A silicon-germanium electro-absorption modulator and a method for manufacturing the same

Abstract

The present invention relates to a germanium silicon electro-absorption modulator and a manufacturing method thereof, wherein the germanium silicon electro-absorption modulator comprises a polysilicon layer and a silicon substrate; an N-doped region, wherein the N-doped region is arranged in the polysilicon layer; a P-doped region, wherein the P-doped region is arranged in the silicon substrate, wherein a first silicon dioxide layer is arranged inside the silicon substrate, and the P-doped region is located on the upper surface of the first silicon dioxide layer; a germanium silicon photonic crystal waveguide, wherein the germanium silicon photonic crystal waveguide is vertically arranged between the N-doped region and the P-doped region, and a second silicon dioxide layer is filled around the germanium silicon photonic crystal waveguide, wherein the lower surface of the second silicon dioxide layer is connected to the silicon substrate, and the upper surface is connected to the polysilicon layer. The present invention enhances the absorption of light by the material through the slow light effect of the germanium silicon photonic crystal waveguide, thereby improving the performance of the device.

Description

Technical Field

[0001] The present invention relates to the field of silicon-based optoelectronic technology, and in particular to a germanium silicon electro-absorption modulator and a manufacturing method thereof. Background Art

[0002] Currently, the widely used silicon-based electro-optic modulators can be roughly divided into three types: (1) Mach-Zehnder (MZI) modulator based on free carrier dispersion effect. The advantages are large optical bandwidth and high-speed performance. Its electro-optical cutoff frequency can reach 50 GHz. The disadvantages are large active area and high energy consumption. At the same time, its traveling wave electrode structure design is relatively complex. (2) Micro-ring modulator. The advantages of micro-ring modulator are compact structure and low device energy consumption. The disadvantage is that since the micro-ring modulator is based on the resonance principle, its optical bandwidth is particularly narrow, and its performance is greatly affected by process and temperature changes. (3) Electro-absorption modulator. Electro-absorption (EA) modulator has the advantages of large optical bandwidth, high speed and compact structure. The electrode structure is a lumped electrode, which is easy to design and the active area is smaller than that of MZI modulator. Therefore, it has the characteristics of low cost and low power consumption. It has great application potential in digital communication and analog communication.

[0003] Photonic crystal refers to an artificial microstructure formed by periodic arrangement of media with different dielectric constants. From the perspective of material structure, photonic crystal is a type of artificially designed crystal with periodic dielectric structure on the optical scale. An important characteristic of photonic crystal is the slow light effect. When light is transmitted in a photonic crystal, slow light is generated due to backscattering and total scattering, which can effectively increase the material's absorption of light. Summary of the invention

[0004] The technical problem to be solved by the present invention is to provide a germanium silicon electro-absorption modulator and a manufacturing method thereof, which enhances the absorption of light by the material through the slow light effect of the germanium silicon photonic crystal waveguide, thereby improving the device performance.

[0005] The technical solution adopted by the present invention to solve the technical problem is: to provide a germanium silicon electro-absorption modulator, comprising:

[0006] A polysilicon layer and a silicon substrate;

[0007] An N-doped region, wherein the N-doped region is disposed in the polysilicon layer;

[0008] A P-doped region, wherein the P-doped region is disposed in the silicon substrate, wherein a first silicon dioxide layer is disposed inside the silicon substrate, and the P-doped region is located on an upper surface of the first silicon dioxide layer;

[0009] The silicon germanium photonic crystal waveguide is vertically arranged between the N-doped region and the P-doped region, and is surrounded by a second silicon dioxide layer, wherein the lower surface of the second silicon dioxide layer is connected to the silicon substrate, and the upper surface is connected to the polysilicon layer.

[0010] The germanium silicon photonic crystal waveguide is obtained by etching a plurality of circular air holes on a germanium silicon waveguide and then filling the circular air holes with a growing oxide layer.

[0011] The lattice constant of the circular air hole is a=0.48-0.52 μm, and the radius of the circular air hole is r=0.38-0.44a.

[0012] The N-doped region includes an electron medium doped region and an electron heavily doped region, and the electron medium doped region and the electron heavily doped region are connected.

[0013] The P-doped region includes a hole-doped region and a hole-heavy doped region, and the hole-doped region and the hole-heavy doped region are connected.

