CN108183157B - Light-emitting diode and preparation method thereof - Google Patents

Abstract

The invention discloses a light emitting diode and a preparation method, belonging to the field of optoelectronic manufacturing technology. The invention comprises a substrate, an n-type GaN layer, an active layer, a p-type GaN layer, a transparent conductive layer, a p-electrode, an n-electrode, a passivation layer, and a Bragg reflection layer, wherein the transparent conductive layer is stacked on the p-type GaN layer, the p-electrode is arranged on the transparent conductive layer, the passivation layer is exposed at the surface opposite to the substrate of the above structure, the Bragg reflection layer is on the passivation layer, and the passivation layer is arranged as a first refractive index layer, a second refractive index layer, and a third refractive index layer, wherein the second refractive index layer comprises a plurality of convex lens units, and the refractive index of the second refractive index layer is greater than that of the first refractive index layer and the third refractive index layer, so that the light that should be incident on the Bragg reflection layer structure at a large angle is incident on the Bragg reflection layer at a relatively vertical angle after passing through the convex lens unit, thereby improving the light collection efficiency of the diode.

Description

A kind of light-emitting diode and preparation method thereof

technical field

The invention relates to the field of optoelectronic manufacturing technology, in particular to a light emitting diode and a preparation method.

Background technique

LED (Light Emitting Diode, Light Emitting Diode) has the advantages of small size, long life, low power consumption, etc., and is currently widely used in automobile signal lights, traffic signal lights, display screens and lighting equipment.

An existing LED chip mainly includes a substrate and an epitaxial layer grown on the substrate. A p-type primary electrode and an n-type primary electrode are formed on the epitaxial layer, and a passivation layer is also covered on the epitaxial layer. A Bragg reflective layer is set on the Bragg reflective layer, and a p-type secondary electrode and an n-type secondary electrode are set on the Bragg reflective layer. The p-type secondary electrode and the n-type secondary electrode are respectively connected to the p-type primary electrode and the n-type primary Electrode connection. The Bragg reflective layer includes alternately stacked high-refractive index material layers and low-refractive index material layers. The Bragg reflective layer has a high reflectivity for light of a specific wavelength, so that it can reflect the light to the substrate side and improve the luminous efficiency of the LED. .

Since the light emitted by the LED chip is directed in all directions, when the light is incident on the Bragg reflective layer, the incident angle of some light is very small, while the incident angle of some light is very large. The reflectivity of the Bragg reflective layer for light rays at different incident angles is also different. The Bragg reflective layer can better reflect light with a small incident angle, and the reflectivity for light with a larger incident angle is relatively low. Therefore, the existing Bragg reflective The degree to which the layer improves the light extraction rate of the LED is limited.

Contents of the invention

In order to improve the luminous efficiency of LEDs, embodiments of the present invention provide a light emitting diode and a preparation method thereof. Described technical scheme is as follows:

A light emitting diode, the light emitting diode comprises a substrate, an epitaxial layer formed on the substrate, an n-type primary electrode and a p-type primary electrode formed on the epitaxial layer, an a passivation layer, a Bragg reflection layer covering the passivation layer, an n-type secondary electrode and a p-type secondary electrode formed on the Bragg reflection layer, and the n-type secondary electrode communicates with the The n-type primary electrode is connected, the p-type secondary electrode is connected to the p-type primary electrode through a via hole,

It is characterized in that the passivation layer includes a first refractive index layer, a second refractive index layer and a third refractive index layer stacked on the epitaxial layer in sequence, and the refractive index of the second refractive index layer is higher than that of the The refractive index of the first refractive index layer and the third refractive index layer, the second refractive index layer includes a plurality of convex lens units arranged in the same layer, each of the convex lens units close to the first refractive index layer The surface and the surface close to the third refractive index layer are spherical crown surfaces, the orthographic projection of each of the convex lens units on the substrate is circular, and in a direction parallel to the substrate, each of the convex lens units The thickness of the convex lens unit gradually becomes thinner from the middle to the edge.

Optionally, the second refractive index layer is made of any one of Ti ₃ O ₅ , TiO ₂ , ZrO ₂ , and HfO ₂ .

