Micro light emitting element and method for manufacturing the same

Abstract

The present application provides a kind of micro light emitting element and its preparation method, by setting epitaxial stack on the surface of non-doped semiconductor layer, the epitaxial stack at least includes along sequentially stacked first type semiconductor layer, second active region and second type semiconductor layer;And, the second electrode led out on the second type semiconductor layer and the first electrode led out on the first type semiconductor layer;And, the exposed surface of the epitaxial stack is provided with mirror.Wherein, the non-doped semiconductor layer is provided with first active region interlayer, and photonic crystal structure is arranged on the non-doped semiconductor layer, so that at least part of the photons released by the second active region is reflected by the mirror, and after being absorbed by the first active region interlayer, it is emitted along the normal direction of the first active region interlayer through the photonic crystal structure.

Description

Technical Field

[0001] This invention relates to the field of light-emitting diodes, and more particularly to a micro light-emitting element and its fabrication method. Background Technology

[0002] Micro-component technology refers to the high-density integration of tiny arrays of components on a substrate. Currently, Mini / Micro-LED technology is becoming a hot research topic, with industry eagerly anticipating the market entry of high-quality micro-component products. High-quality Mini / Micro-LED products will have a profound impact on existing traditional display products such as LCD / OLED. Therefore, improving the photoelectric conversion efficiency of micro-light-emitting elements has become paramount in advancing display development.

[0003] The photoelectric conversion process of micro-light-emitting elements consists of two steps. First, electricity is converted into light inside the device; this efficiency is called the internal quantum efficiency. With the maturity of technology, the internal quantum efficiency has approached 100%. After light is emitted from inside the device, it needs to escape from the device itself; its escape capability is called the light emission efficiency (LEE). Blue-green LEDs are typically made of GaN with a refractive index of around 2.5, while red LEDs are typically made of GaAs with a refractive index of 3.3. Due to the high refractive index of the materials, most light has difficulty escaping the LED due to total internal reflection, resulting in a low LEE. To improve the LEE, many methods have been devised to modify the device structure, such as rough surfaces, tilted sidewalls, PSS substrates, gratings, embedded photonic crystals, surface-mount photonic crystals, and DBRs, to alter or add new structures to the device.

[0004] Among these approaches, embedded photonic crystals can not only improve the light extraction efficiency of micro-light-emitting elements (LEDs), but also enhance their emission pattern using their photonic bandgap. For near-eye displays, the emission pattern is as important as the luminous efficiency, especially requiring high normal brightness. Therefore, embedded photonic crystals have become a crucial research direction. However, to enable photonic crystals to improve the emission pattern of micro-LEDs, the fabrication of embedded photonic crystals typically involves drilling holes deep into the active region. This method directly reduces the effective light-emitting area of ​​the active region, increases leakage channels, and degrades the device performance of the micro-LEDs.

[0005] In view of this, the inventors have specifically designed a micro light-emitting element and its preparation method, which leads to this invention. Summary of the Invention

[0006] The purpose of this invention is to provide a micro light-emitting element and its preparation method to solve the problem of low light extraction efficiency of micro light-emitting elements.

[0007] To achieve the above objectives, the technical solution adopted by the present invention is as follows:

[0008] A micro light-emitting element includes a substrate and a plurality of LED chips located on the surface of the substrate, each LED chip comprising:

[0009] An epitaxial stack disposed on the surface of an undoped semiconductor layer, the epitaxial stack comprising at least a first type semiconductor layer, a second active region, and a second type semiconductor layer stacked sequentially; and a second electrode led out from the second type semiconductor layer and a first electrode led out from the first type semiconductor layer; and a reflector provided on the exposed surface of the epitaxial stack.

[0010] The undoped semiconductor layer is provided with a first active region interlayer, and a photonic crystal structure is provided on the undoped semiconductor layer, so that at least part of the photons released by the second active region are reflected by the mirror, absorbed by the first active region interlayer, and emitted along the normal of the first active region interlayer through the photonic crystal structure.

[0011] Preferably, the first active region interlayer and the second active region each include a plurality of periodic units composed of quantum wells and quantum barriers, and the number of periods in the first active region interlayer is not less than the number of periods in the second active region.

[0012] Preferably, the photonic crystal structure comprises a plurality of columnar structures formed by etching the undoped semiconductor layer.

