Photodiode and preparation method thereof, active region structure and electronic equipment

Abstract

The invention relates to the technical field of photodiodes, and relates to a photodiode and a preparation method thereof, an active region structure and electronic equipment, so as to obtain a high-quality InyGa1-yAs absorption layer. The photodiode comprises an N-type contact layer, an active region structure and a P-type contact layer which are sequentially stacked, the active region structure comprises a multiplication structure layer, a charge layer, a transition layer and an absorption layer which are sequentially stacked, the absorption layer is an InyGa1-yAs layer, the transition layer comprises N InxGa1-xAs buffer layers, N is a positive integer larger than 1, x is larger than 0 and smaller than 1, and x is larger than 0 and smaller than 1 in the direction from the charge layer to the absorption layer. The content of the In component in the N-layer InxGa1-xAs buffer layer is gradually increased, and the absolute value of the difference between the surface, facing the absorption layer, of the transition layer and the content of the In component in the absorption layer is smaller than or equal to 0.2, so that the InyGa1-yAs absorption layer with higher quality can be obtained, and effective absorption of long-wavelength light is realized.

Description

Technical Field

[0001] The present application relates to the technical field of photodiodes, and in particular to a photodiode and a preparation method thereof, an active region structure and an electronic device. Background Art

[0002] Photodiodes can convert optical signals into electrical signals. The specific process is as follows: When light shines on a photodiode, photogenerated carriers are generated, forming a photocurrent. Therefore, photodiodes can be used in the field of optical communications. In this field, wavelengths of 1310nm and 1550nm are relatively common. To absorb light with wavelengths of 1310nm and 1550nm, existing photodiodes generally use InGaAs materials to prepare the absorption layer. However, in practical applications, the quality of InGaAs materials used as absorption layers still remains a problem. For example, the light absorption efficiency of the InGaAs absorption layer is not high enough, resulting in low photoelectric conversion efficiency. Moreover, the InGaAs material has a large absorption coefficient for long-wavelength light, which reduces the generation rate of photogenerated carriers, resulting in a slow response speed, which affects the application of photodiodes in fields such as high-speed optical communications. Summary of the Invention

[0003] The embodiments of the present application provide a photodiode and a method for manufacturing the same, an active region structure, and an electronic device, for improving the performance of the InGaAs absorption layer of the photodiode.

[0004] In the first aspect, the present application provides a photodiode, which comprises: an N-type contact layer, an active region structure, and a P-type contact layer stacked in sequence; the active region structure comprises: a multiplication structure layer, a charge layer, a transition layer, and an absorption layer stacked in sequence on one side surface of the N-type contact layer. y Ga 1-y As layer, and 0.38≤y≤0.82, can be obtained by In y Ga 1-y The As layer effectively absorbs long wavelength light such as 1310nm and 1550nm. In addition, the difference in lattice constant between the charge layer material and the absorption layer material is greater than or equal to a first threshold, so that there is a lattice mismatch problem between the charge layer material and the absorption layer material. When there is a lattice mismatch problem between the charge layer material and the absorption layer material, it is difficult to obtain a high-quality absorption layer by epitaxy. To this end, a transition layer is provided, which includes an N layer of In x Ga 1-x As buffer layer, in the direction from the charge layer to the absorption layer, the N layer In x Ga 1-xThe gradual increase in the In content of the As buffer layer can better eliminate the surface residue of the transition layer facing the absorption layer, which is conducive to obtaining a smoother surface of the transition layer, reducing defects such as dislocations, and at the same time, fewer dislocations are transmitted into the absorption layer, which helps to increase the generation rate of photogenerated carriers. In addition, the absolute value of the difference between the In content of the transition layer facing the absorption layer and the In content of the absorption layer is less than or equal to 0.2, so that the lattice constant of the material of the transition layer facing the absorption layer can be matched with the lattice constant of the absorption layer material as much as possible, thereby obtaining higher quality In by epitaxy. y Ga 1-y The As absorption layer helps to improve its absorption efficiency and the intensity of the absorption peak, thereby improving the photoelectric conversion efficiency and effectively improving the performance of the photodiode.

[0005] Wherein, 0<x<1, wherein N is a positive integer greater than 1, for example, N can be 2, 3, 4, 5, 6, 7, 8, 9, etc. It is understood that the specific value of N is not limited in this application, and the specific value is determined based on the total change of the In component in the transition layer and the In content of each layer. x Ga 1-x The variation of In component in As buffer layer is designed.

[0006] The photodiode in the present application has a multiplication structure layer, and when a reverse bias voltage is applied during operation, an avalanche multiplication effect can be generated. Therefore, the photodiode in the present application can be an avalanche photodiode (APD).

[0007] Exemplarily, the value of the first threshold is determined based on the material types of the absorption layer and the charge layer. For example, when the charge layer is made of GaAs, the first threshold can be set to 1.4%, and the difference in lattice constant between the charge layer material and the absorption layer material is greater than or equal to 1.4%. The difference in lattice constant between the charge layer material and the absorption layer material refers to the percentage of the absolute value of the difference between the lattice constant of the charge layer material and the lattice constant of the absorption layer material to the lattice constant of the absorption layer material.

[0008] For example, the absolute value of the difference between the In component content in the surface of the transition layer facing the absorber layer and the In component content in the absorber layer may be 0.2, 0.18, 0.16, 0.14, 0.10, 0.08, 0.05, etc. For example, the absolute value of the difference between the In component content in the surface of the transition layer facing the absorber layer and the In component content in the absorber layer is less than or equal to 0.16.

[0009] In a possible embodiment, the content of In component in the surface of the transition layer facing the charge layer is less than or equal to 0.1.

[0010] In one possible embodiment, any layer of In x Ga 1-x The content of the In component in the As buffer layer changes linearly or in steps from one end close to the charge layer toward one end of the absorption layer, so that the content of the In component in the transition layer changes linearly or in steps from one end close to the charge layer toward one end of the absorption layer, which helps to guide the threading dislocations of the transition layer to the side wall instead of extending upward, thereby reducing the dislocations transferred to the absorption layer, and thus obtaining an absorption layer with higher epitaxial quality.

[0011] It is worth mentioning that due to process limitations or other factors, some deviations or errors may exist in the actual process, resulting in the "linear gradient" described above not being completely accurate. For example, the "linear gradient" described above may be a linear gradient allowed within the allowable error range. Of course, "linear gradient" can also be understood as "basic linear gradient" or "completely linear gradient". Therefore, as long as the "linear gradient" relationship described above roughly meets the above conditions, it falls within the scope of protection of this application.

[0012] It is understandable that the meaning of the step-by-step change can be understood from the description of "linear gradient" above, which will not be repeated here.

[0013] For example, any layer In x Ga 1-x The variation of In content in the As buffer layer is linearly related to its thickness, so that each layer of In x Ga 1-x The change in the In component of the As buffer layer increases linearly with the increase in its thickness. The change in the In component of the entire transition layer changes linearly, which helps to eliminate the surface residue of the transition layer toward the absorption layer, thereby obtaining a transition layer with a smoother surface.

[0014] In one possible embodiment, any layer of In x Ga 1-x The As buffer layer has a first surface facing the charge layer and a second surface facing the absorption layer. The difference between the content of In component in the first surface and the content of In component in the second surface is less than or equal to 0.2, that is, each layer of In x Ga 1-x The variation of In component in As buffer layer is less than or equal to 0.2. It can be understood that any layer of In x Ga 1-x The smaller the change in the In component in the As buffer layer, the x Ga 1-x The change of In composition in the As buffer layer is closer to linear.

[0015] It is understandable that reducing the Inx Ga 1-x The change of In composition in the contact surface of the As buffer layer can make the change of In composition in the transition layer closer to linear. For example, the In composition of any two adjacent layers is x Ga 1-x The content of In component in the contact surface of the As buffer layer is the same.

[0016] The thickness of the transition layer is 1000 nm or less. In practice, excessively thick transition layers increase the length of the photodiode, thereby increasing carrier transit time and affecting the frequency characteristics of the photodiode. Therefore, a transition layer thickness of 1000 nm or less helps achieve a more linear change in the In composition of the transition layer without increasing carrier transit time.

[0017] In one possible embodiment, any layer of In x Ga 1-x The thickness of the As buffer layer is less than or equal to 100 nm. x Ga 1-x The thicker the As buffer layer, the greater the change in the In content. Therefore, in order to make any layer of In x Ga 1-x The change of In composition in the As buffer layer is closer to linear. x Ga 1-x The thickness of the As buffer layer does not exceed 100 nm.

[0018] It is understood that when the change in the In component of the transition layer is closer to linear, the surface of the transition layer is smoother. For example, the surface roughness of the transition layer toward the absorption layer is less than or equal to 3nm. When the transition layer is smoother, an absorption layer with higher absorption efficiency can be obtained by epitaxy. For example, the absorption peak intensity of the absorption layer is greater than or equal to 800cd / m 2 .

[0019] In one possible embodiment, the charge layer is a P-type doped GaAs layer, and the molecular formula of the material of the transition layer facing the charge layer is In 0.02 Ga 0.98 As, the molecular formula of the material of the transition layer facing the absorption layer is In 0.54 Ga 0.46 As, thus epitaxy can be used to obtain higher quality In 0.38 Ga 0.62 The As absorption layer further improves the absorption efficiency of light with a wavelength of 1310 nm and improves the performance of the photodiode.

[0020] For example, in the direction from the charge layer to the absorption layer, the transition layer includes a first buffer layer, a second buffer layer, a third buffer layer, a fourth buffer layer and a fifth buffer layer stacked in sequence; wherein the first buffer layer is In x1 Ga 1-x1 As buffer layer, x1 = 0.02-0.067, and along the direction from the charge layer to the absorption layer, x1 increases linearly or stepwise. The second buffer layer is In x2 Ga 1-x2 As buffer layer, x2 = 0.067-0.216, and along the direction from the charge layer to the absorption layer, x2 increases linearly or stepwise. The third buffer layer is In x3 Ga 1-x3 As buffer layer, x3 = 0.216-0.3, and along the direction from the charge layer to the absorption layer, x3 increases linearly or stepwise. The fourth buffer layer is In x4 Ga 1-x4 As buffer layer, x4 = 0.3-0.4, and along the direction from the charge layer to the absorption layer, x4 increases linearly or stepwise. The fifth buffer layer is In x5 Ga 1-x5 As buffer layer, x5=0.4-0.54, and along the direction from the charge layer to the absorption layer, x5 increases linearly or stepwise.

