Micro Light-Emitting Diode with an All-Inclusive DBR Structure and Method for Preparing the Same

Abstract

The present invention discloses a preparation method of a micro light-emitting diode with an all-inclusive DBR structure, comprising the following steps: preparing a body; covering the top of the body with a top film layer and covering the side of the body with a side film layer; wherein, the side film layer covers the side surface of the top film layer and / or the top film layer covers the top surface of the side film layer; both the top film layer and the side film layer are obtained by alternately depositing a first dielectric thin film layer and a second dielectric thin film layer; preparing the top film layer and the side film layer: determining the materials, initial single-layer thicknesses and initial numbers of layers of the first dielectric thin film layer and the second dielectric thin film layer; optimizing the initial single-layer thicknesses and the initial numbers of layers to obtain the optimal single-layer thicknesses and numbers of layers; and coating the body according to the optimal single-layer thicknesses and numbers of layers to obtain the micro light-emitting diode with the all-inclusive DBR structure.

Description

Technical Field

[0001] The present invention belongs to the technical field of micro light-emitting diodes, and particularly relates to a preparation method of a micro light-emitting diode with a full-encapsulation DBR structure and a micro light-emitting diode prepared by using the preparation method. Background Art

[0002] DBR (Distributed Bragg Reflector) is a reflector used in a waveguide. When light passes through different media, reflection occurs at the interface, and the magnitude of the reflectivity is related to the refractive index between the media. Therefore, if thin films with different refractive indices are stacked alternately and periodically, when light passes through these thin films with different refractive indices, since the light reflected from each layer undergoes interference due to the change in the phase angle and then combines with each other, strong reflected light is obtained. If the number of multi-films becomes very large and the difference in the refractive indices n1, n2, n3... of the thin films becomes very small, light is like traveling in the same medium, and the reflection coefficient becomes very small. Due to the multiple interference of light, the interference effect is very obvious, so the selection of the wavelength becomes very sensitive. When using a situation similar to a grating, such a periodic structure is called a distributed Bragg reflector.

[0003] Micro LED (Micro Light-Emitting Diode), as a new type of display and lighting technology, shows great potential in the fields of high-density display, wearable devices, micro projection, etc. due to its advantages such as high brightness, low power consumption, fast response, and high resolution. However, the light emitted by a pure Micro-LED is approximately a Lambert radiator, as Figure 1 shown.

[0004] To solve the problem of light divergence, in recent years, people have used DBR to collimate the light emitted by Micro-LEDs. This technology of coating the surface of Micro-LEDs has greatly improved the collimation of light output. As shown in the simulation structure diagram of a Micro-LED with a non-full-encapsulation DBR coating in Figure 2 (c), Figure 2 (a) and Figure 2 (b) are respectively the corresponding top light output diagram and the overall light output angle distribution diagram, Figure 3 and the overall light output angle distribution diagram of a Micro-LED with only sidewall DBR coating.

[0005] For Micro-LEDs, the size is generally below 100um. At this size, traditional geometric optical formulas are no longer applicable, and physical optics, that is, micro-nano optics, dominates. At this time, the diffraction and interference effects of light are very obvious. For the above non-all-inclusive DBR coating method, since there is a very obvious junction between the top DBR and the sidewall DBR, this will lead to two main problems: The first problem is the light leakage problem at the corners. Since the junction is not fully enclosed, light will leak from these junctions, greatly reducing the energy of the light and also increasing the angle of the finally emitted light, which is very unfavorable for the collimation of light. The second problem is that the interference effect of light at the corners is very serious. This interference effect has an important impact on the performance of micro-nano optical devices, including the propagation, scattering, absorption, and emission of light waves. When light waves encounter the edges of micro-nano structures, diffraction occurs. Diffraction causes the light waves to form new wavefronts around the structure, which may affect the propagation path and intensity distribution of the light waves. At the corners of micro-nano structures, light waves with different paths may interfere with each other, forming bright and dark interference fringes, which also affect the collimation of light. Summary of the Invention

[0006] In view of this, aiming at the deficiencies of the prior art, the purpose of the present invention is to provide an improved preparation method for micro light-emitting diodes, and the prepared micro light-emitting diodes have an all-inclusive DBR structure.

