Structure for improving light extraction efficiency of Micro-LED and manufacturing method

Abstract

The invention relates to a structure for improving the light extraction efficiency of a Micro-LED and a manufacturing method, and the structure comprises a basic function layer, a micro-lens optical regulation and control layer and a micro-nano secondary structure which are sequentially arranged from bottom to top, and the micro-lens optical regulation and control layer and the micro-nano secondary structure form a core optical function unit; the micro-lens optical regulation and control layer is a tightly-arranged hemispherical micro-lens array, the bottom face of each micro-lens is a circular plane completely attached to the top end of the basic function layer, the micro-nano secondary structure is located on the outer spherical face of the micro-lens optical regulation and control layer, and the micro-nano secondary structure and the hemispherical curved face of the micro-lens optical regulation and control layer form a sawtooth-shaped protruding array. The height direction of the sawtooth-shaped protrusions always extends in the spherical surface normal direction of the position where the sawtooth-shaped protrusions are located, a micro lens and a micro-nano secondary structure are designed on the Micro-LED device in an integrated mode, Micro-LED emergent light beams are shaped, the proportion of front emergent light beams is increased, the divergence angle is reduced, meanwhile, the light extraction efficiency can be improved, and the performance limit of the Micro-LED device is broken through.

Description

Technical Field

[0001] This invention relates to the field of semiconductor device manufacturing technology, and in particular to a structure and manufacturing method for improving the light extraction efficiency of Micro-LEDs. Background Technology

[0002] The gallium nitride (GaN) material used in Micro-LED devices has a refractive index of approximately 2.5, which differs significantly from the refractive index of the dielectric material. Due to total internal reflection, most of the light emitted from the active region is refracted and reflected within the Micro-LED device, failing to effectively exit from the Micro-LED into the air medium. As the size of Micro-LEDs decreases from hundreds of micrometers to several micrometers, the scale effect becomes significant. The proportion of the Micro-LED sidewalls relative to the entire device increases, resulting in more light emanating from the sidewalls rather than the top. This leads to a larger divergence angle of the Micro-LED light source and makes it prone to crosstalk with light emitted from adjacent devices, reducing display clarity and other performance indicators. Therefore, shaping the emitted beam of Micro-LEDs to increase the proportion of the front-facing beam and reduce the divergence angle is of great importance. Summary of the Invention

[0003] The purpose of this invention is to provide a structure and manufacturing method for improving the light extraction efficiency of Micro-LEDs, so as to solve the problems existing in the prior art.

[0004] The above-mentioned technical objective of the present invention is achieved through the following technical solution: The structure and manufacturing method for improving the light extraction efficiency of Micro-LEDs include a basic functional layer, a microlens optical control layer and a micro-nano secondary structure arranged from bottom to top. The microlens optical control layer and the micro-nano secondary structure constitute the core optical functional unit. The microlens optical control layer is a closely packed hemispherical microlens array. Each microlens is hemispherical in shape, and the center of each microlens is located at the geometric center of the basic functional layer. The bottom surface of the microlens is a circular plane that is completely attached to the top of the basic functional layer. The difference between the refractive index of the microlens material and the refractive index of the micro / nano secondary structure is less than 0.1. The arrangement period of the microlens array is strictly matched with the pixel spacing of the Micro-LED. The micro / nano secondary structure is located on the outer spherical surface of the microlens optical control layer. The micro / nano secondary structure and the hemispherical curved surface of the microlens optical control layer form a sawtooth protrusion array. The base of each sawtooth protrusion is tangent to the spherical surface of the microlens. The height direction of the sawtooth protrusion always extends along the normal direction of the spherical surface at its location. The spacing between adjacent sawtooth protrusions is less than half of the working wavelength. The distribution density of the sawtooth protrusions in the apex region of the microlens is higher than that in the edge region of the microlens.

[0005] By adopting the above technical solution, microlenses and micro-nano secondary structures are integrated and designed on Micro-LED devices to shape the emitted beam of Micro-LED, increase the proportion of the front emitted beam, reduce the divergence angle, and improve the light extraction efficiency, thus breaking through the performance limits of Micro-LED devices.