[0021] Among them, the thickness of the transition layer is 300nm, the thickness of the first buffer layer is 27nm, the thickness of the second buffer layer is 86nm, the thickness of the third buffer layer is 48nm, the thickness of the fourth buffer layer is 58nm, and the thickness of the fifth buffer layer is 81nm.

[0022] For example, in the direction from the charge layer to the absorption layer, the transition layer includes a first buffer layer, a second buffer layer, a third buffer layer, a fourth buffer layer and a fifth buffer layer stacked in sequence; wherein the first buffer layer is In x1 Ga 1-x1 As buffer layer, x1 = 0.02, the second buffer layer is In x2 Ga 1-x2 As buffer layer, x2 = 0.067, the third buffer layer is In x3 Ga 1-x3 As buffer layer, x3 = 0.216, the fourth buffer layer is In x4 Ga 1-x4 As buffer layer, x4=0.3, the fifth buffer layer is In x5 Ga 1-x5As buffer layer, x5 = 0.4. The In content in the transition layer gradually increases by gradually increasing the In content in each buffer layer. It is understood that the number of buffer layers in the transition layer and the In content in each buffer layer are not limited to the above embodiment and can be flexibly set according to specific needs to achieve a more linear change in the In content in the transition layer.

[0023] In another possible embodiment, the charge layer is a P-type doped GaAs layer, and the molecular formula of the material of the transition layer facing the charge layer is In 0.02 Ga 0.98 As, the molecular formula of the material of the transition layer facing the absorption layer is In 0.69 Ga 0.31 As, thus epitaxy can be used to obtain higher quality In 0.53 Ga 0.47 The As absorption layer further improves the absorption efficiency of light with a wavelength of 1550nm and improves the performance of the photodiode.

[0024] For example, in the direction from the charge layer to the absorption layer, the transition layer includes a first buffer layer, a second buffer layer, a third buffer layer, a fourth buffer layer, a fifth buffer layer and a sixth buffer layer stacked in sequence; wherein the first buffer layer is In x1 Ga 1-x1 As buffer layer, x1 = 0.02-0.067, and along the direction from the charge layer to the absorption layer, x1 increases linearly or stepwise. The second buffer layer is In x2 Ga 1-x2 As buffer layer, x2 = 0.067-0.216, and along the direction from the charge layer to the absorption layer, x2 increases linearly or stepwise. The third buffer layer is In x3 Ga 1-x3 As buffer layer, x3 = 0.216-0.3, and along the direction from the charge layer to the absorption layer, x3 increases linearly or stepwise. The fourth buffer layer is In x4 Ga 1-x4 As buffer layer, x4 = 0.3-0.4, and along the direction from the charge layer to the absorption layer, x4 increases linearly or stepwise. The fifth buffer layer is In x5 Ga 1-x5 As buffer layer, x5 = 0.4-0.54, and along the direction from the charge layer to the absorption layer, x5 increases linearly or stepwise. The sixth buffer layer is In x6 Ga 1-x6 As buffer layer, x6=0.54-0.69, and along the direction from the charge layer to the absorption layer, x6 increases linearly or stepwise.

[0025] Exemplarily, the thickness of the transition layer is 387 nm, the thickness of the first buffer layer is 27 nm, the thickness of the second buffer layer is 86 nm, the thickness of the third buffer layer is 48 nm, the thickness of the fourth buffer layer is 58 nm, the thickness of the fifth buffer layer is 81 nm, and the thickness of the sixth buffer layer is 87 nm.

[0026] For example, in the direction from the charge layer to the absorption layer, the transition layer includes a first buffer layer, a second buffer layer, a third buffer layer, a fourth buffer layer, a fifth buffer layer and a sixth buffer layer stacked in sequence; wherein the first buffer layer is In x1 Ga 1-x1 As buffer layer, x1 = 0.02, the second buffer layer is In x2 Ga 1-x2 As buffer layer, x2 = 0.067, the third buffer layer is In x3 Ga 1-x3 As buffer layer, x3 = 0.216, the fourth buffer layer is In x4 Ga 1-x4 As buffer layer, x4=0.3, the fifth buffer layer is In x5 Ga 1-x5 As buffer layer, x5=0.4, the sixth buffer layer is In x6 Ga 1-x6 As buffer layer, x6 = 0.54. The In content in the transition layer is gradually increased by gradually increasing the In content in each buffer layer.

[0027] It can be understood that the number of buffer layers in the transition layer, the change in the In component in each buffer layer, and the thickness of each buffer layer can be adjusted as needed, as long as the change in the In component in the transition layer presents a linear gradient or a step-like change with the change in its thickness.

[0028] In one possible embodiment, the multiplication structure layer includes multiple P-doped GaAs spacer layers and a multiplication layer disposed between any two adjacent P-doped GaAs spacer layers. The multiplication layer may be made of InAs, InAs quantum dot (QD) material, or the like. For example, when the multiplication structure layer is made of InAs, the k value of InAs is close to 0, which can significantly reduce excess noise in the device, thereby increasing the multiplication gain of the photodiode and, consequently, improving the overall performance of the photodiode.

[0029] For example, when the material of the multiplication structure layer is InAs QD, the InAs QD material has a wide band gap, which can avoid tunneling dark current; and the quantum effect of InAs QD can suppress phonon scattering, reduce kinetic energy loss, and optimize the multiplication characteristics; in addition, InAs QD can improve the spatial certainty of collision ionization and reduce the avalanche excess noise coefficient. Therefore, the spatial certainty of carrier collision ionization in the photodiode including the multiplication structure layer based on InAs QD material is improved, the excess noise is significantly reduced, and the multiplication gain is significantly improved, which can effectively avoid tunneling dark current. In addition, there is a large band gap between the InAs QD material and the GaAs matrix material, and the carriers can obtain additional kinetic energy to increase the avalanche gain. The photodiode has higher sensitivity and a larger dynamic range, which enables it to perform better in various application scenarios.

[0030] In the second aspect, the present application provides an active region structure, which includes: a multiplication structure layer, a charge layer, a transition layer and an absorption layer stacked in sequence; the absorption layer is In y Ga 1-y As layer, wherein 0.38≤y≤0.82; the difference in lattice constant between the material of the charge layer and the material of the absorption layer is greater than or equal to a first threshold; the transition layer includes an N layer In x Ga 1-x As buffer layer, where N is a positive integer greater than 1, 0<x<1, and the direction from the charge layer to the absorption layer, N layers In x Ga 1-x The content of the In component in the As buffer layer gradually increases, and the absolute value of the difference between the content of the In component in the surface of the transition layer facing the absorption layer and the content of the In component in the absorption layer is less than or equal to 0.2.

[0031] For various possible implementations and beneficial effects of the active region structure in the second aspect, please refer to the various possible implementations and corresponding beneficial effects in the first aspect, and the repeated parts will not be discussed here.

[0032] In a third aspect, the present application provides a photodiode, which comprises: an N-type InP contact layer, a multiplication structure layer, an In y Ga 1-y As charge layer, In y Ga 1-y As absorption layer and P-type contact layer, wherein 0.38≤y≤0.82; the multiplication structure layer includes multiple layers of In y Ga 1-y As spacer layer, and any two adjacent In layers y Ga 1-y As multiplication layer between the spacer layers and with Iny Ga 1-y As charge layer contacts In y Ga 1-y As spacer layer.

[0033] In the above photodiode, In y Ga 1-y The As absorption layer satisfies 0.38≤y≤0.82, which can effectively absorb long wavelength light such as 1310nm and 1550nm. In addition, by selecting an N-type InP contact layer and epitaxially growing a multiplication structure layer and an InP contact layer on the surface of the N-type InP contact layer, the As absorption layer can effectively absorb long wavelength light such as 1310nm and 1550nm. y Ga 1-y As charge layer, In y Ga 1-y As charge layer and In y Ga 1-y The lattice constant of the As absorber layer is matched to obtain high-quality In y Ga 1-y The As absorption layer helps to improve its absorption efficiency and the intensity of the absorption peak, thereby improving the photoelectric conversion efficiency and effectively improving the performance of the photodiode.

[0034] In one possible embodiment, the material of the multiplication layer may be InAs, InAs quantum dot (QD) material, etc. Exemplarily, when the material of the multiplication structure layer is InAs, the k value of InAs is close to 0, which can significantly reduce the excess noise of the device, thereby increasing the multiplication gain of the photodiode, and further improving the overall performance of the photodiode. Exemplarily, when the material of the multiplication structure layer is InAsQD, the band gap of the InAs QD material is wide, the excess noise is significantly reduced, the multiplication gain is significantly improved, tunneling dark current can be effectively avoided, and the photodiode has higher sensitivity and stability.

[0035] In a fourth aspect, the present application provides an electronic device, which includes the photodiode of the first aspect, or includes the photodiode of the third aspect.

[0036] The electronic device in this application may be an image sensor, a solar cell, an optical communication receiver, or an infrared imager. Because it includes the photodiode of the first aspect of this application, or the photodiode of the third aspect, the electronic device can effectively absorb long wavelength light waves such as 1310 nm and 1550 nm, resulting in high photoelectric conversion efficiency. The electronic device also has higher sensitivity and stability.

[0037] In a fifth aspect, the present application provides a method for preparing the photodiode of the first aspect, the method comprising the following steps:

[0038] forming an N-type contact layer;

[0039] An active region structure is formed on a surface of one side of the N-type contact layer;

[0040] forming a P-type contact layer on a surface of the active area structure away from the N-type contact layer;

[0041] Wherein, an active area structure is formed on the surface of one side of the N-type contact layer, including:

[0042] On one side of the N-type contact layer, a multiplication structure layer, a charge layer, a transition layer and an absorption layer are sequentially formed. The absorption layer is In y Ga 1-y As layer, wherein 0.38≤y≤0.82, and the difference in lattice constant between the material of the charge layer and the material of the absorption layer is greater than or equal to a first threshold;

[0043] Wherein, forming a transition layer on one surface of the charge layer comprises:

[0044] Sequentially form N layers of In x Ga 1-x As buffer layer, where N is a positive integer greater than 1, 0<x<1, and the direction from the charge layer to the absorption layer, N layers In x Ga 1-x The content of the In component in the As buffer layer gradually increases, and the absolute value of the difference between the content of the In component in the surface of the transition layer facing the absorption layer and the content of the In component in the absorption layer is less than or equal to 0.2.

