Avalanche photodiode and preparation method thereof

Abstract

The present invention discloses an avalanche photodiode and a preparation method thereof, comprising a substrate and a p-type contact layer, a heavily p-type doped electron blocking layer, a gradient doped multi-quantum well absorption layer, an electric field regulation layer, a multiplication layer and an n-type contact layer sequentially grown on the substrate from bottom to top, and also comprising a p-contact and an n-contact, wherein the p-contact is arranged on the p-type contact layer, and the n-contact is arranged on the n-type contact layer. By using a gradient doped multi-quantum well structure as an absorption layer to separate photogenerated electrons and photogenerated holes, noise can be reduced and the sensitivity and rate of the avalanche photodiode can be improved.

Description

Technical Field

[0001] The present invention relates to the technical field of semiconductor optoelectronic devices, and in particular to an avalanche photodiode and a preparation method thereof. Background Art

[0002] Semiconductor photodetectors are the core components of the receiving part of optical fiber communication technology. As optical fiber communication technology develops rapidly towards higher transmission rates, larger data capacity and longer transmission distances, the performance requirements for photodetectors are also increasing. Among many semiconductor photodetectors, APD (Avalanche Photo Diode) has become an important optical signal receiving chip in optical fiber communication systems due to its superior frequency response characteristics and internal gain capability.

[0003] APD operates under high reverse bias and can generate photogenerated carriers in the absorption layer by absorbing incident light. When these photogenerated carriers collide and ionize with the lattice under the action of a strong electric field, an avalanche effect is triggered, causing the photocurrent generated by a single carrier to be significantly amplified to a macroscopic level, thereby achieving single-photon detection. This feature makes APD widely used in fiber-optic communications, laser ranging, quantum key distribution, quantum imaging, biological detection, and fiber-optic sensing. In short-distance optical communication systems (such as access networks), intensity modulation and direct detection schemes are usually used. With the continuous improvement of the transmission distance and rate of these systems, higher requirements are placed on the conversion rate and receiving sensitivity of photoelectric conversion devices. Therefore, the development of a photoelectric conversion device that can meet the requirements of high speed and high sensitivity has important application prospects and commercial value.

[0004] At present, the mainstream APDs on the market are mostly based on the gain layer of indium phosphide (InP) or indium aluminum arsenide (InAlAs) materials to achieve the conversion of optical signals. However, these materials have high intrinsic noise characteristics, especially their electron-hole ionization rate ratio (that is, k value), which limits the further improvement of APDs based on these materials in sensitivity and speed. Therefore, in order to meet the higher performance requirements of future optical communications and related fields, it is urgent to explore the design of APDs with new materials and structures to break through the bottleneck of existing technologies. Summary of the invention

[0005] In order to solve the problem of slow diffusion speed of photogenerated electrons in the p-type doped light absorption layer in ordinary single-line carrier photodetectors, the present invention application provides an avalanche photodiode on the one hand, including a substrate, a p-type contact layer grown on the substrate from bottom to top, a heavily p-type doped electron blocking layer, a gradient doped multi-quantum well absorption layer, an electric field regulation layer, a multiplication layer and an n-type contact layer, and also includes a p-contact and an n-contact, the p-contact being evaporated on the p-type contact layer and located on the outside of the heavily p-type doped electron blocking layer, and the n-contact being evaporated on the n-type contact layer.

[0006] Preferably, the graded doped multi-quantum well absorption layer comprises multiple layers of graded doped quantum well layers and undoped barrier layers grown in alternating cycles, and each of the graded doped quantum well layers is composed of a semiconductor having a band gap energy corresponding to a target wavelength of light.

[0007] Preferably, the graded doped multi-quantum well absorption layer comprises multiple layers of undoped quantum well layers and graded doped barrier layers grown alternately and cyclically, and each of the undoped quantum well layers is composed of a semiconductor having a band gap energy corresponding to a target wavelength of light.

[0008] Preferably, the doping concentration of the multi-layer gradually doped quantum well layer or the multi-layer gradually doped barrier layer decreases layer by layer from the light entering side, or the doping concentration increases layer by layer from the light entering side, and the maximum doping concentration is .

