VCSEL chip manufacturing method and laser

Abstract

The invention relates to the technical field of semiconductor lasers, in particular to a VCSEL chip manufacturing method and a laser. The preparation method comprises the following steps: growing on a substrate by adopting an epitaxial technology to obtain a VCSEL (Vertical Cavity Surface Emitting Laser) substrate; growing on the top of the VCSEL substrate by adopting a growth process to obtain a surface lens, wherein the refractive index of the surface lens gradually changes upwards from the VCSEL substrate; growing an h-BN film on the top of the surface lens to obtain a VCSEL (Vertical Cavity Surface Emitting Laser) with the lens; the VCSEL chip is oxidized through a wet oxidation method, an oxidation layer is obtained on the outer surface of the surface lens, so that the surface lens has a light beam focusing effect, and the VCSEL chip is obtained. According to the VCSEL chip prepared by the embodiment of the invention, the surface lens with the step structure and the h-BN film which have the focusing function are effectively integrated with the VCSEL, so that the stability of the whole device of the VCSEL chip is ensured.

Description

Technical Field

[0001] This invention relates to the field of semiconductor laser technology, and more specifically, to a method for fabricating a VCSEL chip and the VCSEL chip itself. Background Technology

[0002] VCSEL is a semiconductor laser structure in which an optical resonant cavity is formed in a direction perpendicular to the semiconductor epitaxial wafer, and the emitted laser beam is perpendicular to the substrate surface.

[0003] Vertical cavity surface-emitting lasers often use GaAs (gallium arsenide) as a substrate. However, it is well known that GaAs has poor heat dissipation performance and its refractive index changes with increasing temperature. Therefore, operating the chip at high temperatures will lead to a decrease in device performance.

[0004] In the process of developing this invention, the inventors discovered that common methods for improving beam focusing performance in existing VCSELs include bonding microlenses to the exit cavity surface and etching diffraction gratings within the cavity. However, bonding microlenses suffers from complex processes, low integration with the chip, and high costs, and can easily introduce additional optical losses and packaging stress. While etching diffraction gratings can control the beam to some extent, it lacks design flexibility, makes it difficult to achieve large-angle beam focusing optimization, and requires extremely high process precision; even small etching errors can lead to a significant decrease in focusing performance. Meanwhile, traditional VCSELs mainly dissipate heat through the substrate or by adding auxiliary structures such as heat sinks and heat plates to the outside of the device. However, because the heat generated in the active region of the VCSEL is concentrated and difficult to conduct quickly to the substrate, and external heat dissipation measures increase the system size and cost, the temperature of the active region of the VCSEL rises sharply when operating at high power, causing problems such as wavelength redshift, increased threshold current, and shortened device lifetime, which seriously restricts its performance improvement and application expansion. In addition, existing VCSEL focusing structures mostly rely on photolithography to define patterns. Photolithography has problems such as resolution limitations, high cost, and complex process. Moreover, it is difficult to accurately control the shape and size of the pattern when fabricating complex lens structures. Summary of the Invention

[0005] In view of the above problems, the present invention is proposed to provide a method for fabricating a VCSEL chip and a laser that overcomes or at least partially solves the above problems.

[0006] In a first aspect, embodiments of the present invention provide a method for fabricating a VCSEL chip, comprising the following steps: VCSEL substrates were grown on a substrate using epitaxial technology; A surface lens is obtained by growing a molecular beam on the top of a VCSEL substrate, and the refractive index of the surface lens is set to gradually change upward from the VCSEL substrate. An h-BN thin film is grown on top of the surface lens to obtain a VCSEL with a lens. The VCSEL chip is oxidized using a wet oxidation method, and an oxide layer is obtained on the outer surface of the surface lens, which enables the surface lens to have a beam focusing function, thus obtaining the VCSEL chip.

[0007] Furthermore, the method of growing a surface lens on the top of a VCSEL substrate using molecular beam epitaxy involves growing an AlGaAs layer with a gradient aluminum content in a predetermined region on the top of the VCSEL substrate using a molecular beam epitaxy process, thereby creating a surface lens on the VCSEL substrate. The surface lens has a multilayer structure, and the refractive index of the multilayer structure increases layer by layer from the VCSEL substrate upwards.

[0008] Furthermore, the multilayer structure comprises multiple lens layers stacked together, and the cross-sectional area of ​​the lens layers gradually decreases from VCSEL upwards, with the side surface of the surface lens having a stepped structure.

[0009] Furthermore, the process of growing an h-BN thin film on top of the surface lens involves placing the VCSEL substrate into a molecular beam epitaxy (MBE) equipment and controlling the temperature within a certain range. Simultaneously, active atomic nitrogen or nitrogen free radicals are added to overcome the inertness of molecular nitrogen; Then, by controlling the molecular beam source, an h-BN film of a certain thickness is grown on the top of the surface lens of the VCSEL substrate.

[0010] Furthermore, the controlled molecular beam source comprises a nitrogen-rich B / N molecular beam, and the B / N flow ratio is controlled at 0.01-0.1.

