An LED device and a method of manufacturing the same

Abstract

The application provides an LED device and a preparation method thereof. The LED device comprises: a semiconductor substrate layer; a reflection structure on the semiconductor substrate layer, the reflection structure comprising a first set of reflection units to an Nth set of reflection units stacked in sequence from bottom to top, N being an integer greater than or equal to 2; any nth set of reflection units comprising at least one nth reflection unit, the nth reflection unit comprising an nth lower reflection layer and an nth upper reflection layer; the refractive index of the nth lower reflection layer being less than that of the nth upper reflection layer; the doping concentration of the first lower reflection layer in the first set of reflection units to the Nth lower reflection layer in the Nth set of reflection units increasing; the first lower reflection layer to the Nth lower reflection layer all having holes, and the hole rate of the first lower reflection layer to the Nth lower reflection layer increasing; and a light-emitting layer on the side of the reflection structure away from the semiconductor substrate layer. The light-emitting efficiency and the light-emitting uniformity of the LED device are improved.

Description

Technical Field

[0001] This invention relates to the field of semiconductor technology, and more specifically to an LED device and its fabrication method. Background Technology

[0002] As LEDs have evolved, the size of LED chips has become increasingly smaller. However, in the red light wavelength range of 615nm to 650nm, the main emitting layer still uses quaternary materials (such as AlGaInP). The luminous efficiency of these materials deteriorates significantly with smaller chip sizes (Micro LED chip size). Therefore, designing a structure using an InGaN emitting layer to emit wavelengths from 615nm to 650nm offers relatively higher luminous efficiency for smaller chip sizes at the same wavelength. Furthermore, the epitaxial structure can be implemented using the same substrate materials as conventional short-wavelength (blue and green) LEDs, and the chip fabrication and packaging methods can be improved by adopting the same methods used for blue and green LEDs.

[0003] However, existing LED devices cannot simultaneously achieve both luminous efficiency and luminous uniformity. Summary of the Invention

[0004] In view of this, the present invention provides an LED device and its preparation method to solve the problem that LED devices in the prior art cannot simultaneously achieve luminous efficiency and luminous uniformity.

[0005] This invention provides an LED device, comprising: a semiconductor substrate layer; a reflective structure located on the semiconductor substrate layer, the reflective structure comprising a first group of reflective units to an Nth group of reflective units stacked sequentially from bottom to top, where N is an integer greater than or equal to 2; any nth group of reflective units includes at least one nth reflective unit, the nth reflective unit including an nth lower reflective layer and an nth upper reflective layer; the refractive index of the nth lower reflective layer is less than the refractive index of the nth upper reflective layer; n is an integer greater than or equal to 1 and less than or equal to N; the doping concentration of the first lower reflective layer in the first group of reflective units to the Nth lower reflective layer in the Nth group of reflective units increases progressively, each of the first lower reflective layer to the Nth lower reflective layer has a hole, and the porosity of the first lower reflective layer to the Nth lower reflective layer increases progressively; and a light-emitting layer located on the side of the reflective structure opposite to the semiconductor substrate layer.

[0006] Optionally, the materials of the first lower reflective layer to the Nth lower reflective layer are all GaN doped with n-type conductive ions, and the materials of the first upper reflective layer to the Nth upper reflective layer are all single-crystal undoped GaN.

[0007] Optionally, the size of the holes in the first lower reflective layer to the Nth lower reflective layer increases.

[0008] Optionally, any nth group of reflective units may include three to five stacked nth reflective units.

[0009] Optionally, N equals 5, and the reflective structure includes a first group of reflective units, a second group of reflective units, a third group of reflective units, a fourth group of reflective units, and a fifth group of reflective units stacked sequentially from bottom to top; the doping concentration of the first lower reflective layer to the fifth lower reflective layer increases.

[0010] Optionally, the doping concentration of the first lower reflective layer in the first set of reflective units is 9E17 atom / cm³. 3 ~2E18atom / cm 3 The doping concentration of the second lower reflective layer in the second set of reflective units is 3E18 atom / cm³. 3 ~5E18atom / cm 3 The doping concentration of the third lower reflective layer in the third group of reflective units is 6E18 atom / cm³. 3 ~8E18atom / cm 3 The doping concentration of the fourth lower reflective layer in the fourth group of reflective units is 9E18 atom / cm³. 3 ~2E19atom / cm 3 The doping concentration of the fifth lower reflective layer in the fifth group of reflective units is 3E19 atom / cm³. 3 ~5E19atom / cm 3 .

[0011] Optionally, the thicknesses of the first lower reflective layer to the Nth lower reflective layer are equal, and the thicknesses of the first upper reflective layer to the Nth upper reflective layer are equal.

[0012] Optionally, the thickness of the first lower reflective layer to the Nth lower reflective layer is 20nm~150nm; the thickness of the first upper reflective layer to the Nth upper reflective layer is 20nm~80nm.

[0013] Optionally, it may also include a first bonding layer located between the semiconductor substrate layer and the reflective structure.

[0014] Optionally, the first connecting layer includes an amorphous undoped first buffer layer, a monocrystalline undoped second buffer layer, and a monocrystalline undoped third buffer layer stacked sequentially from bottom to top, wherein the lattice constant of the second buffer layer is smaller than that of the first and third buffer layers.

[0015] Optionally, the material of the first buffer layer is undoped amorphous GaN, the material of the second buffer layer is undoped monocrystalline AlN, and the material of the third buffer layer is undoped monocrystalline GaN.

[0016] Optionally, it may also include an electron injection layer located between the reflective structure and the light-emitting layer.

[0017] Optionally, it may also include a second bonding layer located between the reflective structure and the electron injection layer.

[0018] Optionally, it may also include a buffer structure located between the electron injection layer and the light-emitting layer.

[0019] Optionally, the second bonding layer is undoped single-crystal GaN.

[0020] Optionally, the buffer structure further includes: the buffer structure comprising at least one buffer unit group, the buffer unit group comprising at least one buffer unit, the buffer unit comprising a stacked lower buffer layer and an upper buffer layer; the lower buffer layer in any buffer unit is located below the upper buffer layer, and the conduction band of the upper buffer layer is higher than the conduction band of the lower buffer layer; the light-emitting layer comprises a plurality of stacked sub-light-emitting groups, the sub-light-emitting groups comprising stacked quantum well layers and barrier layers, the quantum well layer in any sub-light-emitting group being located below the barrier layer; the conduction band of the lower buffer layer is higher than the conduction band of the quantum well layer.

[0021] Optionally, the quantum well layer contains the same elements as the lower buffer layer; the barrier layer and the upper buffer layer are made of the same material.

[0022] Optionally, both the lower buffer layer and the light-emitting layer contain In, and the In content in the lower buffer layer is less than the In content in the quantum well layer.

[0023] Optionally, the buffer structure includes multiple buffer unit groups, and for the multiple buffer unit groups, in the direction of arrangement from bottom to top, the In content in the lower buffer layer of the multiple buffer unit groups increases.