[0009] Preferably, the conduction band bottom energy of the heavily p-type doped electron blocking layer is higher than the conduction band bottom energy of the graded doped multi-quantum well absorption layer.

[0010] Preferably, the substrate is a semi-insulating gallium arsenide substrate or a semi-insulating indium phosphide substrate or a semi-insulating silicon substrate.

[0011] Preferably, the conduction band bottom energy of the undoped barrier layer is higher than the conduction band bottom energy of the graded doped quantum well layer, and the valence band top energy of the undoped barrier layer is lower than the valence band top energy of the graded doped quantum well layer.

[0012] Preferably, the thickness of each graded doped quantum well layer is 0.5 to 30 nanometers.

[0013] Preferably, each undoped barrier layer has a thickness of 0.5 to 30 nanometers and a height of 200 to 500 millielectronvolts.

[0014] Another aspect of the present invention provides a method for preparing an avalanche photodiode, the method comprising the following steps:

[0015] S1, sending the substrate into the sample injection chamber and buffer chamber of the molecular beam epitaxy equipment in sequence for pretreatment, and sending the pretreated substrate into the molecular beam epitaxy growth chamber for high-temperature deoxidation treatment;

[0016] S2, growing a p-type contact layer, a heavily p-type doped electron blocking layer, a gradient doped multi-quantum well absorption layer, an electric field control layer, a multiplication layer and an n-type contact layer from bottom to top on the substrate after high-temperature deoxidation, to obtain an avalanche photodiode sample;

[0017] S3, masking and etching the avalanche photodiode sample to expose the p-type contact layer;

[0018] S4, flattening the avalanche photodiode whose p-type contact layer is etched and exposed, and coating it with an insulating layer;

[0019] S5, opening a window on the p-type contact layer of the avalanche photodiode coated with an insulating layer and evaporating a p-contact;

[0020] S6. Open a window on the n-type contact layer of the avalanche photodiode coated with an insulating layer and evaporate an n-contact.

[0021] The above-mentioned avalanche photodiode and preparation method include a substrate and a p-type contact layer, a heavily p-type doped electron blocking layer, a gradient doped multi-quantum well absorption layer, an electric field control layer, a multiplication layer and an n-type contact layer grown on the substrate from bottom to top, and also include a p-contact and an n-contact, wherein the p-contact is arranged on the p-type contact layer, and the n-contact is arranged on the n-type contact layer. By using a gradient doped multi-quantum well structure as an absorption layer to separate photogenerated electrons and photogenerated holes, noise can be reduced and the sensitivity and speed of the avalanche photodiode can be improved. BRIEF DESCRIPTION OF THE DRAWINGS

[0022] Figure 1 is a schematic diagram of the growth structure of an avalanche photodiode in one embodiment of the present invention;

[0023] Figure 2 Schematic diagram of carrier transport energy band corresponding to an avalanche photodiode in one embodiment of the present invention.

[0024] Description of reference numerals:

[0025] 1. p-type contact layer; 2. heavily p-type doped electron blocking layer; 3. gradient doped multi-quantum well absorption layer; 4. electric field control layer; 5. multiplication layer; 6. n-type contact layer; 7. p-contact; 8. n-contact; 9. substrate; 10. incident light; 11. transport energy band of p-type contact layer; 12. transport energy band of heavily p-type doped electron blocking layer; 13. transport energy band of gradient doped multi-quantum well absorption layer; 14. transport energy band of electric field control layer; 15. transport energy band of multiplication layer; 16. transport energy band of n-type contact layer. DETAILED DESCRIPTION

[0026] In order to enable those skilled in the art to better understand the technical solution of the present invention, the present invention is further described in detail below in conjunction with the accompanying drawings.

[0027] See also Figure 1 , Figure 1 The figure is a schematic diagram of the growth structure of an avalanche photodiode according to an embodiment of the present invention.

