Light emitting diode epitaxial wafer preparation method, light emitting diode epitaxial wafer, and apparatus

Abstract

The application provides a light emitting diode epitaxial wafer preparation method, a light emitting diode epitaxial wafer and equipment. The light emitting diode preparation method comprises the following steps: sequentially depositing an aluminum nitride buffer layer and an aluminum gallium nitride layer on a substrate; depositing a first hetero layer on the aluminum gallium nitride layer; etching part of the substrate composite layer; sequentially depositing a second hetero layer and a third hetero layer; sequentially depositing a gallium nitride layer, an N-type gallium nitride layer, a light emitting layer and a P-type gallium nitride layer; stripping the substrate to form a composite epitaxial wafer; and etching part of the composite epitaxial wafer with a sodium hydroxide solution to form a light emitting diode epitaxial wafer. By etching the substrate composite layer, a patterned initial composite substrate is obtained, and the epitaxial wafer grown has the advantage of higher external quantum efficiency. By setting the second hetero layer and the third hetero layer, the substrate can be stripped without damaging the epitaxial structure. The method for obtaining a patterned epitaxial structure by etching is relatively simple, and a higher quality patterned epitaxial structure can be obtained.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of semiconductor, in particular to a light emitting diode epitaxial wafer preparation method, a light emitting diode epitaxial wafer and equipment. BACKGROUND

[0002] The light emitting diode is an electronic component for converting electrical energy into light energy, and the light emitting diode epitaxial wafer is the basic structure of the light emitting diode. The existing light emitting diode epitaxial wafer is usually grown on a patterned or non-patterned substrate, including an aluminum nitride buffer layer, an N-type gallium nitride layer, a light emitting layer and a P-type gallium nitride layer.

[0003] The light emitting efficiency of the light emitting diode is affected by the internal quantum efficiency and the external quantum efficiency. The light emitting diode epitaxial wafer grown using a flat non-patterned substrate has the problem of low external quantum efficiency. The patterned substrate usually has a plurality of protruding structures on the surface of the substrate, which is beneficial to obtain a patterned epitaxial wafer, change the light emitting angle and improve the external quantum efficiency of the epitaxial wafer, thereby further improving the light efficiency of the light emitting diode.

[0004] However, substrate peeling is required in the preparation process of the light emitting diode. For the patterned substrate, there are problems of height difference and uneven interface inclination angle at the interface between the substrate and the epitaxial structure. In the peeling process, the light emitting diode epitaxial wafer is prone to abnormal conditions such as hidden cracks and damage to the peeling surface, and the peeling quality is low, which makes it difficult to achieve both the external quantum efficiency and the peeling quality of the light emitting diode epitaxial wafer. SUMMARY

[0005] In view of the deficiencies of the prior art, the purpose of the present application is to provide a light emitting diode epitaxial wafer preparation method, a light emitting diode epitaxial wafer and equipment, which aims to solve the problem that the external quantum efficiency and the peeling quality of the light emitting diode epitaxial wafer are difficult to achieve in the prior art.

[0006] In order to achieve the above-mentioned purpose, the present application is realized by the following technical scheme:

[0007] A light emitting diode epitaxial wafer preparation method, comprising the following steps:

[0008] A substrate is provided, and an aluminum nitride buffer layer and an aluminum gallium nitride layer are sequentially deposited on the substrate;

[0009] A first hetero layer is deposited on the aluminum gallium nitride layer, the aluminum nitride buffer layer, the aluminum gallium nitride layer and the first hetero layer form a substrate composite layer, and the thickness of the first hetero layer ranges from 0.5 to 2 microns;

[0010] Etching part of the substrate composite layer until the substrate is exposed, the substrate composite layer after etching forms a plurality of substrate composite parts, the substrate composite parts include a plurality of first hetero parts formed by the first hetero layer after etching, and the substrate composite parts and the substrate combine to form an initial composite substrate;

[0011] Depositing a second hetero layer and a third hetero layer on the initial composite substrate in sequence to form a final composite substrate;

[0012] Depositing a gallium nitride layer, an N-type gallium nitride layer, a light emitting layer and a P-type gallium nitride layer on the final composite substrate in sequence to form an epitaxial structure, the top surface of the gallium nitride layer is lower than the top of the first hetero part;

[0013] Peeling off the substrate to form a composite epitaxial wafer, and using a sodium hydroxide solution to etch one end of the composite epitaxial wafer away from the P-type gallium nitride layer until the gallium nitride layer is etched to stop, thereby forming a light emitting diode epitaxial wafer.