[0006] In a further embodiment, the basic functional layer includes a metal layer for reflecting backlight, a substrate, a current spreading layer for achieving uniform current spreading, an epitaxial layer containing a light-emitting active region, and a passivation layer for insulating protection. The epitaxial layer includes a p-GaN layer, an MQW layer, and an n-GaN layer. The substrate is located on top of the metal layer, the epitaxial layer is located on top of the substrate, the passivation layer is located on top of the epitaxial layer, and the current spreading layer is located on top of the passivation layer.

[0007] In a further embodiment, the protrusions of the micro / nano secondary structure form a circumferentially uniformly distributed ring array on the outer surface region of the microlens sphere, and the symmetrical design ensures the equivalent control effect of incident light at different azimuth angles.

[0008] In a further embodiment, the protrusions of the micro-nano secondary structure are located on the outer surface region of the microlens sphere. The protrusions of the micro-nano secondary structure form a circumferentially uniformly distributed ring array, and the symmetrical design ensures the equivalent control effect of incident light at different azimuth angles.

[0009] In a further embodiment, the micro / nano secondary structure is made of the same material as the microlens.

[0010] In a further embodiment, the material of the current spreading layer is a transparent conductive film.

[0011] A method for fabricating a structure to improve the light extraction efficiency of Micro-LEDs includes the following steps: S1. Fabricate the substrate, epitaxial layer, and light-emitting mesa; S2, optically transparent materials are prepared on the surface of Micro-LED wafers; S3. Photoresist thermal reflow fabrication of microlens mask layer; S4. Reactive ion etching is used to prepare microlens arrays; S5. High-precision secondary micro / nano structure master fabrication; S6, PDMS flexible secondary micro / nano structure template replication; S7. Hemispherical surface pretreatment and fabrication of patterned mask for secondary micro / nano structures; S8, plasma etching of micro-nano secondary structures.

[0012] In summary, the present invention has the following beneficial effects: 1. By altering the interface morphology through micro-nano secondary structures on the surface of microlenses, the propagation of light is guided and modulated. While ensuring that the microlenses shape the emitted beam from the Micro-LED device, the micro-nano secondary structures can improve the light transmittance of the pixel edge region under large incident angles, thereby significantly suppressing total internal reflection of light emitted from the pixel edge region inside the microlens. This balances light shaping effect and light extraction efficiency, thus greatly improving the optical performance of the Micro-LED device. Attached Figure Description

[0013] Figure 1 This is a schematic diagram of the overall structure of the present invention; Figure 2 This is a schematic diagram illustrating the extensional structure of the present invention; Figure 3 This is a schematic diagram of the structure of the light-emitting platform of the present invention; Figure 4 This is a schematic diagram of the structure of the deposition passivation layer covering the light-emitting platform of the present invention; Figure 5 This is a schematic diagram of the passivation layer being etched to create windows according to the present invention; Figure 6 This is a schematic diagram of the structure of the n-current extension layer of the present invention; Figure 7 This is a schematic diagram of the structure of the optical material covering the light-emitting platform of the present invention; Figure 8 This is a schematic diagram of the microlens structure mask pattern of the present invention; Figure 9 This is a schematic diagram of the structure of microlens pattern etching and transfer to optical material according to the present invention; Figure 10 This is a schematic diagram of the micro / nano secondary structure mask pattern of the present invention.

[0014] In the figure, 1 is the metal layer; 2 is the substrate; 3 is the p-GaN layer; 4 is the MQW layer; 5 is the n-GaN layer; 6 is the passivation layer; 7 is the current spreading layer; 8 is the microlens optical control layer; 9 is the microlens array; and 10 is the micro / nano secondary structure. Detailed Implementation

[0015] The present invention will be further described in detail below with reference to the accompanying drawings.