Optionally, the refractive index of the second refractive index layer is 2.2-2.6, the refractive index of the first refractive index layer is 1.4-1.7, and the refractive index of the third refractive index layer is 1.4-1.7.

Optionally, the ratio of the radius of the orthographic projection of the convex lens unit on the substrate to the radius of the spherical crown surface is 0.50-0.97.

Optionally, the diameter of the orthographic projection of the convex lens unit on the substrate is 4 μm˜12 μm.

Optionally, the distance between the edges of adjacent convex lens units is 5 μm˜10 μm.

Optionally, the thickness of the second refractive index layer is 30-100 nm.

Optionally, the orthographic projection of the surface of the passivation layer far away from the substrate on the substrate is located in the substrate, and the Bragg reflection layer covers the surface of the passivation layer far away from the substrate. bottom surface and multiple sides of the passivation layer.

A method for preparing a light-emitting diode, the method comprising:

providing a substrate;

growing an epitaxial layer on said substrate;

making an n-type primary electrode and a p-type primary electrode on the epitaxial layer;

forming a passivation layer on the epitaxial layer;

forming a Bragg reflection layer on the passivation layer;

forming an n-type secondary electrode and a p-type secondary electrode on the Bragg reflection layer,

Wherein, the n-type secondary electrode is connected to the n-type primary electrode through a via hole, the p-type secondary electrode is connected to the p-type primary electrode through a via hole, and the passivation layer includes layers sequentially stacked on the A first refractive index layer, a second refractive index layer, and a third refractive index layer on the epitaxial layer, the refractive index of the second refractive index layer is greater than that of the first refractive index layer and the third refractive index layer Refractive index, the second refractive index layer includes a plurality of convex lens units arranged in the same layer, the orthographic projection of the convex lens units on the substrate is circular, and in a direction parallel to the substrate, each of the The thickness of the convex lens unit gradually becomes thinner from the middle to the edge.

Optionally, forming a passivation layer on the epitaxial layer includes:

forming a first refractive index layer on the epitaxial layer;

performing patterning on the first refractive index layer to form a first pattern on the first refractive index layer, the first pattern including a plurality of arc-shaped grooves arranged in an array;

forming a second refractive index layer on the first refractive index layer;

Patterning the second refractive index layer to form a second pattern on the second refractive index layer, the second pattern includes a plurality of arc-shaped protrusions arranged in an array, and the arc-shaped surface The protrusions are arranged in one-to-one correspondence with the arc-shaped grooves;

A third refractive index layer is formed on the second refractive index layer.

The beneficial effect brought by the technical solution provided by the embodiment of the present invention is: by setting the passivation layer as a stacked first refractive index layer, a second refractive index layer and a third refractive index layer, wherein the refractive index of the second refractive index layer The refractive index is greater than the refractive index of the first refractive index layer and the third refractive index layer. The second refractive index layer includes a plurality of convex lens units arranged in the same layer. The orthographic projection of the convex lens units on the substrate is circular. In the direction of , the thickness of each convex lens unit gradually becomes thinner from the middle to the edge, and each convex lens unit is equivalent to a convex lens, which can converge the light rays directed to the Bragg reflective layer, so that more light rays can be incident at a smaller incident angle To the Bragg reflective layer, so that the Bragg reflective layer can reflect more light, thereby improving the luminous efficiency of the light-emitting diode.

Description of drawings

In order to more clearly illustrate the technical solutions in the embodiments of the present invention, the drawings that need to be used in the description of the embodiments will be briefly introduced below. Obviously, the drawings in the following description are only some embodiments of the present invention. For those skilled in the art, other drawings can also be obtained based on these drawings without creative effort.

