Micro LED based on composite micro lens group and preparation method thereof

Abstract

The invention discloses a Micro-LED based on a composite micro lens group and a preparation method thereof, and the Micro-LED comprises a Micro-LED pixel array located above a drive circuit, the Micro-LED pixel array comprises a plurality of Micro-LED pixels arranged at intervals, and each Micro-LED pixel comprises a Micro-LED tube core and a composite micro lens group covering the Micro-LED tube core; the composite micro lens group comprises a porous GaN micro lens, a cathode transparent film layer and a refractive index gradient film layer which are sequentially arranged in the direction far away from the Micro-LED tube core; the refractive index gradient film layer is located on the cathode transparent film layer. The Micro-LED realizes light collection and collimation through the refractive index gradient film layer, reduces the loss of reflected light, and effectively improves the light extraction efficiency.

Description

Technical Field

[0001] The present invention relates to the field of Micro-LED technology, and in particular to a Micro LED based on a composite microlens group and a preparation method thereof. Background Art

[0002] Nowadays, Micro-LED is considered by relevant technicians to be the most promising display technology. Its brightness, response speed, lifespan, operating temperature and other indicators are far superior to traditional display technologies such as OLED and LCD, and GaN-based materials are currently the preferred materials for the research and development of Micro-LED. However, a major problem that currently restricts the commercial development of Micro-LED is the relatively low efficiency of the device. There are two reasons for the low efficiency of Micro-LED. One is the low internal quantum efficiency and electrical injection efficiency caused by dislocation, defects, stress, device structure and other reasons of GaN-based epitaxial wafers; the other is the restriction of chip light extraction efficiency. Considering that the refractive index of GaN in the green light band (520nm) is close to 2.5 and that of air is 1, under the theoretical condition of vertical incidence, the Fresnel loss of the light output is higher than 80%. At the same time, the self-luminescence of Micro-LED pixels will also lead to the problem of light dispersion. Due to the intrinsic nature of semiconductor band transition luminescence, a single pixel emits light everywhere in space. This feature not only affects the collection of light from the main viewing angle, resulting in low luminous efficiency and insufficient display brightness of Micro-LED, but also causes light crosstalk between tiny pixels.

[0003] A major focus of Micro-LED device research and development is the design and preparation of light-emitting enhancement devices. Most reports use light-emitting enhancement devices such as single microlenses, photonic crystals, and Bragg reflectors. However, at this stage, the light-emitting efficiency and light-emitting effect of Micro-LED devices need to be further improved. Summary of the invention

[0004] Technical purpose: In view of the low efficiency of the Micro-LED device structure in the prior art, and the defects such as large divergence angle, low light extraction efficiency and light crosstalk due to the self-luminous nature, the present invention discloses a Micro LED based on a composite microlens group and a preparation method thereof.

[0005] Technical solution: In order to achieve the above technical objectives, the present invention adopts the following technical solution.

[0006] A Micro LED based on a composite microlens group, comprising:

[0007] Driving circuit;

[0008] A Micro-LED pixel array located above the driving circuit; the Micro-LED pixel array includes a plurality of Micro-LED pixels arranged at intervals, each Micro-LED pixel includes a Micro-LED tube core and a composite micro lens group covering the Micro-LED tube core; a pixel passivation layer is provided on the side wall of the Micro-LED tube core;

[0009] The composite microlens group includes a porous GaN microlens, a cathode transparent film layer, and a refractive index gradient film layer which are sequentially arranged in a direction away from the Micro-LED tube core; the porous GaN microlens is located on the top of the Micro-LED tube core, and the centers of the two are collinear; the cathode transparent film layer is located on the porous GaN microlens, the side wall of the Micro-LED tube core, and the pixel passivation layer;

[0010] The refractive index gradient film layer is located on the cathode transparent film layer; the refractive index gradient film layer is a multi-layer film layer structure, the number of film layers is at least two, and the refractive index of each film layer decreases layer by layer in the direction away from the Micro-LED tube core, and each film layer forms a microlens that coincides with the center of the Micro-LED tube core, and the porous GaN microlens, the microlens formed by the refractive index gradient film layer and the center of the Micro-LED tube core are all collinear.

