Germanium-silicon photodetector based on transparent electrodes

Abstract

The present application relates to a kind of germanium silicon photodetector based on transparent electrode, belong to photodetector field.The detector includes flat plate silicon waveguide;Doped germanium layer is located in the upper surface of flat plate silicon waveguide;P doped layer and N doped layer are located in the inside of doped germanium layer, and the lower surface of germanium upper transparent electrode;Germanium upper transparent electrode is located in the upper surface of P doped layer, N doped layer and doped germanium layer.P doped layer, doped germanium layer, N doped layer form horizontal PIN junction;Germanium upper transparent electrode absorbs the photo-generated carrier generated by doped germanium layer absorption light, forms photoelectric current.The present application reduces electrode spacing, improves bandwidth, changes traditional metal electrode to transparent electrode at the same time, uses the light transmission of transparent electrode, restores the responsivity drop caused by reducing the spacing of metal electrode, and transparent electrode is designed as point contact structure, further improves responsivity, solves the problem of bandwidth and responsivity restriction.

Description

Technical Field

[0001] This invention belongs to the field of photodetectors and relates to a germanium-silicon photodetector based on transparent electrodes. Background Technology

[0002] Germanium-silicon photodetectors are crucial devices for photoelectric conversion in silicon photonics technology. Because silicon photonics is compatible with mature CMOS processes, it can meet the market demand for low-cost photonic device integration. Silicon materials have an intrinsic absorption limit in the 1550 nm communication band, making them unsuitable for direct near-infrared detection. Germanium, with its narrow bandgap of 1.55 eV (corresponding to the 1550 nm absorption peak) and low lattice mismatch (4.2%) with silicon, has become an ideal choice for silicon-based photodetectors.

[0003] In terms of structural design, germanium-silicon detectors are mainly divided into surface-incident and waveguide-coupled types. Surface-incident types have simple structures and high coupling efficiency, making them suitable for free-space optical receiving modules; while waveguide-coupled types (such as vertical PIN or horizontal PIN structures) achieve efficient optical signal transmission through evanescent wave or docking coupling, are easy to integrate with other photonic devices, and have become the mainstream choice for on-chip optical interconnects.

[0004] Germanium-silicon photodetectors play a crucial role in silicon photonic devices. Breakthroughs in their performance, including bandwidth and responsivity, are key to meeting the explosive growth in data communication demands, especially in the field of photoelectric conversion.

[0005] However, the bandwidth improvement of germanium-silicon photodetectors is subject to many constraints. For example, in germanium-silicon photodetectors with a lateral PIN structure, the RC time and transit time are inversely proportional to the bandwidth. Reducing the electrode spacing can reduce the bulk resistance, i.e., reduce the series resistance, thereby reducing the RC time. At the same time, a smaller electrode spacing brings a stronger electric field strength, thereby reducing the transit time. However, reducing the electrode spacing will cause the metal electrode to cover a larger area of ​​the light absorption region of the doped germanium layer, resulting in a decrease in responsivity. This creates a contradiction between responsivity and bandwidth, requiring new technical solutions to solve the problem. Summary of the Invention

[0006] In view of this, the purpose of the present invention is to provide a germanium-silicon photodetector based on transparent electrodes, which solves the technical problem that the responsivity and bandwidth are inversely proportional when using traditional metal electrodes in germanium-silicon photodetectors to reduce the electrode spacing to increase bandwidth.

[0007] To achieve the above objectives, the present invention provides the following technical solution: A germanium-silicon photodetector based on transparent electrodes includes a planar silicon waveguide 101, a germanium-doped layer 102, a P-doped layer 103 and an N-doped layer 104, and transparent electrodes on germanium (including a germanium-doped transparent electrode positive electrode 105 and a germanium-doped transparent electrode negative electrode 106).

[0008] The planar silicon waveguide 101 has a planar structure and is made of Si.

[0009] The germanium-doped layer 102 is located on the upper surface of the planar silicon waveguide 101. It has a trapezoidal strip structure and is made of doped Ge.

[0010] The P-doped layer 103 and the N-doped layer 104 are located inside the germanium-doped layer 102 and on the lower surface of the transparent electrode on the germanium layer, with a doping level on the order of [missing information]. .

