Vertical Cavity Surface Emitting Laser
By forming vias or through holes in the insulating substrate and filling metal materials, and the N-side metal layer and P-side metal layer are not directly conducted through the substrate, the problem of insufficient heat dissipation performance of VCSEL chips is solved, achieving more efficient heat dissipation and reducing series resistance.
Patent Information
- Application Number
- CN202411970384.X
- Authority / Receiving Office
- CN · China
- Patent Type
- Applications(China)
- Current Assignee / Owner
- Filing Date
- 2024-12-30
- Publication Date
- 2025-04-01
AI Technical Summary
With the development of VCSEL technology, the chip size of VCSEL vehicle-mounted lidar chips has increased, resulting in an increase in the demand for heat dissipation, and the existing technology is difficult to effectively improve the heat dissipation performance of vertical cavity surface emitting lasers.
Through holes or through holes are formed in the insulating substrate, and metal materials are filled in the vias/through holes. At the same time, the N-side metal layer and the P-side metal layer do not directly conduct through the substrate, reducing the series resistance.
By filling the substrate with metal material and directly conducting metal layer, the heat dissipation performance of the vertical cavity surface emitting laser is significantly improved, the series resistance is reduced, and the heat dissipation capability of the device is improved.
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Figure CN119742657A_ABST
Abstract
Description
Technical Field
[0001] The present invention relates to the technical field of integrated circuit manufacturing, and in particular to a vertical cavity surface emitting laser. Background Art
[0002] Vertical-Cavity Surface-Emitting Laser (VCSEL) is a semiconductor laser whose laser emission direction is perpendicular to the epitaxial plane. Compared with edge-emitting lasers in which general lasers are emitted from the edge (the emission direction is parallel to the epitaxial direction), VCSEL has the advantages of small far-field divergence angle, easy fiber coupling, small threshold current, high bandwidth and high test efficiency.
[0003] A vertical cavity surface emitting laser generally includes a substrate, an epitaxial structure formed on the front side of the substrate, and an N-side metal layer formed on the back side of the substrate. The epitaxial structure generally includes: an N-type DBR layer, an active layer, a P-type DBR layer, etc.
[0004] With the development of VCSEL technology, the number of epitaxial structure (EPI) junctions of VCSEL automotive laser radar chips is increasing, and the chip size is getting larger and larger, resulting in higher and higher requirements for chip heat dissipation. Summary of the invention
[0005] The object of the present invention is to provide a vertical cavity surface emitting laser to improve the heat dissipation performance of the vertical cavity surface emitting laser.
[0006] In order to solve the above technical problems, the present invention provides a vertical cavity surface emitting laser, comprising:
[0007] An insulating substrate, wherein the insulating substrate has via holes arranged along a thickness direction, and the via holes are filled with a metal material;
[0008] An epitaxial structure formed on the front side of the insulating substrate, the epitaxial structure comprising an N-type DBR layer, an active layer, a P-type DBR layer and a P-side metal layer formed on the P-type DBR layer stacked in sequence from bottom to top, and the epitaxial structure has a groove extending from the surface downward to the surface of the N-type DBR layer or inside the N-type DBR layer; and
[0009] An N-side metal layer is formed at the bottom of the groove.
[0010] Optionally, in the vertical cavity surface emitting laser, the via hole is a through hole arranged to penetrate along the thickness direction.
[0011] Optionally, in the vertical cavity surface emitting laser, the number of the via holes is one or more.
[0012] Optionally, in the vertical cavity surface emitting laser, the epitaxial structure also includes an oxidation restriction layer, which is formed in the P-type DBR layer or between the P-type DBR layer and the active layer, and the unoxidized area of the oxidation restriction layer defines the light-transmitting area of the vertical cavity surface emitting laser.
[0013] Optionally, in the vertical cavity surface emitting laser, the epitaxial structure further includes: a first protective layer and a second protective layer, the first protective layer covers the P-type DBR layer, and the second protective layer covers the bottom wall and side walls of the groove and extends to cover the first protective layer.
[0014] The present invention also provides another vertical cavity surface emitting laser, comprising:
[0015] An insulating substrate having through holes extending through the substrate in a thickness direction;
[0016] An epitaxial structure formed on the front side of the insulating substrate, the epitaxial structure comprising an N-type DBR layer, an active layer, a P-type DBR layer and a P-side metal layer formed on the P-type DBR layer stacked in sequence from bottom to top, and the epitaxial structure has a groove extending from the surface downward to the surface of the active layer or below the surface of the active layer; and
[0017] N-side metal layer, the through hole is filled with metal material, and the metal material filled in the through hole constitutes at least a part of the N-side metal layer.
