2-micron wave band silicon-based germanium surface incidence type high-speed high-responsivity photoelectric detector

Abstract

The invention discloses a 2-micron wave band silicon-based germanium surface incidence type high-speed high-responsivity photoelectric detector, which comprises a p-type doped silicon layer 005, the upper surface of the p-type doped silicon layer 005 is provided with a germanium absorption region 006 and a cathode electrode 011, and the cathode electrode 011 surrounds the germanium absorption region 006; the middle part of the germanium absorption area 006 is provided with a porous resonant cavity array 009, the upper surface of the germanium absorption area 006 is provided with an anode electrode 012, and the anode electrode 012 surrounds the porous resonant cavity array 009. Through direct incidence, a 2-micron optical signal output by an external laser source is input into a germanium absorption region, the optical signal in the germanium absorption region is transversely propagated in the germanium absorption region due to a porous resonant cavity array structure, is finally limited and concentrated in the germanium absorption region, and generates two-photon absorption in the germanium absorption region to generate a free electron hole pair; oriented movement is carried out under external bias voltage loaded through the electrodes, and light current is formed.

Description

Technical Field

[0001] The present invention belongs to the field of photodetectors, and more specifically, it is a silicon-based germanium photodetector that is convenient for large-scale mass production and has a higher yield rate. Background Art

[0002] Photodetectors utilize the photoelectric effect generated by semiconductor materials. When irradiated with light within a specific wavelength range, electron-hole pairs are generated inside the semiconductor material. Through the diffusion or drift motion of carriers, a current is generated, realizing the conversion from optical signals to electrical signals. Photodetectors play a crucial role in optical communication and information processing systems.

[0003] With the continuous growth of the demands for 5G, the Internet of Things, and big data, the capacity of fiber-based communication systems is constantly increasing. However, the bandwidth capacity of current standard single-mode fibers in the 1310nm and 1550nm bands is approaching the theoretical capacity limit, and it may not be possible to achieve additional bandwidth capacity gains using current technologies. Therefore, new technologies are needed to further increase the bandwidth capacity of the Internet to drive the next wave of Internet innovation.

[0004] Compared with the traditional 1310nm and 1550nm communication bands, 2 microns is a communication band with great potential, covering the communication range of 1.7 - 2.1 microns in wavelength and having a larger bandwidth. At the same time, many devices with high performance in the 2-micron band have emerged. For example, the hollow photonic bandgap fiber has a theoretical minimum loss below 0.1 db / km in the 2-micron band, which is lower than that of traditional single-mode fibers. It also has the advantages of high radiation hardness and low thermal sensitivity. The optical gain window of the thulium-doped fiber amplifier is around 1.81 - 2.05 microns, with a gain as high as 36 dB and a noise figure as low as 4.5 dB, and it can be used as an equivalent erbium-doped fiber amplifier in a 2-micron communication system. At the same time, the 2-micron band has great application potential in non-invasive blood glucose optical detection and satellite communication. All these advantages make the 2-micron band likely to become a new communication band with great development prospects.

[0005] However, there are some practical problems with current III-V photodetectors (such as InGaAs / InP) operating in the 2-μm band. Although bulk materials with high indium content, such as InGaAs, have increased the responsivity of 2-μm photodetectors to 0.93 A / W, they face challenges such as difficult acquisition of absorption materials, complex device manufacturing processes, and cumbersome processing. To achieve high-signal-to-noise ratio signal transmission in the 2-μm band, researchers need to obtain photodetectors with high photoelectric conversion efficiency in batches and at low cost. However, based on the current technical route, it is still difficult to achieve large-scale low-cost production. Silicon photonics is a silicon-based material platform for manufacturing photonic integrated circuits. For silicon-based devices, the silicon-based device technology based on silicon-on-insulator (SOI) substrates has developed rapidly in the past two decades. Since the SOI technology is compatible with complementary metal-oxide-semiconductor (CMOS) manufacturing processes, this makes it possible to produce large-scale, compact, and low-cost photodetectors.

[0006] Although silicon-based photodetectors have been widely used in photodetection in the visible and near-infrared regions, silicon is an indirect bandgap material with a bandgap width of 1.12 eV, resulting in a relatively low cut-off wavelength of the absorption spectrum of silicon-based photodetectors, approximately 1.1 μm. Therefore, it cannot be directly applied to the 2-μm band.