[0011] The germanium top electrode is located on the upper surface of the P-doped layer 103, the N-doped layer 104, and the germanium-doped layer 102. The germanium top electrode has a continuous contact or point contact structure with a spacing of 0.5 mm. 1.4µm. The material of the germanium top electrode is a transparent electrode material, which can include oxide transparent conductive materials, such as: ITO (Indium Tin Oxide), AZO (Aluminum-doped Zinc Oxide), FTO (Fluorine-doped Tin Oxide), ATO (Antimony-doped Tin Oxide); carbon-based transparent conductive materials, such as: graphene, carbon nanorods; metal-based transparent conductive materials, such as metal mesh, silver nanowires, stacked disordered silver nanomesh; polymer transparent conductive materials, such as: poly(3,4-ethylenedioxythiophene): polystyrene sulfonic acid.

[0012] P-doped layer 103, germanium-doped layer 102 and N-doped layer 104 are sequentially connected to form a PIN junction; The planar silicon waveguide 101 serves as an optical waveguide, guiding incident light into the germanium-doped layer 102 for light absorption. The transparent electrode on germanium absorbs the photogenerated carriers generated by the absorption of light by the germanium-doped layer 102, forming a photocurrent and realizing the photoelectric detection function.

[0013] The beneficial effects of this invention are as follows: This solution reduces the electrode spacing, decreases the series resistance and RC time, and enhances the electric field effect, accelerates carrier drift, and reduces transit time, thereby improving bandwidth. This solution replaces the traditional metal electrode with a transparent electrode, overcoming the technical problem that reducing the electrode spacing would lead to a larger area of ​​the metal electrode covering the light absorption region of the germanium-doped layer, resulting in a decrease in responsivity. This creates a contradiction between responsivity and bandwidth. This solution improves bandwidth while maintaining responsivity, and further optimizes the electrode structure by changing the continuous contact electrode to a point contact electrode, further ensuring responsivity.

[0014] Other advantages, objectives, and features of the invention will be set forth in part in the description which follows, and in part will be apparent to those skilled in the art from the following examination, or may be learned from practice of the invention. The objectives and other advantages of the invention can be realized and obtained through the following description. Attached Figure Description

[0015] To make the objectives, technical solutions, and advantages of the present invention clearer, the preferred embodiments of the present invention will be described in detail below with reference to the accompanying drawings, wherein: Figure 1 This is a schematic diagram of the structure of the photodetector based on transparent electrodes according to the present invention; Figure 2 This is the equivalent circuit diagram of the photodetector based on transparent electrodes of the present invention; Figure 3 These are the series resistance Rs and junction capacitance Cj for different electrode spacings, electrode materials, and structures; Figure 4 It is the normalized frequency response and bandwidth for different electrode spacings, electrode materials and structures; Figure 5 It refers to the response to different electrode spacings, electrode materials, and structures.

[0016] Figure reference numerals: 101-planar silicon waveguide, 102-doped germanium layer, 103-P-doped layer, 104-N-doped layer, 105-positive transparent electrode on germanium, 106-negative transparent electrode on germanium. Detailed Implementation

[0017] The following specific examples illustrate the implementation of the present invention. Those skilled in the art can easily understand other advantages and effects of the present invention from the content disclosed in this specification. The present invention can also be implemented or applied through other different specific embodiments, and various details in this specification can be modified or changed based on different viewpoints and applications without departing from the spirit of the present invention. It should be noted that the illustrations provided in the following embodiments are only schematic representations of the basic concept of the present invention. Unless otherwise specified, the following embodiments and features can be combined with each other.

[0018] The accompanying drawings are for illustrative purposes only and are schematic diagrams, not actual pictures. They should not be construed as limiting the invention. To better illustrate the embodiments of the invention, some parts in the drawings may be omitted, enlarged, or reduced, and do not represent the actual product dimensions. It is understandable to those skilled in the art that some well-known structures and their descriptions may be omitted in the drawings.

[0019] In the accompanying drawings of the embodiments of the present invention, the same or similar reference numerals correspond to the same or similar components. In the description of the present invention, it should be understood that if terms such as "upper," "lower," "left," "right," "front," and "rear" indicate the orientation or positional relationship based on the orientation or positional relationship shown in the drawings, they are only for the convenience of describing the present invention and simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, or be constructed and operated in a specific orientation. Therefore, the terms used to describe positional relationships in the drawings are only for illustrative purposes and should not be construed as limiting the present invention. For those skilled in the art, the specific meaning of the above terms can be understood according to the specific circumstances.

