Full-color LED micro display array structure, preparation method and full-color LED micro display

Abstract

The application belongs to the field of semiconductor display, and specifically provides a full-color LED micro display array structure, a preparation method and a full-color LED micro display, which comprises a vertical stack of red, green and blue three-primary-color LED pixel groups, each pixel comprising, from bottom to top, a substrate, a first light-emitting unit, a second light-emitting unit, a third light-emitting unit, a metal reflecting layer and a third electrode arranged above the third light-emitting unit, a SiO2 insulating layer arranged above the metal reflecting layer, a first electrode arranged above the SiO2 insulating layer and connected to the first light-emitting unit, a second electrode arranged above the SiO2 insulating layer and connected to the second light-emitting unit, and a fourth electrode arranged above the SiO2 insulating layer and connected to the first light-emitting unit, the second light-emitting unit and the third light-emitting unit, and red light, green light and blue light are emitted from the substrate side. Not only the light-emitting efficiency of blue light and green light LEDs is improved, but also the light down-conversion process is avoided, thereby improving the color rendering index of the vertical stack LED.

Description

Technical Field

[0001] This invention relates to the field of semiconductor displays, and in particular to a full-color LED microdisplay array structure, its fabrication method, and a full-color LED microdisplay. Background Technology

[0002] High-density full-color LED microdisplays are core components for realizing AR consumer applications. Full-color LED microdisplay technology is the key technology driving its practical development. Regarding the realization of full-color LED microdisplays, existing widely adopted full-color LED microdisplay manufacturing technologies rely on color conversion technology between monochrome (blue or violet) LED microarrays and fluorescent materials. The advantage of this technology is that it easily achieves high-density, small-size full-color LED microdisplay arrays. The biggest problem lies in the limitation of the conversion efficiency of the color conversion materials; as the size of monochrome pixels continues to shrink, the conversion efficiency problem becomes particularly prominent. Although existing technologies based on mass transfer of red, green, and blue LEDs have been maturely developed and applied in large-screen full-color LED displays, mainly by mass-transferring red, green, and blue LED arrays into a planar side-by-side structure and independently controlling the three primary colors of each pixel to achieve full color, its advantages include not relying on complex 3D interconnect IC processes, high yield, and high color rendering index. However, it is difficult to obtain high-density, small-size full-color LED microdisplay arrays.

[0003] Currently, various micro-LED transfer and integration technologies for semiconductors such as GaAs and GaN have developed micro-thin-film LEDs with different emission wavelengths and expanded their applications in areas such as biosensing. However, the development of micro-LED display technology based on III-V semiconductors also faces many challenges, including: (1) As the device size shrinks, the carrier recombination caused by edge defects also increases significantly, resulting in a decrease in the luminous performance of micro-LEDs as the size shrinks; (2) As the device size shrinks, the requirements for positioning accuracy in the device processing and transfer integration process are becoming increasingly higher, directly leading to an increase in process costs; (3) Since micro-LEDs with red, green, and blue emission wavelengths are based on III-V semiconductor materials with different compositions, they cannot be grown simultaneously, and the sizes of different devices also have significant differences. They need to be integrated by batch transfer, and the yield control in the integration process is also difficult. Chinese Patent Publication CN114824006A discloses a micro-LED array luminous structure and its preparation method. The micro LED array light-emitting structure includes a substrate and multiple LED array units. The multiple LED array units are distributed and arranged along the surface of the substrate for light emission display. Each of the multiple LED array units is a stacked structure.

[0004] Faced with mass transfer bonding technology and 3D interconnect IC manufacturing processes, the fabrication process suffers from problems such as complex wiring leading to low LED aperture ratio, low transfer bonding efficiency, low yield, and low color rendering index caused by crosstalk between the three primary color lights within each pixel. Summary of the Invention

[0005] To address the problems of low LED aperture ratio, low transfer bonding efficiency, and low yield caused by complex wiring in the existing vertical stacked full-color LED micro-display array fabrication process, as well as low color rendering index caused by crosstalk between the three primary colors within a pixel, this invention provides a full-color LED micro-display array structure, fabrication method, and full-color LED micro-display.

[0006] In a first aspect, the present invention provides a full-color LED micro-display array structure comprising vertically stacked red, green, and blue primary color LED pixels. Each pixel includes, from bottom to top, a substrate, a first light-emitting unit that generates blue light, a second light-emitting unit that generates green light, a third light-emitting unit that generates red light, a metal reflective layer and a third electrode disposed on the third light-emitting unit, a SiO2 insulating layer disposed on the metal reflective layer, a first electrode disposed on the SiO2 insulating layer and connected to the first light-emitting unit, a second electrode disposed on the SiO2 insulating layer and connected to the second light-emitting unit, and a fourth electrode disposed on the SiO2 insulating layer and connected to the first light-emitting unit, the second light-emitting unit, and the third light-emitting unit. The red light, the green light, and the blue light are all emitted from one side of the substrate.

[0007] The first light-emitting unit includes, from bottom to top, a first unintentionally doped GaN layer, a first Si-doped n-GaN layer, a blue light multi-quantum-well active layer, and a first Mg-doped graded p-Al layer. a Ga 1-a An N electron blocking layer, a first Mg-doped p-GaN layer, a first distributed Bragg mirror layer disposed on the first Mg-doped p-GaN layer, and the first unintentionally doped GaN layer being connected to the substrate;

[0008] The second light-emitting unit includes, from bottom to top, a second unintentionally doped GaN layer, a second Si-doped n-GaN layer, a green multi-quantum-well active layer, and a second Mg-doped graded p-Al layer. a Ga 1-a The system includes an N electron blocking layer, a second Mg-doped p-GaN layer, a second distributed Bragg mirror layer disposed on the second Mg-doped p-GaN layer, and a second electrode and a fourth electrode disposed on the SiO2 insulating layer and connected to the second light-emitting unit. The second unintentionally doped GaN layer is connected to the first distributed Bragg mirror layer.

[0009] The third light-emitting unit comprises, from bottom to top, a third unintentionally doped GaN layer, a third Si-doped n-GaN layer, a red-light multi-quantum-well active layer, and a third Mg-doped graded p-Al layer. a Ga 1-a An N-electron blocking layer and a third Mg-doped p-GaN layer are present, and the metal reflective layer is connected to the third Mg-doped p-GaN layer.

[0010] As an alternative, the substrate is a sapphire substrate or a silicon substrate. When the substrate is sapphire, the substrate is removed or the substrate is thinned. When the substrate is silicon, the substrate is removed.

