Front light emitting vertical cavity surface emitting laser and preparation method thereof

Abstract

The invention relates to a front light-emitting vertical cavity surface emitting laser and a preparation method thereof. The laser comprises a substrate, a bottom reflector, a metal conductive channel, a current expansion layer, a hole injection layer, a light-emitting layer, an electron injection layer, a current limiting layer, a top reflector and a top electrode. The substrate is high in heat conduction and electric conduction, the bottom reflector is high in reflectivity, and the light-emitting layer is made of quantum dot materials with adjustable light-emitting wavelengths. The current limiting layer comprises a plurality of opening areas, and each corresponding independent bottom and top reflecting mirror forms a resonant cavity, so that independent control of a single laser is realized, and the threshold current is reduced. The metal conductive channel is connected with the resonant cavity and an external circuit, the area of the reflector is larger than that of the opening area, light leakage is reduced, light output power is improved, light beam quality is optimized, and threshold current is reduced. The preparation method comprises the processes of epitaxial growth, etching, metal filling, deposition, photoetching and the like, and planarization processing is carried out on the surface, so that uniform deposition of the functional layer is ensured, and the performance and the yield of the device are improved.

Description

Technical Field

[0001] The present application relates to the technical field of vertical cavity surface emitting lasers, and in particular to a front-emitting vertical cavity surface emitting laser and a preparation method thereof. Background Art

[0002] Amidst the ongoing advancements in laser technology, the Quantum Dot Vertical-Cavity Surface-Emitting Laser (VCSEL) is emerging as a promising new laser. Quantum dot VCSELs demonstrate advantages in key performance metrics such as low threshold current, temperature stability, and beam quality, representing a new direction in laser technology development. VCSEL-based technology utilizes a vertical resonant cavity to generate a high-quality, coherent beam, precisely controlling the beam divergence angle to within 10 degrees. Compared to traditional light sources, this improves beam collimation by approximately 80%. This advantage results in more concentrated photon propagation, reduces scattering losses, and effectively improves light energy utilization. Furthermore, its multimode oscillation characteristics, combined with dynamic phase modulation technology, effectively suppress speckle noise by over 98%, significantly improving image clarity and quality, and delivering a more realistic and detailed visual experience.

[0003] These innovative features not only redefine the performance standards for near-eye display systems but also, through deep integration with cutting-edge applications such as optical waveguide coupling and holographic imaging, bring new breakthroughs in immersive experiences to a variety of fields, including consumer electronics, industrial simulation, and medical visualization. In consumer electronics, such as AR / VR devices, quantum dot VCSEL technology helps improve display quality, reduce visual fatigue, and drive the development of thinner, lighter, and more efficient devices. However, despite the progress made in quantum dot VCSEL technology, its widespread application in optical communications, optical interconnects, biosensing, and other fields still faces pressing challenges. For example, in terms of fabrication processes, further improving the growth quality of quantum dot materials to achieve lower threshold currents and higher luminous efficiency is a current research focus. Furthermore, in device design, optimizing the vertical resonant cavity structure to improve beam quality and power output is a technical challenge that needs to be overcome. Furthermore, in terms of packaging technology, improving device reliability and stability and extending its lifespan are key factors hindering the large-scale commercialization of quantum dot VCSELs. Therefore, developing a quantum dot VCSEL with front-emitting light characteristics and its efficient preparation method are of great practical significance for promoting the further development and application of this technology. Summary of the Invention

[0004] The purpose of this application is to provide a front-emitting vertical cavity surface emitting laser and its fabrication method. By fabricating a bottom reflector, current spreading layer, and other functional layers with a specific structure on a highly thermally and electrically conductive substrate, and adjusting the cavity length in conjunction with the quantum dot emission wavelength to achieve electrical injection into the quantum dot VCSEL, the technical challenges associated with the fabrication and performance optimization of quantum dot VCSELs are addressed. This objective is achieved through the following technical solutions, specifically including a substrate, a bottom reflector, a metal conductive channel, a first current spreading layer, a hole injection layer, a light-emitting layer, an electron injection layer, a current confinement layer, a second current spreading layer, a top reflector, and a top electrode. The bottom reflector is formed on the substrate, and the first current spreading layer, the hole injection layer, the light emitting layer and the electron injection layer are stacked in sequence; In which, the current limiting layer is located between the electron injection layer and the second current expansion layer, and the current limiting layer includes multiple opening areas, each opening area has an independent corresponding bottom reflector and top reflector, the bottom reflector and the corresponding top reflector corresponding to the opening area serve as a resonant cavity of a laser, and the metal conductive channel is filled between the bottom reflectors.

[0005] In one embodiment, the areas of the top reflector and the bottom reflector are larger than the area of the corresponding opening region in the current confinement layer, and the projections of the top reflector and the bottom reflector on a plane completely cover the opening region.

[0006] In one embodiment, each of the resonant cavities includes a corresponding independent second current spreading layer, and an area of the second current spreading layer is larger than an area of the second current spreading layer corresponding to the top reflector.

[0007] In one embodiment, the upper surfaces of the bottom reflector and the metal conductive channel forming layer are flat surfaces.

[0008] In one embodiment, the bottom reflector comprises an air gap reflector or a grating reflector having the same size as the opening area.

[0009] The present application further provides a method for preparing a front-emitting vertical cavity surface emitting laser, comprising: Depositing various layers forming the bottom reflector on the substrate by epitaxial growth; Filling metal between the plurality of bottom reflectors to form a metal conductive channel; depositing a first current spreading layer; forming a hole injection layer, a light-emitting layer, and an electron injection layer in sequence on the first current spreading layer; forming a current limiting layer on the electron injection layer, wherein the current limiting layer includes a plurality of opening regions; forming a second current spreading layer; forming a top reflector on the second current spreading layer; forming a top electrode on the second current spreading layer; Each opening area has an independent corresponding bottom reflector and top reflector, and the bottom reflector and the top reflector corresponding to the opening area serve as a resonant cavity of a laser.

[0010] In one embodiment, the step of forming the bottom reflector includes patterning a material layer for forming the bottom reflector, and the step of forming the top reflector includes patterning a material layer for forming the top reflector.

[0011] In one embodiment, an area of the bottom reflector and an area of the top reflector are larger than an area of the opening region.