[0007] Germanium and silicon belong to the same group VI materials. Germanium has a smaller bandgap width than silicon, approximately 0.8 eV, and also has advantages such as a large absorption coefficient, high carrier mobility, and compatibility with complementary metal-oxide-semiconductor (CMOS) manufacturing processes. Therefore, silicon-based germanium detectors are a very promising option. Although the absorption cut-off wavelength of germanium is greater than that of silicon and it can operate in the 1310-nm and 1550-nm bands, its intrinsic absorption in the 2-μm band is also very small. To fabricate 2-μm semiconductor devices based on the low-cost and high-yield SOI platform, additional methods are needed to extend the operating band of silicon-based germanium photodetectors to 2 μm. For example, by doping other materials into germanium or introducing nonlinear effects such as two-photon absorption to extend its operating wavelength.

[0008] Generally speaking, when the photoelectric effect occurs, a semiconductor material absorbs a photon and causes the free electrons to transition, generating a pair of electron-hole pairs. However, when the incident light intensity is high enough, nonlinear effects will occur in the semiconductor material. Two-photon absorption is one such nonlinear effect. Introducing two-photon absorption in silicon-based germanium detectors can extend the operating wavelength of the detectors to the 2-μm band. However, two-photon absorption is a weak absorption effect. Under the same input optical power, two-photon absorption is much weaker than intrinsic absorption.

[0009] Enhancing the photon density in the active region of a detector by increasing the input optical power to improve two-photon absorption is not an ideal solution because high-power light sources consume a large amount of energy, and it is difficult to achieve a large laser control device required for high-power lasers based on existing processes. There is also an attempt to increase the detector responsivity by increasing the active area of the photodetector, but this reduces the response speed and bandwidth of the photodetector.

[0010] For a surface-incident photodetector, light enters from above the device. To ensure that the light in the optical path is completely absorbed, this means that the semiconductor requires a thicker absorption layer to fully absorb the incident light. Photon trapping holes are porous resonators that can be integrated into the semiconductor structure. The semiconductor with photon trapping holes changes the light propagation path by guiding light almost perpendicular to the incident direction. This phenomenon helps to enhance the lateral light field in the device, enabling the use of a thinner absorption layer in the photodetector. At the same time, the effective absorption coefficient of a detector with a porous resonator array is much higher than that of a detector without holes. This porous resonator design breaks the trade-off between the efficiency and bandwidth of using indirect bandgap materials to construct detectors.

[0011] How to enhance the light field in the active region of a surface-incident silicon-germanium photodetector based on a porous resonator structure to improve the two-photon absorption effect and achieve photodetection in the 2-micron band is the key to fabricating a surface-incident silicon-germanium photodetector. Summary of the Invention

[0012] The technical problem to be solved by the present invention is:

[0013] Aiming at the difficulty of effectively detecting optical signals in the 2-micron band by current silicon-based photodetectors, the present invention enables a silicon-based detector to perform photodetection in the 2-micron band by using two-photon absorption in nonlinear absorption.

[0014] The technical solution of the present invention is:

[0015] A 2-micron band surface-incident high-speed and high-responsivity silicon-germanium photodetector, comprising a p-type doped silicon layer 005. On the upper surface of the p-type doped silicon layer 005, there are a germanium absorption region 006 and a cathode electrode 011, and the cathode electrode 011 surrounds the germanium absorption region 006. In the middle part of the germanium absorption region 006, there is a porous resonator array 009. On the upper surface of the germanium absorption region 006, there is an anode electrode 012, and the anode electrode 012 surrounds the porous resonator array 009.

[0016] The porous resonator array 009 is formed by arranging a plurality of circular holes. The radius of each circular hole is 300 - 400 nm, and the spacing is 900 - 1100 nm.

[0017] The germanium absorption region 006 is composed of an upper n-type doped germanium layer 013 and a lower intrinsic germanium layer 014.

[0018] The depth of each hole in the multi-hole resonant cavity array 009 is equal to the height of the germanium absorption region 006 .

[0019] The p-type doped silicon layer 005 is heavily doped with boron; and the n-type doped germanium layer 013 is heavily doped with phosphorus.

[0020] The thickness of the p-type doped silicon layer 005 is 200-250 nm, and the radius is 10-15 microns. The thickness of the germanium absorption region 006 is 1-1.1 microns, and the radius is 8-12 microns.