[0011] As an optional solution, the blue light multi-quantum-well active layer is In... x Ga 1-x N / GaN multiple quantum wells or In x Ga 1-x N / Al h Ga 1-h N quantum wells, with component x in the range of 0.15 < x < 0.2, component h in the range of 0.1 < h < 0.2, and potential well In x Ga 1-x The thickness of N is 1–5 nm, with a barrier GaN or Al. h Ga 1-h The thickness of N is 5–15 nm, and the number of quantum well periods is 1–5.

[0012] The green light multi-quantum well active layer is In. y Ga 1-y N / GaN multiple quantum wells or In y Ga 1-y N / Al h Ga 1-h N quantum wells, with component y in the range of 0.26 < y < 0.32, component h in the range of 0.1 < h < 0.2, and potential well In. y Ga 1-y The thickness of N is 3-5 nm, with a barrier GaN or Al. h Ga 1-h The thickness of N is 5–15 nm, and the number of quantum well periods is 1–5.

[0013] The active layer of the red-light multi-quantum-well is In. z Ga 1-z N / GaN multiple quantum wells or In z Ga 1-z N / Al h Ga 1-hN quantum wells, with component z ranging from 0.44 to 0.51, component h ranging from 0.1 to 0.2, and potential well In. z Ga 1-z The thickness of N is 3-5 nm, with a barrier GaN or Al. h Ga 1-h The thickness of N is 5–15 nm, and the number of quantum well periods is 3–8.

[0014] As an optional solution, the thicknesses of the first unintentionally doped GaN layer, the second unintentionally doped GaN layer, and the third unintentionally doped GaN layer are all 500–2000 nm.

[0015] The doping concentrations of the first Si-doped n-GaN layer, the second Si-doped n-GaN layer, and the third Si-doped n-GaN layer are all ≥5×10⁻⁶. 18 / cm 3 The thickness of each is 300–1000 nm;

[0016] The doping concentrations of the first Mg-doped p-GaN layer, the second Mg-doped p-GaN layer, and the third Mg-doped p-GaN layer are all ≥1×10⁻⁶. 18 / cm 3 The thickness of each is 100–300 nm.

[0017] The first Mg-doped component is graded p-Al a Ga 1-a N electron blocking layer, second Mg doped component graded p-Al a Ga 1-a N electron blocking layer, the third Mg doped component graded p-Al a Ga 1-a The doping concentration of the N electron blocking layer is all between 1×10⁻⁶. 17 / cm 3 and 1×10 18 / cm 3 Between these values, component a gradually changes from h to 0, with a thickness of 10–20 nm.

[0018] As an optional solution, the first distributed Bragg reflector layer is a superlattice with alternating growth of AlN and GaN. The thickness of AlN in each cycle is preferably 50 nm, the thickness of GaN is 46 nm, the number of growth cycles is ≥22.5, and the wavelength range with reflectivity greater than 90% is between 430 nm and 460 nm.

[0019] The second distributed Bragg reflector layer is a superlattice with alternating growth of AlN and GaN. The thickness of AlN in each cycle is 58 nm, and the thickness of GaN is preferably 55 nm. The number of growth cycles is ≥17.5, and the wavelength range with reflectivity greater than 90% is between 490 nm and 530 nm.

[0020] As an optional solution, the metal reflective layer is an Al thin film or an Au thin film with a thickness of 50–100 nm;

[0021] As an optional solution, the metal reflective layer is separated from the first electrode, the second electrode, the third electrode, and the fourth electrode by the SiO2 insulating layer, the thickness of which is 500-1000 nm.

[0022] Both the metal reflective layer and the third electrode are in direct contact with the upper surface of the third light-emitting unit, but the metal reflective layer is not connected to the third electrode.

[0023] Secondly, the present invention provides a full-color LED microdisplay having the full-color LED microdisplay array structure as described above.

[0024] Thirdly, the present invention provides a method for fabricating a full-color LED micro-display array structure, comprising:

[0025] S1. Epitaxially grow a first unintentionally doped GaN layer on the substrate;

[0026] S2. Epitaxially grow a first Si-doped n-GaN layer on the first unintentionally doped GaN layer;

[0027] S3. Epitaxially grow a blue light multi-quantum-well active layer on the first Si-doped n-GaN layer;

[0028] S4. Epitaxially grow a first Mg-doped graded p-Al on the blue light multi-quantum-well active layer. a Ga 1-a N electron blocking layer;

[0029] S5, in the first Mg doping composition, the p-Al is gradually changed. a Ga 1-a The first Mg-doped p-GaN layer is epitaxially grown on the N electron blocking layer;

[0030] S6. Epitaxially grow a first distributed Bragg mirror layer on the first Mg-doped p-GaN layer;

[0031] S7. Epitaxially grow a second unintentionally doped GaN layer on the first distributed Bragg mirror layer;

[0032] S8. Epitaxially grow a second Si-doped n-GaN layer on the second unintentionally doped GaN layer;

[0033] S9. Epitaxially grow a green light multi-quantum-well active layer on the second Si-doped n-GaN layer;

[0034] S10. Epitaxially grow a second Mg-doped graded p-Al on the green light multi-quantum-well active layer. a Ga 1-a N electron blocking layer;

[0035] S11, in the second Mg-doped component graded p-Al a Ga 1-a A second Mg-doped p-GaN layer is epitaxially grown on the N electron blocking layer;

[0036] S12. Epitaxially grow a second distributed Bragg mirror layer on the second Mg-doped p-GaN layer;

[0037] S13. An unintentionally doped GaN layer is epitaxially grown on the second distributed Bragg mirror layer;

[0038] S14. Epitaxially grow a third Si-doped n-GaN layer on the third unintentionally doped GaN layer;

[0039] S15. A red-light multi-quantum-well active layer is epitaxially grown on the third Si-doped n-GaN layer;

[0040] S16. Epitaxially grow a third Mg-doped graded p-Al on the red-light multi-quantum-well active layer. a Ga 1-a N electron blocking layer;

[0041] S17, in the third Mg-doped component graded p-Al a Ga 1-a A third Mg-doped p-GaN layer is epitaxially grown on the N electron blocking layer;

[0042] S18. A metal reflective layer is prepared on the third Mg-doped p-GaN layer using photolithography and deposition processes;

[0043] S19. A three-stage stepped via is fabricated from the third Mg-doped p-GaN layer to the first Si-doped n-GaN layer by three photolithography etching steps. The first photolithography etching is performed from the third Mg-doped p-GaN layer to the third Si-doped n-GaN layer, the second photolithography etching is performed from the third Si-doped n-GaN layer down to the second Si-doped n-GaN layer, and the third photolithography etching is performed from the second Si-doped n-GaN layer down to the first Si-doped n-GaN layer. The etching area is reduced in each of the three photolithography etching steps.