[0016] Identical parts are indicated by the same reference numerals. It should be noted that the terms "front," "rear," "left," "right," "upper," and "lower" used in the following description refer to the attached figures. Figure 1In this specification, the terms "bottom surface" and "top surface," "inner" and "outer" refer to the direction toward or away from the geometry of a specific component. Furthermore, the terms "first" and "second" are used for descriptive purposes only and should not be construed as indicating or implying relative importance or implicitly specifying the number of technical features indicated. Thus, a feature defined as "first" or "second" may explicitly or implicitly include one or more of that feature. In the description of this specification, "a plurality of" means two or more, unless otherwise explicitly and specifically defined by the direction of the center.

[0017] Example 1: As Figures 1-10 As shown, the structure for improving the light extraction efficiency of Micro-LED includes a basic functional layer, a microlens optical control layer 8 and a micro-nano secondary structure 10 arranged sequentially from bottom to top. The microlens optical control layer 8 and the micro-nano secondary structure 10 constitute the core optical functional unit. The microlens optical control layer 8 is a closely arranged hemispherical microlens array 9. Each microlens is hemispherical in shape, and the center of each microlens is located at the geometric center of the basic functional layer. The bottom surface of the microlens is a circular plane that is completely attached to the top of the basic functional layer. The difference between the refractive index of the microlens material and the refractive index of the micro / nano secondary structure 10 is less than 0.1. The arrangement period of the microlens array 9 is strictly matched with the pixel pitch of the Micro-LED. The micro / nano secondary structure 10 is located on the outer spherical surface of the microlens optical control layer 8. The micro / nano secondary structure 10 and the hemispherical curved surface of the microlens optical control layer 8 form a sawtooth protrusion array. The base of a single sawtooth protrusion is tangent to the spherical surface of the microlens. The height direction of the sawtooth protrusion always extends along the normal direction of the spherical surface at its location. The spacing between adjacent sawtooth protrusions is less than half of the working wavelength. The distribution density of sawtooth protrusions in the spherical top region of the microlens is higher than that in the edge region of the microlens.

[0018] The basic functional layer includes a metal layer 1 for reflecting backlight, a substrate 2, a current spreading layer 7 for achieving uniform current spreading, an epitaxial layer containing a light-emitting active region, and a passivation layer 6 for insulating protection. The epitaxial layer includes a p-GaN layer 3, an MQW layer 4, and an n-GaN layer 5. Multiple substrates 2, current spreading layers 7, epitaxial layers, and passivation layers 6 are provided. The substrate 2 is distributed on top of the metal layer 1, the epitaxial layer is located on top of the substrate 2, the passivation layer 6 is located on top of the epitaxial layer, and the current spreading layer 7 is located on top of the passivation layer 6.

[0019] The protrusions of the micro-nano secondary structure 10 form a circumferentially uniformly distributed ring array on the outer surface region of the microlens sphere, and the symmetrical design ensures the equivalent control effect of incident light at different azimuth angles.

[0020] The protrusions of the micro / nano secondary structure 10 form a circumferentially uniformly distributed ring array on the outer surface region of the microlens sphere. The symmetrical design ensures the equivalent control effect of incident light at different azimuth angles. The micro / nano secondary structure 10 is made of the same material as the microlens, and the current spreading layer 7 is made of a transparent conductive film.

[0021] Optionally, the optical material is a photocurable transparent optical resin; Optionally, the optical material is silicon dioxide, silicon nitride, or other similar materials; Optionally, the mask pattern for the microlens structure is fabricated by photoresist thermal reflow; Optionally, the microlens structure mask pattern is prepared by two-photon polymerization 3D printing; Optionally, the method for fabricating the micro / nano secondary structure mask pattern on the surface of the microlens array 9 is nanoimprinting; Optionally, the method for fabricating the micro-nano secondary structure mask pattern on the surface of the microlens array 9 is two-photon polymerization 3D printing; Optionally, the mask pattern of the micro / nano secondary structure 10 is a moth-eye structure; Optionally, the mask pattern of the micro / nano secondary structure is a photonic crystal; Optionally, the mask pattern of the micro / nano secondary structure 10 is a grating structure.

