A resonant cavity enhanced germanium-silicon photodetector based on a silicon corner cube

Abstract

This invention provides a cavity-enhanced germanium-silicon photodetector based on silicon corner mirrors, comprising a silicon substrate layer, a germanium absorption region on the silicon substrate layer, and silicon corner mirrors located on the front and rear sides of the germanium absorption region; a germanium via layer is provided above the germanium absorption region, the via layer having a plurality of germanium vias, and a signal electrode is provided at the top of the germanium via layer; silicon via layers are provided on the left and right sides of the germanium absorption region, the silicon via layers having a plurality of silicon vias, and a ground electrode is provided at the top of the silicon via layers; two silicon nitride waveguides are arranged opposite each other, extending from the opposite outer sides of the two silicon via layers toward the sides of the germanium absorption region. The technical solution of this invention has excellent high-power processing capability, achieves polarization-insensitive detection, effectively overcomes the contradiction between responsivity and bandwidth, is fully compatible with CMOS manufacturing processes, and is conducive to large-scale integration and mass production.

Description

Technical Field

[0001] This invention relates to the field of silicon-based optoelectronic integrated chip technology, and in particular to a resonant cavity-enhanced germanium-silicon photodetector based on a silicon corner mirror. Background Technology

[0002] There is an inherent trade-off between the responsivity and bandwidth of a photodetector: increasing the volume of the light absorption region can improve responsivity, but it introduces larger parasitic capacitance, limiting the bandwidth; conversely, reducing the size, while beneficial to bandwidth, can lead to insufficient absorption and decreased responsivity. To balance these two aspects, a resonant cavity enhancement structure can be used, allowing light to travel back and forth multiple times within the absorption region, thereby achieving efficient absorption within a limited size and simultaneously obtaining high responsivity and high bandwidth.

[0003] In existing solutions, distributed Bragg reflectors (DBRs) are a common choice. For example, some schemes use alternating silicon / silicon dioxide DBRs on both sides of the germanium absorption region to form a resonant cavity. This structure requires precise control of the thickness of each layer (e.g., 100–200 nm) and stacking of 15–30 cycles, making the process difficult and sensitive to manufacturing errors, which can easily lead to decreased reflectivity, spectral line broadening, or center wavelength drift. On the other hand, incident detectors use upper and lower DBRs to form a Fabry-Perot cavity. Although this can extend the optical path, it requires the epitaxial growth of multiple reflectors, which is complex, costly, and incompatible with CMOS processes, making large-scale integration difficult. Its vertical mesa structure is also unsuitable for high-density chip-level integration.

[0004] Microring resonators offer another approach to enhancing light intensity. They utilize evanescent field coupling to cause light to resonate within the microring, thereby increasing local light intensity. For example, Chinese patent CN119133273A couples light to a silicon nitride microring resonator via a silicon nitride straight waveguide, and then uses the evanescent field within the microring for lateral coupling to the germanium absorption region within the ring. However, this solution has an extremely narrow optical bandwidth, being efficient only for discrete wavelengths; introducing thermal tuning to broaden the range would increase power consumption, control complexity, and cost.

[0005] To simplify the process, some solutions employ dual-substrate bonding to fabricate the bottom reflector, using silicon oxide / silicon interface reflection to replace the epitaxial DBR. However, this structure is still based on a mesa-type detector, and the bonding process itself is incompatible with standard CMOS processes, making monolithic integration impossible and failing to solve the fundamental problem of deep integration with silicon-based photonics platforms.

[0006] Overall, existing resonance enhancement schemes still have significant limitations in terms of process compatibility, integration, or optical bandwidth, and further exploration is needed to find simpler, higher-performance detector structures that are more suitable for integrated photonic platforms. Summary of the Invention

[0007] To address the above technical problems, this invention discloses a resonant cavity-enhanced germanium-silicon photodetector based on a silicon corner mirror, which has excellent high-power processing capabilities and is compatible with CMOS manufacturing processes, facilitating mass production.

