High saturation photodetector and method of making same

Abstract

The disclosure provides a high-saturation photodetector and a preparation method thereof. The high-saturation photodetector comprises an N-type silicon substrate (1), a carrier transit region (2), a photoelectron active region (3), and a P-type contact layer (4) sequentially grown on the N-type silicon substrate (1), a first metal electrode (81) arranged on the P-type contact layer (4), a second metal electrode (82) arranged on the N-type silicon substrate (1), an electrical isolation layer (7) grown on a mesa of the N-type silicon substrate (1) and surfaces of the carrier transit region (2), the photoelectron active region (3), and the P-type contact layer (4), and an antireflection film grown on an exposed area of an upper surface of the P-type contact layer (4) and an upper surface of the electrical isolation layer (7). Thicknesses of the carrier transit region (2) and the photoelectron active region (3) are designed to be the same so that transit times of photo-generated electrons and holes are the same, and blockage caused by high-power carriers not being timely led out can be reduced.

Description

Technical Field

[0001] The present disclosure relates to the fields of silicon-based optoelectronic technology and photoelectric detection technology, and in particular to a high-saturation photoelectric detector and a preparation method thereof. Background Art

[0002] Exponential traffic growth, the demand for high-speed wireless data communications, and the continuous deployment of innovative wireless technologies, services, and applications are placing tremendous pressure on mobile network operators. To meet the bandwidth requirements of communication systems while reducing energy consumption, wireless communication over fiber (WF) technology, which combines microwave radio frequency (RF) and photonic technologies, has attracted widespread attention.

[0003] Wireless over fiber (RoF) combines the advantages of high-speed optical communications and mobile wireless communications, making it a highly promising development direction for future communication networks. RoF antenna arrays must receive high-power analog signals, requiring detectors with high linearity and high dynamic range. This significantly reduces signal distortion and facilitates improved system transmission capacity. Furthermore, it eliminates the need for expensive and noisy millimeter-wave amplifiers in traditional RoF links, providing high gain, low noise, and a high spurious-free dynamic range. Microwave photonic links and analog signal communication systems require detectors with high saturation photocurrents, and long wavelengths of light favor free-space propagation. Furthermore, the bandgap of germanium-tin alloys is tunable by varying the tin composition, extending the wavelength from 1.55μm to 2μm and even 4μm. Photodetectors fabricated from germanium-tin alloys are also compatible with silicon-based CMOS processes, offering excellent economic benefits. Therefore, the development of long-wavelength, silicon-based, highly saturated germanium-tin detectors is of profound significance. Summary of the Invention

[0004] In view of the above problems, the present invention provides a high-saturation photodetector and a preparation method thereof to solve the above technical problems.

[0005] One aspect of the present disclosure provides a high-saturation photodetector, comprising: an N-type silicon substrate; a carrier transit region grown in a central region of the N-type silicon substrate; a photoelectron active region grown on an upper surface of the carrier transit region; a P-type contact layer grown on an upper surface of the photoelectron active region; a first metal electrode disposed on the P-type contact layer; a second metal electrode disposed on the N-type silicon substrate; an electrical isolation layer grown on an exposed table surface of the N-type silicon substrate, as well as on sidewalls of the carrier transit region, the photoelectron active region, and the P-type contact layer, and an area extending from an edge of the P-type contact layer to the first metal electrode; and an antireflection film grown on an exposed area on an upper surface of the P-type contact layer and on an upper surface of the electrical isolation layer; wherein the thicknesses of the carrier transit region and the photoelectron active region are designed so that the transit times of photogenerated electrons and holes are the same.

[0006] Optionally, the N-type silicon substrate is circular in shape; the carrier transport region, the optoelectronic active region and the P-type contact layer are circular in shape with equal diameters, and the diameters are less than the diameter of the N-type silicon substrate and coaxial with the N-type silicon substrate; the first metal electrode is annular in shape, coaxial with the N-type silicon substrate, and the diameter of the first metal electrode is less than the diameter of the P-type contact layer; the second metal electrode is annular in shape, coaxial with the N-type silicon substrate, and the diameter of the second metal electrode is less than the diameter of the N-type silicon substrate and greater than the diameter of the carrier transport region.

[0007] Optionally, the material of the carrier transport region is fully relaxed germanium material; the material of the optoelectronic active region is germanium-tin material, and the tin content is 13% to 15%, and the absorption wavelength range is 2050 nm to 3200 nm.

