LED epitaxial structure and preparation method thereof

Abstract

The application provides an LED epitaxial structure and a preparation method thereof. The LED epitaxial structure comprises, from bottom to top, a substrate, a bottom buffer layer, an N-type semiconductor layer, an active layer and a P-type semiconductor layer. The active layer comprises a first multiple quantum well structure, a second multiple quantum well structure and a third multiple quantum well structure which are stacked in sequence. The first multiple quantum well structure, the second multiple quantum well structure and the third multiple quantum well structure are all periodic structures formed by the growth of well layers and barrier layers alternately. The barrier layer of the first multiple quantum well structure is a structure layer containing an Al component. The barrier layer of the second multiple quantum well structure is a gallium nitride structure layer. The barrier layer of the third multiple quantum well structure is a structure layer containing an In component. The design of the barrier layer of the active layer can not only enhance the carrier confinement effect of the active layer, slow down the electron migration rate and prevent electron overflow, but also increase the hole injection of the active layer and improve the radiation recombination efficiency, thereby improving the light efficiency.

Description

Technical Field

[0001] This invention relates to the field of semiconductor technology, and in particular to an LED epitaxial structure and its fabrication method. Background Technology

[0002] The application and development of blue, green, amber (between yellow and brown, with a wavelength of around 579.3 nm), and even red light emitted by gallium nitride (GaN)-based light-emitting diodes (LEDs) are attracting increasing attention from enterprises and researchers. GaN-based LEDs often use GaN / InGaN as the active layer. However, the high In content in the InGaN active layer and the large lattice mismatch with GaN create a huge piezoelectric field in the active layer, enhancing polarization, tilting the band structure, and separating the spatial distribution of electrons and holes. This leads to the quantum Stark effect (QCSE), reducing radiative recombination efficiency and affecting light emission. Furthermore, due to their small mass and fast migration speed, electrons easily overflow into the P-type semiconductor layer, while holes have a large mass and slow migration speed, resulting in extremely low injection efficiency into the active layer, thus affecting the luminous efficacy of the LED.

[0003] Therefore, it is necessary to design an LED epitaxial structure to improve radiative recombination efficiency and thus enhance luminous efficacy. Summary of the Invention

[0004] The purpose of this invention is to provide an LED epitaxial structure and its preparation method to improve the radiative recombination efficiency of LEDs, thereby enhancing luminous efficacy.

[0005] To achieve the above and other related objectives, the present invention provides an LED epitaxial structure comprising, from bottom to top: a substrate, a bottom buffer layer, an N-type semiconductor layer, an active layer, and a P-type semiconductor layer. The active layer comprises a first multiple quantum well structure, a second multiple quantum well structure, and a third multiple quantum well structure stacked sequentially. The first, second, and third multiple quantum well structures are all periodic structures formed by alternating growth of well layers and barrier layers. The barrier layer of the first multiple quantum well structure is an Al-containing structural layer, the barrier layer of the second multiple quantum well structure is a gallium nitride structural layer, and the barrier layer of the third multiple quantum well structure is an In-containing structural layer.

[0006] Optionally, in the LED epitaxial structure, the barrier layer of the first multi-quantum-well structure is made of Al. x Ga 1-x The values ​​of N and x range from 0.02 to 0.05, and x gradually decreases along the growth direction of the first multi-quantum-well structure.

[0007] Optionally, in the LED epitaxial structure, the material of the third multiple quantum well structure includes In. y Ga1-y The values ​​of N and y range from 0.01 to 0.02, and y gradually increases along the growth direction of the third multi-quantum well structure.

[0008] Optionally, in the LED epitaxial structure, the number of cycles of the first multi-quantum well structure > the number of cycles of the second multi-quantum well structure > the number of cycles of the third multi-quantum well structure.

[0009] Optionally, in the LED epitaxial structure, the sum of the number of periods of the first multiple quantum well structure, the second multiple quantum well structure, and the third multiple quantum well structure is an integer between 6 and 20.

[0010] Optionally, in the LED epitaxial structure, the thickness of the single-layer barrier in the first multi-quantum well structure is greater than the thickness of the single-layer barrier in the second multi-quantum well structure, which is greater than the thickness of the single-layer barrier in the third multi-quantum well structure.

[0011] Optionally, in the LED epitaxial structure, the thickness of the single-layer barrier in the first multiple quantum well structure is 11nm to 13nm, the thickness of the single-layer barrier in the second multiple quantum well structure is 10nm to 11nm, and the thickness of the single-layer barrier in the third multiple quantum well structure is 8nm to 10nm.

[0012] Optionally, in the LED epitaxial structure, the barrier layer in the first multiple quantum well structure is doped with Si, and the Si doping concentration is 5E16cm⁻¹. -3 ~5E17cm -3 The barrier layer in the third multiple quantum well structure is doped with Mg, and the Mg doping concentration is 5E16cm⁻¹. -3 ~5E17cm -3 .

[0013] Optionally, in the LED epitaxial structure, each well layer in the active layer includes a quantum well preparation layer, an intermediate quantum well layer, and a quantum well cap layer stacked sequentially, wherein the quantum well preparation layer is an InN layer, the intermediate quantum well layer and the quantum well cap layer are both InGaN layers, and the In composition of the intermediate quantum well layer is greater than the In composition of the quantum well cap layer.

[0014] Optionally, in the LED epitaxial structure, the material of the intermediate quantum well layer includes In. a Ga 1-a N, and the value of a ranges from 0.08 to 0.15, and the material of the quantum well cap layer includes In. b Ga 1-b N, and the value of b ranges from 0.05 to 0.07.

[0015] Optionally, in the LED epitaxial structure, the thickness of the quantum well preparation layer is 0.3nm to 0.5nm, the thickness of the intermediate quantum well layer is 2nm to 4nm, and the thickness of the quantum well cap layer is 0.3nm to 0.5nm.

[0016] Optionally, in the LED epitaxial structure, the active layer further includes an intermediate buffer layer, which is located between the N-type semiconductor layer and the first multiple quantum well structure. The intermediate buffer layer includes a front multiple quantum well structure or a combined structure formed by a gallium nitride layer and a front multiple quantum well structure.

[0017] Optionally, in the LED epitaxial structure, the active layer further includes a final barrier layer, which is located between the third multiple quantum well structure and the P-type semiconductor layer. The material of the final barrier layer includes at least one of AlN, AlGaN, and AlGaInN.

[0018] Optionally, in the LED epitaxial structure, the LED epitaxial structure further includes an unintentionally doped layer located between the bottom buffer layer and the N-type semiconductor layer, and the material of the unintentionally doped layer includes GaN.

[0019] Optionally, in the LED epitaxial structure, the P-type semiconductor layer includes a low-temperature P-type layer, an electron blocking layer, a P-type current spreading layer, and a P-type ohmic contact layer stacked sequentially.

