Epitaxial wafer, method of manufacture and light emitting diode

Abstract

The application discloses an epitaxial wafer, a preparation method and a light emitting diode. The epitaxial wafer comprises a substrate, a plurality of convex structures arranged on one side of the substrate, the convex structures being periodically arranged, a concave structure being formed between adjacent convex structures, and adjacent concave structures being connected; a first buffer layer located on the side close to the concave structure; a non-doped GaN layer located on the side away from the substrate of the first buffer layer; at least one concave microstructure existing in the non-doped GaN layer, and the same concave microstructure being periodically arranged; at least part of the concave microstructure and the convex structure being at least partially overlapped in the direction perpendicular to the substrate; an N-type GaN layer, a multi-quantum well active layer, a second buffer layer and a P-type GaN layer being sequentially arranged on the side away from the substrate of the non-doped GaN layer. By introducing the concave microstructure into the non-doped GaN layer, the dislocation density and stress release in the subsequently grown GaN layer are reduced, the crystal quality is improved, and the light emission efficiency is improved.

Description

TECHNICAL FIELD

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

[0002] With the continuous development of science and technology, light emitting diode has been widely used in people's daily life, work and industry, and has brought great convenience to people's life. Light emitting diode (LED) has many advantages such as high efficiency, low energy consumption, long service life, no pollution, small size, rich color and so on, and is an important solid-state lighting device.

[0003] However, the existing technology has high difficulty in realizing high-power lighting of light emitting diode, low light output efficiency, and cannot meet the market demand. In the manufacturing process of light emitting diode, an epitaxial layer is grown on the prepared substrate. Due to the lattice matching and thermal expansion coefficient matching problems between the substrate and the epitaxial material, the epitaxial material has a very high dislocation density and internal stress, thereby reducing the internal quantum efficiency. SUMMARY

[0004] The present application provides an epitaxial wafer, a preparation method and a light emitting diode to improve the quality of epitaxial crystal and improve the light output efficiency.

[0005] In a first aspect, an embodiment of the present application provides an epitaxial wafer, comprising:

[0006] A substrate, one side of the substrate is provided with a plurality of protruding structures, the recess structures are periodically arranged, the recess structures are formed between adjacent protruding structures, and adjacent recess structures are connected;

[0007] A first buffer layer is located on the side close to the recess structure;

[0008] A non-doped GaN layer is located on the side away from the substrate of the first buffer layer; at least one concave microstructure exists in the non-doped GaN layer, and the same kind of concave microstructure is periodically arranged; along the direction perpendicular to the substrate, the concave microstructure and the protruding structure at least partially overlap;

[0009] An N-type GaN layer, a multi-quantum well active layer, a second buffer layer and a P-type GaN layer are sequentially arranged on the side away from the substrate of the non-doped GaN layer.

[0010] Optionally, the concave microstructure includes a first concave microstructure and a second concave microstructure,

[0011] Along the direction perpendicular to the substrate, the first concave microstructure and the protruding structure at least partially overlap; the second concave microstructure does not overlap with the protruding structure.

[0012] Optionally, the center of the bottom surface of the first concave microstructure is coincident with the center of the bottom surface of the convex structure in orthographic projection.

[0013] Optionally, the center of the bottom surface of the second concave microstructure is coincident with the center of gravity of the figure formed by the lines connecting the centers of the bottom surfaces of the at least three adjacent convex structures in orthographic projection.

[0014] Optionally, the shape of the concave microstructure comprises at least one of a conical shape, a circular truncated cone shape, and a spherical cap shape.

[0015] Optionally, the radius of the bottom surface of the first concave microstructure is R1, the radius of the bottom surface of the second concave microstructure is R2, the radius of the bottom surface of the convex structure is R3, and the arrangement period of the convex structure is P, wherein R1

[0016] In a second aspect, an embodiment of the present application provides a preparation method of an epitaxial wafer, comprising:

[0017] providing a substrate, wherein one side of the substrate is provided with convex structures, the convex structures are arranged periodically, and concave structures are formed between adjacent convex structures, and adjacent concave structures are connected;

[0018] preparing a first buffer layer on one side of the substrate;

[0019] preparing a non-doped GaN layer on the side of the first buffer layer away from the substrate and forming at least one concave microstructure in the non-doped GaN layer, and the same kind of concave microstructure is arranged periodically; along the direction perpendicular to the substrate, at least part of the concave microstructure at least partially overlaps with the convex structure;

[0020] sequentially preparing an N-type GaN layer, a multi-quantum well active layer, a second buffer layer, and a P-type GaN layer on the side of the non-doped GaN layer away from the substrate to form an epitaxial wafer.

