A method for manufacturing a semiconductor device

Abstract

The application belongs to the field of photoelectric detection, and specifically discloses a kind of cascade avalanche photodiode and preparation method thereof, by the application, the APD from bottom to top includes substrate, buffer layer, cascade multiplication zone, first energy band gradient layer, light absorption layer, second energy band gradient layer and window layer in turn.Light absorption layer adopts InGaAs material, cascade multiplication structure adopts InAlGaAs material, and each layer realizes lattice matching.Cascade multiplication structure includes N multiplication units and N-1 first charge layers;N-1 first charge layers are arranged between N multiplication units;N is greater than 2.The electric field distribution of the cascade multiplication structure proposed in the application decreases in a ladder shape, the effective width of the multiplication zone has extensibility, which can reduce the "average" electric field of the multiplication layer, increase the gain, reduce the APD breakdown voltage, and reduce the dark current.The APD provided by the application is suitable for high-sensitivity detection scenarios such as high-speed optical communication, laser radar, optical time domain reflectometer, biomedical imaging, etc.

Description

Technical Field

[0001] This application belongs to the field of photoelectric detection, and more specifically, relates to a cascaded avalanche photodiode (APD) and its fabrication method. Background Technology

[0002] An APD (Automatic Photodetector) is a highly sensitive photodetector with an internal photomultiplication effect. It converts weak light signals into detectable electrical signals through an avalanche multiplication process under reverse bias. Indium gallium arsenide (InGaAs) material, due to its moderate bandgap, can effectively respond to short-wavelength infrared light in the range of 950 nm to 1700 nm, making it a core material in the field of short-wavelength infrared detection. Indium aluminum arsenide (InAlAs) material has good lattice matching with InGaAs and indium phosphide (InP) and exhibits excellent avalanche breakdown characteristics, often used as the multiplication layer material in APDs.

[0003] InGaAs / InAlAs APDs have been widely used in near-infrared optical communication and sensing, demonstrating advantages such as high detection efficiency, fast response rate, and high sensitivity. However, compared with SiAPDs, the main problem with existing InGaAs / InAlAs APDs is that their gain is still insufficient. In current technologies, InGaAs / InAlAs APDs mostly adopt a single-stage multiplication structure. To achieve high multiplication gain, it is often necessary to increase the reverse bias voltage, which leads to increased excess noise and dark current. At the same time, although cascaded APDs can improve gain and reduce excess noise, this type of APD multiplication structure connects several p+in+ thin-layer structures in series to form a "cascade". The electric field of the multiplication layer is large, and the electric field variation in the cascade structure is large, resulting in problems such as large dark current and high breakdown voltage (Vbr) of the APDs. InGaAs / AlGaAsSb APDs already exist. Although the low-noise multiplication material AlGaAsSb has been selected, the overall performance of the devices has not shown a significant advantage in photodetection. This indicates that the existing cascaded APD structure has the problem of unreasonable design of the multiplication layer thickness. An excessively thin multiplication unit will cause a direct tunneling effect, resulting in a sharp increase in leakage current. Summary of the Invention

[0004] To address the shortcomings of existing technologies, the purpose of this application is to provide a cascaded avalanche photodiode and its fabrication method, aiming to solve the problems of how to improve APD gain and reduce dark current.

[0005] To achieve the above objectives, in a first aspect, this application provides a cascaded avalanche photodiode, comprising: a cascaded multiplication structure and a light absorption layer; The cascaded multiplication structure includes: N multiplication units and N-1 first charge layers; the N-1 first charge layers are alternately arranged between the N multiplication units; N is an integer greater than 2.

[0006] In one possible implementation, the multiplication unit is made of indium aluminum gallium arsenide (In). x Al y Ga 1-x-y As, where x and y range from 0 to 1; The material of the first charge layer includes, but is not limited to, n-type indium aluminum arsenide (In). x Al 1-x As or indium phosphide InP, where x ranges from 0 to 1.