[0014] Compared with the prior art, the present application has the following advantages: by depositing the aluminum nitride buffer layer, the aluminum gallium nitride layer and the first hetero layer on the substrate to form the substrate composite layer, the substrate composite part with a convex surface of the substrate is obtained after etching the substrate composite layer, and the initial composite substrate is patterned, and the epitaxial wafer grown by using the patterned substrate has the advantage of high external quantum efficiency; by depositing the second hetero layer and the third hetero layer on the initial composite substrate, the growth quality of the subsequent epitaxial structure is improved, and a gap is formed between the epitaxial structure and the substrate, thereby avoiding direct contact, when the substrate is peeled off, whether the peeling process causes hidden cracks or damage to the peeling surface only affects the second hetero layer and the third hetero layer, thereby avoiding damage to the epitaxial structure, due to the difference in material, the etching speed of the second hetero layer, the third hetero layer and the aluminum gallium nitride layer in the sodium hydroxide solution is different from that of the gallium nitride layer in the epitaxial structure, the etching speed of the gallium nitride layer in the sodium hydroxide solution is slow, therefore, the method for further obtaining a complete patterned epitaxial structure by etching is simple, and compared with the traditional physical peeling method which is easy to cause hidden cracks and damage, a higher quality patterned epitaxial structure can be obtained; by setting a thicker first hetero layer, when the composite epitaxial wafer is etched to the gallium nitride layer, the first hetero part and part of the hetero layer wrapping the first hetero part are still left in the light emitting diode epitaxial wafer, the light emitting diode epitaxial wafer has a high-quality patterned structure, which is beneficial to improving the light emitting angle and improving the external quantum efficiency.

[0015] Further, the thickness of the aluminum nitride buffer layer ranges from 0.1 to 0.5 microns;

[0016] Further, the thickness of the aluminum gallium nitride layer is in the range of

[0017] Further, the material of the second hetero layer is aluminum nitride, and the thickness of the second hetero layer is in the range of The material of the third hetero layer is aluminum gallium nitride, and the thickness of the third hetero layer is equal to the thickness of the aluminum gallium nitride layer.

[0018] Further, the thickness of the gallium nitride layer is in the range of

[0019] Further, the first hetero part is conical.

[0020] The embodiment of the present application also provides a light emitting diode epitaxial wafer prepared by the light emitting diode preparation method in the above technical solution.

[0021] The embodiment of the present application also provides a device comprising the light emitting diode epitaxial wafer in the above technical solution. BRIEF DESCRIPTION OF DRAWINGS

[0022] Figure 1 It is a flow chart of the light emitting diode epitaxial wafer preparation method in the embodiment of the present application;

[0023] Figure 2 It is a schematic diagram of preparing the initial composite substrate in the light emitting diode epitaxial wafer preparation method in the embodiment of the present application;

[0024] Figure 3 It is a schematic diagram of depositing the gallium nitride layer on the final composite substrate in the light emitting diode epitaxial wafer preparation method in the embodiment of the present application;

[0025] Figure 4 It is a structural schematic diagram of the epitaxial structure in the light emitting diode epitaxial wafer preparation method in the embodiment of the present application;

[0026] Figure 5 It is a structural schematic diagram of the light emitting diode epitaxial wafer in another embodiment of the present application;

[0027] Explanation of main element symbols:

[0028] first hetero part 100 first hetero layer 101 substrate 110 aluminum nitride buffer layer 120 gallium aluminum nitride layer 130 second hetero layer 210 third hetero layer 220 gallium nitride layer 300 composite epitaxial layer 400

[0029] The following specific embodiments will further illustrate the present application in combination with the above drawings. DETAILED DESCRIPTION

[0030] For the purpose of promoting an understanding of the application, the application will be described in greater detail below with reference to the illustrative embodiments. In order to facilitate an understanding of this application, a more complete appreciation of the disclosure and its advantages will be gained as more details of the application become apparent in the following written specification and appended claims. The application will be described with reference to the accompanying drawings in which:

[0031] It is to be understood that where an element is referred to as being "on" another element, it can be directly on the other element or intervening elements can also be present. Where an element is referred to as being "connected" or "coupled" to another element, it can be directly connected or coupled to the other element or intervening elements can also be present. As used herein the terms "vertical", "horizontal", "left", "right" and the like are merely used for the purpose of illustration and description.