Fig. 1 is a structural diagram of a light emitting diode provided by an embodiment of the present invention;

Fig. 2 is a diagram of the spatial position relationship between the convex lens unit and the substrate provided by the embodiment of the present invention;

Fig. 3 is a schematic structural diagram of another light-emitting diode provided by an embodiment of the present invention;

Fig. 4 is an optical path diagram of a convex lens unit provided by an embodiment of the present invention;

Fig. 5 is a flow chart of the preparation of a light-emitting diode provided by an embodiment of the present invention;

6-7 are schematic diagrams of the preparation process of the light-emitting diode provided by the embodiment of the present invention;

Fig. 8 is a flow chart of the preparation of a passivation layer provided by an embodiment of the present invention;

FIG. 9 is a schematic diagram of an etching process of a first refractive index layer provided by an embodiment of the present invention;

Fig. 10 is a schematic structural diagram of a mask for etching a first refractive index layer provided by an embodiment of the present invention;

Fig. 11 is a schematic diagram of the preparation process of a second refractive index layer provided by an embodiment of the present invention;

Fig. 12 is a schematic structural diagram of a mask for etching a second refractive index layer provided by an embodiment of the present invention;

Fig. 13 is a schematic diagram of an etching process of a second refractive index layer provided by an embodiment of the present invention;

Fig. 14 is a schematic structural view of a prepared passivation layer provided by an embodiment of the present invention;

15 to 17 are schematic diagrams of a manufacturing process of a light emitting diode provided by an embodiment of the present invention.

Detailed ways

In order to make the object, technical solution and advantages of the present invention clearer, the implementation manner of the present invention will be further described in detail below in conjunction with the accompanying drawings.

Fig. 1 is a structural diagram of a light emitting diode provided by an embodiment of the present invention. As shown in FIG. 1 , a light-emitting diode includes a substrate 1, an epitaxial layer 20 formed on the substrate 1, an n-type primary electrode 8 and a p-type primary electrode 7 formed on the epitaxial layer 20, and an The passivation layer 9, the Bragg reflection layer 10 covered on the passivation layer 9, the n-type secondary electrode 11 and the p-type secondary electrode 14 formed on the Bragg reflection layer 10, the n-type secondary electrode 11 and the The n-type primary electrode 8 is connected, and the p-type secondary electrode 14 is connected to the p-type primary electrode 7 through a via hole.

The passivation layer 9 includes a first refractive index layer 91, a second refractive index layer 92 and a third refractive index layer 93 sequentially stacked on the epitaxial layer 20, the second refractive index layer 92 has a higher refractive index than the first refractive index layer 91 and the refractive index of the third refractive index layer 93 . The second refractive index layer 92 includes a plurality of convex lens units 92a arranged in the same layer, and the surface of each convex lens unit 92a close to the first refractive index layer 91 (the spherical crown surface 92b as shown in FIG. 1 ) and the surface close to the third refractive index The surface of the ratio layer 93 (the spherical crown surface 92c as shown in Figure 1) is a spherical crown surface, and the orthographic projection of each convex lens unit 92a on the substrate 1 is circular, and in the direction parallel to the substrate 1 , the thickness of each convex lens unit 92a gradually becomes thinner from the middle to the edge.

By setting the light emitting diode to include a substrate, an epitaxial layer formed on the substrate, a primary electrode formed on the epitaxial layer, a passivation layer covering the epitaxial layer, a Bragg reflection layer covering the passivation layer, and forming The secondary electrode on the Bragg reflection layer is connected to the primary electrode through a via hole. Wherein, the passivation layer includes a first refraction index layer, a second refraction index layer and a third refraction index layer stacked on the epitaxial layer in sequence, so that the refraction index of the second refraction index layer is greater than that of the first refraction index layer and the third refraction index layer. The refractive index of the index layer, and the second refractive index layer includes a plurality of convex lens units arranged in the same layer, so that the light that should be incident on the structure of the Bragg reflection layer at a large angle, when passing through the convex lens unit, the optical path shifts, which can be relatively A perpendicular angle is incident on the Bragg reflective layer, so that the Bragg reflective layer can reflect this part of the light, improving the light extraction efficiency of the diode.

As shown in FIG. 1, the epitaxial layer 20 may include an n-type GaN layer 2, an active layer 3, a p-type GaN layer 4, and a transparent conductive layer 6 grown sequentially on a substrate 1. The n-type GaN layer 2, the active layer 3. The p-type GaN layer 4 and the transparent conductive layer 6 , the n-type primary electrode 8 is disposed on the n-type GaN layer, and the p-type primary electrode 7 is disposed on the transparent conductive layer 6 .