[0020] To achieve the above and other related objectives, the present invention also provides a method for fabricating an LED epitaxial structure, comprising the following steps:

[0021] Provide a substrate;

[0022] A bottom buffer layer, an N-type semiconductor layer, and an active layer are sequentially grown on the substrate. The active layer includes a first multiple quantum well structure, a second multiple quantum well structure, and a third multiple quantum well structure stacked sequentially. The first multiple quantum well structure, the second multiple quantum well structure, and the third multiple quantum well structure are all periodic structures formed by alternating growth of well layers and barrier layers. The barrier layer of the first multiple quantum well structure is a structure layer containing Al, the barrier layer of the second multiple quantum well structure is a gallium nitride structure layer, and the barrier layer of the third multiple quantum well structure is a structure layer containing In.

[0023] A P-type semiconductor layer is grown on the active layer.

[0024] Optionally, in the method for fabricating the LED epitaxial structure, the barrier layer of the first multi-quantum-well structure is made of Al. x Ga 1-xThe values ​​of N and x range from 0.02 to 0.05, and x gradually decreases along the growth direction of the first multi-quantum-well structure.

[0025] Optionally, in the method for fabricating the LED epitaxial structure, the material of the third multiple quantum well structure includes In. y Ga 1-y The values ​​of N and y range from 0.01 to 0.02, and y gradually increases along the growth direction of the third multi-quantum well structure.

[0026] Optionally, in the method for fabricating the LED epitaxial structure, the number of cycles in the first multi-quantum well structure > the number of cycles in the second multi-quantum well structure > the number of cycles in the third multi-quantum well structure.

[0027] Optionally, in the method for fabricating the LED epitaxial structure, the sum of the number of periods of the first multiple quantum well structure, the second multiple quantum well structure, and the third multiple quantum well structure is an integer between 6 and 20.

[0028] Optionally, in the method for fabricating the LED epitaxial structure, the thickness of the single-layer barrier in the first multi-quantum well structure is greater than the thickness of the single-layer barrier in the second multi-quantum well structure, which is greater than the thickness of the single-layer barrier in the third multi-quantum well structure.

[0029] Optionally, in the method for fabricating the LED epitaxial structure, the thickness of the single-layer barrier in the first multiple quantum well structure is 11 nm to 13 nm, the thickness of the single-layer barrier in the second multiple quantum well structure is 10 nm to 11 nm, and the thickness of the single-layer barrier in the third multiple quantum well structure is 8 nm to 10 nm.

[0030] Optionally, in the method for fabricating the LED epitaxial structure, Si is doped in the barrier layer of the first multiple quantum well structure, and the Si doping concentration is 5E16cm⁻¹. -3 ~5E17cm -3 The barrier layer in the third multiple quantum well structure is doped with Mg, and the Mg doping concentration is 5E16cm⁻¹. -3 ~5E17cm -3 .

[0031] Optionally, in the method for fabricating the LED epitaxial structure, each well layer in the active layer includes a quantum well preparation layer, an intermediate quantum well layer, and a quantum well cap layer stacked sequentially, wherein the quantum well preparation layer is an InN layer, the intermediate quantum well layer and the quantum well cap layer are both InGaN layers, and the In composition of the intermediate quantum well layer is greater than the In composition of the quantum well cap layer.

[0032] Optionally, in the method for fabricating the LED epitaxial structure, the material of the intermediate quantum well layer includes In. a Ga 1-a N, and the value of a ranges from 0.08 to 0.15, and the material of the quantum well cap layer includes In. b Ga 1-b N, and the value of b ranges from 0.05 to 0.07.

[0033] Optionally, in the method for fabricating the LED epitaxial structure, the thickness of the quantum well preparation layer is 0.3 nm to 0.5 nm, the thickness of the intermediate quantum well layer is 2 nm to 4 nm, and the thickness of the quantum well cap layer is 0.3 nm to 0.5 nm.

[0034] Optionally, in the method for fabricating the LED epitaxial structure, the active layer further includes an intermediate buffer layer, which is located between the N-type semiconductor layer and the first multiple quantum well structure. The intermediate buffer layer includes a front multiple quantum well structure or a combined structure formed by a gallium nitride layer and a front multiple quantum well structure.

[0035] Optionally, in the method for fabricating the LED epitaxial structure, the active layer further includes a final barrier layer, which is located between the third multiple quantum well structure and the P-type semiconductor layer. The material of the final barrier layer includes at least one of AlN, AlGaN, and AlGaInN.

[0036] Optionally, in the method for fabricating the LED epitaxial structure, the method further includes forming an unintentionally doped layer between the bottom buffer layer and the N-type semiconductor layer, and the material of the unintentionally doped layer includes GaN.

[0037] Optionally, in the method for fabricating the LED epitaxial structure, growing the P-type semiconductor layer on the active layer includes forming a low-temperature P-type layer, an electron blocking layer, a P-type current spreading layer, and a P-type ohmic contact layer that are stacked sequentially on the active layer.

[0038] Compared with the prior art, the technical solution of the present invention has the following beneficial effects:

[0039] The active layer of the LED epitaxial structure provided by this invention includes a first multiple quantum well structure, a second multiple quantum well structure, and a third multiple quantum well structure stacked sequentially. The barrier layer of the first multiple quantum well structure is an Al-based layer, the barrier layer of the second multiple quantum well structure is a gallium nitride layer, and the barrier layer of the third multiple quantum well structure is an In-based layer. This barrier layer design not only reduces piezoelectric polarization caused by large differences in lattice constants between the active and well layers, thus reducing the QCSE effect, but also enhances the confinement of electrons by the Al-based barrier layer of the first multiple quantum well structure, while the In-based barrier layer of the third multiple quantum well structure has a low barrier that facilitates hole injection, improving radiative recombination efficiency and ultimately enhancing luminous efficacy.

[0040] Secondly, the active layer of the LED epitaxial structure provided by this invention comprises a quantum well preparation layer, an intermediate quantum well layer, and a quantum well cap layer stacked sequentially. The quantum well preparation layer is an InN layer, and the intermediate quantum well layer and the quantum well cap layer are both InGaN layers. The InN in the quantum well preparation layer has a low energy band, which facilitates the formation of localized quantum well states, enhances the confinement of charge carriers by the active layer, and can reduce the QCSE effect. The intermediate quantum well layer is a majority carrier confinement region where electrons and holes form radiative recombination emission. The quantum well cap layer can effectively alleviate the stress between the well layer and the barrier layer, improving the crystal quality.

[0041] Moreover, by combining the barrier layer design and the well layer design of the active layer, this invention can not only improve the confinement of carriers by the active layer, prevent electron overflow, and increase hole injection, but also reduce the piezoelectric field on the well layer, improve the QCSE effect, enhance the probability of electron and hole distribution overlap, and improve optical efficiency.