[0018] Optionally, in the another vertical cavity surface emitting laser, the N-side metal layer further extends outward from the through hole to the back side formed on at least a portion of the insulating substrate.
[0019] Optionally, in the another vertical cavity surface emitting laser, the number of the through holes is one or more. When the number of the through holes is more than one, the N-side metal layer also covers the back side of the insulating substrate.
[0020] Optionally, in the other vertical cavity surface emitting laser, the epitaxial structure also includes an oxidation restriction layer, which is formed in the P-type DBR layer or between the P-type DBR layer and the active layer, and the unoxidized area of the oxidation restriction layer defines the light-transmitting area of the vertical cavity surface emitting laser.
[0021] Optionally, in the other vertical cavity surface emitting laser, the epitaxial structure further includes: a first protective layer and a second protective layer, the first protective layer covers the P-type DBR layer, the second protective layer covers the bottom wall and side walls of the groove and extends to cover the first protective layer.
[0022] In summary, the vertical cavity surface emitting laser provided by the present invention forms a via hole or a through hole in the substrate, and fills the via hole / through hole with metal material to improve the heat dissipation performance. In addition, in the vertical cavity surface emitting laser provided by the present invention, the N-side metal layer and the P-side metal layer are directly connected without passing through the substrate, which can reduce the series resistance, thereby further improving the heat dissipation capacity of the device. BRIEF DESCRIPTION OF THE DRAWINGS
[0023] Figure 1 A schematic diagram of the structure of a vertical cavity surface emitting laser provided in Embodiment 1 of the present invention;
[0024] Figure 2 A schematic diagram of the structure of a vertical cavity surface emitting laser provided in Embodiment 2 of the present invention;
[0025] The descriptions of the reference numerals are as follows:
[0026] 11-insulating substrate; 12-N-type DBR layer; 13-active layer; 14-P-type DBR layer; 15-P-side metal layer; 16-N-side metal layer; 17-oxidation restriction layer; 18-first protective layer; 19-second protective layer;
[0027] 100-via; 200-groove; 300-through hole. DETAILED DESCRIPTION
[0028] In order to make the purpose, advantages and features of the present invention clearer, the present invention is described in detail in conjunction with the accompanying drawings and specific embodiments. It should be noted that the drawings are all in a very simplified form and use non-precise proportions, which are only used to conveniently and clearly assist in explaining the purpose of the embodiments of the present invention. In addition, the structure shown in the drawings is often a part of the actual structure. In particular, the emphasis required to be shown in each drawing is different, and sometimes different proportions are used. It should be recognized that relative terms such as "above", "below", "top", "bottom", "above" and "below" shown in the drawings can be used to describe the relationship between various elements. These relative terms are intended to cover different orientations of elements other than the orientations depicted in the drawings. For example, if the device is inverted relative to the view in the drawings, for example, an element described as "above" another element will now be below the element. It should also be understood that, unless otherwise specified or indicated, the terms "first", "second", "third" and the like in the specification are only used to distinguish between the various components, elements, steps, etc. in the specification, rather than to represent the logical relationship or sequential relationship between the various components, elements, steps, etc.
[0029] [Example 1]
[0030] See also Figure 1This embodiment provides a vertical cavity surface emitting laser, the vertical cavity surface emitting laser comprising:
[0031] An insulating substrate 11, wherein the insulating substrate 11 has a via hole 100 arranged along a thickness direction, and the via hole 100 is filled with a metal material;
[0032] An epitaxial structure formed on the front side of the insulating substrate 11, the epitaxial structure comprising an N-type DBR layer 12, an active layer 13, a P-type DBR layer 14 and a P-side metal layer 15 formed on the P-type DBR layer 14 stacked in sequence from bottom to top, and the epitaxial structure has a groove 200 extending from the surface downward to the surface of the N-type DBR layer 12 or inside the N-type DBR layer 12; and,
[0033] The N-side metal layer 16 is formed at the bottom of the trench 200 .