[0028] In one embodiment, an avalanche photodiode includes a substrate 9, a p-type contact layer 1, a heavily p-type doped electron blocking layer 2, a gradient doped multi-quantum well absorption layer 3, an electric field control layer 4, a multiplication layer 5 and an n-type contact layer 6, which are sequentially grown on the substrate 9 from bottom to top, and further includes a p-contact 7 and an n-contact 8, wherein the p-contact 7 is evaporated on the p-type contact layer 1 and is located outside the heavily p-type doped electron blocking layer 2, and the n-contact 8 is evaporated on the n-type contact layer 6. The electric field control layer 4 is provided to control the energy band and electric field difference between the gradient doped multi-quantum well absorption layer 3 and the multiplication layer 5.

[0029] Figure 1 The avalanche photodiode including the gradient doped multi-quantum well absorption layer shown in the figure is cylindrical in shape as a whole, wherein the substrate 9 may be a semi-insulating gallium arsenide (GaAs) substrate, a semi-insulating silicon substrate, or a semi-insulating indium phosphide (InP) substrate, and the n-type contact layer 6 is specifically a circular metal electrode formed on the p-type contact layer 1 by evaporating metal in a window reserved in advance by a mask, and the circular metal electrode is located outside the heavily p-type doped electron blocking layer 2, and the incident light 10 can enter from below the substrate 9. The carrier transport energy band diagram corresponding to this structure is shown in FIG. Figure 2 .

[0030] Further, the gradient doped multi-quantum well absorption layer 3 comprises multiple layers of gradient doped quantum well layers and undoped barrier layers grown in alternating cycles, and each layer of the gradient doped quantum well layer is composed of a semiconductor having a band gap energy corresponding to the target wavelength of light; or:

[0031] The graded doped multi-quantum well absorption layer 3 comprises multiple layers of undoped quantum well layers and graded doped barrier layers grown in alternating cycles, and each undoped quantum well layer is composed of a semiconductor having a band gap energy corresponding to the target wavelength of light.

[0032] Specifically, the quantum well structure is a semiconductor physics concept that involves a structure formed by the growth of two different semiconductor materials in the form of a sandwich. The characteristic of this structure is that the middle semiconductor material layer is sandwiched by barrier layers (such as AlAs and GaAs) on both sides. When the thickness of the active layer is reduced to the order of Bohr radius or de Broglie wavelength, the quantum size effect appears. At this time, the carriers are confined in the potential well formed by the active layer, which is called a quantum well, which leads to a significant change in the characteristics of free carriers. The quantum well is a narrow bandgap ultra-thin layer sandwiched between two wide bandgap barrier thin layers. The basic characteristic of the quantum well is that the wave function of the carrier (electron or hole) is localized in one-dimensional direction due to the limitation of the well width. This means that although the carrier has two-dimensional freedom in the plane parallel to the well wall, the conduction band and valence band will split into sub-bands in the direction perpendicular to the well wall. This splitting causes the electronic state density in the quantum well to have a step-like relationship with the energy, rather than a parabolic shape in three-dimensional bulk materials.

[0033] The absorption layer of the avalanche photodiode (that is, the gradient doped multi-quantum well absorption layer 3) is constructed by using a gradient doped multi-quantum well absorption layer. When external light is irradiated on the avalanche photodiode, the gradient doped multi-quantum well absorption layer 3 can absorb photons to generate electron-hole pairs. After applying a reverse bias voltage to the p-type contact layer 1 and the n-type contact layer 6, under the electric field generated by the electric field control layer 4, the photogenerated free electrons in the gradient doped multi-quantum well absorption layer 3 are accelerated to drift to the multiplication layer 5 through the quantum well barrier by electron tunneling, while the photogenerated holes cannot reach the multiplication layer 5 due to the limitation of the barrier, thereby realizing the separation of photogenerated electrons and holes, so that only the photogenerated free electrons can reach the multiplication layer 5. When the drift speed is large enough, the photogenerated free electrons will collide with the lattice atoms of the multiplication layer 5 to ionize new electron-hole pairs again, thereby generating a collision ionization effect, which can reduce noise and improve the sensitivity and speed of the avalanche photodiode.

