electrode 005 and the outer racetrack electrode 003, leaving only the electrode plate 022 on the upper surface exposed.

[0035] Embodiment 2:

[0036] See attached Figure 1 , Figure 2 , Figure 3 The main structure of the micro-ring photodetector provided by the present invention includes: a silicon substrate 014, a silicon dioxide buried oxide layer 013 and a silicon waveguide layer 012 on the upper surface of the silicon substrate 014, and the thickness of the silicon buried oxide layer is 200nm;

[0037] According to the process requirements provided by the wafer factory, the silicon waveguides involved in the present invention are all ridge waveguides, and the photolithography method adopts 150nm deep etching, that is, the total height of the silicon waveguide layer 012 is 220nm, and the etching area is 150nm. The silicon waveguide layer includes a straight ridge waveguide 001, that is, a busbar waveguide; a racetrack-shaped silicon microring 006;

[0038] The silicon waveguide layer is etched to a fixed value to accommodate a single-mode optical signal with a wavelength of 2 μm;

[0039] Specifically, the width 017 of the busbar waveguide 001 is 510 nm, and the width 016 of the silicon microring 006 is 550 nm. In order to reduce the loss caused by waveguide bending, the radius of the racetrack-shaped silicon microring 006 is designed to be 6 μm, that is, the distance from the center of the silicon racetrack-shaped microring semicircular waveguide to the center of the semicircle is 6 μm;

[0040] The shortest distance Gap 018 between the busbar waveguide 001 and the silicon microring is 310nm. When a 2μm wavelength optical signal is input to the input end of the microring detector and Gap 018 is 310nm, the attenuation factor in the ring is equal to the transmission coefficient in the microring coupling region, and the microring is in a critical coupling state. At this time, the resonant light intensity in the ring reaches the maximum.

[0041] Preferably, the external laser can be input to the photodetector input end 019 by using an end coupler, which has the advantages of high coupling efficiency and polarization insensitivity.

[0042] Preferably, the external laser input can use a grating coupler, which is easy to align during testing;

[0043] The upper surface of the straight segment of the silicon microring is epitaxially grown with a germanium absorption layer to form a Ge-on-Si structure with the silicon microring. The two-photon absorption coefficient of germanium in the 2μm band is about 4000 times that of silicon, thereby further increasing the two-photon absorption effect in the ring.

[0044] Furthermore, for the Ge-on-Si waveguide structure, when the light field is directionally coupled between the Ge layer and the silicon layer, it should be coupled back to the Si layer at the end of the Ge layer, and will not be scattered and lost at the edge of the Ge layer. The appropriate length of the germanium absorption layer can make the light energy in the Ge-on-Si microring be absorbed by the germanium layer multiple times, thereby further increasing the two-photon absorption effect in the ring and improving the detector's responsiveness. According to the FDTD numerical simulation results, for a 2μm optical signal, the coupling length between the silicon microring and the germanium microring in the Ge-on-Si microring structure is about 0.68μm, so the length of the germanium absorption layer in the absorption region 004 can be designed to be 6.1μm; refer to the attached Figure 2 , the height 015 of the germanium absorption layer is 300nm. When the height of the germanium absorption layer is scanned from 150nm to 300nm, the mode field area of ​​the Ge layer optical signal gradually increases. Considering the semiconductor manufacturing process, the height 015 of the germanium absorption layer is designed to be 300nm. The numerical analysis results show that most of the optical field of the 2μm wavelength optical signal base film in the Ge-on-Si waveguide is concentrated in the Ge absorption layer;

[0045] Reference Figure 2 A contact electrode plate 024 is made on the upper surface of the silicon dioxide protective layer 009 to connect with the middle electrode 005. The contact electrode plate 024 is an ohmic contact electrode, and the material is one or a combination of aluminum, chromium, gold, titanium, palladium or silver. The contact electrode plate 024 and the middle electrode 005 are prepared by resistance thermal evaporation, electron beam evaporation or magnetron sputtering.

[0046] The working principle of the silicon-based micro-ring photodetector of the present invention is:

[0047] The 2μm optical signal output by an external laser source is input into the bus waveguide 001 through an end coupler or a grating coupler, and is coupled to the silicon racetrack microring 006 through evanescent wave coupling in the coupling region where the bus waveguide 001 is close to the silicon racetrack microring 006. During the transmission of the silicon racetrack microring 006, the optical signal is directionally coupled with the germanium microring 004, and mainly produces two-photon absorption in the germanium absorption layer 004, generating free electron-hole pairs, which move directionally under the external bias voltage loaded through the electrode to form a photocurrent.