[0011] Furthermore, the growth rate of the h-BN film is stably controlled at 0.1-0.5 Å / s during growth.

[0012] Furthermore, the thickness of the h-BN film is controlled at 50-70 nm.

[0013] Furthermore, the outer surface of the surface lens is obtained by: oxidizing the surface lens with a VCSEL chip using a wet oxidation process, wherein the temperature of the oxidation furnace is raised to 190-220°C during oxidation, and an oxidation solution is added to oxidize the surface lens for a period of time.

[0014] Furthermore, the oxidation solution has a ratio of H2O2:H3PO4:H2O = 1:1:12.

[0015] The second aspect discloses a laser, including a VCSEL chip fabricated using any of the fabrication methods.

[0016] The beneficial effects of the above-described technical solutions provided in the embodiments of the present invention include at least the following: This invention provides a method for fabricating a VCSEL chip. The fabrication method of this invention is highly compatible with existing VCSEL epitaxial growth, wet oxidation and other processes, and can be directly applied to existing production lines, reducing the use of photolithography equipment, reducing the cost and difficulty of technology upgrades, and has good prospects for industrial application.

[0017] The VCSEL chip obtained by this preparation method effectively integrates the surface lens with a stepped structure that has a focusing function and the h-BN thin film with the VCSEL, ensuring the overall stability of the VCSEL chip device.

[0018] The VCSEL chip in this embodiment can efficiently focus the divergent beam emitted by the VCSEL through the surface lens disposed at the light emission point of the VCSEL, so that the beam is converged into a smaller spot and the beam divergence angle is significantly reduced; and the h-BN film disposed on the surface lens can quickly dissipate the heat generated by the focused beam and the heat conducted from the active region, effectively reducing the impact of heat on the VCSEL.

[0019] Other features and advantages of the invention will be set forth in the following description, and will be apparent in part from the description, or may be learned by practicing the invention. The objects and other advantages of the invention may be realized and obtained by means of the structures particularly pointed out in the written description and the accompanying drawings.

[0020] The technical solution of the present invention will be further described in detail below with reference to the accompanying drawings and embodiments. Attached Figure Description

[0021] To more clearly illustrate the specific embodiments of the present invention or the technical solutions in the prior art, the accompanying drawings used in the description of the specific embodiments or the prior art will be briefly introduced below. In all the drawings, similar elements or parts are generally identified by similar reference numerals. In the drawings, the elements or parts are not necessarily drawn to scale.

[0022] Figure 1 This is a schematic diagram of a traditional VCSEL laser; Figure 2 This is a schematic diagram of the VCSEL laser according to the first embodiment of the present invention; Figure 3 This is a schematic diagram of the surface lens according to the first embodiment of the present invention; Figure 4This is the present invention. Figure 3 A diagram from another perspective; Figure 5 This is the present invention. Figure 4 AA section view; Figure 6 This is a schematic diagram of the surface lens according to the second embodiment of the present invention; Figure 7 This is the present invention. Figure 6 AA section view; Figure 8 This is a diagram showing the output light field distribution of the fundamental mode and higher-order modes of a traditional VCSEL. Figure 9 These are the light field distribution diagrams of the fundamental mode and higher-order modes of this invention; Figure 10 This is a magnified view of the output fundamental mode and higher-order mode optical field distribution of a traditional VCSEL; Figure 11 This is an enlarged view of the optical field distribution of the fundamental mode and higher-order modes of the present invention.

[0023] The image shows: 100. Laser; 10. VCSEL substrate; 101. Substrate; 102. N-type DBR section; 103. N-electrode; 104. Active region layer; 105. P-type DBR section; 106. P-electrode; 107. Surface lens; 108. h-BN thin film; 1070, First lens layer; 1071, Second lens layer; 1072, Third lens layer; 1073, Fourth lens layer; 1074, Fifth lens layer; 1075, Sixth lens layer; 1076, Oxide layer. Detailed Implementation

[0024] The embodiments of the technical solution of the present invention will now be described in detail with reference to the accompanying drawings. These embodiments are merely illustrative of the technical solution of the present invention and are therefore intended to limit the scope of protection of the present invention.

[0025] It should be noted that, unless otherwise stated, the technical or scientific terms used in this application should have the ordinary meaning as understood by one of ordinary skill in the art to which this invention pertains.

[0026] In the description of this application, it should be understood that the terms "center", "longitudinal", "lateral", "length", "width", "thickness", "upper", "lower", "front", "rear", "left", "right", "vertical", "horizontal", "top", "bottom", "inner", "outer", "clockwise", "counterclockwise", "axial", "radial", "circumferential", etc., indicating the orientation or positional relationship are based on the orientation or positional relationship shown in the accompanying drawings, and are only for the convenience of describing the present invention and simplifying the description, and are not intended to indicate or imply that the device or element referred to must have a specific orientation, or be constructed and operated in a specific orientation, and therefore should not be construed as a limitation of the present invention.

[0027] Furthermore, the terms "first," "second," etc., 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. In the description of this invention, "a plurality of" means two or more, unless otherwise explicitly defined.