[0021] Optionally, the step of preparing a non-doped GaN layer on the side of the first buffer layer away from the substrate and forming at least one concave microstructure in the non-doped GaN layer comprises:

[0022] preparing a first non-doped GaN section on the side of the first buffer layer away from the substrate;

[0023] forming a concave hole on the surface of the side of the first non-doped GaN section away from the substrate;

[0024] A second undoped GaN section is prepared on the side of the first undoped GaN section away from the substrate, the second undoped GaN section is connected on the side of the concave hole away from the substrate, and a concave microstructure is formed between the first undoped GaN section and the second undoped GaN section.

[0025] Optionally, a concave hole is formed on the surface of the side of the first undoped GaN section away from the substrate, including:

[0026] A mask layer is deposited on the side of the first undoped GaN section away from the substrate.

[0027] A photolithography or imprint process is performed on the mask layer to form at least one hole mask pattern, and the same kind of hole mask pattern is arranged periodically.

[0028] A dry etching process is performed on the hole mask pattern to form at least one concave hole, and the same kind of concave hole is arranged periodically.

[0029] In a third aspect, the embodiments of the present application provide a light emitting diode, including the epitaxial wafer of any one of the first aspect.

[0030] The technical scheme of the embodiments of the present application, through the epitaxial wafer including: a substrate, a plurality of protruding structures arranged on one side of the substrate, the protruding structures arranged periodically, the adjacent protruding structures forming a pit structure, and the adjacent pit structures connected; a first buffer layer located on the side close to the pit structure; an undoped GaN layer located on the side of the first buffer layer away from the substrate; at least one concave microstructure existing in the undoped GaN layer, and the same kind of concave microstructure arranged periodically; in the direction perpendicular to the substrate, the concave microstructure and the protruding structure at least partially overlap; an N-type GaN layer, a multi-quantum well active layer, a second buffer layer and a P-type GaN layer arranged in sequence on the side of the undoped GaN layer away from the substrate. By introducing the concave microstructure in the undoped GaN layer, the dislocation density and stress release in the subsequent growth of the GaN layer are reduced, thereby improving the crystal quality and increasing the light emission efficiency.

[0031] It should be understood that the content described in this part is not intended to identify the key or important features of the embodiments of the present application, nor is it used to limit the scope of the present application. Other features of the present application will become apparent from the following description. BRIEF DESCRIPTION OF DRAWINGS

[0032] In order to more clearly illustrate the technical solutions in the embodiments of the present application, the following will briefly introduce the drawings needed to be used in the embodiment description. Obviously, the drawings in the following description are only some embodiments of the present application, and other drawings can also be obtained by those skilled in the art without creating laborious work.

[0033] Figure 1 A structure schematic diagram of an epitaxial wafer provided by an embodiment of the present application is shown in FIG. 1.

[0034] Figure 2 A structure schematic diagram of an epitaxial wafer provided by an embodiment of the present application is shown in FIG. 1. Figure 1 A structure schematic diagram of an epitaxial wafer provided by an embodiment of the present application is shown in FIG. 1.

[0035] Figure 3 A structure schematic diagram of an epitaxial wafer provided by an embodiment of the present application is shown in FIG. 1. Figure 1 A structure schematic diagram of an epitaxial wafer provided by an embodiment of the present application is shown in FIG. 1.

[0036] Figure 4 A structure schematic diagram of an epitaxial wafer provided by an embodiment of the present application is shown in FIG. 1. Figure 1 A structure schematic diagram of an epitaxial wafer provided by an embodiment of the present application is shown in FIG. 1.

[0037] Figure 5 A structure schematic diagram of an epitaxial wafer provided by an embodiment of the present application is shown in FIG. 1.

[0038] Figure 6 A structure schematic diagram of an epitaxial wafer provided by an embodiment of the present application is shown in FIG. 1.

[0039] Figure 7 A structure schematic diagram of an epitaxial wafer provided by an embodiment of the present application is shown in FIG. 1.

[0040] Figure 8 A structure schematic diagram of an epitaxial wafer provided by an embodiment of the present application is shown in FIG. 1.

[0041] Figure 9 A structure schematic diagram of an epitaxial wafer provided by an embodiment of the present application is shown in FIG. 1.

[0042] Figure 10 A structure schematic diagram of an epitaxial wafer provided by an embodiment of the present application is shown in FIG. 1.