[0044] S20. A single-stage via is prepared from the third Mg-doped p-GaN layer to the second Mg-doped p-GaN layer by a single photolithography etching process;

[0045] S21. A single-stage via is prepared from the third Mg-doped p-GaN layer to the first Mg-doped p-GaN layer by a single photolithography etching process;

[0046] S22. A SiO2 insulating layer is deposited on the surface of the sample obtained in step S21 using plasma-enhanced chemical vapor deposition.

[0047] S23. A first electrode, a second electrode, a third electrode, and a fourth electrode are fabricated by photolithography etching and film deposition processes, wherein the first electrode is connected downward from the surface of the SiO2 insulating layer to the first Mg-doped p-GaN layer, the second electrode is connected downward from the surface of the SiO2 insulating layer to the second Mg-doped p-GaN layer, the third electrode is directly connected to the third Mg-doped p-GaN layer, and the fourth electrode is connected downward from the surface of the SiO2 insulating layer to the first Si-doped n-GaN layer, the second Si-doped n-GaN layer, and the third Si-doped n-GaN layer in sequence;

[0048] S24. Process the substrate to ensure that light is emitted from one side of the substrate.

[0049] As an optional approach, processing the substrate to ensure that light exits from one side of the substrate includes:

[0050] When the substrate is a sapphire substrate, the substrate is removed or thinned to allow light to exit from one side of the substrate.

[0051] When the substrate is a silicon substrate, the silicon substrate is removed to allow light to exit from one side of the substrate.

[0052] This invention provides a full-color LED microdisplay array structure, fabrication method, and full-color LED microdisplay. It obtains three-primary-color light-emitting diode materials through epitaxial growth, solving the problems of low transfer bonding efficiency and low yield caused by complex processes involving multiple bonding and substrate removal in existing technologies. By introducing in-situ grown blue and green distributed Bragg reflectors, it solves the problem of low color rendering index caused by crosstalk between the three primary colors within each pixel. Through-hole connection and insulation isolation technology, it solves the problem of low LED aperture ratio caused by complex wiring in existing technologies. In the described full-color LED microdisplay array and its fabrication method, each pixel is a vertically stacked layer of red, green, and blue primary-color LEDs, arranged from bottom to top as follows: blue LED light-emitting unit, AlN / GaN distributed Bragg reflector with blue light as the center wavelength, green LED light-emitting unit, AlN / GaN distributed Bragg reflector with green light as the center wavelength, and red LED unit. The vertically stacked red, green, and blue LED pixels are interconnected by their respective P-type control terminals and the n-type common terminals of the three LEDs, forming four connection endpoints. These endpoints are distributed in a coplanar manner through vias and insulation isolation technology. Red, green, and blue light are emitted from one side of the substrate, which not only avoids the low aperture ratio of LEDs caused by complex wiring processes but also enables the fabrication of ultra-high resolution full-color LED microdisplays. The introduction of the blue and green light distribution Bragg reflector effectively suppresses the back-emission of blue and green light, improving the light extraction efficiency of the blue and green LEDs while preventing the down-conversion process, thereby improving the color rendering index of the vertically stacked LEDs. Attached Figure Description

[0053] Figure 1 This is a schematic diagram of a full-color LED micro-display array structure provided in an embodiment of the present invention;

[0054] Figure 2 This is a schematic diagram of a full-color LED micro-display array structure provided in an embodiment of the present invention;

[0055] Figure 3 This is a schematic diagram of the reflectivity curve of the AlN / GaN distributed Bragg mirror used in the blue LED of a full-color LED micro-display array structure provided in an embodiment of the present invention;

[0056] Figure 4 This is a schematic diagram of the reflectivity curve of the AlN / GaN distributed Bragg mirror used for the green LED in a full-color LED micro-display array structure provided in an embodiment of the present invention.

[0057] Figure reference numerals: 1. Substrate; 2. First unintentionally doped GaN layer; 3. First Si-doped n-GaN layer; 4. Blue light multi-quantum-well active layer; 5. First Mg-doped composition-gradient p-Al.a Ga 1-a 6. N-type electron blocking layer; 7. First Mg-doped p-GaN layer; 8. First distributed Bragg mirror layer; 9. Second unintentionally doped GaN layer; 10. Second Si-doped n-GaN layer; 11. Green light multi-quantum well active layer; 12. Second Mg-doped composition-gradient p-Al layer. a Ga 1-a 12. N-type electron blocking layer, 13. Second Mg-doped p-GaN layer, 14. Second distributed Bragg mirror layer, 15. Third unintentionally doped GaN layer, 16. Third Si-doped n-GaN layer, 17. Red-light multi-quantum-well active layer, 18. Third Mg-doped composition-gradient p-Al layer a Ga 1-a 18. N electron blocking layer, 19. Third Mg-doped p-GaN layer, 20. Metal reflective layer, 21. SiO2 insulating layer, 22. Third electrode, 23. Second electrode, 24. Fourth electrode, 25. First electrode. Detailed Implementation

[0058] To enable those skilled in the art to better understand the present invention, the technical solutions of the present invention will be clearly and completely described below with reference to the accompanying drawings of the embodiments of the present invention. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort should fall within the scope of protection of the present invention.

[0059] The terms "first," "second," "third," "fourth," etc., used in the specification, claims, and accompanying drawings of this invention are used to distinguish similar objects and are not necessarily used to describe a specific order or sequence. It should be understood that such data can be interchanged where appropriate so that the embodiments described herein can be implemented in orders other than those illustrated or described herein. Furthermore, the terms "comprising" and "having," and any variations thereof, are intended to cover a non-exclusive inclusion; for example, a process, method, system, product, or apparatus that comprises a series of steps or units is not necessarily limited to those steps or units explicitly listed, but may include other steps or units not explicitly listed or inherent to such processes, methods, products, or apparatus.

[0060] like Figure 1As shown, this embodiment of the invention provides a full-color LED micro-display array structure, comprising vertically stacked red, green, and blue primary color LED pixels. Each pixel includes, from bottom to top, a substrate 1, a first light-emitting unit that generates blue light, a second light-emitting unit that generates green light, a third light-emitting unit that generates red light, a metal reflective layer 19 and a third electrode 21 disposed on the third light-emitting unit, a SiO2 insulating layer 20 disposed on the metal reflective layer 19, a first electrode 24 disposed on the SiO2 insulating layer 20 and connected to the first light-emitting unit, a second electrode 22 disposed on the SiO2 insulating layer 20 and connected to the second light-emitting unit, and a fourth electrode 23 disposed on the SiO2 insulating layer 20 and connected to the first light-emitting unit, the second light-emitting unit, and the third light-emitting unit. The red light, the green light, and the blue light are all emitted from one side of the substrate 1.

