CN111916526A - Negative feedback type single photon avalanche photodiode and manufacturing method thereof - Google Patents

Abstract

The present invention relates to the technical field of semiconductor optoelectronics, in particular to a negative feedback type single-photon avalanche photodiode and a manufacturing method thereof, comprising: a substrate, a buffer layer, an absorption layer, a gradient layer, a charge layer and a cap layer; The incident light window and the N electrode, the N electrode is symmetrically distributed around the incident light window; a buffer layer, an absorption layer, a gradient layer, a charge layer and a cap layer are arranged in sequence above the substrate; a stepped structure P-type doped region is arranged on the cap layer, A P electrode is grown on the P-type doped region; a dielectric film is provided on the upper surface of the cap layer, a negative feedback resistor with a semi-closed convoluted ring structure is provided in the middle of the dielectric film, a pad is provided on the dielectric film, and one end of the negative feedback resistor is connected to The P electrode is connected, and the other end is connected to the pad. The invention can realize the rapid quenching and rapid recovery of the Geiger avalanche of the single-photon avalanche photodiode SPAD, improve the photon detection rate of the SPAD, reduce the post-pulse effect, and have the function of photon detection without predicting the arrival time.

Description

A kind of negative feedback type single photon avalanche photodiode and its manufacturing method

technical field

The invention relates to the technical field of semiconductor optoelectronics, in particular to a negative feedback single-photon avalanche photodiode and a manufacturing method thereof.

Background technique

With the continuous development of quantum secure communication, single-photon detection, laser ranging and other technologies, single-photon detectors have been rapidly developed and widely used. Single-photon avalanche photodiode (Single Photon Avalanche Diode, SPAD) is used for the detection of photon signals and is one of the core chips of single-photon detectors.

In order to achieve single-photon detection, the SPAD based on the Separate Absorption Charge Multiplication (SACM) structure must work in the Geiger mode, that is, the voltage across the SPAD is above its avalanche voltage. In Geiger mode, the photon signal detected by the SPAD outputs a macroscopically detectable electrical signal, but if it continues to work in the Geiger mode, the SPAD will not only be damaged by breakdown, but also cannot detect subsequent incident photon signals. In order to realize the continuous operation of the detector, reducing the applied avalanche voltage across the SPAD and quenching the Geiger avalanche multiplication of the SPAD is one of the effective methods. At present, single-photon detectors mainly have three quenching modes: gated quenching mode, active quenching mode, and passive quenching mode.

In gated quench mode, a voltage pulse is applied across the SPAD, and photons are detected within the gate pulse width. High detection rates in GHz can be achieved when the photon arrival times are predictable.

In the active quenching mode, the active quenching circuit pulls down the bias voltage of the SPAD after detecting the rising edge of the avalanche signal to quench the Geiger avalanche. Active quenching is suitable for single-photon detection with unpredictable photon arrival time, but limited by the reaction time of active quenching circuit, the Geiger avalanche duration is maintained at the ns level, which not only increases the post-pulse probability of SPAD, but also cannot achieve GHz high speed probe.

In passive quenching mode, a large resistor is connected in series with the SPAD. When the avalanche effect occurs in the SPAD, the avalanche current causes the voltage of the two sections of the negative feedback resistor to increase, so that the bias voltage across the SPAD drops below the breakdown voltage. , quenching the Geiger avalanche. Passive quenching is suitable for single-photon detection with unpredictable photon arrival time. However, due to the influence of parasitic parameters, the quenching time and Geiger avalanche recovery time are both long. Passive quenching circuits are generally used in low detection frequencies and low detection accuracy requirements. under high conditions.

SUMMARY OF THE INVENTION

In order to solve the problem of long quenching time and recovery time affected by parasitic parameters in passive quenching mode, the present invention provides a negative feedback single-photon avalanche photodiode and a manufacturing method thereof.