[0043] Figure 11 A structure schematic diagram of an epitaxial wafer provided by an embodiment of the present application is shown in FIG. 1. DETAILED DESCRIPTION

[0044] In order to make the person skilled in the art better understand the present application, the technical solutions in the embodiments of the present application will be described clearly and completely below with reference to the drawings in the embodiments of the present application. Obviously, the described embodiments are only a part of the embodiments of the present application, rather than all the embodiments. Based on the embodiments in the present application, all other embodiments obtained by the person skilled in the art without creative labor should belong to the protection scope of the present application.

[0045] It should be noted that the terms "first", "second", and the like in the description and in the claims of the present application and the above-described drawings are used to distinguish similar objects, and do not necessarily indicate a specific order or sequence. It should be understood that the data thus used can be interchanged under appropriate circumstances, so that the embodiments of the application described herein can be implemented in an order other than that illustrated or described herein. In addition, the terms "include" and "have" and any variations thereof are intended to cover non-exclusive inclusion, for example, a process, method, system, product or device that includes a series of steps or units does not necessarily have to be limited to only those steps or units clearly listed, but can include other steps or units not clearly listed or inherent to such a process, method, product or device.

[0046] Figure 1 A structure schematic diagram of an epitaxial wafer provided for an embodiment of the present application, Figure 2 For Figure 1 A cross-sectional structure schematic diagram along the cross-sectional line AA' is shown in Figure 1 And Figure 2 As shown in the drawings, the epitaxial wafer 100 includes: a substrate 101, a plurality of protruding structures 102 are arranged on one side of the substrate 101, the protruding structures 102 are periodically arranged, a concave structure 110 is formed between adjacent protruding structures 102, and adjacent concave structures 110 are connected; a first buffer layer 103 is located on the side close to the concave structure 110; a non-doped GaN layer 104 is located on the side away from the substrate 101 of the first buffer layer 103; at least one concave microstructure 105 exists in the non-doped GaN layer 104, and the same concave microstructure 105 is periodically arranged; along the direction X perpendicular to the substrate 101, the concave microstructure 105 and the protruding structure 102 at least partially overlap; an N-type GaN layer 106, a multi-quantum well active layer 107, a second buffer layer 108 and a P-type GaN layer 109 are sequentially arranged on the side away from the substrate 101 of the non-doped GaN layer 104.

[0047] The substrate 101 can be a sapphire substrate 101, and a plurality of protruding structures 102 are etched to form a plurality of protruding structures 102 on one side of the substrate 101 by patterning design, and the concave structures 110 are synchronously prepared by the same process. The concave structures 110 are formed between adjacent protruding structures 102, the side walls of the concave structures 110 are the side walls of the adjacent protruding structures 102, the adjacent concave structures 110 are connected, and the concave structures 110 on the substrate 101 form connected concaves in the direction perpendicular to the substrate 101. For example, Figure 1As shown, the convex structure 102 can be a conical structure, the projection of the convex structure 102 is a circle, the structure and size of the convex structure 102 are the same, and the convex structure 102 is arranged periodically. The first buffer layer 103 is formed by a low-temperature growth process of MOCVD on the side close to the convex structure 102, and the material of the first buffer layer 103 can be gallium nitride, aluminum nitride or aluminum gallium nitride. The first buffer layer 103 is arranged to reduce the dislocation density between the undoped GaN and the substrate 101, and to ensure the performance of the epitaxial wafer 100. The undoped GaN layer 104 is formed by a high-temperature growth process of MOCVD on the side away from the substrate 101 of the first buffer layer 103; at least one concave microstructure 105 is formed in the undoped GaN layer 104, and the same concave microstructure 105 is arranged periodically, and the periodic arrangement methods of different concave microstructures 105 are different, but the sizes of different concave microstructures 105 can be the same or different. The specific arrangement method and size design can be selected according to the actual design requirements, and the embodiment of the present application does not make specific limitation. The N-type GaN layer 106, the multi-quantum well active layer 107, the second buffer layer 108 and the P-type GaN layer 109 are sequentially arranged on the side away from the substrate 101 of the undoped GaN layer 104 to form the epitaxial wafer 100, and the material of the second buffer layer 108 can be AlGaN. The material selection of the first buffer layer 103 and the second buffer layer 108 is various, and can be selected according to the actual design requirements, and the embodiment of the present application does not make specific limitation. Exemplarily, two kinds of concave microstructures 105 are taken as an example for display, that is, the patterned air gap is formed in the undoped GaN, so that the existence of the concave microstructure 105 eliminates the generation of part of the dislocations. Along the direction X perpendicular to the substrate 101, the gravity center of the figure formed by the center lines of the adjacent at least three bottom surfaces of the convex structure 102 on one side of the substrate 101 coincides with the normal projection of the gravity center of the concave microstructure 105, the concave microstructure 105 can reduce the generation of random dislocations in the epitaxial growth process, and due to the large difference in refractive index between GaN and air, the existence of the concave microstructure 105 can increase the critical angle of total reflection, realize the modulation of the light emitted from the patterned area of the substrate 101, and also can adjust the size of the concave microstructure 105 according to the size of the convex structure 102 and the concave structure 110 in the substrate 101, and perform partial area light modulation, thereby increasing the light emission and improving the light emission efficiency; a plurality of convex structures 102 are formed on one side of the substrate 101, and the top end of the convex structure 102 is easy to generate dislocations in the epitaxial lateral growth process; the arrangement of the concave microstructure 105 overlapping with the convex structure 102 along the direction X perpendicular to the substrate 101 can effectively reduce or annihilate the dislocations in the subsequent epitaxial lateral growth process, reduce the dislocation density in the doped GaN layer, improve the crystal quality, and thus ensure the service life of the light-emitting diode composed of the epitaxial wafer 100.

