LED epitaxial structure and preparation method thereof

Abstract

This invention relates to the field of light-emitting diode (LED) technology, and discloses an LED epitaxial structure and its fabrication method. The LED epitaxial structure comprises, in sequence, a substrate, a buffer layer, an N-type semiconductor layer, a low-temperature stress relief layer, an N-type composite epitaxial layer, a multiple quantum well light-emitting layer, a P-type composite epitaxial layer, an electron blocking layer, and a P-type semiconductor layer; the N-type composite epitaxial layer is periodically alternating Al₂O₃. x1 The superlattice layer formed by the GaN layer and the first GaN layer; the P-type composite epitaxial layer is a periodically alternating layer of Al. x2 GaN layer and In y2 The superlattice layer formed by the GaN layer; Al x1 The GaN layer contains several penetrating Al... x1 The first V-shaped hole in the GaN layer, the first GaN layer fills the first V-shaped hole and is located in Al x1 On a GaN layer. Implementing this invention can reduce the stress and defect density of the epitaxial layer material, improve the quality of the multi-quantum-well light-emitting layer, improve the light extraction efficiency of the chip, and thus improve the luminous efficiency of the light-emitting diode.

Description

Technical Field

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

[0002] Light-emitting diodes (LEDs), as a new type of energy-saving and environmentally friendly light source, have received considerable attention in recent years, with many countries regarding LED-related semiconductor lighting as a strategic technology. Through extensive research and experimentation, semiconductor lighting technology has made rapid progress, truly realizing the commercialization of semiconductor lighting. Various types of LEDs are widely used in indication, display, backlighting, and projection fields. These achievements in semiconductor lighting are mainly attributed to advancements in GaN-based LED technology. Compared to other material systems, GaN-based LEDs have significant advantages in both efficiency and reliability.

[0003] To obtain high-brightness LEDs, it is crucial to improve both the internal and external quantum efficiency of the device. Currently, GaN-based LED devices with InGaN quantum wells as the active layer are widely used in various fields. However, due to the lack of suitable homogeneous epitaxial substrates, GaN is typically grown on sapphire, silicon carbide, or silicon substrates with significant lattice mismatch. This lattice mismatch between GaN and the substrate undoubtedly creates numerous dislocation defects, affecting its epitaxial quality. Furthermore, because of the significant lattice mismatch between InGaN and GaN in the quantum well active layer, the InGaN quantum well is subjected to compressive stress from GaN. Both dislocation defects and compressive stress negatively impact LED device performance, thus reducing the internal quantum efficiency. Additionally, while the internal quantum efficiency of blue GaN-based LEDs can reach over 80%, the external quantum efficiency of high-power LED chips is typically only around 40%. One of the main factors limiting the improvement of external quantum efficiency is the low light extraction efficiency of the chip. This is because the refractive index of GaN material (n=2.5) differs greatly from that of air (n=1) and sapphire substrate (n=1.75), resulting in critical angles of total internal reflection at the air-GaN interface and the sapphire substrate-GaN interface being only 23.6° and 44.4°, respectively. Only a small amount of light generated in the active region can escape from the bulk material.

[0004] To improve the light extraction efficiency of chips, the main technical solutions currently used both domestically and internationally include distributed Bragg reflector (DBR) structures, patterned substrate (PSS) technology, surface roughening technology, and photonic crystal technology. PSS requires a high degree of pattern regularity, and given the hardness of sapphire substrates, achieving uniformity and consistency across the entire pattern using either dry or wet etching processes presents challenges. Furthermore, the fabrication process demands sophisticated equipment and advanced technology, leading to high costs. DBR and photonic crystal fabrication processes are relatively complex and costly. Surface roughening technology, employing either dry or wet etching processes, also presents significant challenges.

[0005] Therefore, in order to improve the luminous efficiency and performance of light-emitting diodes, the key is to improve the internal quantum efficiency and light extraction efficiency of the device. Summary of the Invention

[0006] The technical problem to be solved by the present invention is to provide an LED epitaxial structure that can reduce the stress and defect density of the epitaxial layer material, improve the quality of the multi-quantum-well light-emitting layer, improve the light extraction efficiency of the chip, and thus improve the luminous efficiency of the light-emitting diode.