[0034] Taking the example that the gradient doped multi-quantum well absorption layer 3 includes multiple layers of gradient doped quantum well layers and undoped barrier layers grown in alternating cycles, the gradient doped multi-quantum well absorption layer 3 includes multiple layers of gradient doped quantum well layers and undoped barrier layers grown in alternating cycles, and therefore, the total thickness of the gradient doped multi-quantum well absorption layer 3 depends on the number of cyclic growths of the gradient doped quantum well layers and the undoped barrier layers. When growing the gradient doped multi-quantum well absorption layer 3, the growth of one layer of gradient doped quantum well layer and one layer of undoped barrier layer is called one alternating cycle growth, and the total thickness of the gradient doped multi-quantum well absorption layer 3 can be made to meet the preset requirements by increasing the number of alternating cycle growths. For example, it can be set that in one alternating cycle growth, the thickness of the gradient doped quantum well layer and the undoped barrier layer does not exceed 60 nanometers, and the number of cyclic growths can be set to 1 to 30 times according to the total thickness requirement of the gradient doped multi-quantum well absorption layer 3.

[0035] Furthermore, the doping concentration of the multi-layer gradually doped quantum well layer or the multi-layer gradually doped barrier layer decreases layer by layer from the light entering side, or the doping concentration increases layer by layer from the light entering side, and the maximum doping concentration is .

[0036] Specifically, in order to achieve the separation of photogenerated carriers, in the traditional p-type doped absorption layer, the incident light is absorbed and generates electrons and holes. Since the majority carriers in the traditional p-type doped absorption layer are holes, the electrons as minority carriers become active carriers. The electrons diffuse to the electric field regulation layer 4, and the diffusion rate will be relatively smaller than the rate of electron drift, which is not conducive to improving the sensitivity and rate of the avalanche photodiode. In this application, a light gradient doping method (such as light p-type doping or light n-type doping, the doping concentration of the light p-type doping decreases layer by layer from the light entering side, and the doping concentration of the light n-type doping increases layer by layer from the light entering side) is adopted to reduce the doping concentration, and since the absorption layer is a quantum well, the total thickness of the absorption layer is relatively small, so that even if the electrons diffuse to the electric field regulation layer 4, it will not have a significant impact on the rate, and the light p-type doping can balance the narrow bandgap absorption layer material under high reverse bias conditions. The high electric field strength causes high dark current and low gain, which is conducive to reducing the dark current of the infrared detection avalanche photodiode and increasing the breakdown voltage stability.

[0037] Taking molecular beam epitaxy growth as an example, there are two ways to grow the gradient doped multi-quantum well absorption layer 3:

[0038] The first is direct doping, that is, in the process of cyclic growth of quantum well layers / barrier layers, starting from the side where light enters, the target temperature of light p-type doping is set to decrease layer by layer or the target temperature of light n-type doping is set to increase layer by layer, so as to achieve a gradual doping concentration in the process of multi-layer quantum well growth. Different temperatures of the doping source will lead to different doping concentrations: the lower the temperature of the doping source, the lower the doping concentration, and vice versa, the higher the temperature of the doping source, the higher the doping concentration. In this direct doping method, doping is only introduced into the quantum well layer, and the barrier layer is undoped. In order to prevent excessively high doping concentrations from introducing additional noise, the maximum concentration of n-type or p-type doping in the gradient-doped multi-layer quantum well structure should be set at the following.

[0039] The second is modulation doping, that is, in the process of cyclic growth of quantum well layer / barrier layer, only the barrier layer is doped, while the quantum well layer is not doped. The doping concentration of the barrier layer is controlled by setting the target temperature of light p-type doping to decrease layer by layer, or setting the target temperature of light n-type doping to increase layer by layer, so as to achieve the gradual doping concentration in the growth process of multi-layer barrier layer. The maximum doping concentration of light n-type doping or light p-type doping in the gradient doping multi-layer quantum well structure should be set at the following.