[0008] Optionally, the composition of the optoelectronic active region is gradually changed, and the lattice of the contact surface between the optoelectronic active region and the P-type contact layer is equal.

[0009] Optionally, the material of the P-type contact layer is germanium-tin material, and the doping element is boron, and the tin content is less than 6%.

[0010] Optionally, the antireflection film includes a silicon nitride antireflection film grown on the upper surface of the P-type contact layer and the upper surface of the electrical isolation layer, and in contact with the first metal electrode and the second metal electrode; and a silicon oxide antireflection film covering the silicon nitride antireflection film.

[0011] Optionally, the material of the electrical isolation layer is silicon oxide.

[0012] Optionally, the thickness of the electrical isolation layer is greater than one half of the sum of the thicknesses of the carrier transport region, the optoelectronic active region and the P-type contact layer.

[0013] Optionally, the first metal electrode and the second metal electrode have a nickel layer as a bottom layer and an aluminum layer as a top layer.

[0014] Another aspect of the present disclosure provides a preparation method applied to the high-saturation photodetector of any one of the first aspect, comprising: growing a fully relaxed germanium layer as a carrier transit layer on a cleaned N-type silicon substrate by a two-step method; optimizing and reconstructing the surface of the carrier transit layer by cyclic annealing, using the lattice seeds of the surface to epitaxially grow a germanium-tin material to form a photoelectron active region; epitaxially growing a P-type contact layer on the photoelectron active region, the P-type contact layer forming a PIN structure with the N-type silicon substrate; etching the carrier transit layer, the photoelectron active region and the P-type contact layer to the N-type silicon substrate to form a mesa of the carrier transit layer, the photoelectron active region and the P-type contact layer in the central region of the N-type silicon substrate; growing an electrical isolation layer on the exposed region of the N-type silicon substrate and the surface of the mesa, then etching an opening on the electrical isolation layer to expose the surface of the N-type substrate and the P-type contact layer, and then depositing a nickel layer and an aluminum layer in sequence after photolithography to form a first metal electrode and a second metal electrode; growing an antireflection film on the exposed region of the upper surface of the P-type contact layer and the upper surface of the electrical isolation layer to complete the preparation of a high-saturation photodetector.

[0015] The above at least one technical solution adopted in the embodiments of the present disclosure can achieve the following beneficial effects:

[0016] According to the high-saturation photodetector provided by the present disclosure, the drift velocities of electrons and holes in the carrier transit region and the photoelectron active region are calculated, the thicknesses of the transit region and the photoelectron active region are designed so that the transit times of photo-generated electrons and holes are the same, thereby reducing the blockage caused by the non-timely extraction of carriers under high power. BRIEF DESCRIPTION OF DRAWINGS

[0017] For a more complete understanding of the present disclosure and its advantages, reference is now made to the following description taken in conjunction with the accompanying drawings in which:

[0018] Figure 1 A schematic diagram of a high-saturation photodetector provided by an embodiment of the present disclosure is schematically shown;

[0019] Figure 2 A light response curve and a dark current curve of a high-saturation photodetector provided by an embodiment of the present disclosure under high-power illumination are schematically shown;

[0020] Figure 3 A schematic diagram of an electric field in a PIN structure of a high-saturation photodetector provided by an embodiment of the present disclosure is schematically shown.

[0021] LEGEND DESCRIPTION

[0022] 1 - N-type silicon substrate; 2 - carrier transit region; 3 - photoelectron active region; 4 - P-type contact layer; 5 - silicon oxide anti-reflection coating; 6 - silicon nitride anti-reflection coating; 7 - electrical isolation layer; 81 - first metal electrode; 82 - second metal electrode. DETAILED DESCRIPTION

[0023] Hereinafter, embodiments of the present disclosure will be described with reference to the accompanying drawings. It is to be understood, however, that the description is merely exemplary and is not intended to limit the scope of the present disclosure. In the following detailed description of the embodiments of the present disclosure, numerous specific details are set forth in order to provide a thorough understanding of the embodiments of the present disclosure. However, it would be apparent to those skilled in the art that the embodiments of the present disclosure can be practiced without these specific details. In other instances, well-known structures and methods are not described in detail in order to avoid obscuring the concepts of the present disclosure.

[0024] The terms used herein are merely used to describe specific embodiments and are not intended to limit the present disclosure. The terms "include", "comprise" and the like used herein indicate the presence of the described features, steps, operations, and / or components, but do not exclude the presence or addition of one or more other features, steps, operations, or components.