[0061] The first light-emitting unit comprises, from bottom to top, a first unintentionally doped GaN layer 2, a first Si-doped n-GaN layer 3, a blue light multi-quantum-well active layer 4, and a first Mg-doped p-Al layer with graded composition. a Ga 1-a The system comprises an N-electron blocking layer 5, a first Mg-doped p-GaN layer 6, and a first distributed Bragg reflector layer 7 disposed on the first Mg-doped p-GaN layer 6. It also includes a first electrode 24 and a fourth electrode 23 disposed on the SiO2 insulating layer 20 and connected to the first light-emitting unit. The first unintentionally doped GaN layer 2 is connected to the substrate 1.

[0062] The second light-emitting unit includes, from bottom to top, a second unintentionally doped GaN layer 8, a second Si-doped n-GaN layer 9, a green multi-quantum-well active layer 10, and a second Mg-doped graded p-Al layer. a Ga 1-a The system comprises an N-electron blocking layer 11, a second Mg-doped p-GaN layer 12, and a second distributed Bragg reflector layer 13 disposed on the second Mg-doped p-GaN layer 12. It also includes a second electrode 22 and a fourth electrode 23 disposed on the SiO2 insulating layer 20 and connected to the second light-emitting unit. The second unintentionally doped GaN layer 8 is connected to the first distributed Bragg reflector layer 7.

[0063] The third light-emitting unit includes, from bottom to top, a third unintentionally doped GaN layer 14, a third Si-doped n-GaN layer 15, a red-light multi-quantum-well active layer 16, and a third Mg-doped graded p-Al layer. a Ga 1-aThe system comprises an N-electron blocking layer 17, a third Mg-doped p-GaN layer 18, a metal reflective layer 19 disposed on the third Mg-doped p-GaN layer 18, and a third electrode 21, and also includes a fourth electrode 23 disposed on the SiO2 insulating layer 20 and connected to the third light-emitting unit. The metal reflective layer 19 is connected to the third Mg-doped p-GaN layer 19.

[0064] like Figure 2 As shown, substrate 1 is a (001)-plane or (110)-plane sapphire substrate or a (111)-plane silicon substrate. The thickness of the first unintentionally doped GaN layer 2, the second unintentionally doped GaN layer 8, and the third unintentionally doped GaN layer 14 is 500-2000 nm, with a preferred thickness of 1000 nm.

[0065] The doping concentration of the first Si-doped n-GaN layer 3, the second Si-doped n-GaN layer 9, and the third Si-doped n-GaN layer 15 is ≥5×10⁻⁶. 18 / cm 3 The thickness is 300-1000 nm, with a preferred thickness of 500 nm.

[0066] The blue light-emitting multi-quantum-well active layer 4 of the first light-emitting unit can be In x Ga 1-x N / GaN multiple quantum wells or In x Ga 1- x N / Al h Ga 1-h N quantum wells, with component x in the range of 0.15 < x < 0.2, component h in the range of 0.1 < h < 0.2, and potential well In x Ga 1-x The thickness of N is 1–5 nm, with a barrier GaN or Al. h Ga 1-h The thickness of N is 5–15 nm, and the number of quantum well periods is 1–5.

[0067] The green multi-quantum-well active layer 10 of the second light-emitting unit can be In y Ga 1-y N / GaN multiple quantum wells or In y Ga 1- y N / Al h Ga 1-h N quantum wells, with component y in the range of 0.26 < y < 0.32, component h in the range of 0.1 < h < 0.2, and potential well In. y Ga 1-y The thickness of N is 3-5 nm, with a barrier GaN or Al. h Ga 1-hThe thickness of N is 5–15 nm, and the number of quantum well periods is 1–5.

[0068] The red-light multi-quantum-well active layer 16 of the third light-emitting unit can be In z Ga 1-z N / GaN multiple quantum wells or In z Ga 1- z N / Al h Ga 1-h N quantum wells, with component z ranging from 0.44 to 0.51, component h ranging from 0.1 to 0.2, and potential well In. z Ga 1-z The thickness of N is 3-5 nm, with a barrier GaN or Al. h Ga 1-h The thickness of N is 5–15 nm, and the number of quantum well periods is 3–8; the first Mg doping composition is graded p-Al. a Ga 1-a N electron blocking layer 5, second Mg doped composition graded p-Al a Ga 1-a N electron blocking layer 11, third Mg doped composition graded p-Al a Ga 1-a The doping concentration of the N electron blocking layer 17 is between 1 × 10⁻⁶. 17 / cm 3 and 1×10 18 / cm 3 Between these layers, component a gradually changes from h to 0, with a thickness of 10–20 nm; the doping concentration of the first Mg-doped p-GaN layer 6, the second Mg-doped p-GaN layer 12, and the third Mg-doped p-GaN layer 18 is ≥1×10⁻⁶. 18 / cm 3 The thickness is 100-300 nm, with a preferred thickness of 200 nm.

[0069] Both the first distributed Bragg mirror layer 7 and the second distributed Bragg mirror layer 13 are superlattices with alternating AlN and GaN growth. The number of AlN / GaN cycles and the growth thickness of AlN and GaN in each cycle are adjusted according to the different center wavelengths of the mirrors. Specifically, the wavelength range where the reflectivity of the first distributed Bragg mirror layer 7 is greater than 90% is between 430nm and 460nm. Therefore, the thickness of AlN in each cycle is preferably 50nm, the thickness of GaN is preferably 46nm, and the number of growth cycles is ≥22.5, preferably 25.5. The wavelength range where the reflectivity of the second distributed Bragg mirror layer 13 is greater than 90% is between 490nm and 530nm. Therefore, the thickness of AlN in each cycle is preferably 58nm, the thickness of GaN is preferably 55nm, and the number of growth cycles is ≥17.5, preferably 20.5.

[0070] This invention provides a full-color LED microdisplay array structure, fabrication method, and full-color LED microdisplay. It obtains three-primary-color light-emitting diode materials through epitaxial growth, solving the problems of low transfer bonding efficiency and low yield caused by complex processes involving multiple bonding and substrate removal in existing technologies. By introducing in-situ grown blue and green distributed Bragg reflectors, it solves the problem of low color rendering index caused by crosstalk between the three primary colors within each pixel. Through-hole connection and insulation isolation technology, it solves the problem of low LED aperture ratio caused by complex wiring in existing technologies. In the described full-color LED microdisplay array and its fabrication method, each pixel is a vertically stacked layer of red, green, and blue primary-color LEDs, arranged from bottom to top as follows: blue LED light-emitting unit, AlN / GaN distributed Bragg reflector with blue light as the center wavelength, green LED light-emitting unit, AlN / GaN distributed Bragg reflector with green light as the center wavelength, and red LED unit. The vertically stacked red, green, and blue LED pixels are interconnected by their respective P-type control terminals and the n-type common terminals of the three LEDs, forming four connection endpoints. These endpoints are distributed in a coplanar manner through vias and insulation isolation technology. Red, green, and blue light are emitted from one side of the substrate, which not only avoids the low aperture ratio of LEDs caused by complex wiring processes but also enables the fabrication of ultra-high resolution full-color LED microdisplays. The introduction of the blue and green light distribution Bragg reflector effectively suppresses the back-emission of blue and green light, improving the light extraction efficiency of the blue and green LEDs while preventing the down-conversion process, thereby improving the color rendering index of the vertically stacked LEDs.