[0042] Finally, the active layer in the LED epitaxial structure provided by this invention grows a final barrier layer after the third quantum well structure is grown, which can prevent electron leakage, increase the confinement of electrons by the active layer, improve radiative recombination efficiency, and enhance luminous efficacy. Attached Figure Description

[0043] Figure 1 This is a schematic diagram of an LED epitaxial structure according to an embodiment of the present invention;

[0044] Figure 2 This is a schematic diagram of the structure of a first multi-quantum well structure according to an embodiment of the present invention;

[0045] Figure 3 This is a schematic diagram of the structure of a second multiple quantum well structure according to an embodiment of the present invention;

[0046] Figure 4 This is a schematic diagram of the third multi-quantum well structure according to an embodiment of the present invention;

[0047] Figure 5 This is a flowchart of a method for preparing an LED epitaxial structure according to an embodiment of the present invention;

[0048] Figures 1-5 middle,

[0049] 10-Substrate, 11-Bottom buffer layer, 12-Unintentionally doped layer, 13-N-type semiconductor layer, 14-Intermediate buffer layer, 15-First multiple quantum well structure, 151-First barrier layer, 152-First well layer, 16-Second multiple quantum well structure, 161-Second barrier layer, 162-Second well layer, 17-Third multiple quantum well structure, 171-Third barrier layer, 172-Third well layer, 18-Final barrier layer, 19-Low-temperature P-type layer, 20-Electron blocking layer, 21-P-type current spreading layer, 22-P-type ohmic contact layer. Detailed Implementation

[0050] The LED epitaxial structure and its fabrication method proposed in this invention will be further described in detail below with reference to the accompanying drawings and specific embodiments. The advantages and features of this invention will become clearer from the following description. It should be noted that the drawings are all in a very simplified form and use non-precise proportions, and are only used to facilitate and clarify the illustration of the embodiments of this invention.

[0051] To improve radiative recombination efficiency, this invention provides an LED epitaxial structure. Please refer to [link to relevant documentation]. Figure 1 The LED epitaxial structure, from bottom to top, includes: a substrate 10, a bottom buffer layer 11, an N-type semiconductor layer 13, an active layer, and a P-type semiconductor layer.

[0052] The active layer may include a first multi-quantum well structure 15, a second multi-quantum well structure 16, and a third multi-quantum well structure 17 stacked sequentially, and the first multi-quantum well structure 15, the second multi-quantum well structure 16, and the third multi-quantum well structure 17 are all periodic structures formed by alternating well layers and barrier layers. For example, Figure 2 The first multi-quantum-well structure 15 is a periodic structure formed by alternating growth of a first barrier layer 151 and a first well layer 152. Figure 3 The second multiple quantum well structure 16 is a periodic structure formed by the alternating growth of the second barrier layer 161 and the second well layer 162. Figure 4 The third multi-quantum well structure 17 described herein is a periodic structure formed by alternating growth of the third barrier layer 171 and the third well layer 172.

[0053] The barrier layer (first barrier layer 151) of the first multiple quantum well structure 15 is an Al-based structural layer, the barrier layer (second barrier layer 161) of the second multiple quantum well structure 16 is a gallium nitride structural layer, and the barrier layer (third barrier layer 171) of the third multiple quantum well structure 17 is an In-based structural layer. This embodiment, through the barrier layer design of the active layer, not only reduces piezoelectric polarization caused by the large difference in lattice constants between the active and well layers, thus reducing the QCSE effect, but also, the fact that the barrier layer of the first multiple quantum well structure 15 is an Al-based structural layer enhances the confinement of electrons by the active layer, while the barrier layer of the third multiple quantum well structure 17 is an In-based structural layer with a low barrier, which facilitates hole injection, thereby improving radiative recombination efficiency and enhancing luminous efficacy.

[0054] Each well layer in the active layer comprises a quantum well preparation layer, an intermediate quantum well layer, and a quantum well cap layer stacked sequentially. Specifically, the first well layer 152, the second well layer 162, and the third well layer 172 have identical structures, each consisting of a quantum well preparation layer, an intermediate quantum well layer, and a quantum well cap layer stacked sequentially. In this embodiment, the quantum well preparation layer is preferably an InN layer, and the intermediate quantum well layer and the quantum well cap layer are preferably InGaN layers. The In composition of the intermediate quantum well layer is preferably greater than that of the quantum well cap layer. In this embodiment, the InN band structure of the quantum well preparation layer is relatively low, which can form localized quantum well states, thereby enhancing the confinement of carriers by the active layer, reducing the QCSE effect, and increasing the probability of spatial overlap between electrons and holes. The lower In composition of the quantum well cap layer compared to the intermediate quantum well layer helps alleviate stress between the well layer and the barrier layer, improving crystal quality.

[0055] The active layer may further include an intermediate buffer layer 14, which is located between the first multiple quantum well structure 15 and the N-type semiconductor layer 13. The intermediate buffer layer 14 prepares the multiple quantum well structure for growing the active layer and helps to alleviate stress between the substrate 10 and the epitaxial structure. Further, the intermediate buffer layer 14 may be a front multiple quantum well structure or a combination of a gallium nitride layer and a front multiple quantum well structure, wherein the gallium nitride layer in the combination structure is close to the N-type semiconductor layer 13, and the front multiple quantum well structure is close to the first multiple quantum well structure 15.

[0056] The active layer may further include a final barrier layer 18, which is located between the third multiple quantum well structure 17 and the P-type semiconductor layer. The final barrier layer 18 is used to prevent electron leakage, increase the confinement of electrons by the active layer, and prevent electrons from overflowing into the P-type semiconductor layer and causing nonradiative recombination.

[0057] Furthermore, the LED epitaxial structure may also include an unintentionally doped layer 12 located between the bottom buffer layer 11 and the N-type semiconductor layer 13. The unintentionally doped layer 12 can optimize epitaxial growth, obtain high crystal quality, and can serve as a roughening layer for vertical chip processes. Moreover, the N-type semiconductor layer 13 grown on the unintentionally doped layer 12 has high quality and good expansion capability.

[0058] See Figure 5 The above-described method for fabricating the LED epitaxial structure is illustrated. In this embodiment, the fabrication process of the LED epitaxial structure may include any one of MOCVD (metal-organic chemical vapor deposition), molecular beam epitaxy, HVPE (hydride vapor phase epitaxy), plasma-assisted chemical vapor deposition, and sputtering, preferably MOCVD.

[0059] The method for preparing the LED epitaxial structure specifically includes the following steps:

[0060] Step S1: Provide substrate 10;

[0061] Step S2: A bottom buffer layer 11, an N-type semiconductor layer 13, and an active layer are grown on the substrate 10. The active layer includes a first multiple quantum well structure 15, a second multiple quantum well structure 16, and a third multiple quantum well structure 17 stacked sequentially. The first multiple quantum well structure 15, the second multiple quantum well structure 16, and the third multiple quantum well structure 17 are all periodic structures formed by alternating growth of well layers and barrier layers. The barrier layer of the first multiple quantum well structure 15 is a structure layer containing Al, the barrier layer of the second multiple quantum well structure 16 is a gallium nitride structure layer, and the barrier layer of the third multiple quantum well structure 17 is a structure layer containing In.

[0062] Step S3: Grow a P-type semiconductor layer on the active layer.

[0063] Step S1 is performed, providing a substrate 10. The substrate 10 can be made of materials such as sapphire, silicon, silicon carbide, gallium nitride, or InGaN. The flip-chip substrate needs to be able to transmit light emitted from the active layer; to improve light extraction efficiency, a patterned transparent substrate, such as a patterned sapphire substrate, is preferred.