[0008] The technical solution adopted by this invention is as follows: A resonant cavity-enhanced germanium-silicon photodetector based on silicon corner mirrors includes a silicon substrate layer, a germanium absorption region on the silicon substrate layer, and silicon corner mirrors located on the front and rear sides of the germanium absorption region on the silicon substrate layer. The germanium absorption region and the silicon corner mirrors together constitute an optical resonant cavity. The upper part of the germanium absorption region is provided with a germanium layer via layer, which has a plurality of germanium layer vias, and a signal electrode is provided at the top of the germanium layer via layer; silicon layer via layers are provided on the left and right sides of the germanium absorption region, which have a plurality of silicon layer vias, and a ground electrode is provided at the top of the silicon layer via layer; two silicon nitride waveguides are arranged opposite to each other, and the two silicon nitride waveguides extend from the opposite outer sides of the two silicon layer via layers toward the side of the germanium absorption region, for coupling the evanescent wave of the optical signal into the germanium absorption region.

[0009] In this technical solution, the optical signal is first split on-chip, then input through silicon nitride waveguides on both sides, and coupled into the germanium absorption region via evanescent wave coupling. After absorbing photons, the germanium absorption region generates electron-hole pairs. Under the influence of the built-in electric field, the electrons and holes move in opposite directions, forming a photocurrent. Electrons are collected through vias in the germanium layer to the signal electrode for output, while holes flow through vias in the silicon layer to the ground electrode.

[0010] Because the germanium absorption region is relatively short (typically 2-5 μm wide and 5-10 μm long) and small in volume, incident light may not be completely absorbed on its first pass. Upon reaching the end of the germanium absorption region, the unabsorbed light is reflected back into the region by a silicon corner mirror, undergoing secondary or even multiple absorptions. The light propagates back and forth within the resonant cavity formed by the two mirrors until the photons are fully absorbed. This resonance enhancement mechanism significantly improves the device's quantum efficiency and responsivity. Simultaneously, the compact germanium absorption region structure helps reduce the device's RC time constant and carrier transit time, thus ensuring the detector's high bandwidth characteristics.

[0011] As can be seen, the technical solution of the present invention, through the synergistic design of resonant cavity enhancement and lateral waveguide coupling, maintains high bandwidth while improving responsivity, effectively alleviating the inherent contradiction between responsivity and bandwidth in traditional photodetectors.

[0012] As a further improvement of the present invention, a plurality of germanium layer vias and a plurality of silicon layer vias are arranged in an array, and in the horizontal direction, the silicon layer vias and the germanium layer vias are staggered.

[0013] As a further improvement of the present invention, the width of the silicon nitride waveguide gradually decreases from the outside of the silicon via layer. Further, the width of the silicon nitride waveguide gradually decreases from 1000-800 nm to 100-500 nm.

[0014] As a further improvement of the present invention, the distance between the silicon nitride waveguide and the germanium absorption region is 100-200 nm.

[0015] As a further improvement of the present invention, the silicon substrate layer is p-doped, and the region where the silicon substrate layer contacts the silicon layer via is p++ doped to form an ohmic contact between the semiconductor and the metal.

[0016] As a further improvement of the present invention, the region in contact with the germanium absorption region and the germanium layer via is N++ doped to form an ohmic contact between the semiconductor and the metal.

[0017] As a further improvement of the present invention, the silicon corner reflector is an isosceles right-angled triangle structure etched in the silicon layer, with its two right-angled sidewalls serving as reflective surfaces to reflect light incident along a direction parallel to the silicon substrate back along its original path.

[0018] The present invention discloses an optical communication receiving device, comprising a resonant cavity enhanced germanium-silicon photodetector based on a silicon corner mirror as described above.