[0020] In order to overcome the contradiction that existing germanium-silicon photodetectors reduce the responsivity due to the larger area of ​​the metal electrode covering the light absorption region of the germanium-doped layer during the process of reducing the electrode spacing to decrease the RC time and transit time and thus increase the bandwidth, the present invention proposes a photodetector based on transparent electrodes.

[0021] Example 1: like Figure 1 As shown, this embodiment provides a photodetector based on transparent electrodes, including: a planar silicon waveguide 101, a germanium-doped layer 102, a P-doped layer 103 and an N-doped layer 104, and a transparent electrode positive 105 and a transparent electrode negative 106 on germanium.

[0022] The planar silicon waveguide 101 is made of Si and has a planar structure with a length of 22 μm, a width of 4.6 μm, and a height of 0.3 μm.

[0023] The germanium-doped layer 102 is made of doped Ge and has a trapezoidal strip structure. It is 18 μm long, 2 μm wide on the upper surface, 1.65 μm wide on the lower surface, and 0.3 μm high. It is located on the upper surface of the planar silicon waveguide 101.

[0024] P-doped layer 103 and N-doped layer 104, with doping concentrations on the order of... It is located inside the germanium-doped layer 102 and on the lower surface of the transparent electrode 104 on the germanium layer.

[0025] The positive electrode 105 and negative electrode 106 of the transparent electrode on germanium are made of ITO transparent conductive material. The structure is a point contact type. Each contact point is 0.2 μm long, 0.2 μm wide and 1 μm high. There are a total of 6 pairs of contact points for the left and right positive and negative electrodes. The positive electrode 105 is in contact with the P-doped layer 103 and the negative electrode 106 is in contact with the N-doped layer 104. The electrode spacing is 0.6 μm.

[0026] P-doped layer 103, germanium-doped layer 102, and N-doped layer 104 are sequentially connected to form a PIN junction. Incident light is input from one end of planar silicon waveguide 101 and guided into germanium-doped layer 102 for light absorption. At the same time, a -1V bias voltage is applied to the positive electrode 105 to form a large depletion region in the intrinsic region. The intrinsic region absorbs photons to generate electron-hole pairs. The electric field sweeps these charge carriers out of the depletion region to generate photocurrent and realize photoelectric detection function.

[0027] Example 2: Based on the photodetector based on transparent electrodes provided in Example 1, the transparent electrode on germanium can be a continuous contact structure.

[0028] Verification experiment: Under the design scheme of Example 1, the obtained responsivity is 0.79 A / W ( Figure 3 (d)), with a bandwidth of 75GHz ( Figure 5 (d) exhibits excellent performance, with a response of 0.83 A / W compared to traditional metal Al electrodes, with an electrode spacing of 1.4 μm and a continuous contact structure. Figure 3 (a)), bandwidth 42GHz ( Figure 5 (a) fully realizes the main idea of ​​this invention: to improve bandwidth while reducing electrode spacing by utilizing ITO transparent electrodes and optimized electrode structures, while ensuring responsivity.

[0029] The following will use equivalent circuit models and the results of various indicators for different electrode materials, different electrode spacings, and different electrode structures to illustrate the principle of the present invention and demonstrate its intent.

[0030] like Figure 2The diagram shown is the equivalent circuit diagram of a photodetector. Reducing the electrode spacing to increase bandwidth essentially involves reducing the depletion region width, decreasing or even eliminating the high-resistivity neutral region, causing charge carriers to drift rather than diffuse, and significantly reducing the bulk resistance. The bulk resistance formula is:

[0031] in, For volume resistance, Resistivity The electrode spacing is (d). For effective cross-sectional area.