[0028] In this application, unless otherwise expressly specified and limited, the terms "installation," "connection," "linking," and "fixing," etc., should be interpreted broadly. For example, they can refer to a fixed connection, a detachable connection, or an integral part; they can refer to a mechanical connection or an electrical connection; they can refer to a direct connection or an indirect connection through an intermediate medium; they can refer to the internal communication of two components or the interaction between two components. Those skilled in the art can understand the specific meaning of the above terms in this invention according to the specific circumstances.

[0029] In this application, unless otherwise expressly specified and limited, "above" or "below" the second feature can mean that the first feature is in direct contact with the second feature, or that the first feature is in indirect contact with the second feature through an intermediate medium. Furthermore, "above," "on top of," and "over" the second feature can mean that the first feature is directly above or diagonally above the second feature, or simply that the first feature is at a higher horizontal level than the second feature. "Below," "below," and "under" the second feature can mean that the first feature is directly below or diagonally below the second feature, or simply that the first feature is at a lower horizontal level than the second feature.

[0030] VCSEL is a semiconductor laser structure in which an optical resonant cavity is formed perpendicular to the semiconductor epitaxial wafer, and the emitted laser beam is perpendicular to the substrate surface. It is widely used in consumer electronics, military, medical and other fields, such as 3D sensing, AR / VR, robotics, LiDAR, smart manufacturing, IoT, data centers, etc. Specific applications include autonomous driving, video surveillance, LiDAR, machine vision, gesture recognition, facial recognition and other fields.

[0031] See attached document Figure 1As shown, in one embodiment, the semiconductor laser light-emitting structure may include an N-type DBR portion 102, an active region layer 104, and a P-type DBR portion 105 on a substrate 101. The semiconductor laser light-emitting structure may include a III-V compound semiconductor material. For example, the semiconductor laser light-emitting structure may include a GaAs-based compound semiconductor material. For example, the semiconductor laser light-emitting structure may include at least one of GaInP, AlGaInP, GaAs, GaInAs, AlGaAs, and AlGaInAs.

[0032] As an example embodiment, substrate 101 may be a semiconductor substrate 101. For example, a Si substrate, a GaAs substrate, or the like may be used as the substrate. If necessary, a buffer layer and a seed layer, in which the material for forming the semiconductor laser light-emitting structure is lattice-matched with that of substrate 101, may be provided between substrate 101 and the semiconductor laser light-emitting structure.

[0033] The active region layer 104 may include one or more quantum wells or quantum dots.

[0034] The N-electrode 103 can be disposed on a portion of the N-type DBR section 102. The active region layer 104 can be disposed in a region of the N-type DBR section 102 not occupied by the N-electrode 103. The P-electrode 106 can be disposed on a portion of the P-type DBR section 105.

[0035] Figure 2 The semiconductor laser shown is merely an example, and the scope of the invention is not limited thereto. Figure 2 The limitations of semiconductor lasers are illustrated. Semiconductor lasers may include... Figure 2 Various additional components / layers not shown.

[0036] In an example embodiment, the laser 100 has a surface lens 107. For example, a semiconductor laser may have a VCSEL chip that generates laser light, and the surface lens 107 is provided at the light emission point of the VCSEL chip.

[0037] In an example embodiment, a surface lens 107 is disposed on the light output side of the active region layer 104. For example, on the side of the active region layer 104 opposite to the N-type DBR portion 102, the surface lens 107 can be used as an uplight shaper for the cavity forming the VCSEL by pairing with the P-type DBR portion 105.

[0038] The inventors of this application have continued their research on how to effectively solve the problems of large beam divergence, poor heat dissipation, and complex manufacturing processes inherent in VCSEL chip structures. Their research includes at least: how to focus the beam emitted by the VCSEL using a surface lens 107 structure, and how to incorporate a heat dissipation structure on the surface lens 107. This application integrates the focusing structure of the surface lens 107 with the heat dissipation structure of the h-BN thin film 108 into the PDBR section of the VCSEL, thereby improving beam focusing performance while constructing an efficient heat dissipation channel. After extensive and repeated research, the inventors present the VCSEL chip and laser of this application.

[0039] Before describing the embodiments of the present invention in detail, the design concept of the present invention will be summarized below. (Refer to the appendix.) Figure 3 As shown, this invention designs a VCSEL chip, which includes a VCSEL substrate 10, a surface lens 107, and an h-BN thin film 108. The refractive index of the surface lens 107 is set to gradually change from bottom to top, so that the light beam is more focused when passing through the surface lens 107, reducing the beam divergence angle and improving the beam quality of the VCSEL. Then, the light beam enters the h-BN thin film 108 from the surface lens 107. The h-BN thin film 108 can dissipate the heat generated by the focused light beam to the outside, reducing the temperature generated during operation. This effectively enhances the reliability and stability of the VCSEL and can meet the needs of high-power and high-precision application scenarios.