[0012] In one embodiment, the electron injection layer and the hole injection layer are formed by spraying or spin coating, and the quantum dot layer is formed as the light-emitting layer by inkjet printing, photolithography or spin coating.

[0013] Compared with the prior art, this application has the following beneficial effects: This application fabricates various functional layers, such as the bottom reflector and current spreading layer, with a specific structure on a highly thermally and electrically conductive substrate. The highly thermally conductive substrate can quickly conduct away the heat generated during laser operation, effectively reducing the device's operating temperature, improving its stability and reliability, and extending its service life. The highly conductive substrate ensures uniform current distribution and efficient transmission, reducing current losses during transmission and helping to lower the laser's power consumption.

[0014] The current-confining layer includes multiple openings, each with its own corresponding bottom and top reflectors, forming independent resonant cavities. This allows each laser to operate independently without interfering with each other, significantly improving the laser's integration and array capabilities. In practical applications, the light-emitting state of each resonant cavity can be flexibly controlled as needed, achieving diverse light-emitting modes to meet the needs of different scenarios. This ensures that light is fully reflected and amplified within the resonant cavity, minimizing light energy leakage and improving the laser's light output efficiency and beam quality.

[0015] The independent second current spreading layer provides uniform current injection into the corresponding resonant cavity, ensuring uniform emission from the quantum dot light-emitting layer and improving the laser's uniformity and stability. The flat top surface of the bottom reflector and the metal conductive channel formation layer facilitates uniform deposition of subsequent functional layers, reducing interlayer defects and stress concentration caused by surface unevenness, thereby improving the overall quality and reliability of the device.

[0016] The preparation method of the present application deposits the various layers of the bottom reflector by epitaxial growth, which can accurately control the structure and size of the bottom reflector to ensure the consistency of its performance. Metal is filled between multiple bottom reflectors to form a metal conductive channel, and the surface is flattened to provide a good foundation for the deposition of subsequent functional layers. The electron injection layer and the hole injection layer are formed by spraying or spin coating, and the quantum dot layer is formed as the light-emitting layer by inkjet printing, photolithography or spin coating. These methods have the advantages of simple process, low cost, and easy large-area preparation, which are conducive to reducing the production cost of the laser and promoting its large-scale commercial application. In summary, the front-emitting vertical cavity surface emitting laser and its preparation method of the present application have obvious advantages in improving the performance, stability and reliability of the laser, reducing power consumption and production costs, etc. through the combined effect of the above-mentioned technical features. BRIEF DESCRIPTION OF THE DRAWINGS

[0017] Figure 1 1 is a schematic structural diagram of a front-emitting vertical cavity surface emitting laser in one embodiment of the present application; Figure 2 This is a flow chart of a method for preparing a front-emitting vertical cavity surface emitting laser in one embodiment of the present application; Figure 3 This is a structural diagram of a method for preparing a front-emitting vertical cavity surface emitting laser in one embodiment of the present application; Figure 4 This is a schematic structural diagram of a single laser in a front-emitting vertical cavity surface emitting laser according to another embodiment of the present application; Figure 5 It is a schematic structural diagram of a single laser in a front-emitting vertical cavity surface emitting laser according to another embodiment of the present application.

[0018] Explanation of the accompanying drawings: 100, substrate; 210, bottom reflector; 220, metal conductive channel; 230, air gap reflector; 240, grating reflector; 300, first current spreading layer; 410, hole injection layer; 420, light-emitting layer; 430, electron injection layer; 500, current limiting layer; 600, second current spreading layer; 700, top reflector; 800, top electrode. DETAILED DESCRIPTION

[0019] In order to make the above-mentioned objects, features and advantages of the present application more obvious and easy to understand, the specific implementation methods of the present application are described in detail below in conjunction with the accompanying drawings. It will be understood that the specific embodiments described herein are only used to explain the present application, rather than to limit the present application. It should also be noted that, for ease of description, only some, rather than all, structures related to the present application are shown in the accompanying drawings. Based on the embodiments in the present application, all other embodiments obtained by ordinary technicians in this field without making creative work are within the scope of protection of this application.

[0020] As used herein, the terms "comprise," "comprising," and "having," and any variations thereof, are intended to cover non-exclusive inclusions. For example, a process, method, system, product, or apparatus comprising a series of steps or elements is not limited to the listed steps or elements but may optionally include steps or elements not listed, or may optionally include other steps or elements inherent to the process, method, product, or apparatus.

[0021] References to "embodiments" herein mean that a particular feature, structure, or characteristic described in connection with the embodiments may be included in at least one embodiment of the present application. The appearance of this phrase in various places in the specification does not necessarily refer to the same embodiment, nor does it constitute an independent or alternative embodiment that is mutually exclusive of other embodiments. It is understood, both explicitly and implicitly, by those skilled in the art that the embodiments described herein may be combined with other embodiments.

[0022] Vertical-cavity surface-emitting lasers (VCSELs) have achieved widespread application in optical communications, 3D sensing, and other fields due to their unique vertical light-emitting structure, ease of integration, and high modulation rate. Quantum dot VCSELs, a key offshoot, offer superior performance in terms of low threshold current, temperature stability, and beam quality, owing to the advantages of quantum dot materials, such as size-tunable luminescence properties, high quantum yield, and excellent temperature stability. This has opened up new opportunities for the development of laser technology. The high-quality, coherent beam generated by the vertical resonant cavity effectively controls the beam divergence angle, significantly improving beam collimation. Combining multimode oscillation with dynamic phase modulation technology significantly suppresses speckle noise, enhancing image clarity. However, despite the promising prospects of quantum dot VCSELs, achieving large-scale deployment and optimizing their performance remain challenging. These challenges include further improving the laser's light extraction efficiency, achieving more precise frontal light emission control, and optimizing the fabrication process to reduce costs and increase product yield. In this context, this application provides a front-emitting vertical cavity surface emitting laser and its preparation method, aiming to solve the problems existing in the prior art through a unique technical design. Next, this application will introduce in detail the specific structure of the front-emitting vertical cavity surface emitting laser and its preparation method. Figures 1 to 3The front-emitting vertical cavity surface emitting laser of the present application includes a substrate 100, a bottom reflector 210, a metal conductive channel 220, a first current spreading layer 300, a hole injection layer 410, a light-emitting layer 420, an electron injection layer 430, a current limiting layer 500, a second current spreading layer 600, a top reflector 700 and a top electrode 800, wherein the bottom reflector 210 is formed on the substrate 100, the first current spreading layer 300, the hole injection layer 410, the light-emitting layer 420 and the electron injection layer 430 are stacked in sequence, wherein the current limiting layer 500 is located between the electron injection layer 430 and the second current spreading layer 600, the current limiting layer 500 includes a plurality of opening areas, each opening area has an independent corresponding bottom reflector 210 and a top reflector 700, the bottom reflector 210 and the corresponding top reflector 700 corresponding to the opening area serve as a resonant cavity of a laser, and the metal conductive channel 220 is filled between the bottom reflector 210.