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

[0008] A preparation method for a micro light-emitting diode with an all-inclusive DBR structure, comprising the following steps:

[0009] Prepare the body;

[0010] The top of the body is covered with a top film layer, and the side of the body is covered with a side film layer; wherein, the side film layer covers the side of the top film layer and / or the top film layer covers the top surface of the side film layer; both the top film layer and the side film layer are obtained by alternately depositing a first dielectric thin film layer and a second dielectric thin film layer;

[0011] Prepare the top film layer and the side film layer:

[0012] Determine the materials, initial single-layer thicknesses of the first dielectric thin film layer and the second dielectric thin film layer, and the initial number of layers of the top film layer and the side film layer;

[0013] Optimize the initial single-layer thickness and the initial number of layers, and obtain the optimal single-layer thickness and the number of layers;

[0014] Coat the body according to the optimal single-layer thickness and the number of layers to obtain the micro light-emitting diode with an all-inclusive DBR structure.

[0015] According to some preferred implementation aspects of the present invention, the structure of the body from bottom to top is successively an aluminum oxide (Al 2 O 3 ) layer of a sapphire substrate, an n-GaN layer, a quantum well layer, and a p-GaN layer. Preferably, the side film layer covers a part of the n-GaN layer and the sides of the quantum well layer and the p-GaN layer.

[0016] According to some preferred implementation aspects of the present invention, the top surface of the side film layer is higher than the top surface of the body and extends upward to be flush with the top surface of the top film layer; and / or, the side surface of the top film layer extends outward to be flush with the side surface of the side film layer.

[0017] According to some preferred implementation aspects of the present invention, the optimization is to use a particle swarm algorithm to simulate the collimation effect of the emitted light of the micro light-emitting diode, and determine the optimal single-layer thickness and number of layers according to the simulated collimation effect of the emitted light.

[0018] According to some preferred implementation aspects of the present invention, the optimization includes the following steps:

[0019] Apply FDTD simulation, execute the particle swarm algorithm, and obtain the optimized single-layer thickness and number of layers;

[0020] Based on the optimized single-layer thickness and number of layers; traverse the angular range from 0° to 30°, and calculate the phase delay of each thin film layer;

[0021] Define the transfer matrices of the first dielectric thin film layer and the second dielectric thin film layer:

[0022]

[0023] In the formula, are respectively the phase changes of the plane wave passing through the upper and lower surfaces of the two dielectric thin film layers once; are respectively the phase delays encountered when the light travels in the two dielectric thin film layers;

[0024] Define the DBR transfer matrix;

[0025] M = (M1 * M2) N ;

[0026] A = M(1,1);

[0027] B = M(1,2);

[0028] C = M(2,1);

[0029] D = M(2,2);

[0030] Calculate the transmittance and reflectance according to the following formula:

[0031]

[0032] Wherein, r is the reflection coefficient of the film system, R is the reflectance, and T is the transmittance; respectively represent the phase delays encountered when light propagates in the 0th layer and the Gth layer of the medium; among them, the 0th layer is the dielectric thin film layer attached to the body, and the Gth layer is any layer in the remaining dielectric thin film layers;

[0033] Calculate the ratio of the transmittance in a specific angle range (0 - 30°) to the transmittance in the entire angle range (0 - 90°), and determine the optimal single-layer thickness and number of layers according to the result of the transmittance ratio.

[0034] According to some preferred implementation aspects of the present invention, the phase delay is calculated according to the following formula:

[0035]

[0036] Wherein, are respectively the phase delays of the two dielectric thin film layers, are respectively the refractive indices of the two dielectric thin film layers, are respectively the thicknesses of the two dielectric thin film layers, are respectively the incident angles of the incident light on the surfaces of the two dielectric thin film layers, is the wavelength of the incident light.

[0037] According to some preferred implementation aspects of the present invention, are respectively calculated according to the following formulas:

[0038]

[0039] Wherein, h1 and h2 are respectively the thicknesses of the two dielectric thin film layers, that is, d1 and d2, represents the incident angle of the light.

[0040] According to some preferred implementation aspects of the present invention, are respectively calculated according to the following formulas:

[0041]

[0042] Wherein, is the vacuum permittivity, is the vacuum permeability, represents the incident angle of the light.

[0043] According to some preferred implementation aspects of the present invention, the ratio of the transmittance is calculated by the following formula:

[0044]

[0045] Wherein, T 30 is the transmittance within the range of a specific angle of 0 - 30°; T 90 is the transmittance within the range of a specific angle of 0 - 90°.