[0045] Among them, the difference in lattice constants between the material of the charge layer and the material of the absorption layer is greater than or equal to a first threshold value, that is, there is a lattice mismatch problem between the material of the charge layer and the material of the absorption layer. The value of the first threshold value is determined according to the material type of the two. For example, when the material of the charge layer is GaAs material, the difference in lattice constants between the material of the charge layer and the material of the absorption layer is greater than or equal to 1.4%. When there is a lattice mismatch problem between the material of the charge layer and the material of the absorption layer, it is difficult to obtain a high-quality absorption layer. In view of this, in the preparation method of the present application, an N-type contact layer is sequentially formed on the surface of one side of the N-type contact layer. x Ga 1-x As buffer layer, where N is a positive integer greater than 1, 0<x<1, and the direction from the charge layer to the absorption layer, N layers In x Ga 1-xThe content of In component in the As buffer layer gradually increases, which can better eliminate the surface residue of the transition layer toward the absorption layer, which is conducive to obtaining a smoother surface of the transition layer, reducing defects such as dislocations, and at the same time, fewer dislocations are transmitted into the absorption layer. Moreover, the absolute value of the difference between the content of In component in the surface of the transition layer toward the absorption layer and the content of In component in the absorption layer is less than or equal to 0.2, so that the lattice constants of the material in the surface of the transition layer toward the absorption layer and the material of the absorption layer are matched as much as possible, thereby obtaining higher quality In. x Ga 1-x As absorption layer, thereby improving its absorption efficiency and the intensity of the absorption peak to obtain a high-performance photodiode.

[0046] In a sixth aspect, the present application provides a method for preparing the photodiode according to the third aspect, the method comprising the following steps:

[0047] forming an N-type InP contact layer;

[0048] On one side of the N-type InP contact layer, a multiplication structure layer, an InP layer, and a y Ga 1-y As charge layer, In y Ga 1-y As absorption layer and P-type contact layer, wherein 0.38≤y≤0.82;

[0049] Wherein, a multiplication structure layer is formed on one surface of the N-type InP contact layer, including:

[0050] A multilayer spaced InP layer is formed on one side of the N-type InP contact layer. y Ga 1-y As spacer layer and multiplication layer, and with In y Ga 1-y As charge layer contacts In y Ga 1-y As spacer layer.

[0051] The above preparation method is to prepare an N-type InP contact layer and form a multi-layer spaced InP contact layer on one side of the N-type InP contact layer. y Ga 1-y As spacer layer and multiplication layer, and in y Ga 1-y In y Ga 1-y As charge layer, because In y Ga 1-y As charge layer material and In y Ga 1-y The lattice constant of the material of the As absorption layer matches, so high-quality In yGa 1-y As absorption layer, improves its absorption efficiency, thereby improving the photoelectric conversion efficiency of the photodiode. BRIEF DESCRIPTION OF THE DRAWINGS

[0052] Figure 1 A schematic structural diagram of a photodiode in an embodiment provided in this application;

[0053] Figure 2 A schematic structural diagram of an active region structure in an embodiment provided in this application;

[0054] Figure 3 A schematic structural diagram of a transition layer in an embodiment provided in this application;

[0055] Figure 4 A schematic structural diagram of a multiplication structure layer in an embodiment provided in this application;

[0056] Figure 5 A schematic diagram of the structure and components of a photodiode in an embodiment provided in this application;

[0057] Figure 6 A schematic diagram of a transition layer including five buffer layers in an embodiment provided in the present application;

[0058] Figure 7 This is an AFM image of the transition layer in an embodiment provided in this application;

[0059] Figure 8 This is an AFM image of the transition layer in the prior art;

[0060] Figure 9 Photoluminescence curves of a transition layer in an embodiment provided in the present application and a transition layer in the prior art;

[0061] Figure 10 A schematic diagram of the structure and components of a photodiode in another embodiment provided by the present application;

[0062] Figure 11 A schematic diagram of a transition layer including six buffer layers in an embodiment provided in the present application;

[0063] Figure 12 This is a schematic structural diagram of a photodiode in another embodiment provided in the present application.

[0064] Reference numerals:

[0065] 100 - N-type contact layer; 200 - active area structure; 210 - multiplication structure layer; 211 - multiplication layer; 212 - spacer layer; 220 - charge layer; 230 - transition layer; 231 - first buffer layer; 232 - second buffer layer; 233 - third buffer layer; 234 - fourth buffer layer; 235 - fifth buffer layer; 236 - sixth buffer layer; 240 - absorption layer; 300 - P-type contact layer; 400 - substrate layer;

[0066] 01-first surface; 02-second surface. DETAILED DESCRIPTION

[0067] In order to make the purpose, technical solutions and advantages of this application clearer, this application will be further described in detail below with reference to the accompanying drawings.

[0068] The terms used in the following embodiments are only for the purpose of describing specific embodiments and are not intended to limit the present application. As used in the specification and appended claims of this application, the singular expressions "a", "an", "above", "the", and "this" are intended to also include expressions such as "one or more", unless the context clearly indicates otherwise.

[0069] References to "one embodiment" or "some embodiments" in this specification mean that a particular feature, structure, or characteristic described in conjunction with that embodiment is included in one or more embodiments of the present application. Thus, phrases such as "in one embodiment," "in some embodiments," "in other embodiments," and "in yet other embodiments" appearing in various places in this specification do not necessarily refer to the same embodiment, but rather mean "one or more but not all embodiments," unless otherwise specifically emphasized. The terms "including," "comprising," "having," and variations thereof mean "including but not limited to," unless otherwise specifically emphasized.

[0070] Among them, the photodiode of the present application may be a single-tube photodiode or an array photodiode. The photodiode can be applied to optical communications, lighting, automatic control, consumer electronics, ranging, infrared light detection (reconnaissance, early warning, guidance, imaging) and other fields. Among them, in the field of optical communications, 1310nm and 1550nm wavelengths are relatively commonly used wavelengths. In order to absorb light with wavelengths of 1310nm and 1550nm, indium gallium arsenide (InGaAs) materials are usually used to prepare the absorption layer in existing photodiodes. However, in actual applications, the absorption efficiency of InGaAs materials as absorption layers is still not high enough, resulting in low photoelectric conversion efficiency. Moreover, the absorption coefficient of InGaAs materials for long-wavelength light is large, which makes the generation rate of photogenerated carriers low, resulting in a slow response speed, which will affect the application of photodiodes in fields such as high-speed optical communications.

[0071] In order to solve the above technical problems, the embodiment of the present application provides a photodiode, Figure 1 This is a schematic diagram of the structure of a photodiode in an embodiment provided in this application. Figure 2 This is a schematic diagram of the active area structure in an embodiment of the present application, referring to Figure 1 and Figure 2 The photodiode includes an N-type contact layer 100, an active region structure 200, and a P-type contact layer 300 stacked in sequence; the active region structure 200 includes a multiplication structure layer 210, a charge layer 220, a transition layer 230, and an absorption layer 240 stacked in sequence on one side surface of the N-type contact layer 100; wherein the absorption layer 240 is In y Ga 1-y As layer, and 0.38≤y≤0.82, can effectively improve the absorption efficiency of long wavelength light waves such as 1310nm and 1550nm, thereby improving the photoelectric conversion efficiency; In addition, the difference in lattice constant between the material of the charge layer 220 and the material of the absorption layer 240 is greater than or equal to the first threshold, so that the material of the charge layer 220 and the material of the absorption layer 240 have a lattice mismatch problem, and therefore it is difficult to obtain high-quality In epitaxy. y Ga 1-y As absorption layer 240. To this end, in the present application, a transition layer 230 is provided between the charge layer 220 and the absorption layer 240. The transition layer 230 includes an N-layer In x Ga 1-x As buffer layer, along the direction from the charge layer 220 to the absorption layer 240, N layer In x Ga 1-xThe content of the In component in the As buffer layer gradually increases, which can better eliminate the surface residue of the transition layer 230 facing the absorption layer 240, which is conducive to a smoother surface and reduces defects such as dislocations. At the same time, fewer dislocations are transmitted into the absorption layer 240, reducing the impact of defects such as dislocations on the absorption layer 240, thereby improving the generation rate of photogenerated carriers. In addition, the absolute value of the difference between the content of the In component in the surface of the transition layer 230 facing the absorption layer 240 and the content of the In component in the absorption layer 240 is less than or equal to 0.2, so that the lattice constant of the material at one end of the transition layer 230 facing the absorption layer 240 can be matched with the lattice constant of the material of the absorption layer 240 as much as possible, so that higher quality In can be obtained by epitaxy. y Ga 1-y The As absorption layer 240 helps to improve its absorption efficiency and the intensity of the absorption peak, thereby improving the photoelectric conversion efficiency and further effectively improving the performance of the photodiode.

[0072] Wherein, N is a positive integer greater than 1, and 0<x<1. The value of the first threshold is determined according to the material types of the charge layer and the absorption layer. For example, when the material of the charge layer is gallium arsenide (GaAs), the first threshold can be set to 1.4%, and the difference in lattice constant between the material of the charge layer and the material of the absorption layer is greater than or equal to 1.4%.

[0073] The photodiode in the present application has a multiplication structure layer, and when a reverse bias voltage is applied during operation, it can produce an avalanche multiplication effect. Therefore, the photodiode in the present application can be an APD.

[0074] The transition layer in the prior art is usually only one In x Ga 1-x As film layer, and In x Ga 1-x The In component content in the As film layer changes linearly. In this application, the transition layer has 2 or more In layers. x Ga 1-x Compared with the existing technology, the As buffer layer can make the content of In component closer to linear gradient. Theoretically, the more buffer layers there are in the transition layer, the better the In content. x Ga 1-x The smaller the variation range of In composition in the As buffer layer, the In x Ga 1-xThe closer the change of the In component in the As buffer layer is to a linear change. It can be understood that when the change of the In component in the transition layer is closer to a linear change, the surface of the transition layer is smoother. The surface roughness of the transition layer of the photodiode facing the absorption layer in the present application is less than or equal to 3nm, and the surface roughness of the transition layer in the prior art is generally greater than or equal to 4nm. Among them, when the transition layer is smoother, an absorption layer with higher absorption efficiency and higher absorption peak intensity can be obtained by epitaxy. For example, the intensity of the absorption peak of the absorption layer in the present application is greater than or equal to 800cd / m 2 .