[0023] The bottom reflector 210 is formed on the substrate 100. The substrate 100 is made of a material with high thermal and electrical conductivity. The high thermal conductivity can quickly conduct away the heat generated during the operation of the laser, effectively reducing the operating temperature of the device and avoiding device performance degradation or even damage due to excessive temperature, thereby improving the stability and reliability of the laser and extending its service life. The high electrical conductivity provides a good channel for the transmission of current in the device, reducing losses during current transmission and helping to reduce the power consumption of the laser. As an important component of the resonant cavity, the bottom reflector 210's high reflectivity can repeatedly reflect light within the resonant cavity, enhancing the light gain and providing a basis for achieving laser emission.

[0024] The first current spreading layer 300, the hole injection layer 410, the light-emitting layer 420, and the electron injection layer 430 are stacked in sequence. The first current spreading layer 300 plays the role of evenly distributing the current, ensuring that the current can be evenly injected into the subsequent layers, avoiding device damage and uneven performance caused by local current concentration. The hole injection layer 410 is responsible for injecting holes into the light-emitting layer 420, and the electron injection layer 430 is responsible for injecting electrons into the light-emitting layer 420, forming carrier recombination in the light-emitting layer 420, thereby achieving light emission. The light-emitting layer 420 uses quantum dot materials. Quantum dots have size-adjustable light-emitting properties. By controlling the size of the quantum dots, the light-emitting wavelength can be precisely controlled to meet the specific wavelength requirements of different application scenarios. At the same time, the quantum dot material has a high quantum yield, which can convert more electrical energy into light energy, thereby improving the luminous efficiency of the laser.

[0025] The current limiting layer 500 is located between the electron injection layer 430 and the second current expansion layer 600. This is one of the key points of the laser structure of the present application. The current limiting layer 500 includes multiple opening areas, each of which has an independent corresponding bottom reflector 210 and top reflector 700. The bottom reflector 210 and the corresponding top reflector 700 corresponding to the opening area serve as a resonant cavity of a laser. On the one hand, it enables each laser to work independently without interfering with each other, greatly improving the integration and arraying capability of the laser. In practical applications, the light-emitting state of each resonant cavity can be flexibly controlled according to needs to achieve a variety of light-emitting modes to meet the needs of different scenarios. On the other hand, the current limiting layer 500 can effectively limit the distribution range of the current, so that the current is mainly concentrated in the light-emitting layer 420 corresponding to the opening area, improving the recombination efficiency of the carriers, further enhancing the light gain, reducing the threshold current of the laser, and enabling the laser to achieve laser emission at a lower current, thereby reducing power consumption.

[0026] The metal conductive channel 220 is filled between the bottom reflector 210 and serves to connect each resonant cavity with the external circuit. The metal conductive channel 220 has good conductivity and can ensure that the current is smoothly transmitted between each resonant cavity and between the resonant cavity and the external circuit, thereby ensuring the normal operation of the laser. At the same time, the presence of the metal conductive channel 220 also helps to improve the overall mechanical strength of the device and enhance the reliability of the device. The second current expansion layer 600 is located above the current limiting layer 500, and its function is to further expand the current and increase the injection density of carriers. The top reflector 700 and the bottom reflector 210 together constitute a resonant cavity. Its high reflectivity characteristics can further reflect and amplify light in the resonant cavity, achieve the same photon properties, and meet the conditions for laser output. The top electrode 800 is used to connect to the external circuit, provide operating voltage for the laser, and realize the drive and control of the laser.

[0027] In the further design of the front-emitting vertical cavity surface emitting laser of the present application, the areas of the top reflector 700 and the bottom reflector 210 are both larger than the area of the opening area in the corresponding current limiting layer 500. Moreover, when observed from a direction perpendicular to the plane where the functional layers are located, the projections of the top reflector 700 and the bottom reflector 210 on the plane can completely cover the opening area. In the resonant cavity of the laser, light needs to be reflected back and forth between the bottom reflector 210 and the top reflector 700 to achieve light gain. When the areas of the top reflector 700 and the bottom reflector 210 are larger than the area of the opening area in the corresponding current limiting layer 500, and their projections completely cover the opening area, it can ensure that the light emitted from the light-emitting layer 420 can be effectively reflected by the reflector in all directions, reducing the possibility of light leaking out from the edge of the opening area, so that more light can be fully reflected and amplified in the resonant cavity, thereby improving the light reflection efficiency, enhancing the light gain, and helping to increase the optical output power of the laser.

[0028] Since the reflector completely covers the opening area, the reflection path of light in the resonant cavity is more regular and stable, so that the light beam emitted by the laser can maintain good coherence and directionality during propagation, effectively optimizing the beam quality. At the same time, reducing the divergence of the light beam and lowering the beam divergence angle make the light beam emitted by the laser more concentrated and able to maintain a higher light intensity at a longer distance. This is of great significance for the application of lasers in optical communications, laser ranging and other fields. By improving the light reflection efficiency and optimizing the beam quality, the laser can achieve laser emission at a lower current, and more light can be amplified in the resonant cavity, so there is no need for excessively high current to excite enough photons to achieve laser oscillation, thereby reducing the threshold current of the laser. The reduction in threshold current means that at the same light output power, the laser has lower power consumption and higher luminous efficiency.