[0007] In one possible implementation, the cascaded multiplication structure further includes: a second charge layer; the second charge layer is disposed above the uppermost multiplication unit among the N multiplication units; Preferably, the material of the second charge layer includes, but is not limited to, p-type In. x Al 1-x As or InP, the value of x ranges from 0 to 1.

[0008] In one possible implementation, it also includes: a substrate, a buffer layer, a first bandgap layer, and a window layer; The substrate, buffer layer, cascaded multiplication structure, first bandgap layer, light absorption layer, and window layer are arranged sequentially from bottom to top. Preferably, the cascaded avalanche photodiode further includes a second bandgap layer, which is disposed between the light absorption layer and the window layer.

[0009] In one possible implementation, an n-type ohmic contact electrode is fabricated on a buffer layer or substrate; And / or a p-type ohmic contact electrode is fabricated above the window layer.

[0010] In one possible implementation, the material of the first bandgap layer is In. x Al y Ga 1-x-y As, where x and y range from 0 to 1; The light-absorbing layer is made of indium gallium arsenide (In). x Ga 1-x As, where x ranges from 0 to 1; The material of the second bandgap layer is indium gallium arsenide phosphide (In). x Ga 1-x As y P 1-y , where x and y range from 0 to 1.

[0011] In one possible implementation, the material of the window layer includes, but is not limited to, InP, In x Al 1-x As, where x ranges from 0 to 1; And / or the substrate material is heavily doped n-type InP.

[0012] Secondly, this application provides a method for fabricating the cascaded avalanche photodiode described in the first aspect above, comprising the following steps: A buffer layer is formed on the substrate layer; A cascaded multiplication structure, a bandgap layer, a light absorption layer, and a window layer are sequentially grown on the buffer layer. To prepare diffusion holes, one or more diffusion processes are performed on the window layer using diffusion or ion implantation to form a planar PN junction above the window layer based on one or more diffusion holes. The diffusion process includes, but is not limited to, zinc atom closed-tube diffusion process or metal-organic chemical vapor deposition.

[0013] In one possible implementation, the preparation of the diffusion pore includes: A diffusion hole is formed on the window layer, and diffusion is performed through the diffusion hole. Based on the primary diffusion hole, a secondary diffusion hole is formed, and secondary diffusion is performed through the secondary diffusion hole to form the planar PN junction; the secondary diffusion hole and the primary diffusion hole form a concentric structure.

[0014] In one possible implementation, a groove is dug around one or more diffusion holes to obtain a grooved hole; the grooved hole and the one or more diffusion holes form a concentric structure; preferably, the concentric structure includes, but is not limited to, a concentric circle structure or a concentric polygon structure.

[0015] In summary, compared with the prior art, the technical solutions conceived in this application have the following main technical advantages: This application provides a cascaded avalanche photodiode and its fabrication method. The proposed cascaded multiplication structure abandons the p-type of previously reported cascaded multiplication periodic structures. + Layer, composed of p + in + The structure was changed to in + Cascading structures can avoid p + Type doping introduces additional defects to the entire device, reducing the difficulty of epitaxial growth.

[0016] This application provides a cascaded avalanche photodiode and its fabrication method. The electric field of the multiplication layer is not only dominated by the p-type charge layer, but also constrained by the n-type charge layer in the cascaded multiplication structure. This cascaded multiplication structure APD reduces the dependence on the p-type charge layer. The p-type charge layer and the n-type charge layer together determine to a certain extent how many subsequent multiplication layers participate in ionization.

[0017] This application provides a cascaded avalanche photodiode and its fabrication method. The proposed cascaded multiplication structure can reduce the "average" electric field of the multiplication layer, thereby increasing gain, reducing breakdown voltage, and reducing dark current.