[0048] In this embodiment of the invention, at least one concave microstructure is formed in undoped GaN. Along the direction perpendicular to the substrate, part of the concave microstructure overlaps with the protruding structure on one side of the substrate. By setting the concave microstructure, dislocations generated during subsequent epitaxial growth can be effectively reduced or annihilated, the dislocation density in the epitaxial layer can be reduced, the crystal quality can be improved, and the performance of the subsequent epitaxial wafer can be guaranteed.

[0049] Optional, Figure 3 for Figure 1 A schematic diagram of the cross-sectional structure along section line BB'. Figure 4 for Figure 1 A schematic diagram of the cross-sectional structure along section line CC', as shown below. Figure 3 and Figure 4 As shown, the concave microstructure 105 includes a first concave microstructure 1051 and a second concave microstructure 1052. Along the direction X perpendicular to the substrate 101, the first concave microstructure 1051 overlaps at least partially with the protrusion structure 102; the second concave microstructure 1052 does not overlap with the protrusion structure 102.

[0050] The concave microstructure 105 includes a first concave microstructure 1051 and a second concave microstructure 1052 with different arrangement periods. Both the first concave microstructure 1051 and the second concave microstructure 1052 are located in the same layer of the substrate 101. Along the direction X perpendicular to the substrate 101, the projection of the first concave microstructure 1051 overlaps with the patterned protrusion structure 102 on one side of the substrate 101, and the projection of the second concave microstructure 1052 overlaps with the unpatterned connected pit structure 110 on one side of the substrate 101. The first concave microstructure 1051 can reduce or annihilate some dislocations during the epitaxial lateral growth process, reduce the dislocation density in the epitaxial layer, improve the crystal quality, and thus reduce non-radiative recombination in the active region and improve the light extraction efficiency. The second concave microstructure 1052 can reduce random dislocations generated during the epitaxial growth process and can also perform light extraction modulation to further improve the light extraction efficiency, thereby ensuring the performance of the epitaxial wafer 100.

[0051] Optional, continue to refer to Figure 1 The center a of the bottom surface of the first concave microstructure 1051 coincides with the center b of the bottom surface of the convex structure 102.

[0052] The first concave microstructure 1051 and the convex structure 102 overlap in the direction X perpendicular to the substrate 101, the arrangement period of the first concave microstructure 1051 is the same as that of the convex structure 102, the center a of the bottom surface of the first concave microstructure 1051 coincides with the center b of the bottom surface of the convex structure 102, the size of the bottom surface of the first concave microstructure 1051 is less than or equal to that of the convex structure 102, for example, the bottom surface of the first concave microstructure 1051 is circular, the bottom surface of the convex structure 102 is circular, the size of the bottom surface of the first concave microstructure 1051 is less than that of the convex structure 102, that is, the center of the bottom surface of the first concave microstructure 1051 coincides with the center of the bottom surface of the convex structure 102, the shape and size of adjacent first concave microstructures 1051 are the same, and the first concave microstructure 1051 can effectively reduce the dislocation concentration phenomenon at the top of the convex structure 102 in the epitaxial production process, thereby ensuring the crystal quality after epitaxial growth.