[0040] Specifically, since the speed at which photogenerated electrons reach the electric field control layer and the multiplication layer through diffusion in the absorption layer is slower than that through drift, the thickness of the absorption layer can be reduced by using a gradient doped multi-layer quantum well as a light absorption layer. Therefore, even if it is a p-type doped quantum well absorption layer, the photogenerated electrons reach the electric field control layer and the multiplication layer through diffusion, and the reduction in thickness can make up for this deficiency. And the advantage of p-type doping is that it can balance the problem of high dark current and low gain caused by high electric field intensity of narrow bandgap absorption layer materials under high reverse bias. It has a promoting effect on reducing the dark current of infrared detection avalanche photodiodes and increasing the breakdown voltage stability.

[0041] In the present application, the multilayer gradually doped quantum well layer can be doped by light p-type, starting from the incident light side, and the doping concentration is reduced layer by layer, and the obtained absorption layer is also called a light p-type gradually doped multi-quantum well absorption layer. The doping concentration can also be stopped at half the thickness of the absorption layer, so that the absorption layer can be more matched with the band gap of the electric field regulation layer 4 and the multiplication layer 5. Stopping the doping concentration at half the thickness of the absorption layer means that only the first half of the light incident side of the absorption layer is inserted with gradually doping, and the latter half is not doped. The multilayer gradually doped quantum well layer can also be doped by light n-type, starting from the light incident side, and the doping concentration is increased layer by layer, and the obtained absorption layer is also called a light n-type gradually doped multi-quantum well absorption layer. The advantage of light n-type doping is that in devices where electrons are the main carriers, the carrier drift velocity can be increased, thereby accelerating the speed at which carriers are collected in the collection layer. Additionally, in the lightly n-type gradient-doped multi-quantum well absorption layer, the doping concentration is higher on the side close to the electric field regulation layer 4. Under reverse bias conditions, the energy band structure and electric field distribution will be more matched with the electric field regulation layer 4 and the multiplication layer 5, ensuring that the photogenerated carriers enter the multiplication layer 5 at high speed and the high electric field for multiplication is distributed in the multiplication layer 5 rather than the gradient-doped multi-quantum well absorption layer 3, thereby ensuring the stability of the breakdown voltage and reducing additional noise.

[0042] The multi-layer gradient doped barrier layer can also be doped with light p-type, starting from the incident light side, with the doping concentration decreasing layer by layer, or with light n-type, starting from the light incident side, with the doping concentration increasing layer by layer. The specific method is the same as described above and will not be repeated here.

[0043] Furthermore, the bottom energy of the conduction band of the heavily p-type doped electron blocking layer 2 is higher than the bottom energy of the conduction band of the graded doped multi-quantum well absorption layer 3 .

[0044] Specifically, the bottom energy of the conduction band of the heavily p-type doped electron blocking layer 2 should be as high as possible without losing the material quality. The "as high as possible" here is based on the difficulty of growth. Generally, in order to make the bottom energy of the conduction band of the heavily p-type doped electron blocking layer 2 high, the p-type doping concentration should be larger, but too high concentration doping may cause doping deactivation problems; increasing the bottom energy of the conduction band can also be achieved by changing the material composition of the heavily p-type doped electron blocking layer 2, but during the growth process, if the material composition is changed, lattice mismatch problems may be introduced, thereby generating dislocations that affect the quality of the device. Therefore, from the perspective of energy band design, the bottom energy of the conduction band of the heavily p-type doped electron blocking layer 2 should be as high as possible. The bottom energy of the conduction band of the gradually doped multi-quantum well absorption layer 3 is to prevent the photogenerated electrons from diffusing to the p-type contact layer 1, so that all the photogenerated electrons will move to the gradually doped multi-quantum well absorption layer 3 and then enter the electric field control layer 4 and the multiplication layer 5 to be accelerated.

[0045] Furthermore, the bottom energy of the conduction band of the barrier layer is higher than the bottom energy of the conduction band of the gradient doped quantum well layer, and the top energy of the valence band of the barrier layer is lower than the top energy of the valence band of the gradient doped quantum well layer.