[0013] Preferably, the columnar structure is formed by etching along the back side of the undoped semiconductor layer to the first active region interlayer.

[0014] Preferably, each of the columnar structures is any one of a cone shape, column shape, pyramid shape, or hemispherical shape.

[0015] Preferably, the arrangement of each columnar structure is a square or a triangular grid.

[0016] Preferably, the microdisplay device includes a GaN-based light-emitting diode; then, the undoped semiconductor layer includes a U-GaN layer, the first type semiconductor layer includes an N-type GaN layer, and the second type semiconductor layer includes a P-type GaN layer.

[0017] Preferably, the reflector includes at least one of a DBR structure, an ODR structure, and a metal reflector.

[0018] Preferably, in order to broaden the emission angle and improve the light extraction rate, the reflector covers the exposed surface of the epitaxial stack.

[0019] Preferably, when the reflector is made of a conductive material and extends to the sidewall of the epitaxial stack, a passivation layer is also provided on the sidewall of the epitaxial stack to prevent short circuits of the microdisplay device.

[0020] Preferably, the passivation layer comprises SiO2, SiC, AlN, SiONx, and SiN. x One or more of them.

[0021] Preferably, if a local area of ​​the epitaxial stack is etched to a portion of the first type semiconductor layer to form a groove and a mesa, then the first electrode is formed on the surface of the groove by embedding the reflector through a through-hole, and the second electrode is formed on the surface of the mesa by embedding the reflector through a through-hole.

[0022] Preferably, a transparent conductive layer is provided on the table surface.

[0023] Preferably, the material of the transparent conductive layer includes one or more of ITO, ZnO, IWO, and AZO.

[0024] Preferably, the micro-light-emitting element includes a Mini-LED chip or a Micro-LED chip.

[0025] The present invention also provides a method for fabricating a micro light-emitting element, the method comprising the following steps:

[0026] Step S01: Provide a substrate;

[0027] Step S02: An undoped semiconductor layer and an epitaxial stack are sequentially grown on the surface of the substrate. The epitaxial stack includes at least a first type semiconductor layer, a second active region, and a second type semiconductor layer grown sequentially. The undoped semiconductor layer is provided with a first active region interlayer.

[0028] Step S03: Etch a portion of the epitaxial stack to a portion of the first type semiconductor layer to form several grooves and mesa;

[0029] Step S04: Prepare a transparent conductive layer on each of the aforementioned mesa surfaces;

[0030] Step S05: Etch along the surface of the epitaxial stack to the surface of the substrate to form a plurality of light-emitting units arranged at intervals through channels;

[0031] Step S06: Fabricate a reflector on the epitaxial stack of each of the light-emitting units, and use photolithography and masking processes to make the reflector have through holes that expose the groove and the mesa;

[0032] Step S07: Fabricate a first electrode and a second electrode. The first electrode is stacked on the groove through a through-hole, and the second electrode is stacked on the mesa through a through-hole; thereby obtaining a plurality of mutually isolated LED chips.

[0033] Step S08: Peel off the substrate;

[0034] Step S09: Fabricate a photonic crystal structure on the undoped semiconductor layer;

[0035] Step S10: Provide a substrate and bond each of the LED chips to the substrate.

[0036] Preferably, the first active region interlayer and the second active region each include a plurality of periodic units composed of quantum wells and quantum barriers, and the number of periods in the first active region interlayer is not less than the number of periods in the second active region.

[0037] Preferably, the photonic crystal structure comprises a plurality of columnar structures formed by etching the undoped semiconductor layer.