[0024] Optionally, the buffer unit group includes several stacked buffer units, and the In content of the lower buffer layers in the same buffer unit group is the same.

[0025] Optionally, the thickness of the lower buffer layer is greater than the thickness of the quantum well layer, and the thickness of the upper buffer layer is less than the thickness of the barrier layer.

[0026] The present invention also provides a method for fabricating an LED device, comprising: providing a semiconductor substrate layer; forming a reflective structure on the semiconductor substrate layer, the method of forming the reflective structure comprising forming a first group of reflective units to an Nth group of reflective units stacked sequentially from bottom to top, where N is an integer greater than or equal to 2; the step of forming any nth group of reflective units comprising forming at least one nth reflective unit, the nth reflective unit comprising an nth lower reflective layer and an nth upper reflective layer; the refractive index of the nth lower reflective layer being less than the refractive index of the nth upper reflective layer; n being an integer greater than or equal to 1 and less than or equal to N; the doping concentration of the first lower reflective layer in the first group of reflective units to the Nth lower reflective layer in the Nth group of reflective units increasing progressively, each of the first lower reflective layer to the Nth lower reflective layer having a hole, and the porosity of the first lower reflective layer to the Nth lower reflective layer increasing progressively; and forming a light-emitting layer on the side of the reflective structure opposite to the semiconductor substrate layer.

[0027] Optionally, it further includes: forming a first bonding layer on the semiconductor substrate before forming the reflective structure; and after forming the first bonding layer, the first bonding layer is located between the reflective structure and the semiconductor substrate.

[0028] Optionally, the step of forming the first interlayer includes: sequentially depositing an amorphous undoped first buffer layer, a monocrystalline undoped second buffer layer, and a monocrystalline undoped third buffer layer on the semiconductor substrate, wherein the lattice constant of the second buffer layer is smaller than the lattice constants of the first and third buffer layers.

[0029] Optionally, it further includes forming an electron injection layer on the side of the reflective structure opposite to the semiconductor substrate before forming the light-emitting layer.

[0030] Optionally, it also includes forming a second bonding layer on the side of the reflective structure opposite to the semiconductor substrate before forming the electron injection layer.

[0031] Optionally, it also includes forming a buffer structure on the side of the electron injection layer opposite to the semiconductor substrate layer before forming the light-emitting layer.

[0032] Optionally, the method of forming the buffer structure includes: forming at least one buffer unit group, the buffer unit group including at least one buffer unit, the buffer unit including a stacked lower buffer layer and an upper buffer layer; the lower buffer layer in any buffer unit is located below the upper buffer layer, and the conduction band of the upper buffer layer is higher than the conduction band of the lower buffer layer; the method of forming the light-emitting layer includes: forming a plurality of stacked sub-light-emitting groups, the sub-light-emitting groups including stacked quantum well layers and barrier layers, the quantum well layer in any sub-light-emitting group being located below the barrier layer; the conduction band of the lower buffer layer is higher than the conduction band of the quantum well layer.

[0033] Optionally, the quantum well layer contains the same elements as the lower buffer layer; the barrier layer and the upper buffer layer are made of the same material.

[0034] Optionally, the thickness of the lower buffer layer is greater than the thickness of the quantum well layer, and the thickness of the upper buffer layer is less than the thickness of the barrier layer.

[0035] Optionally, the step of forming the reflective structure includes: sequentially forming a first group of initial reflective units to an Nth group of initial reflective units on a semiconductor substrate layer; the step of forming any nth group of initial reflective units includes forming at least one nth initial reflective unit, the nth initial reflective unit including an nth initial lower reflective layer and an nth upper reflective layer; immersing the first group of initial reflective units to the Nth group of initial reflective units in an electrolyte; the first initial lower reflective layer to the Nth initial lower reflective layer undergoes an electrochemical reaction with the electrolyte, such that any nth initial lower reflective layer forms an nth lower reflective layer, and any nth initial reflective unit forms an nth reflective unit, and any nth group of initial reflective units forms an nth group of reflective units.

[0036] The technical solution provided by this invention has the following effects: The LED device provided by this invention has holes in all of the first to Nth lower reflective layers, making the refractive index of the nth lower reflective layer lower than that of the nth upper reflective layer. This refractive index difference between the nth and nth lower and upper reflective layers gives the reflective structure a resonant cavity DBR reflective layer effect, increasing the reflectivity of the reflective structure and thus improving luminous efficiency. The porosity of the first to Nth lower reflective layers increases progressively, so as n increases, the refractive index difference between the nth and nth upper reflective layers becomes larger, further improving the luminous efficiency of the reflective structure. Because the doping concentration of the first to Nth lower reflective layers in the first group of reflective units on the semiconductor substrate increases progressively, the growth quality of the first to Nth lower reflective layers is improved, defects in the first to Nth lower reflective layers are reduced, and the uniformity of the holes in the first to Nth lower reflective layers is improved. This, in turn, reduces the reflectivity difference between different regions of the reflective structure, ultimately improving the luminous uniformity of the LED device. Therefore, the LED device improves both luminous efficiency and luminous uniformity.

[0037] The LED manufacturing method provided by the present invention improves luminous efficiency and luminous uniformity for the same reasons mentioned above. Attached Figure Description

[0038] To more clearly illustrate the specific embodiments of the present invention or the technical solutions in the prior art, the drawings used in the description of the specific embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are some embodiments of the present invention. For those skilled in the art, other drawings can be obtained from these drawings without creative effort.

[0039] Figure 1 This is a schematic diagram of the structure of an LED device according to an embodiment of the present invention; Figure 2 This is a schematic diagram of the reflection structure in an LED device according to an embodiment of the present invention; Figures 3 to 6 This is a schematic diagram of the LED device fabrication process in an example of the present invention. Detailed Implementation

[0040] An LED device includes: a semiconductor substrate; a reflective structure located on the semiconductor substrate, the reflective structure including a plurality of n-type doped GaN layers and a plurality of undoped GaN layers, the undoped GaN layers and the n-type doped GaN layers being alternately stacked; each of the plurality of n-type doped GaN layers having holes; the refractive index of the n-type doped GaN layers having holes being less than the refractive index of the undoped GaN layers; and a light-emitting layer located on the side of the reflective structure opposite to the semiconductor substrate, the light-emitting layer including an InGaN quantum well layer.