[0034] The vertical cavity surface emitting laser provided in this embodiment improves heat dissipation performance from two aspects:
[0035] (1) forming a via hole 100 in the substrate and filling the via hole 100 with metal material to dissipate heat;
[0036] (2) The substrate is an insulating substrate, and the P-side metal layer 15 and the N-side metal layer 16 are directly connected without passing through the substrate. In this way, the series resistance can be reduced, thereby improving the heat dissipation performance of the device.
[0037] Preferably, the via hole 100 is a through hole that is arranged to penetrate along the thickness direction, so that the heat conduction effect of the via hole 100 can be greatly improved. In some other embodiments, the via hole 100 may not be arranged to penetrate.
[0038] Optionally, there are one or more vias 100. When the number of vias 100 increases, the heat dissipation performance of the device can be improved, and the design can be made according to the heat dissipation requirements. Figure 1 The number of the vias 100 in the example is three. Figure 1 In the embodiment, the two via holes 100 are aligned with the groove 200 , but this arrangement does not constitute a limitation to the present application, that is, the present application does not limit the positions of the via holes 100 .
[0039] The metal material filled in the via hole 100 can be a metal with a good heat transfer coefficient, such as Cu, Ag, Au, etc.
[0040] In the epitaxial structure, the active layer 13 and the N-type DBR layer 12 and the P-type DBR layer 14 on both sides form a Fabry-Perot resonant cavity.
[0041] The N-type DBR layer 12 may be formed by stacking at least two semiconductor material layers with different refractive indices. For example, the N-type DBR layer 12 is an overlapping structure of a first refractive index and a second refractive index, and the first refractive index is greater than the second refractive index. The N-type DBR layer 12 may include an N-type aluminum gallium arsenide layer (AlGaAs) and an N-type gallium arsenide layer (GaAs) stacked in sequence. Aluminum gallium arsenide is a high refractive index material, and gallium arsenide is a low refractive index material. Multiple layers of high refractive index N-type aluminum gallium arsenide layers and multiple layers of low refractive index N-type gallium arsenide layers are stacked to form the N-type DBR layer 12. Moreover, based on the conventional structure of the DBR, the refractive index of the multiple layers of the N-type aluminum gallium arsenide layers may change gradually, and the refractive index of the multiple layers of the N-type gallium arsenide layers may also change gradually. Of course, the present application is not limited to this.
[0042] Similar to the N-type DBR layer 12, the P-type DBR layer 14 is also formed by stacking at least two semiconductor materials with different refractive indices. For example, the P-type DBR layer 14 is an overlapping structure of a first refractive index and a second refractive index, and the first refractive index is greater than the second refractive index. The P-type DBR layer 14 may include a P-type aluminum gallium arsenide layer (AlGaAs) and a P-type gallium arsenide layer (GaAs) arranged in sequence. Aluminum gallium arsenide is a high refractive index material, and gallium arsenide is a low refractive index material. Multiple layers of high refractive index P-type aluminum gallium arsenide layers and multiple layers of low refractive index P-type gallium arsenide layers are stacked to form the P-type DBR layer 14. Moreover, based on the conventional structure of DBR, the refractive index of multiple layers of the P-type aluminum gallium arsenide layers can change gradually, and the refractive index of multiple layers of the P-type gallium arsenide layers can also change gradually, and of course it is not limited to this. Compared with the N-type DBR layer 12, the Al doping concentration of the P-type DBR layer 14 is higher, and it is more susceptible to oxidation and corrosion.
[0043] The active layer 13 may include a plurality of pairs of quantum well composite layers, and the quantum well composite layers may include overlappingly grown aluminum gallium arsenide (AlxGaAs) barriers, gallium indium arsenide (InGaAs) potential wells, and AlxGaAs barriers.
[0044] The groove 200 in the epitaxial structure is obtained by etching downward from the surface. In this embodiment, the etching can be stopped when the N-type DBR layer 12 is reached. The specific process may include: firstly, a patterned photoresist layer is formed above the P-type DBR layer 14, and the window of the photoresist layer defines the position of the groove 200; then, the P-type DBR layer 14 and the active layer 13 are sequentially etched using the photoresist layer as a mask, or the P-type DBR layer 14, the active layer 13 and a part of the thickness of the N-type DBR layer 12 are sequentially etched using the photoresist layer as a mask to form the groove 200.