[0040] See attached document Figure 2 As shown, an embodiment of the present invention provides a VCSEL chip, which includes: a VCSEL substrate 10; Surface lens 107 is disposed on the light-emitting surface of the VCSEL substrate 10; h-BN thin film 108 is disposed on the side of the surface lens 107 away from the VCSEL substrate 10; The refractive index of the surface lens 107 gradually increases from bottom to top, and is used for focusing the beam spot.

[0041] Understandably, in this embodiment, a surface lens 107 with a gradually changing refractive index is formed on the VCSEL substrate 10 through a growth process. The surface lens 107 reduces the beam divergence angle of the VCSEL and improves the concentration of light energy. Simultaneously, an h-BN film 108 is formed on top of the surface lens 107, covering the side of the surface lens 107 away from the VCSEL substrate 10. The h-BN film 108 effectively achieves efficient heat dissipation, reducing the impact of heat generated during VCSEL operation.

[0042] In this embodiment, a surface lens 107 is provided on the top of the VCSEL substrate 10. The surface lens 107 has a beam focusing function through a gradient refractive index, which can efficiently focus the diverging beam emitted by the VCSEL, converge the beam into a smaller spot, and significantly reduce the beam divergence angle.

[0043] In this embodiment, by growing a surface lens 107 on the VCSEL substrate 10, and the refractive index of the surface lens 107 gradually increases from bottom to top, the quality of the light beam is effectively improved. Furthermore, by depositing an h-BN thin film 108 on the surface lens 107, the heat generated by the VCSEL can be dissipated, while simultaneously protecting the oxide layer of the VCSEL.

[0044] In this embodiment, the h-BN film 108, with its high thermal conductivity (400-600 W / (m·K)), can quickly dissipate the heat generated during the focusing process and the heat conducted from the active region. Simultaneously, the h-BN film 108 exhibits good optical transparency in the visible and near-infrared bands, while showing minimal absorption loss at the VCSEL output, thus not affecting beam quality, and also protecting the underlying oxide structure.

[0045] In this embodiment, the lattice of the h-BN thin film 108 can be selected as an AlGaAS lattice structure. This lattice structure can effectively reduce the overall surface stress of the thin film. The h-BN thin film 108 is deposited on the surface lens 107 by physical vapor deposition (PVD) or chemical vapor deposition (CVD).

[0046] See attached document Figure 3 As shown in the embodiment, the surface lens 107 has a stepped structure. The stepped structure has multiple steps on the outer surface of the surface lens 107. By combining the stepped structure with the gradually changing refractive index from bottom to top, the diverging beam emitted by the VCSEL can be effectively focused, converging the beam into a smaller spot and significantly reducing the beam divergence angle.

[0047] In actual operation, the VCSEL emits a light beam, which then enters the surface lens 107. Since the refractive index of the surface lens 107 gradually changes from bottom to top, the light beam becomes more focused when passing through the surface lens 107, reducing the beam divergence angle and improving the beam quality of the VCSEL. The light beam then enters the h-BN film 108 from the surface lens 107. The h-BN film 108 can dissipate the heat generated by the focused light beam to the outside, reducing the temperature generated during operation. This effectively enhances the reliability and stability of the VCSEL, meeting the needs of high-power and high-precision applications.

[0048] See attached document Figure 4 and 5 As shown in the embodiment, the outer surface of the surface lens 107 is provided with an oxide layer 1076.

[0049] Understandably, by using a wet oxidation process to form an oxide layer 1076 on the outer surface of the surface lens 107, and the refractive index of the oxide layer 1076 in the surface lens 107 is lower than the refractive index of the unoxidized layer, the oxidation reduces the refractive index of the oxidized portion of the surface lens 107, and the refractive index of the lens layer in the surface lens 107 is gradually changed. This structural arrangement makes the light beam more focused when it is emitted from the surface lens 107.

[0050] In a further embodiment, the surface lens 107 is composed of multiple lens layers stacked together, and the lens layers are configured with a gradient refractive index, wherein the refractive index of the lens layer gradually decreases from the center to the edge.

[0051] Understandably, in order to focus the diverging beam emitted by the VCSEL, the embodiment is that the surface lens 107 is composed of multiple lens layers stacked together, the refractive index of the surface lens 107 gradually increases from bottom to top, and the refractive index at the edge position and the center position of the lens layer are different, thus increasing the focusing effect when the beam is emitted from the surface lens 107.

[0052] In some embodiments, the surface lens 107 is composed of 32 lens layers stacked together, and the refractive index of the 32 lens layers gradually increases from bottom to top, and the refractive index of each lens layer gradually decreases from the center to the edge; see attached figure. Figure 5 As shown, in other embodiments, the surface lens 107 is composed of 30 lens layers stacked together, and the refractive index of the 30 lens layers gradually increases from bottom to top. Furthermore, the refractive index of the center position and the edge position of the lens layer are different. That is, the refractive index of the oxidized part at the edge of the lens layer is lower than that of the unoxidized part due to changes in internal composition. Thus, at least two parts of a single lens layer have different refractive indices.

[0053] In a further embodiment, the refractive index of the lens layer near the edge is controlled to be 1.5-1.65; the refractive index of the lens layer near the center is controlled to be 2.8-3.4.