[0038] As can be seen from the above technical solution, the micro light-emitting element provided by the present invention comprises an epitaxial stack on the surface of an undoped semiconductor layer, the epitaxial stack including at least a first type semiconductor layer, a second active region, and a second type semiconductor layer stacked sequentially; a second electrode led out from the second type semiconductor layer and a first electrode led out from the first type semiconductor layer; and a reflector provided on the exposed surface of the epitaxial stack. The undoped semiconductor layer has a first active region interlayer, and a photonic crystal structure is provided on the undoped semiconductor layer, so that at least a portion of the photons emitted by the second active region are reflected by the reflector, absorbed by the first active region interlayer, and then emitted along the normal of the first active region interlayer through the photonic crystal structure. Specifically, when the micro light-emitting element of the present invention is injected with current through the first electrode and the second electrode, at least a portion of the light emitted by the second active region is reflected by the mirror and irradiates the first active region interlayer. Since the first active region interlayer has no electron injection, its conduction band contains a large number of vacancies compared to the second active region. This means that the first active region interlayer can effectively absorb the photons radiated by the second active region. After a certain period of time, the absorbed photons will be re-radiated. During the re-radiation, due to the band gap of the transversely existing photonic crystal structure, the non-normal light will be suppressed, and the normal light perpendicular to the plane of the first active region interlayer will be enhanced. At the same time, photons that are not absorbed by the first active region interlayer escape from the light-emitting element after being affected by the diffraction ability of the photonic crystal structure, thereby further improving the light extraction efficiency.

[0039] Secondly, the first active region interlayer and the second active region each include a plurality of periodic units composed of quantum wells and quantum barriers, and the number of periods in the first active region interlayer is not less than the number of periods in the second active region. Thus, without affecting the effective light-emitting area of ​​the second active region, the photon absorption capability of the first active region interlayer is guaranteed, thereby further improving the light extraction efficiency of the micro-light-emitting element.

[0040] This invention also provides a method for fabricating micro-component structures, which achieves the above-mentioned technical effects while being simple to operate and easy to implement. Attached Figure Description

[0041] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on the provided drawings without creative effort.

[0042] Figure 1 This is a schematic diagram of the structure of the micro light-emitting element provided in an embodiment of the present invention;

[0043] Figures 2.1 to 2.10 This is a schematic diagram of the structure corresponding to the method for fabricating the micro light-emitting element provided in the embodiments of the present invention;

[0044] Figure 3 This is a schematic diagram of a photonic crystal structure arranged in a triangular lattice, provided in an embodiment of the present invention.

[0045] Figure 4 This is a schematic diagram of a photonic crystal structure arranged in a square grid, provided in an embodiment of the present invention.

[0046] Explanation of symbols in the diagram:

[0047] 1. Substrate;

[0048] 2. Undoped semiconductor layer; 21, 23: U-GaN layer; 22. First active region interlayer;

[0049] 3. Type I semiconductor layer;

[0050] 4. Second active region;

[0051] 5. Type II semiconductor layer;

[0052] 6. Transparent conductive layer;

[0053] 7. Reflector;

[0054] 8. First electrode;

[0055] 9. Second electrode;

[0056] 10. Substrate;

[0057] 11. Groove;

[0058] 12. Countertop;

[0059] 13. Ditch;

[0060] 14. Through hole;

[0061] 15. Columnar structure. Detailed Implementation

[0062] To make the content of this invention clearer, the following description, in conjunction with the accompanying drawings, further illustrates the invention. This invention is not limited to this specific embodiment. All other embodiments obtained by those skilled in the art based on the embodiments of this invention without inventive effort are within the scope of protection of this invention.

[0063] like Figure 1 As shown, a micro light-emitting element includes a substrate 10 and a plurality of LED chips located on the surface of the substrate 10, each of the LED chips comprising:

[0064] An epitaxial stack is disposed on the surface of the undoped semiconductor layer 2. The epitaxial stack includes at least a first type semiconductor layer 3, a second active region 4 and a second type semiconductor layer 5 stacked sequentially; and a second electrode 9 led out from the second type semiconductor layer 5 and a first electrode 8 led out from the first type semiconductor layer 3; and a reflector 7 is provided on the exposed surface of the epitaxial stack.

[0065] The undoped semiconductor layer 2 is provided with a first active region interlayer 22, and a photonic crystal structure is provided on the undoped semiconductor layer 2, so that at least part of the photons released by the second active region 4 are reflected by the mirror 7, absorbed by the first active region interlayer 22, and emitted along the normal of the first active region interlayer 22 through the photonic crystal structure.

[0066] It should be emphasized that, in order to highlight the technical inventive points of this invention, in the embodiments of this invention, Figure 1 This illustration only shows one LED chip in the micro-light-emitting device. In actual use, the surface of substrate 1 contains tens of thousands of LED chips, depending on the specific situation. This application does not limit this.