[0041] In the aforementioned structure, each of the n-type doped GaN layers contains pores, resulting in a lower refractive index for the n-type doped GaN layers compared to those without pores. The difference in refractive index between the pore-filled n-type doped GaN layers and the undoped GaN layers creates a resonant cavity DBR (Distributed Bragg Reflector) effect, improving the reflectivity and thus enhancing luminous efficiency. The method for forming the n-type doped GaN layer includes: forming an initial n-type doped GaN layer on the semiconductor substrate; placing the device in an electrolyte, causing an electrochemical reaction between the electrolyte and the initial n-type doped GaN layer, resulting in the formation of an n-type doped GaN layer with pores. To further improve the reflectivity of the reflective structure, it is necessary to increase the porosity of the n-type doped GaN layer, thereby increasing the difference in refractive index between the n-type doped GaN layer and the undoped GaN layer. Methods to improve the porosity of n-type doped GaN layers include increasing the doping concentration of the initial n-type doped GaN layer, which increases the porosity formed by the reaction between the initial n-type doped GaN layer and the electrolyte. However, increasing the doping concentration of each initial n-type doped GaN layer affects the quality of the initially n-type doped GaN layer grown on the semiconductor substrate. Defects exist in the initial n-type doped GaN layer, and the intense reaction between the initial n-type doped GaN layer and the electrolyte further contributes to poor uniformity of the pores within the n-type doped GaN layer. This poor pore uniformity results in varying reflectivity in different regions of the reflective structure, leading to inconsistent reflectivity and ultimately poor luminous uniformity in the LED device.

[0042] Based on this, the present invention provides an LED device and its preparation method, which improves the luminous efficiency and luminous uniformity of the LED device.

[0043] The technical solution of the present invention will now be clearly and completely described with reference to the accompanying drawings. Obviously, the described embodiments are only some, not all, of the embodiments of the present invention. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0044] In the description of this invention, it should be noted that the terms "center," "upper," "lower," "left," "right," "vertical," "horizontal," "inner," and "outer," etc., indicate the orientation or positional relationship based on the orientation or positional relationship shown in the accompanying drawings. They are used only for the convenience of describing the invention and for simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, or be constructed and operated in a specific orientation. Therefore, they should not be construed as limitations on the invention. Furthermore, the terms "first," "second," and "third" are used for descriptive purposes only and should not be construed as indicating or implying relative importance.

[0045] In the description of this invention, it should be noted that, unless otherwise explicitly specified and limited, the terms "installation," "connection," and "linking" should be interpreted broadly. For example, they can refer to a fixed connection, a detachable connection, or an integral connection; they can refer to a mechanical connection or an electrical connection; they can refer to a direct connection or an indirect connection through an intermediate medium; they can also refer to the internal connection of two components; and they can refer to a wireless connection or a wired connection. Those skilled in the art can understand the specific meaning of the above terms in this invention based on the specific circumstances.

[0046] Furthermore, the technical features involved in the different embodiments of the present invention described below can be combined with each other as long as they do not conflict with each other.

[0047] This embodiment provides an LED device, in conjunction with a reference. Figure 1 and Figure 2 ,include: Semiconductor substrate layer 100; A reflective structure A is located on the semiconductor substrate 100. The reflective structure A includes a first group of reflective units A1 to an Nth group of reflective units stacked sequentially from bottom to top, where N is an integer greater than or equal to 2. Any nth group of reflective units includes at least one nth reflective unit, and the nth reflective unit includes an nth lower reflective layer and an nth upper reflective layer. The refractive index of the nth lower reflective layer is less than the refractive index of the nth upper reflective layer. n is an integer greater than or equal to 1 and less than or equal to N. The doping concentration of the first lower reflective layer 211 in the first group of reflective units A1 to the Nth lower reflective layer in the Nth group of reflective units increases, and the first lower reflective layer 211 to the Nth lower reflective layer all have pores, and the porosity of the first lower reflective layer 211 to the Nth lower reflective layer increases. The light-emitting layer 150 is located on the side of the reflective structure A opposite to the semiconductor substrate layer 100.

[0048] In this embodiment, the first lower reflective layer 211 to the Nth lower reflective layer all have holes, making the refractive index of the nth lower reflective layer less than that of the nth upper reflective layer. This refractive index difference between the nth and nth lower reflective layers gives the reflective structure a resonant cavity DBR reflective layer effect, increasing the reflectivity of the reflective structure and thus improving luminous efficiency. The porosity of the first lower reflective layer to the Nth lower reflective layer increases, so as n increases, the refractive index difference between the nth lower reflective layer and the nth upper reflective layer becomes larger, further improving the luminous efficiency of the reflective structure. Since the doping concentration of the first lower reflective layer to the Nth lower reflective layer in the first group of reflective units on the semiconductor substrate 100 increases, the growth quality of the first lower reflective layer to the Nth lower reflective layer is improved, defects in the first lower reflective layer to the Nth lower reflective layer are reduced, and the uniformity of the holes in the first lower reflective layer to the Nth lower reflective layer is improved. This, in turn, reduces the reflectivity difference in different regions of the reflective structure, ultimately improving the luminous uniformity of the LED device.

[0049] The semiconductor substrate 100 includes a sapphire substrate, a silicon substrate, or a silicon carbide substrate.

[0050] In one embodiment, the upper surface of the semiconductor substrate 100 is flat. In another embodiment, the upper surface of the semiconductor substrate has a plurality of spaced protrusions. The protrusions include conical shapes. The spacing between adjacent protrusions is 0.5 micrometers to 2.5 micrometers, for example, 0.5 micrometers, 1 micrometer, 1.5 micrometers, 2 micrometers, or 2.5 micrometers. The width of the protrusions is 0.5 micrometers to 3 micrometers, for example, 0.5 micrometers, 1 micrometer, 1.5 micrometers, 2 micrometers, or 2.5 micrometers or 3 micrometers.

[0051] The LED device further includes a first bonding layer 110 located between the semiconductor substrate layer 100 and the reflective structure A. The first bonding layer 110 includes an amorphous undoped first buffer layer, a monocrystalline undoped second buffer layer, and a monocrystalline undoped third buffer layer stacked sequentially from bottom to top. The lattice constant of the second buffer layer is smaller than that of the first and third buffer layers.

[0052] In one embodiment, the first buffer layer is made of undoped amorphous GaN, the second buffer layer is made of undoped monocrystalline AlN, and the third buffer layer is made of undoped monocrystalline GaN.

[0053] When the upper surface of the semiconductor substrate 100 has a plurality of spaced protrusions, a first buffer layer covers the surface of the protrusions and the surface of the semiconductor substrate between the protrusions; a second buffer layer conformally covers the first buffer layer; a third buffer layer fills part of the space between the protrusions and covers the second buffer layer. The thickness of the third buffer layer is greater than the height of the protrusions, while the thicknesses of the first and second buffer layers are both less than the height of the protrusions. The first, second, and third buffer layers are grown in a 3D manner on the surface of the semiconductor substrate, and the material defects on adjacent protrusion surfaces cancel each other out, resulting in a higher quality third buffer layer. The quality of the reflective structure A of the material on the third buffer layer can be improved.

[0054] The lattice constant of the second buffer layer is smaller than that of the first buffer layer, making the difference between the lattice constant of the second buffer layer and the lattice constant of the semiconductor substrate layer smaller than the difference between the lattice constant of the first buffer layer and the lattice constant of the semiconductor substrate layer. This improves the quality of the second buffer layer. The material of the second buffer layer is different from that of the third buffer layer.