A negative feedback single-photon avalanche photodiode, comprising: a substrate, a buffer layer, an absorption layer, a gradient layer, a charge layer and a cap layer, an incident light window and an N electrode are arranged under the substrate, and the N electrodes are symmetrically distributed on the incident light Around the light window; a buffer layer, an absorption layer, a gradient layer, a charge layer and a cap layer are arranged in sequence above the substrate; a P-type doped region with a stepped structure is arranged in the middle of the upper part of the cap layer, and the upper surface of the P-type doped region is A P electrode is grown in the middle area; a layer of dielectric film is provided on the upper surface of the cap layer, and the dielectric film covers the P electrode; Pad, one end of the negative feedback resistor is connected to the P electrode, and the other end is connected to the pad.

Further, the negative feedback resistor adopts a semi-closed convoluted ring structure to increase the resistance value and reduce parasitic parameters, and the outer end of the negative feedback resistor is connected to the pad for signal extraction.

Further, the negative feedback resistor adopts a high resistivity material, including any one or a combination of CrSi, NiCr or a-Si.

Further, the negative feedback resistors of the semi-closed convoluted ring structure are distributed around the P electrode, and the inner end of the semi-closed convoluted ring of the negative feedback resistor is connected to the P electrode.

Further, indium gallium arsenide phosphorous In _(1-x) Ga _x As _y P _(1-y) gradient layer (referred to as InGaAsP) is selected for the gradient layer, so as to realize the gradient of the forbidden band width from the InGaAs absorption layer to the InP charge layer, The thickness of each layer is 0.01-0.05um.

Further, the substrate is made of highly doped InP material, and the doping concentration is not less than 2×10 ¹⁸ cm ⁻³ ; the buffer layer is made of doped InP material, and the doping concentration is less than or equal to 2×10 ¹⁸ cm ^-3 , the thickness of the buffer layer is 0.2-1um; the absorption layer is made of undoped InGaAs material, and the thickness of the absorption layer is 0.4-3um; the charge layer is made of doped InP material, and the doping concentration is 1× 10 ¹⁶ to 5×10 ¹⁷ cm ^-3 , the thickness of the charge layer is 0.08 to 0.4um; the cap layer is made of non-doped InP material, and the thickness is 2 to 4um.

Further, the bonding pad adopts any one or a combination of titanium platinum gold TiPtAu or chromium gold CrAu metal materials.

Further, the P electrode adopts any one or a combination of titanium platinum gold TiPtAu or chromium gold CrAu metal materials.

A method for fabricating a negative feedback single-photon avalanche photodiode, comprising the following steps:

S1, using epitaxial equipment to grow a multiplication epitaxial structure SACM, including: sequentially growing an InP buffer layer, an InGaAs absorber layer, an InGaAsP graded layer, an InP charge layer and an InP cap layer on an InP substrate;

S2, depositing a diffusion mask layer on the upper surface of the InP cap layer of the multiplication epitaxial structure, that is, growing a dielectric film;

S3, using the photolithography process to make the designed pattern on the mask layer and etching the dielectric film in the pattern, exposing the InP cap layer to form a diffusion window;

S4, using a diffusion process to diffuse the P-type impurity source into the InP material of the cap layer in the diffusion window to form a P-type doping region;

S5, repeating the steps S2-S4, successively reducing the diffusion window through the photolithography process, and successively increasing the diffusion depth through the diffusion process to form a stepped P-type doped region;

S6. A stripping photoresist film of negative feedback resistance is made on the dielectric film of the P-type doped region by a stripping process, and a high-resolution pattern inversion positive/negative change photoresist is used. The main steps of making a peeling photoresist film on the dielectric film include: substrate baking, gluing, pre-baking, exposure, reverse baking, flood exposure, development, and post-baking; the thickness of the photoresist film layer is 0.5- 1.0μm;

S7. Use the magnetron sputtering evaporation process to evaporate the high resistivity metal resistance film to form a negative feedback resistor. The resistance value of the negative feedback resistor is controlled by controlling the rate and time of the magnetron sputtering. unit area of resistance;