[0021] Below the p-type doped silicon layer 005 are a buried oxide layer 007 and a silicon substrate 008 in sequence, and a silicon dioxide protection layer 004 covers the p-type doped silicon layer 005 and the germanium absorption region 006 .

[0022] The cathode electrode 011 and the anode electrode 012 are exposed from the upper surface of the silicon dioxide protection layer 004 and are connected to the GSG pins 003 through the metal layer 002 .

[0023] The working principle of the silicon-based incident photodetector of the present invention is:

[0024] The 2-micron light signal output by an external laser source is input into the germanium absorption zone through direct incidence. Due to the porous resonant cavity array structure, the light signal in the germanium absorption zone propagates laterally in the germanium absorption zone and is eventually confined and concentrated in the germanium absorption zone. Two-photon absorption occurs in the germanium absorption zone, generating free electron-hole pairs, which move in a direction under the external bias voltage loaded through the electrode to form a photocurrent.

[0025] Beneficial effects of the present invention:

[0026] The present invention utilizes the two-photon absorption effect of semiconductor materials, and utilizes a silicon-based platform and a porous resonant cavity structure to realize a 2-micron band photoelectric detector with low cost, low preparation difficulty, and high integration. While retaining the characteristics of compatibility with mature complementary metal oxide semiconductor technology, the detector adds a porous resonant cavity array structure in the germanium absorption region, so that the incident light propagates laterally in the absorption region, and the light is well confined and concentrated in the germanium absorption region. In numerical simulation, good detection effects are achieved, and high responsiveness and high bandwidth are achieved. At the same time, due to the porous resonant cavity array structure, the detector is insensitive to the polarization of the incident light. This provides a new idea for the design of future 2-micron band and infrared band photoelectric detectors to which it belongs. BRIEF DESCRIPTION OF THE DRAWINGS

[0027] Figure 1 It is an overall top view of the silicon-based surface-incident photodetector in the present invention.

[0028] Figure 2 for Figure 1Top view of the middle detector part.

[0029] Figure 3 For Figure 2 Cross-sectional view of the middle detector.

[0030] Reference numerals: detector body 001; metal layer 002; GSG pin 003; silicon dioxide protective layer 004; p-type doped silicon layer 005; germanium absorption region 006; buried oxide layer 007; silicon substrate 008; porous resonator array 009; detector cross-section 010; cathode electrode 011; anode electrode 012; n-type doped germanium layer 013; intrinsic germanium layer 014. Detailed implementation manners

[0031] Example 1:

[0032] A silicon-based photodetector includes a detector body 001, a metal layer 002, and a GSG pin 003.

[0033] Wherein the detector body consists of a p-type doped silicon layer 005, a germanium absorption region 006 epitaxially grown above the p-type doped silicon layer 005, and the germanium absorption region 006 consists of an n-type doped germanium layer 013 and an intrinsic germanium layer 014.

[0034] The p-type doped silicon layer 005 is heavily doped with boron; the n-type doped germanium layer 013 is heavily doped with phosphorus.

[0035] A porous resonator array 009 is obtained by etching in the germanium absorption region, and its depth is equal to the height of the germanium absorption region 006, that is, the porous resonator array 009 exists in the n-type doped germanium layer 013 and the intrinsic germanium layer 014. The radius of each hole in the porous resonator array 009 is 350 nm, and the pitch is 980 nm.

[0036] A cathode electrode 011 is installed above the p-type doped silicon layer 005, and an anode electrode 012 is installed above the germanium absorption region 006. A silicon dioxide protective layer 004 is injected on the buried oxide layer 007 to coat the p-type doped silicon layer 005 and the germanium absorption region 006. Both the metal layer 002 and the GSG pin 003 are above the silicon dioxide protective layer 004, and the metal layer 002 is responsible for connecting the cathode electrode 011 and the anode electrode 012 to the GSG pin 003.

[0037] There is a buried oxide layer 007 and a silicon substrate 008 under the p-type doped silicon layer 005.

[0038] Example 2:

[0039] Referring to the attached Figure 1 、 Figure 2 , the main structure of the surface-incident photodetector provided by the present invention includes:

[0040] Silicon substrate 008, on the upper surface of which there is a buried oxide layer 007 and a p-type doped silicon layer 005. The thickness of the silicon buried oxide layer 007 is 2000 nm, and the thickness of the p-type doped silicon layer 005 is 220 nm with a radius of 12 microns.