[0045] In addition, in this embodiment, the epitaxial structure may further include: an oxidation restriction layer 17, the oxidation restriction layer 17 is formed in the P-type DBR layer 14 or between the P-type DBR layer 14 and the active layer 13, and the unoxidized area of the oxidation restriction layer 17 defines the light-transmitting area of the vertical cavity surface-emitting laser. Further, the epitaxial structure may further include: a first protective layer 18 and a second protective layer 19, the first protective layer 18 covers the P-type DBR layer 14, and the second protective layer 19 covers the bottom wall and side walls of the groove 200, and extends to cover the first protective layer 18.
[0046] The steps of forming the epitaxial structure may be specifically as follows:
[0047] S1, sequentially forming the N-type DBR layer 12, the active layer 13 and the P-type DBR layer 14 on the front side of the substrate;
[0048] S2, forming a P-side metal layer 15 on the surface of the P-type DBR layer 14, and forming a first protective layer 18, wherein the first protective layer 18 covers the P-type DBR layer 14 and the P-side metal layer 15;
[0049] S3, etching the first protective layer 18, the P-type DBR layer 14, and the active layer 13 in sequence and stopping on the surface of the N-type DBR layer 12 to form the groove 200, or etching the first protective layer 18, the P-type DBR layer 14, the active layer 13, and the N-type DBR layer 12 in sequence and stopping in the N-type DBR layer 12 to form the groove 200; Figure 2 As shown in FIG. , an example is made by stopping etching in the N-type DBR layer 12 when forming the groove 200;
[0050] S4 , forming a second protection layer 19 , wherein the second protection layer 19 covers the bottom wall and the side wall of the trench 200 and extends to cover the first protection layer 18 .
[0051] Optionally, after forming the second protective layer 19, the step of forming the epitaxial structure further includes:
[0052] S5, etching the second protective layer 19 and the first protective layer 18 and stopping on the P-side metal layer 15 to form a through hole, and filling the through hole with metal material to form a P-side metal contact layer (not shown), the P-side metal contact layer and the P-side metal layer 15 are electrically connected.
[0053] When the metal material is filled in the through hole to form the P-side metal contact layer, the metal material may cover a portion of the surface of the second protective layer 19, so that the top width of the P-side metal contact layer is greater than the width of the through hole, thereby increasing the ohmic contact area of the P-side metal contact layer. In some other embodiments, the P-side metal layer 15 may not be formed first, but after the second protective layer 19 is formed, the second protective layer 19 and the first protective layer 18 are etched in sequence and stopped at the P-type DBR layer 14 to form a through hole, and the metal material is filled in the through hole to directly form the P-side metal layer 15.
[0054] The P-side metal layer 15 may include a single layer or multiple layers of metal, specifically may include a gold, germanium or nickel layer. Exemplarily, the P-side metal layer 15 may be formed by electron beam evaporation, sputtering, electroplating or any other metal coating process.
[0055] The material of the first protective layer 18 may be silicon nitride, silicon oxide, or silicon oxynitride, etc., and the material of the second protective layer 19 may be silicon nitride, silicon oxide, silicon oxynitride, or aluminum oxide, etc. When the materials of the first protective layer 18 and the second protective layer 19 are silicon nitride, silicon oxide, silicon oxynitride, etc., they may be formed by a physical vapor deposition (PVD) process or a chemical vapor deposition (CVD) process, etc., and when the material of the second protective layer 19 is aluminum oxide, it may be formed by an atomic layer deposition (ALD) process, etc.
[0056] Optionally, after the second protective layer 19 is formed, the N-side metal layer 16 can be etched from the second protective layer 19 at the bottom of the groove 200 to expose a portion of the bottom of the groove 200, and then the N-side metal layer 16 is formed; or, the N-side metal layer 16 can be first formed at the bottom of the groove 200, and then the second protective layer 19 can be deposited to form.
[0057] Optionally, the PEI structure further includes an oxidation restriction layer 17, and the oxidation restriction layer 17 is formed between the P-type DBR layer 14 and the active layer 13, and can also be formed in the P-type DBR layer 14. When the oxidation restriction layer 17 is formed between the P-type DBR layer 14 and the active layer 13, an oxidation pre-restriction layer can be first formed between the oxidation restriction layer 17 and the P-type DBR layer 14, and after the groove 200 is formed, an oxidation process is performed on the oxidation pre-restriction layer, so that the peripheral area of the oxidation pre-restriction layer close to the groove 200 is oxidized, and the middle area away from the groove 200 is not oxidized, so as to obtain the oxidation restriction layer 17. When the oxidation restriction layer 17 is formed in the P-type DBR layer 14, an oxidation process can also be performed on the P-type DBR layer 14 after the groove 200 is formed. During the oxidation process, the high Al component layer (such as Al 0.98 Ga 0.02 As) is oxidized into Al2O3, so as to obtain the oxidation restriction layer 17 in which the area close to the trench 200 is oxidized and the area away from the trench 200 is not oxidized. Figure 1 As shown in FIG. , the oxidation restriction layer 17 is formed between the P-type DBR layer 14 and the active layer 13 as an example.