[0071] Accordingly, this embodiment of the invention provides a full-color LED microdisplay with the aforementioned full-color LED microdisplay array structure. The LED display mentioned in this embodiment is a display screen that displays various information such as text, graphics, images, animations, market data, videos, and video recordings by controlling semiconductor light-emitting diodes. It can be widely used in large squares, commercial advertising, sports stadiums, information dissemination, news releases, securities trading, etc., and can meet the needs of different environments.

[0072] Accordingly, this invention provides a method for fabricating a full-color LED micro-display array structure, comprising:

[0073] S1. Epitaxially grow a first unintentionally doped GaN layer on the substrate;

[0074] S2. Epitaxially grow a first Si-doped n-GaN layer on the first unintentionally doped GaN layer;

[0075] S3. Epitaxial growth of a blue light multi-quantum-well active layer on the first Si-doped n-GaN layer;

[0076] S4. Epitaxial growth of graded p-Al with first Mg doping composition on blue light multi-quantum-well active layer. a Ga 1-a N electron blocking layer;

[0077] S5, in the first Mg doping composition, the p-Al is gradually changed. a Ga 1-a The first Mg-doped p-GaN layer is epitaxially grown on the N electron blocking layer;

[0078] S6. Epitaxially grow a first distributed Bragg mirror layer on the first Mg-doped p-GaN layer;

[0079] S7. Epitaxially grow a second unintentionally doped GaN layer on the first distributed Bragg mirror layer;

[0080] S8. Epitaxially grow a second Si-doped n-GaN layer on the second unintentionally doped GaN layer;

[0081] S9. Epitaxial growth of a green light multi-quantum-well active layer on the second Si-doped n-GaN layer;

[0082] S10. Epitaxial growth of second Mg-doped graded p-Al on a green light multi-quantum-well active layer. a Ga 1-a N electron blocking layer;

[0083] S11, in the second Mg-doped composition graded p-Al a Ga 1-a A second Mg-doped p-GaN layer is epitaxially grown on the N electron blocking layer;

[0084] S12. Epitaxially grow a second distributed Bragg mirror layer on the second Mg-doped p-GaN layer;

[0085] S13. Epitaxially grow a third unintentionally doped GaN layer on the second distributed Bragg mirror layer;

[0086] S14. Epitaxially grow a third Si-doped n-GaN layer on the third unintentionally doped GaN layer;

[0087] S15. A red-light multi-quantum-well active layer is epitaxially grown on the third Si-doped n-GaN layer;

[0088] S16. Epitaxial growth of third Mg-doped graded p-Al on a red-light multi-quantum-well active layer. a Ga 1-a N electron blocking layer;

[0089] S17, in the third Mg doping composition, the p-Al is gradually changed. aGa 1-a A third Mg-doped p-GaN layer is epitaxially grown on the N electron blocking layer;

[0090] S18. A metal reflective layer is prepared on the third Mg-doped p-GaN layer using photolithography and deposition processes;

[0091] S19. A three-stage via is fabricated from the third Mg-doped p-GaN layer to the first Si-doped n-GaN layer by three photolithography etching steps. The first photolithography etching etches from the third Mg-doped p-GaN layer to the third Si-doped n-GaN layer, the second photolithography etching etches down from the third Si-doped n-GaN layer to the second Si-doped n-GaN layer, and the third photolithography etching etches down from the second Si-doped n-GaN layer to the first Si-doped n-GaN layer. The etching area is reduced in each of the three photolithography etching steps.

[0092] S20. A single-stage via is prepared from the third Mg-doped p-GaN layer to the second Mg-doped p-GaN layer by a single photolithography etching process;

[0093] S21. A single-stage via is prepared from the third Mg-doped p-GaN layer to the first Mg-doped p-GaN layer by a single photolithography etching process;

[0094] S22. A SiO2 insulating layer is deposited on the surface of the sample obtained in step S21 using plasma-enhanced chemical vapor deposition.

[0095] S23. First, second, third, and fourth electrodes are prepared by photolithography etching and coating processes. The first electrode is connected to the first Mg-doped p-GaN layer from the surface of the SiO2 insulating layer downwards. The second electrode is connected to the second Mg-doped p-GaN layer from the surface of the SiO2 insulating layer downwards. The third electrode is directly connected to the third Mg-doped p-GaN layer. The fourth electrode is connected to the first, second, and third Si-doped n-GaN layers sequentially from the surface of the SiO2 insulating layer downwards.

[0096] S24. Process the substrate to ensure that light is emitted from one side of the substrate.

[0097] In S24, when the substrate is a sapphire substrate, the substrate is removed or thinned to allow light to be emitted from one side of the substrate; when the substrate is a silicon substrate, the silicon substrate is removed to allow light to be emitted from one side of the substrate.

[0098] This invention provides a method for fabricating a full-color LED micro-display array structure. Taking a sapphire substrate as an example, the method includes:

[0099] S1. A 1000nm unintentionally doped GaN layer is epitaxially grown on a (110) sapphire substrate;

[0100] S2, Epitaxial growth with a doping concentration of 5×10⁻⁶ is performed on the first unintentionally doped GaN layer. 18 / cm 3 The first Si-doped n-GaN layer has a thickness of 500 nm;

[0101] S3, Epitaxial growth of In on the first Si-doped n-GaN layer 0.18 Ga 0.82 N / GaN multi-quantum-well active layer, blue multi-quantum-well active light-emitting layer with a center wavelength of 450nm, potential well In 0.18 Ga 0.82 The thickness of N is 1.5 nm, the thickness of the barrier GaN is 5 nm, and the number of quantum well periods is 3.