As shown in Figure 1, in this embodiment, the active layer 3 can be a multi-quantum well structure, the active layer 3 includes alternately stacked InGaN layers 31 and GaN layers 32, and the number of cycles of the alternately stacked InGaN layers 31 and GaN layers 32 It can be 6-15 nm, and the thickness of the InGaN layer 31 can be 2-5 nm.

It should be noted that the structure of the active layer 3 shown in FIG. 1 is only for illustration and is not intended to limit the number of layers of the InGaN layer 31 and the GaN layer 32 in the active layer 3 .

Optionally, the second refractive index layer 92 is made of any one of Ti ₃ O ₅ , TiO ₂ , ZrO ₂ , and HfO ₂ . layer requires high refractive index.

Preferably, the second refractive index layer 92 is made of Ti ₃ O ₅ or TiO ₂ .

Optionally, the first refractive index layer 91 can be made of any one of SiO ₂ , MgO, and Al ₂ O ₃ , and the third refractive index layer 93 can be made of any one of SiO ₂ , MgO, and Al ₂ O ₃ made. These kinds of materials have good anti-oxidation effect and can protect the internal structure of light-emitting diodes. Preferably, the first refractive index layer 91 and the third refractive index layer 93 are made of the same material. Choosing the same material to make the first refractive index layer and the second refractive index layer can reduce the manufacturing cost of the diode.

Preferably, both the first refractive index layer 91 and the third refractive index layer 93 are made of SiO ₂ .

Optionally, the refractive index of the second refractive index layer 92 is 2.2-2.6, the refractive index of the first refractive index layer 91 is 1.4-1.7, and the refractive index of the third refractive index layer 93 is 1.4-1.7. By setting the refractive index of the second refractive index layer to 2.2-2.6, and setting the refractive indices of the first refractive index layer and the third refractive index layer to 1.4-1.7, the second refractive index layer and the first refractive index layer and the second refractive index layer The three refractive index layers cooperate with each other to achieve better light-gathering effect.

Optionally, in the embodiment of the present invention, the refractive index of the first refractive index layer 91 and the refractive index of the third refractive index layer 93 may be the same.

Optionally, the thickness of the second refractive index layer 92 is 30-100 nm. Setting the thickness of the second refractive index layer within this range can maximize the light extraction effect of the second refractive index layer. If the thickness of the second refractive index layer is less than 30-100nm, the spherical crown surface of the etched convex lens unit will be too small, which is not conducive to light convergence; The intrinsic absorption of the material is not conducive to the extraction of light.

In this embodiment, the thickness of the second refractive index layer 92 is the thickness value of the maximum thickness on the convex lens unit 92a.

Optionally, the diameter of the orthographic projection of the convex lens unit 92a on the substrate 1 may be 4 μm˜12 μm. In order to facilitate the production of the convex lens unit. For the convex lens unit, after-baking the photoresist makes the side of the photoresist parallel to the surface of the substrate change in slope, so as to obtain the desired etched curved surface corresponding to the spherical crown surface of the convex lens unit. If the diameter of the convex lens unit is too small, it will be difficult to realize the fabrication of the convex lens unit by photolithography. If the diameter is too large, it will be difficult to form the surface curvature required by the spherical crown surface of the convex lens unit on the photoresist.

Optionally, the distance between the edges of adjacent convex lens units 92a is 5 μm˜10 μm. When the size of the convex lens units 92a is constant, the distance between the edges of adjacent convex lens units 92a is set to 5 μm˜10 μm to facilitate the production of the convex lens units. If the distance between the edges of adjacent convex lens units is too large, the density of the convex lens units will be low, reducing the extraction of light. If the distance between the edges of adjacent convex lens units is too small, interference will occur between the convex lens units and the convex lens will be affected. The extraction of rays by the unit.

Optionally, the orthographic projection of the surface of the passivation layer 9 far away from the substrate on the substrate is located in the substrate, and the Bragg reflection layer 10 covers the surface of the passivation layer 9 far away from the substrate 1 and much of the passivation layer 9. on one side. By covering the surface of the passivation layer far away from the substrate 1 and the multiple sides of the passivation layer with the Bragg reflection layer, the range in which the Bragg reflection layer can reflect light is larger.