[0022] Specific implementation process: 1. Fabricate the substrate, epitaxial layer, and light-emitting mesa.

[0023] A 2-inch substrate 2 (430±10μm thick) was provided, and epitaxial layers were grown sequentially using a metal-organic chemical vapor deposition (MOCVD) system. First, a 2.0μm thick n-GaN layer (Si doping concentration 5×10⁻⁶) was deposited at 1050℃ and 100mbar pressure. 18 cm -3 ); then a 5-period InGaN / GaN multi-quantum-well layer was grown (well / barrier thickness 3nm / 10nm); a 200nm thick p-GaN layer (Mg doping concentration 1×10) was then deposited. 19 cm -3 A 150 nm ITO thin film (In₂O₃:SnO₂ = 90:10 wt%) was magnetron sputtered onto the p-GaN surface as the p-current spreading layer 7, with a sheet resistance ≤15 Ω / sq; finally, Ni / Au (20 nm / 100 nm) was deposited by electron beam evaporation, and ohmic contacts were formed by rapid thermal annealing at 400-500 °C (contact resistance ≤1×10⁻⁶). -4 Ω・cm 2 ).

[0024] The light-emitting mesa was formed by ICP-RIE dry etching, followed by spin coating of 3μm thick AZ4620 photoresist and i-line lithography (dosage 220mJ / cm). 2 The pattern was defined; an etching gas combination of Cl2 / BCl3 / Ar (30 / 15 / 10 sccm) was used, with ICP power of 500W and RF power of 300W. The endpoint was determined by monitoring the disappearance of the N2 characteristic peak (GaN decomposition products) using OES. Subsequently, a 200nm thick SiN layer was deposited by PECVD. x Passivation layer 6 (SiH4 / NH3 / N2=50 / 200 / 500 sccm, 300℃) is selectively etched with CF4 / O2 (40 / 5 sccm) to expose the light-emitting surface, forming a Micro-LED wafer.

[0025] 2. Fabrication of optically transparent materials on the surface of Micro-LED wafers.

[0026] An 8μm thick SiO2 layer was deposited on the surface of a Micro-LED wafer using PECVD, and the SiO2 layer was planarized using chemical mechanical polishing (CMP) to obtain a flat surface, providing a basis for microlens forming.

[0027] 3. Photoresist thermal reflow fabrication of microlens mask layer.

[0028] Before thermal reflow fabrication of microlens arrays, the substrate needs to be pretreated with plasma. O2 plasma (100W RF power, 30s processing time) is used to remove organic contaminants from the surface, reduce the contact angle from 65° to below 15°, and ensure the adhesion between the photoresist and the substrate.

[0029] Photoresist is spin-coated onto the surface of a Micro-LED wafer using a spin-coating method. The mask pattern is transferred to the photoresist layer via ultraviolet exposure, and development forms a periodic columnar or square photoresist array with dimensional accuracy controllable within ±0.5μm. The subsequent thermal reflow process involves heating the photoresist in an oven or on a hot plate (typically 90-180℃ for 30-120 seconds). Utilizing the viscoelastic flow properties of the photoresist, the sharp-edged structure is reconstructed into a smooth curved surface under surface tension. This intensifies the movement of photoresist molecular chains, reduces surface energy, and ultimately forms a spherical or aspherical lens prototype with adjustable curvature radius. The surface roughness can be reduced from tens of nanometers initially to 1-2 nm, meeting optical-grade surface requirements.

[0030] By adjusting the photoresist thickness, photolithographic pattern size, and thermal reflow temperature, microlens arrays with focal lengths of 10-500 μm can be achieved, enabling the fabrication of lens structures with high aspect ratios (>5:1) to meet the requirements for high numerical aperture (NA>0.5).

[0031] 4. Fabrication of microlens arrays by reactive ion etching.