[0053] Optionally, with reference back to Figure 1 , the center c of the figure formed by the connection of the centers b of the bottom surfaces of the at least three adjacent convex structures 102 coincides with the center d of the bottom surface of the second concave microstructure 1052.

[0054] For example, the bottom surface of the convex structure 102 is circular, the bottom surface of the second concave microstructure 1052 is circular, and the figure formed by the connection of the centers of the bottom surfaces of the three convex structures 102 is an equilateral triangle, that is, the center of the equilateral triangle coincides with the center of the bottom surface of the second concave microstructure 1052, as shown in Figure 1 , six second concave microstructures 1052 are arranged around the same convex structure 102 in the direction X perpendicular to the substrate 101, the second concave microstructures 1052 are uniformly distributed around the convex structure 102, the second concave microstructure 1052 and the pit 110 formed by the connection of one side of the substrate 101 overlap, the shape of the second concave microstructure 1052 can increase the critical angle of total reflection, thereby modulating the angle of the outgoing light, improving the light extraction efficiency, and the arrangement of the second concave microstructure 1052 can ensure that the dislocations are offset or annihilated in the subsequent epitaxial growth process, reduce the dislocations, and reduce the penetration of the dislocations to the upper layer, thereby improving the crystal quality and the use effect of the epitaxial wafer 100.

[0055] Optionally, with reference back to Figure 1 , the radius of the bottom surface of the first concave microstructure 1051 is R1, the radius of the bottom surface of the second concave microstructure 1052 is R2, the radius of the bottom surface of the convex structure 102 is R3, and the arrangement period of the convex structure 102 is P, wherein R1 By reasonably controlling the relationship among the bottom radius of the first concave microstructure 1051, the bottom radius of the second concave microstructure 1052, the bottom radius of the convex structure 102, and the arrangement period of the convex structure 102, and reasonably selecting the etching depth and the bottom opening diameter of the concave microstructure 105 in combination with the lateral growth speed of GaN and the longitudinal growth speed of GaN, the etching depth / opening diameter>GaN lateral growth speed / GaN longitudinal growth speed is ensured, and then the reasonable arrangement of the first concave microstructure 1051, the second concave microstructure 1052, and the convex structure 102 is ensured, thereby reducing the dislocation density in the epitaxial growth process, improving the crystal quality, and then reducing the non-radiative recombination of the active region and improving the light extraction efficiency.

[0056] Optionally, with reference to Figure 2 、 Figure 3 and Figure 4 , the shape of the concave microstructure 105 includes at least one of a conical shape, a circular truncated cone shape, and a spherical cap shape. Figure 2 、 Figure 3 and Figure 4 exemplarily show that the first concave microstructure 1051 and the second concave microstructure 1052 are both conical shapes, the shapes of the first concave microstructure 1051 and the second concave microstructure 1052 can be the same or different, and the specific shape can be selected according to actual design requirements, which is not limited in the embodiments of the present application.

[0057] Figure 5 A flowchart of a preparation method of an epitaxial wafer provided by the embodiments of the present application is shown in Figure 2 and 5 , and the method comprises the following steps.

[0058] S101, providing a substrate, the substrate is provided with convex structures on one side, and the convex structures are arranged periodically; the concave structures are formed between adjacent convex structures, and the adjacent concave structures are connected.

[0059] In the embodiments of the present application, the substrate 101 is cleaned, and a mask is prepared on one side of the substrate 101 and etched to form the convex structures 102 arranged periodically, which can be a circular truncated cone, a cone, or the like, and the concave structures 110 are formed between the adjacent convex structures 102.

[0060] S102, preparing a first buffer layer on one side of the substrate.

[0061] In the embodiments of the present application, the first buffer layer 103 is prepared on one side of the patterned substrate 101 by a MOCVD low-temperature growth process, which can reduce the dislocation density between the substrate 101 and the subsequently generated undoped GaN layer 104, ensure the growth quality of the crystal, and then ensure the use effect of the prepared epitaxial wafer 100 in the light-emitting diode.

[0062] S103, preparing a non-doped GaN layer on the side of the first buffer layer away from the substrate and forming at least one concave microstructure in the non-doped GaN layer, and the same concave microstructure is arranged periodically; along the direction perpendicular to the substrate, the concave microstructure and the convex structure at least partially overlap.