In addition, the included angle θ between the sidewall 20a of the epitaxial layer 20 and the substrate 1 is larger than 90°, so that the light emitted from the sidewall of the epitaxial layer can be better irradiated on the Bragg reflection layer for reflection.

Optionally, the material of the transparent conductive layer 6 is ITO (Indium Tin Oxides, indium tin oxide). ITO has high light transmittance and good electrical conductivity, can reduce light absorption, and is beneficial to improve luminous efficiency.

In this embodiment, the Bragg reflection layer 10 includes alternately grown high-refractive-index material layers and low-refractive-index material layers, and the optical thickness of each high-refractive-index material layer and each low-refractive-index material layer is set by the active layer. emits 1/4 of the wavelength of light.

Optionally, FIG. 2 is a diagram of the spatial position relationship between the convex lens unit and the substrate provided by the embodiment of the present invention. As shown in FIG. 2 , the radius r of the orthographic projection of the convex lens unit 92a on the substrate 1 and the The ratio of the radius R is 0.50-0.97. The ratio of the radius of the orthographic projection of the convex lens unit on the substrate to the radius of the spherical crown surface is set to 0.50-0.97, which facilitates the production of the convex lens unit and can also achieve a better light-gathering effect.

Fig. 3 is a schematic structural view of another light-emitting diode provided by an embodiment of the present invention. As shown in Fig. 3, a current blocking layer 5 is also provided between the p-type GaN layer 4 and the transparent conductive layer 6, and the current blocking layer 5 is beneficial to The horizontal expansion of the current.

Fig. 4 is the optical path diagram of the convex lens unit provided by the embodiment of the present invention. As shown in Fig. 4, the light that should be incident on the Bragg reflection layer structure at a large angle is offset when passing through the convex lens unit 92a, and can be approximately vertical Angle of incidence on the Bragg reflector.

Fig. 5 is a flow chart of manufacturing a light emitting diode provided by an embodiment of the present invention. As shown in Figure 5, the preparation method comprises:

S1: Provide a substrate.

In this embodiment, the substrate 1 is a sapphire substrate.

S2: growing an epitaxial layer on the substrate.

S3: Fabricate an n-type primary electrode and a p-type primary electrode on the epitaxial layer.

S4: forming a passivation layer on the epitaxial layer.

S5: forming a Bragg reflection layer on the passivation layer.

S6: forming an n-type secondary electrode and a p-type secondary electrode on the Bragg reflection layer.

Wherein, the n-type secondary electrode is connected to the n-type primary electrode through the via hole, and the p-type secondary electrode is connected to the p-type primary electrode through the via hole. The passivation layer includes a first refractive index layer, a second Two refractive index layers and a third refractive index layer, the refractive index of the second refractive index layer is greater than the refractive index of the first refractive index layer and the third refractive index layer, the second refractive index layer includes a plurality of convex lens units arranged in the same layer, The orthographic projection of the convex lens unit on the substrate is circular, and in a direction parallel to the substrate, the thickness of each convex lens unit gradually becomes thinner from the middle to the edge.

By setting the light emitting diode to include a substrate, an epitaxial layer formed on the substrate, a primary electrode formed on the epitaxial layer, a passivation layer covering the epitaxial layer, a Bragg reflection layer covering the passivation layer, and forming The secondary electrode on the Bragg reflection layer is connected to the primary electrode through a via hole. Wherein, the passivation layer includes a first refraction index layer, a second refraction index layer and a third refraction index layer stacked on the epitaxial layer in sequence, so that the refraction index of the second refraction index layer is greater than that of the first refraction index layer and the third refraction index layer. The refractive index of the index layer, and the second refractive index layer includes a plurality of convex lens units arranged in the same layer, so that the light that should be incident on the structure of the Bragg reflection layer at a large angle, when passing through the convex lens unit, the optical path shifts, which can be relatively A perpendicular angle is incident on the Bragg reflective layer, so that the Bragg reflective layer can reflect this part of the light, improving the light extraction efficiency of the diode.

6-7 are schematic diagrams of the preparation process of the light emitting diode provided by the embodiment of the present invention.