[0075] For example, the absolute value of the difference between the In content of the surface of the transition layer facing the absorber layer and the In content of the absorber layer can be 0.2, 0.18, 0.16, 0.14, 0.10, 0.08, 0.05, etc., where the surface of the transition layer facing the absorber layer refers to the surface of the transition layer that directly contacts the absorber layer. For example, the absolute value of the difference between the In content of the surface of the transition layer facing the absorber layer and the In content of the absorber layer is less than or equal to 0.16.

[0076] As an optional embodiment, the content of In component in the surface of the transition layer facing the charge layer is less than or equal to 0.1, wherein the surface of the transition layer facing the charge layer refers to the surface of the transition layer directly in contact with the charge layer.

[0077] As an optional embodiment, any layer of In x Ga 1-x The content of the In component in the As buffer layer changes linearly or in steps from one end close to the charge layer toward one end of the absorption layer, so that the content of the In component in the transition layer changes linearly or in steps from one end close to the charge layer toward one end of the absorption layer, which helps to guide the threading dislocations of the transition layer to the side wall instead of extending upward, thereby reducing the dislocations transferred to the absorption layer, and thus obtaining an absorption layer with a smoother surface.

[0078] The linear or step-wise change of the In component content means that the rate of increase of the In component from the end close to the charge layer to the end of the absorption layer approaches a constant value. x Ga 1-x The variation of In content in the As buffer layer is linearly related to its thickness, so that each layer of In x Ga 1-x The variation of In content in the As buffer layer increases linearly with the increase of its thickness, i.e., In x Ga 1-xThe thicker the As buffer layer, the greater the change in the In composition, so that the change in the In composition in the entire transition layer is linear, which helps to eliminate the surface residue of the transition layer toward the absorption layer, thereby obtaining a transition layer with a smoother surface.

[0079] Figure 3 This is a schematic diagram of the structure of the transition layer in an embodiment provided in this application, refer to Figure 3 , along the direction from the charge layer 220 to the absorption layer 240, the N layer In x Ga 1-x The As buffer layer is sequentially a first buffer layer 231, a second buffer layer 232, and so on. N can be 2, 3, 4, 5, 6, 7, 8, 9, etc. It is understood that the present application does not limit the specific value of N, which can be determined based on the total change in the In component of the transition layer 230 and the In content of each layer. x Ga 1-x The variation of In component in As buffer layer is designed.

[0080] In a specific embodiment, any layer of In x Ga 1-x The As buffer layer has a first surface 01 facing the charge layer 220 and a second surface 02 facing the absorption layer 240. The difference between the content of In component in the first surface 01 and the content of In component in the second surface 02 is less than or equal to 0.2, that is, each layer of In x Ga 1-x The variation of In content in the As buffer layer is less than or equal to 0.2. Figure 3 As shown, the N-1th buffer layer has a first surface 01 facing the charge layer 220 and a second surface 02 facing the absorption layer 240. The first surface 01 and the second surface 02 are arranged opposite to each other. The two surfaces of the remaining buffer layers are arranged in the same way, which will not be repeated here. It can be understood that any layer of In x Ga 1-x The smaller the change in the In component in the As buffer layer, the x Ga 1-x The change of In composition in the As buffer layer is closer to linear.

[0081] It is understandable that any two adjacent layers of In x Ga 1-x The smaller the change of In composition in the contact surface of the As buffer layer, the closer the change of In composition in the transition layer is to linearity. x Ga 1-x The content of In components in the contact surface of the As buffer layer is the same, thereby avoiding a large change in the content of In components in the transition layer.

[0082] As an optional embodiment, the thickness of the transition layer is less than or equal to 1000nm. If the thickness of the transition layer is too large, the length of the photodiode will increase, thereby increasing the transit time of the carriers and further affecting the frequency characteristics of the photodiode. x Ga 1-x The thickness of the As buffer layer is less than or equal to 100 nm. x Ga 1-x The thicker the As buffer layer, the greater the change in the In content. Therefore, in order to make any layer of In x Ga 1-x The change of In composition in the As buffer layer is closer to linear. x Ga 1-x The thickness of the As buffer layer does not exceed 100 nm.

[0083] For example, the absorption layer of the photodiode in this application is In y Ga 1-y As layer, wherein 0.38≤y≤0.82, y can be 0.38, 0.53, 0.82, etc., and is selected based on factors such as spectral response, band gap, absorption coefficient, stability, etc. For example, when the absorption layer is In 0.38 Ga 0.62 When the absorption layer is In, the operating wavelength of the photodiode is about 1310nm. 0.53 Ga 0.47 As layer, the operating wavelength of the photodiode is about 1550nm.

[0084] In a photodiode, the function of the multiplication structure layer is to amplify the photoelectric signal and improve the sensitivity of detection. By optimizing the performance parameters of the multiplication structure layer, the performance and stability of the photodiode can be further improved. Among them, the selection of the multiplication structure layer material is crucial to the performance of the photodiode. Therefore, when selecting the multiplication structure layer material, the ionization coefficient of its electrons and holes should be as small as possible compared to the k value. Currently, the most widely used multiplication structure layer materials are mainly indium phosphide (InP) and indium aluminum arsenic phosphide (InAlAs). Among them, the band gap width of InAlAs material is 1.47eV, and the k value is about 0.2, which is lower than that of InP material. Table 1 below compares the performance of avalanche photodiodes (APDs) currently using InP and InAlAs multiplication materials.

[0085] Table 1 Performance comparison of different types of APD

[0086]

[0087] Referring to Table 1, InAlAs materials, whose electron and hole ionization coefficients are lower than the k value, exhibit lower dark current and higher gain-bandwidth product when used as the material for the multiplication structure layer. Therefore, lowering the k value of the multiplication structure layer material can significantly improve APD performance. However, the electron and hole ionization coefficients of InP and InAlAs are still not high enough compared to the k value, and the location of impact ionization is highly uncertain, thus limiting improvements in APD dark current and gain.

[0088] Among other III-V materials, InAs has been shown to have a k value close to zero, making it an ideal material for the multiplication layer of an APD. However, InAs has a small bandgap of approximately 0.35 eV. The multiplication layer of a Separate Absorption, Grading, Charge, and Multiplication (SAGCM) APD requires a high external electric field, which easily generates tunneling dark current in the APD, significantly affecting device performance. Therefore, InAs-based APDs can only be constructed as a PIN structure, where the I layer serves as both the absorption layer and the multiplication layer. It is impossible to isolate the InAs material as a single multiplication layer. Electrons and holes in the I layer participate in avalanche multiplication simultaneously, significantly impacting device performance due to excess avalanche noise, and the device multiplication gain remains insufficient.

[0089] In view of this, in the photodiode of the embodiment of the present application, Figure 4 As shown, Figure 4 This is a schematic diagram of the structure of a multiplication structure layer in an embodiment provided in the present application. The multiplication structure layer 210 includes multiple P-doped GaAs spacer layers 212 and a multiplication layer 211 disposed between any two adjacent P-doped GaAs spacer layers 212. The material of the multiplication layer 211 can be InAs, InAs quantum dot (QD) material, etc. For example, when the material of the multiplication layer 211 is InAs, the k value of InAs is close to 0, which can significantly reduce the excess noise of the device, thereby increasing the multiplication gain of the photodiode, and thus improving the overall performance of the photodiode.

[0090] For example, when the multiplication layer material is InAs QD, compared with traditional materials such as InP and InAlAs, InAsQD has unique advantages as the multiplication structure layer material of APD for the following reasons: ① The k value of InAs is close to 0, which can significantly reduce the excess noise of the device. At the same time, the wide band gap of the InAs QD matrix material can avoid tunneling dark current; ② The quantum effect of QD can suppress phonon scattering, reduce kinetic energy loss, and optimize the multiplication characteristics; ③ InAs QD can improve the spatial certainty of impact ionization and reduce the avalanche excess noise coefficient. Therefore, the overall performance of APDs including multiplication structure layers made of InAs QD material is significantly improved.

[0091] In addition, the photodiode in the present application separates the multiplication structure layer and the absorption layer by setting a transition layer. Different materials can be selected for the two as needed, which can significantly reduce avalanche excess noise and improve the multiplication gain of the photodiode.

[0092] Continue to refer to Figure 1 and Figure 2 The photodiode in the present application also includes a substrate layer 400 provided on the side of the N-type contact layer 100 facing away from the active area structure 200. It is understandable that the choice of substrate has an important influence on the quality of epitaxial growth. Among them, the function of the charge layer 220 is to adjust the electric field strength of the multiplication structure layer 210 and the absorption layer 240, while separating the multiplication structure layer 210 from the absorption layer 240. Among them, the function of the N-type contact layer 100 is to achieve the conduction and collection of electrons, transport photogenerated electrons from the absorption layer 240 to the external circuit, and at the same time block the flow of holes. Therefore, the material of the N-type contact layer 100 needs to be compatible with the material of the absorption layer 240, not prone to chemical reaction or diffusion, and at the same time be able to form a good ohmic contact with the N electrode. Among them, the function of the P-type contact layer 300 is to achieve the conduction and collection of holes, transport photogenerated holes from the absorption layer 240 to the external circuit, and at the same time block the flow of electrons. Therefore, the material of the P-type contact layer 300 needs to be compatible with the material of the absorption layer 240 , not prone to chemical reaction or diffusion, and at the same time be able to form a good ohmic contact with the P electrode.

[0093] To obtain a high-quality InAs multiplication layer, a substrate material with a large lattice mismatch with the multiplication layer material, such as gallium arsenide (GaAs), should be selected to prevent InAs material clustering and resulting in uneven InAs size. The following describes the structure and composition of the photodiode in detail, using GaAs as the substrate material, InAs QDs as the multiplication layer material, and InGaAs as the absorption layer material.