[0029] Each resonant cavity is equipped with a corresponding independent second current spreading layer 600, whose area is significantly larger than the area of the corresponding top reflector 700. The independent second current spreading layer 600 provides a dedicated current spreading path for each resonant cavity. Because the area of the second current spreading layer 600 is larger than that of the corresponding top reflector 700, the current can be evenly diffused over a larger area after reaching the second current spreading layer 600, avoiding localized current concentration at the edge of the top reflector 700 and enabling more uniform current injection into the light-emitting area of the resonant cavity. This uniform current injection ensures uniform carrier distribution within the light-emitting layer 420, thereby achieving uniform distribution of laser luminescence intensity. This improves the laser's emission uniformity, reduces bright or dark spots caused by uneven current distribution, and enhances the quality of the output beam. The larger area of the second current spreading layer 600 provides more space for light emitted from the light-emitting layer 420 to propagate and scatter before reaching the top reflector 700, helping more light reach the top reflector 700 at the appropriate angle and be reflected, thereby improving light extraction efficiency. Each resonant cavity is equipped with an independent second current expansion layer 600, so that each resonant cavity is independent of each other in current injection and light-emitting control, which provides convenience for array integration and independent control of lasers. The light-emitting state of each resonant cavity can be flexibly controlled according to actual needs to achieve diversified light-emitting modes.

[0030] In the structural design of the front-emitting vertical cavity surface emitting laser of the present application, the upper surface of the bottom reflector 210 and the metal conductive channel 220 forming layer can also be processed to make it present a flat surface. During the preparation process, the flattening technology is used to flatten the upper surface of the bottom reflector 210 and the metal conductive channel 220 forming layer to remove the protrusions, depressions and rough structures that may exist on the surface, ensuring that the entire upper surface is highly flat on a microscopic scale. During the preparation process of the laser, subsequent functional layers such as the first current spreading layer 300 and the hole injection layer 410 need to be deposited on the upper surface of the bottom reflector 210 and the metal conductive channel 220 forming layer. The flat surface can provide a uniform and stable deposition substrate 100 for these functional layers. When the surface is flat, the deposited material can be evenly covered on the surface, avoiding problems such as uneven deposition thickness and incomplete local coverage caused by surface unevenness, which helps to reduce the generation of interlayer defects such as voids and cracks.

[0031] When light propagates between the functional layers inside the laser, the flatness of the surface has a significant impact on the propagation path and loss of light. If the upper surface of the layer formed by the bottom reflector 210 and the metal conductive channel 220 is uneven, the light will encounter various irregular surface structures during the propagation process, causing light scattering. Scattering will change the propagation direction of some light, making it impossible to reflect and amplify in the resonant cavity according to the expected path, thereby increasing light loss. A flat surface can reduce the scattering of light, allowing light to propagate more smoothly between the functional layers, improving the reflection efficiency and gain of light, and thus improving the light output efficiency of the laser. A flat surface can ensure that current is evenly transmitted in the metal conductive channel 220, avoiding the situation of local current concentration or uneven distribution caused by surface unevenness. Uniform current distribution helps to reduce current loss during transmission. Good current distribution can also ensure that each functional layer can evenly receive current, improve the injection efficiency and recombination efficiency of carriers, and further optimize the performance of the laser. During actual production, the flatness of the upper surface of the layer forming the bottom reflector 210 and the metal conductive path 220 directly impacts the manufacturing yield of the laser. An uneven surface can easily lead to problems such as poor deposition of subsequent functional layers and unstable device performance, thereby increasing scrap rates and production costs. Achieving a flat surface can reduce adverse factors in the production process, improve device consistency and reliability, and thus increase manufacturing yield. This not only helps reduce the production cost of individual devices, but also improves production efficiency and meets the needs of large-scale production.

[0032] Please see further Figures 4 and 5Specifically, the bottom reflector 210 can also use an air-gap reflector 230 or a grating reflector 240 that precisely matches the size of the opening area in the current confinement layer 500. For the air-gap reflector 230, by controlling the material deposition and etching processes in specific areas, an air gap structure of a specific height and width is formed between adjacent reflective layers. The size of these air gaps is consistent with the size of the opening area. The grating reflector 240, on the other hand, uses photolithography and etching techniques to create a grating structure with a specific period, duty cycle, and depth on the surface of the reflective layer. The size of the grating is also exactly the same as the size of the opening area. The sizes of the air-gap reflector 230 and the grating reflector 240 are the same as the size of the opening area, which can accurately control the light field distribution and mode characteristics within the resonant cavity. The refractive index difference between the air and the surrounding medium in the air-gap reflector 230 is large, and light will be strongly reflected at the air gap. By precisely designing the size of the air gap, light of a specific wavelength and mode can be effectively screened for oscillation and amplification within the resonant cavity, achieving laser output. The grating reflector 240 utilizes the diffraction effect of the grating. Only light that meets specific wavelength and angle conditions can form a stable oscillation mode in the resonant cavity. Since the grating size is consistent with the opening area size, it can ensure that the light field in the resonant cavity matches the grating structure, further enhancing the mode selection capability. It has important application value in optical communications, spectral analysis and other fields, and can improve the accuracy and resolution of signal transmission.

[0033] By using an air gap reflector 230 or a grating reflector 240 with the same size as the opening area, the size and structure of the resonant cavity can be controlled, allowing the laser to achieve a smaller size while maintaining high performance. This is beneficial for the application of lasers in fields with high space requirements, such as optoelectronic integrated chips, and improves the integration of the device. In arrayed lasers, the same reflector size design makes the structure of each laser unit more consistent, facilitating large-scale integration and packaging. At the same time, because the reflector can control the resonant cavity mode and reflection characteristics, the mutual interference between the units can be reduced during the integration process, improving the overall performance and reliability of the arrayed laser.

[0034] See also Figure 2The present application further provides a method for preparing a front-emitting vertical cavity surface emitting laser, comprising: depositing various layers of a bottom reflector 210 on a substrate 100 by epitaxial growth; filling metal between a plurality of the bottom reflectors 210 to form a metal conductive channel 220; depositing a first current spreading layer 300; forming a hole injection layer 410, a light-emitting layer 420, and an electron injection layer 430 in sequence on the first current spreading layer 300; forming a current limiting layer 500 on the electron injection layer 430, wherein the current limiting layer 500 includes a plurality of opening areas; forming a second current spreading layer 600; forming a top reflector 700 on the second current spreading layer 600; forming a top electrode 800 on the second current spreading layer 600; wherein each opening area has an independently corresponding bottom reflector 210 and a top reflector 700, and the bottom reflector 210 and the corresponding top reflector 700 of the opening area serve as a resonant cavity of a laser.