[0014] The technical solution adopted by the present invention to solve the technical problem is: to provide a method for manufacturing a germanium silicon electro-absorption modulator, comprising:

[0015] Step (1): obtaining a silicon substrate, wherein a first silicon dioxide layer is disposed inside the silicon substrate;

[0016] Step (2): providing a P-doped region in the silicon substrate, wherein the P-doped region is located on the upper surface of the first silicon dioxide layer;

[0017] Step (3): vertically disposing a germanium silicon waveguide above the P-doped region;

[0018] Step (4): etching the germanium silicon waveguide to form a germanium silicon photonic crystal waveguide;

[0019] Step (5): filling a second silicon dioxide layer around the germanium silicon photonic crystal waveguide until the height of the second silicon dioxide layer is flush with the upper surface of the germanium silicon photonic crystal waveguide;

[0020] Step (6): covering the upper surface of the second silicon dioxide layer with a polysilicon layer;

[0021] Step (7): Arrange an N-doped region inside the polysilicon layer and on the upper surface of the germanium silicon photonic crystal waveguide.

[0022] Between step (1) and step (2), the step of etching the silicon substrate to form ridge-shaped silicon is also included;

[0023] The P-doped region is arranged in a main protruding area of ​​the ridge-shaped silicon and is located on an upper surface of the first silicon dioxide layer.

[0024] The step (4) is specifically as follows: a plurality of circular air holes are etched on the germanium silicon waveguide, and then the circular air holes are filled with an oxide layer to obtain a germanium silicon photonic crystal waveguide.

[0025] The step (7) also includes a step (8): covering the upper surface of the polysilicon layer with a third silicon dioxide layer, and arranging a first electrode and a second electrode on the upper surface of the third silicon dioxide layer, connecting the first electrode to the P-doped region through a first metal through hole, and connecting the second electrode to the N-doped region through a second metal through hole.

[0026] Beneficial Effects

[0027] Due to the adoption of the above technical solution, the present invention has the following advantages and positive effects compared with the prior art: the present invention applies germanium silicon photonic crystal waveguide to the active area waveguide, and can enhance the absorption of light by the material through the slow light effect of the photonic crystal, thereby improving the device performance and reducing the size of the device; compared with the traditional electro-absorption modulator, the present invention adopts a vertical structure, which is more convenient to change the electric field distribution by fine-tuning the position and concentration of the doping area, thereby obtaining better performance. BRIEF DESCRIPTION OF THE DRAWINGS

[0028] Figure 1 is a cross-sectional schematic diagram of a silicon-germanium electro-absorption modulator according to an embodiment of the present invention;

[0029] Figure 2 is a top view of a germanium silicon photonic crystal waveguide according to an embodiment of the present invention;

[0030] Figure 3 It is a schematic diagram of light transmission in a germanium silicon photonic crystal waveguide according to an embodiment of the present invention.

[0031] Illustration: 1. Silicon substrate, 2. First silicon dioxide layer, 3. P-doped region, 4. Germanium silicon photonic crystal waveguide, 5. Second silicon dioxide layer, 6. Polysilicon layer, 7. N-doped region, 8. Third silicon dioxide layer, 9. First metal through hole, 10. Second metal through hole, 11. First electrode, 12. Second electrode. DETAILED DESCRIPTION

[0032] The present invention will be further described below in conjunction with specific embodiments. It should be understood that these embodiments are only used to illustrate the present invention and are not intended to limit the scope of the present invention. In addition, it should be understood that after reading the content taught by the present invention, those skilled in the art can make various changes or modifications to the present invention, and these equivalent forms fall within the scope limited by the appended claims of the application equally.

[0033] The embodiment of the present invention relates to a silicon-germanium electro-absorption modulator, see Figure 1 ,include:

[0034] A polysilicon layer 6 and a silicon substrate 1;

[0035] An N-doped region 7, wherein the N-doped region 7 is disposed in the polysilicon layer 6;

[0036] A P-doped region 3, wherein the P-doped region 3 is disposed in the silicon substrate 1 (or the ridge silicon after etching the silicon substrate 1), wherein a first silicon dioxide layer 2 is disposed inside the silicon substrate 1, and the P-doped region 3 is located on the upper surface of the first silicon dioxide layer 2;

[0037] The silicon-germanium photonic crystal waveguide 4 is vertically arranged between the N-doped region 7 and the P-doped region 3. The silicon-germanium photonic crystal waveguide 4 is filled with a second silicon dioxide layer 5. The lower surface of the second silicon dioxide layer 5 is connected to the silicon substrate 1, and the upper surface is connected to the polysilicon layer 6.