[0054] Understandably, in order to make the beam more focused, the embodiment stacks multiple lens layers to form the surface lens 107, and the refractive index of the lens layers increases from bottom to top, and the refractive index is controlled between 2.8 and 3.4; then, the outer surface of the surface lens 107 is oxidized by a wet oxidation process to obtain an oxide layer 1076, so that the refractive index of the edge of the lens layer is controlled between 1.5 and 1.65. In this embodiment, not only does the overall refractive index gradually change from bottom to top, but the refractive index of the edge of the lens layer is also different from that of the center. This embodiment can efficiently focus the diverging beam emitted by the VCSEL, converge the beam into a smaller spot, and significantly reduce the beam divergence angle.

[0055] In some embodiments, the surface lens 107 is composed of multiple lens layers, and the refractive index of the lens layers is set from bottom to top to 2.8-3.4, wherein the refractive index of the bottommost lens layer is 3, the refractive index of the topmost lens layer is 3.4, and the refractive index of the outer surface of the surface lens 107 after oxidation is 1.5; in other embodiments, the surface lens 107 is composed of multiple lens layers, and the refractive index of the lens layers is set from bottom to top to 2.8-3.4, wherein the refractive index of the bottommost lens layer is 2.8, the refractive index of the topmost lens layer is 3.1, and the refractive index of the outer surface of the surface lens 107 after oxidation is 1.65; in still other embodiments, the surface lens 107 is composed of multiple lens layers, and the refractive index of the lens layers is set from bottom to top to 2.8-3.4, wherein the refractive index of the bottommost lens layer is 2.8, the refractive index of the topmost lens layer is 3.2, and the refractive index of the outer surface of the surface lens 107 after oxidation is 1.6.

[0056] See attached document Figure 3 and 5 As shown in the embodiment, the stepped structure is configured such that the side of the surface lens 107 has multiple steps, and each step corresponds to each of the lens layers.

[0057] It is understood that the surface lens 107 is composed of multiple lens layers, and the side surface of the surface lens 107 has multiple steps. Specifically, each lens layer in the surface lens corresponds to a step. It can also be considered that the cross-section of each lens layer forming the surface lens 107 is different, and the cross-section of the lens layer in the surface lens 107 gradually decreases from bottom to top, and the side surface of the surface lens 107 forms a stepped structure.

[0058] For further explanation, please refer to the appendix. Figure 5 As shown, in order to enhance the beam focusing effect, this embodiment sets the outer surface of the surface lens 107 as a stepped structure surface; however, it is not excluded that, referring to the appendix... Figure 6 and 7 As shown, the outer surface of the surface lens 107 is set as a smooth surface.

[0059] In a further embodiment, the thickness of the h-BN thin film 108 is controlled to be 50-70 nm.

[0060] Understandably, by depositing a certain thickness of h-BN film 108 on the VCSEL substrate 10, the h-BN film 108 can quickly dissipate the heat generated by the VCSEL substrate 10 and the heat conducted from the active region; at the same time, it has good optical transparency in the visible and near-infrared bands, has minimal light absorption loss on the VCSEL substrate 10, does not affect the beam quality, and can also protect the underlying oxide layer.

[0061] In some embodiments, a surface lens 107 is disposed on the beam emitting surface of the VCSEL substrate 10. The surface lens 107 has a stepped structure and is a multi-layered surface lens 107. An h-BN film 108 with a thickness of 50 nm is disposed on the side of the surface lens 107 away from the VCSEL substrate 10. In other embodiments, a surface lens 107 is disposed on the beam emitting surface of the VCSEL substrate 10. The surface lens 107 has a stepped structure and is a multi-layered surface lens 107. An h-BN film 108 with a thickness of 70 nm is disposed on the side of the surface lens 107 away from the VCSEL substrate 10. In still other embodiments, a surface lens 107 is disposed on the beam emitting surface of the VCSEL substrate 10. The surface lens 107 has a stepped structure and is a multi-layered surface lens 107. An h-BN film 108 with a thickness of 60 nm is disposed on the side of the surface lens 107 away from the VCSEL substrate 10.

[0062] Based on the same inventive concept, refer to the appendix. Figure 2 As shown, a VCSEL laser is also disclosed, comprising: the VCSEL chip described in any one of the above.

[0063] For specific examples and explanations of the beneficial effects of the VCSEL laser described in this embodiment, please refer to the description of the VCSEL chip above, which will not be repeated here.

[0064] Based on the same inventive concept, a method for fabricating a VCSEL chip is also disclosed, the steps of which include: Step S001: VCSEL substrate 10 is obtained by growing on the substrate using epitaxial technology.

[0065] In one example, a VCSEL with a conventional structure is first grown using a VCSEL growth process.