[0094] Figure 5A schematic diagram of the structure and components of a photodiode in an embodiment of the present application is provided, with reference to Figure 5 When the substrate layer 400 is a GaAs substrate layer 400, the N-type contact layer 100 can be an n-type heavily doped GaAs contact layer, the multiplication structure layer 210 includes six stacked GaAs spacer layers 212 and an InAsQD multiplication layer 211 provided between any two adjacent GaAs spacer layers 212, the charge layer 220 is a P-type doped GaAs charge layer 220, and the absorption layer 240 is an In 0.38 Ga 0.62 As absorption layer 240, the P-type contact layer 300 can be p-type In 0.38 Ga 0.62 As contact layer.

[0095] For example, the molecular formula of the material of the surface of the transition layer facing the charge layer is In 0.02 Ga 0.98 As, the molecular formula of the material of the transition layer facing the absorption layer is In 0.54 Ga 0.46 As, thus epitaxy can be used to obtain higher quality In 0.38 Ga 0.62 As absorption layer, thereby extending the operating band of the photodiode to 1310nm. The number of transition layers, the variation of the In content in each buffer layer, and the thickness of each buffer layer can be flexibly set according to actual needs, as long as the variation of the In content in the transition layer is close to linear.

[0096] Figure 6 This is a schematic diagram of a transition layer including five buffer layers in an embodiment provided in this application, with reference to Figure 6 , from the charge layer 220 to the absorption layer 240, the transition layer 230 includes a first buffer layer 231, a second buffer layer 232, a third buffer layer 233, a fourth buffer layer 234 and a fifth buffer layer 235 stacked in sequence; wherein the first buffer layer 231 is In x1 Ga 1-x1 As buffer layer, x1 = 0.02-0.067, and along the direction from the charge layer 220 to the absorption layer 240, x1 increases linearly or stepwise. The second buffer layer 232 is In x2 Ga 1-x2 As buffer layer, x2 = 0.067-0.216, and along the direction from the charge layer 220 to the absorption layer 240, x2 increases linearly or stepwise. The third buffer layer 233 is In x3 Ga 1-x3As buffer layer, x3 = 0.216-0.3, and along the direction from the charge layer 220 to the absorption layer 240, x3 increases linearly or stepwise. The fourth buffer layer 234 is In x4 Ga 1-x4 As buffer layer, x4=0.3-0.4, and along the direction from the charge layer 220 to the absorption layer 240, x4 increases linearly or stepwise. The fifth buffer layer 235 is In x5 Ga 1-x5 As buffer layer, x5=0.4-0.54, and along the direction from the charge layer 220 to the absorption layer 240, x5 increases linearly or in a step-wise manner.

[0097] Among them, the thickness of the transition layer 230 may be 300nm; illustratively, the thickness of the first buffer layer 231 is 27nm, the thickness of the second buffer layer 232 is 86nm, the thickness of the third buffer layer 233 is 48nm, the thickness of the fourth buffer layer 234 is 58nm, and the thickness of the fifth buffer layer 235 is 81nm.

[0098] The existing photodiode includes a GaAs substrate layer, an N-type GaAs contact layer, a multiplication structure layer, a P-type doped GaAs charge layer, a transition layer, an In 0.38 Ga 0.62 As absorption layer, and P-type In 0.38 Ga 0.62 As contact layer, where the transition layer is only an In z Ga 1-z As film layer, z=0.2-0.5, and z increases linearly along the direction from the charge layer to the absorption layer, and the thickness of the transition layer is 300nm.

[0099] Continue to refer to Figure 5 and Figure 6 The photodiode in this application may include a GaAs substrate layer 400, an N-type GaAs contact layer, an active region structure 200, and a P-type In 0.38 Ga 0.62 As contact layer; the active area structure 200 includes: a multiplication structure layer 210, a P-type doped GaAs charge layer 220, a transition layer 230 and an In 0.38 Ga 0.62 As absorption layer 240; transition layer 230 includes a first buffer layer 231, a second buffer layer 232, a third buffer layer 233, a fourth buffer layer 234 and a fifth buffer layer 235 stacked in sequence; wherein the first buffer layer 231 is an In x1 Ga 1-x1As buffer layer, x1 = 0.02-0.067, and along the direction from the charge layer 220 to the absorption layer 240, x1 increases linearly or stepwise. The second buffer layer 232 is In with a thickness of 86 nm. x2 Ga 1-x2 As buffer layer, x2 = 0.067-0.216, and along the direction from the charge layer 220 to the absorption layer 240, x2 increases linearly or stepwise. The third buffer layer 233 is In with a thickness of 48 nm. x3 Ga 1-x3 As buffer layer, x3 = 0.216-0.3, and along the direction from the charge layer 220 to the absorption layer 240, x3 increases linearly or stepwise. The fourth buffer layer 234 is In with a thickness of 58 nm. x4 Ga 1-x4 As buffer layer, x4=0.3-0.4, and along the direction from the charge layer 220 to the absorption layer 240, x4 increases linearly or stepwise. The fifth buffer layer 235 is In with a thickness of 81 nm. x5 Ga 1-x5 As buffer layer, x5=0.4-0.54, and along the direction from the charge layer 220 to the absorption layer 240, x5 increases linearly or in a step-wise manner.

[0100] Compared with the prior art, the transition layer in the above-mentioned photodiode can make the content of the In component more close to a linear gradient. Figure 7 and Figure 8 , Figure 7 This is an AFM image of the transition layer in an embodiment provided in this application. Figure 8 is the AFM image of the transition layer in the prior art, from which it can be directly obtained Figure 7 and Figure 8 It is known that the root mean square (RMS) of the surface roughness of the transition layer of the prior art is 4.42 nm, and the RMS of the surface roughness of the transition layer in the embodiment of the present application is 2.73 nm. Therefore, the transition layer in the embodiment of the present application has a smaller surface roughness, indicating that the change in the In component in the transition layer in the embodiment of the present application is closer to a linear gradient, which is conducive to a smoother surface.

[0101] Figure 9 The photoluminescence curves of the transition layer in an embodiment of the present application and the transition layer in the prior art are shown in FIG. Figure 9, L1 represents the absorption peak of the transition layer of the prior art, L2 represents the absorption peak of the transition layer in the present application, the peak intensity of the absorption peak of the transition layer in the prior art is less than 400 a.u., the peak intensity of the absorption peak of the transition layer in the embodiment of the present application is greater than 900 a.u., therefore, the peak intensity of the absorption peak of the transition layer in the embodiment of the present application is stronger, indicating that the transition layer in the present application has fewer defects such as dislocations, and at the same time, fewer dislocations are transmitted into the absorption layer, and the In epitaxially obtained 0.38 Ga 0.62 The quality of the As absorption layer is better, which is beneficial to improving its absorption efficiency and photoelectric conversion efficiency.

[0102] As an optional embodiment, in the direction from the charge layer to the absorption layer, the transition layer includes a first buffer layer, a second buffer layer, a third buffer layer, a fourth buffer layer and a fifth buffer layer stacked in sequence; wherein the first buffer layer is In x1 Ga 1-x1 As buffer layer, x1 = 0.02, the second buffer layer is In x2 Ga 1-x2 As buffer layer, x2 = 0.067, the third buffer layer is In x3 Ga 1-x3 As buffer layer, x3 = 0.216, the fourth buffer layer is In x4 Ga 1-x4 As buffer layer, x4=0.3, the fifth buffer layer is In x5 Ga 1-x5 As buffer layer, x5 = 0.4. The In content in the transition layer gradually increases by gradually increasing the In content in each buffer layer. It is understood that the number of buffer layers in the transition layer and the In content in each buffer layer are not limited to the above embodiment and can be flexibly set according to specific needs to achieve a more linear change in the In content in the transition layer.

[0103] Figure 10 A schematic diagram of the structure and components of a photodiode in another embodiment of the present application is provided, with reference to Figure 10 When the substrate layer 400 is a GaAs substrate layer 400, the N-type contact layer 100 can be an n-type heavily doped GaAs contact layer, the multiplication structure layer 210 includes six stacked GaAs spacer layers 212 and an InAs QD multiplication layer 211 provided between any two adjacent GaAs spacer layers 212, the charge layer 220 is a P-type doped GaAs charge layer 220, and the absorption layer 240 is an In 0.53 Ga 0.47 As absorption layer 240, the P-type contact layer 300 can be p-type In 0.53 Ga 0.47 As contact layer.

[0104] For example, the molecular formula of the material of the surface of the transition layer 230 facing the charge layer 220 is In 0.02 Ga 0.98 As, the molecular formula of the material of the surface of the transition layer 230 facing the absorption layer 240 is In 0.69 Ga 0.31 As, thus epitaxy can be used to obtain higher quality In 0.53 Ga 0.47 As absorption layer 240, thereby extending the operating band of the photodiode to 1550nm. It is understood that the number of buffer layers in the transition layer 230, the variation in the In content of each buffer layer, and the thickness of each buffer layer can be adjusted as needed, as long as the variation in the In content of the transition layer 230 exhibits a linear gradient or a step-like variation with the thickness of the transition layer 230.

[0105] For example, Figure 11 A schematic diagram of a transition layer including six buffer layers in an embodiment provided in this application, referring to Figure 11 , from the charge layer 220 to the absorption layer 240, the transition layer 230 includes a first buffer layer 231, a second buffer layer 232, a third buffer layer 233, a fourth buffer layer 234, a fifth buffer layer 235 and a sixth buffer layer 236 stacked in sequence; wherein the first buffer layer 231 is In x1 Ga 1-x1 As buffer layer, x1 = 0.02-0.067, and along the direction from the charge layer 220 to the absorption layer 240, x1 increases linearly or stepwise. The second buffer layer 232 is In x2 Ga 1- x2 As buffer layer, x2 = 0.067-0.216, and along the direction from the charge layer 220 to the absorption layer 240, x2 increases linearly or stepwise. The third buffer layer 233 is In x3 Ga 1-x3 As buffer layer, x3 = 0.216-0.3, and along the direction from the charge layer 220 to the absorption layer 240, x3 increases linearly or stepwise. The fourth buffer layer 234 is In x4 Ga 1-x4 As buffer layer, x4=0.3-0.4, and along the direction from the charge layer 220 to the absorption layer 240, x4 increases linearly or stepwise. The fifth buffer layer 235 is In x5 Ga 1-x5 As buffer layer, x5=0.4-0.54, and along the direction from the charge layer 220 to the absorption layer 240, x5 increases linearly or stepwise. The sixth buffer layer 236 is Inx6 Ga 1-x6 As buffer layer, x6=0.54-0.69, and along the direction from the charge layer 220 to the absorption layer 240, x6 increases linearly or in a step-like manner.

