InGaAs single-photon avalanche diode and preparation method thereof

Abstract

The invention discloses an indium gallium arsenic single photon avalanche diode, which comprises a substrate and an epitaxial wafer grown on the substrate, the epitaxial wafer comprises a buffer layer, an absorption layer, a transition layer, a charge layer, a cap layer, an electrode contact layer, a dielectric film and a P electrode, wherein the electrode contact layer is made of indium gallium arsenic phosphorus. The electrode contact layer is made of an intrinsic gradient component material grown on the epitaxial wafer, and the electrode contact layer is made of indium gallium arsenic phosphorus. According to the avalanche photodiode and the preparation method thereof, on the premise that dark current and frequency response of a device are not affected, the ohmic contact characteristic of the device is effectively improved, the contact resistance is reduced, and meanwhile the avalanche photodiode is not prone to falling off.

Description

Technical Field

[0001] The present invention relates to the technical field of semiconductor photodetectors, and particularly to a single photon avalanche diode (SPAD) based on indium gallium arsenide (InGaAs) material, which is applicable to high-sensitivity light detection applications in low-light environments, such as quantum communication, lidar (LiDAR), medical imaging, and photon counting. Background Art

[0002] A single photon avalanche diode (SPAD) is a high-sensitivity photodetector capable of detecting single photons and has wide applications in fields such as weak light detection, quantum optics, and precision measurement. Compared with traditional photodetectors, SPAD can operate in Geiger mode, and amplify the electron-hole pairs excited by a single photon into detectable electrical signals through the avalanche multiplication effect, achieving extremely high detection sensitivity.

[0003] In current technologies, alloy systems represented by Au-Be (gold-beryllium) and Au-Zn-Pd (gold-zinc-palladium) have good contact resistance. For example, in the published document with the publication number CN102115833A, publication date July 6, 2011, and patent name "Gold-beryllium Material for Semiconductor Devices, Its Preparation Method and Application", the gold-beryllium material for semiconductor devices, its preparation method and application are disclosed. The composition and mass percentage of the gold-beryllium alloy: Be: 1-5%, Au: the balance. The preparation method is as follows: calculate and weigh the raw materials according to the component and mass percentage ratio; put gold and beryllium into an alumina crucible in sequence according to the order for semiconductor devices, then put the crucible into a semi-circular sealable quartz glass cover and evacuate; heat with a resistance furnace, raise the temperature to melt gold and beryllium, stop heating after refining; cool to below 50 °C to obtain a gold-beryllium intermediate alloy; melt and refine the obtained gold-beryllium intermediate alloy with gold in the same method to obtain a gold-beryllium alloy with a lower beryllium content; melt, continuously cast, and draw the alloy with gold again to obtain a bonding alloy wire. It is the basic alloy material for preparing high-quality tunnel diodes and is applied to the circuits and electrodes on binary compound semiconductor thin films; it can also prepare bonding alloy wires, which is beneficial to achieving ohmic contact between gold and semiconductors.

[0004] However, because Be and Pd are toxic and some require a solid phase regrowth (SPR) process with complex technology, in the alloy process represented by the Au-Zn-Au system, both Zn and Au have poor adhesion to the substrate, are easy to fall off, and have poor contact resistance, affecting the reliability of the process and the performance of the device. Summary of the Invention

[0005] The technical problem to be solved by the present invention is to implement an avalanche photodiode and a preparation method thereof, which can effectively improve the ohmic contact characteristics of the device, reduce the contact resistance, and are not easily detached, without affecting the dark current and frequency response of the device.

[0006] To achieve the above object, the technical solution adopted by the present invention is: an indium gallium arsenide single-photon avalanche diode, comprising:

[0007] a substrate, and an epitaxial wafer grown on the substrate;

[0008] The epitaxial wafer includes:

[0009] a buffer layer, grown on the upper surface of the buffer layer;

[0010] an absorption layer, grown on the upper surface of the buffer layer;

[0011] a transition layer, grown on the upper surface of the absorption layer;

[0012] a charge layer, grown on the upper surface of the transition layer;

[0013] a cap layer, grown on the upper surface of the charge layer;

[0014] an electrode contact layer, grown on the upper surface of the cap layer;

[0015] a dielectric film, covering the electrode contact layer;

[0016] a P electrode, embedded in the dielectric film and connected to the zinc diffusion in the electrode contact layer;

[0017] The material of the electrode contact layer is indium gallium arsenide phosphide.

[0018] The material of the electrode contact layer is an intrinsic graded composition material grown by the epitaxial wafer, and the material of the electrode contact layer is indium gallium arsenide phosphide.