[0102] S4, In 0.18 Ga 0.82 Epitaxial growth of p-Al with a first Mg doping composition gradient on N / GaN multi-quantum-well active layer a Ga 1-a An N-electron blocking layer with composition a gradually decreasing from 0.1 to 0, a thickness of 15 nm, and a doping concentration of 2 × 10⁻⁶. 17 / cm 3 ;

[0103] S5, in the first Mg doping composition, the p-Al is gradually changed. a Ga 1-a The first Mg-doped p-GaN layer, with a thickness of 200 nm and a doping concentration of 1 × 10⁻⁶, is epitaxially grown on the N electron blocking layer. 18 / cm 3 ;

[0104] S6. Epitaxially grow a first distributed Bragg reflector layer on the first Mg-doped p-GaN layer. In each cycle, the AlN thickness is 50 nm and the GaN thickness is 46 nm. The number of growth cycles is 25.5. The center wavelength of the reflector is 450 nm, and the wavelength range with reflectivity greater than 90% is between 430 nm and 460 nm. Figure 3 As shown;

[0105] S7. An unintentionally doped GaN layer of 1000 nm is epitaxially grown on the first distributed Bragg reflector layer.

[0106] S8. Epitaxial growth with a doping concentration of 5×10⁻⁶ is performed on the second unintentionally doped GaN layer. 18 / cm 3 A second Si-doped n-GaN layer with a thickness of 500 nm;

[0107] S9, Epitaxial growth of In on the second Si-doped n-GaN layer 0.3 Ga 0.7N / GaN multi-quantum-well active layer, green multi-quantum-well active light-emitting layer with a center wavelength of 520nm, potential well In 0.3 Ga 0.7 The thickness of N is 2nm, the thickness of the barrier GaN is 8nm, and the number of quantum well periods is 5.

[0108] S10, In 0.3 Ga 0.7 Epitaxial growth of a second Mg-doped p-Al layer on an N / GaN multi-quantum-well active layer with a graded composition a Ga 1-a An N-electron blocking layer with composition a gradually decreasing from 0.1 to 0, a thickness of 15 nm, and a doping concentration of 2 × 10⁻⁶. 17 / cm 3 ;

[0109] S11, in the second Mg-doped composition graded p-Al a Ga 1-a A second Mg-doped p-GaN layer with a thickness of 200 nm and a doping concentration of 1 × 10⁻⁶ is epitaxially grown on the N electron blocking layer. 18 / cm 3 ;

[0110] S12. A second distributed Bragg reflector layer is epitaxially grown on the second Mg-doped p-GaN layer. In each cycle, the AlN thickness is 58 nm and the GaN thickness is 55 nm. The number of growth cycles is 20.5. The center wavelength of the reflector is 520 nm, and the wavelength range with reflectivity greater than 90% is between 490 nm and 530 nm. Figure 4 As shown;

[0111] S13. An unintentionally doped GaN layer of 1000 nm is epitaxially grown on the second distributed Bragg mirror layer.

[0112] S14. Epitaxially grow a GaN layer with a doping concentration of 5×10⁻⁶ on the third unintentionally doped GaN layer. 18 / cm 3 A third Si-doped n-GaN layer with a thickness of 500 nm;

[0113] S15, Epitaxial growth of In on the third Si-doped n-GaN layer 0.46 Ga 0.54 N / GaN multi-quantum-well active layer, red multi-quantum-well active light-emitting layer with a center wavelength of 650nm, potential well In 0.46 Ga 0.54 The thickness of N is 4nm, the thickness of the barrier GaN is 10nm, and the number of quantum well periods is 3.

[0114] S16, In 0.46 Ga 0.54Epitaxial growth of a third Mg-doped p-Al layer on an N / GaN multi-quantum-well active layer with a graded composition a Ga 1-a An N-electron blocking layer with composition a gradually decreasing from 0.1 to 0, a thickness of 15 nm, and a doping concentration of 2 × 10⁻⁶. 17 / cm 3 ;

[0115] S17, in the third Mg doping composition, the p-Al is gradually changed. a Ga 1-a A third Mg-doped p-GaN layer with a thickness of 200 nm and a doping concentration of 1 × 10⁻⁶ is epitaxially grown on the N electron blocking layer. 18 / cm 3 ;

[0116] S18. A 50 nm Al metal reflective layer was prepared on the third Mg-doped p-GaN layer using photolithography and deposition processes.

[0117] S19. A three-stage stepped via is fabricated from the third Mg-doped p-GaN layer to the first Si-doped n-GaN layer using three photolithography etching processes. The first photolithography etching etches from the third Mg-doped p-GaN layer to the third Si-doped n-GaN layer with an etching depth of 300 nm. The second photolithography etching etches downwards from the third Si-doped n-GaN layer to the second Si-doped n-GaN layer with an etching depth of 4200 nm. The third photolithography etching etches downwards from the second Si-doped n-GaN layer to the first Si-doped n-GaN layer with an etching depth of 4200 nm. The etching area and the etching edge length are reduced by 1 μm in each of the three photolithography etching processes.

[0118] S20. A single-stage via is prepared from the third Mg-doped p-GaN layer to the second Mg-doped p-GaN layer by a single photolithography etching process, with an etching depth of 4150 nm.

[0119] S21. A single-stage via is prepared from the third Mg-doped p-GaN layer to the first Mg-doped p-GaN layer by a single photolithography etching process, with an etching depth of 8350 nm.

[0120] S22. A 100 nm thick SiO2 insulating layer is deposited on the surface of the sample obtained in the above steps using plasma-enhanced chemical vapor deposition.

[0121] S23. First, second, third, and fourth electrodes are fabricated by photolithography etching and film deposition processes. The electrodes are gold electrodes with a thickness of 50 nm. The first electrode is connected to the first Mg-doped p-GaN layer from the surface of the SiO2 insulating layer downwards. The second electrode is connected to the second Mg-doped p-GaN layer from the surface of the SiO2 insulating layer downwards. The third electrode is directly connected to the third Mg-doped p-GaN layer. The fourth electrode is connected to the first Si-doped n-GaN layer, the second Si-doped n-GaN layer, and the third Si-doped n-GaN layer sequentially from the surface of the SiO2 insulating layer downwards.

[0122] S24. Thin the sapphire substrate to 100μm to complete the fabrication of the full-color LED microdisplay array structure.