[0063] In the embodiment of the present application, the non-doped GaN layer 104 is prepared on the side of the first buffer layer 103 away from the substrate 101, and the concave microstructure 105 is formed in the non-doped GaN layer 104. The concave microstructure 105 includes at least two types, and the concave microstructure 105 forms an air gap in the GaN layer, so that the dislocation in the epitaxial growth process can be moved or annihilated, thereby effectively reducing the dislocation density in the epitaxial growth process. At the same time, along the direction X perpendicular to the substrate 101, the concave microstructure 105 and the connected concave pit structure 110 exist in the overlap, so that the concave microstructure 105 can reduce the generation of random dislocations. In addition, due to the difference in refractive index between GaN and air being greater than the difference in refractive index between GaN and the substrate 101, the opening size of the concave microstructure 105, the light direction, the total reflection area and the light extraction efficiency can be adjusted by adjusting the sidewall inclination angle of the air gap and the diameter of the convex structure 102 through the etching process.

[0064] S104, sequentially preparing an N-type GaN layer, a multi-quantum well active layer, a second buffer layer and a P-type GaN layer on the side of the non-doped GaN layer away from the substrate to form an epitaxial wafer.

[0065] In the embodiment of the present application, the concave microstructure is formed in the non-doped GaN layer, and along the direction perpendicular to the substrate, part of the concave microstructure 105 and the convex structure on the side of the substrate exist in the overlap. The setting of the concave microstructure can effectively reduce or annihilate the dislocation generated in the subsequent epitaxial growth process, reduce the dislocation density in the epitaxial layer, improve the crystal quality, and further ensure the use effect of the subsequent epitaxial wafer.

[0066] Figure 6 Another flowchart of the preparation method of the epitaxial wafer provided by the embodiment of the present application is shown in Figure 7 A flowchart of the preparation method of the epitaxial wafer provided by the embodiment of the present application is shown in Figure 8 A flowchart of the preparation method of the epitaxial wafer provided by the embodiment of the present application is shown in Figure 9 A flowchart of the preparation method of the epitaxial wafer provided by the embodiment of the present application is shown in Figure 2 、 Figure 6 、 Figure 7 、 Figure 8 and Figure 9 The method comprises the following steps:

[0067] S201, providing a substrate, a side of the substrate is provided with a convex structure, the convex structure is arranged periodically; adjacent convex structures form a concave structure, and adjacent concave structures are connected.

[0068] S202, preparing a first buffer layer on one side of the substrate.

[0069] S203, preparing a first undoped section on the side of the first buffer layer away from the substrate.

[0070] The first undoped GaN section 1041 is prepared on the side of the first buffer layer 103 away from the substrate 101 by a MOCVD high-temperature growth process, the first undoped GaN section 1041 covers the substrate 101, and the height of the first undoped GaN section 1041 beyond the substrate 101 is about 2 microns, facilitating subsequent preparation of the concave microstructure 105.

[0071] S204, forming a concave hole on the surface of the side of the first undoped GaN section away from the substrate.

[0072] The concave hole 11 is formed on the surface of the side of the first undoped GaN section 1041 away from the substrate 101 by ICP dry etching, and then the dry etching by-products are removed by organic cleaning and inorganic cleaning, so as to obtain a composite substrate with the concave hole 11 on the surface.

[0073] S205, preparing a second undoped GaN section on the side of the first undoped GaN section away from the substrate, the second undoped GaN section is connected on the side of the concave hole away from the substrate, at least one concave microstructure is formed between the first undoped GaN section and the second undoped GaN section; the same concave microstructure is arranged periodically; at least part of the concave microstructures overlap at least part of the concave structures in the direction perpendicular to the substrate.

[0074] The second undoped GaN section 1042 with a certain thickness is prepared on the side of the first undoped GaN section 1041 with the concave hole 11 away from the substrate 101 by a MOCVD high-temperature growth process, the second undoped GaN section 1042 can be connected on the top of the concave hole, and the concave microstructure 105 is formed between the first undoped GaN section 1041 and the second undoped GaN section 1042, the concave microstructure 105 is an air gap, and the concave microstructure 105 is arranged periodically; at least part of the concave microstructures 105 overlap the connected concave structures 110 in the direction X perpendicular to the substrate 101, the setting of the concave microstructure 105 can effectively reduce or eliminate dislocations generated in the subsequent epitaxial growth process, improve the crystal quality, adjust the light direction, increase the total reflection area, improve the light efficiency, and ensure the use effect of the subsequent epitaxial wafer 100.

[0075] S206, an N-type GaN layer, a multi-quantum-well active layer, a second buffer layer, and a P-type GaN layer are sequentially prepared on the side of the second undoped GaN portion away from the substrate 101 to form an epitaxial wafer.