[0106] Exemplarily, the thickness of the transition layer 230 is 387 nm; exemplary, the thickness of the first buffer layer 231 is 27 nm, the thickness of the second buffer layer 232 is 86 nm, the thickness of the third buffer layer 233 is 48 nm, the thickness of the fourth buffer layer 234 is 58 nm, the thickness of the fifth buffer layer 235 is 81 nm, and the thickness of the sixth buffer layer 236 is 87 nm.

[0107] Specifically, refer to Figure 10 and Figure 11 , Figure 10 A schematic diagram of the structure and components of a photodiode in another embodiment provided in this application, Figure 11 Schematic diagram of a transition layer including six buffer layers in an embodiment provided by the present application. The photodiode includes a GaAs substrate layer 400, an N-type heavily doped GaAs contact layer, an active region structure 200, and a P-type In 0.53 Ga 0.47 As contact layer; the active area structure 200 includes a multiplication structure layer 210, a P-type doped GaAs charge layer 220, a transition layer 230 and an In 0.53 Ga 0.47 As absorption layer 240; transition layer 230 includes a first buffer layer 231, a second buffer layer 232, a third buffer layer 233, a fourth buffer layer 234, a fifth buffer layer 235 and a sixth buffer layer 236 stacked in sequence; wherein the first buffer layer 231 is an In x1 Ga 1-x1 As buffer layer, x1 = 0.02-0.067, and along the direction from the charge layer 220 to the absorption layer 240, x1 increases linearly or stepwise. The second buffer layer 232 is In with a thickness of 86 nm. x2 Ga 1-x2 As buffer layer, x2 = 0.067-0.216, and along the direction from the charge layer 220 to the absorption layer 240, x2 increases linearly or stepwise. The third buffer layer 233 is In with a thickness of 48 nm. x3 Ga 1-x3 As buffer layer, x3 = 0.216-0.3, and along the direction from the charge layer 220 to the absorption layer 240, x3 increases linearly or stepwise. The fourth buffer layer 234 is In with a thickness of 58 nm. x4 Ga1- x4 As buffer layer, x4=0.3-0.4, and along the direction from the charge layer 220 to the absorption layer 240, x4 increases linearly or stepwise. The fifth buffer layer 235 is In with a thickness of 81 nm. x5 Ga 1-x5 As buffer layer, x5 = 0.4-0.54, and along the direction from the charge layer 220 to the absorption layer 240, x5 increases linearly or stepwise. The sixth buffer layer 236 is In with a thickness of 87 nm. x6 Ga 1-x6 As buffer layer, x6=0.54-0.69, and along the direction from the charge layer 220 to the absorption layer 240, x6 increases linearly or in a step-like manner.

[0108] As an optional embodiment, in the direction from the charge layer to the absorption layer, the transition layer includes a first buffer layer, a second buffer layer, a third buffer layer, a fourth buffer layer, a fifth buffer layer and a sixth buffer layer stacked in sequence; wherein the first buffer layer is In x1 Ga 1-x1 As buffer layer, x1 = 0.02, the second buffer layer is In x2 Ga 1-x2 As buffer layer, x2 = 0.067, the third buffer layer is In x3 Ga 1-x3 As buffer layer, x3 = 0.216, the fourth buffer layer is In x4 Ga 1- x4 As buffer layer, x4=0.3, the fifth buffer layer is In x5 Ga 1-x5 As buffer layer, x5=0.4, the sixth buffer layer is In x6 Ga 1-x6 As buffer layer, x6 = 0.54. The In content in the transition layer gradually increases by gradually increasing the In content in each buffer layer. It is understood that the number of buffer layers in the transition layer and the In content in each buffer layer are not limited to the above embodiment and can be flexibly set according to specific needs to achieve a more linear change in the In content in the transition layer.

[0109] Based on the same technical concept, an active region structure is also provided in the embodiment of the present application. The active region structure includes an InAs multiplication structure layer, a charge layer, a transition layer and an absorption layer stacked in sequence; the absorption layer is InAs. y Ga 1-yAs layer, wherein 0.38≤y≤0.82; the difference in lattice constant between the material of the charge layer and the material of the absorption layer is greater than or equal to a first threshold; the transition layer includes an N layer In x Ga 1-x As buffer layer, where N is a positive integer greater than 1, 0<x<1, and the direction from the charge layer to the absorption layer, N layers In x Ga 1-x The content of the In component in the As buffer layer gradually increases, and the absolute value of the difference between the content of the In component in the surface of the transition layer facing the absorption layer and the content of the In component in the absorption layer is less than or equal to 0.2.

[0110] The value of the first threshold is determined according to the material types of the two layers. The difference in lattice constant between the charge layer material and the absorption layer material is greater than or equal to the first threshold, that is, there is a lattice mismatch between the charge layer material and the absorption layer material, making it difficult to obtain a high-quality absorption layer by epitaxy. In order to solve the above problem, in the active region structure of the present application, a transition layer is provided between the charge layer and the absorption layer. The transition layer includes an N-layer In x Ga 1-x As buffer layer, and along the direction of the charge layer pointing to the absorption layer, N layer In x Ga 1-x The content of the In component in the As buffer layer gradually increases, which can better eliminate the surface residue of the transition layer toward the absorption layer, which is conducive to obtaining a smoother surface of the transition layer, reducing defects such as dislocations, and at the same time, fewer dislocations are transmitted into the absorption layer, so that the quality of the absorption layer obtained by epitaxy is higher, and there are fewer defects such as dislocations, which helps to increase the generation rate of photogenerated carriers. In addition, the absolute value of the difference between the content of the In component in the surface of the transition layer facing the absorption layer and the content of the In component in the absorption layer is less than or equal to 0.2, so that the lattice constants of the material of the end of the transition layer facing the absorption layer and the material of the absorption layer are matched as much as possible, thereby obtaining an In component with higher epitaxial quality. y Ga 1-y The As absorption layer has a value of 0.38≤y≤0.82, thereby improving the absorption of light waves with long wavelengths such as 1310nm and 1550nm, and improving the overall performance of the active region structure.

[0111] Figure 12 This is a schematic diagram of the structure of a photodiode in another embodiment provided in this application, referring to Figure 12 In the embodiment of the present application, another photodiode is provided. The photodiode comprises: an N-type InP substrate layer 400, an N-type InP contact layer 100, a multiplication structure layer 210, an In y Ga 1-y As charge layer 220, In y Ga 1-yAs absorption layer 240 and P-type contact layer 300, wherein 0.38≤y≤0.82; multiplication structure layer 210 includes multiple layers of In y Ga 1-y As spacer layer 212, and any two adjacent In y Ga 1-y The multiplication layer 211 between the As spacer layer 212 and the In y Ga 1-y As charge layer 220 contacts In y Ga 1-y As spacer layer 212 .

[0112] In the above-mentioned photodiode, indium phosphide (InP) is selected as the substrate layer 400 material to match the lattice of the absorption layer 240 material, thereby reducing the lattice mismatch and stress accumulation during the epitaxial growth process, and high-quality InP can be obtained by epitaxy. y Ga 1-y The As absorption layer 240, with 0.38≤y≤0.82, can effectively achieve the absorption efficiency of long wavelength light such as 1310nm and 1550nm, improve the photoelectric conversion efficiency, and thus effectively improve the performance of the photodiode.

[0113] In one possible embodiment, the material of the multiplication layer may be InAs, InAs quantum dot (QD) material, etc. Among them, when InAs material is used as the multiplication layer material, the k value of InAs material is close to 0, which can reduce the excess noise of the device, thereby improving the multiplication gain of the photodiode, and further improving the overall performance of the photodiode. Among them, when InAs QD is used as the multiplication layer material, its band gap is wide, which can avoid tunneling dark current, can improve the spatial certainty of collision ionization, and reduce the avalanche excess noise coefficient; and the quantum effect of QD can suppress phonon scattering, reduce kinetic energy loss, optimize the multiplication characteristics, thereby improving the sensitivity and stability of the photodiode.

[0114] Among them, 0.38≤y≤0.82, y can be 0.38, 0.53, 0.82, etc. It can be understood that the specific value of y is selected according to factors such as spectral response, band gap width, absorption coefficient, stability, etc.

[0115] For example, when the charge layer is In 0.38 Ga 0.62 As charge layer, high-quality In 0.38 Ga 0.62 As absorption layer can efficiently absorb light waves with a wavelength of 1310nm, thus improving the photoelectric conversion efficiency of the photodiode in the 1310nm working band; when the charge layer is In 0.53Ga 0.47 As charge layer, high-quality In 0.53 Ga 0.47 The As absorption layer can efficiently absorb light waves with a wavelength of 1550nm, thereby improving the photoelectric conversion efficiency of the photodiode in the 1550nm working band.

[0116] The present application also provides an electronic device, which includes the photodiode in various possible embodiments of the present application. The electronic device in the present application may be an image sensor, a solar cell, an optical communication receiver, or an infrared imager. Because it includes the photodiode in various possible embodiments of the present application, the electronic device has high-quality In y Ga 1-y The As absorption layer can achieve efficient absorption of light waves with long wavelengths such as 1310nm and 1550nm, has high photoelectric conversion efficiency and photogenerated carrier generation rate, and the electronic device has high sensitivity and stability.

[0117] The structures of the photodiode and the electronic device including the photodiode in this application are described in detail above. The method for preparing the photodiode will be described below.

[0118] The present invention also provides a method for preparing a photodiode, which comprises the following steps:

[0119] forming an N-type contact layer;

[0120] An active region structure is formed on a surface of one side of the N-type contact layer;

[0121] forming a P-type contact layer on a surface of the active area structure away from the N-type contact layer;

[0122] Wherein, an active area structure is formed on the surface of one side of the N-type contact layer, including:

[0123] On one side of the N-type contact layer, a multiplication structure layer, a charge layer, a transition layer and an absorption layer are sequentially formed. The absorption layer is In y Ga 1-y As layer, wherein 0.38≤y≤0.82; and the difference in lattice constant between the material of the charge layer and the material of the absorption layer is greater than or equal to a first threshold;

[0124] Wherein, forming a transition layer by epitaxial growth on one side of the charge layer comprises:

[0125] Sequentially form N layers of In x Ga 1-x As buffer layer, where N is a positive integer greater than 1, 0<x<1, and the direction from the charge layer to the absorption layer, N layers In x Ga1-x The content of the In component in the As buffer layer gradually increases, and the absolute value of the difference between the content of the In component in the surface of the transition layer facing the absorption layer and the content of the In component in the absorption layer is less than or equal to 0.2.