[0038] The germanium silicon photonic crystal waveguide 4 is obtained by etching a plurality of circular air holes on a germanium silicon waveguide and then filling the circular air holes with a growing oxide layer.

[0039] The N-doped region 7 includes an electron medium-doped region and an electron heavily-doped region, and the electron medium-doped region and the electron heavily-doped region are connected; the P-doped region 3 includes a hole medium-doped region and a hole heavily-doped region, and the hole medium-doped region and the hole heavily-doped region are connected.

[0040] It also includes a third silicon dioxide layer 8, which is arranged on the upper surface of the polysilicon layer 6, and a first electrode 11 and a second electrode 12 are arranged on the third silicon dioxide layer 8. The first electrode 11 is connected to the P-doped region 3 through a first metal through hole 9, and the second electrode 12 is connected to the N-doped region 7 through a second metal through hole 10.

[0041] It is worth mentioning that the germanium silicon photonic crystal waveguide 4 of the germanium silicon electro-absorption modulator of this embodiment adopts a vertical structure and applies the Franz-Keldysh (FK) effect, the principle of which is that the band gap of the material will change with the change of the external electric field, thereby changing the absorption characteristics. At the same time, the germanium silicon waveguide area adopts a linear defect photonic crystal structure (i.e., a waveguide has circular holes around it in a two-dimensional structure), so that light produces a slow light effect in the waveguide, increasing the material's absorption of light. The thickness of the germanium silicon photonic crystal waveguide 4 of this embodiment is 300nm.

[0042] The electro-absorption modulator of this embodiment adopts a vertical design structure, which makes it easier to change the electric field distribution by fine-tuning the position and concentration of the doping region to obtain better performance. The traditional electro-absorption modulator is a horizontal structure, and adjusting the position and concentration of the doping region can only affect the electric field distribution in the horizontal direction. In a vertical structure, changing the position and concentration can affect the electric field distribution in both the horizontal and vertical directions.

[0043] Furthermore, the structure of the SiGe photonic crystal waveguide 4 is as follows: Figure 2 As shown, circular air holes are etched on a germanium silicon plate, and then an oxide layer is grown to fill the circular holes to form a triangular lattice photonic crystal structure (i.e., three adjacent circular air holes form an equilateral triangle), the width of the line defect part is 500nm, the lattice constant of the circular air hole is a=0.48~0.52μm, and the radius of the circular air hole is r=0.38~0.44a. Figure 3 FIG. 4 is the transmission condition of light in the germanium silicon photonic crystal waveguide 4. FIG.

[0044] This embodiment also relates to a method for manufacturing a germanium-silicon electro-absorption modulator, comprising:

[0045] Step (1): obtaining a silicon substrate 1, wherein a first silicon dioxide layer 2 is disposed inside the silicon substrate 1, and the thickness of the first silicon dioxide layer 2 is 2 μm or 3 μm;

[0046] Step (2): etching the silicon substrate 1 to form ridge-shaped silicon;

[0047] Step (3): providing a P-doped region 3 in the main protruding region of the ridge-shaped silicon, and making the P-doped region 3 located on the upper surface of the first silicon dioxide layer 2;

[0048] In other embodiments, the P-doped region 3 may also be directly disposed in the silicon substrate 1;

[0049] Step (4): vertically disposing a germanium silicon waveguide above the P-doped region 3;

[0050] Step (5): etching the germanium silicon waveguide to form a germanium silicon photonic crystal waveguide 4;

[0051] Step (6): filling the recessed area of ​​the ridge silicon with a second silicon dioxide layer 5 until the height of the second silicon dioxide layer 5 is flush with the upper surface of the germanium silicon photonic crystal waveguide 4;

[0052] Step (7): Covering the upper surface of the second silicon dioxide layer 5 with a polysilicon layer 6;

[0053] Step (8): Disposing an N-doped region 7 inside the polysilicon layer 6 and on the upper surface of the germanium silicon photonic crystal waveguide 4;

[0054] Step (9): Cover the upper surface of the polysilicon layer 6 with a third silicon dioxide layer 8, and set a first electrode 11 and a second electrode 12 on the upper surface of the third silicon dioxide layer 8, connect the first electrode 11 to the P-doped region 3 through a first metal through hole 9, and connect the second electrode 12 to the N-doped region 7 through a second metal through hole 10.