[0032] The bulk resistance is the series resistance. By reducing the volume resistance of the main body, the series resistance is also reduced, thus reducing the series resistance. By reducing the volume resistance of the main body, the series resistance is also reduced. Meanwhile, due to the junction capacitance formula:

[0033] in, For junction capacitance, Where is the dielectric constant. W As the depletion region width increases, the electrode spacing decreases, leading to an increase in junction capacitance, but overall... The significant decrease in results in a substantial increase in the bandwidth of the RC time-limited function. The bandwidth formula for the RC time-limited function is:

[0034] in, for , Limited bandwidth, For series resistance, This is the junction capacitance.

[0035] like Figure 3 As shown, Figure 3 In Figure (a), the electrode material is Al, the electrode structure is a continuous contact structure, and the electrode spacing is 1.4 μm. and This is a traditional design; Figure 3 Rs and Cj when the electrode material is Al, the electrode structure is a continuous contact structure, and the electrode spacing is 0.6 μm; Figure 3 In (c), the electrode material is ITO transparent conductive material, the electrode structure is a continuous contact structure, and Rs and Cj are when the electrode spacing is 0.6um; Figure 3The electrode material (d) is ITO transparent conductive material, and the electrode structure is a point contact structure. The Rs and Cj values ​​are shown when the electrode spacing is 0.6 μm. It can be seen that when the bias voltage is -1V, Rs are 7Ω, 3.3Ω, 3.4Ω, and 4.1Ω, respectively. Figure 3 (a) to Figure 2 In (b), as the electrode spacing decreases, Rs decreases significantly. Figure 3 (b) to Figure 3 (c) Figure 3 In (d), changing the electrode material from Al to ITO transparent conductive material slightly increases Rs because the resistivity of ITO transparent material is higher than that of Al metal material, which leads to a sacrifice of some bandwidth. This is a necessary sacrifice to ensure response recovery, and the bandwidth sacrifice is very slight compared to the bandwidth improvement brought by reducing the electrode spacing.

[0036] Meanwhile, reducing the electrode spacing also leads to an increase in electric field strength, which in turn increases carrier velocity and reduces transit time. This can also improve bandwidth from the perspective of bandwidth limited by transit time.

[0037] As shown in 4, Figure 4 In (a), the electrode material is Al, the electrode structure is a continuous contact structure, the electrode spacing is 1.4 μm, and the normalized frequency response has a bandwidth of 42 GHz. This is a traditional design. Figure 4 (b) is the normalized frequency response with a bandwidth of 87 GHz when the electrode material is Al, the electrode structure is a continuous contact structure, the electrode spacing is 0.6 μm. Figure 4 (c) is the normalized frequency response with a bandwidth of 76 GHz when the electrode material is ITO transparent conductive material, the electrode structure is a continuous contact structure, the electrode spacing is 0.6 μm. Figure 4 In section (d), the normalized frequency response with a bandwidth of 75 GHz is achieved when the electrode material is ITO transparent conductive material, the electrode structure is a point contact structure, and the electrode spacing is 0.6 μm. Figure 4 (a) to Figure 4 Figure (b) shows that reducing the electrode spacing can significantly improve the bandwidth, from 42 GHz to 87 GHz; from Figure 4 (b) to Figure 4 In (c), the bandwidth decreased from 87 GHz to 76 GHz, which is a necessary sacrifice of bandwidth due to the greater resistivity of ITO material compared to Al.

[0038] like Figure 5 As shown, Figure 5 In (a), the responsivity is 0.83 A / W when the electrode material is Al, the electrode structure is a continuous contact structure, and the electrode spacing is 1.4 μm. This is the traditional design. Figure 5In Figure (b), the responsivity is 0.53 A / W when the electrode material is Al, the electrode structure is a continuous contact structure, and the electrode spacing is 0.6 μm. Figure 5 In the middle (c), the responsivity is 0.72 A / W when the electrode material is ITO transparent conductive material, the electrode structure is a continuous contact structure, and the electrode spacing is 0.6 μm. Figure 5 In the middle (d), the responsivity is 0.78 A / W when the electrode material is ITO transparent conductive material, the electrode structure is a point contact structure, and the electrode spacing is 0.6 μm.