[0019] The change rule of the graded composition of the electrode contact layer is In 1-x Ga x As y P 1-y , where x changes with y;

[0020] The y value changes from the upper surface of InP and is calculated to the upper surface of the graded composition material InGaAsP, changing from 0 to 0.6. The material on the upper surface of the electrode contact layer is In 0.718 Ga 0.282 As 0.6 P 0.4 .

[0021] The thickness of the material of the electrode contact layer is 20 nanometers to 200 nanometers, and the doping concentration on the upper surface is 10 19 atoms per cubic centimeter.

[0022] The electrode contact layer is infiltrated with zinc diffusion, and the zinc diffusion penetrates into the cap layer. The P electrode is made of non-alloyed contact Ti-Pt-Au.

[0023] The indium gallium arsenide single-photon avalanche diode has a back-illuminated structure without a back lens. An N electrode is provided on the bottom surface of the substrate. The N electrode has a flat structure, and an antireflection film is provided at the edge of the N electrode. The thickness of the antireflection film is greater than the thickness of the N electrode.

[0024] The indium gallium arsenide single-photon avalanche diode has a back-illuminated structure with a back lens. An N electrode is provided on the bottom surface of the substrate. The N electrode has a structure that gradually thins towards the edge, and an antireflection film is provided at the edge of the N electrode. The thickness of the antireflection film is greater than the thickness of the N electrode.

[0025] The indium gallium arsenide single-photon avalanche diode has a front-illuminated structure. Both the N electrode and the P electrode are made on the front surface. The dielectric film is colored on the side surface of the epitaxial wafer. An antireflection film is provided outside the dielectric film on the side surface of the epitaxial wafer. The common technical characteristic is that the doping type of the electrode contact layer material is graded doping;

[0026] The graded growth modes of the electrode contact layer include: continuous grading and discrete grading, discrete grading.

[0027] A method for manufacturing an indium gallium arsenide single-photon avalanche diode includes preparing an epitaxial wafer on a substrate. A buffer layer, an absorption layer, a transition layer, a charge layer, a cap layer, and an electrode contact layer are sequentially epitaxially grown on the epitaxial wafer. Zinc diffusion is performed on the surface of the epitaxial wafer, and then the P electrode and the N electrode are fabricated by means of photolithography and etching;

[0028] During manufacturing, the material of the electrode contact layer is selected as InGaAsP.

[0029] When zinc diffusion is performed on the surface of the epitaxial wafer, the doping concentration on the upper surface of InGaAsP reaches or approaches 10 19 Atoms / cm 3 , and the P electrode process uses non-alloyed contact Ti-Pt-Au.

[0030] For the avalanche photodiode and the manufacturing method thereof in the present invention, a buffer layer, an absorption layer, a transition layer, a charge layer, a cap layer, and an electrode contact layer are sequentially epitaxially grown on a substrate. The material of the electrode contact layer is InGaAsP, and the electrode contact layer is an epitaxially grown intrinsic graded composition material, and the doping concentration on the upper surface is 10 19Atoms per cubic centimeter. The P-type electrode is made of non-alloyed Ti-Pt-Au contacts. Utilizing the high adhesion of Ti, the high toughness of Pt, and the good conductivity and corrosion resistance of Au, without affecting the dark current and frequency response of the device, it effectively improves the ohmic contact characteristics of the device, reduces the contact resistance, and is not prone to falling off at the same time. Brief Description of the Drawings

[0031] The following briefly describes the content expressed in each drawing in the specification of the present invention and the marks in the drawings:

[0032] Figure 1 It is a schematic structural diagram of a back-illuminated avalanche photodiode without a back lens;

[0033] Figure 2 It is a schematic structural diagram of a back-illuminated avalanche photodiode with a back lens;

[0034] Figure 3 It is a schematic structural diagram of a front-illuminated avalanche photodiode;

[0035] Figure 4 It is a schematic flow diagram of a method for manufacturing an avalanche photodiode;

[0036] The marks in the above-mentioned drawings are all:

[0037] 1. Substrate; 2. Buffer layer; 3. Absorption layer; 4. Transition layer; 5. Charge layer; 6. Cap layer; 7. Electrode contact layer; 8. P electrode; 9. Dielectric film; 10. N electrode; 11. Antireflection film;

[0038] Among them, the zinc diffusion range is represented by a. Detailed Embodiments

[0039] The following, with reference to the drawings, through the description of the embodiments, further details are provided for the specific embodiments of the present invention, such as the shapes, structures, mutual positions and connection relationships of the various components involved, the functions and working principles of each part, the manufacturing process, and the operation and usage methods, to help those skilled in the art have a more complete, accurate and in-depth understanding of the inventive concept and technical solution of the present invention.