[0032] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this application belongs. The terminology used in the description of the application herein is for the purpose of describing particular embodiments only and is not intended to be limiting of the application. As used herein, the singular forms "a", "an" and "the" are intended to include the plural forms as well, unless the context clearly indicates otherwise.

[0033] Referring to Figure 1 The method for preparing the LED epitaxial wafer in the embodiment of the application comprises the following steps:

[0034] S10: providing a substrate, and sequentially depositing an aluminum nitride buffer layer and an aluminum gallium nitride layer on the substrate;

[0035] Preferably, referring to Figure 2 The substrate 110 is a sapphire substrate, and the upper surface of the substrate 110 is flat. The aluminum nitride buffer layer 120 and the aluminum gallium nitride layer 130 are deposited on the flat surface of the substrate 110.

[0036] Specifically, the step S10 comprises:

[0037] The thickness of the aluminum nitride buffer layer ranges from 0.1 μm to 1 μm.

[0038] Preferably, the thickness of the aluminum nitride buffer layer 120 is selected from 0.1 μm to 1 μm. It can be understood that depositing the aluminum nitride buffer layer 120 on the sapphire substrate is beneficial to improving the surface roughness and improving the growth quality of the subsequent epitaxial structure on the surface.

[0039] The thickness of the aluminum gallium nitride layer ranges from 1 μm to 5 μm.

[0040] Preferably, the thickness of the aluminum gallium nitride layer 130 is selected from 1 μm to 5 μm. The preparation is performed by using a MOCVD (Metal-Organic Chemical Vapor Deposition) process. Further, after the deposition of the aluminum nitride buffer layer 120 and the aluminum gallium nitride layer 130 is completed, a high-temperature annealing planarization treatment is performed.

[0041] S20: depositing a first hetero layer on the aluminum gallium nitride layer, the aluminum nitride buffer layer, the aluminum gallium nitride layer and the first hetero layer combining to form a substrate composite layer, and the thickness of the first hetero layer ranges from 0.1 μm to 1 μm.

[0042] Preferably, the material of the first hetero layer 101 can be selected from high-transparency and low-refractive-index dielectric materials such as silicon oxide, magnesium fluoride and silicon nitride, and the preparation process can be performed by using PVD (Physical Vapor Deposition) or CVD (Chemical Vapor Deposition). Preferably, the first hetero layer 101 in the embodiment is selected from silicon oxide, and the PECVD (Plasma Enhance Chemical Vapor Deposition) process is used, and the thickness is 0.1 μm to 1 μm. After the deposition of the first hetero layer 101 is completed, a planarization treatment is performed on the first hetero layer 101.

[0043] S30: etching part of the substrate composite layer until the substrate is exposed, and the substrate composite layer after etching forms a plurality of substrate composite parts, the substrate composite parts include a plurality of first hetero parts formed by the first hetero layer after etching, and the substrate composite parts and the substrate combine to form an initial composite substrate.

[0044] Preferably, please refer to Figure 2 For the preparation of a periodic mask to prepare a periodic structure, a photoresist or nano-imprint glue can be spin-coated or sprayed on the first hetero layer 101, and the number of layers is one or more. In the embodiment, a photoresist layer is covered by using a spin-coating method, the photoresist layer is changed into a photoresist mask layer by using a pattern transfer technology, the photoresist mask layer has a periodic pattern thereon, dry etching is performed according to the periodic pattern, and the etching is performed until the side of the substrate 110 facing the aluminum nitride buffer layer 120. A plurality of substrate composite parts are periodically arranged, the shape of the substrate composite part is axisymmetric, and has an inclined surface. Specifically, the shape of the substrate composite part is conical. Understandably, the initial composite substrate has a periodic structure protruding outward, the periodic structure has a different refractive index from the epitaxial layer, and is easy to change the angle of the emitted light, which is beneficial to improve the light-emitting efficiency of the light-emitting diode epitaxial wafer.

[0045] Specifically, the step S30 comprises:

[0046] The first heterogeneous part is conical.

[0047] Preferably, the first heterogeneous part 100 is located at the top end of the substrate composite part, the first heterogeneous part 100 is conical, the refractive index of the first heterogeneous part is greatly different from the refractive index of the common epitaxial layer material, and the combination of the two forms a patterned composite epitaxy, which can change the light angle in the light-emitting diode, thereby greatly improving the external quantum efficiency and being beneficial to improving the light efficiency of the light-emitting diode product.