[0011] A method for preparing a Micro LED based on a composite microlens group, for manufacturing the Micro LED based on a composite microlens group as described above, comprises the following steps:

[0012] Step 1: a plurality of unconnected electrode connection holes are provided on the upper surface of the driving circuit; a reflective metal film layer is evaporated on the upper surface of the driving circuit, and then a processed Micro-LED epitaxial wafer is bonded; the Micro-LED epitaxial wafer is a GaN-based Micro-LED epitaxial wafer; the processed Micro-LED epitaxial wafer includes a hole injection layer, a light-emitting layer, an electron injection layer, and a doping gradient layer which are sequentially arranged in a direction away from the driving circuit;

[0013] Step 2: A porous GaN microlens array is formed on the top of the Micro-LED epitaxial wafer after etching, wherein the porous GaN microlens array includes a plurality of porous GaN microlenses;

[0014] Step 3: The portion of the Micro-LED epitaxial wafer after etching except for the porous GaN microlens array is formed into a Micro-LED die array, wherein the Micro-LED die array includes a plurality of Micro-LED dies corresponding to the porous GaN microlenses one by one, a pixel passivation layer is formed on the side wall of the Micro-LED die, and a cathode transparent film layer is formed on the top of the porous GaN microlens, on the pixel passivation layer, and on the side wall of the Micro-LED die;

[0015] Step 4: forming a refractive index gradient film layer on the cathode transparent film layer.

[0016] Beneficial effects:

[0017] (1) The composite microlens group structure for improving the efficiency of Micro-LED provided by the present invention has mature technical means, and the whole process adopts traditional semiconductor preparation technology, with a simple process flow and high stability.

[0018] (2) The prepared Micro-LED has good uniformity and can strongly converge the light emitted by the Micro-LED pixels, achieve light convergence and collimation, and effectively reduce reflection loss, effectively improve light extraction efficiency, and improve the photoelectric conversion efficiency of the Micro-LED chip.

[0019] (3) The microlens array module can also effectively protect the underlying Micro-LED die as a passivation protection thick film. BRIEF DESCRIPTION OF THE DRAWINGS

[0020] Figure 1 This is a schematic diagram of a Micro LED single pixel structure based on a composite microlens group according to an embodiment of the present invention;

[0021] Figure 2 A schematic top view of a Micro LED based on a composite microlens group according to an embodiment of the present invention;

[0022] Figure 3 to Figure 8 is a preparation flow chart of an embodiment of the present invention;

[0023] Among them, 10-Micro-LED pixel, 101-driving circuit, 102-electrode connection hole, 103-reflective metal film layer, 20-Micro-LED epitaxial wafer, 201-Micro-LED tube core, 202-pixel passivation layer, 203-cathode transparent film layer, 211'-porous GaN film layer, 211-porous GaN microlens, 301'-filling layer first film layer, 301-filling layer first film layer microlens, 302-filling layer second film layer microlens; DETAILED DESCRIPTION

[0024] In order to enable those skilled in the art to better understand the solution of the present application, the technical solution in the embodiments of the present application will be clearly and completely described below in conjunction with the drawings in the embodiments of the present application. Obviously, the described embodiments are only part of the embodiments of the present application, not all of the embodiments. Based on the embodiments in the present application, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of this application.

[0025] As attached Figure 1 and attached Figure 2 As shown, a Micro LED based on a composite microlens group of this embodiment includes:

[0026] The driving circuit 101 may be a PCB driving circuit, a TFT-based driving circuit, a CMOS driving circuit, etc. When the driving circuit adopts a CMOS driving circuit, a Si-based CMOS driving circuit is preferred;

[0027] A Micro-LED pixel array is located above the driving circuit 101; in the present embodiment, a plurality of electrode connection holes 102 are provided in the driving circuit 101, a reflective metal film layer 103 is provided on the upper surface of the driving circuit 101, and the Micro-LED pixel array is connected to the driving circuit 101 via the reflective metal film layer 103 and the electrode connection holes 102; the reflective metal film layer 103 is made of metal, specifically Ag, Pt, Al, etc.; the electrode connection holes 102 are not interconnected.

[0028] The micro-LED pixel array includes a plurality of micro-LED pixels 10 arranged at intervals, each micro-LED pixel includes a micro-LED tube core 201 and a composite micro lens group covering the micro-LED tube core; each micro-LED tube core 201 corresponds to an electrode connection hole 102;

[0029] The Micro-LED tube core is a GaN-based semiconductor Micro-LED tube core, and all Micro-LED tube cores 201 constitute a Micro-LED tube core array 2; the side wall of the Micro-LED tube core 201 is provided with a pixel passivation layer 202, and the pixel passivation layer 202 is used to protect the side wall of the Micro-LED tube core 201;

[0030] The composite microlens group includes a porous GaN microlens 211, a cathode transparent film layer 203, and a refractive index gradient film layer which are sequentially arranged in a direction away from the Micro-LED tube core 201; the porous GaN microlens 211 is located on the top of the Micro-LED tube core 201, and the centers of the two are collinear; the refractive index of the porous GaN microlens 211 gradually decreases from the direction of contacting the Micro-LED tube core 201 to the direction away from the Micro-LED tube core 201, and satisfies n p ∈(n T , 2.5).