[0064] Step S2 is performed to grow a bottom buffer layer 11 on the substrate 10 to mitigate lattice mismatch and thermal mismatch between the substrate 10 and the epitaxial structure. This reduces defects and dislocations in the epitaxial structure caused by surface defects of the substrate 10 or by lattice mismatch or thermal mismatch between the substrate 10 and the epitaxial structure, and provides a high-quality growth surface for the structural layer above the bottom buffer layer 11.

[0065] The material of the bottom buffer layer 11 can be at least one selected from AlN, GaN, AlGaN, InN, InGaN, and AlGaInN. Further, the material of the bottom buffer layer 11 is preferably GaN. In this embodiment, the thickness of the bottom buffer layer 11 is preferably in the range of 10 nm to 20 nm, for example, 15 nm.

[0066] After the step of growing the bottom buffer layer 11 on the substrate 10, the method for fabricating the LED epitaxial structure may further include: growing an unintentionally doped layer 12 on the bottom buffer layer 11, that is, the LED epitaxial structure may further include an unintentionally doped layer 12 located between the bottom buffer layer 11 and the N-type semiconductor.

[0067] In this embodiment, the thickness of the unintentionally doped layer 12 is preferably in the range of 2 μm to 5 μm. The material of the unintentionally doped layer 12 is preferably GaN, but is not limited thereto. The unintentionally doped layer 12 in this embodiment can optimize epitaxial growth, obtain high crystal quality, and can be used as a roughening layer for vertical chip design. Furthermore, high-quality N-type semiconductor 13 with good scalability can be obtained by growing on the unintentionally doped layer 12.

[0068] After the step of growing an unintentionally doped layer 12 on the bottom buffer layer 11, the N-type semiconductor layer 13 is grown on the unintentionally doped layer 12. In this embodiment, the N-type semiconductor layer 13 serves as an ohmic contact and current spreading layer. The N-type semiconductor layer 13 can be a conventional N-type layer, and its material is preferably at least one of GaN and AlGaN, but is not limited thereto. The N-type semiconductor layer 13 is doped with an n-type dopant, and the n-type dopant is preferably Si, but is not limited thereto. The Si doping concentration in the N-type semiconductor layer 13 is preferably greater than 1E19 cm⁻¹. -3 The thickness of the N-type semiconductor layer 13 is preferably in the range of 0.5 μm to 3 μm, for example, 2 μm.

[0069] After the step of growing the N-type semiconductor layer 13 on the unintentionally doped layer 12, an active layer is grown on the N-type semiconductor layer 13. The active layer may include a first multiple quantum well structure 15, a second multiple quantum well structure 16, and a third multiple quantum well structure 17. Furthermore, the active layer may also include an intermediate buffer layer 14 located between the N-type semiconductor layer 13 and the first multiple quantum well structure 15, and a final barrier layer 18 located between the third multiple quantum well structure 17 and the P-type semiconductor layer. Therefore, in this embodiment, after the step of growing the N-type semiconductor layer 13 on the unintentionally doped layer 12, an intermediate buffer layer 14 is grown on the N-type semiconductor layer 13. The intermediate buffer layer 14 prepares for the growth of the multiple quantum well structure of the active layer and helps to alleviate stress between the substrate and the epitaxial structure.

[0070] The intermediate buffer layer 14 in this embodiment may include a front multiple quantum well structure or a combination structure formed by a gallium nitride layer and a front multiple quantum well structure. Preferably, the intermediate buffer layer 14 is composed of a front multiple quantum well structure, which is a periodic structure formed by alternating growth of well layers and barrier layers, with a period number of w. That is, the front multiple quantum well structure is formed by alternating stacking of w pairs of well layers and barrier layers, and the value of w is preferably in the range of 5 to 20.

[0071] In this embodiment, the barrier layer in the pre-multiple quantum well structure is preferably made of GaN, but is not limited thereto. The thickness of the single-layer barrier layer in the pre-multiple quantum well structure is preferably in the range of 3 nm to 10 nm, for example, 8 nm. The barrier layer in the pre-multiple quantum well structure is preferably doped with Si, and further, the Si doping concentration is preferably in the range of 5E16cm⁻¹. -3 ~1E18cm -3 The material of the well layer in the aforementioned multi-quantum-well structure is preferably In. m Ga 1-m N, where m is preferably in the range of 0.01 to 0.03, and the thickness of the single-layer well layer is preferably in the range of 1.5 nm to 3 nm, for example 2 nm.

[0072] After the step of growing the intermediate buffer layer 14 on the N-type semiconductor layer 13, the first multiple quantum well structure 15 is grown on the intermediate buffer layer 14. The first multiple quantum well structure 15 is a periodic structure formed by alternating growth of well layers and barrier layers, with a period number of A, that is, the first multiple quantum well structure 15 is formed by A pairs of well layers and barrier layers stacked alternately. Specifically, the first multiple quantum well structure 15 includes A pairs of first well layers 152 and first barrier layers 151, wherein the value of A is preferably in the range of 3 to 9.

[0073] The barrier layer (first barrier layer 151) of the first multiple quantum well structure 15 is an Al-containing structural layer. The Al content in the barrier layer of the first multiple quantum well structure 15 results in a higher potential barrier, which helps to slow down the electron migration rate and prevent electrons from overflowing from the active layer to the P-type semiconductor layer, thus enhancing the confinement of electrons by the active layer. In this embodiment, the Al content of the barrier layer of the first multiple quantum well structure 15 preferably gradually decreases along the growth direction of the first multiple quantum well structure 15 (from the N-type semiconductor layer 13 to the P-type semiconductor layer), resulting in a gradually lower potential barrier. This facilitates the injection of more holes into all well layers of the active layer, achieving a more uniform distribution of holes within the well layers. It also better releases lattice mismatch stress and thermal stress, thereby improving the crystal quality of the LED epitaxial structure. Furthermore, the material of the first barrier layer 151 of the first multiple quantum well structure 15 is preferably Al. x Ga 1-xN, and the value of x is preferably in the range of 0.02 to 0.05. The thickness of the first barrier layer 151 of the first multi-quantum well structure 15 is preferably 11 nm to 13 nm, for example, 12 nm. In this embodiment, the thicker the first barrier layer 151 of the first multi-quantum well structure 15, the more it can enhance the confinement of electrons by the active layer.

[0074] The first barrier layer 151 of the first multiple quantum well structure 15 is doped with Si, and the Si doping concentration is preferably in the range of 5E16cm. -3 ~5E17cm -3 The first barrier layer 151 of the first multiple quantum well structure 15 can replace Ga by doping with Si, which can reduce the QCSE effect and also provide electrons. In this embodiment, if the Si doping concentration of the first barrier layer 151 of the first multiple quantum well structure 15 is too low, the expected effect will not be achieved, while if the doping concentration is too high, Si will easily enter the first well layer 152, affecting the crystal quality of the active layer.