[0035] The method specifically includes the following steps: Selecting a suitable substrate 100 material with high thermal conductivity, good lattice matching, and stable physical and chemical properties. Using techniques such as photolithography, the substrate is patterned and then placed in a molecular beam epitaxy (MBE) or metal-organic chemical vapor deposition (MOCVD) apparatus. By controlling epitaxial growth parameters such as temperature, gas flow rate, and growth rate, the various layers of the bottom reflector 210 are sequentially deposited. These layers typically consist of alternating semiconductor materials with different refractive indices to achieve high reflectivity and complete epitaxial growth.

[0036] In the gaps between the prepared bottom reflectors 210, metal materials such as gold (Au) and aluminum (Al) are deposited using methods such as physical vapor deposition (PVD) or chemical vapor deposition (CVD). By controlling the deposition parameters, the metal material is uniformly filled between the bottom reflectors 210, forming a low-resistance metal conductive channel 220. The surface after filling can be treated to ensure surface flatness, providing a completely flat substrate 100 for the deposition of subsequent functional layers. The treated substrate 100 is then placed back into the epitaxial growth apparatus, and the first current spreading layer 300 is deposited via epitaxial growth. This layer is typically made of a semiconductor material with high conductivity and good transparency. During the growth process, the growth conditions are controlled to ensure that the thickness and doping concentration of the first current spreading layer 300 are uniform, thereby achieving uniform current spreading in the horizontal direction.

[0037] The hole injection layer 410, the light-emitting layer 420, and the electron injection layer 430 are formed in sequence: thin films are prepared on the first current spreading layer 300 in a specific order to form the hole injection layer 410, the light-emitting layer 420, and the electron injection layer 430, respectively. The hole injection layer 410 is usually made of a material with high hole mobility. The light-emitting layer 420 is the core light-emitting region of the laser. Structural materials such as quantum dots are selected. By controlling their size and composition, the emission wavelength can be controlled. The electron injection layer 430 is made of a material with high electron mobility to efficiently inject electrons into the light-emitting layer 420. During the growth process, parameters such as the growth temperature, gas flow rate, and growth rate of each layer are controlled to ensure good interface quality between the layers and reduce the generation of defects and impurities.

[0038] On the electron injection layer 430, a current limiting layer 500 is formed by photolithography. First, the pattern of the current limiting layer 500 is defined on the surface of the electron injection layer 430 by a photolithography process, and then the current limiting layer 500 is prepared by epitaxial growth, including multiple opening areas on the electron injection layer 430. The size and position of these opening areas should be controlled according to the design requirements of the laser to ensure that each opening area has an independent corresponding bottom reflector 210 and top reflector 700 to form an independent resonant cavity structure. The material of the current limiting layer 500 is usually a semiconductor material with a high resistivity. Its function is to limit the lateral expansion of the current, so that the current is concentrated in the light-emitting layer 420 corresponding to the opening area, thereby improving the carrier recombination efficiency and the lateral light field limiting capability.

[0039] After forming the current confining layer 500, a second current spreading layer 600 is deposited using an epitaxial growth method similar to that used for the first current spreading layer 300. The material selection and growth conditions for this layer should match those of the first current spreading layer 300 to ensure uniform current spreading in the vertical direction. Simultaneously, by optimizing the growth process, a good ohmic contact is formed between the second current spreading layer 600 and the current confining layer 500, reducing contact resistance and improving current injection efficiency. A top reflector 700 is formed on the second current spreading layer 600 using an epitaxial growth process similar to that used for the bottom reflector 210. The number of layers, material composition, and thickness of the top reflector 700 should be controlled according to the laser design requirements to achieve a high reflectivity that matches that of the bottom reflector 210. During the growth process, the growth quality of each layer is controlled to ensure the surface flatness and good optical performance of the top reflector 700. Finally, the top electrode 800 material, such as titanium (Ti) / gold (Au) alloy, is deposited on the top reflector 700 by electron beam evaporation or sputtering, and the top electrode 800 is patterned through photolithography and etching processes to form an electrode structure that matches the laser array.

[0040] By controlling process parameters such as epitaxial growth, the dimensions and performance of key structures such as the bottom reflector 210, top reflector 700, and current limiting layer 500 of each laser unit can be ensured to be highly consistent. This makes the characteristics of each resonant cavity the same, thereby improving the consistency of performance parameters such as output power, wavelength, and threshold current of each laser unit in the entire laser array. Using epitaxial growth to deposit each functional layer in sequence can ensure good interface quality between each layer and reduce the generation of interface defects and impurities. This helps to reduce carrier recombination losses at the interface and improve carrier injection efficiency and recombination efficiency. At the same time, the current limiting layer 500 can limit the distribution range of the current, so that the current is concentrated in the light-emitting layer 420, thereby enhancing the carrier injection efficiency. The high reflectivity characteristics of the top reflector 700 and the bottom reflector 210 can repeatedly reflect and amplify light in the resonant cavity, further improving the light output efficiency and enabling the laser to output a higher power beam.

[0041] The low resistance characteristics of the metal conductive channel 220 can reduce the loss of current during transmission and reduce the internal resistance of the device. At the same time, the uniform current expansion layer can ensure the uniform distribution of current in the device, avoiding the increase in resistance and heat caused by local concentration of current. In addition, by optimizing the materials and structures of each functional layer, the probability of non-radiative recombination of carriers is reduced, and the energy loss in the form of heat is reduced, thereby reducing the power consumption of the laser and improving energy utilization efficiency. The light-emitting layer 420 uses structural materials such as quantum dots, and by controlling its size and composition, it can achieve precise control of the light-emitting wavelength. During the preparation process, strict epitaxial growth process control can ensure the uniformity and consistency of the light-emitting layer 420 material, thereby ensuring that the light-emitting wavelength of each laser unit meets the design requirements.