[0066] For example: Select a high-quality GaAs substrate and place it sequentially into an ultrasonic cleaning tank containing acetone, alcohol, and deionized water for 15 minutes each to remove organic matter, oil, and particulate impurities from the substrate surface. After cleaning, dry the substrate with high-purity nitrogen gas. Molecular beam epitaxy (MBE) was used to grow N-type distributed beam bream (DBR), the active region, and P-type DBR sequentially on a cleaned GaAs substrate, according to the design. During the growth of the N-type DBR, AlGaAs layers with 90% Al content and GaAs layers with 0% Al content were alternately grown, with the thickness of each layer precisely controlled according to requirements (corresponding to one-quarter of the thickness at 850nm wavelength), resulting in 34 pairs of DBRs with high reflectivity. The active region employed a multi-quantum-well structure, growing five cycles of InGaAs quantum wells and GaAs barrier layers. The P-type DBR growth method was similar to that of the N-type DBR, but with P-type doping, resulting in 23 pairs of AlGaAs / GaAs layers.

[0067] Step S002: A surface lens 107 is grown on the top of a VCSEL substrate 10 using a molecular beam epitaxy process. The refractive index of the surface lens 107 is set to gradually change upward from the VCSEL substrate 10.

[0068] In a further embodiment, the surface lens 107 obtained by growing a molecular beam on the top of the VCSEL substrate 10 is: growing an AlGaAs layer with a gradient aluminum content in a predetermined area on the top of the VCSEL substrate 10 by a molecular beam epitaxy process, wherein the VCSEL substrate has a surface lens. The surface lens 107 has a multi-layer structure, and the refractive index of the multi-layer structure is set to gradually increase from the VCSEL substrate 10 upwards, with the refractive index controlled between 2.8 and 3.4.

[0069] Reference Appendix Figure 5 As shown in the embodiment, the multilayer structure further comprises multiple stacked lens layers, and the cross-sectional area of ​​the lens layers gradually decreases from VCSEL upwards, with the side surface of the surface lens 107 having a stepped structure. In the embodiment, the refractive index of the lens layers is controlled to a maximum of 3.4 and a minimum of 2.8. For example, in some embodiments, the first lens layer has a refractive index of 3.4 and the sixth lens layer has a refractive index of 2.8.

[0070] For example: In this embodiment, a circular stepped surface lens 107 is grown on top of a P-type DBR using molecular beam epitaxy (MBE) technology. By adjusting the parameters during growth, multiple AlGaAs layers with a gradient distribution of aluminum content are grown in a predetermined area.

[0071] Furthermore, the refractive index gradient was achieved by controlling the Al doping composition of each layer. Specifically, the refractive index of the lowest layer closest to the VCSEL was the lowest, gradually increasing as growth progressed upwards, with the highest refractive index of the highest layer furthest from the VCSEL. The refractive index of the surface lens 107 was controlled between 2.8 and 3.4. During the growth process, parameters such as growth temperature, beam current intensity, and time were strictly controlled to ensure the crystal quality and thickness uniformity of each layer.

[0072] For further explanation, please refer to the appendix. Figure 3 As shown, in order to enhance the beam focusing effect, this embodiment sets the outer surface of the surface lens 107 as a stepped structure surface; however, it is not excluded that, referring to the appendix... Figure 6 As shown, the outer surface of the surface lens 107 is set as a smooth surface.

[0073] Step S003: An h-BN thin film 108 is grown on top of the surface lens 107 to obtain a VCSEL with a lens.

[0074] The h-BN film 108, with its high thermal conductivity (400-600 W / (m·K)), can quickly dissipate the heat generated during the focusing process and the heat conducted from the active region. Simultaneously, the h-BN film 108 exhibits good optical transparency in the visible and near-infrared bands, while showing minimal absorption loss at the VCSEL output, thus not affecting beam quality, and also protecting the underlying oxide structure.

[0075] In this embodiment, the lattice of the h-BN thin film 108 can be selected as an AlGaAS lattice structure. This lattice structure can effectively reduce the overall surface stress of the thin film. The h-BN thin film 108 is deposited on the surface lens 107 by physical vapor deposition (PVD) or chemical vapor deposition (CVD).

[0076] In a further embodiment, the growth of the h-BN thin film 108 on the top of the surface lens 107 is performed using molecular beam epitaxy (MBE) to grow the h-BN thin film 108. Specific steps include: The VCSEL substrate 10 is placed in a molecular beam epitaxy (MBE) equipment, and the temperature is controlled within a certain range. Simultaneously, active atomic nitrogen or nitrogen free radicals are added to overcome the inertness of molecular nitrogen; Then, by controlling the molecular beam source, an h-BN thin film 108 of a predetermined thickness is grown on the top of the surface lens 107 of the VCSEL substrate 10.

[0077] In a further embodiment, the precisely controlled molecular beam source is a nitrogen-rich B / N molecular beam, and the B / N flux ratio is controlled at 0.01-0.1.

[0078] In a further embodiment, the growth rate of the h-BN film 108 is stably controlled at 0.1-0.5 Å / s during growth; and the thickness of the h-BN film 108 is controlled at 50-70 nm.