[0031] The cathode transparent film layer 203 is located on the porous GaN microlens 211, the side wall of the Micro-LED die 201, and the pixel passivation layer 202; the cathode transparent film layer 203 is made of indium tin oxide (ITO), aluminum-doped zinc oxide (AZO), etc., with a refractive index n T Satisfy n T∈(1.8, 2.3); the cathode transparent film layer 203 forms a conductive channel through the porous GaN microlens 211, the Micro-LED die 201 and the reflective metal film layer 103;

[0032] The refractive index gradient film layer is located on the cathode transparent film layer 203; the refractive index gradient film layer is a multi-layer film layer structure, the number of film layers is at least two, and the refractive index of each film layer decreases layer by layer in the direction away from the Micro-LED tube core 201, and each film layer forms a microlens coinciding with the center of the Micro-LED tube core 201, and the porous GaN microlens 211, the microlens formed by the refractive index gradient film layer and the Micro-LED tube core 201 are all collinear in the center;

[0033] The refractive index range of the microlens formed by the film layer closest to the Micro-LED die 201 is n1∈(1.5, n T ), the refractive index range of the microlens formed by the film layer farthest from the Micro-LED die 201 is [1, 1.5];

[0034] The material of each film layer is one of silicon dioxide, silicon oxynitride, hafnium dioxide, aluminum oxide, silicon nitride, magnesium oxide, aluminum nitride, (Al, Ga, N) ternary alloy, amorphous glass, UV photoresist, etc., and each film layer selects a specific material according to the actual application scenario;

[0035] In this embodiment, the refractive index gradient film layer includes a first filling layer microlens 301 and a second filling layer microlens 302 which are sequentially arranged in a direction away from the Micro-LED tube core 201, and the first filling layer microlens 301 completely covers the cathode transparent film layer 203; the second filling layer microlens 302 completely covers the first filling layer microlens 301, and the first filling layer microlens 301 and the second filling layer microlens 302 both form microlenses, that is, the first filling layer microlens 301 and the second filling layer microlens 302 form a protrusion at the corresponding position of each Micro-LED tube core 201, the protruding portion forms a microlens, and the center of the protruding portion coincides with the center of the Micro-LED tube core 201.

[0036] The first film layer microlens 301 of the filling layer is a hemispherical microlens prepared by a semiconductor process. The ratio of the microlens of the first film layer microlens 301 to the line width of the Micro-LED core is in the range of 0.5 to 3. The second film layer microlens 302 of the filling layer to the outermost film layer microlens (if any) completely covers the first film layer microlens 301 of the filling layer, naturally forming a microlens shape.

[0037] The composite microlens group in the present invention is a multi-layer gradient refractive index microlens group. The Micro-LED pixel realizes the focusing and collimation of the light emitted by the Micro-LED core through the composite microlens group, reduces the loss of reflected light, and effectively improves the light extraction efficiency.

[0038] The Micro-LED described in the present invention can effectively improve the photoelectric conversion efficiency and is used to realize a micro display chip with ultra-high resolution and ultra-high brightness.

[0039] This embodiment also discloses a method for preparing a Micro LED based on a composite microlens group, which is used to prepare the Micro LED based on the composite microlens group described above, comprising the following steps:

[0040] Step 1: Figure 3 As shown, a plurality of unconnected electrode connection holes 102 are provided on the upper surface of the driving circuit 101; a reflective metal film layer 103 is evaporated on the upper surface of the driving circuit 101, and then a processed Micro-LED epitaxial wafer is bonded, the Micro-LED epitaxial wafer 20 is a GaN-based Micro-LED epitaxial wafer, and the GaN-based Micro-LED epitaxial wafer includes a substrate, a buffer layer, a doping gradient layer, an electron injection layer, a light-emitting layer and a hole injection layer arranged in sequence from bottom to top; the substrate and the buffer layer in the Micro-LED epitaxial wafer are removed to form a processed Micro-LED epitaxial wafer; the processed Micro-LED epitaxial wafer includes a hole injection layer, a light-emitting layer, an electron injection layer, and a doping gradient layer arranged in sequence in a direction away from the driving circuit 101;