[0046] According to some preferred implementation aspects of the present invention, the initial single-layer thickness is 1 / 4 wavelength of the material of the dielectric layer.

[0047] According to some preferred implementation aspects of the present invention, the coating includes using electron beam evaporation technology to deposit on the upper surface of the body to form the top film layer; and / or, the coating includes using atomic layer deposition technology to deposit on the side surface of the body to form the side film layer.

[0048] According to some preferred implementation aspects of the present invention, the step further includes surface treatment of the body before coating: dipping the etched micro light-emitting diode body into a surface treatment solution for surface treatment, and after surface treatment, cleaning and drying; the surface treatment solution is an aqueous solution of tetramethylammonium hydroxide.

[0049] According to some preferred implementation aspects of the present invention, the first dielectric thin film layer is one of titanium dioxide and silicon dioxide, and the second dielectric thin film layer is the other of titanium dioxide and silicon dioxide.

[0050] The present invention also provides a micro light-emitting diode prepared by the preparation method as described above.

[0051] Due to the application of the above technical solution, the present invention has the following advantages compared with the prior art. The preparation method of the micro light-emitting diode of the present invention can prepare a micro light-emitting diode with a full-wrap DBR coating structure, which can effectively prevent the light leakage effect and interference diffraction effect generated at the side wall and top corners of the traditional DBR coating, improve the energy of the emitted light, and can effectively collimate the light emitted by the Micro-LED. Description of the Drawings

[0052] In order to more clearly illustrate the technical solutions in the embodiments of the present invention, the following will briefly introduce the drawings required for the description of the embodiments. Obviously, the following drawings are only some embodiments of the present invention. For those of ordinary skill in the art, without creative efforts, other drawings can also be obtained based on these drawings.

[0053] Figure 1 is the overall light-emitting angle distribution diagram of the Micro-LED without DBR structure;

[0054] Figure 2 Schematic diagram of simulation of Micro-LED with a non-full-coverage DBR structure. Among them, Fig. (a) is the top emission diagram, (b) is the overall emission angle distribution diagram of the Micro-LED, and (c) is the simulation structure diagram;

[0055] Figure 3 Overall emission angle distribution diagram of Micro-LED with a DBR structure plated on the sidewall;

[0056] Figure 4 Schematic diagram of simulation of a micro light-emitting diode with a full-coverage DBR structure in a preferred embodiment of the present invention. Among them, Fig. (a) is the top emission diagram, (b) is the overall emission angle distribution diagram of the Micro-LED, and (c) is the simulation structure diagram;

[0057] Figure 5 Schematic diagram of simulation of a micro light-emitting diode with a full-coverage DBR structure in another preferred embodiment of the present invention. Among them, Fig. (a) is the top emission diagram, (b) is the overall emission angle distribution diagram of the Micro-LED, and (c) is the simulation structure diagram;

[0058] Figure 6 Schematic structure diagram of a micro light-emitting diode with a full-coverage DBR structure in the first preferred embodiment of the present invention;

[0059] In the drawings, the reference numerals are: alumina layer - 1, n-GaN layer - 2, quantum well layer - 3, p-GaN layer - 4, top film layer - 5, side film layer - 6. Detailed implementation manners

[0060] In order to enable those skilled in the art to better understand the solution of the present invention, the technical solutions in the embodiments of the present invention will be clearly and completely described below in conjunction with the accompanying drawings in the embodiments of the present invention. Obviously, the described embodiments are only a part of the embodiments of the present invention, rather than all the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative efforts shall fall within the protection scope of the present invention.

[0061] Embodiment 1 Micro light-emitting diode with a full-coverage DBR structure

[0062] The micro light-emitting diode with a full-coverage DBR structure in this embodiment includes a body, a top film layer 5 covering the top of the body, and a side film layer 6 covering the side of the body. As Figure 6 shown, the structure of the body from bottom to top is alumina (Al 2 O 3), layer 1, n-GaN layer 2, quantum well layer 3, p-GaN layer 4, the n-GaN layer 2, quantum well layer 3 and p-GaN layer 4 form a light-emitting structure, and the side film layer 6 covers the side of the light-emitting structure (n-GaN layer, quantum well layer and p-GaN layer), and the side of the alumina (Al 2 O 3 ) layer 1 may not be covered by the side film layer 6.