[0019] Compared with the prior art, the beneficial effects of the present invention are as follows: First, it possesses excellent high-power processing capabilities. Thanks to the significantly weaker nonlinear effects (primarily two-photon absorption) of silicon nitride compared to silicon, the device can withstand higher power optical signal inputs without the risk of melting. Through evanescent wave coupling between the silicon nitride double-sided waveguides and the germanium absorption region, the optical field is uniformly distributed within the absorption region, avoiding absorption saturation or material damage caused by excessively high local light intensity. This significantly improves the reliability and stability of the device under high-power operating conditions.

[0020] Second, it achieves polarization-insensitive detection. Compared to traditional silicon waveguides, which typically only support transverse electric mode transmission due to thickness limitations, the silicon nitride waveguide used in this invention has a larger thickness and mode field size, enabling it to simultaneously and efficiently support the transmission of both transverse electric and transverse magnetic modes. This makes the detector insensitive to changes in the polarization state of the incident light, greatly simplifying the optical system design and improving its flexibility and adaptability in complex practical application environments.

[0021] Third, it effectively overcomes the contradiction between responsivity and bandwidth. By integrating silicon corner mirrors based on photolithography on both sides of the germanium absorption region, a highly efficient Fabry-Perot resonant cavity is constructed. Unabsorbed light within the cavity can pass through the absorption region multiple times after reflection, thereby significantly improving quantum efficiency and responsivity by effectively extending the optical path while maintaining the compact physical size of the absorption region (ensuring high bandwidth), fundamentally optimizing the overall bandwidth-responsivity performance. Furthermore, the silicon corner mirror structure is simpler than the distributed Bragg mirror process, requiring no high-precision etching, and can achieve comparable broadband high reflectivity in the O to L communication band.

[0022] Fourth, it is fully compatible with CMOS manufacturing processes, facilitating large-scale integration and mass production: all key structures of the device, including photolithographically defined silicon corner mirrors, selected-area epitaxially grown germanium absorption regions, ion-implanted PN junctions, and silicon nitride deposition and patterning, can be implemented using standard CMOS process lines. This feature ensures that the invention can be seamlessly integrated with existing silicon-based optoelectronic integration platforms, providing a solid foundation for high-volume, low-cost manufacturing and reliable technical support for large-scale applications in high-density integration scenarios such as data center optical interconnects. Attached Figure Description

[0023] Figure 1 This is a schematic diagram of the resonant cavity-enhanced germanium-silicon photodetector based on a silicon corner mirror according to Embodiment 1 of the present invention.

[0024] Figure 2 This is a cross-sectional view of Embodiment 1 of the present invention.

[0025] Figure 3 This is a top view of Embodiment 1 of the present invention, ignoring the ground electrode and the signal electrode.

[0026] Figure 4 This is a simulation diagram of the light field distribution inside the silicon corner mirror obtained in Embodiment 1 of the present invention.

[0027] Figure 5 This is a graph showing the change in reflectivity of a silicon corner mirror as a function of wavelength, obtained from simulation in Embodiment 1 of the present invention.

[0028] The reference numerals in the figures include: 1-Silicon substrate layer, 2-Silicon corner mirror, 3-Germanium absorption region, 4-Silicon via layer, 5-Ground electrode, 6-Signal electrode, 7-Germanium via layer, 8-Silicon nitride waveguide, 9-Region where silicon substrate layer and silicon via layer contact (i.e., P++ doped region), 10-Region where germanium absorption region and germanium via layer contact (i.e., N++ doped region). Detailed Implementation

[0029] The preferred embodiments of the present invention will be described in further detail below.