[0055] The material of the third buffer layer, the material of any nth upper reflective layer, and the main material of any nth lower reflective layer are all the same. In this way, the third buffer layer provides a better matrix for the growth of the reflective structure A.

[0056] In one embodiment, the materials of the first lower reflective layer to the Nth lower reflective layer are all GaN doped with n-type conductive ions, including Si ions or Ge ions. The materials of the first upper reflective layer to the Nth upper reflective layer are all undoped single-crystal GaN.

[0057] When the nth group of reflective elements includes multiple nth lower reflective layers, the difference in hole size among the multiple nth lower reflective layers in the nth group of reflective elements is relatively small.

[0058] In one embodiment, the size of the pores in the first to the Nth lower reflective layers increases progressively, with the pore size in the nth lower reflective layer increasing as n increases. The pore density in the first to the Nth lower reflective layers also increases progressively, with the pore density in the nth lower reflective layer increasing as n increases. If the doping concentration in each lower reflective layer before pore formation is consistently high, it can cause severe internal compressive stress buildup. High-concentration doped lower reflective layers can lead to excessive defects (e.g., vertical line defects) and localized doping inhomogeneities. This results in more uncontrollable factors during subsequent electrochemical reactions to form pores, easily leading to pores with disordered morphologies. Therefore, in this embodiment, the doping concentration of the first lower reflective layer to the Nth lower reflective layer gradually changes from low to high concentration. This will result in the highly doped lower reflective layer having high crystal quality and stable uniformity. During the electrochemical reaction, a gradient hole will be formed from the surface layer of the epitaxial wafer downwards. The lower reflective layer closer to the surface plays a crucial role in light reflection and internal stress release. During the electrochemical reaction closer to the surface, a gradient hole will be formed from the surface layer of the epitaxial wafer downwards. The higher the surface, the greater the density and size of the holes, resulting in high reflectivity and wide reflection wavelength, and a more significant stress release effect. However, the morphology and uniformity of the holes depend on the doping status of the lower reflective layer. Therefore, the gradient hole layer obtained in this way can obtain a hole layer with a uniform morphology close to the surface of the epitaxial wafer. Compared with the holes formed by a high-concentration lower reflective layer without gradient design, the final effect will be greatly improved.

[0059] In one embodiment, any nth group of reflective units includes three to five stacked nth reflective units. It should be noted that in other embodiments, the number of nth reflective units in any nth group can be other than a certain number. In this embodiment, three stacked nth reflective units are used as an example. Any nth reflective unit has an nth lower reflective layer and an nth upper reflective layer. It should be noted that the number of nth reflective units in the nth group can vary with n, or it can be the same regardless of n.

[0060] The following description uses N=5 as an example to illustrate the reflection structure. The reflection structure A includes, from bottom to top, a first group of reflection units A1, a second group of reflection units A2, a third group of reflection units A3, a fourth group of reflection units A4, and a fifth group of reflection units A5. The first group of reflection units A1 includes three stacked first reflection units, each comprising a first lower reflection layer 211 and a first upper reflection layer 212. The second group of reflection units A2 includes three stacked second reflection units, each comprising a second lower reflection layer 221 and a second upper reflection layer 222. The third group of reflection units A3 includes three stacked third reflection units, each comprising a third lower reflection layer 231 and a third upper reflection layer 232. The fourth group of reflection units A4 includes three stacked fourth reflection units, each comprising a fourth lower reflection layer 241 and a fourth upper reflection layer 242. The fifth group of reflection units A5 includes three stacked fifth reflection units, each comprising a fifth lower reflection layer 251 and a fifth upper reflection layer 252. The doping concentration of the second lower reflective layer 221 is greater than that of the first lower reflective layer 211, the doping concentration of the third lower reflective layer 231 is greater than that of the second lower reflective layer 221, the doping concentration of the fourth lower reflective layer 241 is greater than that of the third lower reflective layer 231, and the doping concentration of the fifth lower reflective layer 251 is greater than that of the fourth lower reflective layer 241.

[0061] When N equals 5, the doping concentration of the first lower reflective layer 211 in the first set of reflective units A1 is 9E17atom / cm². 3 ~2E18atom / cm 3 The doping concentration of the second lower reflective layer 221 in the second set of reflective units A2 is 3E18 atom / cm³. 3 ~5E18atom / cm 3 The doping concentration of the third lower reflective layer 231 in the third group of reflective units A3 is 6E18 atom / cm³. 3 ~8E18atom / cm 3 The doping concentration of the fourth lower reflective layer 241 in the fourth reflective unit A4 is 9E18 atom / cm³. 3 ~2E19atom / cm 3 The doping concentration of the fifth lower reflective layer 251 in the fifth reflective unit A5 is 3E19 atom / cm³. 3 ~5E19atom / cm 3 .

[0062] The thicknesses of the first lower reflective layer 211 to the Nth lower reflective layer are equal. The thicknesses of the first upper reflective layer to the Nth upper reflective layer are also equal. In one embodiment, the thicknesses of the first lower reflective layer to the Nth lower reflective layer are all 20 nm to 150 nm; the thicknesses of the first upper reflective layer to the Nth upper reflective layer are all 20 nm to 80 nm. The descriptions of thickness herein refer to the thickness of a single-layer nth lower reflective layer being 20 nm to 150 nm, and the thickness of a single-layer nth upper reflective layer being 20 nm to 80 nm.

[0063] In this embodiment, the LED device further includes an electron injection layer 130, located between the reflective structure A and the light-emitting layer 150. The electron injection layer 130 is made of GaN doped with n-type conductive ions, such as Si ions. In one embodiment, the thickness of the electron injection layer 130 is 1µm-3µm. The doping concentration of n-type conductive ions in the electron injection layer 130 is 1E18 atoms / cm³. 3 Up to 5E19atom / cm 3 .

[0064] In this embodiment, the LED device further includes a second bonding layer 120, located between the reflective structure A and the electron injection layer 130. In one embodiment, the second bonding layer 120 is undoped single-crystal GaN. In one embodiment, the thickness of the second bonding layer 120 is 0.2µm-1.5µm.

[0065] In this embodiment, the LED device further includes a buffer structure 140 located between the electron injection layer 130 and the light-emitting layer 150.

[0066] The buffer structure 140 includes at least one buffer unit group, the buffer unit group includes at least one buffer unit, the buffer unit includes a stacked lower buffer layer and an upper buffer layer; in any buffer unit, the lower buffer layer is located below the upper buffer layer, and the conductor strip of the upper buffer layer is higher than the conductor strip of the lower buffer layer.

[0067] The light-emitting layer 150 includes several stacked sub-light-emitting groups, each sub-light-emitting group comprising a stacked quantum well layer and a barrier layer, wherein the quantum well layer in any sub-light-emitting group is located below the barrier layer. The conduction band of the lower buffer layer is higher than the conduction band of the quantum well layer. In this embodiment, the upper buffer layer at the top of the buffer structure 140 serves as the barrier layer of the bottom quantum well layer in the light-emitting layer.