[0063] Both the top film layer 5 and the side film layer 6 are obtained by alternately depositing a first dielectric thin film layer and a second dielectric thin film layer. The first dielectric thin film layer is one of titanium dioxide and silicon dioxide, and the second dielectric thin film layer is the other of titanium dioxide and silicon dioxide. In this embodiment, preferably, the first dielectric thin film layer is silicon dioxide, the second dielectric thin film layer is titanium dioxide, and the first dielectric thin film layer made of silicon dioxide is in contact with the body.

[0064] The side film layer 6 covers the side of the top film layer 5 and / or the top film layer 5 covers the top surface of the side film layer 6. Specifically, the top surface of the side film layer 6 is higher than the top surface of the body and extends upward to be flush with the top surface of the top film layer 5; and / or, the side surface of the top film layer 5 extends outward to be flush with the side surface of the side film layer 6. As Figure 4 (c) and Figure 5 (c) shows, the micro light-emitting diode with an all-inclusive DBR structure in this embodiment is preferably two structures, specifically as follows:

[0065] The first: The side of the micro light-emitting diode body is covered with a side film layer 6, and the height of the side film layer 6 is the same as the total height of the light-emitting structure (n-GaN layer 2, quantum well layer 3, p-GaN layer 4) in the body. The top of the body is covered with a top film layer 5. Structurally, after the top film layer 5 completely covers the top surface of the body, it extends to the side of the body and completely covers the top of the side film layer 6, and the side surface of the top film layer 5 is flush with the side surface of the side film layer 6. That is, in the cross-sectional view, the length of the top film layer 5 is the same as the total length of the body and the side film layers 6 on both sides of it, as Figure 4 (c) shows.

[0066] The second: The top of the micro light-emitting diode body is covered with a top film layer 5, and the area of the top film layer 5 is the same as the size of the upper surface area of the body, that is, the side surface of the top film layer 5 is flush with the side surface of the body. The side of the light-emitting structure in the body is covered with a side film layer 6. Structurally, after the side film layer 6 covers the side of the light-emitting structure (n-GaN layer, quantum well layer and p-GaN layer) in the body, it extends upward and completely covers the side surface of the top film layer 5, and the upper surface of the side film layer 6 is flush with the upper surface of the top film layer 5. That is, the height of the side film layer 6 is the same as the total height of the light-emitting structure and the top film layer 5 in the body, as Figure 5 (c) shows.

[0067] That is, for the micro light-emitting diode with an all-inclusive DBR structure in this embodiment, its top film layer 5 and side film layer 6 are in contact to form a complete coverage of the body of the micro light-emitting diode, and the contact surface between the top film layer 5 and the side film layer 6 is a horizontal plane or a vertical plane. In some other preferred embodiments, the contact surface between the top film layer 5 and the side film layer 6 can be an inclined plane or other forms, as long as a structure that can achieve full coverage is realized.

[0068] Preferably, the side wall of the body (n-GaN layer, quantum well layer and p-GaN layer) forms a certain angle with the vertical plane, the angle is close to 90°, preferably 80 - 90°, and the side wall is inclined downward or upward from top to bottom. The DBR structure in this embodiment is also applicable to the structure with an inclined side wall of the micro light-emitting diode body, and can also achieve a good light output collimation effect.

[0069] Embodiment 2 Preparation method of micro light-emitting diode with all-inclusive DBR structure

[0070] This embodiment provides a preparation method of the micro light-emitting diode with an all-inclusive DBR structure in Embodiment 1, which specifically includes the following steps:

[0071] Step 1. Prepare the body

[0072] Prepare the body, and the structure of the body from bottom to top is successively an alumina (Al 2 O 3 ) layer 1 of the sapphire substrate, an n-GaN layer 2, a quantum well layer 3, and a p-GaN layer 4, where the n-GaN layer 2, the quantum well layer 3, and the p-GaN layer 4 form a light-emitting structure, as Figure 6 shown.

[0073] Step 2. Determine the materials, initial single-layer thicknesses of the first dielectric thin film layer and the second dielectric thin film layer in the DBR structure, and the initial number of layers of the top film layer 5 and the side film layer 6.

[0074] The top of the body is covered with a top film layer 5, and the side of the light-emitting structure of the body is covered with a side film layer 6. Among them, both the top film layer 5 and the side film layer 6 are obtained by alternately depositing the first dielectric thin film layer and the second dielectric thin film layer.