[0030] Example 1: As Figures 1-3 As shown, a resonant cavity-enhanced germanium-silicon photodetector based on silicon corner mirrors 2 includes a silicon substrate layer 1, on which a germanium absorption region 3 is provided. Silicon corner mirrors 2 are provided on the front and rear sides of the germanium absorption region 3, and the germanium absorption region 3 and the silicon corner mirrors 2 together form an optical resonant cavity. A germanium layer via layer 7 is provided on the upper part of the germanium absorption region 3, and the germanium layer via layer 7 has a plurality of germanium layer vias. A signal electrode 6 is provided on the top of the germanium layer via layer 7. Silicon layer via layers 4 are provided on the left and right sides of the germanium absorption region 3, and the silicon layer via layer 4 has a plurality of silicon layer vias. A ground electrode 5 is provided on the top of the silicon layer via layer 4. Two silicon nitride waveguides 8 are arranged opposite each other, and the two silicon nitride waveguides 8 extend from the opposite outer sides of the two silicon layer via layers 4 toward the side of the germanium absorption region 3, for coupling the evanescent wave of the optical signal into the germanium absorption region 3. A plurality of germanium layer vias and a plurality of silicon layer vias are arranged in an array, and in the horizontal direction, the silicon layer vias and the germanium layer vias are staggered.

[0031] like Figure 2 In the optical coupling structure shown, because the refractive index of the germanium absorption region 3 is greater than that of the silicon nitride waveguide 8, and the distance between them is 100-200 nm, light will enter the germanium region via evanescent wave coupling during propagation. The germanium layer via 7 is used to connect the device and the electrode.

[0032] like Figure 3 As shown, the silicon substrate layer 1 is p-doped, and the region 9 where the silicon substrate layer contacts the silicon layer via is p++ doped to form an ohmic contact between the semiconductor and the metal. The region 10 where the germanium absorption region contacts the germanium layer via is n++ doped to form an ohmic contact between the semiconductor and the metal.

[0033] The width of the silicon nitride waveguide 8 gradually decreases from the outside of the silicon via layer 4. The width of the silicon nitride waveguide 8 gradually decreases from 1000-800nm ​​to 100-500nm.

[0034] The silicon corner reflector 2 is an isosceles right-angled triangle structure etched in the silicon layer, with its two right-angled sidewalls serving as reflective surfaces to reflect light incident along a direction parallel to the silicon substrate back along its original path.

[0035] like Figure 4 The simulated light field distribution within the silicon corner mirror 2, as shown, clearly demonstrates light reflection. Figure 5 The simulation results of the silicon corner reflector 2 show that its reflectivity varies with wavelength. It can be seen that it has a reflectivity of no less than 0.8 in the entire communication band. Compared with the distributed Bragg reflector, its working wavelength range is greatly widened. At the same time, it has lower requirements for assembly process and is less sensitive to process errors.

[0036] The silicon corner mirror 2 is analogous to the principle of a right-angle mirror in geometric optics, forming an isosceles right-angled triangle structure through etching in the silicon layer. Incident light, after passing through one sidewall, is deflected by 90 degrees, then reflected by the other sidewall, deflected again by 90 degrees, and finally returns in the opposite direction to the incident light, thus achieving efficient light reflection. This structure has a simple manufacturing process, is fully compatible with CMOS technology, and is suitable for efficient on-chip optical path reflection and resonant cavity construction.

[0037] In this embodiment, the optical signal is first split on-chip and then input through silicon nitride waveguides 8 on both sides, entering the germanium absorption region 3 via evanescent wave coupling. After absorbing photons, the germanium absorption region 3 generates electron-hole pairs. Under the influence of the built-in electric field, the electrons and holes move in opposite directions, forming a photocurrent. Electrons are collected through vias in the germanium layer and output to the signal electrode 6, while holes flow through vias in the silicon layer to the ground electrode 5.

[0038] Because the germanium absorption region 3 is relatively short (5-10 μm) and small in volume, incident light may not be completely absorbed on its first pass. After propagating to the end of the germanium absorption region 3, the unabsorbed light is reflected back into the germanium absorption region 3 by the silicon corner mirror 2, undergoing secondary or even multiple absorptions. The light propagates back and forth within the resonant cavity formed by the silicon corner mirror 2 until the photons are fully absorbed. This resonance enhancement mechanism significantly improves the quantum efficiency and responsivity of the device. At the same time, the compact germanium absorption region 3 structure helps to reduce the RC time constant and carrier transit time of the device, thereby ensuring the high bandwidth characteristics of the detector.