[0058] The unoxidized area in the middle of the oxidation limiting layer 17 is a light-transmitting area, and current can be injected from the light-transmitting area, so that the laser is concentrated in the center of the device. By controlling the oxidation depth from the outside to the inside, the aperture size of the unoxidized part can be controlled, that is, the size of the oxidation limiting hole can be controlled. When a voltage is applied to both sides of the device, the aperture size of the oxidation limiting hole will affect the current of the longitudinal active layer 13, thereby controlling the power characteristics of the vertical cavity surface emitting laser.
[0059] [Example 2]
[0060] See also Figure 2 This embodiment provides a vertical cavity surface emitting laser, the vertical cavity surface emitting laser comprising:
[0061] An insulating substrate 11, wherein the insulating substrate 11 has a through hole 300 extending through the substrate along a thickness direction;
[0062] An epitaxial structure formed on the front side of the insulating substrate 11, the epitaxial structure comprising an N-type DBR layer 12, an active layer 13, a P-type DBR layer 14 and a P-side metal layer 15 formed on the P-type DBR layer 14 stacked in sequence from bottom to top, and the epitaxial structure has a groove 200 extending from the surface downward to the surface of the active layer 13 or below the surface of the active layer 13; and
[0063] The N-side metal layer 16 , the through hole 300 is filled with a metal material, and the metal material filled in the through hole 300 constitutes at least a part of the N-side metal layer 16 .
[0064] The vertical cavity surface emitting laser provided in this embodiment also improves the heat dissipation performance from two aspects:
[0065] (1) forming a via hole 100 in the substrate and filling the via hole 100 with metal material to dissipate heat;
[0066] (2) The substrate uses an insulating substrate 11, and the P-side metal layer 15 and the N-side metal layer 16 are directly connected without the substrate, which can reduce the series resistance and thus improve the heat dissipation performance of the device.
[0067] Preferably, the N-side metal layer 16 further extends outward from the inside of the through hole 300 to the back side of at least a portion of the insulating substrate 11, so as to increase the ohmic contact area of the N-side metal layer 16. If the N-side metal layer 16 is also formed on the back side of at least a portion of the insulating substrate 11, the substrate should be thinned from the back side of the substrate before etching the insulating substrate 11 to form the through hole 300.
[0068] Optionally, the number of the through holes 300 is one or more. When the number of through holes 300 increases, the heat dissipation performance of the device can be increased, and the design can be specifically performed according to the heat dissipation requirements. When the number of the through holes 300 is multiple, the N-side metal layer 16 also covers the back side of the insulating substrate 11, so that multiple parts of the N-side metal layer 16 can be conductive with each other.
[0069] By comparison, it can be seen that this embodiment is different from the first embodiment in the following ways:
[0070] (1) The etching depth of the groove 200 is different. In the first embodiment, the bottom of the groove 200 is located on the surface of the N-type DBR layer 12 or in the N-type DBR layer 12, so that the N-side metal layer 16 can be conductive with the P-side metal layer 15. In this embodiment, the bottom of the groove 200 is located at or below the surface of the active layer 13. For example, in this embodiment, the bottom of the groove 200 can be located in the active layer 13, in the N-type DBR layer 12, or in the substrate, etc. Figure 2 As shown, the bottom of the groove 200 is located in the active layer 13 as an example;
[0071] (2) The formation position of the N-side metal layer 16 is different and the purpose of setting the via 100 / through hole 300 in the substrate is different. In the first embodiment, the N-side metal layer 16 is formed at the bottom of the groove 200, and the via 100 is filled with metal material for heat dissipation. In the present embodiment, the metal material filled in the through hole 300 is used to serve as at least a part of the N-side metal layer 16. That is, in the present embodiment, the through hole 300 is used as a heat dissipation hole and is also used to achieve direct conduction between the N-side metal layer 16 and the P-side metal layer 15.
[0072] Except for the different etching depth of the groove 200, the remaining steps of forming the epitaxial structure in this embodiment are similar to those in the first embodiment. For the specific step process and the description of the materials used for each film layer, please refer to the first embodiment and will not be repeated here.