[0025] All terms used herein, including technical and scientific terms, have the same meanings as those generally understood by those skilled in the art unless otherwise defined. It should be noted that the terms used herein should be interpreted as having meanings consistent with the context of the specification, and should not be interpreted in an idealized or overly formal manner.

[0026] As Figure 1 shown, the high-saturation photodetector according to the embodiments of the present disclosure includes an N-type silicon substrate 1, a carrier transit region 2, a photoelectron active region 3, a P-type contact layer 4, a first metal electrode 81, a second metal electrode 82, an electrical isolation layer 7, and an anti-reflection coating.

[0027] The carrier transit region 2 is grown in the center region of the N-type silicon substrate 1; the photoelectron active region 3 is grown on the upper surface of the carrier transit region 2; the P-type contact layer 4 is grown on the upper surface of the photoelectron active region 3; the first metal electrode 81 is disposed on the P-type contact layer 4; the second metal electrode 82 is disposed on the N-type silicon substrate 1; the electrical isolation layer 7 is grown on the exposed mesa of the N-type silicon substrate 1, and on the sidewalls of the carrier transit region 2, the photoelectron active region 3, and the P-type contact layer 4, and on the region extending from the edge of the P-type contact layer 4 to the first metal electrode 81; the anti-reflection coating is grown on the exposed region of the upper surface of the P-type contact layer 4 and on the upper surface of the electrical isolation layer 7; and the thicknesses of the carrier transit region 2 and the photoelectron active region 3 are designed to be the same for the transit times of the photo-generated electrons and holes.

[0028] Referring to Figure 1, the shape of the N-type silicon substrate 1 is a circle; the carrier transit region 2, the optoelectronic active region 3 and the P-type contact layer 4 are circles with equal diameters, and the diameters are smaller than the diameter of the N-type silicon substrate 1, and coaxial with the N-type silicon substrate 1; the shape of the first metal electrode 81 is a ring, coaxial with the N-type silicon substrate 1, and the diameter is smaller than the P-type contact layer 4; the shape of the second metal electrode 82 is a ring, coaxial with the N-type silicon substrate 1, and the diameter is smaller than the N-type silicon substrate 1 and larger than the carrier transit region 2. It should be noted that, Figure 1 The high-saturation photodetector structure shown is one of the illustrative structural forms of the high-saturation photodetector provided by the present disclosure, but is not limited thereto.

[0029] In the present embodiment, the optoelectronic active region 3 is epitaxially grown by means of gradual change of components, and the P-type contact layer 4 doped with B elements is epitaxially grown on the optoelectronic active region 3. The optoelectronic active region uses an alloy material with a component of 13-15%, and the material of the P-type contact layer 4 is a germanium-tin material doped with boron elements and with a tin content less than 6%. The gradual change of components is used to slow down the relaxation speed of the crystal, and the lattice of the outermost layer of the optoelectronic active region 3 is approximately equal to the completely relaxed lattice of the P-type contact layer 4.

[0030] In the present embodiment, the antireflection film includes a silicon nitride antireflection film 6 grown on the upper surface of the P-type contact layer 4 and the upper surface of the electrical isolation layer 7, and in contact with the first metal electrode 81 and the second metal electrode 82; and a silicon oxide antireflection film 5 covering the silicon nitride antireflection film 6. Light is incident from the free space, and through the antireflection effect of the double-layered silicon oxide and silicon nitride, the light enters the high-saturation photodetector with the effect of antireflection. Alternatively, the antireflection film can also use a single-layer film or other antireflection film solutions.

[0031] In the present embodiment, the electrical isolation layer 7 uses silicon oxide compatible with silicon technology, and plays the role of fixing the suspended bonds of the side wall and the electrical isolation of the device side wall. The thickness of the electrical isolation layer 7 is greater than one-half of the sum of the thicknesses of the carrier transit region 2, the optoelectronic active region 3 and the P-type contact layer 4, according to the thicknesses of the carrier transit region 2, the optoelectronic active region 3 and the P-type contact layer 4 and the design.

[0032] In the present embodiment, the bottom layer of the first metal electrode 81 and the second metal electrode 82 is a nickel layer, and the upper layer is an aluminum layer, which can form good adhesion with the semiconductor surface and form a good ohmic contact.