S8, repeating the peeling process and the evaporation process to make a pad and a P electrode connected to both ends of the negative feedback resistor, one end of the negative feedback resistor is connected to the P-type doped region through the P electrode, and the other end is connected to the pad;

S9. Continue to deposit a dielectric film on the negative feedback resistor, the pad and the P electrode by using the dielectric film process;

S10, using a photolithography process to etch the P electrode and the dielectric film on the pad;

S11. Thinning and polishing the epitaxial wafer substrate according to the light input requirements from the back side, depositing an anti-reflection film on the substrate using a dielectric film process, and using a photolithography process to etch the area on the substrate that is not concentric with the doped region The anti-reflection coating forms the incident light window;

S12, an evaporation process is used to fabricate a metal N electrode connected to the substrate.

Beneficial effects of the present invention:

The invention adopts the negative feedback resistance of the semi-closed gyroscopic ring structure and the monolithic design of the single-photon avalanche photodiode, and reduces the influence of parasitic parameters by means of monolithic integration; Geiger avalanche time can reduce the trapping effect of deep-level defects on carriers, reduce the probability of post-pulse of the device, and improve the parameter performance of the device; it is also conducive to the free running of the SPAD chip and the detection of photons that do not predict the arrival time. In addition, the integrated negative feedback structure design of the present invention uses integrated design to reduce parasitic parameters, which can improve the quenching and recovery time of SPAD, realize rapid quenching and rapid recovery, and improve the application requirements of high-speed detection of SPAD; It can realize the independent work needs of each pixel and meet the technical requirements of multi-echo detectors of the laser focal plane.

Description of drawings

The present invention will be described in further detail below with reference to the accompanying drawings and specific embodiments.

1 is a schematic diagram of a cross-sectional structure of an NFAD according to an embodiment of the present invention;

2 is a top view of an NFAD according to an embodiment of the present invention;

3 is an epitaxial structure diagram of an embodiment of the present invention;

Fig. 4 is the NFAD equivalent circuit of the embodiment of the present invention;

5 is a schematic diagram of an integrated resistor structure according to an embodiment of the present invention;

FIG. 6 is a schematic diagram of a diffused resistor integrated structure according to an embodiment of the present invention;

7 is a process flow diagram of a method for fabricating a negative feedback single-photon avalanche photodiode according to an embodiment of the present invention.

Detailed ways

The technical solutions in the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings in the embodiments of the present invention. Obviously, the described embodiments are only a part of the embodiments of the present invention, but not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative efforts shall fall within the protection scope of the present invention.

1-2 are schematic diagrams of the structure of the NFAD of the present invention, a negative feedback type single-photon avalanche photodiode, including: a substrate, a buffer layer, an absorption layer, a gradient layer, a charge layer and a cap layer, and the substrate is provided with an incident light window and an N electrode, and the N electrode is symmetrically arranged around the incident light window; a buffer layer, an absorption layer, a charge layer and a cap layer are sequentially arranged above the substrate; a P-type doping layer is arranged in the middle of the upper part of the cap layer The upper surface of the P-type doped region is provided with a P electrode in the middle position; a dielectric film is provided on the upper surface of the cap layer, and the dielectric film covers the P electrode; the middle part of the dielectric film above the P electrode A negative feedback resistor with a semi-closed convoluted ring structure is provided. The dielectric film is used to reduce the damage of the negative feedback resistor by external factors and to protect the parameters of the negative feedback resistor from being stable. The upper surface of the dielectric film is provided with a pad, and the negative feedback resistor is One end of the feedback resistor is connected to the P electrode, and the other end is connected to the pad.

In one embodiment, the substrate is made of doped indium phosphide InP material, the doping concentration is not less than 2×10 ¹⁸ cm ⁻³ , and the thickness of the substrate is 0.2˜1 μm.