[0076] In this embodiment of the invention, a concave microstructure is formed between the first undoped GaN portion and the second undoped GaN portion. Along the direction perpendicular to the substrate, part of the concave microstructure overlaps with the pit structure on one side of the substrate. By setting the concave microstructure, dislocations generated during subsequent epitaxial growth can be effectively reduced or eliminated, the dislocation density in the epitaxial layer can be reduced, and the crystal quality can be improved. At the same time, the light emission direction can be adjusted, the total reflection area can be increased, the light emission efficiency can be improved, and the use effect of the subsequent epitaxial wafer can be guaranteed.

[0077] Figure 10 This is a schematic flowchart of another method for preparing an epitaxial wafer provided in an embodiment of the present invention, as shown below. Figure 2 , Figure 7 , Figure 8 , Figure 9 and Figure 10 As shown, the method includes:

[0078] S301 provides a substrate, on one side of which is provided a protrusion structure, the protrusion structure being arranged periodically; a pit structure is formed between adjacent protrusion structures, and adjacent pit structures are connected.

[0079] S302, a first buffer layer is prepared on one side of the substrate.

[0080] S303, a first undoped GaN fraction is prepared on the side of the first buffer layer away from the substrate.

[0081] S304, a mask layer is deposited on the side of the first undoped GaN fraction away from the substrate.

[0082] S305, at least one hole mask pattern is formed by photolithography or imprinting on the mask layer, and the same hole mask pattern is arranged periodically.

[0083] In this process, a mask layer 12 is prepared on the side of the first undoped GaN portion 1041 away from the substrate 101. The mask layer 12 is patterned using photolithography or imprinting to form multiple cylindrical or conical hole mask patterns 121. The hole mask patterns 121 are arranged in a certain period. The multiple hole mask patterns 121 are etched by ICP dry etching to form concave holes. Then, the dry etching byproducts are removed by organic cleaning and inorganic cleaning to obtain a composite substrate with high cleanliness and concave holes 11 on the surface.

[0084] S306, a dry etching process is used to form at least one concave hole on the hole mask pattern, and the same type of concave hole is arranged periodically.

[0085] The hole mask pattern 121 is subjected to a dry etching process to form at least one concave hole 11, the arrangement period of different concave holes 11 is different, and the shape and size of the concave holes 11 can be the same or different, which is selected according to actual design requirements.

[0086] S307, a second undoped GaN section is prepared on the side of the first undoped GaN section away from the substrate, the second undoped GaN section is connected on the side of the concave hole away from the substrate, and at least one concave microstructure is formed between the first undoped GaN section and the second undoped GaN section; the same concave microstructure is periodically arranged; along the direction perpendicular to the substrate, the concave microstructure and the convex structure at least partially overlap.

[0087] At least one concave microstructure 105 is formed in the first undoped GaN section 1041 and the second undoped GaN section 1042, the same concave microstructure 105 is periodically arranged, along the direction X perpendicular to the substrate 101, the concave microstructure 105 and the pit structure 110 at least partially overlap, so that the concave microstructure 105 can reduce the generation of random dislocations in the epitaxial growth process, and at the same time, the existence of the concave microstructure 105 can increase the critical angle of total reflection, realize the modulation of light emitted by the patterned area of the substrate 101, and then increase the light emission and improve the light emission efficiency.

[0088] S308, an N-type GaN layer, a multi-quantum well active layer, a second buffer layer and a P-type GaN layer are sequentially prepared on the side of the second undoped GaN section away from the substrate to form an epitaxial wafer.

[0089] The embodiment of the present application forms at least one concave microstructure arranged periodically between the first undoped GaN section and the second undoped GaN section, part of the concave microstructure 105 and the convex structure on the side of the substrate partially overlap along the direction perpendicular to the substrate, the setting of the concave microstructure can effectively reduce or eliminate the dislocations generated in the subsequent epitaxial growth process, reduce the dislocation density in the epitaxial layer, improve the crystal quality, adjust the light emission direction, increase the total reflection area, improve the light emission efficiency, and ensure the use effect of the subsequent epitaxial wafer.

[0090] Figure 11 A structure schematic diagram of a light emitting diode provided by the embodiment of the present application is shown in the figure. Figure 11 As shown in the figure, the light emitting diode 200 comprises the epitaxial wafer 100 described in any one of the above embodiments.

[0091] The light emitting diode 200 further comprises a P electrode 201 on the side of the P type GaN layer 109 and an N electrode 202 on the side of the N type GaN layer 106, and a transparent conductive layer 203 between the P type GaN layer 109 and the P electrode, to ensure the diffusion effect of the current and the use effect of the light emitting diode 200.