[0018] This application provides a cascaded avalanche photodiode and its fabrication method. By combining a planar diffusion structure with a mesa process, the carrier hysteresis effect is effectively reduced. At the same time, the use of an electron initial injection structure can fully utilize the material performance advantages of the cascaded multiplication layer. Attached Figure Description

[0019] Figure 1 A schematic diagram of the architecture of a cascaded avalanche photodiode provided in an embodiment of this application; Figure 2 This is a schematic diagram of the architecture of the cascade multiplication structure provided in the embodiments of this application; Figure 3 A cascaded APD epitaxial structure diagram provided for an embodiment of this application; Figure 4 A schematic diagram of the electric field distribution of a cascaded APD provided in this application embodiment; Figure 5 To and Figure 4 In comparison, here is a schematic diagram of the electric field distribution of a cascaded APD in an existing technology; Figure 6 A cascaded APD process route diagram provided for embodiments of this application; Figure 7 This is a schematic diagram of a cascaded APD two-dimensional electric field provided for an embodiment of this application.

[0020] In all the accompanying drawings, the same reference numerals are used to denote the same elements or structures, where: 101 represents n + Type InP substrate; 102 is n +103 is the nth doped buffer layer of i-type InAlGaAs; 104 is the nth heavily doped charge layer of n-type InAlGaAs; 105 is the second doped layer of i-type InAlGaAs; 106 is the second heavily doped charge layer of n-type InAlGaAs; 107 is the first doped layer of i-type InAlGaAs; 108 is the first heavily doped charge layer of p-type InAlGaAs; 109 is the bandgap layer of InAlGaAs; 110 is the absorption layer of InGaAs; 111 is the P bandgap transition layer of InGaAs; 112 is the p-type InP window layer; 113 is the p-type InGaAs ohmic contact layer. Detailed Implementation

[0021] To make the objectives, technical solutions, and advantages of this application clearer, the following detailed description is provided in conjunction with the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are merely illustrative and not intended to limit the scope of this application.

[0022] In the description of this application, it should be understood that the terms "first" and "second" are used for descriptive purposes only and should not be construed as indicating or implying relative importance or implicitly specifying the number of technical features indicated. Therefore, a feature defined as "first" or "second" may explicitly or implicitly include one or more of that feature. In the description of this application, "multiple" means two or more, unless otherwise explicitly specified.

[0023] Furthermore, throughout this specification, references to "an embodiment"; "an embodiment," "an example," or similar language indicate that a particular feature, structure, or characteristic described in connection with that embodiment is included in at least one embodiment of this application. Therefore, the appearance of the phrase "in one embodiment;" throughout this specification, and similar language, may, but not necessarily, refer to the same embodiment.

[0024] Figure 1 This is a schematic diagram of the architecture of a cascaded avalanche photodiode provided in an embodiment of this application; as shown Figure 1 As shown, it includes, from bottom to top, a substrate, a buffer layer, a cascaded multiplication structure, a first bandgap layer, a light absorption layer, a second bandgap layer, and a window layer.

[0025] Among them, such as Figure 2 As shown, the cascaded multiplication structure includes: N multiplication units, N-1 first charge layers, and 1 second charge layer; the N-1 first charge layers are alternately arranged between the N multiplication units; N is an integer greater than 2. Further, see... Figure 2As shown, the above cascaded multiplication structure is arranged from bottom to top as follows: Nth multiplication unit, N-1th first charge layer, N-1th multiplication unit, N-2th first charge layer, ..., 2nd first charge layer, 2nd multiplication unit, 1st first charge layer, 1st multiplication unit and 2nd charge layer.

[0026] That is, the second charge layer is positioned above the topmost multiplication unit.

[0027] In some embodiments, the material of the multiplication unit may be indium aluminum gallium arsenide (In). x Al y Ga 1-x-y As, where x and y range from 0 to 1; The materials of the first charge layer include, but are not limited to, n-type indium aluminum arsenide (In). x Al 1-x As or indium phosphide InP, where x ranges from 0 to 1.