[0041] The surface of one side of the processed Micro-LED epitaxial wafer is a doped gradient layer; the reflective metal film layer 103 is prepared by electron beam evaporation, thermal evaporation, magnetron sputtering, etc. The material of the reflective metal film layer 103 includes Ag, Pt, Al, etc. The reflective metal film layer 103 realizes the electrical connection between the hole injection layer and the driving circuit;

[0042] Step 2: A porous GaN microlens array is formed on the top of the Micro-LED epitaxial wafer after etching, and the porous GaN microlens array includes a plurality of porous GaN microlenses 211; Figure 4 As shown, the doped gradient layer on the upper surface of the processed Micro-LED epitaxial wafer is made into a porous GaN film layer 211' with a gradient refractive index by electrochemical etching or the like, and the porous GaN film layer 211' further forms a porous GaN microlens array, and the porous GaN microlens array includes a plurality of porous GaN microlenses 211, and the center of each porous GaN microlens 211 coincides with the center of the electrode connection hole 102;

[0043] The refractive index n of the porous GaN microlens 211 is pFrom bottom to top, that is, gradually decreasing in the direction away from the driving circuit 101, and satisfying n p ∈(n T , 2.5), where n T is the refractive index of the cathode transparent film layer 203;

[0044] Step 3: The portion of the Micro-LED epitaxial wafer after etching except for the porous GaN microlens array is formed into a Micro-LED die array, wherein the Micro-LED die array includes a plurality of Micro-LED dies 201 corresponding to the porous GaN microlenses 211 one by one, a pixel passivation layer 202 is formed on the side wall of the Micro-LED die 201, and a cathode transparent film layer 203 is formed on the top of the porous GaN microlens 211, on the pixel passivation layer 202, and on the side wall of the Micro-LED die 201; Figure 5 As shown, etching is performed on the processed Micro-LED epitaxial wafer, and the portion other than the porous GaN microlens array is further etched to prepare a Micro-LED die array, wherein the Micro-LED die array includes a plurality of disconnected Micro-LED die 201; the line width of a single Micro-LED die 201 in the Micro-LED die array is less than 10 microns, and the spacing between adjacent Micro-LED die 201 is less than 5 microns, and the center of each Micro-LED die 201 coincides with the center of the electrode connection hole 102, that is, the center of the porous GaN microlens 211, the center of the Micro-LED die 201, The centers of the electrode connection holes 102 correspond to each other and overlap one by one; the preparation of the Micro-LED die array can be carried out by a sidewall passivation process, and the growth process of the pixel passivation layer 202 includes atomic layer deposition (ALD) and plasma enhanced chemical vapor deposition (PEVD), and a pixel passivation layer 202 is formed on the sidewall of each Micro-LED die 201. Specifically, the pixel passivation layer 202 is in contact with the hole injection layer and the light-emitting layer in the Micro-LED die 201; the material of the pixel passivation layer 202 includes aluminum oxide, silicon oxide, aluminum nitride, and silicon nitride, and the pixel passivation layer is used to ensure that the cathode transparent film layer 203 is electrically isolated from the hole injection layer and the light-emitting layer in the Micro-LED die 201;

[0045] Then, a cathode transparent film layer 203 is formed on the side wall of the Micro-LED die array, on the pixel passivation layer 202, and on the top of the porous GaN microlens 211. The cathode transparent film layer 203 is connected; the cathode transparent film layer realizes an ohmic contact on one side of the electron injection layer in the Micro-LED die 201; the cathode transparent film layer includes but is not limited to indium tin oxide (ITO), aluminum-doped zinc oxide (AZO), etc., and the refractive index of the cathode transparent electrode layer satisfies n T ∈(1.8, 2.3).