[0075] Each well layer (first well layer 152) in the first multi-quantum well structure 15 comprises a quantum well preparation layer, an intermediate quantum well layer, and a quantum well cap layer stacked sequentially. That is, the first well layer 152 is composed of a quantum well preparation layer, an intermediate quantum well layer, and a quantum well cap layer stacked sequentially. The quantum well preparation layer is preferably an InN layer, and the intermediate quantum well layer and the quantum well cap layer are both preferably InGaN layers, with the In content of the intermediate quantum well layer preferably being greater than that of the quantum well cap layer. In this embodiment, the growth temperature of the quantum well preparation layer, the intermediate quantum well layer, and the quantum well cap layer is preferably 750°C to 850°C. Further, the growth temperatures of the quantum well preparation layer, the intermediate quantum well layer, and the quantum well cap layer are preferably equal.

[0076] The material of the quantum well preparation layer is preferably InN; the material of the intermediate quantum well layer is preferably InN. a Ga 1-a N, and the value of a is preferably in the range of 0.08 to 0.15; the quantum well cap layer is preferably In. b Ga 1-b N, and the value of b is preferably in the range of 0.05 to 0.07. In this embodiment, the InN in the quantum well preparation layer has a low band structure, and In easily aggregates to form localized states in the quantum well, thus enhancing the confinement of carriers by the active layer, thereby increasing the probability of overlap in the spatial distribution of electrons and holes and reducing the QCSE effect; the intermediate quantum well layer is a majority carrier confinement region, where electrons and holes form radiative recombination luminescence; and the InGaN in the quantum well layer cap layer has a lower In composition than the InGaN in the intermediate quantum well layer, which helps to alleviate the stress between the well layer and the barrier layer and improve the crystal quality.

[0077] In this embodiment, since InN has a small bandgap width and can be used as a deep well to increase the confinement effect of the active layer on carriers, but InN has a large lattice constant, which will cause a large compressive stress. Therefore, the thickness of the quantum well preparation layer needs to be very thin, which can be 1 to 2 atomic layer thicknesses. Further, the thickness of the quantum well preparation layer is preferably 0.3 nm to 0.5 nm.

[0078] The middle quantum well layer serves as a light-emitting quantum well, and its thickness is preferably 2 nm to 4 nm, which helps the electrons and holes to be evenly distributed in the active layer and increases the probability of radiative recombination. The InGaN of the quantum well layer cap can help relieve the stress between the barrier layer and the well layer, and can be designed to be 1 to 2 atomic layer thicknesses. Further, the thickness of the quantum well layer cap is preferably 0.3 nm to 0.5 nm.

[0079] After the step of growing the first multi-quantum well structure 15 on the middle buffer layer 14, a second multi-quantum well structure 16 is grown on the first multi-quantum well structure 15. The second multi-quantum well structure 16 is a periodic structure formed by the alternating growth of well layers and barrier layers, and the number of periods is B, that is, the second multi-quantum well structure 16 is composed of B pairs of well layers and barrier layers stacked alternately. Specifically, the second multi-quantum well structure 16 includes B pairs of second well layers 162 and second barrier layers 161, preferably B < A, and the value range of B is preferably 2 to 7.

[0080] The barrier layer (second barrier layer 161) of the second multi-quantum well structure 16 is a gallium nitride structure layer, that is, the material of the barrier layer of the second multi-quantum well structure 16 is GaN. In this embodiment, the second multi-quantum well structure 16 may not be doped, may be doped with Si or may be doped with Mg. Preferably, the second multi-quantum well structure 16 is not doped. The thickness of a single second barrier layer 161 in the second multi-quantum well structure 16 is less than the thickness of a single first barrier layer 151 in the first multi-quantum well structure 15. Further, the thickness of a single second barrier layer 161 of the second multi-quantum well structure 16 is preferably 10 nm to 11 nm, for example, 10 nm.

[0081] The well layer of the second multi-quantum well structure 16, that is, the second well layer 162, may be composed of a quantum well preparation layer, a middle quantum well layer, and a quantum well layer cap stacked in sequence. The structure and growth conditions of the second well layer 162 in this embodiment are preferably the same as those of the first well layer 152.

[0082] After the step of growing the second quantum well structure 16 on the first quantum well structure 15, a third quantum well structure 17 is grown on the second quantum well structure 16. The third quantum well structure 17 is a periodic structure formed by alternating well layers and barrier layers, with a period of C, meaning the third quantum well structure 17 is formed by alternating stacks of C pairs of well layers and barrier layers. Specifically, the third quantum well structure 17 includes a C pair of third well layers 172 and a third barrier layer 171, where the value of C preferably ranges from 1 to 4. In this embodiment, preferably, the number of periods in the first quantum well structure 15 > the number of periods in the second quantum well structure 16 > the number of periods in the third quantum well structure 17, i.e., A > B > C. The first multiple quantum well structure 15 has a relatively large number of cycles, which slows down the electron migration rate and increases the confinement of electrons by the active layer. Furthermore, the transition barrier from the first barrier layer 151 of the first multiple quantum well structure 15 to the second barrier layer 161 of the second multiple quantum well structure 16 and then to the third barrier layer 171 of the third multiple quantum well structure 17 gradually decreases. This helps holes not only occupy well layers near the P-type semiconductor layer but also occupy many other well layers, even those near the N-type semiconductor layer 13, thus facilitating hole occupation of all well layers in the active layer. Further, the total number of cycles of the well layers and barriers in the first multiple quantum well structure 15, the second multiple quantum well structure 16, and the third multiple quantum well structure 17 is an integer between 6 and 20. For example, the first multiple quantum well structure 15 has 6 cycles, the second multiple quantum well structure 16 has 4 cycles, and the third multiple quantum well structure 17 has 2 cycles.

[0083] The barrier layer (third barrier layer 171) of the third multiple quantum well structure 17 is an In-containing structural layer. Because the In-containing barrier is low, the barrier layer of the third multiple quantum well structure 17 can reduce the blocking effect on holes, making it easier for holes to migrate to more well layers. Simultaneously, the barrier layer of the third multiple quantum well structure 17 can alleviate the compressive stress between the barrier layer and the well layers. In this embodiment, the In content of the barrier layer of the third multiple quantum well structure 17 preferably gradually increases along the growth direction of the third multiple quantum well structure 17. A higher In content indicates a lower barrier, meaning a weaker blocking effect on holes, making it easier for holes to migrate to more well layers, and also better relieving the compressive stress between the barrier layer and the well layers. Furthermore, the material of the barrier layer of the third multiple quantum well structure 17 is preferably In. y Ga 1-yN, and the value of y is preferably in the range of 0.01 to 0.02. Since a thicker barrier layer near the N-type semiconductor layer 13 can enhance the confinement of electrons by the active layer, and a thinner barrier layer near the P-type semiconductor layer can reduce the barrier layer's obstruction of holes, increasing the probability of holes migrating to more well layers, it helps holes occupy all well layers of the active layer (i.e., the first well layer 152, the second well layer 162, and the third well layer 172) and improves the distribution of holes in each well layer. Therefore, it is preferred that the thickness of the first barrier layer 151 in the first multi-quantum well structure 15 is greater than the thickness of the second barrier layer 161 in the second multi-quantum well structure 16, which is greater than the thickness of the third barrier layer 171 in the third multi-quantum well structure 17. In this embodiment, the first barrier layer 151 of the first multiple quantum well structure 15 is the thickest barrier layer among the first multiple quantum well structure 15, the second multiple quantum well structure 16, and the third multiple quantum well structure 17. This helps to slow down electron migration and make electrons more evenly distributed in each well layer, rather than concentrated in one or a few well layers. The In composition of the third multiple quantum well structure 17 gradually increases along the growth direction of the third multiple quantum well structure 17 (from the N-type semiconductor layer 13 to the P-type semiconductor layer), and the third barrier layer 171 of the third multiple quantum well structure 17 is the thinnest barrier layer among the first multiple quantum well structure 15, the second multiple quantum well structure 16, and the third multiple quantum well structure 17. This helps to increase hole injection and improve hole injection efficiency, so that holes are not only distributed in one well layer near the P-type semiconductor layer, but also in more well layers, and even in well layers near the N-type semiconductor layer 13, thereby increasing the recombination probability of electrons and holes and improving radiative recombination efficiency. Furthermore, the thickness of the third barrier layer 171 of the single layer of the third multi-quantum well structure 17 is preferably 8 nm to 10 nm, for example, 9 nm.