[0028] The material of the second charge layer includes, but is not limited to, p-type In. x Al 1-x As or InP, the value of x ranges from 0 to 1.

[0029] Furthermore, the aforementioned cascade multiplication structure can be understood as a pinin....-ni structure, which discards the p-type of previously reported cascade multiplication periodic structures. + Layer, composed of p + in + The structure was changed to in + Cascaded structure. Its beneficial effect is that it can avoid p + The p-type doping introduces additional defects to the entire device, reducing the difficulty of epitaxial growth. Furthermore, compared to previously reported APDs, this cascaded multiplication structure APD reduces its dependence on the p-type charge layer. This is because the electric field of the entire multiplication layer is governed not only by the p-type charge layer but also by the n-type charge layer in the cascaded multiplication structure. The p-type and n-type charge layers, to a certain extent, jointly determine the number of subsequent multiplication layers involved in ionization. In summary, the cascaded multiplication structure proposed in this application can reduce the "average" electric field of the multiplication layer, thereby improving gain, reducing breakdown voltage, and lowering dark current.

[0030] Furthermore, an n-type ohmic contact electrode can be fabricated on the buffer layer or substrate; a p-type ohmic contact electrode can be fabricated above the window layer.

[0031] In some embodiments, the buffer layer described above may be an n-type ohmic contact layer; Figure 1 A p-type ohmic contact layer can also be set above the middle window layer. Figure 1 (not shown in the image).

[0032] In some embodiments, the light absorption layer, multiplication layer and contact layer may further comprise III-V group materials or Ge / Si system materials.

[0033] In some embodiments, the material of the first bandgap layer can be In x Al y Ga 1-x-y As, where x and y range from 0 to 1; The material of the aforementioned light-absorbing layer can be indium gallium arsenide (In). x Ga 1-x As, where x ranges from 0 to 1; The material of the second bandgap layer mentioned above can be indium gallium arsenide phosphide (In). x Ga 1-x As y P 1-y , where x and y range from 0 to 1.

[0034] In some embodiments, the material of the window layer includes, but is not limited to, InP, In x Al 1-x As, where x ranges from 0 to 1; the substrate material can be heavily doped n-type InP.

[0035] It should be noted that, as Figure 2 The multiplication region shown above adopts a cascaded multiplication structure, and its electric field distribution can change in a stepped manner, which can reduce the "average" electric field of the multiplication layer.

[0036] Understandably, the cascaded APD proposed in this application employs an electron initial injection structure, which is beneficial for leveraging the advantages of the InAlAs multiplication layer. The multiplication region of the cascaded APD proposed in this application adopts a spatial multilayer structure, and the effective multiplication region thickness for collisional ionization is adjustable. When the bias voltage is increased, more multiplication unit structures participate in collisional ionization, and the APD multiplication layer operates at a relatively low average electric field throughout the entire bias voltage range, which helps to reduce noise while increasing gain.

[0037] In a more specific embodiment, the novel cascade multiplication structure proposed in this application is as follows: Figure 3 As shown. Figure 3 The device structure shown includes: n + Type InP substrate 101; n +p-type doped buffer layer 102; n-type InAlGaAs nth multiplication layer 103; n-type InAlAs heavily doped nth charge layer 104; ...; i-type InAlGaAs second multiplication layer 105; n-type InAlAs heavily doped second charge layer 106; i-type InAlGaAs first multiplication layer 107; p-type InAlAs heavily doped first charge layer 108; InAlGaAs bandgap layer 109; InGaAs absorption layer 110; InGaAs P bandgap transition layer 111; p-type InP window layer 112; p-type InGaAs ohmic contact layer 113.