[0041] On the upper surface of the p-type doped silicon layer 005, a germanium absorption region 006 is grown epitaxially to form a Ge-on-Si structure with the p-type doped silicon layer 005. The two-photon absorption coefficient of germanium at the 2-micron wavelength band is approximately 4000 times that of silicon, thereby enabling the detector to operate at the 2-micron wavelength band.

[0042] Furthermore, for a silicon-based germanium vertical-incidence photodetector, considering the mutual constraint between bandwidth and absorption efficiency, the optical field should be confined in a relatively thin germanium absorption region while achieving high bandwidth and high absorption efficiency. Therefore, a porous resonator array structure is added to the germanium absorption region, enabling the vertically incident light to propagate laterally in the absorption region. According to the bandwidth estimation formula, the total thickness of the germanium absorption region 005 is set to 1.03 microns with a radius of 10 microns, and at this time the bandwidth can reach 49 GHz. Subsequently, according to FDTD numerical simulation, for a 2-micron optical signal, when a porous resonator array with a pore radius of 350 nm and a pitch of 980 nm is added to the Ge-on-Si surface-incidence structure, most of the optical field of the 2-micron optical signal is confined and concentrated in the Ge absorption layer.

[0043] Refer to the appendix Figure 2 , from top to bottom, the germanium absorption region consists of an n-type doped germanium layer 013 with a thickness of 100 nm and an intrinsic germanium layer 014 with a thickness of 930 nm. The cathode electrode 011, anode electrode 012, metal layer 002, and GSG pin 003 are prepared by methods such as resistive thermal evaporation, electron beam evaporation, or magnetron sputtering.

[0044] The above specific embodiments have further detailed the purpose, technical solutions, and beneficial effects of the present invention. It should be understood that the above are only specific embodiments of the present invention and are not used to limit the present invention. Any modifications, equivalent replacements, improvements, etc. made within the spirit and principles of the present invention shall be included within the protection scope of the present invention.

Claims

1. A 2-μm band silicon-based germanium front-illuminated high-speed and high-responsivity photodetector, comprising a p-type doped silicon layer (005), characterized in that: The upper surface of the p-type doped silicon layer (005) has a germanium absorption region (006) and an anode electrode (011), and the anode electrode (011) surrounds the germanium absorption region (006); the middle part of the germanium absorption region (006) has a porous resonator array (009), and the upper surface of the germanium absorption region (006) has a cathode electrode (012), and the cathode electrode (012) surrounds the porous resonator array (009).

2. The 2-μm band silicon-germanium front-illuminated high-speed and high-responsivity photodetector according to claim 1, characterized in that: The porous resonator array (009) is formed by arranging a plurality of circular holes, and the radius of each circular hole is 300 - 400 nm, and the spacing is 900 - 1100 nm.

3. The 2-μm band silicon-germanium front-illuminated high-speed and high-responsivity photodetector according to claim 1, wherein: The germanium absorption region (006) is composed of an upper n-type doped germanium layer (013) and a lower intrinsic germanium layer (014).

4. The 2-μm-band silicon-germanium front-illuminated high-speed and high-responsivity photodetector according to claim 1, wherein: The thickness of the p-type doped silicon layer (005) is 200 - 250 nm, and the radius is 10 - 15 microns. The thickness of the germanium absorption region (006) is 1 - 1.1 microns, and the radius is 8 - 12 microns.

5. The silicon germanium surface incident type high-speed and high responsivity photodetector in the 2-micron band according to any one of claims 1-4, characterized in that: Beneath the p-type doped silicon layer 005 are a buried oxide layer (007) and a silicon substrate (008) in sequence, and a silicon dioxide protection layer (004) covers the p-type doped silicon layer (005) and the germanium absorption region (006).

6. The 2-μm-band silicon-germanium front-illuminated high-speed and high-responsivity photodetector according to claim 5, wherein: The anode electrode (011) and the cathode electrode (012) are exposed from the upper surface of the silicon dioxide protection layer (004), and are respectively connected to the GSG pin (003) through a metal layer (002).

7. The 2-μm band silicon-germanium surface-incident high-speed and high-responsivity photodetector according to claim 5, wherein: The depth of each hole in the porous resonator array (009) is equal to the height of the germanium absorption region (006).

8. The 2-μm band silicon-germanium front-illuminated high-speed and high-responsivity photodetector according to claim 5, wherein: The p-type doped silicon layer (005) is heavily doped with boron; the n-type doped germanium layer (013) is heavily doped with phosphorus.

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