[0033] According to the high-saturation photodetector provided by the embodiment of the present disclosure, when light is incident from free space, the double-layer anti-reflection effect of silicon oxide and silicon nitride is used to increase the transmittance of the light into the device; after the light transmits through the anti-reflection layer, the light is not absorbed or is slightly absorbed in the P-type contact layer 4, and then enters the photoelectron active region 3 to generate carriers. When the light intensity is large, the photo-generated carriers are too many and cannot be extracted in time, causing the intrinsic region (the photoelectron active region and the carrier transit region) to generate charge crowding. In the same uniform medium, the drift speeds of electrons and holes are different, so the time for the photo-generated electron-hole pairs to be collected by the electrode is different, which is an important reason for the decrease of the saturation photocurrent of the detector under high power.

[0034] Therefore, in the embodiment, the photoelectron active region 3 is made of a certain component of germanium tin material to generate electro-optical conversion. The carrier transit region 2 is made of germanium material and does not generate electro-optical conversion; the photoelectron active region 3 and the carrier transit region 2 are intrinsic materials, and no net residual charge is generated, so the electric displacement vector D is continuous in the intrinsic region:

[0035]

[0036] According to the relationship between the electric displacement vector ε and the electric field intensity E:

[0037] ε Ge E Ge = ε GeSn E GeSn

[0038] The relationship between the carrier mobility μ and the migration speed v is:

[0039] μ h，e E = v h，e

[0040] The transit time τ of the carrier is:

[0041] τ h，e = l h，e / v h，e

[0042] By reasonably designing the drift distance l of the holes and the electrons, the transit time of the carriers is approximately equal, which can effectively reduce the accumulation of the photo-generated carriers under large light power.

[0043] In the embodiment, the speed of the electrons in germanium is about twice that of the holes, so the germanium layer does not absorb light of 2 microns and does not generate photo-generated carriers, which is used as the carrier transit region 2 in the embodiment.

[0044] In the embodiment, the material of the carrier transit region 2 is a fully relaxed germanium material; the material of the photoelectron active region 3 is a germanium tin material, wherein the tin content is 13% to 15%, and the absorption wavelength range is 2050nm to 3200nm.

[0045] As shown in Figure 2 The photocurrent of the high-saturation photodetector provided by the embodiment of the present disclosure can be up to 60mA.

[0046] Figure 3 The PIN structure of the high-saturation photodetector provided by the embodiment of the present disclosure is shown.

[0047] Another aspect of the present disclosure provides a preparation method, which is applied to the high-saturation photodetector as shown in Figure 1 The preparation method comprises S1 to S6.

[0048] S1, growing a fully relaxed germanium layer on a clean N-type silicon substrate 1 as a carrier transit layer by a two-step method.

[0049] S2, cyclically annealing to optimize and restructure the surface of the carrier transit layer, and using the lattice seed of the surface to epitaxially grow a germanium tin material to form a photoelectron active region 3.

[0050] S3, epitaxially growing a P-type contact layer 4 on the photoelectron active region 3, and the P-type contact layer 4 and the N-type silicon substrate 1 form a PIN structure.

[0051] S4, etching the carrier transit layer, the photoelectron active region 3 and the P-type contact layer 4 to the N-type silicon substrate 1, and forming a mesa of the carrier transit layer, the photoelectron active region 3 and the P-type contact layer 4 in the central region of the N-type silicon substrate 1.

[0052] S5, growing an electrical isolation layer 7 on the exposed region of the N-type silicon substrate 1 and the surface of the mesa, etching an opening on the electrical isolation layer to expose the surface of the N-type substrate and the P-type contact layer 4, and depositing a nickel layer and an aluminum layer in sequence after photolithography to form a first metal electrode 81 and a second metal electrode 82.

[0053] S6, growing an antireflection film on the exposed region of the upper surface of the P-type contact layer 4 and the upper surface of the electrical isolation layer 7, and completing the preparation of a high-saturation photodetector.

[0054] Those skilled in the art can understand that the features described in various embodiments and / or claims of the present disclosure can be combined or / and integrated in various combinations, even if such combinations or integrations are not explicitly described in the present disclosure. In particular, the features described in various embodiments and / or claims of the present disclosure can be combined and / or integrated in various combinations without departing from the spirit and teachings of the present disclosure. All these combinations and / or integrations fall within the scope of the present disclosure.

[0055] While the disclosure has been illustrated and described with reference to certain exemplary embodiments thereof, it will be understood by those skilled in the art that various changes in form and details can be made therein without departing from the spirit and scope of the disclosure as defined by the appended claims and their equivalents. Therefore, the scope of the disclosure should not be limited to the embodiments described herein but should be accorded the full scope of the appended claims and their equivalents.