[0046] The micro-LED die 201 and the porous GaN micro-lens 211 are both formed by a GaN-based micro-LED epitaxial wafer through a semiconductor process; the porous GaN micro-lens 211 is a porous GaN refractive index gradient lens, which is formed by a doped gradient layer, and the doped gradient layer is Si-doped GaN, which is grown by high-quality epitaxial growth of MOCVD or MBE, and the Si doping concentration is from high (buffer layer side) to low (electron injection layer side) to form a doped gradient film layer, and further a porous GaN film layer with a gradient refractive index is realized through a process, thereby obtaining a porous GaN refractive index gradient lens;

[0047] The Micro-LED die includes an electron injection layer, a hole injection layer, and a light-emitting layer, and the light-emitting wavelengths include red, green, and blue;

[0048] The ratio of the line width of the porous GaN microlens 211 to the line width of the Micro-LED die 201 ranges from 0.5 to 3;

[0049] A refractive index gradient film layer is formed on the cathode transparent film layer. The refractive index gradient film layer is a multi-layer film layer structure. The number of film layers is at least two, and the refractive index of each film layer decreases layer by layer in a direction away from the Micro-LED tube core, and each film layer forms a microlens coinciding with the center of the Micro-LED tube core. In this embodiment, the refractive index gradient film layer is two layers. The following is a process for preparing the refractive index gradient film layer:

[0050] Step 4: forming a first filling layer 301' on the side wall and on the cathode transparent film layer 203; Figure 6 As shown, the first film layer 301' of the growing filling layer completely covers the Micro-LED die, the porous GaN microlens array and the cathode transparent film layer 203; the refractive index n1 of the first film layer 301' of the growing filling layer satisfies n1∈(1, n T );

[0051] Step 5: Etching the first film layer 301' of the filling layer to form a first film layer micro lens 301 of the filling layer, wherein the first film layer micro lens 301 of the filling layer forms a protrusion above each Micro-LED tube core, and the center of the protrusion coincides with the center of the Micro-LED tube core; Figure 7 As shown, the first film layer of the filling layer is etched on the upper surface of the first film layer 301' to form the first film layer microlens 301 of the filling layer;

[0052] Step 6: forming a second filling layer micro lens on the first filling layer micro lens 301; Figure 8 As shown, the second film layer microlens material of the filling layer is grown by a growth device to completely cover the first film layer microlens of the filling layer; the refractive index n2 of the second film layer microlens of the filling layer satisfies n2∈(1, n1);

[0053] For Micro-LED array chips with specific light emission requirements, steps 5 and 6 can be repeated to repeatedly produce multiple filling layer film micro lenses. The refractive index of the subsequent film layers needs to decrease layer by layer, and the refractive index meets n i ∈[n e , n1]. The refractive index of the outermost film layer microlens array grown satisfies n e ∈[1, 1.5];

[0054] The second film layer to the outermost film layer can completely cover the first film layer microlens array to form a microlens shape, or the film layer microlens can be prepared on each film layer;

[0055] The film growth method includes ALD, CVD, PVD, spin coating solution drying and curing, etc.

[0056] The preparation method of the film layer microlens includes using positive photoresist to prepare a positive photoresist pixel array, etching the film layer material and the positive photoresist pixel array to prepare the microlens array; the positive photoresist used in the positive photoresist pixel array is prepared by a spin coating process to ensure its uniformity; the positive photoresist is exposed and developed to form a positive photoresist pixel array. The exposure process is performed using a stepper lithography machine, and the developer is immersed in the developer for development; the positive photoresist pixel array needs to be baked to form the required shape to adapt to the subsequent etching process; the positive photoresist pixel array and the film layer material are etched under certain conditions, and finally the positive photoresist pixel array disappears, the microlens array is formed, and the etching process is performed using inductively coupled plasma etching (ICP).

[0057] The present invention provides a method for preparing a Micro LED based on a composite microlens group with mature technical means, and the whole process adopts a traditional semiconductor preparation process, with a simple process flow and high stability. The prepared Micro LED based on a composite microlens group has good uniformity, can strongly converge the light emitted by the Micro-LED tube core, and effectively reduce reflection loss and improve photoelectric conversion efficiency. The composite microlens group can also be used as a passivation protection thick film, which can effectively protect the underlying Micro-LED tube core.

[0058] The above is only a preferred embodiment of the present invention. It should be pointed out that for ordinary technicians in this technical field, several improvements and modifications can be made without departing from the principle of the present invention. These improvements and modifications should also be regarded as the scope of protection of the present invention.