[0067] Based on the above embodiments, in one embodiment of this application, the first active region interlayer 22 and the second active region 4 each include a plurality of periodic units composed of quantum wells and quantum barriers, and the number of periods of the first active region interlayer 22 is not less than the number of periods of the second active region 4.

[0068] Based on the above embodiments, in one embodiment of this application, the photonic crystal structure includes a plurality of columnar structures 15 formed by etching the undoped semiconductor layer 2.

[0069] Based on the above embodiments, in one embodiment of this application, the columnar structure 15 is formed by etching along the back side of the undoped semiconductor layer 2 to the first active region interlayer 22.

[0070] Based on the above embodiments, in one embodiment of this application, each of the columnar structures 15 is any one of conical, columnar, pyramidal, or hemispherical.

[0071] Based on the above embodiments, in one embodiment of this application, the columnar structures 15 are arranged in a square or triangular grid.

[0072] Based on the above embodiments, in one embodiment of this application, the microdisplay device includes a GaN-based light-emitting diode; then, the undoped semiconductor layer 2 includes a U-GaN layer (21, 23), the first type semiconductor layer 3 includes an N-type GaN layer, and the second type semiconductor layer 5 includes a P-type GaN layer.

[0073] Based on the above embodiments, in one embodiment of this application, the reflector 7 includes at least one of a DBR structure, an ODR structure, and a metal reflector 7.

[0074] Based on the above embodiments, in one embodiment of this application, in order to expand the emission angle and improve the light extraction rate, the reflector 7 covers the exposed surface of the epitaxial stack.

[0075] Based on the above embodiments, in one embodiment of this application, when the reflector 7 is a conductive material and extends to the sidewall of the epitaxial stack, a passivation layer is also provided on the sidewall of the epitaxial stack to prevent short circuit of the microdisplay device.

[0076] Based on the above embodiments, in one embodiment of this application, the passivation layer includes SiO2, SiC, AlN, SiONx, and SiN. x One or more of them.

[0077] Based on the above embodiments, in one embodiment of this application, a local area of ​​the epitaxial stack is etched to a portion of the first type semiconductor layer 3 to form a groove 11 and a mesa 12. Then, the first electrode 8 is formed on the surface of the groove 11 by embedding the reflector 7 through a through-hole 14, and the second electrode 9 is formed on the surface of the mesa 12 by embedding the reflector 7 through a through-hole 14.

[0078] Based on the above embodiments, in one embodiment of this application, a transparent conductive layer 6 is provided on the tabletop 12.

[0079] Based on the above embodiments, in one embodiment of this application, the material of the transparent conductive layer 6 includes one or more of ITO, ZnO, IWO, and AZO.

[0080] Based on the above embodiments, in one embodiment of this application, the micro light-emitting element includes a Mini-LED chip or a Micro-LED chip.

[0081] This invention also provides a method for fabricating a micro light-emitting element, the method comprising the following steps:

[0082] Step S01, as follows Figure 2.1 As shown, a substrate 1 is provided;

[0083] It should be noted that the type of substrate 1 is not limited in the micro light-emitting element of this embodiment. For example, substrate 1 can be, but is not limited to, sapphire substrate 1, silicon substrate 1, etc.

[0084] Step S02, as follows Figure 2.2 As shown, an undoped semiconductor layer 2 and an epitaxial stack are sequentially grown on the surface of the substrate 1. The epitaxial stack includes at least a first type semiconductor layer 3, a second active region 4, and a second type semiconductor layer 5 that are sequentially grown. The undoped semiconductor layer 2 is provided with a first active region interlayer 22.

[0085] Based on the above embodiments, in one embodiment of this application, the first active region interlayer 22 and the second active region 4 each include a plurality of periodic units composed of quantum wells and quantum barriers, and the number of periods of the first active region interlayer 22 is not less than the number of periods of the second active region 4.

[0086] In one embodiment of the present invention, the microdisplay device includes a GaN-based light-emitting diode; then, the undoped semiconductor layer 2 includes a U-GaN layer (21, 23), the first type semiconductor layer 3 includes an N-type GaN layer, and the second type semiconductor layer 5 includes a P-type GaN layer; this application does not limit this.

[0087] Based on the above embodiments, in one embodiment of this application, the quantum barrier includes a GaN layer and the quantum well includes an InGaN layer.