[0040] An avalanche photodiode and a manufacturing method thereof can effectively improve the ohmic contact characteristics of the device, reduce the contact resistance, and are not prone to falling off without affecting the dark current and frequency response of the device. The specific structure is as Figures 1-3 shown. A buffer layer 2, an absorption layer 3, a transition layer 4, a charge layer 5, a cap layer 6, and an electrode contact layer 7 are sequentially epitaxially grown on the substrate 1. The following describes each layer:

[0041] The buffer layer 2 is epitaxially grown on the substrate 1;

[0042] An absorption layer 3, grown on the upper surface of the buffer layer 2;

[0043] A transition layer 4, grown on the upper surface of the absorption layer 3;

[0044] A charge layer 5, grown on the upper surface of the transition layer 4;

[0045] A cap layer 6, grown on the upper surface of the charge layer 5;

[0046] An electrode contact layer 7, grown on the upper surface of the cap layer 6;

[0047] Wherein, the zinc diffusion range is represented by a.

[0048] The material of the electrode contact layer 7 is indium gallium arsenide phosphide (InGaAsP), which is an epitaxially grown intrinsic graded composition material, and the doping concentration on the upper surface is 10 19 Atoms / cm 3 (atoms per cubic centimeter, hereinafter all represented by Atoms / cm 3 ), and the thickness is 20 nm to 200 nm (nanometers, hereinafter all represented by nm). Compared with the prior art where InGaAs and InGaAsP with fixed components are used as the electrode contact layer 7, while maintaining an approximately the same specific contact resistance, it reduces the influence of parameters such as dark current, dark count, afterpulse, and photon timing jitter caused by the light absorption of InGaAs and the heterojunction between the fixed components (InGaAs, InGaAsP) and the InP material.

[0049] The electrode contact layer 7 is an epitaxially grown intrinsic graded composition material, the doping type of the material of the electrode contact layer 7 is graded doping, and the change rule of the graded composition of the electrode contact layer 7 is In 1-x Ga x As y P 1-y , x varies with y, and it follows the valence bond law of the molecular composition compound. The y value changes from 0 to 0.6 starting from the upper surface of InP and calculating to the upper surface of the graded composition material InGaAsP. That is, the material on the uppermost surface is In 0.718 Ga 0.282 As 0.6 P 0.4 , and its corresponding energy band is approximately: Eg = 0.9509 electron volts, and the PL (Photoluminescence) spectrum is approximately: 1305 nm. The grading methods of the epitaxially grown intrinsic graded composition InGaAsP contact layer include: continuous grading and discrete grading. For discrete grading: the total discrete quantity is n (y = 0.6 / n, 0.6*2 / n... 0.6*(n - 1) / n, 0.6, and the corresponding thickness for each segment is w / n).

[0050] Specifically, the material on the upper surface of the electrode contact layer 7 is In 0.718 Ga 0.282 As 0.6 P 0.4 , on the basis of the III-V group avalanche photodiode epitaxial wafer of the InGaAs / InP system, a layer of graded InGaAsP is added as the electrode contact layer 7. The doping concentration on the surface of the electrode contact layer 7 after zinc diffusion in the epitaxial wafer structure of the avalanche photodiode reaches or approaches 10 19 Atoms / cm 3 , and the specific contact resistance is measured by the transmission line model (TLM). The generated specific contact resistance is within 10 -5 -10 -6 Ω·CM 2 , which is specifically related to the zinc diffusion concentration and annealing process, etc. Compared with InGaAs with a fixed composition of the same thickness as the contact layer, its dark current, dark count, time jitter, afterpulse, etc. all decrease, and the corresponding range is: 1% - 15%. Compared with InGaAsP with a fixed composition of the same thickness as the contact layer, its 3dB bandwidth, afterpulse, etc. all decrease, and the corresponding range is: 1% - 5%. It is specifically related to the uniformity of the chip manufacturing process and test conditions such as the test temperature, etc.

[0051] The P electrode 8 is made of non-alloyed Ti-Pt-Au. Compared with making an electrode on P-type InP in the prior art, using the non-alloyed contact of the Ti-Pt-Au system, taking advantage of the high adhesion of Ti, the high toughness of Pt, and the good conductivity and corrosion resistance of Au, the electrode adhesion is improved, the device reliability is improved, and at the same time the contact resistance is reduced, achieving approximately the same order of magnitude as the alloy scheme, which is 10 -5 -10 -6 Ω·CM2 (ohm square centimeter, hereinafter all in Ω·CM 2 ).