[0042] Specifically, the step of forming the bottom reflector 210 includes patterning the material layer forming the bottom reflector 210, and the step of forming the top reflector 700 includes patterning the material layer forming the top reflector 700. A uniform layer of photoresist with a precise thickness is applied to the surface of the selected substrate 100. Light of a specific wavelength is then used to expose the photoresist through a mask, transferring the pattern on the mask to the photoresist. Epitaxial growth conditions are controlled according to design requirements, and the various material layers that comprise the bottom reflector 210 are sequentially deposited. These layers are typically formed by alternating stacks of semiconductor materials with different refractive indices. Parameters such as the thickness, composition, and growth temperature of each layer are controlled to ensure that each layer has the desired optical and electrical properties. After the material layers are deposited, the exposed or unexposed portions (depending on the type of photoresist) of the photoresist are removed through a development process, ultimately forming the bottom reflector 210 with a specific shape, size, and structure.

[0043] Similarly, the steps for forming the top reflector 700 use a similar process. After completing the preparation of other functional layers (such as the second current spreading layer 600, the current limiting layer 500, etc.), the material layers required for the top reflector 700 are epitaxially grown on the corresponding structure. Semiconductor materials with different refractive indices are also grown alternately to achieve high reflectivity. Finally, after the development and degumming process, the top reflector 700 that matches the bottom reflector 210 and meets the laser design requirements is obtained.

[0044] By patterning the material layers of the bottom reflector 210 and the top reflector 700, the size, shape, and position of each resonant cavity can be controlled, allowing multiple independent laser units to be integrated on a single chip. Each unit has an independent bottom reflector 210 and top reflector 700, forming an independent resonant cavity. This structure greatly improves the integration of the device and reduces the device volume. At the same time, the independent resonant cavity structure can reduce the optical and electrical interference between adjacent laser units, improving the performance stability and consistency of each laser unit. The specific shape and size of the bottom reflector 210 and the top reflector 700 formed by the patterning process can precisely control the light field distribution within the resonant cavity, enabling the light to form a stable light field mode within the resonant cavity and reducing the distortion and loss of the light field. For example, using a reflector with a regular pattern such as a circle or square can make the light field uniformly distributed within the resonant cavity, improve the reflection efficiency and gain of the light, and thus enhance the output power and beam quality of the laser. Furthermore, patterning can also create specialized reflector structures, such as the periodic structure in a distributed Bragg reflector (DBR), further optimizing the reflector's optical performance and improving the laser's monochromaticity and directionality. The reflector structure formed through patterning can optimize the current distribution within the resonant cavity, allowing for more concentrated current injection into the light-emitting region. This improves carrier injection and recombination efficiency, further reducing device power consumption.

[0045] In the structural design of a front-emitting vertical cavity surface emitting laser, the areas of the bottom reflector 210 and the top reflector 700 are both larger than the area of the opening in the current confinement layer 500. The larger areas of the bottom reflector 210 and top reflector 700 mean more reflective surfaces participate in the light reflection process. When light reflects back and forth within the resonant cavity, the larger reflector area can more effectively reflect light back to the light-emitting area, reducing light leakage losses. The larger area of the bottom reflector 210 than the opening area allows for better coordination with the underlying current spreading layer and metal conductive channel 220, ensuring uniform current distribution within the area covered by the bottom reflector 210. During the laser fabrication process, certain process errors, such as photolithography deviations, are inevitable. When the areas of the bottom reflector 210 and top reflector 700 are larger than the opening area, the impact of these process errors on laser performance is relatively reduced. As long as the offset is within the range allowed by the reflector area being larger than the opening area, the laser will still function properly because the larger reflector area ensures sufficient reflective surfaces to maintain the function of the resonant cavity. The laser's requirements for process precision are reduced, and the device's production yield is improved.

[0046] In the preparation process of the front-emitting vertical cavity surface emitting laser, targeted process methods are adopted for the formation of different functional layers. For the preparation of the electron injection layer 430 and the hole injection layer 410, spraying or spin coating is adopted. The spraying method is to spray the solution containing the electron injection layer 430 or the hole injection layer 410 material evenly in the form of fine droplets on the surface of the prepared previous layer structure through a spray gun with a specific pressure. During the spraying process, by controlling the parameters such as the movement speed of the spray gun, the spraying distance and the flow rate of the solution, it is ensured that the solution can evenly cover the entire target area, forming an electron injection layer 430 or hole injection layer 410 with uniform thickness. The spin coating method involves dropping an appropriate amount of electron injection layer 430 or hole injection layer 410 material solution onto the surface of a substrate 100 placed on a spin coater. The spin coater is then activated, causing the substrate 100 to spin at a high speed. Under the action of centrifugal force, the solution quickly spreads across the surface of the substrate 100 and forms a uniform thin film. By controlling parameters such as the spin coating speed, spin coating time, and solution concentration, the thickness of the formed layer can be controlled. For the preparation of the light-emitting layer 420, quantum dots are selected as the material for the light-emitting layer 420. The quantum dot layer is formed using inkjet printing, photolithography, or spin coating.

[0047] Both the spray coating method and the spin coating method can make the electron injection layer 430 and the hole injection layer 410 materials uniformly distributed on the surface of the substrate 100. By precisely controlling the process parameters during the spray coating or spin coating process, the thickness of the electron injection layer 430 and the hole injection layer 410 can be controlled. The spray coating method and the spin coating method are both relatively simple and mature process methods that do not require complex equipment and expensive raw materials. Compared with some high-precision vacuum deposition processes, these two methods have the advantages of low cost and simple operation, and are suitable for application in large-scale production. In industrial production, the use of spray coating or spin coating methods can quickly and efficiently prepare a large number of electron injection layers 430 and hole injection layers 410, reducing production costs and improving production efficiency.

[0048] Inkjet printing and photolithography methods can achieve precise patterning of the quantum dot layer. In a front-emitting vertical cavity surface emitting laser, it may be necessary to prepare a light-emitting layer 420 with a specific pattern according to different design requirements, such as forming an array structure to achieve multi-channel laser output, or preparing a light-emitting area with a special shape to optimize the light field distribution. The high-precision patterning capabilities of inkjet printing and photolithography methods can meet these complex design requirements and provide possibilities for functional expansion and performance improvement of lasers. Inkjet printing, photolithography and spin coating methods all have high process flexibility and can adapt to quantum dot material systems of different types and properties. Whether it is oil-soluble quantum dots or water-soluble quantum dots, high-quality quantum dot layer preparation can be achieved by adjusting the process parameters. Specific embodiments Some specific implementation methods will be further introduced below to further explain the technical solution of this application in detail.