[0075] After the materials of the first dielectric thin film layer and the second dielectric thin film layer are determined, their corresponding refractive indices can be determined. At the same time, the material with a lower refractive index is closer to the body of the micro light-emitting diode, and then the order of the first dielectric thin film layer and the second dielectric thin film layer of the top film layer 5 and the side film layer 6 is determined.

[0076] In this embodiment, it is preferred that the first dielectric thin film layer is silicon dioxide and the second dielectric thin film layer is titanium dioxide. And since the refractive index of silicon dioxide is lower, the first dielectric thin film layer made of silicon dioxide is set to be in contact with the body. That is, the top film layer 5 and the side film layer 6 are alternately formed by silicon dioxide and titanium dioxide, and the side closer to the body is silicon dioxide.

[0077] The initial single-layer thickness is 1 / 4 wavelength of the corresponding incident light in the material of the dielectric thin film layer.

[0078] Step 3: Optimize the initial single-layer thickness and the initial number of layers to obtain the optimal single-layer thickness and the number of layers.

[0079] Based on the parameters in Step 2 (material and corresponding refractive index, initial single-layer thickness, initial number of layers), use the FDTD Solutions software for simulation. The simulation material is selected as the body light-emitting structure material of the micro light-emitting diode, which is GaN with a thickness of 1.2 um. At the same time, add a DBR structure to the top and side walls of GaN (corresponding to the top film layer 5 and the side film layer 6 structures in Embodiment 1 respectively). Use the particle swarm algorithm to simulate the collimation effect of the emitted light of the micro light-emitting diode, and determine the optimal single-layer thickness and the number of layers with the best collimation effect of the emitted light as the goal according to the simulated collimation effect of the emitted light.

[0080] The optimization specifically includes the following steps:

[0081] 1. Apply FDTD simulation, execute the particle swarm algorithm, and obtain the optimized single-layer thickness ( ) and the number of layers

[0082] In the process of executing the particle swarm algorithm, it is necessary to set the number of variables, boundary conditions, and the number of particles. The number of variables in this embodiment is 2, which are the single-layer thicknesses d1 and d2 of the first dielectric thin film layer and the second dielectric thin film layer respectively.

[0083] The lower bound lb of the boundary conditions in this embodiment = [0, 0]; the upper bound ub = [100e-9, 60e-9]. The lower bound is the minimum possible value of each optimization variable. When the particle moves in the search space and updates its position, if the newly calculated position exceeds this boundary, the position will be set to the value of the lower bound. The upper bound is the maximum possible value of each optimization variable. Similar to the lower bound, if the new position of the particle exceeds this boundary, it will be restricted to the value of the upper bound.

[0084] The number of particles of the particle swarm algorithm is set to 100 in this embodiment.

[0085] 2. Calculate the phase delay of each thin film layer

[0086] Define the refractive indices of silicon dioxide, titanium dioxide, and gallium nitride. Define the wavelength as 436 nm and the angle range from 0° to 30°.

[0087] Traverse the angle range of 0° - 30°, and calculate the phase delay of each dielectric thin film layer according to the following formula:

[0088]

[0089] In the formula, are the phase delays of the two dielectric thin film layers respectively, are the refractive indices of the two dielectric thin film layers respectively, are the thicknesses of the two optimized dielectric thin film layers respectively, are the incident angles (0° - 30°) on the surface of the thin film layer respectively, is the wavelength of the incident light, which is 436 nm.

[0090] 3. Define the transfer matrices of the first dielectric thin film layer, the second dielectric thin film layer, and the DBR

[0091] Transfer matrix of the first dielectric thin film layer:

[0092]

[0093] Transfer matrix of the second dielectric thin film layer:

[0094]

[0095] In the formula, represent the phase changes of the plane wave passing through the upper and lower surfaces of the two dielectric thin film layers once respectively; represent the phase delays encountered when the light travels in the two dielectric thin film layers respectively;

[0096] Among them, are calculated through the following formulas respectively:

[0097]

[0098] In the formula, h1 and h2 are the thicknesses of the two dielectric thin film layers, that is, d1 and d2, represents the incident angle of the light.