[0039] from Figure 5 (a) to Figure 5 In (b), the responsivity dropped significantly from 0.83 A / W to 0.53 A / W. This is because the reduction in the spacing between the metal electrodes resulted in a larger area of ​​the metal electrodes covering the light absorption region of the germanium-doped layer. The germanium-aluminum interface caused the reflected light angle to exceed the critical angle for total internal reflection at the germanium-silicon dioxide (or germanium-air) interface, disrupting the original waveguide mode. This caused light to escape during germanium conduction, preventing germanium from fully absorbing light and generating more photocurrent, thus leading to a decrease in responsivity. Figure 5 (b) to Figure 5 In (c), the responsivity increased from 0.53 A / W to 0.72 A / W, fully demonstrating that, with a smaller electrode spacing, using ITO transparent conductive material and leveraging the light transmittance of the transparent material can greatly recover the sharp drop in responsivity caused by the reduction in electrode spacing and the increase in the electrode shading area; from Figure 5 (c) to Figure 5 In the middle (d), the responsivity increased from 0.72 A / W to 0.78 A / W, indicating that further optimization of the electrode structure, from a continuous contact structure to a point contact structure, can further restore the responsivity.

[0040] Meanwhile, the dark current did not change significantly in the simulations of these four scenarios compared to the traditional design.

[0041] In summary, this invention improves bandwidth by reducing the electrode spacing, decreasing the series resistance and RC time, enhancing the electric field effect, accelerating carrier drift, and reducing transit time. At the same time, it replaces the traditional metal electrodes with transparent electrodes, utilizing the light transmittance of the transparent electrodes to recover the decrease in responsivity caused by reducing the metal electrode spacing. Furthermore, by designing the transparent electrodes as point contact structures, it further improves responsivity and solves the limitations of bandwidth and responsivity.

[0042] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention and are not intended to limit it. Although the present invention has been described in detail with reference to preferred embodiments, those skilled in the art should understand that modifications or equivalent substitutions can be made to the technical solutions of the present invention without departing from the spirit and scope of the present invention, and all such modifications or substitutions should be covered within the scope of the claims of the present invention.

Claims

1. A germanium-silicon photodetector based on transparent electrodes, characterized in that, It includes a planar silicon waveguide (101), a germanium-doped layer (102), a P-doped layer (103) and an N-doped layer (104), and a transparent electrode on germanium; The germanium-doped layer (102) is located on the upper surface of the planar silicon waveguide (101); the P-doped layer (103) and the N-doped layer (104) are located inside the germanium-doped layer (102) and on the lower surface of the germanium-doped transparent electrode; the germanium-doped electrode is located on the upper surface of the P-doped layer (103), the N-doped layer (104) and the germanium-doped layer (102); The P-doped layer (103), germanium-doped layer (102), and N-doped layer (104) are sequentially connected to form a PIN junction; The planar silicon waveguide (101) serves as an optical waveguide, guiding incident light into the germanium-doped layer (102) for light absorption. The transparent electrode on the germanium absorbs the photogenerated carriers generated by the absorption of light by the germanium-doped layer (102), forming a photocurrent and realizing the photoelectric detection function.

2. The germanium-silicon photodetector based on transparent electrodes according to claim 1, characterized in that, The structure of the germanium upper electrode is either a continuous contact or a point contact structure.

3. The germanium-silicon photodetector based on transparent electrodes according to claim 1 or 2, characterized in that, The spacing between the germanium upper electrodes is 0.

5. 1.4um.

4. The germanium-silicon photodetector based on transparent electrodes according to claim 3, characterized in that, The material of the transparent electrode on germanium is a transparent electrode material, including oxide transparent conductive materials, carbon-based transparent conductive materials, and polymer transparent conductive materials.

5. The germanium-silicon photodetector based on a transparent electrode according to claim 1, characterized in that, The structure of the germanium-doped layer (102) is a trapezoidal strip structure.

6. The germanium-silicon photodetector based on a transparent electrode according to claim 1 or 5, characterized in that, The material of the germanium-doped layer (102) is doped Ge.

7. The germanium-silicon photodetector based on transparent electrodes according to claim 1, characterized in that, The structure of the planar silicon waveguide (101) is a planar structure.

8. The germanium-silicon photodetector based on a transparent electrode according to claim 1 or 7, characterized in that, The material of the planar silicon waveguide (101) is Si.

9. The germanium-silicon photodetector based on transparent electrodes according to claim 1, characterized in that, The doping levels of the P-doped layer (103) and the N-doped layer (104) are on the order of... .

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