[0068] In one embodiment, the quantum well layer contains the same elements as the lower buffer layer; the barrier layer and the upper buffer layer are made of the same material.

[0069] In one embodiment, both the lower buffer layer and the light-emitting layer contain In, and the In content in the lower buffer layer is less than the In content in the quantum well layer.

[0070] In one specific embodiment, the material of the quantum well layer is In. x Ga (1-X) N, the barrier layer is made of undoped single-crystal GaN. The upper buffer layer is made of undoped single-crystal GaN. The lower buffer layer is made of In. y Ga (1-y) N. y is less than x. Where x is 0.30~0.40, and y is 0.05~0.30, for example 0.25. In one embodiment, neither the quantum well layer nor the lower buffer layer is doped with conductive particles.

[0071] In one embodiment, the buffer structure 140 includes a plurality of buffer unit groups. For the plurality of buffer unit groups, the In content in the lower buffer layer of the plurality of buffer unit groups increases in a bottom-to-top direction. The buffer structure includes a first buffer unit group to a Qth buffer unit group stacked from bottom to top, where Q is an integer greater than or equal to 2. Any qth buffer unit group includes at least one qth buffer unit, and any qth buffer unit includes a stacked qth lower buffer layer and a qth upper buffer layer. The In content in the first lower buffer layer to the Qth lower buffer layer increases. Due to the increasing In content in the first lower buffer layer to the Qth lower buffer layer, the stress in the first lower buffer layer to the Qth lower buffer layer is gradually released, thereby reducing the stress of the buffer structure on the light-emitting layer and improving the quality of the light-emitting layer.

[0072] In one example, the buffer unit group comprises several stacked buffer units, with the In content of the lower buffer layers within the same buffer unit group being the same. The In content is the same in multiple q-th lower buffer layers within any q-th buffer unit group.

[0073] In one embodiment, the variation law of the thickness of the first lower buffer layer to the Qth lower buffer layer includes: for any q, when q is the same, the thickness of the qth lower buffer layer is the same; as q increases, the thickness of the qth lower buffer layer gradually decreases. The advantage of this is that as the In content in the first to Qth lower buffer layers increases, a thinner lower buffer layer has fewer defects when the doping concentration is higher, thus improving the growth quality of the lower buffer layer. In one embodiment, the thickness of the first lower buffer layer is 60 nm to 120 nm, and the thickness of the Qth lower buffer layer is 20 nm to 60 nm.

[0074] In one embodiment, the variation law of the thickness of the first upper buffer layer to the Qth upper buffer layer includes: for any q, when q is the same, the thickness of the qth upper buffer layer is the same; from the Qth upper buffer layer to the first upper buffer layer, the thickness of the qth upper buffer layer gradually decreases as q decreases; since the thickness of the qth upper buffer layer is smaller on the side closer to the semiconductor substrate, the qth upper buffer layer has a smaller blocking effect on electrons, and electrons can be transported from the electron injection layer to the light-emitting layer more quickly. This makes the region of electron-hole recombination closer to the light-emitting layer, avoiding light emission from the buffer structure. In a specific embodiment, the thickness of the first upper buffer layer is 60nm~120nm, and the thickness of the Qth upper buffer layer is 120nm~180nm.

[0075] In one specific embodiment, Q equals 2, and the buffer structure 140 includes a first buffer unit group to a second buffer unit group stacked from bottom to top. The first buffer unit group includes a plurality of stacked first buffer units, and any one of the first buffer units includes a stacked first lower buffer layer and a first upper buffer layer. The second buffer unit group includes a plurality of stacked second buffer units, and any one of the second buffer units includes a stacked second lower buffer layer and a second upper buffer layer. In one specific embodiment, the In content y in the first lower buffer layer is 0.05~0.15, and the In content y in the second lower buffer layer is 0.20~0.25.

[0076] It should be noted that in other embodiments, Q is an integer greater than 2, or Q=1.

[0077] In one embodiment, the thickness of the lower buffer layer is greater than the thickness of the quantum well layer, and the thickness of the upper buffer layer is less than the thickness of the barrier layer. This eliminates tunneling effects in the lower buffer layer, and the growth quality of the lower buffer layer is relatively poor compared to that of the quantum well layer. Secondly, the smaller thickness of the upper buffer layer reduces its obstruction of electrons, causing the region where electrons and holes recombine to shift away from the buffer structure and closer to the light-emitting layer. Therefore, no light is emitted from the buffer structure, and it does not interfere with the light emitted by the light-emitting layer. It should be noted that the thicknesses of the lower buffer layer, the quantum well layer, the upper buffer layer, and the barrier layer all refer to the thickness of a single layer.

[0078] In one embodiment, the thickness of the lower buffer layer is greater than the thickness of the quantum well layer, the thickness of the upper buffer layer is less than the thickness of the barrier layer, and as q increases, the thickness of the qth lower buffer layer gradually decreases, and as q decreases, the thickness of the qth upper buffer layer gradually decreases.

[0079] In another embodiment, light is emitted from the lower buffer layer, and the color of the light emitted by the lower buffer layer is different from the color of the light emitted by the quantum well layer, for example, emitting blue light or green light. The light emitted by the quantum well layer and the light emitted by the lower buffer layer are combined to form mixed light.

[0080] The thickness of the single quantum well layer in the light-emitting layer 150 is 20 nanometers to 40 nanometers, and the thickness of the single barrier layer in the light-emitting layer is 100 nanometers to 150 nanometers.

[0081] In this embodiment, the LED device further includes: an electron blocking layer 160 located on the side of the light-emitting layer 150 facing away from the semiconductor substrate layer 100; a hole transport layer 170 located on the side of the electron blocking layer 160 facing away from the light-emitting layer 150; and a contact layer 180 located on the side of the hole transport layer 170 facing away from the light-emitting layer 150. The electron blocking layer is made of AlGaN and has a thickness of 100 nanometers to 300 nanometers. The hole transport layer 170 is made of Mg-doped P-type GaN. The contact layer 180 is made of Mg-doped P-type GaN, and the Mg doping content in the contact layer is greater than the Mg doping content in the hole transport layer 170. In one embodiment, the Mg doping concentration in the hole transport layer 170 is 5E18 atom / cm³. 3 ~1E19 / atom / cm 3 The Mg doping concentration in contact layer 180 is 5E19 atom / cm³. 3 ~5E20 / atom / cm 3 The function of contact layer 180 is to form an ohmic contact, allowing for more effective charge injection.

[0082] In this embodiment, the emission wavelength of the light-emitting layer 150 is 615nm~650nm.