Further, in one embodiment, the substrate is an n-type substrate, the buffer layer is n-type doped, the doping concentration is not greater than 2×10 ¹⁸ cm ⁻³ , and the growth thickness is 0.2˜1 μm.

In one embodiment, the absorption layer is made of undoped InGaAs InGaAs material, and the growth thickness of the absorption layer is 0.4-3um.

In one embodiment, the graded layer adopts a non-doped graded layer of Indium Gallium Arsenide Phosphorus In _(1-x) Ga _x As _y P _(1-y) , so as to realize the forbidden band width from the absorption layer to the charge layer Gradient, the thickness of each layer is 0.01-0.05um.

In one embodiment, the charge layer becomes the electric field control layer again, the charge layer is made of doped indium phosphide lnP material, the doping concentration is 1×10 ¹⁶ to 5×10 ¹⁷ cm ^-3 , and the growth thickness of the charge layer is It is 0.08～0.4um.

In one embodiment, the cap layer is made of non-doped indium phosphide InP material, and the growth thickness of the cap layer is 2-4um.

The invention is based on the SPAD chip of the absorption, charge, multiplication and separation type (SACM) epitaxial structure, and a negative feedback resistance is set between the pad and the P-type doping area to realize the quenching and negative feedback functions of the Geiger avalanche process. The parasitic parameters are small, and it has the functions of fast quenching and fast recovery.

Further, the negative feedback resistor is an integrated negative feedback resistor, and a high resistivity material is selected. In order to meet the reliability requirements of the active area of the SPAD chip with a size of tens of microns, a resistance of the order of megaohms, and a current of the order of mA, the negative feedback resistor needs to use high resistivity materials. Under the condition of the same film thickness and width, the high resistivity material can reduce the length of the resistor, the area of the resistor ring, and reduce the parasitic capacitance of the SPAD. The resistivity of CrSi, NiCr, a-Si and other materials is in the order of 10 ^-6 Ω·m, and the sheet resistance value of the thin film resistor produced by the process is not less than the order of 1KΩ/□, and can meet the design requirements of small size and high reliability , therefore, the optional materials for the negative feedback resistor include: one or more combinations of CrSi, NiCr, and a-Si. The invention adopts the design of integrated negative feedback structure and utilizes the voltage dividing effect of the integrated negative feedback resistor, which is not only beneficial to reduce the Geiger avalanche time, reduce the trapping effect of deep energy level defects on carriers, reduce the post-pulse probability of the device, and improve the device Moreover, it is also beneficial to realize the free operation of the SPAD chip and realize the detection function of photons that do not predict the arrival time; in addition, the integrated negative feedback structure design of the present invention uses the integrated design to reduce parasitic parameters, which can improve the quenching and quenching of the SPAD. The recovery time can meet the application requirements of high-speed detection; in the array chip, the independent work requirements of each pixel can be realized, and the technical requirements of multi-echo detectors of the laser focal plane can be met.

Further, the negative feedback resistor between the P electrode and the P-type doping interval is a semi-closed convoluted ring structure, and the shape of the negative feedback resistor should meet the application requirements of resistance value, capacitance and inductance at the same time. The designed resistance is in the order of megaohms, and the resistivity of the resistance material is in the order of 10 ^-6 Ω·m. Therefore, under the condition of selecting a film thickness that meets the requirements of reliability, it is necessary to extend the resistance length through a ring pattern. As shown in Fig. 5, considering the requirement of low inductance for high-speed operation, the present invention provides a negative feedback resistor with a semi-closed gyroscopic ring structure, which can not only offset the parasitic inductance generated by the opposite current directions on the adjacent resistance rings, but also can Increase the resistance value and reduce parasitic parameters.

Further, a layer of dielectric film is deposited on the negative feedback resistor, which can reduce the interference and damage of the negative feedback resistor by external factors, protect the stability of the parameters of the negative feedback resistor, and improve the performance stability and reliability of the SPAD.