[0032] When transferring photoresist microlens structures to the SiO2 layer of a Micro-LED wafer using reactive ion etching (RIE), high-precision morphology replication is achieved by selecting the etching gas (e.g., CF4 / O2 mixed gas for etching the silicon substrate, and Ar / O2 for etching the glass). During the etching process, ion bombardment and chemical reaction work synergistically, maintaining the curved surface morphology formed by thermal reflow while transforming the lens material from organic photoresist to an inorganic substrate, thus extending the operating temperature range from <200℃ for photoresist to >300℃.

[0033] The etching system employs dual-frequency RF power supply coordination: a 13.56MHz high-frequency power supply controls ion energy (100-500eV), and a 380kHz low-frequency power supply adjusts ion flux (10... 15 -10 17 ions / cm 2 •s). For silicon substrates, an SF6 / O2 mixed gas system (volume ratio 3:1) was selected. Under a vacuum environment of 20 mTorr, a smooth curved surface morphology was formed through the synergistic effect of physical sputtering by ion bombardment and chemical etching by fluorine radicals. The reflection spectrum was monitored in real time during the etching process, and the process was automatically terminated when the characteristic wavelength corresponding to the target focal length (a sudden change in reflectivity at 550 nm) was detected, achieving closed-loop control with a focal length accuracy of ±2 μm.

[0034] Simultaneously introduce Ar + Assisted etching, with anisotropy adjusted by power ranging from 150-300W, stabilizes the lens surface roughness (RMS) below 0.8nm. Combined with the patterning definition of the photoresist mask, microlens arrays with diameters of 5-200μm and focal lengths of 20-800μm can be fabricated, with numerical aperture (NA) covering the range of 0.2-0.8. The etching rate ratio (substrate:mask) is maintained at 8:1, ensuring efficient processing at 3-5μm / h. Simultaneously, pulsed etching mode (50% duty cycle) reduces heat accumulation, keeping the lens surface shape error within λ / 20 (λ=632.8nm).

[0035] 5. High-precision fabrication of secondary micro / nano structure master templates.

[0036] Micro-nano secondary structures possess subwavelength scale structural features. Their patterning relies on ultra-narrow linewidth patterning techniques such as deep ultraviolet lithography (DUV), electron beam lithography (EBL), and interferometric exposure to prepare periodic structural patterns with linewidths of 100-500 nm on the surface of silicon or quartz wafers. After development, a nanoscale photoresist mask is obtained. Then, through methods such as ion beam etching and reactive ion etching, the subwavelength structure is transferred to a substrate to form a nanostructure with vertical sidewalls, obtaining a micro-nano secondary structure master. The etching depth accuracy of the master can reach ±5 nm, and the sidewall perpendicularity is >89.5°.

[0037] 6. Replication of PDMS flexible secondary micro / nano structure templates.

[0038] Dow Corning Sylgard 184 silicone rubber was selected as the raw material. The prepolymer and curing agent were mixed in a clean environment at a mass ratio of 10:1. The mixture was stirred at 300 rpm for 8 minutes using a magnetic stirrer to ensure uniform dispersion. Then, the mixture was degassed under a vacuum of -0.1 MPa for 30 minutes until all bubbles were eliminated (the residual bubble rate with a diameter > 50 μm was < 0.05%) to avoid defects on the template surface.

[0039] The degassed PDMS precursor was uniformly poured onto the surface of the micro / nano secondary structure master template using a pipette. The pouring volume was controlled to ensure that the precursor covered the master template area and formed a 1.5 mm thick liquid layer. To ensure replication accuracy, the pouring process was carried out in a constant temperature and humidity chamber (25℃±1℃, humidity 40%±5%) to avoid uneven flow of the precursor due to environmental fluctuations. The poured master template was then placed in an 80℃ oven for 2 hours for curing. The curing process consisted of two stages: the first 30 minutes were spent in pre-gelation at 40℃ to allow the precursor to initially form an elastic network; the next 90 minutes were spent at 80℃ to complete the cross-linking reaction. DSC testing showed a degree of curing >98%, ensuring that the template had stable mechanical properties (elastic modulus 2.5±0.3MPa, elongation at break >300%).