[0123] This invention provides a method for fabricating a full-color LED microdisplay array structure. The method utilizes epitaxial growth of three-primary-color light-emitting diode materials, addressing the problems of low transfer bonding efficiency and low yield caused by complex processes involving multiple bonding and substrate removal in existing technologies. By introducing in-situ grown blue and green distributed Bragg reflectors, the method solves the problem of low color rendering index caused by crosstalk between the three primary colors within each pixel. Furthermore, through via connections and insulation isolation techniques, the method addresses the problem of low LED aperture ratio caused by complex wiring in existing technologies. In this full-color LED microdisplay array and its fabrication method, each pixel is a vertically stacked layer of red, green, and blue LEDs, arranged from bottom to top as follows: a blue LED light-emitting unit, an AlN / GaN distributed Bragg reflector with a blue center wavelength, a green LED light-emitting unit, an AlN / GaN distributed Bragg reflector with a green center wavelength, and a red LED unit. The vertically stacked red, green, and blue LED pixels are interconnected by their respective P-type control terminals and the n-type common terminals of the three LEDs, forming four connection endpoints. These endpoints are distributed in a coplanar manner through vias and insulation isolation technology. Red, green, and blue light are emitted from one side of the substrate, which not only avoids the low aperture ratio of LEDs caused by complex wiring processes but also enables the fabrication of ultra-high resolution full-color LED microdisplays. The introduction of the blue and green light distribution Bragg reflector effectively suppresses the back-emission of blue and green light, improving the light extraction efficiency of the blue and green LEDs while preventing the down-conversion process, thereby improving the color rendering index of the vertically stacked LEDs.

[0124] It should be understood that the various forms of processes shown above can be used to rearrange, add, or delete steps. For example, the steps described in this disclosure can be executed in parallel, sequentially, or in different orders, as long as the desired result of the technical solution disclosed in this invention can be achieved, and this is not limited herein.

[0125] The specific embodiments described above do not constitute a limitation on the scope of protection of this invention. Those skilled in the art should understand that various modifications, combinations, sub-combinations, and substitutions can be made according to design requirements and other factors. Any modifications, equivalent substitutions, and improvements made within the spirit and principles of this invention should be included within the scope of protection of this invention.

Claims

1. A full color LED microdisplay array structure, characterized in that, The vertical stack includes red, green and blue primary color LED pixel groups, each pixel group including, from bottom to top, a substrate, a first light emitting unit generating blue light, a second light emitting unit generating green light, a third light emitting unit generating red light, a metal reflection layer and a third electrode disposed above the third light emitting unit, a SiO2 insulating layer disposed above the metal reflection layer, a first electrode connecting the first light emitting unit disposed above the SiO2 insulating layer, a second electrode connecting the second light emitting unit disposed above the SiO2 insulating layer, and a fourth electrode connecting the first, second and third light emitting units disposed above the SiO2 insulating layer, wherein the red, green and blue light are emitted from the substrate side; The first light emitting unit comprises, from bottom to top, a first unintentionally doped GaN layer, a first Si-doped n-GaN layer, a blue light multi-quantum well active layer, a first Mg-doped componentally graded p-Al a Ga 1-a N electron blocking layer, a first Mg-doped p-GaN layer, and a first distributed Bragg reflector layer arranged on the first Mg-doped p-GaN layer, wherein the first unintentionally doped GaN layer is connected with the substrate. The second light emitting unit comprises, from bottom to top, a second unintentionally doped GaN layer, a second Si-doped n-GaN layer, a green light multi-quantum well active layer, a second Mg-doped componentally graded p-Al a Ga 1-a N electron blocking layer, a second Mg-doped p-GaN layer, a second distributed Bragg reflector layer arranged on the second Mg-doped p-GaN layer, and further comprising a second electrode and a fourth electrode arranged on the SiO2 insulating layer and connected to the second light emitting unit, wherein the second unintentionally doped GaN layer is connected to the first distributed Bragg reflector layer. The third light emitting unit comprises, from bottom to top, a third unintentionally doped GaN layer, a third Si-doped n-GaN layer, a red light multi-quantum well active layer, a third Mg-doped componentally graded p-Al a Ga 1-a N electron blocking layer, and a third Mg-doped p-GaN layer, and the metal reflection layer is connected with the third Mg-doped p-GaN layer. The fourth electrode is disposed in a three-stage step via hole from the third Mg-doped p-GaN layer to the first Si-doped n-GaN layer, the first electrode is disposed in a single-stage via hole from the third Mg-doped p-GaN layer to the first Mg-doped p-GaN layer, and the second electrode is disposed in a single-stage via hole from the third Mg-doped p-GaN layer to the second Mg-doped p-GaN layer; the first, second and third light emitting units are stacked into a cuboid, the three-stage step via hole in which the fourth electrode is disposed is located at a first edge of the cuboid, the single-stage via hole in which the first electrode is disposed is located at a second edge of the cuboid, and the single-stage via hole in which the second electrode is disposed is located at a third edge of the cuboid; The first electrode is connected to the first Mg-doped p-GaN layer from the surface of the SiO2 insulating layer, the second electrode is connected to the second Mg-doped p-GaN layer from the surface of the SiO2 insulating layer, the third electrode is directly connected to the third Mg-doped p-GaN layer, and the fourth electrode is sequentially connected to the first, second and third Si-doped n-GaN layers from the surface of the SiO2 insulating layer; The first DBR mirror layer is a superlattice of AlN and GaN, the thickness of AlN in each period is 50 nm, the thickness of GaN in each period is 46 nm, the number of growth periods is ≥22.5, and the wavelength range with a reflectivity greater than 90% is between 430 nm and 460 nm; The second DBR mirror layer is a superlattice of AlN and GaN, the thickness of AlN in each period is 58 nm, the thickness of GaN in each period is 55 nm, the number of growth periods is ≥17.5, and the wavelength range with a reflectivity greater than 90% is between 490 nm and 530 nm. 2.The full-color LED micro-display array structure of claim 1, wherein, The substrate is a sapphire substrate or a silicon substrate, when the substrate is a sapphire, the substrate is removed or thinned, and when the substrate is a silicon substrate, the substrate is removed. 3.The full-color LED micro-display array structure of claim 1, wherein, The blue light multi-quantum well active layer is In x Ga 1-x N / GaN multi-quantum well or In x Ga 1-x N / Al h Ga 1-h N multi-quantum well, the component x ranges from 0.15 to 0.2, the component h ranges from 0.1 to 0.2, the potential well In x Ga 1-x N has a thickness of 1-5 nm, the potential barrier GaN or Al h Ga 1-h N has a thickness of 5-15 nm, and the quantum well period number is 1-5. The green light multi-quantum well active layer is In y Ga 1-y N / GaN multi-quantum well or In y Ga 1-y N / Al h Ga 1-h N multi-quantum well, the component y ranges from 0.26 to 0.32, the component h ranges from 0.1 to 0.2, the potential well In y Ga 1-y N has a thickness of 3-5 nm, the potential barrier GaN or Al h Ga 1-h N has a thickness of 5-15 nm, and the quantum well period number is 1-5. The red light multi-quantum well active layer is In z Ga 1-z N / GaN multi-quantum well or In z Ga 1-z N / Al h Ga 1-h N multi-quantum well, the component z ranges from 0.44 to 0.51, the component h ranges from 0.1 to 0.2, the potential well In z Ga 1-z N is 3-5 nm thick, the potential barrier is GaN or Al h Ga 1-h N is 5-15 nm thick, and the quantum well period is 3-8. 4.The full-color LED micro-display array structure of claim 1, wherein, The thickness of the first, second and third unintentionally doped GaN layers is 500-2000 nm. The doping concentration of the first Si-doped n-GaN layer, the second Si-doped n-GaN layer and the third Si-doped n-GaN layer is all ≥5×10 18 / cm 3 , and the thickness is all 300-1000 nm; The doping concentration of the first Mg-doped p-GaN layer, the second Mg-doped p-GaN layer and the third Mg-doped p-GaN layer is all ≥1×10 18 / cm 3 , and the thickness is all 100-300 nm. The first Mg-doped compositionally graded p-Al a Ga 1-a N electron barrier layer, the second Mg-doped compositionally graded p-Al a Ga 1- a N electron barrier layer, the third Mg-doped compositionally graded p-Al a Ga 1-a The doping concentration of the N electron barrier layer is between 1 x 10 17 / cm 3 and 1 x 10 18 / cm 3 , the composition a ranges from h to 0, and the thickness is 10-20 nm. 5.The full-color LED micro-display array structure of claim 1, wherein, The metal reflective layer is an Al thin film or an Au thin film, and the thickness is 50-100 nm. 6.The full-color LED micro-display array structure of claim 1, wherein, The metal reflective layer is separated from the first electrode, the second electrode, the third electrode and the fourth electrode by the SiO2 insulating layer, and the thickness of the SiO2 insulating layer is 500-1000 nm. The metal reflective layer and the third electrode are in direct contact with the upper surface of the third light-emitting unit, and the metal reflective layer is not connected with the third electrode.