Further, the inner end of the semi-closed gyroscopic ring of the negative feedback resistor is connected to the P-type doped region through the P electrode, and the outer end of the semi-closed gyroscopic ring of the negative feedback resistor is connected to the pad for signal extraction, as shown in the figure. 6 shown.

Further, in one embodiment, the P electrode is made of metal, grown on the P-type doped region, and used for connecting with the P-type doped region.

Further, in one embodiment, the P electrode is arranged inside the semi-closed gyroscopic ring structure of the negative feedback resistor, that is, the negative feedback resistance of the semi-closed gyroscopic annular structure is distributed around the P electrode, and the half of the negative feedback resistor is half closed. The inner end of the closed convoluted ring is connected to the P electrode.

In an optional embodiment, a diffusion resistor with a resistivity of the order of 10 ^-6 Ω·m is fabricated on the cap layer of the SACM structure SPAD chip by diffusing a low doping concentration, which can be used as an alternative to the negative feedback resistor material. The method can also meet the design requirements of small size, high reliability and speed.

FIG. 4 shows an equivalent circuit of an NFAD according to an embodiment of the present invention. When a working bias is applied, when the device does not generate a Geiger avalanche, the current flowing through the integrated negative feedback resistor in the equivalent circuit is very small (nA level), so the external working bias is mainly applied to the Geiger avalanche photodiode (SPAD). , a Geiger avalanche electric field is formed within the SPAD. When the photo-generated carriers or dark carriers trigger the Geiger avalanche electric field, amplify the current signal and increase the current (in the order of μA) flowing through the negative feedback resistor, thus generating a large voltage drop across the negative feedback resistor, reducing the The bias voltage across the SPAD quenches the Geiger avalanche, which is the self-quenching process of the NFAD device. After the Geiger avalanche is quenched, the avalanche current will be reduced to the level of nA, and the applied bias voltage will establish a Geiger avalanche electric field in the SPAD to realize the self-recovery of the device.

The negative feedback type single-photon avalanche photodiode of the present invention reduces the influence of parasitic parameters by monolithically integrating the negative feedback resistance, can realize the rapid quenching and rapid recovery of the Geiger avalanche of the single-photon avalanche photodiode (SPAD), and improves the photon detection of the SPAD speed, reduce post-pulse effects, and have the function of photon detection that does not predict the arrival time.

A method for fabricating a negative feedback single-photon avalanche photodiode, including but not limited to the following steps:

S1. Using epitaxial equipment to grow a SACM structure epitaxial wafer, including: sequentially growing an InP buffer layer, an InGaAs absorber layer, a graded layer, an InP charge layer and an InP cap layer on an InP substrate, wherein the growth thickness of the InP buffer layer is 0.2～ 1um, the doping concentration of the InP buffer layer is less than or equal to 2×10 ¹⁸ cm ^-3 ; the non-doped InGaAs is used as the absorber layer, and its growth thickness is 0.4-3um; the graded layer adopts the non-doped InGaAsP material , grow multilayer, the thickness of single layer is 0.01～0.05um; the growth thickness of InP charge layer is 0.08～0.4um, and the doping concentration is 1×10 ¹⁶ ～ 5×10 ¹⁷ cm ^-3 ; InP cap layer adopts non-phosphorus doped Indium oxide material, its growth thickness is 2-4um;

S2, depositing a diffusion mask layer on the upper surface of the InP cap layer of the multiplication epitaxial structure, that is, growing a dielectric film;

S3, using the photolithography process on the mask layer to make the designed pattern and etch the dielectric film in the pattern, exposing the InP cap layer to form a diffusion window;

S4, using a diffusion process to diffuse the P-type impurity source into the InP material of the cap layer in the diffusion window to form a P-type doping region;

S5. Repeat the steps S2-S4, reduce the diffusion window successively through the photolithography process, and gradually increase the diffusion depth through the diffusion process to form a stepped P-type doped region