[0046] Specifically, each gradient doped quantum well layer in the gradient doped multi-quantum well absorption layer 3 is composed of a semiconductor having a band gap energy corresponding to the target wavelength of light, the conduction band bottom energy of the barrier layer should be selected to be higher than the conduction band bottom energy of the gradient doped quantum well layer, and the valence band top energy of the barrier layer should be selected to be lower than the valence band top energy of the gradient doped quantum well layer, thereby limiting the drift of photogenerated holes to the electric field control layer 4.

[0047] In addition, the thickness of the undoped barrier layer should be selected to be a thickness that can achieve the quantum tunneling effect. For example, the thickness of the undoped barrier layer can be 0.5 to 30 nanometers, and the typical height of the undoped barrier layer is 200 to 500 millielectronvolts. The thickness of each gradient doped quantum well layer can be 0.5 to 30 nanometers, and the typical thickness of the gradient doped quantum well layer is 10 nanometers.

[0048] In particular, in the above-mentioned avalanche photodiode, if a reverse bias voltage is applied between the p-contact 7 and the n-contact 8, the photogenerated free electrons will drift to the electric field control layer 4 through the undoped barrier layer by electron tunneling in the gradient doped multi-quantum well absorption layer 3, while the photogenerated holes cannot reach the electric field control layer 4 due to the limitation of the undoped barrier layer, thereby realizing the separation of photogenerated electrons and photogenerated holes.

[0049] It should be noted that the thickness of the gradient doped barrier layer should also be selected to be a thickness that can achieve the quantum tunneling effect. For example, the thickness of the gradient doped barrier layer can be 0.5 to 30 nanometers, and the height can be 200 to 500 millielectronvolts. At this time, the thickness of each undoped quantum well layer can be 0.5 to 30 nanometers.

[0050] In another embodiment, a method for preparing an avalanche photodiode comprises the following steps:

[0051] S1. The substrate 9 is sequentially sent into the sample injection chamber and the buffer chamber of the molecular beam epitaxy equipment for pretreatment, and the pretreated substrate is sent into the molecular beam epitaxy growth chamber for high-temperature deoxidation treatment.

[0052] Specifically, the molecular beam epitaxy equipment includes an injection chamber, a buffer chamber and a molecular beam epitaxial growth chamber. First, the substrate 9 is dehydrated: the substrate 9 is sent to the injection chamber for low-temperature baking, specifically, it is baked at a low temperature of 200 degrees for 12 hours to remove moisture; then it is sent to the buffer chamber for heating to remove residual organic matter. The heating temperature is generally 400-600 degrees, and the heating time is one hour. The specific heating temperature depends on the applied substrate, such as the heating temperature of the silicon substrate is generally 600 degrees, the indium phosphide substrate is generally 400 degrees, and the gallium arsenide substrate is generally 500 degrees. The residual organic matter can be removed by heating, and then the substrate with the residual organic matter removed is sent to the molecular beam epitaxial growth chamber for high-temperature deoxidation treatment.

[0053] S2. A p-type contact layer 1, a heavily p-type doped electron blocking layer 2, a gradient doped multi-quantum well absorption layer 3, an electric field control layer 4, a multiplication layer 5 and an n-type contact layer 6 are grown in sequence from bottom to top on a substrate 9 that has been deoxidized at high temperature to obtain an avalanche photodiode sample.

[0054] S3 . Mask and etch the avalanche photodiode sample to expose the p-type contact layer 1 .

[0055] S4, planarizing the avalanche photodiode with the p-type contact layer 1 etched and exposed, and coating it with an insulating layer.

[0056] The planarization treatment can make the surface of the p-type contact layer 1 smooth, so as to facilitate the subsequent evaporation of the contact layer and ensure the quality of the contact layer.

[0057] S5, using a mask and etching to open a window on the p-type contact layer 1 of the avalanche photodiode coated with an insulating layer, and evaporating metal in the window to form a p-contact 7. The p-contact 7 can be a circular metal electrode, which is located outside the heavily p-type doped electron blocking layer 2.

[0058] S6. Use a mask and etching to open a window on the n-type contact layer 6 of the avalanche photodiode coated with an insulating layer, and evaporate an n-contact 8.