[0052] An epitaxial wafer is prepared on the substrate 1. On the epitaxial wafer, a buffer layer 2, an absorption layer 3, a transition layer 4, a charge layer 5, a cap layer 6, and an electrode contact layer 7 are sequentially epitaxially grown. Zinc diffusion, photolithography, etching, and P-type electrode preparation are performed on the epitaxial wafer, constituting three different implementation modes. Among them Figure 1 is a schematic structural diagram of a back-illuminated avalanche photodiode without a back lens, Figure 2 is a schematic structural diagram of a back-illuminated avalanche photodiode with a back lens, Figure 3 is a schematic structural diagram of a front-illuminated avalanche photodiode.

[0053] The main structures of the three embodiments are the same;

[0054] The indium gallium arsenide single-photon avalanche diode has a back-illuminated structure without a back lens. An N electrode 10 is provided on the bottom surface of the substrate 1. The N electrode 10 has a flat structure. An antireflection film 11 is provided at the edge of the N electrode 10, and the thickness of the antireflection film 11 is greater than that of the N electrode 10.

[0055] The indium gallium arsenide single-photon avalanche diode has a back-illuminated structure with a back lens. An N electrode 10 is provided on the bottom surface of the substrate 1. Its P and N electrodes 10 are made on the front and back sides. The N electrode 10 has a structure that gradually thins towards the edge. An antireflection film 11 is provided at the edge of the N electrode 10, and the thickness of the antireflection film 11 is greater than that of the N electrode 10.

[0056] The indium gallium arsenide single-photon avalanche diode has a front-illuminated structure. Both the N electrode 10 and the P electrode 8 are made on the front surface. The dielectric film 9 is colored on the side of the epitaxial wafer. An antireflection film 11 is provided outside the dielectric film 9 on the side of the epitaxial wafer. The common technical characteristic is that the doping type of the electrode contact layer 7 material is graded doping; the graded growth mode of the electrode contact layer 7 includes: continuous grading and discrete grading, discrete grading.

[0057] In the present invention, a buffer layer 2, an absorption layer 3, a transition layer 4, a charge layer 5, a cap layer 6, and an electrode contact layer 7 are sequentially epitaxially grown on the substrate 1. The material of the electrode contact layer 7 is InGaAsP, and the doping type of the electrode contact layer 7 material is graded doping. The doping concentration on the upper surface is 10 19 Atoms / cm3. The P-type electrode is Ti-Pt-Au with non-alloy contact. Utilizing the high adhesion of Ti, the high toughness of Pt, and the good conductivity and corrosion resistance of Au, without affecting the dark current and frequency response of the device, it effectively improves the ohmic contact characteristics of the device, reduces the contact resistance, and is not easy to fall off at the same time.

[0058] Flow schematic diagram of the preparation method of the avalanche photodiode. The preparation method includes:

[0059] S101. Prepare an epitaxial wafer on the substrate 1. On this epitaxial wafer, a buffer layer 2, an absorption layer 3, a transition layer 4, a charge layer 5, a cap layer 6, and an electrode contact layer 7 are sequentially epitaxially grown; the material of the electrode contact layer 7 is InGaAsP. The material on the upper surface of this electrode contact layer 7 is In 0.718 Ga 0.282 As 0.6 P 0.4 。

[0060] S102. Perform zinc diffusion, photolithography, etching, and P-type electrode preparation on the epitaxial wafer;

[0061] Perform zinc diffusion on the epitaxial wafer to make the doping concentration on the upper surface of the electrode contact layer 7 be 10 19 Atoms / cm 3, the electrode contact layer 7 is an epitaxially grown intrinsic graded composition material with a thickness of 20 nm to 200 nm.

[0062] The P-type electrode is made of non-alloyed contact Ti-Pt-Au.

[0063] In the embodiment of the present invention, on the basis of an avalanche photodiode epitaxial wafer, a buffer layer 2, an absorption layer 3, a transition layer 4, a charge layer 5, a cap layer 6, and an electrode contact layer 7 are sequentially epitaxially grown. The material of the electrode contact layer 7 is InGaAsP with a graded composition. Then, wafer processing steps such as zinc diffusion, photolithography, etching, and P-type electrode preparation are carried out. Among them, the doping concentration on the upper surface of InGaAsP reaches or approaches 10 19 Atoms / cm3. The P-type electrode process uses non-alloyed contact Ti-Pt-Au. By utilizing the high adhesion of Ti, the high toughness of Pt, and the good conductivity and corrosion resistance of Au, a non-alloyed P-type electrode ohmic contact with a small specific contact resistance that is not easily detached and has high reliability is achieved.