[0038] In this structure, the n-type doped buffer layer 102 serves as an n-type ohmic contact layer to achieve n-type ohmic contact; the InGaAs absorption layer 110 absorbs light; the graded layers InAlGaAs 109 and InGaAsP 111 mitigate the hysteresis of carrier transport caused by band discontinuity between InGaAs and InAlAs; the p-type doped InAlAs 108 (first) charge control layer controls the electric field distribution between the absorption layer and the multiplication layer; the unintentionally doped multiplication layers InAlGaAs 103, 105, and 107 multiply carriers within them, thereby generating gain; the n-type doped InAlAs (second) charge control layers 104 and 106 control the electric field distribution between the first and second multiplication layers; and the p-type doped contact layer InGaAs 113 provides p-type ohmic contact. The layers between 103 and 108 form a cascaded multiplication structure 114.

[0039] Figure 4 This is the electric field distribution diagram of the novel cascaded structure APD proposed in this application. 201 represents the light absorption region, and 202 represents the cascade multiplication region. Figure 4 It can be seen that the electric field in the cascaded multiplication region exhibits a step-like decreasing trend.

[0040] Figure 5 The electric field distribution diagram of an existing cascaded APD structure is presented. In the diagram, 301 represents the light absorption region, and 302 represents the cascade multiplication region. Figure 4 and Figure 5 A comparison reveals that in existing cascaded multiplier structures, the electric field in the multiplication region is the same in each unit structure, all exhibiting a high electric field; while in the cascaded multiplier structure of this application, the electric field in the multiplication region shows a step-down trend. It is evident that the cascaded multiplier structure proposed in this application can reduce the "average" electric field of the multiplication layer, thereby increasing gain, reducing breakdown voltage, and decreasing dark current.

[0041] Figure 6The fabrication process route for the cascaded APD in this application includes the following main steps: InGaAs ring fabrication 401, diffusion process 402, mesa fabrication 403, passivation 404, surface SiN antireflection film fabrication 405, and ohmic contact electrode fabrication 406.

[0042] For example, the InGaAs ring fabrication 401 described above includes: defining a ring region and using an etching process to remove local material, wherein the etching depth is precisely controlled in the vertical direction and limited to the InGaAs layer itself, thereby forming an InGaAs ring.

[0043] For example, the diffusion process 402 described above includes: preparing diffusion holes and performing one or more diffusions on the window layer using a zinc atom closed-tube diffusion process, a metal-organic chemical vapor deposition diffusion process, or an ion implantation process.

[0044] As a further example, the diffusion process 402 described above may include: forming a diffusion hole on the window layer and performing a diffusion through the diffusion hole; Furthermore, it may also include: creating a secondary diffusion hole based on the primary diffusion hole, and performing secondary diffusion through the secondary diffusion hole.

[0045] For example, the above-mentioned countertop fabrication 403 includes: making grooves around one or more diffusion holes to obtain grooved holes; the grooved holes and the one or more diffusion holes form a concentric structure; preferably, the concentric structure includes, but is not limited to, a concentric circle structure and a concentric polygon structure.

[0046] For example, the fabrication of the ohmic contact electrode 406 described above includes: fabricating an electrode layer on a diffusion-formed InGaAs ring to form a planar PN junction.

[0047] The key technical feature of this application is the combination of mesa and diffusion processes to significantly reduce the surface APD electric field. Simultaneously, it suppresses the APD carrier hysteresis effect. Passivation and surface SiN fabrication aim to reduce APD dark current and improve APD quantum efficiency; the ohmic contact process is used to achieve ohmic contact between the P and N regions.

[0048] Figure 7 This is a two-dimensional electric field distribution diagram of the APD developed according to the process route of this application. From Figure 7 As can be seen, the electric field is clearly "focused" on the central region (cascaded multiplication region), and the electric field in the multiplication region shows a step-down trend. It is evident that the cascaded multiplication structure proposed in this application can reduce the "average" electric field of the multiplication layer, thereby increasing gain, reducing breakdown voltage, and reducing dark current.

[0049] Those skilled in the art will understand that the APD provided in the embodiments of this application is applicable to high-sensitivity detection scenarios such as electromagnetic wave signal acquisition, high-speed optical communication, lidar, optical time domain reflectometer, and biomedical imaging.