Specifically, step S2 may include:

An epitaxial layer is grown on the substrate.

As shown in FIG. 6 , an epitaxial layer 20 is grown on the substrate 1 , and the epitaxial layer 20 includes an n-type GaN layer 2 , an active layer 3 , a p-type GaN layer 4 and a transparent conductive layer 6 grown on the substrate 1 in sequence.

In addition, a current blocking layer 5 may also be grown between the p-type GaN layer 4 and the transparent conductive layer 6 .

Step S3 may include:

Grooves are made on the epitaxial layer.

A p-type primary electrode is fabricated on the transparent conductive layer, and an n-type primary electrode is fabricated on the n-type GaN layer in the groove.

As shown in Figure 7, a groove 17 is made on the epitaxial layer 20 to expose the n-type GaN layer 2, the n-type primary electrode 8 is arranged on the n-type GaN layer 2, and the p-type primary electrode 7 is arranged on the transparent conductive layer 6 superior.

FIG. 8 is a flow chart for preparing a passivation layer provided by an embodiment of the present invention, and FIGS. 9 to 13 are schematic diagrams of the manufacturing process of a passivation layer structure provided by an embodiment of the present invention. In combination with FIGS. 9-13, it can be seen that step S4 may include:

S41: forming a first refractive index layer on the epitaxial layer.

9 is a schematic diagram of an etching process of a first refractive index layer provided by an embodiment of the present invention. As shown in FIG. 9 , a first refractive index layer 911 is formed on the epitaxial layer 20, and the first refractive index layer 911 can be deposited formed on the epitaxial layer 20 in a manner.

S42: Perform patterning processing on the first refractive index layer 911 to form a first pattern on the first refractive index layer 911 .

Wherein, the first pattern includes a plurality of arc surface grooves 911a arranged in an array.

Specifically, a photoresist 12 can be coated on the first refractive index layer, and the photoresist 12 is exposed using the mask 15 shown in FIG. An arc-shaped groove 911a is formed on the layer 911 . Optionally, the photoresist 12 is a positive photoresist.

S43 : forming the second refractive index layer 921 on the first refractive index layer 911 .

As shown in FIG. 11 , a second refractive index layer 921 is formed on the first refractive index layer 911 .

The second refractive index layer 921 can be formed by deposition.

S44: Perform patterning processing on the second refractive index layer 921 to form a second pattern on the second refractive index layer 921 .

Wherein, the second figure includes a plurality of arc surface protrusions 921a arranged in an array, and the arc surface protrusions 921a are arranged in one-to-one correspondence with the arc surface grooves 911a.

Specifically, a photoresist 13 can be coated on the second refractive index layer, and the photoresist 13 is exposed using the mask 16 shown in FIG. The arc surface protrusion 921a is formed on the rate layer 921 . As shown in Figure 13.

Optionally, the photoresist 13 is a negative photoresist.

S45: forming the third refractive index layer 931 on the second refractive index layer 921 .

As shown in FIG. 14 , a third refractive index layer 931 is formed on the second refractive index layer 921 .

The third refractive index layer 931 can be formed by deposition.

The structure of the light emitting diode after the passivation layer is fabricated is shown in FIG. 15 .

15 to 17 are schematic diagrams of a manufacturing process of a light emitting diode provided by an embodiment of the present invention.

As shown in FIG. 16 , a Bragg reflection layer 10 is formed on the passivation layer 9 after the complete passivation layer is fabricated.

Before step S6 is performed, via holes can be made on the Bragg reflective layer, so that the n-type secondary electrode 14 and the p-type secondary electrode 11 can be connected to the n-type primary electrode 8 and the p-type primary electrode 8 respectively through the via holes.

After the n-type secondary electrode 14 and the p-type secondary electrode 11 are fabricated, a light emitting diode as shown in FIG. 17 can be obtained.

The above descriptions are only preferred embodiments of the present invention, and are not intended to limit the present invention. Any modifications, equivalent replacements, improvements, etc. made within the spirit and principles of the present invention shall be included in the protection of the present invention. within range.