S6, a stripping photoresist film of a negative feedback resistor is formed on the dielectric film of the P-type doped region by a stripping process. Using high-resolution pattern inversion positive/negative change photoresist, a peeling photoresist film is fabricated on the dielectric film in the P-type doped region. The main steps include: substrate baking, gluing, pre-baking, Exposure, reverse baking, flood exposure, development, post-baking; the thickness of the photoresist film layer is 0.5-1.0μm;

S7. Use the magnetron sputtering evaporation process to evaporate the high resistivity metal resistance film to form a negative feedback resistor. The resistance value of the negative feedback resistor is controlled to 1KΩ/□ by controlling the rate and time of the magnetron sputtering, where "□" Represents the unit area of the sheet resistance;

S8, repeating the peeling process and the evaporation process to make a pad and a P electrode connected to both ends of the negative feedback resistor, one end of the negative feedback resistor is connected to the P-type doped region through the P electrode, and the other end is connected to the pad;

S9. Continue to deposit a dielectric film on the negative feedback resistor, the pad and the P electrode by using the dielectric film process;

S10, using a photolithography process to etch the P electrode and the dielectric film on the pad;

S11. Thinning and polishing the epitaxial wafer substrate according to the light input requirements from the back side, depositing an anti-reflection film on the substrate using a dielectric film process, and using a photolithography process to etch the area on the substrate that is not concentric with the doped region The anti-reflection coating forms the incident light window;

S12, an evaporation process is used to fabricate a metal N electrode connected to the substrate.

In order to make the method of the present invention clearer and more complete, the preparation process of the negative feedback single-photon avalanche photodiode is further described by taking the negative feedback type indium gallium arsenide/indium phosphide (InGaAs/InP) avalanche diode as an example for the back incident light. .

1. As shown in Figure 7, the InP-based SACM structure epitaxial wafer shown in Figure 3 is first grown using epitaxial equipment, including: an n-type InP substrate; an n-type InP buffer layer, the growth thickness of which is 0.2-1um, and the doping concentration Not more than 2×10 ¹⁸ cm ^-3 ; undoped InGaAs is used as the absorber layer, and its growth thickness is 0.4-3um; undoped indium gallium arsenide phosphorus (InGaAsP) is used as the graded layer, which is composed of multiple layers with a single layer thickness 0.01～0.05um; n-type InP electric field control layer, namely InP charge layer, its growth thickness is 0.08～0.4um, and the doping concentration is 1×10 ¹⁶ ～5×10 ¹⁷ cm ^-3 ; non-doped indium phosphide cap layer, n-type InP cap layer, its growth thickness is 2 ~ 4um.

2. A diffusion mask layer is deposited on the upper surface of the InP cap layer of the multiplication epitaxial structure, that is, a layer of dielectric film is grown.

3. On the mask layer, a photolithography process is used to make the designed pattern and etch the dielectric film in the pattern to expose the InP cap layer to form a diffusion window.

4. Using a diffusion process, the P-type impurity source is diffused into the InP material of the cap layer in the diffusion window to form a P-type impurity region.

5. Repeat steps 1-4, successively reduce the diffusion window through the photolithography process, and gradually increase the diffusion depth through the diffusion process to form a stepped P-type doped region.

6. Using peeling work, a peeling photoresist film of CrSi alloy resistor is made on the dielectric film of the P-type doped region. Using high-resolution pattern inversion positive/negative change photoresist, a stripped photoresist film layer for evaporation is fabricated on the epitaxial wafer after diffusion. The main steps include: substrate baking, gluing, pre-baking, exposure, Reverse bake, flood exposure, develop, post bake, etc. In order to control the line width of the alloy sheet resistance after stripping, and taking into account the operability of stripping work, the thickness of the photoresist film layer is required to be controlled between 0.5 and 1.0 μm.