[0050] First, the bottom reflector is deposited and fabricated on a substrate. The selected substrate material must possess excellent electrical and thermal conductivity to meet the current transmission and heat dissipation requirements of the laser during operation. Common substrate materials include silicon and gallium nitride. The reflectivity of the bottom reflector is a key indicator of laser performance, requiring a reflectivity greater than 99.9% to ensure efficient light reflection within the resonant cavity and minimize optical losses. There are a variety of bottom reflectors, including but not limited to dielectric film distributed Bragg reflectors (DBRs), nitride DBRs, gratings, and air-gap DBRs. Material selection can be tailored to the reflector type and performance requirements. For example, common dielectric film DBR material combinations include titanium dioxide (TiO2) / silicon dioxide (SiO2) and hafnium dioxide (HfO2) / silicon dioxide (SiO2); nitride DBRs can utilize materials such as AlInN / GaN; and air-gap DBRs employ structures such as air / GaN. Furthermore, high-refractive-index materials such as TiO2 and GaN can also be used to construct the reflector. Different mirror types require tailored fabrication processes to achieve high reflectivity. Common fabrication processes include photolithography, electron beam evaporation, magnetron sputtering, and atomic layer deposition (ALD). Each of these processes has its own unique characteristics, enabling precise control of the mirror's layer thickness, composition, and structure, thereby achieving high reflectivity.

[0051] Advanced techniques such as photolithography and magnetron sputtering are used to assist in the deposition of metal conductive channels. Metallic conductive channels guide current in lasers. Common material combinations include Cr / Au and Ni / Au. These materials offer excellent conductivity and stability, effectively reducing resistance during current transmission and ensuring uniform and efficient current injection into subsequent functional layers. Next, a transparent conductive film (current spreading layer) is deposited on the sample surface. The current spreading layer's primary function is to evenly spread the injected current across the entire light-emitting area, improving current injection efficiency. Possible materials include, but are not limited to, indium tin oxide (ITO), indium zinc oxide (IZO), aluminum zinc oxide (AZO), and fluorine-doped tin oxide (FTO). These materials offer high transmittance and excellent conductivity, ensuring smooth light emission while effectively spreading the current.

[0052] A hole injection layer (HTL) is formed on the current spreading layer using a variety of flexible processes, including spin coating, doctor blade coating, and inkjet printing. The HTL facilitates hole injection from the anode into the light-emitting layer, improving carrier recombination efficiency. Commonly used material combinations include PEDOT:PSS / TFB, PEDOT:PSS / PF8Cz, and ZnO / ZnMgO. These materials exhibit excellent hole transport properties and energy level matching with adjacent layers, effectively lowering the hole injection barrier and enhancing device luminescence performance.

[0053] Next comes the preparation of the quantum dot light-emitting layer film, meticulously crafted using processes such as inkjet, doctor blade coating, and spin coating. Quantum dot materials exhibit a unique quantum confinement effect, enabling precise tuning of the emission wavelength and exhibiting excellent properties such as high luminous efficiency and a narrow emission spectrum. The range of light-emitting layer materials available includes a wide range, including but not limited to CdSe, CdTe, CdS, ZnSe, ZnTe, ZnS, CuInS, CuInSeS, AgInS, AgInSeS, InP, CuZnSe, ZnMnSe, PbS, PbSe, as well as Cd-based alloys, In-based alloys, Zn-based alloys, or perovskite materials. The core-shell size of the quantum dots can be flexibly adjusted based on the selected material and the desired emission wavelength to meet the color requirements of different application scenarios.

[0054] An electron injection layer (ETL) is then formed on the quantum dot layer using processes such as inkjet, spin coating, and doctor blade coating. This layer facilitates the injection of electrons from the cathode into the light-emitting layer, synergizing with the hole injection layer to improve carrier recombination efficiency. Commonly used materials include, but are not limited to, ZnMgO, TCTA, and ZnO.

[0055] Subsequently, a patterned current-limiting layer is deposited using techniques such as thermal evaporation and magnetron sputtering, combined with precision processes such as photolithography and masking. This current-limiting layer limits the current injection region, forming an effective light-emitting area and improving the laser's optical output power and beam quality. Commonly used materials include, but are not limited to, SiO2, AlN, and Al2O3. AlN has excellent insulation and thermal stability, effectively isolating the current and preventing leakage.

[0056] Combining photolithography, masking, and other process methods, thermal evaporation and magnetron sputtering are used to deposit a transparent conductive film as the current spreading layer. This step further optimizes current distribution, ensuring more uniform current injection into the light-emitting area, and improving the device's luminous efficiency and performance stability. Materials used are consistent with those for the current spreading layer described above, including but not limited to ITO, IZO, AZO, FTO, and others.

[0057] Then, using masking, photolithography, and other process methods, a top reflector is fabricated on the sample's light output hole. Together, the top and bottom reflectors form the laser's resonant cavity. Their reflectivity significantly influences the laser's output characteristics, requiring a reflectivity of approximately 99.0%. There are many types of top reflectors, including but not limited to dielectric film DBRs, nitride DBRs, gratings, and photonic crystals. Similar material choices are available for the bottom reflector, including TiO2 / SiO2, HfO2 / SiO2, AlInN / GaN, high-refractive-index TiO2, and high-refractive-index GaN. By precisely controlling the reflector's structure and material, the desired light reflection characteristics can be achieved, ensuring the proper operation of the laser.

[0058] Finally, a metal top electrode is deposited on the sample surface using a coating technique such as magnetron sputtering, completing the device fabrication. The metal top electrode connects to the external circuit and collects current. The material selection must consider conductivity, stability, and contact properties with adjacent layers. Common metal electrode materials include, but are not limited to, Al, Ag, Au, Cr / Au, and other metal combinations. These materials meet the device's current transmission and stability requirements.