7. A full color LED microdisplay, characterized by A full-color LED micro display array structure as claimed in any one of claims 1 to 6.

8. A method for preparing a full-color LED micro-display array structure, characterized in that, Comprising: S1, epitaxially growing a first unintentionally doped GaN layer on a substrate; S2, epitaxially growing a first Si-doped n-GaN layer on the first unintentionally doped GaN layer; S3, epitaxially growing a blue light multi-quantum well active layer on the first Si-doped n-GaN layer; S4. Epitaxially growing a first Mg-doped compositionally graded p-Al a Ga 1-a N electron blocking layer; S5, a first Mg-doped p-GaN layer is epitaxially grown on the N electron blocking layer a Ga 1-a N electron blocking layer; S6, epitaxially growing a first distributed Bragg reflector layer on the first Mg-doped p-GaN layer to form a first light-emitting unit, the first distributed Bragg reflector layer being an AlN and GaN alternately grown superlattice, the thickness of AlN in each period being 50 nm, the thickness of GaN being 46 nm, the number of growth periods being ≥22.5, and the wavelength range with a reflectivity greater than 90% being between 430 nm and 460 nm; S7, epitaxially growing a second unintentionally doped GaN layer on the first distributed Bragg reflector layer; S8, epitaxially growing a second Si-doped n-GaN layer on the second unintentionally doped GaN layer; S9, epitaxially growing a green light multi-quantum well active layer on the second Si-doped n-GaN layer; S10, epitaxially growing a second Mg-doped compositionally graded p-Al a Ga 1-a N electron blocking layer; S11, a second Mg-doped p-GaN layer is epitaxially grown on the N electron blocking layer a Ga 1-a N electron blocking layer; S12, epitaxially growing a second distributed Bragg reflector layer on the second Mg-doped p-GaN layer to form a second light-emitting unit, the second distributed Bragg reflector layer being an AlN and GaN alternately grown superlattice, the thickness of AlN in each period being 58 nm, the thickness of GaN being 55 nm, the number of growth periods being ≥17.5, and the wavelength range with a reflectivity greater than 90% being between 490 nm and 530 nm; S13, epitaxially growing a third unintentionally doped GaN layer on the second distributed Bragg reflector layer; S14, epitaxially growing a third Si-doped n-GaN layer on the third unintentionally doped GaN layer; S15, epitaxially growing a red light multi-quantum well active layer on the third Si-doped n-GaN layer; S16, epitaxially growing a third Mg-doped compositionally graded p-Al a Ga 1-a N electron blocking layer; S17, the third Mg-doped component gradually changes p-Al a Ga 1-a N electron blocking layer, to form a third light emitting unit, the first light emitting unit, the second light emitting unit and the third light emitting unit stack into a cuboid; S18, preparing a metal reflective layer on the third Mg-doped p-GaN layer by using a photolithography and plating process; S19, a three-stage step via hole from the third Mg-doped p-GaN layer to the first Si-doped n-GaN layer is prepared by three times of lithography etching, wherein the first time of lithography etching is from the third Mg-doped p-GaN layer to the third Si-doped n-GaN layer, the second time of lithography etching is from the third Si-doped n-GaN layer to the second Si-doped n-GaN layer, and the third time of lithography etching is from the second Si-doped n-GaN layer to the first Si-doped n-GaN layer, and the etching area is gradually reduced; S20, a single-stage via hole from the third Mg-doped p-GaN layer to the second Mg-doped p-GaN layer is prepared by one time of lithography etching; S21, a single-stage via hole from the third Mg-doped p-GaN layer to the first Mg-doped p-GaN layer is prepared by one time of lithography etching; S22, a SiO2 insulating layer is deposited on the surface of the sample obtained in step S21 by a plasma enhanced chemical vapor deposition process; S23, a first electrode, a second electrode, a third electrode and a fourth electrode are prepared by lithography etching and plating process, wherein the three-stage step via hole of the fourth electrode is arranged at the first edge of the cuboid, the single-stage via hole of the first electrode is arranged at the second edge of the cuboid, the single-stage via hole of the second electrode is arranged at the third edge of the cuboid, the first electrode is connected to the first Mg-doped p-GaN layer from the surface of the SiO2 insulating layer, the second electrode is connected to the second Mg-doped p-GaN layer from the surface of the SiO2 insulating layer, the third electrode is directly connected to the third Mg-doped p-GaN layer, and the fourth electrode is connected to the first Si-doped n-GaN layer, the second Si-doped n-GaN layer and the third Si-doped n-GaN layer from the surface of the SiO2 insulating layer in sequence; S24, the substrate is processed to meet the light emission from one side of the substrate. 9.The method of claim 8, wherein, The processing of the substrate to meet the light emission from one side of the substrate comprises: when the substrate is a sapphire substrate, the substrate is removed or thinned to meet the light emission from one side of the substrate; when the substrate is a silicon substrate, the silicon substrate is removed to meet the light emission from one side of the substrate.

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