[0059] In this embodiment, the substrate 9 is firstly removed of moisture and organic residues by using the injection chamber and buffer chamber of the molecular beam epitaxy equipment, and then is sent into the molecular beam epitaxial growth chamber for high-temperature deoxidation treatment, and a p-type contact layer 1, a heavily p-type doped electron blocking layer 2, a gradient doped multi-quantum well absorption layer 3, an electric field regulation layer 4, a multiplication layer 5 and an n-type contact layer 6 are sequentially grown from bottom to top on the substrate 9 after high-temperature treatment, thereby obtaining an avalanche photodiode sample, and then the avalanche photodiode sample is masked and etched to expose the p-type contact layer 1, and then it is flattened and coated with an insulating layer, and finally, windows are opened on the p-type contact layer 1 and the n-type contact layer 6 of the single-row carrier photodetector coated with the insulating layer, and p-contact 7 and n-contact 8 are evaporated, respectively, thereby obtaining an avalanche photodiode containing a gradient doped multi-quantum well absorption layer.

[0060] Further, the growth method of the gradient doped multi-quantum well absorption layer 3 is as follows: in the process of cyclic growth of quantum well layer / barrier layer, multiple layers of gradient doped quantum well layer and undoped barrier layer can be selected to be grown, at this time, starting from the light entering side, the target temperature of light p-type doping can be set to decrease layer by layer, so that the doping concentration of the multiple layers of gradient doped quantum well absorption layer decreases layer by layer starting from the light entering side, or the target temperature of light n-type doping can be set to increase layer by layer, so that the doping concentration of the multiple layers of gradient doped quantum well absorption layer increases layer by layer starting from the light entering side, and the doping concentration does not exceed ; You can also choose to grow multiple layers of undoped quantum well layers and gradient doped barrier layers. At this time, starting from the light entering side, you can set the target temperature of light p-type doping to decrease layer by layer, so that the doping concentration of the multi-layer gradient doped barrier layer decreases layer by layer from the light entering side, or set the target temperature of light n-type doping to increase layer by layer, so that the doping concentration of the multi-layer gradient doped barrier layer increases layer by layer from the light entering side, and the doping concentration does not exceed .

[0061] The above-mentioned avalanche photodiode and preparation method include a substrate and a p-type contact layer, a heavily p-type doped electron blocking layer, a gradient doped multi-quantum well absorption layer, an electric field control layer, a multiplication layer and an n-type contact layer grown on the substrate from bottom to top, and also include a p-contact and an n-contact, wherein the p-contact is arranged on the p-type contact layer, and the n-contact is arranged on the n-type contact layer. By using a gradient doped multi-quantum well structure as an absorption layer to separate photogenerated electrons and photogenerated holes, only electrons can reach the multiplication layer to achieve avalanche multiplication. At the same time, because of the addition of gradient doping, the electric field and energy band can be regulated, and the energy band and electric field mutation between the absorption layer and the multiplication layer can be reduced, which can reduce noise and improve the sensitivity and speed of the avalanche photodiode.

[0062] The above is a detailed introduction to an avalanche photodiode and a preparation method provided by the present invention. This article uses specific examples to illustrate the principles and implementation methods of the present invention. The description of the above embodiments is only used to help understand the core idea of ​​the present invention. It should be pointed out that for ordinary technicians in this technical field, without departing from the principles of the present invention, the present invention can also be improved and modified in a number of ways, and these improvements and modifications also fall within the scope of protection of the claims of the present invention.

Claims

1. An avalanche photodiode, characterized in that: The invention comprises a substrate (9), a p-type contact layer (1), a heavily p-type doped electron blocking layer (2), a gradient doped multi-quantum well absorption layer (3), an electric field control layer (4), a multiplication layer (5) and an n-type contact layer (6) which are sequentially grown on the substrate (9) from bottom to top, and further comprises a p-contact layer (7) and an n-contact layer (8), wherein the p-contact layer (7) is vapor-deposited on the p-type contact layer (1) and is located outside the heavily p-type doped electron blocking layer (2), and the n-contact layer (8) is vapor-deposited on the n-type contact layer (6); The gradient doped multi-quantum well absorption layer (3) comprises multiple layers of gradient doped quantum well layers and undoped barrier layers that are grown in alternating cycles, and each gradient doped quantum well layer is composed of a semiconductor having a band gap energy corresponding to a target wavelength of light; or, The gradient doped multi-quantum well absorption layer (3) comprises multiple layers of undoped quantum well layers and gradient doped barrier layers that are grown in alternating cycles, and each layer of the undoped quantum well layer is composed of a semiconductor having a band gap energy corresponding to a target wavelength of light.