[0084] The barrier layer of the third multiple quantum well structure 17 is preferably doped with Mg. Too little Mg doping will not achieve the desired effect, while too much Mg doping can easily allow doping sources to enter the third well layer 172, affecting the crystal quality of the active layer. Therefore, in this embodiment, the preferred Mg doping concentration range is 5E16cm⁻¹. -3 ~5E17cm -3 In this embodiment, the barrier layer of the third multiple quantum well structure 17 can be replaced by Ga by doping with Mg, which can provide holes and increase hole mobility.

[0085] The well layer of the third multi-quantum well structure 17, namely the third well layer 172, can be composed of a quantum well preparation layer, an intermediate quantum well layer, and a quantum well layer cap layer stacked sequentially. In this embodiment, the structure and growth conditions of the third well layer 172 are preferably the same as those of the first well layer 152 and the second well layer 162. That is, the growth temperature of each well layer in the active layer in this embodiment is preferably 750°C to 850°C, and each well layer in the active layer includes a quantum well preparation layer, an intermediate quantum well layer, and a quantum well layer cap layer stacked sequentially.

[0086] The barrier design of the active layer in this embodiment not only reduces piezoelectric polarization caused by the large difference in lattice constants between the active and well layers, thus reducing the QCSE effect, but also features a high barrier in the first quantum well structure, which enhances the confinement of electrons by the active layer, and a low barrier in the third quantum well structure, which facilitates hole injection. Therefore, the barrier design of the active layer can improve radiative recombination efficiency and enhance luminous efficacy. Furthermore, this embodiment employs different barrier designs, with the barrier gradually decreasing in potential and thickness along the epitaxial growth direction. The high barrier and thick thickness near the N-type semiconductor layer 13 help slow down the electron migration rate and prevent electron overflow from the active layer, while the low barrier and thin thickness near the P-type semiconductor layer facilitate hole injection and improve hole injection efficiency. Simultaneously, the InN quantum well preparation layer design in the well layer of the active layer in this embodiment, a "deep well," confines carriers within the well layer, and the intermediate quantum well layer alleviates stress between the barrier and well layers, reduces the polarization field, improves the distribution of electrons and holes, and enhances luminous efficacy. Therefore, the combination of barrier layer design and well layer design of the active layer in this embodiment can not only improve the confinement of charge carriers by the active layer, prevent electron overflow, and increase hole injection, but also reduce the piezoelectric field on the well layer, improve the QCSE effect, enhance the probability of electron and hole distribution overlap, and improve optical efficiency.

[0087] After the step of growing the third quantum well structure 17 on the second quantum well structure 16, a final barrier layer 18 is grown on the third quantum well structure 17. The final barrier layer 18 is used to block electron overflow caused by rapid electron migration, that is, the final barrier layer 18 can prevent electron leakage, increase the confinement of electrons by the active layer, improve radiative recombination efficiency, and enhance luminous efficiency.

[0088] The material of the final barrier layer 18 can be at least one of AlN, AlGaN, or AlGaInN, but is not limited thereto. That is, the final barrier layer 18 can be a single-layer structure of AlN, AlGaN, or AlGaInN, or a combination of at least two of them. Further, the material of the final barrier layer 18 is preferably AlN, and the thickness of the final barrier layer 18 is preferably 1 nm to 5 nm.

[0089] Step S3 is performed to grow a P-type semiconductor layer on the active layer. In this embodiment, the P-type semiconductor layer may include a low-temperature P-type layer 19, an electron blocking layer 20, a P-type current spreading layer 21, and a P-type ohmic contact layer 22 stacked sequentially.

[0090] Therefore, after the step of growing the final barrier layer 18 on the third multi-quantum well structure 17, a low-temperature P-type layer 19 is grown on the final barrier layer 18. In this embodiment, the material of the low-temperature P-type layer 19 is preferably GaN, but not limited thereto. The growth temperature of the low-temperature P-type layer 19 is preferably 0°C to 100°C lower than the growth temperature of the well layer of the active layer to prevent damage to the well layer. The thickness of the low-temperature P-type layer 19 is preferably in the range of 20 nm to 40 nm, for example, 30 nm.

[0091] After the step of growing a low-temperature P-type layer 19 on the final barrier layer 18, an electron blocking layer 20 is grown on the low-temperature P-type layer 19. The electron blocking layer 20 can be made of at least one of AlGaN, AlGaInN, and InGaN; that is, the electron blocking layer 20 can be a single-layer structure of AlGaN, AlGaInN, or InGaN, or a combination of at least two of them, to form a high bandgap, suppress electron overflow migration to the P-type current extension layer 21, and avoid non-radiative recombination. Furthermore, in this embodiment, the electron blocking layer 20 is preferably made of Al... q Ga 1-q N, and the value of q is preferably in the range of 0.1 to 0.3. The thickness of the electron blocking layer 20 is preferably in the range of 10 nm to 40 nm, for example, 30 nm.

[0092] After the step of growing the electron blocking layer 20 on the low-temperature P-type layer 19, a P-type current spreading layer 21 is grown on the electron blocking layer 20. The P-type current spreading layer 21 is mainly used for current spreading, and can also be used to fill small defects or surface irregularities formed during epitaxial growth to obtain a smooth and flat epitaxial structure surface. The material of the P-type current spreading layer 21 can be at least one of GaN and AlGaN, but is not limited thereto. Further, the material of the P-type current spreading layer 21 is preferably GaN. The P-type current spreading layer 21 can be doped with Mg or Zn, but is not limited thereto. Further, the P-type current spreading layer 21 is doped with Mg, and the Mg doping concentration is preferably in the range of 1E19cm⁻¹. -3 ~1E20cm -3 In this embodiment, the thickness of the P-type current spreading layer 21 is preferably in the range of 5nm to 50nm, for example, 20nm.