[0126] The above preparation method forms an N layer In between the charge layer and the absorption layer. x Ga 1-x As buffer layer transition layer, where N is a positive integer greater than 1, 0<x<1, from the charge layer to the absorption layer, N layers In x Ga 1-x The content of In in the As buffer layer gradually increases, and the absolute value of the difference between the content of In in the surface of the transition layer facing the absorption layer and the content of In in the absorption layer is less than or equal to 0.2, so that the lattice constant of the material in the surface of the transition layer facing the absorption layer and the material of the absorption layer are matched as much as possible, thereby obtaining higher quality In. y Ga 1-y As absorption layer is used to improve the absorption efficiency, increase the generation rate of photogenerated carriers and the intensity of the absorption peak, thereby obtaining a high-performance photodiode.

[0127] The thin film layers in the above-mentioned preparation method may be formed by molecular beam epitaxy, chemical vapor deposition, or physical vapor deposition.

[0128] As an optional embodiment, a method for preparing the transition layer includes the following steps:

[0129] Determine the total change B of the In component of the transition layer based on the y value, B = y ± 0.2;

[0130] Determine the preset thickness H of the transition layer and In x Ga 1-x The number of As buffer layers N is used to calculate the preset change b of the In component of the nth buffer layer. n , preset thickness h n and the preset growth rate v n , where 1≤n≤N, and n is a positive integer, b n =B / N,h n =b n / B×H,v n =b n / h n ;

[0131] According to the v of the nth buffer layer n and b n growing the nth buffer layer;

[0132] Adjust the preset change amount b of the In composition of the n+1th buffer layer according to the actual thickness of the nth buffer layer and the actual change amount of the In composition. n+1 , preset thickness h n+1 and the preset growth rate v n+1 , and according to the adjusted v n+1 and b n+1 Grow the n+1th buffer layer.

[0133] For example, a method for preparing a photodiode in an optional embodiment of the present application includes the following steps:

[0134] S1: forming a GaAs substrate layer;

[0135] S2: Form a 400nm thick n-type heavily doped 4×10 18 cm -3 GaAs contact layer;

[0136] S3: A multiplication structure layer is formed by epitaxial growth on the surface of the GaAs contact layer facing away from the GaAs substrate layer, wherein the multiplication structure layer includes 6 layers of P-doped GaAs spacer layers and an undoped InAs quantum dot layer disposed between any two adjacent P-doped GaAs spacer layers, and the QD deposition amount in each InAs quantum dot layer is 2.25 MLs, the thickness of the P-doped GaAs spacer layer is 50 nm, and the doping concentration is 8×10 15 cm -3 , the total thickness of the 6-layer P-doped GaAs spacer layer is 300nm;

[0137] S4: A P-type doped GaAs charge layer is formed on the surface of the multiplication structure layer away from the GaAs substrate layer. The thickness of the layer is 70 nm and the doping concentration is 6×10 17 cm -3 ;

[0138] S5: In layers with a thickness of 27 nm are sequentially grown on the surface of the charge layer facing away from the multiplication structure layer. x1 Ga 1-x1 As buffer layer (x1 = 0.02-0.067, and along the direction from the charge layer to the absorption layer, x1 increases linearly or stepwise), In with a thickness of 86nm x2 Ga 1-x2 As buffer layer (x2 = 0.067-0.216, and along the direction from the charge layer to the absorption layer, x2 increases linearly or stepwise), In with a thickness of 48nm x3 Ga 1-x3As buffer layer (x3 = 0.216-0.3, and along the direction from the charge layer to the absorption layer, x3 increases linearly or stepwise), In with a thickness of 58nm x4 Ga 1-x4 As buffer layer (x4 = 0.3-0.4, and along the direction from the charge layer to the absorption layer, x4 increases linearly or stepwise), and In with a thickness of 81nm x5 Ga 1-x5 As buffer layer (x5 = 0.4-0.54, and x5 increases linearly or stepwise along the direction from the charge layer to the absorption layer); and each layer is P-type doped with a doping concentration of 8×10 15 cm -3 ;

[0139] S6: In x5 Ga 1-x5 The As buffer layer is epitaxially doped with In on the side away from the multiplication structure layer. 0.38 Ga 0.62 As absorption layer, thickness 1300nm, doping concentration 8×10 15 cm -3 ;

[0140] S7: In 0.38 Ga 0.62 The surface of the As absorption layer away from the multiplication structure layer is epitaxially doped with P-type heavily doped (P+) In 0.38 Ga 0.62 As contact layer, thickness 100nm, doping concentration 6×10 18 cm -3 .

[0141] For example, in another optional embodiment of the present application, a method for preparing a photodiode includes the following steps:

[0142] S1: forming a GaAs substrate layer;

[0143] S2: Form a 400nm thick n-type heavily doped 4×10 18 cm -3 GaAs contact layer;

[0144] S3: A multiplication structure layer is formed by epitaxial growth on the surface of the GaAs contact layer facing away from the GaAs substrate layer, wherein the multiplication structure layer includes 6 layers of P-doped GaAs spacer layers and an undoped InAs quantum dot layer disposed between any two adjacent P-doped GaAs spacer layers, and the QD deposition amount in each InAs quantum dot layer is 2.25 MLs, the thickness of the P-doped GaAs spacer layer is 50 nm, and the doping concentration is 8×10 15 cm-3 , the total thickness of the 6-layer P-doped GaAs spacer layer is 300nm;

[0145] S4: A P-type doped GaAs charge layer is formed on the surface of the multiplication structure layer away from the GaAs substrate layer. The thickness of the layer is 70 nm and the doping concentration is 6×10 17 cm -3 ;

[0146] S5: On the surface of the charge layer away from the multiplication structure layer, the first buffer layer, the second buffer layer, the third buffer layer, the fourth buffer layer, the fifth buffer layer and the sixth buffer layer are sequentially epitaxially grown. The first buffer layer is an In layer with a thickness of 27 nm. x1 Ga 1-x1 As buffer layer, x1 = 0.02-0.067, and along the direction from the charge layer to the absorption layer, x1 increases linearly or stepwise. The second buffer layer is In with a thickness of 86nm. x2 Ga 1-x2 As buffer layer, x2 = 0.067-0.216, and along the direction from the charge layer to the absorption layer, x2 increases linearly or stepwise. The third buffer layer is In with a thickness of 48nm. x3 Ga 1-x3 As buffer layer, x3 = 0.216-0.3, and along the direction from the charge layer to the absorption layer, x3 increases linearly or stepwise. The fourth buffer layer is In with a thickness of 58nm. x4 Ga 1-x4 As buffer layer, x4 = 0.3-0.4, and along the direction from the charge layer to the absorption layer, x4 increases linearly or stepwise. The fifth buffer layer is In with a thickness of 81nm. x5 Ga 1- x5 As buffer layer, x5 = 0.4-0.54, and along the direction from the charge layer to the absorption layer, x5 increases linearly or stepwise. The sixth buffer layer is In with a thickness of 87nm. x6 Ga 1-x6 As buffer layer, x6 = 0.54-0.69, and along the direction from the charge layer to the absorption layer, x6 increases linearly or stepwise; and each layer is P-type doped with a doping concentration of 8×10 15 cm -3 ;

[0147] S6: In 0.54-0.69 Ga 0.46-0.31 The As buffer layer is epitaxially doped with In on the side away from the multiplication structure layer. 0.53 Ga 0.47 As absorption layer, thickness 1300nm, doping concentration 8×1015 cm -3 ;

[0148] S7: In 0.53 Ga 0.47 The surface of the As absorption layer away from the multiplication structure layer is epitaxially doped with P-type heavily doped (P+) In 0.53 Ga 0.47 As contact layer, thickness 100nm, doping concentration 6×10 18 cm -3 .

[0149] As another optional embodiment, another method for preparing a photodiode is provided in the embodiments of the present application. The method comprises the following steps:

[0150] forming an N-type InP contact layer;

[0151] On one side of the N-type InP contact layer, a multiplication structure layer, an InP layer, and a y Ga 1-y As charge layer, In y Ga 1-y As absorption layer and P-type contact layer, wherein N is a positive integer greater than 1, 0.38≤y≤0.82;

[0152] Wherein, a multiplication structure layer is formed on one surface of the N-type InP contact layer, including:

[0153] A multilayer spaced InP layer is formed on one side of the N-type InP contact layer. y Ga 1-y As spacer layer and multiplication layer, and with In y Ga 1-y As charge layer contacts In y Ga 1-y As spacer layer.

[0154] The above preparation method forms an N-type InP contact layer and forms a multi-layer spaced InP contact layer on one side of the N-type InP contact layer. y Ga 1-y As spacer layer and multiplication layer, and in y Ga 1-y In y Ga 1-y As charge layer, thus obtaining high-quality In y Ga 1-y The As absorption layer, 0.38≤y≤0.82, can effectively achieve the absorption efficiency of light waves with long wavelengths such as 1310nm and 1550nm, improve the photoelectric conversion efficiency, and thus effectively improve the performance of the photodiode.

[0155] The thin film layers in the above-mentioned preparation method may be formed by molecular beam epitaxy, chemical vapor deposition, or physical vapor deposition.

[0156] As an optional embodiment, the material of the multiplication layer may be InAs, InAs quantum dot (QD) material, etc. Among them, when InAs material is used as the multiplication layer material, the k value of InAs material is close to 0, which can reduce the excess noise of the device, thereby improving the multiplication gain of the photodiode, and further improving the overall performance of the photodiode. Among them, when InAsQD is used as the multiplication layer material, its band gap is wide, which can avoid tunneling dark current, improve the spatial certainty of collision ionization, and reduce the avalanche excess noise coefficient; and the quantum effect of QD can suppress phonon scattering, reduce kinetic energy loss, optimize the multiplication characteristics, thereby improving the sensitivity and stability of the photodiode.