[0055] The above embodiments are merely illustrative of the principles and effects of the present invention, and are not intended to limit the present invention. Anyone familiar with the art may modify or alter the above embodiments without departing from the spirit and scope of the present invention. Therefore, all equivalent modifications or alterations made by a person of ordinary skill in the art without departing from the spirit and technical concept disclosed by the present invention shall still be covered by the claims of the present invention.

Claims

1. A silicon-germanium electro-absorption modulator, characterized in that: include: A polysilicon layer and a silicon substrate; An N-doped region, wherein the N-doped region is disposed in the polysilicon layer; A P-doped region, wherein the P-doped region is disposed in the silicon substrate, wherein a first silicon dioxide layer is disposed inside the silicon substrate, and the P-doped region is located on an upper surface of the first silicon dioxide layer; The germanium silicon photonic crystal waveguide is obtained by etching a plurality of circular air holes on the germanium silicon waveguide, and then filling the circular air holes with a growing oxide layer to form a triangular lattice photonic crystal structure; the germanium silicon photonic crystal waveguide is vertically arranged between an N-doped region and a P-doped region, and a second silicon dioxide layer is filled around the germanium silicon photonic crystal waveguide, wherein the lower surface of the second silicon dioxide layer is connected to a silicon substrate, and the upper surface is connected to a polysilicon layer.

2. The silicon-germanium electro-absorption modulator according to claim 1, characterized in that: The lattice constant of the circular air hole is a=0.48-0.52 μm, and the radius of the circular air hole is r=0.38-0.44a.

3. The silicon-germanium electro-absorption modulator according to claim 1, characterized in that: The N-doped region includes an electron medium doped region and an electron heavily doped region, and the electron medium doped region and the electron heavily doped region are connected.

4. The silicon-germanium electro-absorption modulator according to claim 1, characterized in that: The P-doped region includes a hole-doped region and a hole-heavy doped region, and the hole-doped region and the hole-heavy doped region are connected.

5. The silicon-germanium electro-absorption modulator according to claim 1, characterized in that: It also includes a third silicon dioxide layer, which is arranged on the upper surface of the polysilicon layer. A first electrode and a second electrode are arranged on the third silicon dioxide layer. The first electrode is connected to the P-doped region through a first metal through hole, and the second electrode is connected to the N-doped region through a second metal through hole.

6. A method for manufacturing a germanium silicon electro-absorption modulator, characterized in that: include: Step (1): obtaining a silicon substrate, wherein a first silicon dioxide layer is disposed inside the silicon substrate; Step (2): providing a P-doped region in the silicon substrate, and making the P-doped region located on the upper surface of the first silicon dioxide layer; Step (3): vertically disposing a germanium silicon waveguide above the P-doped region; Step (4): etching the germanium silicon waveguide to form a germanium silicon photonic crystal waveguide, specifically: etching a plurality of circular air holes on the germanium silicon waveguide, then filling the circular air holes with a growing oxide layer, and forming a triangular lattice photonic crystal structure to obtain a germanium silicon photonic crystal waveguide; Step (5): filling a second silicon dioxide layer around the germanium silicon photonic crystal waveguide until the height of the second silicon dioxide layer is flush with the upper surface of the germanium silicon photonic crystal waveguide; Step (6): covering the upper surface of the second silicon dioxide layer with a polysilicon layer; Step (7): Arrange an N-doped region inside the polysilicon layer and on the upper surface of the germanium silicon photonic crystal waveguide.

7. The method for manufacturing a silicon-germanium electro-absorption modulator according to claim 6, characterized in that: Between step (1) and step (2), the step of etching the silicon substrate to form ridge-shaped silicon is also included; The P-doped region is arranged in a main protruding area of ​​the ridge-shaped silicon and is located on an upper surface of the first silicon dioxide layer.

8. The method for manufacturing a silicon-germanium electro-absorption modulator according to claim 6, characterized in that: The step (7) also includes a step (8): covering the upper surface of the polysilicon layer with a third silicon dioxide layer, and arranging a first electrode and a second electrode on the upper surface of the third silicon dioxide layer, connecting the first electrode to the P-doped region through a first metal through hole, and connecting the second electrode to the N-doped region through a second metal through hole.

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