[0079] Understandably, to ensure the growth quality of the h-BN film 108 according to actual needs, the growth rate is maintained within a certain range. Simultaneously, to ensure the heat dissipation performance of the h-BN film 108, the thickness of the h-BN film 108 is maintained within a certain range. In some embodiments, the thickness of the h-BN film 108 is 60 nm; in other embodiments, the thickness is 50 nm; and in still other embodiments, the thickness is 70 nm.

[0080] For example: After placing the VCSEL into a molecular beam epitaxy (MBE) apparatus, the substrate temperature is precisely controlled within a range suitable for h-BN growth without damaging the VCSEL structure (especially the quantum well and doping distribution), typically between 400-600°C. Simultaneously, active atomic nitrogen or nitrogen radicals generated by a high-purity boron (B) solid source (e.g., using a high-temperature pyrolysis furnace) and a radio frequency (RF) plasma source are co-evaporated to overcome the inertia of molecular nitrogen. The B / N beam current ratio is precisely controlled, here slightly nitrogen-rich, to promote h-BN formation; the B / N beam current ratio is controlled at 0.01-0.1, and the growth rate is stably maintained at 0.1-0.5 Å / s until the h-BN film thickness reaches 50-70 nm.

[0081] In this embodiment, the crystal structure and growth mode of the h-BN thin film 108 are monitored in real time using in-situ monitoring techniques such as Reflection High Energy Electron Diffraction (RHEED) to ensure the acquisition of high-quality hexagonal boron nitride thin films.

[0082] Step S004: The VCSEL chip is oxidized using a wet oxidation method, and an oxide layer 1076 is obtained on the outer surface of the surface lens 107, so that the surface lens 107 has a beam focusing function, thus obtaining the VCSEL chip.

[0083] In a further embodiment, the oxidation of the outer surface of the surface lens 107 is performed by oxidizing the surface lens 107 with VCSEL using a wet oxidation process. During oxidation, the temperature of the oxidation furnace is raised to 190-220°C, and an oxidation solution is added to oxidize the surface lens 107 for a specified time.

[0084] In a further embodiment, the oxidation solution is H2O2:H3PO4:H2O = 1:1:12.

[0085] For example: A wet oxidation process is employed. The VCSEL substrate 10 with the prepared h-BN thin film 108 is placed in a wet oxidation furnace. An oxidation solution is prepared according to requirements, with a ratio of H2O2:H3PO4:H2O = 1:1:12. The furnace temperature is raised to 210°C to oxidize the lenses in the VCSEL substrate 10, and the oxidation time is controlled to 25 minutes. In this example, by strictly controlling the oxidation rate, the diameter of each unoxidized surface lens 107 is kept between 8-4 μm. After oxidation, the substrate is removed and rinsed thoroughly with deionized water to remove any residual oxidation solution, yielding the final VCSEL chip.

[0086] It should be noted that during the oxidation process, due to the different aluminum content in different regions of AlGaAs in the surface lens 107, the oxidation rate varies. As time goes by, the edge region of the surface lens 107 is gradually oxidized, eventually forming a gradient-type oxide layer 1076 of the focusing surface lens 107.

[0087] Experimental verification: According to the above preparation method, a surface lens 107 is finally obtained on the upper surface of the VCSEL. The surface lens 107 consists of six layers with an overall height of 60 nm. The refractive index of the outer surface of the surface lens 107 is 1.58 through oxidation. The specific data of each layer are shown in the table below:

[0088] In this experiment, the surface lens 107 comprises a first lens layer 1070 to a sixth lens layer 1075, forming a circular boss structure with a stepped outer surface. The sixth lens layer 1075, with the largest cross-sectional area, is in contact with the VCSEL, while the first lens layer 1070, with the smallest cross-sectional area, is furthest from the VCSEL. The refractive index gradually increases from the sixth lens layer 1075 to the first lens layer 1070. Simultaneously, through an oxidation process, the refractive index near the edge of the sixth lens layer 1075 to the first lens layer 1070 is 1.58, and the oxidation distance from the edge to the center is approximately 5-6 μm.

[0089] Then, the VCSEL chip with the above-mentioned graded refractive index surface lens 107 was compared with a traditional VCSEL chip. By observing the output light field distribution diagrams of the two, it can be seen that the VCSEL chip prepared by this method has a significantly better light spot focusing effect, as shown below: See attached document Figure 8 , 910 and 11 Figure 8 The output light field distribution diagrams for the fundamental mode and higher-order modes of a traditional VCSEL; Figure 9 Light field distribution diagrams of the fundamental mode and higher-order modes of the refractive index graded surface lens 107 on the VCSEL are set; Figure 10 A magnified view of the output fundamental mode and higher-order mode optical field distribution of a traditional VCSEL; Figure 11 Enlarged view of the fundamental and higher-order mode light field distributions of the VCSEL with a refractive index graded surface lens 107.

[0090] According to the appendix Figure 8 , 9 As can be seen from Figures 10 and 11, the VCSEL output beam with the addition of a focusing surface lens 107 reduces the beam diameter from 1.2µm to 0.6µm compared to a conventional VCSEL, demonstrating a significant focusing effect. In other words, compared to a conventional VCSEL, the VCSEL in this embodiment can reduce the beam divergence angle by more than 70% and shrink the beam size to one-quarter of its original size, effectively improving the concentration of light energy.