[0048] The above-mentioned specific embodiments further illustrate the purpose, technical solutions and beneficial effects of the present invention in detail. It should be understood that the above-mentioned embodiments are only specific embodiments of the present invention and are not used to limit the present invention. Any modifications, equivalent substitutions, improvements, etc. made within the spirit and principles of the present invention should be included in the protection scope of the present invention.

Claims

1. A silicon-based germanium racetrack micro-ring photodetector, comprising a silicon waveguide layer (012), characterized in that: A ridge-shaped silicon busbar waveguide (001) and a racetrack-shaped silicon microring (006) are provided on the upper surface of the silicon waveguide layer (012); the long axis of the racetrack-shaped silicon microring (006) is perpendicular to the silicon busbar waveguide (001); a partial arc section of the racetrack-shaped silicon microring (006) close to the silicon busbar waveguide (001) is a coupling region (020); and a germanium absorption layer (004) is provided on the upper surface of two straight line sections of the racetrack-shaped outer silicon microring (006).

2. The silicon-based germanium racetrack micro-ring photodetector according to claim 1, characterized in that: A straight middle electrode (005) is installed above two germanium absorption layers (004), an inner racetrack electrode (007) is arranged inside the racetrack-shaped silicon microring (006), and an outer racetrack electrode (003) is arranged outside. The outer racetrack electrode (003) has a notch near the coupling region (020).

3. The silicon-based germanium racetrack micro-ring photodetector according to claim 2, characterized in that: The silicon waveguide layer (012) below the racetrack-shaped silicon microring (006) is lightly doped with phosphorus, and the silicon waveguide layer (012) region below the outer racetrack electrode (003) and the inner racetrack electrode (007) is heavily doped with phosphorus.

4. The silicon-based germanium racetrack micro-ring photodetector according to claim 3, characterized in that: The upper surface of the silicon waveguide layer (012) is lightly doped with phosphorus to form a racetrack-shaped lightly doped region, and phosphorus is heavily doped on both sides of the lightly doped region to form two racetrack-shaped heavily doped regions; a silicon busbar waveguide (001) and a racetrack-shaped silicon microring (006) are obtained by etching, and a germanium absorption layer (004) is epitaxially grown on the upper surface of two straight segments of the racetrack-shaped silicon microring (006).

5. The silicon-based germanium racetrack micro-ring photodetector according to claim 4, characterized in that: Boron is doped in the germanium absorption layer (004), the area near the bottom is lightly doped, and the area near the upper surface is heavily doped.

6. The silicon-based germanium racetrack micro-ring photodetector according to claim 4, characterized in that: The inner racetrack electrode (007), the middle racetrack electrode (005) and the outer racetrack electrode (003) are placed in the corresponding doping areas in sequence, and a silicon dioxide filling layer (009) is injected on the silicon waveguide layer (012) to cover the inner racetrack electrode (007), the middle racetrack electrode (005) and the outer racetrack electrode (003), leaving only the electrode plate (022) on the upper surface exposed.

7. The silicon-based germanium racetrack micro-ring photodetector according to claim 1, characterized in that: The shortest distance between the silicon busbar waveguide (001) and the silicon microring (006) is 310nm. A 2μm wavelength optical signal is re-input into the silicon busbar waveguide (001). The attenuation factor γ in the ring is equal to the transmission coefficient t in the coupling region (020). The microring is in a critical coupling state and the resonant light intensity in the ring reaches a maximum.

8. The silicon-based germanium racetrack micro-ring photodetector according to claim 1, characterized in that: The length of the germanium absorption layer (004) is an odd multiple of the directional coupling length of light between the silicon microring (006) and the germanium absorption layer (004).

9. The silicon-based germanium racetrack micro-ring photodetector according to any one of claims 1 to 9, characterized in that: There is a buried oxide layer (013) and a silicon substrate (014) below the silicon waveguide layer (012).

10. The silicon-based germanium racetrack micro-ring photodetector according to claim 9, characterized in that: Silicon-based germanium racetrack microring photodetector for biological detection.

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