[0093] After the step of growing a P-type current spreading layer 21 on the electron blocking layer 20, a P-type ohmic contact layer 22 is grown on the P-type current spreading layer 21. The material of the P-type ohmic contact layer 22 can be at least one of GaN, AlGaN, and InGaN, but is not limited thereto. Further, the material of the P-type ohmic contact layer 22 is preferably GaN. The P-type ohmic contact layer 22 may be doped with Mg or Zn to form an ohmic contact with the electrode. Further, the P-type ohmic contact layer 22 is doped with Mg; preferably, the Mg doping concentration is greater than 1E19cm⁻¹. -3 In this embodiment, the thickness of the P-type ohmic contact layer 22 is preferably in the range of 3nm to 10nm, for example, 5nm.

[0094] In summary, the active layer of the LED epitaxial structure provided by this invention comprises a first multiple quantum well structure, a second multiple quantum well structure, and a third multiple quantum well structure stacked sequentially. The barrier layer of the first multiple quantum well structure is an Al-based layer, the barrier layer of the second multiple quantum well structure is a gallium nitride layer, and the barrier layer of the third multiple quantum well structure is an In-based layer. This barrier layer design not only reduces piezoelectric polarization caused by large differences in lattice constants between the active and well layers, thus reducing the QCSE effect, but also enhances the confinement of electrons by the Al-based barrier layer of the first multiple quantum well structure. Furthermore, the In-based barrier layer of the third multiple quantum well structure has a low barrier, which facilitates hole injection, thereby improving radiative recombination efficiency and luminous efficacy.

[0095] Secondly, the active layer of the LED epitaxial structure provided by this invention comprises a quantum well preparation layer, an intermediate quantum well layer, and a quantum well cap layer stacked sequentially. The quantum well preparation layer is an InN layer, and the intermediate quantum well layer and the quantum well cap layer are both InGaN layers. The InN in the quantum well preparation layer has a low energy band, which facilitates the formation of localized quantum well states, enhances the confinement of charge carriers by the active layer, and reduces the QCSE effect. The intermediate quantum well layer is a majority carrier confinement region where electrons and holes form radiative recombination emission. The quantum well cap layer effectively alleviates the stress between the well layer and the barrier layer, improving crystal quality.

[0096] Furthermore, the barrier layer of the first quantum well structure of the present invention can be made of AlGaN, and the Al composition gradually decreases along the growth direction of the first quantum well structure. Moreover, the barrier layer of the first quantum well structure is the thickest among the first, second, and third quantum well structures, which helps to slow down the electron migration speed and make the electrons more evenly distributed in each well layer, rather than concentrated in one or a few well layers. The barrier layer of the third quantum well structure of the present invention can be made of InGaN, and the In composition gradually increases along the growth direction of the third quantum well structure. Moreover, the barrier layer of the third quantum well structure is the thinnest among the first, second, and third quantum well structures, which helps to increase hole injection and improve hole injection efficiency. This allows holes to be distributed not only in one well layer near the P-type semiconductor layer, but also in more well layers, and even in well layers near the N-type semiconductor layer, thereby increasing the recombination probability of electrons and holes and improving radiative recombination efficiency.

[0097] Moreover, by combining the barrier layer design and the well layer design of the active layer, this invention can not only improve the confinement of carriers by the active layer, prevent electron overflow, and increase hole injection, but also reduce the piezoelectric field on the well layer, improve the QCSE effect, enhance the probability of electron and hole distribution overlap, and improve optical efficiency.

[0098] Finally, the active layer in the LED epitaxial structure provided by this invention grows a final barrier layer after the third quantum well structure is grown, which can prevent electron leakage, increase the confinement of electrons in the active region, improve radiative recombination efficiency, and enhance luminous efficacy.

[0099] Furthermore, it is understood that although the present invention has been disclosed above with reference to preferred embodiments, these embodiments are not intended to limit the present invention. For any person skilled in the art, many possible variations and modifications can be made to the technical solutions of the present invention based on the disclosed technical content, or equivalent embodiments can be modified accordingly, without departing from the scope of the present invention. Therefore, any simple modifications, equivalent changes, and modifications made to the above embodiments based on the technical essence of the present invention without departing from the content of the present invention shall still fall within the scope of protection of the present invention.

[0100] Furthermore, it should be understood that the invention is not limited to the specific methods, compounds, materials, manufacturing techniques, uses, and applications described herein, which can vary. It should also be understood that the terminology described herein is used only to describe particular embodiments and not to limit the scope of the invention. It must be noted that the singular forms “a,” “an,” and “the” used herein and in the appended claims include plural bases unless the context clearly indicates otherwise. Thus, for example, a reference to “a step” means a reference to one or more steps, and may include secondary steps. All conjunctions used should be understood in the broadest sense. Therefore, the word “or” should be understood to have the definition of logical “or” rather than logical “exclusive”, unless the context clearly indicates otherwise. Structures described herein will be understood to also refer to functional equivalents of that structure. Language that can be interpreted as approximate should be understood in that way unless the context clearly indicates otherwise.

Claims

1. An LED epitaxial structure, characterized in that, From bottom to top, the structure comprises: a substrate, a bottom buffer layer, an N-type semiconductor layer, an active layer, and a P-type semiconductor layer. The active layer includes a first multiple quantum well structure, a second multiple quantum well structure, and a third multiple quantum well structure stacked sequentially. Each of these structures is a periodic structure formed by alternating well and barrier layers. The barrier layer of the first multiple quantum well structure is an Al-based layer, the barrier layer of the second multiple quantum well structure is a gallium nitride layer, and the barrier layer of the third multiple quantum well structure is an In-based layer. The barrier layer of the first multiple quantum well structure is made of Al. x Ga 1-x N, and x gradually decreases along the growth direction of the first multi-quantum-well structure; the barrier layer of the third multi-quantum-well structure is made of In. y Ga 1-y N, and y gradually increases along the growth direction of the third multi-quantum well structure.

2. The LED epitaxial structure as described in claim 1, characterized in that, The value of x ranges from 0.02 to 0.

05.

3. The LED epitaxial structure as described in claim 1, characterized in that, The value of y ranges from 0.01 to 0.

02.

4. The LED epitaxial structure as described in claim 1, characterized in that, The number of cycles in the first multi-quantum well structure > the number of cycles in the second multi-quantum well structure > the number of cycles in the third multi-quantum well structure.

5. The LED epitaxial structure as described in claim 4, characterized in that, The sum of the period numbers of the first, second, and third multiple quantum well structures is an integer between 6 and 20.

6. The LED epitaxial structure as described in claim 1, characterized in that, The thickness of the single-layer barrier in the first multi-quantum well structure is greater than the thickness of the single-layer barrier in the second multi-quantum well structure, which is greater than the thickness of the single-layer barrier in the third multi-quantum well structure.

7. The LED epitaxial structure as described in claim 6, characterized in that, The thickness of the single-layer barrier in the first multiple quantum well structure is 11 nm to 13 nm, the thickness of the single-layer barrier in the second multiple quantum well structure is 10 nm to 11 nm, and the thickness of the single-layer barrier in the third multiple quantum well structure is 8 nm to 10 nm.