[0083] Theoretically, the higher the In content of InGaN material, the longer the wavelength band it can emit. However, when the semiconductor substrate is GaN-based, there is a large difference in lattice constant between the semiconductor substrate and the InGaN material. This makes it difficult for In (indium) to grow into InGaN material directly on the semiconductor substrate, resulting in a low In content and an inability to achieve a longer wavelength and good photoelectric properties. Therefore, a buffer structure is needed to release the stress of lattice mismatch, thereby improving the emission wavelength and photoelectric properties of LED devices.

[0084] The present invention also provides a method for fabricating an LED device, comprising: providing a semiconductor substrate layer; forming a reflective structure on the semiconductor substrate layer, the method of forming the reflective structure comprising forming a first group of reflective units to an Nth group of reflective units stacked sequentially from bottom to top, where N is an integer greater than or equal to 2; the step of forming any nth group of reflective units comprising forming at least one nth reflective unit, the nth reflective unit comprising an nth lower reflective layer and an nth upper reflective layer; the refractive index of the nth lower reflective layer being less than the refractive index of the nth upper reflective layer; n being an integer greater than or equal to 1 and less than or equal to N; the doping concentration of the first lower reflective layer in the first group of reflective units to the Nth lower reflective layer in the Nth group of reflective units increasing progressively, each of the first lower reflective layer to the Nth lower reflective layer having a hole, and the porosity of the first lower reflective layer to the Nth lower reflective layer increasing progressively; and forming a light-emitting layer on the side of the reflective structure opposite to the semiconductor substrate layer.

[0085] The following is combined Figures 3 to 6 This section provides a detailed introduction to the manufacturing process of LED devices.

[0086] refer to Figure 3 A semiconductor substrate 100 is provided; a reflective structure A is formed on the semiconductor substrate 100.

[0087] The semiconductor substrate 100 includes a sapphire substrate, a silicon substrate, or a silicon carbide substrate.

[0088] In one embodiment, the upper surface of the semiconductor substrate 100 is flat. In another embodiment, the upper surface of the semiconductor substrate has a plurality of spaced protrusions. The protrusions are cone-shaped. The spacing between adjacent protrusions is 0.5 micrometers to 2.5 micrometers. The width of the protrusions is 0.5 micrometers to 3 micrometers.

[0089] The method for fabricating the LED device further includes: forming a first bonding layer 110 on the semiconductor substrate layer 100 before forming the reflective structure A; after forming the first bonding layer 110, the first bonding layer 110 is located between the reflective structure A and the semiconductor substrate layer 100.

[0090] In one embodiment, the step of forming the first bonding layer 110 includes: sequentially depositing an amorphous undoped first buffer layer, a monocrystalline undoped second buffer layer, and a monocrystalline undoped third buffer layer on the semiconductor substrate, wherein the lattice constant of the second buffer layer is smaller than the lattice constants of the first buffer layer and the third buffer layer.

[0091] The process for forming the first buffer layer includes metal oxide chemical vapor deposition (MOCVD). The process for forming the second buffer layer includes metal oxide chemical vapor deposition (MOCVD). The process for forming the third buffer layer includes metal oxide chemical vapor deposition (MOCVD).

[0092] The deposition temperature of the first buffer layer is lower than that of the third buffer layer.

[0093] In one embodiment, the first buffer layer is made of undoped amorphous GaN, the second buffer layer is made of undoped monocrystalline AlN, and the third buffer layer is made of undoped monocrystalline GaN.

[0094] The process parameters used to form the first buffer layer include: the nitrogen source used is NH3, the gallium source used is trimethylgallium or triethylgallium, and the temperature is 540 degrees Celsius to 560 degrees Celsius.

[0095] The process parameters used to form the second buffer layer include: the nitrogen source used is NH3, the aluminum source used is trimethylaluminum, the temperature is 900 degrees Celsius to 1050 degrees Celsius, and the chamber pressure is 100 torr to 150 torr.

[0096] The process parameters used to form the third buffer layer include: the nitrogen source used is NH3, the gallium source used is trimethylgallium or triethylgallium, the temperature is 1050 degrees Celsius to 1150 degrees Celsius, and the chamber pressure is 200 torr to 250 torr.

[0097] The method of forming the reflective structure A includes forming a first group of reflective units A1 to a Nth group of reflective units stacked sequentially from bottom to top, where N is an integer greater than or equal to 2; the step of forming any nth group of reflective units includes forming at least one nth reflective unit, the nth reflective unit including an nth lower reflective layer and an nth upper reflective layer; the refractive index of the nth lower reflective layer is less than the refractive index of the nth upper reflective layer; n is an integer greater than or equal to 1 and less than or equal to N; the doping concentration of the first lower reflective layer in the first group of reflective units to the Nth lower reflective layer in the Nth group of reflective units increases progressively, and each of the first lower reflective layer to the Nth lower reflective layer has pores, with the porosity of the first lower reflective layer to the Nth lower reflective layer increasing progressively.

[0098] Specifically, the step of forming the reflective structure A includes: sequentially forming a first group of initial reflective units to an Nth group of initial reflective units on the semiconductor substrate layer 100; the step of forming any nth group of initial reflective units includes forming at least one nth initial reflective unit, the nth initial reflective unit including an nth initial lower reflective layer and an nth upper reflective layer; immersing the first group of initial reflective units to an Nth group of initial reflective units in an electrolyte; the first initial lower reflective layer to an Nth initial lower reflective layer undergoing an electrochemical reaction with the electrolyte, such that any nth initial lower reflective layer forms an nth lower reflective layer, and any nth initial reflective unit forms an nth reflective unit, and any nth group of initial reflective units forms an nth group of reflective units.

[0099] In this embodiment, N=5 is used as an example. In other embodiments, N can take other values.

[0100] In one embodiment, the electrolyte is an acidic electrolyte or an alkaline electrolyte. The acidic electrolyte is one or more of oxalic acid and sodium nitrate. When multiple electrolytes are mixed, the volume ratio of different types of electrolytes is consistent, the total molar concentration of the electrolyte is 0.2~0.5, and the constant voltage applied to the electrochemical reaction is 10V~40V.

[0101] The process for forming the nth initial lower reflective layer includes metal-oxide chemical vapor deposition (MOCVD). The parameters for forming the nth initial lower reflective layer include: a nitrogen source of NH3, a gallium source of trimethylgallium or triethylgallium, an n-type doped source of SiH4, a temperature of 1050°C to 1150°C, and a chamber pressure of 200 torr to 250 torr. As n increases, the amount of SiH4 introduced into the reaction chamber is gradually increased.

[0102] The process for forming the nth upper reflective layer includes metal oxide chemical vapor deposition (MOCVD). The parameters for forming the nth upper reflective layer include: using NH3 as the nitrogen source, trimethylgallium or triethylgallium as the gallium source, a temperature of 1050°C to 1150°C, and a chamber pressure of 200 torr to 250 torr.

[0103] After the electrochemical reaction, a local area of ​​any nth lower reflective layer is hollowed out to form a hole. Different doping concentrations of the nth lower reflective layer will result in different porosity. The higher the doping concentration of the nth lower reflective layer, the larger the hole will be after the electrochemical reaction, thus realizing a structural design with gradually changing porosity.