[0092] It should be noted that the light emitting diode provided by the embodiment comprises the epitaxial wafer 100 provided by any of the embodiments of the present application, which has the same or corresponding beneficial effects of the epitaxial wafer 100, and thus will not be described herein.

[0093] The above detailed description does not constitute a limitation on the protection scope of the present application. It should be understood by those skilled in the art that various modifications, combinations, sub-combinations and substitutions can be made according to design requirements and other factors. Any modification, equivalent replacement and improvement made within the spirit and principle of the present application shall be included in the protection scope of the present application.

Claims

1. An epitaxial wafer, characterized in that, include: A substrate having a plurality of protrusions on one side, the protrusions being arranged periodically, pits being formed between adjacent protrusions, and adjacent pits being connected. The first buffer layer is located on the side closest to the recessed structure; An undoped GaN layer is located on the side of the first buffer layer away from the substrate; at least one concave microstructure exists within the undoped GaN layer, and the same type of concave microstructure is periodically arranged; along a direction perpendicular to the substrate, the concave microstructure and the protruding structure at least partially overlap; An N-type GaN layer, a multi-quantum-well active layer, a second buffer layer, and a P-type GaN layer are sequentially disposed on the side of the undoped GaN layer away from the substrate.

2. The epitaxial wafer according to claim 1, characterized in that, The concave microstructure includes a first concave microstructure and a second concave microstructure. Along a direction perpendicular to the substrate, the first concave microstructure at least partially overlaps with the protruding structure; the second concave microstructure does not overlap with the protruding structure.

3. The epitaxial wafer according to claim 2, characterized in that, The center of the bottom surface of the first concave microstructure coincides with the center of the bottom surface of the convex structure by orthographic projection.

4. The epitaxial wafer according to claim 2, characterized in that, The centroid of the figure formed by connecting the centers of the bottom surfaces of at least three adjacent protruding structures coincides with the orthographic projection of the center of the bottom surface of the second concave microstructure.

5. The epitaxial wafer according to claim 2, characterized in that, The shape of the concave microstructure includes at least one of conical, frustum, and spherical cap shapes.

6. The epitaxial wafer according to claim 5, characterized in that, The bottom radius of the first concave microstructure is R1, the bottom radius of the second concave microstructure is R2, the bottom radius of the convex structure is R3, and the arrangement period of the convex structure is P, where R1 < R3.

7. A method for preparing an epitaxial wafer, characterized in that, include: A substrate is provided, wherein a protrusion structure is provided on one side of the substrate, the protrusion structure is arranged periodically, a pit structure is formed between adjacent protrusion structures, and adjacent pit structures are connected. A first buffer layer is prepared on one side of the substrate; An undoped GaN layer is prepared on the side of the first buffer layer away from the substrate, and at least one concave microstructure is formed in the undoped GaN layer, wherein the same type of concave microstructure is periodically arranged; along the direction perpendicular to the substrate, the concave microstructure and the protruding structure at least partially overlap. An N-type GaN layer, a multi-quantum-well active layer, a second buffer layer, and a P-type GaN layer are sequentially fabricated on the side of the undoped GaN layer away from the substrate to form an epitaxial wafer.

8. The method for preparing an epitaxial wafer according to claim 7, characterized in that, An undoped GaN layer is fabricated on the side of the first buffer layer away from the substrate, and at least one concave microstructure is formed in the undoped GaN layer, including: A first undoped GaN fraction is prepared on the side of the first buffer layer away from the substrate; A concave hole is formed on the surface of the first undoped GaN portion away from the substrate; A second undoped GaN portion is prepared on the side of the first undoped GaN portion away from the substrate, and the second undoped GaN portion is connected to the concave hole on the side away from the substrate, forming a concave microstructure between the first undoped GaN portion and the second undoped GaN portion.

9. The method for preparing an epitaxial wafer according to claim 8, characterized in that, A concave hole is formed on the surface of the first undoped GaN portion away from the substrate, including: A mask layer is deposited on the side of the first undoped GaN portion away from the substrate; The mask layer is subjected to photolithography or imprinting processes to form at least one hole mask pattern, and the same type of hole mask pattern is arranged periodically. The hole mask pattern is subjected to a dry etching process to form at least one concave hole, and the same type of concave hole is arranged periodically.

10. A light-emitting diode, characterized in that, The epitaxial wafer includes any one of claims 1-6.

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