7. The magnetron sputtering evaporation process is used to complete the evaporation of CrSi, and the sheet resistance value of the control alloy film is about 1KΩ/□. When the composition of CrSi target material is fixed, the sheet resistance value of CrSi thin film resistor is mainly related to the thickness of the film. Increasing the thickness will reduce the sheet resistance value of the thin film resistor; reducing the thickness can obtain a higher sheet resistance value, but it will lead to negative The current density flowing through the feedback resistor is too high to meet the reliability design requirements. By precisely controlling the rate and time of magnetron sputtering, the sheet resistance of CrSi is about 1KΩ/□.

8. Repeat the stripping process and use the evaporation process to make TiPtAu electrodes and pads connected to both ends of the CrSi resistor. One end of the CrSi resistor is connected to the P-type doped region through the TiPtAu metal electrode to form a P electrode, and the other end is connected to the TiPtAu metal to form a pad.

9. On CrSi, deposit a dielectric film. The dielectric film process is used to deposit SiO ₂ or SiN _X dielectric film on CrSi, electrodes and pads to protect the CiSi resistance and reduce the influence of the external environment on it.

10. Using the photolithography process, the P electrode and the dielectric film on the pad are selectively etched for the electrical connection of the NFAD.

11. Thinning and polishing the epitaxial wafer substrate according to the light input requirements from the back side, depositing an anti-reflection film on the substrate using a dielectric film process, and using a photolithography process to etch the area on the substrate other than the concentric area of the doping area. The AR coating forms the incident light window.

12. The metal N electrode connected to the substrate is fabricated by an evaporation process.

When introducing elements of various embodiments of the present application, the articles "a," "an," "the," and "said" are intended to mean that there are one or more of the elements. The words "comprising", "comprising" and "having" are all inclusive and mean that there may be additional elements other than the listed elements.

In the description of the present invention, it should be understood that the terms "upper", "upper", "lower", "lower", "middle", "top middle", "one end", "the other end", "upper" , "upper surface", "lower surface", etc. indicate the orientation or positional relationship based on the orientation or positional relationship shown in the accompanying drawings, which are only for the convenience of describing the present invention and simplifying the description, rather than indicating or implying the indicated device or Elements must have a particular orientation, be constructed and operate in a particular orientation and are therefore not to be construed as limitations of the invention.

Although embodiments of the present invention have been shown and described, it will be understood by those skilled in the art that various changes, modifications, and substitutions can be made in these embodiments without departing from the principle and spirit of the invention and modifications, the scope of the present invention is defined by the appended claims and their equivalents.

Claims (9)