[0073] In summary, the vertical cavity surface emitting laser provided in the embodiment of the present invention forms a via or a through hole in the substrate, and fills the via / through hole with metal material to improve the heat dissipation performance. In addition, in the vertical cavity surface emitting laser provided in the embodiment of the present invention, the N-side metal layer and the P-side metal layer are directly connected without passing through the substrate, which can reduce the series resistance, thereby further improving the heat dissipation capacity of the device.
[0074] It should be noted that the various embodiments in this specification are described in a progressive manner, and each embodiment focuses on the differences from other embodiments. The same or similar parts between the various embodiments can be referenced to each other. In addition, the different parts between the various embodiments can also be used in combination with each other, and the present invention is not limited to this.
[0075] In addition, it should be recognized that although the present invention has been disclosed as a preferred embodiment, the above embodiment is not intended to limit the present invention. For any technician familiar with the art, without departing from the scope of the technical solution of the present invention, the technical content disclosed above can be used to make many possible changes and modifications to the technical solution of the present invention, or modified into equivalent embodiments of equivalent changes. Therefore, any simple modification, equivalent change and modification made to the above embodiment according to the technical essence of the present invention without departing from the content of the technical solution of the present invention still belongs to the scope of protection of the technical solution of the present invention.
Claims
1. A vertical cavity surface emitting laser, characterized in that: include: An insulating substrate, wherein the insulating substrate has via holes arranged along a thickness direction, and the via holes are filled with a metal material; An epitaxial structure formed on the front side of the insulating substrate, the epitaxial structure comprising an N-type DBR layer, an active layer, a P-type DBR layer and a P-side metal layer formed on the P-type DBR layer stacked in sequence from bottom to top, and the epitaxial structure has a groove extending from the surface downward to the surface of the N-type DBR layer or in the N-type DBR layer; as well as, An N-side metal layer is formed at the bottom of the groove.
2. The vertical cavity surface emitting laser according to claim 1, characterized in that: The via hole is a through hole that penetrates along the thickness direction.
3. The vertical cavity surface emitting laser according to claim 1 or 2, characterized in that: The number of the via holes is one or more.
4. The vertical cavity surface emitting laser according to claim 1, characterized in that: The epitaxial structure further includes an oxidation restriction layer, which is formed in the P-type DBR layer or between the P-type DBR layer and the active layer. The unoxidized region of the oxidation restriction layer defines a light-transmitting region of the vertical cavity surface emitting laser.
5. The vertical surface-emitting laser according to claim 1, characterized in that: The epitaxial structure further includes: a first protective layer and a second protective layer, wherein the first protective layer covers the P-type DBR layer, and the second protective layer covers the bottom wall and side walls of the trench and extends to cover the first protective layer.
6. A vertical cavity surface emitting laser, characterized in that: include: An insulating substrate having through holes extending through the substrate in a thickness direction; An epitaxial structure formed on the front side of the insulating substrate, the epitaxial structure comprising an N-type DBR layer, an active layer, a P-type DBR layer and a P-side metal layer formed on the P-type DBR layer stacked in sequence from bottom to top, and the epitaxial structure has a groove extending from the surface downward to the surface of the active layer or below the surface of the active layer; as well as, N-side metal layer, the through hole is filled with metal material, and the metal material filled in the through hole constitutes at least a part of the N-side metal layer.
7. The vertical cavity surface emitting laser according to claim 1, characterized in that: The N-side metal layer also extends outward from the through hole to the back side formed on at least a portion of the insulating substrate.
8. The vertical cavity surface emitting laser according to claim 1, characterized in that: The number of the through holes is one or more. When the number of the through holes is more than one, the N-side metal layer also covers the back side of the insulating substrate.
9. The vertical cavity surface emitting laser according to claim 1, characterized in that: The epitaxial structure further includes an oxidation restriction layer, which is formed in the P-type DBR layer or between the P-type DBR layer and the active layer. The unoxidized region of the oxidation restriction layer defines a light-transmitting region of the vertical cavity surface emitting laser.
10. The vertical surface emitting laser according to claim 1, characterized in that: The epitaxial structure further includes: a first protective layer and a second protective layer, wherein the first protective layer covers the P-type DBR layer, and the second protective layer covers the bottom wall and side walls of the trench and extends to cover the first protective layer.