[0088] Step S03, as Figure 2.3 As shown, a local area of ​​the epitaxial stack is etched to a portion of the first type semiconductor layer 3 to form a plurality of grooves 11 and mesa 12;

[0089] In one embodiment of this application, etching the epitaxial stack to form a plurality of grooves 11 and mesa 12 includes using an inductively coupled plasma (ICP) process, wherein the etching gas includes Cl2, Ar and O2. However, this application does not limit this, and the specific method depends on the circumstances.

[0090] Step S04, as Figure 2.4 As shown, a transparent conductive layer 6 is prepared on each of the aforementioned mesa 12;

[0091] In one embodiment of this application, the material of the transparent conductive layer 6 may be ITO, ZnO, IWO, AZO, etc., and its formation process may be electron beam evaporation, sputtering evaporation, etc., depending on the specific circumstances. This application does not limit this process.

[0092] Based on the above embodiments, in one embodiment of this application, an extended electrode is provided on the bottom surface of the platform 12 and / or the groove 11, and the extended electrode is stacked on the surface of the transparent conductive layer 6; wherein, the extended electrode includes one or more of chromium, nickel, aluminum, titanium, platinum, gold, palladium and silver.

[0093] Step S05, as follows Figure 2.5 As shown, the surface of the epitaxial stack is etched to the surface of the substrate 1 to form a plurality of light-emitting units arranged at intervals through the channel 13;

[0094] In one embodiment of this application, the epitaxial stack is deeply etched to the surface of the exposed substrate 1 to form a plurality of light-emitting units arranged at intervals through channels 13; this includes using an inductively coupled plasma (ICP) process, with etching gases including Cl2, Ar, and O2. However, this application does not limit this, and the specific method depends on the circumstances.

[0095] Step S06, as follows Figure 2.6 As shown, a reflector 7 is fabricated on the epitaxial stack of each of the light-emitting units, and through photolithography and masking processes, the reflector 7 has a through hole 14 that exposes the groove 11 and the mesa 12;

[0096] In one embodiment of this application, the reflector 7 includes at least one of a DBR structure, an ODR structure, and a metal reflector 7.

[0097] Based on the above embodiments, in one embodiment of this application, in order to expand the emission angle and improve the light extraction rate, the reflector 7 covers the exposed surface of the epitaxial stack.

[0098] Based on the above embodiments, in one embodiment of this application, when the reflector 7 is made of a conductive material and extends to the sidewall of the epitaxial stack, a passivation layer is further provided on the sidewall of the epitaxial stack to prevent short circuits of the microdisplay device. Specifically, the passivation layer includes SiO2, SiC, AlN, SiONx, and SiN. x One or more of them.

[0099] Step S07, as follows Figure 2.7 As shown, a first electrode 8 and a second electrode 9 are fabricated. The first electrode 8 is stacked on the groove 11 through the through hole 14, and the second electrode 9 is stacked on the platform 12 through the through hole 14; thereby obtaining a plurality of mutually isolated LED chips.

[0100] In one embodiment of this application, the first electrode 8 and the second electrode 9 respectively comprise one or more stacks of chromium, nickel, aluminum, titanium, platinum, gold, palladium, silver, and gold-tin alloy.

[0101] Step S08, as follows Figure 2.8 As shown, the substrate 1 is peeled off;

[0102] Step S09, as follows Figure 2.9 As shown, a photonic crystal structure is fabricated on the undoped semiconductor layer 2;

[0103] In one embodiment of this application, the photonic crystal structure includes a plurality of pillar-shaped structures 15 formed by etching the undoped semiconductor layer 2. Specifically, the plurality of pillar-shaped structures 15 are formed by etching the undoped semiconductor layer 2 using photolithography or nanoimprint lithography.

[0104] Based on the above embodiments, in one embodiment of this application, the columnar structure 15 is formed by etching along the back side of the undoped semiconductor layer 2 to the first active region interlayer 22.

[0105] Based on the above embodiments, in one embodiment of this application, each of the columnar structures 15 is any one of conical, columnar, pyramidal, or hemispherical.