Claims

1. A high saturation photodetector, characterized by, Comprise: N-type silicon substrate (1); Carrier transit region (2) grown in the center region of the N-type silicon substrate (1); Photoelectron active region (3) grown on the upper surface of the carrier transit region (2); P-type contact layer (4) grown on the upper surface of the photoelectron active region (3); The first metal electrode (81) is provided on the P-type contact layer (4); The second metal electrode (82) is provided on the N-type silicon substrate (1); The electrical isolation layer (7) is grown on the exposed mesa of the N-type silicon substrate (1), and on the sidewalls of the carrier transit region (2), the photoelectron active region (3) and the P-type contact layer (4), and the region extending from the edge of the P-type contact layer (4) to the first metal electrode (81); The antireflection film is grown on the exposed region of the upper surface of the P-type contact layer (4) and the upper surface of the electrical isolation layer (7); The thickness of the carrier transit region (2) and the photoelectron active region (3) is designed to be the same as the transit time of photo-generated electrons and holes.

2. The high saturation photodetector of claim 1, wherein, The shape of the N-type silicon substrate (1) is circular; the carrier transit region (2), the photoelectron active region (3) and the P-type contact layer (4) are circular with equal diameters, and the diameters are smaller than the diameter of the N-type silicon substrate (1) and coaxial with the N-type silicon substrate (1); the first metal electrode (81) is annular and coaxial with the N-type silicon substrate (1), and the diameter is smaller than the P-type contact layer (4); the second metal electrode (82) is annular and coaxial with the N-type silicon substrate (1), and the diameter is smaller than the N-type silicon substrate (1) and larger than the carrier transit region (2).

3. The high saturation photodetector of claim 1, wherein, The material of the carrier transit region (2) is fully relaxed germanium material; the material of the photoelectron active region (3) is germanium tin material, wherein the tin content is 13% to 15%, and the absorption wavelength range is 2050nm to 3200nm.

4. The high saturation photodetector of claim 3, wherein, The composition of tin in the photoelectron active region (3) gradually increases from bottom to top, and the lattice of the contact surface between it and the P-type contact layer (4) is equal.

5. The high saturation photodetector of claim 1, wherein, The material of the P-type contact layer (4) is germanium tin material, which is doped with boron element and the tin content is less than 6%.

6. The high saturation photodetector of claim 1, wherein, The antireflection film comprises: The silicon nitride antireflection film is grown on the upper surface of the P-type contact layer (4) and the upper surface of the electrical isolation layer (7), and contacts the first metal electrode (81) and the second metal electrode (82); The silicon oxide antireflection film (5) covers the silicon nitride antireflection film (6).

7. The high saturation photodetector of claim 1, wherein, The material of the electrical isolation layer (7) is silicon oxide.

8. The high saturation photodetector of claim 7, wherein, The thickness of the electrical isolation layer (7) is greater than one half of the sum of the thicknesses of the carrier transit region (2), the photoelectron active region (3) and the P-type contact layer (4).

9. The high saturation photodetector of claim 1, wherein, The bottom layer of the first metal electrode (81) and the second metal electrode (82) is a nickel layer, and the upper layer is an aluminum layer.

10. A method of preparation for the high saturation photodetector according to any one of claims 1 to 9, characterized in that, Comprise: A fully relaxed germanium layer is grown on a clean N-type silicon substrate (1) as a carrier transit layer by a two-step method; Cyclic annealing optimizes and reconstructs the surface of the carrier transition layer, uses the lattice seed of the surface to epitaxially form a photoelectron active region (3) of germanium tin material; Epitaxially forming a P-type contact layer (4) outside the photoelectron active region (3), and the P-type contact layer (4) forms a PIN structure with the N-type silicon substrate (1); Etching the carrier transition layer, the photoelectron active region (3) and the P-type contact layer (4) to the N-type silicon substrate (1), and forming a mesa of the carrier transition layer, the photoelectron active region (3) and the P-type contact layer (4) in the central region of the N-type silicon substrate (1); After growing an electrical isolation layer (7) on the exposed region of the N-type silicon substrate (1) and the surface of the mesa, etching an opening on the electrical isolation layer to expose the surface of the N-type silicon substrate and the P-type contact layer (4), and depositing a nickel layer and an aluminum layer in sequence after photoetching to form a first metal electrode (81) and a second metal electrode (82); Growth of an antireflection film on the exposed region of the upper surface of the P-type contact layer (4) and the upper surface of the electrical isolation layer (7) completes the preparation of a high-saturation photodetector.

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