[0099] Define the transfer matrix of the DBR based on the transfer matrices of the first dielectric thin film layer and the second dielectric thin film layer:

[0100] M = (M1 * M2) N ;

[0101] A = M(1,1);

[0102] B = M(1,2);

[0103] C = M(2, 1);

[0104] D = M(2, 2);

[0105] N is the period, and in this embodiment, N is defined as 10. The transfer matrix of the DBR is obtained by multiplying the transfer matrices of two layers of dielectric thin films. Two thin films form a group, and the square root is taken for as many groups as there are. The resulting final matrix is the transfer matrix of the DBR. The first term of this matrix is defined as A, the second term as B, the third term as C, and the fourth term as D, to calculate the transmittance and reflectance of the micro light-emitting diode with the top film layer 5 and the side film layer 6.

[0106] Based on the transfer matrix of the DBR, the reflectance R and transmittance T are calculated through the following formula:

[0107]

[0108] In the formula, r is the reflection coefficient of the film system, r* is the conjugate complex number of r, R is the reflectance, and T is the transmittance. respectively represent the phase delays encountered when light propagates in the dielectric thin film layer of the 0th layer and the Gth layer, and the calculation method is the same as that of the above formula. Among them, the 0th layer is the dielectric thin film layer in contact with the body, and the Gth layer is any layer in the remaining dielectric thin film layers.

[0109] 4. Calculate the ratio of the transmittance in the specific angle range (0 - 30°) to the transmittance in the full angle range (0 - 90°).

[0110] Calculate the transmittance in the range of 0 - 30°, denoted as T 30 ; Calculate the transmittance in the range of 0 - 90°, denoted as T 90 .

[0111] Through the formula Calculate the ratio of the transmittances of the two. The larger the ratio, the more the light energy is concentrated in the range of 0 - 30°, and the better the collimation effect.

[0112] 5. Determine the optimal single-layer thickness and number of layers according to the result of the transmittance ratio

[0113] The larger the result of the transmittance ratio, the better the collimation effect. According to the structure corresponding to the maximum transmittance ratio, the optimal film layer parameters in step 1 are obtained. That is, step 1 is to optimize and output the single-layer thickness and number of layers of the film layer using FDTD simulation, steps 2 - 4 perform the simulation of the light extraction collimation effect corresponding to the optimized film layer, and according to the light extraction collimation effect of the simulation, select the optimal single-layer thickness and number of layers in step 1.

[0114] In this embodiment, the optimized result is that the top film layer 5 is a periodic film of TiO 2 and SiO 2 with a total of 15 layers. The side film layer 6 is also composed of a periodic film of TiO 2 and SiO 2 with a total of 10 layers, and the side in contact with the body is silica. Finally, the thickness of silicon oxide is optimized to 100 nm, and the thickness of titanium oxide is 43.18 nm.

[0115] Step Four: Surface Treatment

[0116] Before coating, the sidewalls of the Micro-LED are first surface-treated. Since the sidewalls are etched, surface treatment is required. Specifically: Immerse the etched micro-light-emitting diode body in the surface treatment solution for surface treatment, and after surface treatment, wash and dry; the surface treatment solution is an aqueous solution of tetramethylammonium hydroxide.

[0117] Specifically, the surface treatment solution is an aqueous solution of tetramethylammonium hydroxide formed by mixing TMAH and deionized water at a volume ratio of 1:3. The immersion time is 1 h, and the immersion temperature is 82 °C; after taking it out, wash it with deionized water multiple times, and then blow it dry with a nitrogen gun.

[0118] Step Five: Coat the body according to the optimal single-layer thickness and number of layers determined above, including using electron beam evaporation technology to evaporate on the upper surface of the body to form the top film layer 5 and using atomic layer deposition (ALD) technology to deposit on the side of the body's light-emitting structure to form the side film layer 6, obtaining a micro-light-emitting diode with a full-encapsulation DBR structure.

[0119] Due to traditional coating technologies such as electron beam evaporation, electron beam evaporation is a technology that uses a high-energy electron beam to heat the material to the evaporation state and then deposits it on the substrate in a vacuum environment to form a thin film. Although this technology can achieve the coating effect, due to the vaporous material, it can only precisely control and ensure the coating quality on the directly facing sample surface, while in other directions such as the sidewalls, especially the vertical sidewalls, it is not possible to well guarantee the coating parameters, and it is very easy to fail to deposit and form breakpoints.