[0091] In this embodiment, the gradient distribution of aluminum content and the difference in wet oxidation rate of AlGaAs material are utilized to directly form a stepped surface lens 107 without photolithography, with a gradually changing refractive index from bottom to top. This overcomes the limitations of photolithography process and enables low-cost, high-precision fabrication of complex curved surface focusing structures.

[0092] The preparation method used in this example is highly compatible with existing VCSEL epitaxial growth, wet oxidation and other processes. It can be directly applied to existing production lines, reducing the use of photolithography equipment, lowering the cost and difficulty of technology upgrades, and has good prospects for industrial application.

[0093] In this embodiment, the VCSEL chip obtained by the above preparation method effectively integrates the surface lens 107 with focusing function and the h-BN thin film 108 with the VCSEL, ensuring the overall stability of the VCSEL chip device. In this embodiment, the surface lens 107, located at the light emission point of the VCSEL, can efficiently focus the diverging beam emitted by the VCSEL, converging the beam into a smaller spot and significantly reducing the beam divergence angle. Furthermore, the h-BN thin film 108 on the surface lens 107 rapidly dissipates the heat generated by the focused beam and the heat conducted from the active region, effectively reducing the impact of heat on the VCSEL.

[0094] Based on the same inventive concept, a method of using a laser is also disclosed, wherein the laser comprises the aforementioned VCSEL chip.

[0095] For example, this VCSEL chip can be used in fields such as planar lenses, holographic optics, autonomous driving, remote sensing, ultra-high resolution imaging, beam generation, and polarization devices.

[0096] For specific examples and explanations of the beneficial effects of the method described in this embodiment, please refer to the above description of the saturated absorber, which will not be repeated here.

[0097] Obviously, those skilled in the art can make various modifications and variations to this invention without departing from its spirit and scope. This disclosure is not limited to the precise structures described above and shown in the accompanying drawings, and various modifications and changes can be made without departing from its scope. The scope of this disclosure is limited only by the appended claims. Thus, if these modifications and variations of the invention fall within the scope of the claims of the invention and their equivalents, the invention is also intended to include these modifications and variations.

Claims

1. A method for fabricating a VCSEL chip, characterized in that the steps include... include: VCSEL substrates were obtained by growing on a substrate using epitaxial technology; A surface lens is obtained on top of a VCSEL substrate using a growth process, wherein the refractive index of the surface lens gradually changes upward from the VCSEL substrate; An h-BN thin film is grown on top of the surface lens to obtain a VCSEL with a lens. A wet oxidation method is used to oxidize the VCSEL, and an oxide layer is obtained on the outer surface of the surface lens, which enables the surface lens to have a beam focusing function, thus obtaining a VCSEL chip.

2. The preparation method according to claim 1, characterized in that, The method of obtaining a surface lens on the top of a VCSEL substrate using molecular beam epitaxy involves growing an AlGaAs layer with a gradient aluminum content in a predetermined region on the top of the VCSEL substrate using a molecular beam epitaxy process, thereby creating a surface lens on the VCSEL substrate. The surface lens has a multilayer structure, and the refractive index of the multilayer structure increases layer by layer from the VCSEL substrate upwards.

3. The preparation method according to claim 2, characterized in that, The multilayer structure comprises multiple lens layers stacked together, and the cross-sectional area of ​​the lens layers decreases progressively from VCSEL upwards, with the side surface of the surface lens exhibiting a stepped structure.

4. The preparation method according to claim 1, characterized in that, The process of growing an h-BN thin film on top of the surface lens involves placing the VCSEL substrate into a molecular beam epitaxy (MBE) equipment and controlling the temperature within a certain range. Adding reactive atomic nitrogen or nitrogen free radicals is used to overcome the inertness of molecular nitrogen. Then, by controlling the molecular beam source, an h-BN film of a predetermined thickness is grown on the top of the surface lens.

5. The preparation method according to claim 4, characterized in that, The controlled molecular beam source includes a nitrogen-rich B / N molecular beam, and the B / N flow ratio is controlled at 0.01-0.

1.

6. The preparation method according to claim 4, characterized in that, During the growth of the h-BN film, the growth rate is stably controlled at 0.1-0.5 Å / s.

7. The preparation method according to claim 4, characterized in that, The thickness of the h-BN film is controlled at 50-70 nm.

8. The preparation method according to claim 1, characterized in that, The oxide layer on the outer surface of the surface lens is obtained by: oxidizing the surface lens with a VCSEL chip through a wet oxidation process, wherein the temperature of the oxidation furnace is raised to 190-220°C during oxidation, and an oxidation solution is added to oxidize the surface lens for a specified time.

9. The preparation method according to claim 8, characterized in that, The oxidation solution has a ratio of H2O2:H3PO4:H2O = 1:1:

12.

10. A laser, characterized in that, This includes preparing a VCSEL chip using any one of the preparation methods of claims 1-9.

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