[0106] Based on the above embodiments, in one embodiment of this application, the columnar structures 15 are arranged in a square or triangular grid. See details for further information. Figure 3 , Figure 4 ,in, Figure 3The triangles in the diagram illustrate that the arrangement of the columnar structures 15 is a triangular grid. Figure 4 The square in the diagram illustrates that the arrangement of the columnar structures 15 is a grid.

[0107] Step S10, as follows Figure 2.10 As shown, a substrate 10 is provided, and each of the LED chips is bonded to the substrate 10.

[0108] Based on the above embodiments, in one embodiment of this application, the first active region interlayer 22 and the second active region 4 each include a plurality of periodic units composed of quantum wells and quantum barriers, and the number of periods of the first active region interlayer 22 is not less than the number of periods of the second active region 4.

[0109] As can be seen from the above technical solution, the micro light-emitting element provided in this embodiment of the invention comprises an epitaxial stack on the surface of an undoped semiconductor layer 2, the epitaxial stack including at least a first type semiconductor layer 3, a second active region 4, and a second type semiconductor layer 5 stacked sequentially; a second electrode 9 led out from the second type semiconductor layer 5 and a first electrode 8 led out from the first type semiconductor layer 3; and a reflector 7 provided on the exposed surface of the epitaxial stack. The undoped semiconductor layer 2 is provided with a first active region interlayer 22, and a photonic crystal structure is provided on the undoped semiconductor layer 2, so that at least a portion of the photons emitted by the second active region 4 are reflected by the reflector 7, absorbed by the first active region interlayer 22, and emitted along the normal of the first active region interlayer 22 through the photonic crystal structure. Specifically, when the micro light-emitting element of the present invention is injected with current through the first electrode 8 and the second electrode 9, at least part of the light emitted by the second active region 4 is reflected by the reflector 7 and irradiates the first active region interlayer 22. Since the first active region interlayer 22 has no electron injection, its conduction band contains a large number of vacancies compared to the second active region 4. This means that the first active region interlayer 22 can effectively absorb the photons radiated by the second active region 4. After a certain period of time, the absorbed photons will be re-radiated. When re-radiated, due to the band gap of the transversely existing photonic crystal structure, its non-normal light will be suppressed, and the normal light perpendicular to the plane of the first active region interlayer 22 will be enhanced. At the same time, photons that are not absorbed by the first active region interlayer 22 escape from the light-emitting element after being affected by the diffraction ability of the photonic crystal structure, thereby further improving the light extraction efficiency.

[0110] Secondly, the first active region interlayer 22 and the second active region 4 each include a plurality of periodic units composed of quantum wells and quantum barriers, and the number of periods in the first active region interlayer 22 is not less than the number of periods in the second active region 4. Thus, without affecting the effective light-emitting area of ​​the second active region 4, the photon absorption capability of the first active region interlayer 22 is guaranteed, thereby further improving the light extraction efficiency of the micro-light-emitting element.

[0111] This invention also provides a method for fabricating a micro-element structure, which achieves the above-mentioned technical effects while being simple to operate and easy to implement.

[0112] The various embodiments in this specification are described in a progressive manner, with each embodiment focusing on the differences from other embodiments. The same or similar parts between the various embodiments can be referred to each other.

[0113] It should also be noted that, in this document, relational terms such as "first" and "second" are used merely to distinguish one entity or operation from another, and do not necessarily require or imply any such actual relationship or order between these entities or operations. Furthermore, the terms "comprising," "including," or any other variations thereof are intended to cover non-exclusive inclusion, such that an article or apparatus comprising a list of elements includes not only those elements but also other elements not expressly listed, or elements inherent to such an article or apparatus. Without further limitations, an element defined by the phrase "comprising one..." does not exclude the presence of other identical elements in the article or apparatus that includes the aforementioned element.

[0114] The above description of the disclosed embodiments enables those skilled in the art to make or use this application. Various modifications to these embodiments will be readily apparent to those skilled in the art, and the general principles defined herein may be implemented in other embodiments without departing from the spirit or scope of this application. Therefore, this application is not to be limited to the embodiments shown herein, but is to be accorded the widest scope consistent with the principles and novel features disclosed herein.