8. The LED epitaxial structure as described in claim 1, characterized in that, The barrier layer in the first multiple quantum well structure is doped with Si, and the Si doping concentration is 5E16cm⁻¹. -3 ~5E17cm -3 The barrier layer in the third multiple quantum well structure is doped with Mg, and the Mg doping concentration is 5E16cm⁻¹. -3 ~5E17cm -3 .

9. The LED epitaxial structure as described in claim 1, characterized in that, Each well layer in the active layer includes a quantum well preparation layer, an intermediate quantum well layer, and a quantum well cap layer stacked sequentially. The quantum well preparation layer is an InN layer, and the intermediate quantum well layer and the quantum well cap layer are both InGaN layers. The In composition of the intermediate quantum well layer is greater than that of the quantum well cap layer.

10. The LED epitaxial structure as described in claim 9, characterized in that, The material of the intermediate quantum well layer includes In. a Ga 1-a N, and the value of a ranges from 0.08 to 0.15, and the material of the quantum well cap layer includes In. b Ga 1-b N, and the value of b ranges from 0.05 to 0.

07.

11. The LED epitaxial structure as described in claim 9, characterized in that, The thickness of the quantum well preparation layer is 0.3 nm to 0.5 nm, the thickness of the intermediate quantum well layer is 2 nm to 4 nm, and the thickness of the quantum well cap layer is 0.3 nm to 0.5 nm.

12. The LED epitaxial structure as described in claim 1, characterized in that, The active layer further includes an intermediate buffer layer, which is located between the N-type semiconductor layer and the first multiple quantum well structure. The intermediate buffer layer includes a front multiple quantum well structure or a combined structure formed by a gallium nitride layer and a front multiple quantum well structure.

13. The LED epitaxial structure as described in claim 1, characterized in that, The active layer further includes a final barrier layer located between the third multiple quantum well structure and the P-type semiconductor layer, wherein the material of the final barrier layer includes at least one of AlN, AlGaN, and AlGaInN.

14. The LED epitaxial structure as described in claim 1, characterized in that, The LED epitaxial structure further includes an unintentionally doped layer located between the bottom buffer layer and the N-type semiconductor layer, and the material of the unintentionally doped layer includes GaN.

15. The LED epitaxial structure as described in claim 1, characterized in that, The P-type semiconductor layer comprises a low-temperature P-type layer, an electron blocking layer, a P-type current spreading layer, and a P-type ohmic contact layer stacked sequentially.

16. A method for fabricating an LED epitaxial structure, characterized in that, Includes the following steps: Provide a substrate; A bottom buffer layer, an N-type semiconductor layer, and an active layer are sequentially grown on the substrate. The active layer comprises a first multiple quantum well structure, a second multiple quantum well structure, and a third multiple quantum well structure stacked sequentially. Each of these structures is a periodic structure formed by alternating well and barrier layers. The barrier layer of the first multiple quantum well structure is an Al-based layer, the barrier layer of the second multiple quantum well structure is a gallium nitride layer, and the barrier layer of the third multiple quantum well structure is an In-based layer. The barrier layer of the first multiple quantum well structure is made of Al. x Ga 1-x N, and x gradually decreases along the growth direction of the first multi-quantum-well structure; the barrier layer of the third multi-quantum-well structure is made of In. y Ga 1-y N, and y gradually increases along the growth direction of the third multi-quantum-well structure; A P-type semiconductor layer is grown on the active layer.

17. The method for preparing an LED epitaxial structure as described in claim 16, characterized in that, The value of x ranges from 0.02 to 0.

05.

18. The method for preparing an LED epitaxial structure as described in claim 16, characterized in that, The value of y ranges from 0.01 to 0.

02.

19. The method for preparing an LED epitaxial structure as described in claim 16, characterized in that, The number of cycles in the first multi-quantum well structure > the number of cycles in the second multi-quantum well structure > the number of cycles in the third multi-quantum well structure.

20. The method for preparing the LED epitaxial structure as described in claim 19, characterized in that, The sum of the period numbers of the first, second, and third multiple quantum well structures is an integer between 6 and 20.

21. The method for preparing the LED epitaxial structure as described in claim 16, characterized in that, The thickness of the single-layer barrier in the first multi-quantum well structure is greater than the thickness of the single-layer barrier in the second multi-quantum well structure, which is greater than the thickness of the single-layer barrier in the third multi-quantum well structure.

22. The method for preparing an LED epitaxial structure as described in claim 21, characterized in that, The thickness of the single-layer barrier in the first multiple quantum well structure is 11 nm to 13 nm, the thickness of the single-layer barrier in the second multiple quantum well structure is 10 nm to 11 nm, and the thickness of the single-layer barrier in the third multiple quantum well structure is 8 nm to 10 nm.

23. The method for preparing an LED epitaxial structure as described in claim 16, characterized in that, The barrier layer in the first multiple quantum well structure is doped with Si, and the Si doping concentration is 5E16cm⁻¹. -3 ~5E17cm -3 The barrier layer in the third multiple quantum well structure is doped with Mg, and the Mg doping concentration is 5E16cm⁻¹. -3 ~5E17cm -3 .

24. The method for preparing an LED epitaxial structure as described in claim 16, characterized in that, Each well layer in the active layer includes a quantum well preparation layer, an intermediate quantum well layer, and a quantum well cap layer stacked sequentially. The quantum well preparation layer is an InN layer, and the intermediate quantum well layer and the quantum well cap layer are both InGaN layers. The In composition of the intermediate quantum well layer is greater than that of the quantum well cap layer.

25. The method for preparing an LED epitaxial structure as described in claim 24, characterized in that, The material of the intermediate quantum well layer includes In. a Ga 1-a N, and the value of a ranges from 0.08 to 0.15, and the material of the quantum well cap layer includes In. b Ga 1-b N, and the value of b ranges from 0.05 to 0.

07.

26. The method for preparing an LED epitaxial structure as described in claim 24, characterized in that, The thickness of the quantum well preparation layer is 0.3 nm to 0.5 nm, the thickness of the intermediate quantum well layer is 2 nm to 4 nm, and the thickness of the quantum well cap layer is 0.3 nm to 0.5 nm.

27. The method for preparing an LED epitaxial structure as described in claim 16, characterized in that, The active layer further includes an intermediate buffer layer, which is located between the N-type semiconductor layer and the first multiple quantum well structure. The intermediate buffer layer includes a front multiple quantum well structure or a combined structure formed by a gallium nitride layer and a front multiple quantum well structure.

28. The method for preparing an LED epitaxial structure as described in claim 16, characterized in that, The active layer further includes a final barrier layer located between the third multiple quantum well structure and the P-type semiconductor layer, wherein the material of the final barrier layer includes at least one of AlN, AlGaN, and AlGaInN.

29. The method for preparing an LED epitaxial structure as described in claim 16, characterized in that, The preparation method further includes forming an unintentionally doped layer between the bottom buffer layer and the N-type semiconductor layer, wherein the material of the unintentionally doped layer includes GaN.

30. The method for preparing an LED epitaxial structure as described in claim 16, characterized in that, Growing the P-type semiconductor layer on the active layer includes forming a low-temperature P-type layer, an electron blocking layer, a P-type current spreading layer, and a P-type ohmic contact layer that are stacked sequentially on the active layer.

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