[0048] S40: sequentially depositing a second heterogeneous layer and a third heterogeneous layer on the initial composite substrate to form a final composite substrate;

[0049] Please refer to Figure 3 , the exposed part of sapphire material on the initial composite substrate, if growing gallium nitride epitaxial on the upper surface of the initial composite substrate, is easy to cause lattice mismatch and other phenomena that have negative effects on the quality of epitaxial growth, and when the sapphire substrate is peeled off, the epitaxial layer directly contacting the sapphire substrate is easy to be damaged; through the second heterogeneous layer 210 and the third heterogeneous layer 220, it is beneficial to improve the quality of epitaxial growth and reduce lattice mismatch, and when the sapphire substrate is peeled off, if the case of hidden crack or peeling surface damage occurs, only the second heterogeneous layer 210 and even the third heterogeneous layer 220 are affected, the second heterogeneous layer 210 and the third heterogeneous layer 220 effectively protect the epitaxial layer and improve the quality of the epitaxial layer after the substrate is peeled off.

[0050] Specifically, the step S40 comprises:

[0051] The material of the second heterogeneous layer is aluminum nitride, and the thickness of the second heterogeneous layer is in the range of The material of the third heterogeneous layer is aluminum gallium nitride, and the thickness of the third heterogeneous layer is equal to the thickness of the aluminum gallium nitride layer.

[0052] Preferably, the second heterogeneous layer 210 and the third heterogeneous layer 220 are both subjected to planarization treatment by high-temperature annealing, and the aluminum nitride is used as a buffer layer for growing subsequent structures, the thickness of the second heterogeneous layer 210 is selected from The thickness of the third heterogeneous layer 220 is The second heterogeneous layer 210 and the third heterogeneous layer 220 are prepared by MOCVD process. Understandably, the aluminum nitride as a buffer layer can improve the surface roughness, so that the structure grown on the aluminum nitride in the subsequent preparation process is more flat, and further, the aluminum gallium nitride layer 130 and the third heterogeneous layer 220 both have the characteristics of surface flatness.

[0053] S50: sequentially depositing a gallium nitride layer, an N-type gallium nitride layer, a light-emitting layer, and a P-type gallium nitride layer on the final composite substrate to form an epitaxial structure, a top surface of the gallium nitride layer being lower in height than a top of the first heterogeneous part;

[0054] Preferably, referring to Figure 3 , since the top surface of the gallium nitride layer 300 is lower in height than the top of the first heterogeneous part 100, the gallium nitride layer 300 is distributed only in the gaps between the substrate composite parts, and a gallium nitride buffer layer with a periodic pattern is naturally deposited without a patterning process, referring to Figure 4 , the N-type gallium nitride layer, the light-emitting layer, and the P-type gallium nitride layer combine to form a composite epitaxial layer 400, the composite epitaxial layer 400 covering the final composite substrate and the gallium nitride layer 300, the N-type gallium nitride layer being homoepitaxially grown on the gallium nitride layer 300, which weakens the abnormal influence of the patterned bottom morphology and is beneficial to improving the crystal quality, and further, the aluminum gallium nitride of the third heterogeneous layer 220 has the dual advantages of aluminum nitride and gallium nitride, and when the flat buffer layer for epitaxial growth is thick, the problem of insufficient epitaxial recrystallization is prone to occur, and the N-type gallium nitride layer can also grow along part of the inclined surface of the aluminum gallium nitride of the third heterogeneous layer 220 during deposition, and the growth quality of the epitaxial layer is excellent.

[0055] Specifically, the step S50 includes:

[0056] The thickness of the gallium nitride layer ranges from 10 nm to 1000 nm.

[0057] Preferably, the thickness of the gallium nitride layer 300 is selected from The gallium nitride layer 300 has a high breakdown voltage, low sensitivity to ionizing radiation, and high thermal conductivity, which is beneficial to stable operation in a high-temperature environment.

[0058] S60: peeling off the substrate to form a composite epitaxial wafer, and using a sodium hydroxide solution to etch an end of the composite epitaxial wafer opposite to the P-type gallium nitride layer until the gallium nitride layer is etched to stop, to form a light-emitting diode epitaxial wafer.