1. a negative feedback type single-photon avalanche photodiode, comprising: substrate, buffer layer, absorption layer, gradient layer, charge layer and cap layer, it is characterized in that, below substrate is provided with incident light window and N electrode, and The N electrodes are symmetrically distributed around the incident light window; a buffer layer, an absorption layer, a graded layer, a charge layer and a cap layer are arranged in sequence above the substrate; a P-type doping region with a stepped structure is arranged in the middle of the upper part of the cap layer, and the P-type doping layer A P electrode is grown on the upper surface of the area; a layer of dielectric film is arranged on the upper surface of the cap layer, and the dielectric film covers the P electrode; the middle of the dielectric film is provided with a negative feedback resistor with a semi-closed convoluted ring structure, and the dielectric film is provided with There is a pad, one end of the negative feedback resistor is connected to the P electrode, and the other end is connected to the pad. 2 . The negative feedback type single-photon avalanche photodiode according to claim 1 , wherein the negative feedback resistor adopts a semi-closed convoluted ring structure, and the outer end of the negative feedback resistor is connected to the pad. 3 . 3. a kind of negative feedback type single photon avalanche photodiode according to claim 2 is characterized in that, described negative feedback resistor adopts high resistivity material, comprises any one or more in CrSi, NiCr or a-Si combination of species. 4 . The negative feedback type single-photon avalanche photodiode according to claim 3 , wherein the negative feedback resistance of the semi-closed gyroscopic ring structure is distributed around the P electrode, and the inner end of the negative feedback resistance is connected to the P electrode. 5 . 5. A kind of negative feedback type single photon avalanche photodiode according to claim 1, is characterized in that, described gradient layer selects Indium Gallium Arsenide Phosphorus In _{(1-x) Gax} Asy P _{(1-y) gradient} layer, the gradient layer thickness is 0.1 ~ 0.5um. 6. The negative feedback single-photon avalanche photodiode according to claim 1, wherein the substrate adopts a highly doped InP material, and the doping concentration is not less than 2×10 ¹⁸ cm ⁻³ ; The buffer layer is made of doped InP material, the doping concentration is less than or equal to 2×10 ¹⁸ cm ^-3 , and the thickness of the buffer layer is 0.2-1um; the absorption layer is made of undoped InGaAs material, and the thickness of the absorption layer is 0.4 to 3um; the charge layer is made of doped InP material, the doping concentration is 1×10 ¹⁶ to 5×10 ¹⁷ cm ^-3 , and the thickness of the charge layer is 0.08 to 0.4um; the cap layer is made of non-doped The InP material has a thickness of 2 to 4um. 7 . The negative feedback single-photon avalanche photodiode according to claim 1 , wherein the bonding pad is made of any one or a combination of titanium platinum gold TiPtAu or chromium gold CrAu materials. 8 . 8 . The negative feedback single-photon avalanche photodiode according to claim 1 , wherein the P electrode adopts any one or a combination of titanium platinum gold TiPtAu or chromium gold CrAu materials. 9 . 9. A method for making a negative feedback single-photon avalanche photodiode, comprising the following steps: S1, using epitaxial equipment to grow a multiplication epitaxial structure SACM, including: sequentially growing an InP buffer layer, an InGaAs absorber layer, an InGaAsP graded layer, an InP charge layer and an InP cap layer on an InP substrate; S2, depositing a diffusion dielectric film on the upper surface of the InP cap layer of the multiplicative epitaxial structure; S3, using the photolithography process to make the designed pattern on the dielectric film and etch the dielectric film in the pattern, exposing the InP cap layer to form a diffusion window; S4, using a diffusion process to diffuse the P-type impurity source into the InP material of the cap layer in the diffusion window to form a P-type doping region; S5, repeating steps S2-S4, successively reducing the diffusion window through the photolithography process, and successively increasing the diffusion depth through the diffusion process to form a stepped P-type doped region; S6. A stripping photoresist film of negative feedback resistance is made on the dielectric film of the P-type doped region by a stripping process, and a high-resolution pattern inversion positive/negative change photoresist is used. The main steps of making a peeling photoresist film on the dielectric film include: substrate baking, gluing, pre-baking, exposure, reverse baking, flood exposure, development, and post-baking; the thickness of the photoresist film layer is 0.5- 1.0μm; S7. Use the magnetron sputtering evaporation process to evaporate the high resistivity metal resistance film to form a negative feedback resistor. The resistance value of the negative feedback resistor is controlled to 1KΩ/□ by controlling the rate and time of the magnetron sputtering, where "□" Represents the unit area of the sheet resistance; S8, repeating the peeling process and the evaporation process to make a pad and a P electrode connected to both ends of the negative feedback resistor, one end of the negative feedback resistor is connected to the P-type doped region through the P electrode, and the other end is connected to the pad; S9. Continue to deposit a dielectric film on the negative feedback resistor, the pad and the P electrode by using the dielectric film process; S10, using a photolithography process to etch the P electrode and the dielectric film on the pad; S11. Thinning and polishing the epitaxial wafer substrate according to the light input requirements from the back side, depositing an anti-reflection film on the substrate using a dielectric film process, and using a photolithography process to etch the area on the substrate that is not concentric with the doped region The anti-reflection coating forms the incident light window; S12, an evaporation process is used to fabricate a metal N electrode connected to the substrate.

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