[0059] As can be seen from the foregoing, the present application provides a front-emitting vertical cavity surface emitting laser and a preparation method thereof. The front-emitting vertical cavity surface emitting laser of the present application includes, from bottom to top, a substrate, a bottom reflector, a metal conductive channel, a first current spreading layer, a hole injection layer, a light-emitting layer, an electron injection layer, a current limiting layer, a second current spreading layer, a top reflector and a top electrode. Among them, the substrate is made of high thermal conductivity and high electrical conductivity materials to provide good heat dissipation and current transmission channels for the device. The first current spreading layer, the hole injection layer, the light-emitting layer and the electron injection layer are stacked in sequence, the first current spreading layer realizes uniform current distribution, the hole injection layer and the electron injection layer respectively inject holes and electrons into the light-emitting layer, forming carrier recombination and luminescence in the light-emitting layer. The light-emitting layer adopts quantum dot material, and the light-emitting wavelength can be precisely controlled by controlling the size of the quantum dots. At the same time, the high quantum yield of the quantum dots improves the luminescence efficiency.

[0060] The current confinement layer, located between the electron injection layer and the second current spreading layer, contains multiple openings, each corresponding to an independent bottom and top reflector, forming an independent resonant cavity. This design enables the laser to operate independently, improving integration and array capabilities. The current confinement layer also effectively limits current distribution, improving carrier recombination efficiency and reducing threshold current.

[0061] In a further design of the present application, the areas of the top and bottom reflectors are both larger than the opening areas in the corresponding current confinement layers, and the projections completely cover the opening areas, thereby reducing light leakage, improving light reflection efficiency and light gain, optimizing beam quality, and reducing threshold current. At the same time, each resonant cavity is configured with an independent second current expansion layer, which is larger in area than the corresponding top reflector. This ensures uniform current injection, improves luminous uniformity, reduces current crowding, improves light extraction efficiency, and facilitates array integration and independent control. The bottom reflector can also use an air gap reflector or a grating reflector that precisely matches the size of the opening area in the current confinement layer to precisely control the light field distribution and mode characteristics within the resonant cavity, improve laser monochromaticity, reduce spectral broadening, and improve signal transmission accuracy and resolution.

[0062] The method for preparing a front-emitting vertical cavity surface emitting laser of the present application includes epitaxially growing various layers of a bottom reflector on a substrate; filling metal between the bottom reflectors to form a metal conductive channel; sequentially depositing a first current spreading layer, a hole injection layer, a light-emitting layer, and an electron injection layer; forming a current limiting layer comprising a plurality of opening areas on the electron injection layer; forming a second current spreading layer; and forming a top reflector and a top electrode on the second current spreading layer. Wherein, the steps of forming the bottom reflector and the top reflector both include patterning the corresponding material layers to precisely control the size, shape, and position of the resonant cavity, improve the device integration and performance stability, optimize the light field distribution and current distribution, and reduce the device power consumption. For the electron injection layer and the hole injection layer, a spray coating method or a spin coating method is used for preparation, which can achieve uniform distribution of the layers and precise control of thickness, and has a simple process and low cost, and is suitable for large-scale production. For the light-emitting layer, an inkjet printing, photolithography, or spin coating method is used to form a quantum dot layer, which can achieve patterning and high process flexibility, and adapt to different quantum dot material systems. In summary, the front-emitting vertical cavity surface emitting laser and its preparation method of the present application effectively solve the problems existing in the prior art through unique technical design and precise process control, and improve the performance, integration and preparation efficiency of the laser.

[0063] The above is only a specific implementation of the present application. Any other improvements made based on the concept of the present application are considered to be within the scope of protection of the present application.

Claims

1. A front-emitting vertical cavity surface emitting laser, characterized in that: It includes a substrate, a bottom reflector, a metal conductive channel, a first current spreading layer, a hole injection layer, a light-emitting layer, an electron injection layer, a current limiting layer, a second current spreading layer, a top reflector and a top electrode; The bottom reflector is formed on the substrate, and the first current spreading layer, the hole injection layer, the light emitting layer and the electron injection layer are stacked in sequence; In which, the current limiting layer is located between the electron injection layer and the second current expansion layer, and the current limiting layer includes multiple opening areas, each opening area has an independent corresponding bottom reflector and top reflector, the bottom reflector and the corresponding top reflector corresponding to the opening area serve as a resonant cavity of a laser, and the metal conductive channel is filled between the bottom reflectors.

2. The front-emitting vertical cavity surface emitting laser according to claim 1, characterized in that: The areas of the top reflector and the bottom reflector are larger than the area of the corresponding opening region in the current confinement layer, and the projections of the top reflector and the bottom reflector on a plane completely cover the opening region.

3. The front-emitting vertical cavity surface emitting laser according to claim 2, characterized in that: Each of the resonant cavities includes a corresponding independent second current spreading layer, and an area of the second current spreading layer is larger than an area of the second current spreading layer corresponding to the top reflective mirror.

4. The front-emitting vertical cavity surface emitting laser according to claim 1, characterized in that: The upper surfaces of the bottom reflector and the metal conductive channel forming layer are flat surfaces.

5. The front-emitting vertical cavity surface emitting laser according to claim 1, characterized in that: The bottom reflector includes an air gap reflector or a grating reflector having the same size as the opening area.

6. A method for preparing a front-emitting vertical cavity surface emitting laser, characterized in that: include: Depositing various layers forming the bottom reflector on the substrate by epitaxial growth; Filling metal between the plurality of bottom reflectors to form a metal conductive channel; depositing a first current spreading layer; forming a hole injection layer, a light-emitting layer, and an electron injection layer in sequence on the first current spreading layer; forming a current limiting layer on the electron injection layer, wherein the current limiting layer includes a plurality of opening regions; forming a second current spreading layer; forming a top reflector on the second current spreading layer; forming a top electrode on the second current spreading layer; Each opening area has an independent corresponding bottom reflector and top reflector, and the bottom reflector and the top reflector corresponding to the opening area serve as a resonant cavity of a laser.

7. The method for preparing a front-emitting vertical cavity surface emitting laser according to claim 6, characterized in that: The step of forming the bottom reflector includes patterning a material layer for forming the bottom reflector, and the step of forming the top reflector includes patterning a material layer for forming the top reflector.

8. The method for preparing a front-emitting vertical cavity surface emitting laser according to claim 7, characterized in that: An area of the bottom reflector and an area of the top reflector are larger than an area of the opening region.

9. The method for preparing a front-emitting vertical cavity surface emitting laser according to claim 6, characterized in that: The electron injection layer and the hole injection layer are formed by spraying or spin coating, and the quantum dot layer is formed as the light-emitting layer by inkjet printing, photolithography or spin coating.

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