[0050] Those skilled in the art will readily understand that the above description is merely a preferred embodiment of this application and is not intended to limit this application. Any modifications, equivalent substitutions, and improvements made within the spirit and principles of this application should be included within the protection scope of this application.

Claims

1. A cascaded avalanche photodiode, characterized in that, include: Cascaded multiplication structure and light absorption layer; The cascaded multiplication structure includes: N multiplication units and N-1 first charge layers; the N-1 first charge layers are alternately arranged between the N multiplication units; N is an integer greater than 2.

2. The cascaded avalanche photodiode as described in claim 1, characterized in that, The multiplication unit is made of indium aluminum gallium arsenide (In). x Al y Ga 1-x-y As, where x and y range from 0 to 1; The material of the first charge layer includes, but is not limited to, n-type indium aluminum arsenide (In). x Al 1-x As or indium phosphide InP, where x ranges from 0 to 1.

3. The cascaded avalanche photodiode as described in claim 1, characterized in that, The cascaded multiplication structure further includes: a second charge layer; the second charge layer is disposed above the uppermost multiplication unit among the N multiplication units; Preferably, the material of the second charge layer includes, but is not limited to, p-type In. x Al 1-x As or InP, the value of x ranges from 0 to 1.

4. The cascaded avalanche photodiode as described in any one of claims 1 to 3, characterized in that, Also includes: Substrate, buffer layer, first bandgap layer and window layer; The substrate, buffer layer, cascaded multiplication structure, first bandgap layer, light absorption layer, and window layer are arranged sequentially from bottom to top. Preferably, the cascaded avalanche photodiode further includes a second bandgap layer, which is disposed between the light absorption layer and the window layer.

5. The cascaded avalanche photodiode as described in claim 4, characterized in that, Fabricate n-type ohmic contact electrodes on a buffer layer or substrate; And / or a p-type ohmic contact electrode is fabricated above the window layer.

6. The cascaded avalanche photodiode as described in claim 4, characterized in that, The material of the first bandgap layer is In x Al y Ga 1-x-y As, where x and y range from 0 to 1; The light-absorbing layer is made of indium gallium arsenide (In). x Ga 1-x As, where x ranges from 0 to 1; The material of the second bandgap layer is In x Al y Ga 1-x-y As or Indium gallium arsenide phosphorus In x Ga 1-x As y P 1-y , where x and y range from 0 to 1.

7. The cascaded avalanche photodiode as described in claim 4, characterized in that, The material of the window layer includes, but is not limited to, InP, In x Al 1-x As, where x ranges from 0 to 1; And / or the substrate material is heavily doped n-type InP.

8. A method for fabricating a cascaded avalanche photodiode according to any one of claims 1 to 7, characterized in that, Includes the following steps: A buffer layer is formed on the substrate layer; A cascaded multiplication structure, a bandgap layer, a light absorption layer, and a window layer are sequentially grown on the buffer layer. To prepare diffusion holes, one or more diffusion processes are performed on the window layer using diffusion or ion implantation to form a planar PN junction above the window layer based on one or more diffusion holes. The diffusion process includes, but is not limited to, zinc atom closed-tube diffusion process or metal-organic chemical vapor deposition.

9. The preparation method according to claim 8, characterized in that, The preparation of the diffusion pores includes: A diffusion hole is formed on the window layer, and diffusion is performed through the diffusion hole. Based on the primary diffusion hole, a secondary diffusion hole is formed, and secondary diffusion is performed through the secondary diffusion hole to form the planar PN junction; the secondary diffusion hole and the primary diffusion hole form a concentric structure.

10. The preparation method according to claim 8, characterized in that, A groove is dug around one or more diffusion holes to obtain a grooved hole; the grooved hole and the one or more diffusion holes form a concentric structure; preferably, the concentric structure includes, but is not limited to, a concentric circle structure and a concentric polygon structure.

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