[0157] Obviously, those skilled in the art may make various changes and modifications to the present application without departing from the scope of the present application. Thus, if these modifications and variations of the present application fall within the scope of the claims of the present application and their equivalents, the present application is intended to include these modifications and variations.

Claims

1. A photodiode, characterized in that: include: An N-type contact layer, an active area structure, and a P-type contact layer are stacked in sequence; The active region structure includes: a multiplication structure layer, a charge layer, a transition layer and an absorption layer stacked in sequence on one side surface of the N-type contact layer; The absorption layer is In y Ga 1-y As layer, where 0.38≤y≤0.82; The difference in lattice constant between the material of the charge layer and the material of the absorption layer is greater than or equal to a first threshold; The transition layer includes N layers of In x Ga 1-x As buffer layer, wherein N is a positive integer greater than 1, 0<x<1, along the direction from the charge layer to the absorption layer, the N layer In x Ga 1-x The content of the In component in the As buffer layer gradually increases, and the absolute value of the difference between the content of the In component in the surface of the transition layer facing the absorption layer and the content of the In component in the absorption layer is less than or equal to 0.

2.

2. The photodiode according to claim 1, wherein Any layer of In x Ga 1-x The content of the In component in the As buffer layer changes linearly or stepwise from one end close to the charge layer toward one end of the absorption layer.

3. The photodiode according to claim 2, wherein Any layer of In x Ga 1-x The variation of In content in the As buffer layer is linearly related to its thickness.

4. The photodiode according to any one of claims 1 to 3, wherein: Any layer of In x Ga 1-x The As buffer layer has a first surface facing the charge layer and a second surface facing the absorption layer, and a difference between an In component content in the first surface and an In component content in the second surface is less than or equal to 0.

2.

5. The photodiode according to claim 4, wherein Any two adjacent layers of In x Ga 1-x The content of In component in the contact surface of As buffer layer is the same.

6. The photodiode according to any one of claims 1 to 5, wherein: The absolute value of the difference between the In component content in the surface of the transition layer facing the absorption layer and the In component content in the absorption layer is less than or equal to 0.16; Alternatively, the content of In component in the surface of the transition layer facing the charge layer is less than or equal to 0.

1.

7. The photodiode according to any one of claims 1 to 6, wherein: The thickness of the transition layer is less than or equal to 1000 nm; Or, any layer of In x Ga 1-x The thickness of the As buffer layer is less than or equal to 100 nm.

8. The photodiode according to any one of claims 1 to 7, wherein: The surface roughness of the transition layer toward the absorption layer is less than or equal to 3 nm; Or, the absorption peak intensity of the absorption layer is greater than or equal to 800 cd / m 2 .

9. The photodiode according to any one of claims 1 to 8, wherein: The charge layer is a P-type doped GaAs layer, and the molecular formula of the material of the transition layer facing the charge layer is In 0.02 Ga 0.98 As, the molecular formula of the material of the surface of the transition layer facing the absorption layer is In 0.54 Ga 0.46 As, the absorption layer is In 0.38 Ga 0.62 As layer.

10. The photodiode according to claim 9, wherein From the direction of the charge layer to the absorption layer, the transition layer includes a first buffer layer, a second buffer layer, a third buffer layer, a fourth buffer layer and a fifth buffer layer stacked in sequence; Wherein, the first buffer layer is In x1 Ga 1-x1 As buffer layer, x1=0.02-0.067, and x1 increases linearly or stepwise along the direction from the charge layer to the absorption layer; The second buffer layer is In x2 Ga 1-x2 As buffer layer, x2=0.067-0.216, and x2 increases linearly or stepwise along the direction from the charge layer to the absorption layer; The third buffer layer is In x3 Ga 1-x3 As buffer layer, x3=0.216-0.3, and x3 increases linearly or stepwise along the direction from the charge layer to the absorption layer; The fourth buffer layer is In x4 Ga 1-x4 As buffer layer, x4=0.3-0.4, and x4 increases linearly or stepwise along the direction from the charge layer to the absorption layer; The fifth buffer layer is In x5 Ga 1-x5 As buffer layer, x5=0.4-0.54, and along the direction from the charge layer to the absorption layer, x5 increases linearly or in a step-like manner.

11. The photodiode according to claim 10, wherein The thickness of the transition layer is 300 nm, the thickness of the first buffer layer is 27 nm, the thickness of the second buffer layer is 86 nm, the thickness of the third buffer layer is 48 nm, the thickness of the fourth buffer layer is 58 nm, and the thickness of the fifth buffer layer is 81 nm.

12. The photodiode according to any one of claims 1 to 8, wherein: The charge layer is a P-type doped GaAs layer, and the molecular formula of the material of the transition layer facing the charge layer is In 0.02 Ga 0.98 As, the molecular formula of the material of the surface of the transition layer facing the absorption layer is In 0.69 Ga 0.31 As, the absorption layer is In 0.53 Ga 0.47 As layer.

13. The photodiode according to claim 12, wherein From the direction of the charge layer to the absorption layer, the transition layer includes a first buffer layer, a second buffer layer, a third buffer layer, a fourth buffer layer, a fifth buffer layer and a sixth buffer layer stacked in sequence; Wherein, the first buffer layer is In x1 Ga 1-x1 As buffer layer, x1=0.02-0.067, and x1 increases linearly or stepwise along the direction from the charge layer to the absorption layer; The second buffer layer is In x2 Ga 1-x2 As buffer layer, x2=0.067-0.216, and x2 increases linearly or stepwise along the direction from the charge layer to the absorption layer; The third buffer layer is In x3 Ga 1-x3 As buffer layer, x3=0.216-0.3, and x3 increases linearly or stepwise along the direction from the charge layer to the absorption layer; The fourth buffer layer is In x4 Ga 1-x4 As buffer layer, x4=0.3-0.4, and x4 increases linearly or stepwise along the direction from the charge layer to the absorption layer; The fifth buffer layer is In x5 Ga 1-x5 As buffer layer, x5=0.4-0.54, and x5 increases linearly or stepwise along the direction from the charge layer to the absorption layer; The sixth buffer layer is In x6 Ga 1-x6 As buffer layer, x6=0.54-0.69, and along the direction from the charge layer to the absorption layer, x6 increases linearly or in a step-like manner.

14. The photodiode according to claim 13, wherein The thickness of the transition layer is 387nm, the thickness of the first buffer layer is 27nm, the thickness of the second buffer layer is 86nm, the thickness of the third buffer layer is 48nm, the thickness of the fourth buffer layer is 58nm, the thickness of the fifth buffer layer is 81nm, and the thickness of the sixth buffer layer is 87nm.

15. The photodiode according to any one of claims 1 to 14, wherein: The multiplication structure layer includes a plurality of P-doped GaAs spacer layers and a multiplication layer arranged between any two adjacent P-doped GaAs spacer layers.

16. The photodiode according to claim 15, wherein The material of the multiplication layer is InAs or InAsQD.

17. An active region structure, characterized in that: include: A multiplication structure layer, a charge layer, a transition layer, and an absorption layer are stacked in sequence; The difference in lattice constant between the material of the charge layer and the material of the absorption layer is greater than or equal to a first threshold; The absorption layer is In y Ga 1-y As layer, where 0.38≤y≤0.82; The transition layer includes N layers of In x Ga 1-x As buffer layer, wherein N is a positive integer greater than 1, 0<x<1, from the direction of the charge layer to the absorption layer, the N layer In x Ga 1-x The content of the In component in the As buffer layer gradually increases, and the absolute value of the difference between the content of the In component in the surface of the transition layer facing the absorption layer and the content of the In component in the absorption layer is less than or equal to 0.

2.

18. A photodiode, characterized in that: include: The N-type InP contact layer, the multiplication structure layer, and the InP layer are stacked in sequence. y Ga 1-y As charge layer, In y Ga 1-y As absorption layer and P-type contact layer, wherein 0.38≤y≤0.82; The multiplication structure layer includes multiple layers of In y Ga 1-y As spacer layer, and the In y Ga 1-y As spacer layers between the multiplication layers, and with the In y Ga 1-y As charge layer contacts the In y Ga 1-y As spacer layer.

19. The photodiode according to claim 18, wherein The material of the multiplication layer is InAs or InAsQD.

20. An electronic device, characterized in that: The photodiode comprises the photodiode according to any one of claims 1 to 16, or the photodiode according to claim 18 or 19.

21. A method for preparing a photodiode according to any one of claims 1 to 16, characterized in that: The steps include: forming an N-type contact layer; forming an active region structure on a surface of one side of the N-type contact layer; forming a P-type contact layer on a surface of the active area structure away from the N-type contact layer; Wherein, an active area structure is formed on one surface of the N-type contact layer, comprising: A multiplication structure layer, a charge layer, a transition layer and an absorption layer are sequentially formed on one side of the N-type contact layer. The absorption layer is In y Ga 1-y As layer, wherein 0.38≤y≤0.82, and the difference in lattice constant between the material of the charge layer and the material of the absorption layer is greater than or equal to a first threshold; Wherein, forming a transition layer on one side surface of the charge layer comprises: Sequentially form N layers of In x Ga 1-x As buffer layer, wherein N is a positive integer greater than 1, 0<x<1, from the direction of the charge layer to the absorption layer, the N layer In x Ga 1-x The content of the In component in the As buffer layer gradually increases, and the absolute value of the difference between the content of the In component in the surface of the transition layer facing the absorption layer and the content of the In component in the absorption layer is less than or equal to 0.

2.

22. A method for preparing a photodiode according to claim 18 or 19, characterized in that: The steps include: forming an N-type InP contact layer; On one side of the N-type InP contact layer, a multiplication structure layer, an InP contact layer, and a second InP contact layer are sequentially formed. y Ga 1-y As charge layer, In y Ga 1-y As absorption layer and P-type contact layer, wherein 0.38≤y≤0.82; Wherein, a multiplication structure layer is formed on one surface of the N-type InP contact layer, comprising: A plurality of In layers spaced apart are formed on one side of the N-type InP contact layer. y Ga 1-y As spacer layer and multiplication layer, and with the In y Ga 1-y As charge layer contacts the In y Ga 1-y As spacer layer.

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