[0120] Therefore, in this embodiment, the sidewall film layer is deposited by atomic layer deposition (ALD). Atomic layer deposition is an advanced chemical vapor deposition technology used to prepare thin film materials on the surface of a substrate. It deposits atoms or molecules of a substance layer by layer onto the substrate evenly through the principle of self-limiting reactions. In a typical ALD process, two different precursor gases are introduced alternately. The first gas undergoes a chemical reaction on the substrate surface and adsorbs a layer of molecules. After this gas is removed, the second gas is introduced and reacts with the intermediate product generated by the first gas. Once the active sites on the surface are covered by the first precursor and reach saturation, this stage stops. Then, the next step is carried out to continue growing another layer under the action of a new chemical substance. ALD has the advantages of extremely high thickness control accuracy and composition uniformity. Due to its unique process characteristics, ALD can be applied to various types of material synthesis and the manufacture of complex structures with different shapes and sizes.

[0121] Therefore, in this embodiment, electron beam evaporation technology is used to grow the top thin film, while atomic layer deposition technology is used for the more difficult sidewalls. In this way, the thin films on the top layer and sidewalls can be precisely controlled and reach the required thickness.

[0122] Based on the preparation method in the above-mentioned Embodiment 2, two types of micro light-emitting diodes with a full-package DBR structure in Embodiment 1 are simulated to reflect the collimated light-emitting effects of the two structures. Among them, Simulation Example 1 corresponds to the first structure in Embodiment 1, and Simulation Example 2 corresponds to the second structure in Embodiment 1.

[0123] Simulation Example 1

[0124] Judging from the simulation results, as Figure 4 shown in Figures 4(a) and 4(b), the energy distribution at the top meets the expectations, and the energy is the highest at the two corners. Since the corners of the DBR are wrapped, the light that originally would leak out from the sidewalls is all reflected at the corners, greatly reducing light leakage and enhancing the emitted light energy. Moreover, the overall light-emitting angle is also smaller than that of the Micro-LED coated with a non-full-package DBR, indicating that Figure 4 the structure in Figure 4(c) indeed plays a role in collimating the light emission.

[0125] Simulation Example 2

[0126] As Figure 5 shown in Figures 5(a) and 5(b), the energy distribution at the top meets the expectations, and the energy is the highest at the two corners. Since the corners of the DBR are wrapped, the light that originally would leak out from the sidewalls is all reflected at the corners, greatly reducing light leakage and enhancing the emitted light energy. Moreover, the overall light-emitting angle is also smaller than that of the Micro-LED coated with a non-full-package DBR, indicating that Figure 5The structure of (c) indeed plays a role in collimating the outgoing light.

[0127] At the same time, by comparing the results of Simulation Example 2 and Simulation Example 1, Figure 4 and Figure 5 , it can be found that in Simulation Example 2, both the overall outgoing light angle and the light energy at the top are better than those in Simulation Example 1. That is, the DBR structure in which the side film layer 6 of the Micro-LED wraps the side of the top film layer 5 (the second structure in Embodiment 1) has more application potential than the DBR structure in which the top film layer 5 of the Micro-LED wraps the top surface of the side film layer 6 (the first structure in Embodiment 1). However, regardless of which film layer structure method, compared with Figure 2 the Micro-LED structure with non-full-coverage DBR coating, it has a better collimation function for the outgoing light angle.

[0128] The micro light-emitting diode with the full-coverage DBR film layer structure of the present invention can achieve better light collimation and stronger outgoing light energy than the micro light-emitting diode with a non-full-coverage DBR structure. Compared with the prior art, since the micro light-emitting diode of the present invention adopts a full-coverage DBR film layer structure, the sidewall DBR corners of the Micro-LED are wrapped by the top DBR. Therefore, the outgoing light energy of the present invention is higher, and the beam interference, diffraction, and light leakage phenomena at the corners are improved. At the same time, the light emitted by the Micro-LED has better collimation after passing through the present invention, and has the value of popularization and application.

[0129] The above embodiments are only used to illustrate the technical concept and characteristics of the present invention, and their purpose is to enable those who are familiar with this technology to understand the content of the present invention and implement it accordingly. It should not be used to limit the protection scope of the present invention. Any equivalent changes or modifications made according to the spirit and essence of the present invention should be covered within the protection scope of the present invention.