[0059] Preferably, the composite epitaxial wafer is peeled off from the sapphire substrate by laser peeling, which is a process of focusing high-energy laser to the interface between the substrate and the composite epitaxial wafer, melting part of the composite epitaxial wafer by laser scanning step by step, so as to separate the substrate 110 from the composite epitaxial wafer. After laser peeling, the composite epitaxial wafer is immersed in a high-concentration sodium hydroxide solution. Aluminum nitride and aluminum gallium nitride react quickly with the sodium hydroxide solution, while gallium nitride reacts slowly with the sodium hydroxide solution. The corrosion speed of aluminum gallium nitride and gallium nitride in the sodium hydroxide solution is quite different. Therefore, during the preparation of the light emitting diode epitaxial wafer, the bottom layer of aluminum nitride and aluminum gallium nitride can be efficiently removed by chemical corrosion, and hidden cracks in the physical structure are prevented. When the end of the composite epitaxial wafer opposite to the P-type gallium nitride layer is corroded to the gallium nitride layer 300, the process is stopped, and the formed light emitting diode epitaxial wafer is taken out. If the top surface height of the third hetero layer 220 is greater than the top surface height of the aluminum gallium nitride layer 130, the silicon oxide material of the first hetero part 100 is still corroded by the sodium hydroxide solution, and the light emitting diode epitaxial wafer with a flat bottom can still be obtained by chemical immersion. If the top surface height of the third hetero layer 220 is less than the top surface height of the aluminum gallium nitride layer 130, part of the aluminum gallium nitride layer 130 is still connected to the bottom of the first hetero part 100 when the sodium hydroxide solution corrodes to the gallium nitride layer 300. The remaining part of the aluminum gallium nitride layer 130 has a common bottom surface with the gallium nitride layer 300 after chemical immersion. Since the aluminum gallium nitride layer 130 grows on the flat surface of the aluminum nitride buffer layer 120, it also has good flatness.

[0060] It can be understood that the bottom of the light emitting diode epitaxial wafer has a complete patterned structure, wherein the first hetero part 100, part of the second hetero layer 210 and part of the third hetero layer 220 have a refractive index difference between them and the composite epitaxial layer, which can improve the light extraction efficiency. When the substrate 110 is peeled off, the gallium nitride layer 300 and the composite epitaxial layer 400 are not affected under the protection of the second hetero layer 210 and the third hetero layer 220, and the peeling quality is greatly improved.

[0061] Please refer to Figure 5In some embodiments, the present application also provides a light emitting diode epitaxial wafer prepared by the light emitting diode epitaxial wafer preparation method in the above embodiments. Preferably, the light emitting diode epitaxial wafer comprises an epitaxial structure, a plurality of first heterogeneous parts 100, a plurality of second heterogeneous layers 210, and a plurality of third heterogeneous layers 220, the second heterogeneous layer 210 covers the top surface of the first heterogeneous part 100, the third heterogeneous layer 220 covers the surface of the second heterogeneous layer 210 away from the first heterogeneous part 100, the third heterogeneous layer 220, the second heterogeneous layer 210, and the first heterogeneous part 100 are one-to-one corresponding, the epitaxial structure covers the surface of the third heterogeneous layer 220 away from the second heterogeneous layer 210, the epitaxial structure comprises a gallium nitride layer 300, an N-type gallium nitride layer, a light emitting layer, and a P-type gallium nitride layer arranged from bottom to top, and the top surface of the gallium nitride layer 300 is lower than the top of the first heterogeneous part 100.

[0062] Specifically, the substrate used by the light emitting diode epitaxial wafer is a sapphire substrate, the bottom ends of the epitaxial structure, the plurality of first heterogeneous parts 100, the plurality of second heterogeneous layers 210, and the plurality of third heterogeneous layers 220 share a bottom surface, the material of the first heterogeneous part 100 is selected from silicon oxide, and the height range is The thickness range of the second heterogeneous layer 210 is The thickness range of the third heterogeneous layer 220 is Further, the height of the first heterogeneous part 100 is selected from The thickness of the second heterogeneous layer 210 is selected from The thickness of the third heterogeneous layer 220 is selected from The shape of the first heterogeneous part 100 is conical, the plurality of first heterogeneous parts 100 form a periodic arrangement, a plurality of periodic through holes are distributed on the gallium nitride layer 300, the through holes correspond to the positions of the first heterogeneous parts 100, so that the first heterogeneous parts 100 pass through the gallium nitride layer 300 to combine the second heterogeneous layer 210 and the third heterogeneous layer 220 to form a patterned epitaxial buffer layer, and the N-type gallium nitride layer, the light emitting layer, and the P-type gallium nitride layer combine to form a composite epitaxial layer 400. Understandably, the bottom of the light emitting diode epitaxial wafer is provided with a heterogeneous periodic microstructure, wherein the silicon oxide of the first heterogeneous part 100 has the characteristics of high transparency and low refractive index, and the refractive index difference between the composite epitaxial layer 400 is beneficial to change the light emitting angle and improve the light emitting efficiency.