2. The avalanche photodiode according to claim 1, characterized in that When the gradient doped multi-quantum well absorption layer (3) includes multiple layers of gradient doped quantum well layers and multiple layers of undoped barrier layers that are grown alternately and cyclically, the doping concentration of the multiple layers of gradient doped quantum well layers decreases layer by layer starting from the light entering side, or the doping concentration increases layer by layer starting from the light entering side, and the maximum doping concentration is 5×10 17 cm -3 ; or, When the gradient doped multi-quantum well absorption layer (3) includes multiple layers of undoped quantum well layers and multiple layers of gradient doped barrier layers that are grown alternately and cyclically, the doping concentration of the multiple layers of gradient doped barrier layers decreases layer by layer starting from the light entering side, or the doping concentration increases layer by layer starting from the light entering side, and the maximum doping concentration is 5×10 17 cm -3 .

3. The avalanche photodiode according to claim 1, wherein: The conduction band bottom energy of the heavily p-type doped electron blocking layer (2) is higher than the conduction band bottom energy of the gradient doped multi-quantum well absorption layer (3).

4. The avalanche photodiode according to claim 1, wherein: The substrate (9) is a semi-insulating gallium arsenide substrate or a semi-insulating indium phosphide substrate or a semi-insulating silicon substrate.

5. The avalanche photodiode according to claim 1, wherein: The conduction band bottom energy of the undoped barrier layer is higher than the conduction band bottom energy of the graded doped quantum well layer, and the valence band top energy of the undoped barrier layer is lower than the valence band top energy of the graded doped quantum well layer.

6. The avalanche photodiode according to claim 5, characterized in that The thickness of each layer of the graded doped quantum well layer is 0.5 to 30 nanometers.

7. The avalanche photodiode according to claim 6, characterized in that The thickness of each undoped barrier layer is specifically 0.5 to 30 nanometers, and the height is 200 to 500 millielectronvolts.

8. A method for preparing an avalanche photodiode, characterized in that: The method comprises the following steps: S1, sequentially sending the substrate (9) into the sample injection chamber and the buffer chamber of the molecular beam epitaxy equipment for pretreatment, and sending the pretreated substrate into the molecular beam epitaxy growth chamber for high-temperature deoxidation treatment; S2. A p-type contact layer (1), a heavily p-type doped electron blocking layer (2), a gradient doped multi-quantum well absorption layer (3), an electric field control layer (4), a multiplication layer (5) and an n-type contact layer (6) are grown in sequence from bottom to top on a substrate (9) that has been subjected to high-temperature deoxidation, to obtain an avalanche photodiode sample; wherein the gradient doped multi-quantum well absorption layer (3) comprises multiple layers of gradient doped quantum well layers and undoped potential barrier layers grown in alternating cycles, and each layer of the gradient doped quantum well layer is composed of a semiconductor having a band gap energy corresponding to a target wavelength of light; or, the gradient doped multi-quantum well absorption layer (3) comprises multiple layers of undoped quantum well layers and gradient doped potential barrier layers grown in alternating cycles, and each layer of the undoped quantum well layer is composed of a semiconductor having a band gap energy corresponding to a target wavelength of light; S3, masking and etching the avalanche photodiode sample to expose the p-type contact layer (1); S4, flattening the avalanche photodiode after etching and exposing the p-type contact layer (1) and coating it with an insulating layer; S5, opening a window on the p-type contact layer (1) of the avalanche photodiode coated with an insulating layer and evaporating a p-contact (7); S6, opening a window on the n-type contact layer (6) of the avalanche photodiode coated with an insulating layer and evaporating an n-contact (8).

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