Claims

1. A Micro LED based on a composite microlens group, characterized in that: include: Driving circuit; Micro-LED pixel array located above the driving circuit; The Micro-LED pixel array includes a plurality of Micro-LED pixels arranged at intervals, each Micro-LED pixel includes a Micro-LED tube core and a composite micro lens group covering the Micro-LED tube core; a pixel passivation layer is provided on the side wall of the Micro-LED tube core; The composite microlens group includes a porous GaN microlens, a cathode transparent film layer, and a refractive index gradient film layer which are sequentially arranged in a direction away from the Micro-LED tube core; the porous GaN microlens is located on the top of the Micro-LED tube core, and the centers of the two are collinear; The cathode transparent film layer is located on the porous GaN microlens, the sidewall of the Micro-LED die, and the pixel passivation layer; The refractive index gradient film layer is located on the cathode transparent film layer; the refractive index gradient film layer is a multi-layer film layer structure, the number of film layers is at least two, and the refractive index of each film layer decreases layer by layer in the direction away from the Micro-LED tube core, and each film layer forms a microlens that coincides with the center of the Micro-LED tube core, and the porous GaN microlens, the microlens formed by the refractive index gradient film layer and the center of the Micro-LED tube core are all collinear.

2. The Micro LED based on a composite microlens group according to claim 1, characterized in that: The refractive index range of the microlens formed by the film layer closest to the Micro-LED die is (1.5, n T ), the refractive index range of the microlens formed by the film layer farthest from the Micro-LED die is [1,1.5], where n T is the refractive index of the cathode transparent film layer.

3. The Micro LED based on a composite microlens group according to claim 1, characterized in that: The porous GaN microlens is formed by a doped gradient layer, the doped gradient layer is Si-doped GaN, and the Si doping concentration decreases from high to low to form a doped gradient film layer.

4. The Micro LED based on a composite microlens group according to claim 1, characterized in that: The material of the cathode transparent film layer is indium tin oxide or aluminum doped zinc oxide, and the refractive index of the cathode transparent film layer satisfies n T ∈(1.8, 2.3).

5. The Micro LED based on a composite microlens group according to claim 1, characterized in that: The refractive index of the porous GaN microlens gradually decreases as it moves away from the Micro-LED die, and the refractive index satisfies n p ∈(n T , 2.5), where n T is the refractive index of the cathode transparent film layer.

6. The Micro LED based on a composite microlens group according to claim 1, characterized in that: The ratio of the porous GaN microlens to the line width of the Micro-LED core ranges from 0.5 to 3.

7. The Micro LED based on a composite microlens group according to claim 1, characterized in that: Materials of the refractive index gradient film layer include silicon dioxide, silicon oxynitride, hafnium dioxide, aluminum oxide, silicon nitride, magnesium oxide, aluminum nitride, (Al, Ga, N) ternary alloy, amorphous glass, and UV photoresist.

8. The Micro LED based on a composite microlens group according to claim 1, characterized in that: A plurality of electrode connection holes are provided in the driving circuit, a reflective metal film layer is provided on the upper surface of the driving circuit, and the Micro-LED pixel array is connected to the driving circuit through the reflective metal film layer and the electrode connection holes.

9. A method for preparing a Micro LED based on a composite microlens group, used to manufacture a Micro LED based on a composite microlens group as claimed in any one of claims 1 to 8, characterized in that: The following steps are involved: Step 1: a plurality of unconnected electrode connection holes are provided on the upper surface of the driving circuit; a reflective metal film layer is evaporated on the upper surface of the driving circuit, and then a processed Micro-LED epitaxial wafer is bonded; the Micro-LED epitaxial wafer is a GaN-based Micro-LED epitaxial wafer; the processed Micro-LED epitaxial wafer includes a hole injection layer, a light-emitting layer, an electron injection layer, and a doping gradient layer which are sequentially arranged in a direction away from the driving circuit; Step 2: A porous GaN microlens array is formed on the top of the Micro-LED epitaxial wafer after etching, wherein the porous GaN microlens array includes a plurality of porous GaN microlenses; Step 3: The portion of the Micro-LED epitaxial wafer after etching except for the porous GaN microlens array is formed into a Micro-LED die array, wherein the Micro-LED die array includes a plurality of Micro-LED dies corresponding to the porous GaN microlenses one by one, a pixel passivation layer is formed on the side wall of the Micro-LED die, and a cathode transparent film layer is formed on the top of the porous GaN microlens, on the pixel passivation layer, and on the side wall of the Micro-LED die; Step 4: forming a refractive index gradient film layer on the cathode transparent film layer.

10. The method for preparing a Micro LED based on a composite microlens group according to claim 9, characterized in that: The pixel passivation layer contacts the hole injection layer and the light-emitting layer in the Micro-LED tube core; the cathode transparent film layer realizes ohmic contact on one side of the electron injection layer in the Micro-LED tube core; The pixel passivation layer is used to ensure that the cathode transparent film layer is electrically isolated from the hole injection layer and the light-emitting layer in the Micro-LED tube core.

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