[0040] After curing, the template was demolded using a step-by-step edge peeling method. A precision translation stage was used to lift the template from one corner of the master template at a speed of 0.3 mm / s. The high elasticity of PDMS prevented stress concentration. Microscopic observation showed no residual PDMS residue on the template, and the master template structure remained undamaged. The replicated template surface formed micro-nano secondary structure features complementary to the master template. A 50 nm aluminum layer was deposited on the back of the template using magnetron sputtering, transforming it into a high-contrast optical mark with a positioning accuracy of ±0.8 μm.

[0041] To enhance the interfacial bonding between the template and the subsequent SiO2 sol, the surface of the template pits was modified by immersing it in a 0.5% APTES ethanol solution for 15 minutes. This allowed silane molecules to graft amino groups (-NH2) onto the PDMS surface via hydrolysis. XPS analysis showed that the amino group coverage was >90%, and the contact angle decreased from 72° to 25°. This ensured that the TEOS hydrolysis products (Si-OH) in the sol could form hydrogen bonds with the template surface, which would then be converted into Si-O-Si covalent bonds after curing (with the bonding strength increased to 8 MPa). The edge thickness uniformity of the template was measured with a micrometer, with a deviation of <±10 μm, ensuring consistent sol flow resistance during centrifugal filling.

[0042] 7. Surface pretreatment and patterned mask design.

[0043] Using an oxygen plasma treatment system (Oxford Instruments PlasmaLab), high-purity O2 was introduced, with a power setting of 250W and a treatment time of 60 seconds, to reduce the O2 content in the plasma. + Ion bombardment of the surface removes residual organic impurities while introducing hydroxyl (-OH) groups. Contact angle measurements after treatment show that the contact angles of the apex, equator, and basal regions all decrease to 35°±5°, with regional differences ≤10%. AFM-detected roughness Ra≤1.5nm ensures surface hydrophilicity while avoiding overtreatment that could damage the integrity of the microlenses.

[0044] A complete imprinting adhesive is applied to the surface of the microlens array using either a spray coating or spin coating method. The amount of imprinting adhesive is calculated based on the dimensions of the micro / nano secondary structure. Pressure is applied to a flexible secondary micro / nano structure template using nanoimprinting, causing the template to deform and tightly adhere to the surface of the Micro-LED wafer microlens array. Under external force, the imprinting adhesive completely fills the micro / nano secondary structure. Subsequently, the imprinting adhesive is cured by irradiation with ultraviolet light, and finally, the template is demolded, resulting in a micro / nano secondary structure mask on the surface of the Micro-LED wafer microlens array.

[0045] 8. Plasma etching of micro / nano secondary structures.

[0046] Reactive ion etching (RIE) was used to transfer micro / nano secondary structure patterns onto the surface of a microlens array. A CF4 / O2 (4:1) gas combination was employed. CF4 provided F radicals, while O2 purged etching byproducts through oxidation (generating volatile products such as CO2 and CO), reducing polymer deposition. Etching parameters were adjusted: ICP power was reduced to 400W, bias voltage was increased to 100V to enhance ion bombardment energy, chamber pressure was maintained at 8 mTorr, and gas flow rates were 20 sccm for CF4 and 5 sccm for O2. Under this formulation, the ratio of lateral etching rate (15 nm / min) to vertical etching rate (20 nm / min) was 1:1. During etching, the sample stage simultaneously underwent ±5° oscillation scanning to compensate for etching rate differences caused by the curvature of the microlens, ensuring that the etching depth deviation of the micro / nano secondary structures on the microlens array surface was <3%.

[0047] In the embodiments disclosed in this invention, the terms "installation," "connection," "linking," and "fixing" should be interpreted broadly. For example, "connection" can be a fixed connection, a detachable connection, or an integral connection; "linking" can be a direct connection or an indirect connection through an intermediate medium. Those skilled in the art can understand the specific meaning of the above terms in the embodiments disclosed in this invention according to the specific circumstances.