[0104] refer to Figure 4 An electron injection layer 130 is formed on the side of the reflective structure A opposite to the semiconductor substrate layer 100.

[0105] In this embodiment, the method further includes: forming a second bonding layer 120 on the side of the reflective structure A away from the semiconductor substrate layer 100 before forming the electron injection layer 130; and forming a buffer structure 140 on the side of the electron injection layer 130 away from the semiconductor substrate layer 100.

[0106] The method of forming the buffer structure 140 includes: forming at least one buffer unit group, the buffer unit group including at least one buffer unit, the buffer unit including a stacked lower buffer layer and an upper buffer layer; the lower buffer layer in any buffer unit is located below the upper buffer layer, and the conductor strip of the upper buffer layer is higher than the conductor strip of the lower buffer layer.

[0107] The process for forming the electron injection layer 130 includes metal oxide chemical vapor deposition (MOCVD). The material of the electron injection layer 130 is GaN doped with n-type conductive particles. The parameters for forming the electron injection layer 130 include: the nitrogen source used is NH3, the gallium source used is trimethylgallium or triethylgallium, the n-type doping source is SiH4, the temperature is 1050°C to 1150°C, and the chamber pressure is 200 torr to 300 torr.

[0108] The process for forming the second bonding layer 120 includes metal-oxide chemical vapor deposition (MOCVD). The second bonding layer 120 is undoped single-crystal GaN. The parameters for forming the second bonding layer 120 include: using NH3 as the nitrogen source, trimethylgallium or triethylgallium as the gallium source, a temperature of 800°C to 900°C, and a chamber pressure of 200 torr to 300 torr.

[0109] The process for forming the buffer structure 140 includes metal-oxide chemical vapor deposition (MOCVD). When the buffer structure 140 includes a first buffer unit group and a second buffer unit group, the parameters for forming the first lower buffer layer in the first buffer unit include: using a gallium source including trimethylgallium or triethylgallium, using a nitrogen source including NH3, using an indium source including trimethylindium, a temperature of 750°C to 850°C, and a chamber pressure of 150 torr to 250 torr. The parameters for forming the first upper buffer layer in the first buffer unit include: using a gallium source including trimethylgallium or triethylgallium, using a nitrogen source including NH3, a temperature of 750°C to 850°C, and a chamber pressure of 150 torr to 250 torr. The parameters for forming the second lower buffer layer in the second buffer unit include: using a gallium source including trimethylgallium or triethylgallium, using a nitrogen source including NH3, using an indium source including trimethylindium, a temperature of 800°C to 900°C, and a chamber pressure of 150 torr to 250 torr. The parameters for forming the second upper buffer layer in the second buffer unit include: using a gallium source including trimethylgallium or triethylgallium, using a nitrogen source including NH3, a temperature of 700°C to 800°C, and a chamber pressure of 150 torr to 250 torr.

[0110] refer to Figure 5 A light-emitting layer 150 is formed on the side of the reflective structure A opposite to the semiconductor substrate layer 100.

[0111] In this embodiment, a light-emitting layer 150 is formed on the side of the buffer structure opposite to the semiconductor substrate layer 100.

[0112] The method of forming the light-emitting layer 150 includes: forming a plurality of stacked sub-light-emitting groups, each sub-light-emitting group including a stacked quantum well layer and a barrier layer, wherein the quantum well layer in any one sub-light-emitting group is located below the barrier layer.

[0113] The conduction band of the lower buffer layer is higher than that of the quantum well layer.

[0114] In one embodiment, the quantum well layer contains the same elements as the lower buffer layer; the barrier layer and the upper buffer layer are made of the same material.

[0115] In one embodiment, the thickness of the lower buffer layer is greater than the thickness of the quantum well layer, and the thickness of the upper buffer layer is less than the thickness of the barrier layer.

[0116] refer to Figure 6An electron blocking layer 160 is formed on the side of the light-emitting layer 150 away from the semiconductor substrate layer 100; a hole transport layer 170 is formed on the side of the electron blocking layer 160 away from the light-emitting layer 150; and a contact layer 180 is formed on the side of the hole transport layer 170 away from the light-emitting layer 150.

[0117] The descriptions of the electron blocking layer 160, hole transport layer 170, and contact layer 180 are as described above and will not be repeated here.

[0118] Obviously, the above embodiments are merely illustrative examples for clear explanation and are not intended to limit the implementation. Those skilled in the art will recognize that other variations or modifications can be made based on the above description. It is neither necessary nor possible to exhaustively list all possible implementations here. However, obvious variations or modifications derived therefrom are still within the scope of protection of this invention.

Claims

1. An LED device, characterized in that, include: Semiconductor substrate layer; A reflective structure located on the semiconductor substrate layer, the reflective structure comprising a first group of reflective units to an Nth group of reflective units stacked sequentially from bottom to top, where N is an integer greater than or equal to 2; any nth group of reflective units includes at least one nth reflective unit, the nth reflective unit includes an nth lower reflective layer and an nth upper reflective layer; the refractive index of the nth lower reflective layer is less than the refractive index of the nth upper reflective layer; n is an integer greater than or equal to 1 and less than or equal to N; the doping concentration of the first lower reflective layer in the first group of reflective units to the Nth lower reflective layer in the Nth group of reflective units increases progressively, and each of the first lower reflective layer to the Nth lower reflective layer has a hole, with the porosity of the first lower reflective layer to the Nth lower reflective layer increasing progressively; The light-emitting layer is located on the side of the reflective structure away from the semiconductor substrate. The light-emitting layer includes several stacked sub-light-emitting groups. Each sub-light-emitting group includes a stacked quantum well layer and a barrier layer. The quantum well layer in any sub-light-emitting group is located below the barrier layer. An electron injection layer located between the reflective structure and the light-emitting layer; A buffer structure located between the electron injection layer and the light-emitting layer, the buffer structure comprising at least one buffer unit group, the buffer unit group comprising at least one buffer unit, the buffer unit comprising a stacked lower buffer layer and an upper buffer layer; the lower buffer layer in any buffer unit is located below the upper buffer layer, the conduction band of the upper buffer layer is higher than the conduction band of the lower buffer layer, and the conduction band of the lower buffer layer is higher than the conduction band of the quantum well layer.

2. The LED device according to claim 1, characterized in that, The materials of the first lower reflective layer to the Nth lower reflective layer are all GaN doped with n-type conductive ions, and the materials of the first upper reflective layer to the Nth upper reflective layer are all single-crystal undoped GaN.

3. The LED device according to claim 1, characterized in that, The size of the holes in the first lower reflective layer to the Nth lower reflective layer increases progressively.

4. The LED device according to claim 1, characterized in that, Any nth group of reflective units includes three to five stacked nth reflective units.