[0064] The present invention has been described exemplarily above with reference to the accompanying drawings. Obviously, the specific implementation of the present invention is not limited by the above-mentioned manner. As long as various non-substantive improvements are made by adopting the method concept and technical solution of the present invention, or the concept and technical solution of the present invention are directly applied to other occasions without improvement, they are all within the protection scope of the present invention.

Claims

1. An indium gallium arsenide single-photon avalanche diode, characterized in that, Comprising: A substrate, and an epitaxial wafer grown on the substrate; The epitaxial wafer includes: A buffer layer grown on the upper surface of the buffer layer; An absorption layer grown on the upper surface of the buffer layer; A transition layer grown on the upper surface of the absorption layer; A charge layer grown on the upper surface of the transition layer; A cap layer grown on the upper surface of the charge layer; An electrode contact layer grown on the upper surface of the cap layer; A dielectric film covering the electrode contact layer; A P electrode embedded in the dielectric film and connected to the zinc diffusion in the electrode contact layer; The material of the electrode contact layer is indium gallium arsenide phosphide.

2. The indium gallium arsenide single-photon avalanche diode according to claim 1, characterized in that: The material of the electrode contact layer is an intrinsic graded composition material grown for the epitaxial wafer, and the material of the electrode contact layer is indium gallium arsenide phosphide.

3. The indium gallium arsenide single-photon avalanche diode according to claim 2, characterized in that: The variation rule of the gradient component of the electrode contact layer is In 1-x Ga x As y P 1-y , where x varies with y; The change in the y value is calculated starting from the upper surface of InP and varies from 0 to 0.6 from the upper surface of the graded composition material InGaAsP. The material on the upper surface of the electrode contact layer is In 0.718 Ga 0.282 As 0.6 P 0.4 .

4. The indium gallium arsenide single-photon avalanche diode according to claim 3, wherein: The material thickness of the electrode contact layer is 20 nanometers to 200 nanometers, and the doping concentration on the upper surface is 10 19 atoms per cubic centimeter.

5. The indium gallium arsenide single-photon avalanche diode according to any one of claims 1-4, characterized in that: The electrode contact layer is infiltrated with zinc diffusion, the zinc diffusion penetrates to the cap layer, and the P electrode is made of non-alloyed contact Ti-Pt-Au.

6. The indium gallium arsenide single-photon avalanche diode according to claim 5, wherein: The indium gallium arsenide single-photon avalanche diode is a back-illuminated structure without a back lens, an N electrode is provided on the bottom surface of the substrate, the N electrode is a flat structure, and an antireflection film is provided on the edge of the N electrode, and the thickness of the antireflection film is greater than the thickness of the N electrode.

7. The indium gallium arsenide single-photon avalanche diode according to claim 5, wherein: The indium gallium arsenide single-photon avalanche diode is a back-illuminated structure with a back lens, an N electrode is provided on the bottom surface of the substrate, the N electrode is a structure that gradually thins towards the edge, and an antireflection film is provided on the edge of the N electrode, and the thickness of the antireflection film is greater than the thickness of the N electrode.

8. The indium gallium arsenide single-photon avalanche diode according to claim 5, wherein: The indium gallium arsenide single-photon avalanche diode is a front-illuminated structure, both the N electrode and the P electrode are made on the front side, the dielectric film is colored on the side of the epitaxial wafer, and an antireflection film is provided outside the dielectric film on the side of the epitaxial wafer. The common technical characteristic is that the doping type of the material of the electrode contact layer is graded doping; The graded growth mode of the electrode contact layer includes: continuous grading and discrete grading, discrete grading.

9. A preparation method of an indium gallium arsenide single-photon avalanche diode, characterized in that: An epitaxial wafer is prepared on the substrate, and a buffer layer, an absorption layer, a transition layer, a charge layer, a cap layer and an electrode contact layer are sequentially epitaxially grown on the epitaxial wafer. Zinc diffusion is performed on the surface of the epitaxial wafer, and then the P electrode and the N electrode are fabricated by photolithography and etching; During fabrication, the material of the electrode contact layer is selected as InGaAsP.

10. The method for preparing an indium gallium arsenide single-photon avalanche diode according to claim 9, wherein: When zinc diffusion is performed on the surface of the epitaxial wafer, the doping concentration on the upper surface of InGaAsP reaches or approaches 10 19 Atoms / cm 3 , and the P electrode process uses non-alloyed Ti-Pt-Au contacts.

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