[0048] This specific embodiment is merely an explanation of the present invention and is not intended to limit the invention. After reading this specification, those skilled in the art can make modifications to this embodiment without contributing any inventive step, but such modifications are protected by patent law as long as they are within the scope of the claims of the present invention.

Claims

1. A structure for improving the light extraction efficiency of Micro-LEDs, characterized in that, It includes a basic functional layer, a microlens optical control layer and a micro-nano secondary structure arranged from bottom to top, wherein the microlens optical control layer and the micro-nano secondary structure constitute the core optical functional unit; The microlens optical control layer is a closely packed array of hemispherical microlenses. Each microlens is hemispherical, with its center located at the geometric center of the Micro-LED light-emitting surface. The bottom surface of each microlens is a circular plane that is completely flush with the top of the basic functional layer. The difference between the refractive index of the microlens material and the refractive index of the micro / nano secondary structure is less than 0.

1. The arrangement period of the microlens array is strictly matched with the pixel spacing of the Micro-LED. The micro / nano secondary structure is located on the outer spherical surface of the microlens optical control layer. The micro / nano secondary structure and the hemispherical curved surface of the microlens optical control layer form a sawtooth protrusion array. The base of each sawtooth protrusion is tangent to the spherical surface of the microlens. The height direction of the sawtooth protrusion always extends along the normal direction of the spherical surface at its location. The spacing between adjacent sawtooth protrusions is less than half of the working wavelength. The distribution density of the sawtooth protrusions in the apex region of the microlens is higher than that in the edge region of the microlens.

2. The structure for improving the light extraction efficiency of Micro-LED according to claim 1, characterized in that, The basic functional layer includes a metal layer for reflecting backlight, a substrate, a current spreading layer for achieving uniform current spreading, an epitaxial layer containing a light-emitting active region, and a passivation layer for insulating protection. The epitaxial layer includes a p-GaN layer, an MQW layer, and an n-GaN layer. Multiple substrates, current spreading layers, epitaxial layers, and passivation layers are provided. The substrate is distributed on top of the metal layer, the epitaxial layer is located on top of the substrate, the passivation layer is located on top of the epitaxial layer, and the current spreading layer is located on top of the passivation layer.

3. The structure for improving the light extraction efficiency of Micro-LED according to claim 1, characterized in that: The protrusions of the micro-nano secondary structure form a circumferentially uniformly distributed ring array on the outer surface of the microlens sphere, and the symmetrical design ensures the equivalent control effect of incident light at different azimuth angles.

4. The structure for improving the light extraction efficiency of Micro-LED according to claim 1, characterized in that: The protrusions of the micro-nano secondary structure are located on the outer surface region of the microlens sphere. The protrusions of the micro-nano secondary structure form a circumferentially uniformly distributed ring array. The symmetrical design ensures the equivalent control effect of incident light at different azimuth angles.

5. The structure for improving the light extraction efficiency of Micro-LED according to claim 1, characterized in that: The micro / nano secondary structure is made of the same material as the microlens.

6. The structure for improving the light extraction efficiency of Micro-LED according to claim 2, characterized in that: The material of the current spreading layer is a transparent conductive film.

7. A method for fabricating a structure for improving the light extraction efficiency of Micro-LEDs as described in any one of claims 1 to 6, characterized in that, Includes the following steps: S1. Fabricate the substrate, epitaxial layer, and light-emitting mesa; S2, Fabrication of optically transparent materials on Micro-LED wafer surfaces; S3. Photoresist thermal reflow fabrication of microlens mask layer; S4. Reactive ion etching is used to prepare microlens arrays; S5. High-precision secondary micro / nano structure master fabrication; S6, PDMS flexible secondary micro / nano structure template replication; S7. Hemispherical surface pretreatment and fabrication of patterned mask for secondary micro / nano structures; S8, plasma etching of micro-nano secondary structures.

Images