5. The LED device according to claim 4, characterized in that, N equals 5, and the reflective structure includes a first group of reflective units, a second group of reflective units, a third group of reflective units, a fourth group of reflective units, and a fifth group of reflective units stacked sequentially from bottom to top; the doping concentration increases from the first lower reflective layer to the fifth lower reflective layer.

6. The LED device according to claim 5, characterized in that, The doping concentration of the first lower reflective layer in the first group of reflective units is 9E17atom / cm². 3 ~2E18atom / cm 3 The doping concentration of the second lower reflective layer in the second set of reflective units is 3E18 atom / cm³. 3 ~5E18atom / cm 3 The doping concentration of the third lower reflective layer in the third group of reflective units is 6E18 atom / cm³. 3 ~8E18atom / cm 3 The doping concentration of the fourth lower reflective layer in the fourth group of reflective units is 9E18 atom / cm³. 3 ~2E19atom / cm 3 The doping concentration of the fifth lower reflective layer in the fifth group of reflective units is 3E19 atom / cm³. 3 ~5E19atom / cm 3 .

7. The LED device according to claim 1, characterized in that, The thicknesses of the first lower reflective layer to the Nth lower reflective layer are equal, and the thicknesses of the first upper reflective layer to the Nth upper reflective layer are equal.

8. The LED device according to claim 7, characterized in that, The thickness of the first lower reflective layer to the Nth lower reflective layer is 20nm~150nm; the thickness of the first upper reflective layer to the Nth upper reflective layer is 20nm~80nm.

9. The LED device according to claim 1, characterized in that, Also includes: A first bonding layer located between the semiconductor substrate layer and the reflective structure.

10. The LED device according to claim 9, characterized in that, The first connecting layer includes an amorphous undoped first buffer layer, a monocrystalline undoped second buffer layer, and a monocrystalline undoped third buffer layer stacked sequentially from bottom to top. The lattice constant of the second buffer layer is smaller than that of the first and third buffer layers.

11. The LED device according to claim 10, characterized in that, The first buffer layer is made of undoped amorphous GaN, the second buffer layer is made of undoped monocrystalline AlN, and the third buffer layer is made of undoped monocrystalline GaN.

12. The LED device according to claim 1, characterized in that, Also includes: The second connecting layer is located between the reflective structure and the electron injection layer.

13. The LED device according to claim 12, characterized in that, The second bonding layer is undoped single-crystal GaN.

14. The LED device according to claim 12, characterized in that, The quantum well layer contains the same elements as the lower buffer layer; the barrier layer and the upper buffer layer are made of the same material.

15. The LED device according to claim 14, characterized in that, Both the lower buffer layer and the light-emitting layer contain In, and the In content in the lower buffer layer is less than the In content in the quantum well layer.

16. The LED device according to claim 15, characterized in that, The buffer structure includes multiple buffer unit groups. For the multiple buffer unit groups, in the direction from bottom to top, the In content in the lower buffer layer of the multiple buffer unit groups increases.

17. The LED device according to claim 15, characterized in that, The buffer unit group includes several stacked buffer units, and the In content of the lower buffer layer in the same buffer unit group is the same.

18. The LED device according to claim 14 or 15, characterized in that, The thickness of the lower buffer layer is greater than the thickness of the quantum well layer, and the thickness of the upper buffer layer is less than the thickness of the barrier layer.

19. A method for fabricating an LED device, characterized in that, include: Provide semiconductor substrate layer; A reflective structure is formed on the semiconductor substrate. The method of forming the reflective structure includes forming a first group of reflective units to an Nth group of reflective units stacked sequentially from bottom to top, where N is an integer greater than or equal to 2. The step of forming any nth group of reflective units includes forming at least one nth reflective unit, which includes an nth lower reflective layer and an nth upper reflective layer. The refractive index of the nth lower reflective layer is less than the refractive index of the nth upper reflective layer. n is an integer greater than or equal to 1 and less than or equal to N. The doping concentration of the first lower reflective layer in the first group of reflective units to the Nth lower reflective layer in the Nth group of reflective units increases. All of the first lower reflective layers to the Nth lower reflective layers have holes, and the porosity of the first lower reflective layer to the Nth lower reflective layer increases. A light-emitting layer is formed on the side of the reflective structure away from the semiconductor substrate. The method of forming the light-emitting layer includes: forming a plurality of stacked sub-light-emitting groups, each sub-light-emitting group including a stacked quantum well layer and a barrier layer, wherein the quantum well layer in any sub-light-emitting group is located below the barrier layer. Before forming the light-emitting layer, an electron injection layer is formed on the side of the reflective structure away from the semiconductor substrate, and a buffer structure is formed on the side of the electron injection layer away from the semiconductor substrate. The method of forming the buffer structure includes: forming at least one buffer unit group, the buffer unit group including at least one buffer unit, the buffer unit including a stacked lower buffer layer and an upper buffer layer; the lower buffer layer in any buffer unit is located below the upper buffer layer, the conduction band of the upper buffer layer is higher than the conduction band of the lower buffer layer, and the conduction band of the lower buffer layer is higher than the conduction band of the quantum well layer.

20. The method for preparing an LED device according to claim 19, characterized in that, Also includes: Before forming the reflective structure, a first bonding layer is formed on the semiconductor substrate layer; After the first bonding layer is formed, the first bonding layer is located between the reflective structure and the semiconductor substrate layer.

21. The method for preparing an LED device according to claim 20, characterized in that, The step of forming the first interlayer includes: sequentially depositing an amorphous undoped first buffer layer, a monocrystalline undoped second buffer layer, and a monocrystalline undoped third buffer layer on the semiconductor substrate, wherein the lattice constant of the second buffer layer is smaller than the lattice constants of the first and third buffer layers.

22. The method for preparing an LED device according to claim 19, characterized in that, Also includes: Before forming the electron injection layer, a second bonding layer is formed on the side of the reflective structure opposite to the semiconductor substrate.

23. The method for preparing an LED device according to claim 22, characterized in that, The quantum well layer contains the same elements as the lower buffer layer; the barrier layer and the upper buffer layer are made of the same material.

24. The method for preparing an LED device according to claim 22, characterized in that, The thickness of the lower buffer layer is greater than the thickness of the quantum well layer, and the thickness of the upper buffer layer is less than the thickness of the barrier layer.

25. The method for preparing an LED device according to claim 19, characterized in that, The steps of forming the reflective structure include: sequentially forming a first group of initial reflective units to an Nth group of initial reflective units on a semiconductor substrate layer; the step of forming any nth group of initial reflective units includes forming at least one nth initial reflective unit, the nth initial reflective unit including an nth initial lower reflective layer and an nth upper reflective layer; immersing the first group of initial reflective units to the Nth group of initial reflective units in an electrolyte; the first initial lower reflective layer to the Nth initial lower reflective layer undergoes an electrochemical reaction with the electrolyte, such that any nth initial lower reflective layer forms an nth lower reflective layer, and any nth initial reflective unit forms an nth reflective unit, and any nth group of initial reflective units forms an nth group of reflective units.

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