Claims

1. A micro light-emitting element, comprising a substrate and a plurality of LED chips located on the surface of the substrate, characterized in that, Each of the aforementioned LED chips includes: An epitaxial stack disposed on the surface of an undoped semiconductor layer, the epitaxial stack comprising at least a first type semiconductor layer, a second active region, and a second type semiconductor layer stacked sequentially; and a second electrode led out from the second type semiconductor layer and a first electrode led out from the first type semiconductor layer; and a reflector provided on the exposed surface of the epitaxial stack. The undoped semiconductor layer is provided with a first active region interlayer, and a photonic crystal structure is provided on the undoped semiconductor layer, so that at least part of the photons released by the second active region are reflected by the mirror, absorbed by the first active region interlayer, and emitted along the normal of the first active region interlayer through the photonic crystal structure.

2. The micro light-emitting element according to claim 1, characterized in that, The first active region sandwich layer and the second active region each include a plurality of periodic units composed of quantum wells and quantum barriers, and the number of periods in the first active region sandwich layer is not less than the number of periods in the second active region.

3. The micro light-emitting element according to claim 1, characterized in that, The photonic crystal structure includes a plurality of columnar structures formed by etching the undoped semiconductor layer.

4. The micro light-emitting element according to claim 3, characterized in that, The columnar structure is formed by etching along the back side of the undoped semiconductor layer into the first active region interlayer.

5. The micro light-emitting element according to claim 3, characterized in that, Each of the columnar structures is in the shape of a cone, column, pyramid, or hemisphere.

6. The micro light-emitting element according to claim 3, characterized in that, The columnar structures are arranged in a square or triangular grid.

7. The micro light-emitting element according to claim 1, characterized in that, The micro light-emitting element includes a GaN-based light-emitting diode; therefore, the undoped semiconductor layer includes a U-GaN layer, the first type semiconductor layer includes an N-type GaN layer, and the second type semiconductor layer includes a P-type GaN layer.

8. The micro light-emitting element according to claim 1, characterized in that, The reflector includes at least one of the following: DBR structure, ODR structure, and metal reflector.

9. The micro light-emitting element according to claim 1, characterized in that, If a local area of ​​the epitaxial stack is etched to a portion of the first type semiconductor layer to form a groove and a mesa, then the first electrode is formed on the surface of the groove by embedding the reflector through a through-hole, and the second electrode is formed on the surface of the mesa by embedding the reflector through a through-hole.

10. The micro light-emitting element according to claim 9, characterized in that, A transparent conductive layer is provided on the platform.

11. The micro light-emitting element according to claim 1, characterized in that, The micro-light-emitting element includes a Mini-LED chip or a Micro-LED chip.

12. A method for fabricating a micro light-emitting element, characterized in that, The preparation method includes the following steps: Step S01: Provide a substrate; Step S02: An undoped semiconductor layer and an epitaxial stack are sequentially grown on the surface of the substrate. The epitaxial stack includes at least a first type semiconductor layer, a second active region, and a second type semiconductor layer grown sequentially. The undoped semiconductor layer is provided with a first active region interlayer. Step S03: Etch a portion of the epitaxial stack to a portion of the first type semiconductor layer to form several grooves and mesa; Step S04: Prepare a transparent conductive layer on each of the aforementioned mesa surfaces; Step S05: Etch along the surface of the epitaxial stack to the surface of the substrate to form a plurality of light-emitting units arranged at intervals through channels; Step S06: Fabricate a reflector on the epitaxial stack of each of the light-emitting units, and use photolithography and masking processes to make the reflector have through holes that expose the groove and the mesa; Step S07: Fabricate a first electrode and a second electrode. The first electrode is stacked on the groove through a through-hole, and the second electrode is stacked on the mesa through a through-hole; thereby obtaining a plurality of mutually isolated LED chips. Step S08: Peel off the substrate; Step S09: Fabricate a photonic crystal structure on the undoped semiconductor layer; Step S10: Provide a substrate and bond each of the LED chips to the substrate.

13. The method for fabricating a micro light-emitting element according to claim 12, characterized in that, The first active region sandwich layer and the second active region each include a plurality of periodic units composed of quantum wells and quantum barriers, and the number of periods in the first active region sandwich layer is not less than the number of periods in the second active region.

14. The method for fabricating a micro light-emitting element according to claim 12, characterized in that, The photonic crystal structure includes a plurality of columnar structures formed by etching the undoped semiconductor layer.

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