Claims (10)

1. A light-emitting diode, the light-emitting diode comprising a substrate, an epitaxial layer formed on the substrate, an n-type primary electrode and a p-type primary electrode formed on the epitaxial layer, covered on the epitaxial layer A passivation layer on the passivation layer, a Bragg reflective layer covering the passivation layer, an n-type secondary electrode and a p-type secondary electrode formed on the Bragg reflective layer, and the n-type secondary electrode passes through the via hole connected to the n-type primary electrode, the p-type secondary electrode is connected to the p-type primary electrode through a via hole, It is characterized in that the passivation layer includes a first refractive index layer, a second refractive index layer and a third refractive index layer stacked on the epitaxial layer in sequence, and the refractive index of the second refractive index layer is higher than that of the The refractive index of the first refractive index layer and the third refractive index layer, the second refractive index layer includes a plurality of convex lens units arranged in the same layer, each of the convex lens units close to the first refractive index layer The surface and the surface close to the third refractive index layer are all spherical crown surfaces, the orthographic projection of each of the convex lens units on the substrate is circular, and in a direction parallel to the substrate, each of the convex lens units The thickness of the convex lens unit gradually becomes thinner from the middle to the edge. 2 . The light emitting diode according to claim 1 , wherein the second refractive index layer is made of any one of Ti ₃ O ₅ , TiO ₂ , ZrO ₂ , and HfO ₂ . 3. The light emitting diode according to claim 1, characterized in that, the refractive index of the second refractive index layer is 2.2-2.6, the refractive index of the first refractive index layer is 1.4-1.7, and the refractive index of the first refractive index layer is 1.4-1.7. The refractive index of the tri-refractive index layer is 1.4-1.7. 4 . The light emitting diode according to claim 1 , wherein the ratio of the radius of the orthographic projection of the convex lens unit on the substrate to the radius of the spherical cap is 0.50˜0.97. 5 . The light emitting diode according to claim 1 , wherein the diameter of the orthographic projection of the convex lens unit on the substrate is 4 μm˜12 μm. 6 . The light emitting diode according to claim 1 , wherein the distance between the edges of adjacent convex lens units is 5 μm˜10 μm. 7. The light emitting diode according to claim 1, characterized in that, the thickness of the second refractive index layer is 30-100 nm. 8. The light emitting diode according to claim 1, wherein the orthographic projection of the surface of the passivation layer away from the substrate on the substrate is located in the substrate, and the Bragg reflection layer Covering on the surface of the passivation layer away from the substrate and multiple sides of the passivation layer. 9. A method for preparing a light-emitting diode, characterized in that the method comprises: providing a substrate; growing an epitaxial layer on said substrate; making an n-type primary electrode and a p-type primary electrode on the epitaxial layer; forming a passivation layer on the epitaxial layer; forming a Bragg reflection layer on the passivation layer; forming an n-type secondary electrode and a p-type secondary electrode on the Bragg reflection layer, Wherein, the n-type secondary electrode is connected to the n-type primary electrode through a via hole, the p-type secondary electrode is connected to the p-type primary electrode through a via hole, and the passivation layer includes layers sequentially stacked on the A first refractive index layer, a second refractive index layer, and a third refractive index layer on the epitaxial layer, the refractive index of the second refractive index layer is greater than that of the first refractive index layer and the third refractive index layer Refractive index, the second refractive index layer includes a plurality of convex lens units arranged in the same layer, the orthographic projection of the convex lens units on the substrate is circular, and in a direction parallel to the substrate, each of the The thickness of the convex lens unit gradually becomes thinner from the middle to the edge. 10. The preparation method according to claim 9, wherein forming a passivation layer on the epitaxial layer comprises: forming a first refractive index layer on the epitaxial layer; performing patterning on the first refractive index layer to form a first pattern on the first refractive index layer, the first pattern including a plurality of arc-shaped grooves arranged in an array; forming a second refractive index layer on the first refractive index layer; Patterning the second refractive index layer to form a second pattern on the second refractive index layer, the second pattern includes a plurality of arc-shaped protrusions arranged in an array, and the arc-shaped surface The protrusions are arranged in one-to-one correspondence with the arc-shaped grooves; A third refractive index layer is formed on the second refractive index layer.