[0007] To solve the above-mentioned technical problems, the first aspect of the present invention provides an LED epitaxial structure, comprising a substrate, a buffer layer, an N-type semiconductor layer, a low-temperature stress relief layer, an N-type composite epitaxial layer, a multi-quantum-well light-emitting layer, a P-type composite epitaxial layer, an electron blocking layer, and a P-type semiconductor layer stacked sequentially. The N-type composite epitaxial layer is an Al layer that has been grown in a periodic alternating pattern. x1 The superlattice layer formed by the GaN layer and the first GaN layer; The multi-quantum-well light-emitting layer is an In-type material that is periodically and alternately grown. y1 The superlattice layer formed by the GaN layer and the second GaN layer; The P-type composite epitaxial layer is an Al layer that has been periodically and alternately grown. x2 GaN layer and In y2 The superlattice layer formed by the GaN layer; Wherein, the Al x1 The GaN layer contains several penetrations through the Al. x1 The first V-shaped hole in the GaN layer, the first GaN layer fills the first V-shaped hole and is located in the Al x1 On the GaN layer.

[0008] As an improvement to the above solution, the Al x2 The GaN layer contains several penetrations through the Al. x2 The second V-shaped hole in the GaN layer, the In y2 The GaN layer fills the second V-shaped hole and is located in the Al. x2On the GaN layer.

[0009] As an improvement to the above scheme, the distribution density of the first V-shaped holes is 1.28 × 10⁻⁶. 7 / cm 2 -6.79×10 12 / cm 2 The diameter of the first V-shaped hole is less than 2 nm.

[0010] As an improvement to the above scheme, the distribution density of the second V-shaped holes is 1.59 × 10⁻⁶. 7 / cm 2 -9.68×10 12 / cm 2 The diameter of the second V-shaped hole is less than 1.8 nm.

[0011] As an improvement to the above scheme, the first GaN layer is a Si-doped GaN layer with a Si doping concentration of 1.28 × 10⁻⁶. 17 / cm 3 -6.97×10 17 / cm 3 ; The second GaN layer is a Si-doped GaN monolayer or GaN multilayer structure, with a Si doping concentration of 1.5 × 10⁻⁶. 17 / cm 3 -8.6×10 17 / cm 3 ; The In y2 The GaN layer is a Mg-doped InGaN layer with a Mg doping concentration of 1.6 × 10⁻⁶. 17 / cm 3 -7.5×10 19 / cm 3 .

[0012] As an improvement to the above scheme, the number of periods of the N-type composite epitaxial layer is 2-20; The Al x1 The GaN layer is an undoped AlGaN layer, where 0.01 ≤ x1 ≤ 0.30. x1 The GaN layer is grown to a thickness of 0.2 nm-2 nm; The thickness of the first GaN layer is 0.3nm-5nm.

[0013] As an improvement to the above scheme, the number of periods of the multi-quantum-well light-emitting layer is 3-16; The In y1The GaN layer is an undoped InGaN monolayer or InGaN multilayer structure, wherein 0.05 ≤ y1 ≤ 0.39; the In y1 The GaN layer thickness ranges from 2.1 nm to 4.8 nm. The growth thickness of the second GaN layer is 5nm-16nm.

[0014] As an improvement to the above scheme, the number of periods of the P-type composite epitaxial layer is 2-30; The Al x2 The GaN layer is an undoped AlGaN layer, where 0.01 ≤ x² ≤ 0.27; the Al x2 The GaN layer thickness ranges from 0.15 nm to 1.8 nm. The In y2 In the GaN layer, 0.003 ≤ y2 ≤ 0.09; the In y2 The GaN layer thickness ranges from 0.28 nm to 4.7 nm.

[0015] A second aspect of the present invention provides a method for preparing the aforementioned LED epitaxial structure, comprising the following steps: (1) Provide a substrate; (2) A buffer layer is sequentially grown on the substrate; (3) An N-type semiconductor layer is grown on the buffer layer; (4) A low-temperature stress relief layer is grown on the N-type semiconductor layer; (5) An N-type composite epitaxial layer is grown on the low-temperature stress relief layer; (6) A multi-quantum-well light-emitting layer is grown on the N-type composite epitaxial layer; (7) A P-type composite epitaxial layer is grown on the multi-quantum-well light-emitting layer; (8) An electron blocking layer is grown on the P-type composite epitaxial layer; (9) A P-type semiconductor layer is grown on the electron blocking layer; The N-type composite epitaxial layer is an Al layer that has been grown in a periodic alternating pattern. x1 The superlattice layer formed by the GaN layer and the first GaN layer; The multi-quantum-well light-emitting layer is an In-type material that is periodically and alternately grown. y1 The superlattice layer formed by the GaN layer and the second GaN layer; The P-type composite epitaxial layer is an Al layer that has been periodically and alternately grown. x2 GaN layer and In y2 The superlattice layer formed by the GaN layer; Wherein, the Al x1 The GaN layer contains several penetrations through the Al. x1The first V-shaped hole in the GaN layer, the first GaN layer fills the first V-shaped hole and is located in the Al x1 On the GaN layer.