[0130] In the ranges disclosed herein, the endpoints and any values are not limited to the exact ranges or values. These ranges or values should be understood to include values close to these ranges or values. For numerical ranges, between the endpoint values of each range, between the endpoint values of each range and individual point values, and between individual point values, they can be combined with each other to obtain one or more new numerical ranges, and these numerical ranges should be regarded as specifically disclosed herein.

Claims

1. A method for preparing a micro light emitting diode having an all-inclusive DBR structure, characterized in that: The steps include: A body is prepared; the top of the body is covered with a top film layer, and the side of the body is covered with a side film layer; wherein the side film layer covers the side of the top film layer or the top film layer covers the top surface of the side film layer; the top film layer and the side film layer are both obtained by alternately depositing a first dielectric film layer and a second dielectric film layer; the body comprises a substrate layer, an n-GaN layer, a quantum well layer, and a p-GaN layer from bottom to top, the top film layer is located above the p-GaN layer, and the side film layers cover the side of the n-GaN layer, the quantum well layer, and the p-GaN layer; Prepare the top and side membrane layers: Determine the material of the first dielectric film layer and the second dielectric film layer, the initial single layer thickness, and the initial number of layers of the top film layer and the side film layer; Optimize the initial single layer thickness and the initial number of layers, and obtain the optimal single layer thickness and the number of layers; Coating the main body according to the optimal single layer thickness and number of layers to obtain the micro light emitting diode with the all-inclusive DBR structure; Wherein, the optimization comprises the following steps: Apply FDTD simulation and execute particle swarm algorithm to obtain the optimized single layer thickness and number of layers; Based on the optimized single layer thickness and number of layers, the phase delay of each thin film layer is calculated from the angle range of 0° to 30°; Define the transmission matrix of the first dielectric film layer and the second dielectric film layer: Where, δ1 and δ2 are the phase changes of the upper and lower surfaces of the plane wave passing through the two dielectric thin film layers; η1 and η2 are the phase delays encountered by the light when propagating in the two dielectric thin film layers; Define the transmission matrix of the DBR structure: M = (M1*M2) N ; Where N is the period; A=M(1,1); B=M(1,2); C=M(2,1); D=M(2,2) Based on the transmission matrix of the DBR structure, the transmittance is calculated according to the following formula: R=r*r * ;T=1-R Where r is the reflection coefficient of the film system, r* is the conjugate complex of r, R is the reflectivity, T is the transmittance; η0, η G They represent the phase delay encountered by light when propagating in the 0th and Gth layers of media respectively; Calculate the ratio of transmittance within a specific angle range to the transmittance within the entire angle range; determine the optimal single layer thickness and number of layers based on the transmittance ratio result.

2. The preparation method according to claim 1, characterized in that: The top surface of the side film layer is higher than the top surface of the body and extends upward to be flush with the top surface of the top film layer; or, the side surface of the top film layer extends outward to be flush with the side surface of the side film layer.

3. The preparation method according to claim 1, characterized in that: The phase delay is calculated according to the following formula: Wherein, Δ1 and Δ2 are phase delays of the two dielectric thin film layers, n1 and n2 are refractive indices of the two dielectric thin film layers, d1 and d2 are thicknesses of the two dielectric thin film layers, θ1 and θ2 are incident angles onto the surfaces of the two dielectric thin film layers, and λ is the wavelength of the incident light.

4. The preparation method according to claim 1, characterized in that: δ1 and δ2 are calculated by the following formulas: Where h1 and h2 are the thicknesses of the two dielectric thin film layers, and θ represents the incident angle of the light.

5. The preparation method according to claim 1, characterized in that: η1 and η2 are calculated by the following formulas: In the formula, ε0 is the dielectric constant of vacuum, μ0 is the magnetic permeability of vacuum, and θ represents the incident angle of light.

6. The preparation method according to claim 1, characterized in that: The transmittance ratio is calculated by the following formula: Where, T 30 is the transmittance within a specific angle range of 0-30°; T 90 It is the transmittance within a specific angle range of 0-90°.

7. The preparation method according to claim 1, characterized in that: The coating includes using electron beam evaporation technology to perform evaporation on the upper surface of the body to form the top film layer; the coating includes using atomic layer deposition technology to perform deposition on the side of the body to form the side film layer.

8. A micro light emitting diode prepared by the preparation method according to any one of claims 1 to 7.

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