[0039] The technical solution in this embodiment improves responsivity while maintaining high bandwidth through the synergistic design of resonant cavity enhancement and lateral waveguide coupling, effectively alleviating the inherent contradiction between responsivity and bandwidth in traditional photodetectors.

[0040] Example 2: An optical communication receiving device comprising a cavity-enhanced germanium-silicon photodetector based on a silicon corner mirror as described in Example 1.

[0041] The above description, in conjunction with specific preferred embodiments, provides a further detailed explanation of the present invention. It should not be construed that the specific implementation of the present invention is limited to these descriptions. For those skilled in the art, various simple deductions or substitutions can be made without departing from the concept of the present invention, and all such modifications and substitutions should be considered within the scope of protection of the present invention.

Claims

1. A resonant cavity-enhanced germanium-silicon photodetector based on a silicon corner mirror, characterized in that: The device includes a silicon substrate layer, on which a germanium absorption region is provided, and silicon corner mirrors are provided on both the front and rear sides of the germanium absorption region. The germanium absorption region and the silicon corner mirrors together form an optical resonant cavity. The upper part of the germanium absorption region is provided with a germanium layer via layer, which has a plurality of germanium layer vias, and a signal electrode is provided at the top of the germanium layer via layer; silicon layer via layers are provided on the left and right sides of the germanium absorption region, which have a plurality of silicon layer vias, and a ground electrode is provided at the top of the silicon layer via layer; two silicon nitride waveguides are arranged opposite to each other, and the two silicon nitride waveguides extend from the opposite outer sides of the two silicon layer via layers toward the side of the germanium absorption region, for coupling the evanescent wave of the optical signal into the germanium absorption region.

2. The resonant cavity-enhanced germanium-silicon photodetector based on a silicon corner mirror according to claim 1, characterized in that: A plurality of germanium layer vias and a plurality of silicon layer vias are arranged in an array, and in the horizontal direction, the silicon layer vias and the germanium layer vias are staggered.

3. The resonant cavity-enhanced germanium-silicon photodetector based on a silicon corner mirror according to claim 1, characterized in that: The width of the silicon nitride waveguide gradually decreases from the outside of the silicon via layer.

4. The resonant cavity-enhanced germanium-silicon photodetector based on a silicon corner mirror according to claim 3, characterized in that: The width of the silicon nitride waveguide gradually decreases from 1000-800nm ​​to 100-500nm.

5. The resonant cavity-enhanced germanium-silicon photodetector based on a silicon corner mirror according to claim 1, characterized in that: The distance between the silicon nitride waveguide and the germanium absorption region is 100-200 nm.

6. The resonant cavity-enhanced germanium-silicon photodetector based on a silicon corner mirror according to claim 1, characterized in that: The silicon substrate layer is P-doped, and the region where the silicon substrate layer contacts the silicon layer via is P++ doped.

7. The resonant cavity-enhanced germanium-silicon photodetector based on a silicon corner mirror according to claim 1, characterized in that: The region where the germanium absorption region contacts the germanium layer via is N++ doped.

8. The resonant cavity-enhanced germanium-silicon photodetector based on a silicon corner mirror according to claim 1, characterized in that: The silicon corner mirror is an isosceles right-angled triangle structure etched in the silicon layer, with its two right-angled sidewalls serving as reflective surfaces to reflect light incident along a direction parallel to the silicon substrate back along its original path.

9. An optical communication receiving device, characterized in that, The invention comprises a resonant cavity-enhanced germanium-silicon photodetector based on a silicon corner mirror as described in any one of claims 1 to 8.

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