[0063] Further, in the preparation of the light emitting diode epitaxial wafer, the gallium nitride layer 300 is at the bottom and the third hetero layer 220 is at the side of the area to be deposited when the composite epitaxial layer 400 is deposited, a relatively stable and sufficient recrystallization process is maintained during the deposition process, the composite epitaxial layer 400 grown has a high quality, and the gallium nitride layer 300 is exposed after the substrate is stripped and soaked in a high-concentration sodium hydroxide solution, the redundant structure is removed, the bottom of the light emitting diode epitaxial wafer is less damaged, the phenomenon that the traditional laser stripping easily causes hidden cracks or other damages on the stripping surface is avoided, and the high epitaxial quality and high light emitting efficiency are combined.

[0064] In some embodiments, the present application also provides a device comprising the light emitting diode epitaxial wafer as described in the above embodiments.

[0065] In the description of the present specification, the description of the terms "one embodiment", "some embodiments", "an example", "a specific example", or "some examples" and the like means that the specific features, structures, materials or characteristics described in connection with the embodiment or example are included in at least one embodiment or example of the present application. In the present specification, the illustrative description of the above terms does not necessarily mean the same embodiment or example. Moreover, the specific features, structures, materials or characteristics described can be combined in any one or more embodiments or examples in a suitable manner.

[0066] The above-described embodiments only express several implementation manners of the present application, the description is relatively specific and detailed, but it cannot be understood as the limitation of the patent scope of the present application. It should be noted that, for ordinary skilled in the art, without departing from the concept of the present application, several modifications and improvements can be made, which are all within the protection scope of the present application. Therefore, the protection scope of the patent of the present application should be subject to the appended claims.

Claims

1. A method for preparing a light-emitting diode epitaxial wafer, characterized in that: The steps include: Providing a substrate, and sequentially depositing an aluminum nitride buffer layer and an aluminum gallium nitride layer on the substrate; Depositing a first heterogeneous layer on the aluminum gallium nitride layer, wherein the aluminum nitride buffer layer, the aluminum gallium nitride layer, and the first heterogeneous layer are combined to form a substrate composite layer, and the thickness of the first heterogeneous layer is in a range of 5000Å to 20000Å; Etching a portion of the substrate composite layer until the substrate is exposed, wherein the etched substrate composite layer forms a plurality of substrate composite portions, wherein the substrate composite portions include a plurality of first heterogeneous portions formed by the etched first heterogeneous layer, and the plurality of substrate composite portions and the substrate form an initial composite substrate; Depositing a second heterogeneous layer and a third heterogeneous layer on the initial composite substrate in sequence to form a final composite substrate, wherein the second heterogeneous layer is made of aluminum nitride and has a thickness ranging from 10 Å to 50 Å, and the third heterogeneous layer is made of aluminum gallium nitride and has a thickness equal to that of the aluminum gallium nitride layer; Depositing a gallium nitride layer, an N-type gallium nitride layer, a light-emitting layer, and a P-type gallium nitride layer in sequence on the final composite substrate to form an epitaxial structure, wherein a top surface height of the gallium nitride layer is lower than a top height of the first heterogeneous portion; The substrate is peeled off to form a composite epitaxial wafer, and one end of the composite epitaxial wafer facing away from the P-type gallium nitride layer is etched using a sodium hydroxide solution. The second heterogeneous layer, the third heterogeneous layer, and the aluminum gallium nitride layer etch at different rates from the gallium nitride layer in the epitaxial structure in the sodium hydroxide solution. The etching is stopped when the gallium nitride layer is reached, thereby forming a light-emitting diode epitaxial wafer.

2. The method for preparing a light emitting diode epitaxial wafer according to claim 1, wherein: The thickness of the aluminum nitride buffer layer ranges from 10Å to 100Å.

3. The method for preparing a light emitting diode epitaxial wafer according to claim 1, wherein: The thickness of the aluminum gallium nitride layer ranges from 1000Å to 5000Å.

4. The method for preparing a light emitting diode epitaxial wafer according to claim 1, wherein: The thickness of the gallium nitride layer ranges from 100Å to 2000Å.

5. The method for preparing a light emitting diode epitaxial wafer according to claim 1, wherein: The first heterogeneous portion is cone-shaped.

Images