[0016] As an improvement to the above solution, the Al x1 The growth temperature of the GaN layer is 780℃-980℃, and the growth pressure is 30 torr-360 torr; the growth temperature of the first GaN layer is 800℃-1080℃, and the growth pressure is 30 torr-360 torr. The In y1 The growth temperature of the GaN layer is 650℃-900℃, and the growth pressure is 30 torr-360 torr; the growth temperature of the second GaN layer is 800℃-980℃, and the growth pressure is 30 torr-360 torr. The Al x2 The GaN layer is grown at a temperature of 780℃-980℃ and a growth pressure of 30 torr-360 torr; the In... y2 The growth temperature of the GaN layer is 750℃-1030℃, and the growth pressure is 30 torr-360 torr.

[0017] Implementing this invention has the following beneficial effects: In this invention, an N-type composite epitaxial layer and a P-type composite epitaxial layer are respectively disposed on the lower and upper sides of the multi-quantum-well light-emitting layer to form a composite structure of N-type composite epitaxial layer-multi-quantum-well light-emitting layer-P-type composite epitaxial layer. This structure can reduce the stress and defect density of the epitaxial layer material, improve the quality of the multi-quantum-well light-emitting layer, enhance the radiative recombination efficiency in the multi-quantum-well light-emitting layer, and significantly increase the proportion of photon efferent material in the multi-quantum-well light-emitting layer, thereby improving the light extraction efficiency of the chip and thus improving the luminous efficiency of the light-emitting diode.

[0018] The first V-shaped hole in the N-type composite epitaxial layer can effectively release the mismatch stress caused by lattice mismatch and thermal mismatch between the sub-layers of the epitaxial material, significantly improve the quality of the epitaxial material, and in the process of multiple merging, the dislocation defects in the material will be continuously deflected and merged, reducing the dislocation density of the epitaxial material, improving the quality of the epitaxial material, and thus improving the radiative recombination efficiency in the multi-quantum-well emitting layer. Attached Figure Description

[0019] Figure 1 : A schematic diagram of an LED epitaxial structure in this invention; Figure 2 : A schematic diagram of the N-type composite epitaxial layer in this invention; Figure 3 : A schematic diagram of the structure of the P-type composite epitaxial layer in this invention.

[0020] Figure reference numerals: 100 - substrate; 200 - buffer layer; 300 - N-type semiconductor layer; 400 - low-temperature stress relief layer; 500 - N-type composite epitaxial layer; 501 - Al x1 GaN layer; 502 - First GaN layer; 600 - Multi-quantum-well emitting layer; 700 - P-type composite epitaxial layer; 701 - Al x2 GaN layer; 702-In y2 GaN layer; 800-electron blocking layer; 900-P-type semiconductor layer. Detailed Implementation

[0021] To make the objectives, technical solutions, and advantages of the present invention clearer, the present invention will be further described in detail below with reference to specific embodiments.

[0022] In the description of this application, it is necessary to understand that the orientation or positional relationship indicated by terms such as "upper", "lower", "top", "bottom", "inner", and "outer" are based on the orientation or positional relationship shown in the accompanying drawings. They are intended only to facilitate the description of the present invention and to simplify the description, and are not intended to indicate or imply that the components 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 present invention.

[0023] The "range" disclosed in this application is defined by a lower limit and an upper limit. A given range is defined by selecting a lower limit and an upper limit, which define the boundaries of the particular range. The range defined in this way can include or exclude endpoints and can be arbitrarily combined; that is, any lower limit can be combined with any upper limit to form a range.

[0024] To address the above problems, the first aspect of this invention provides an LED epitaxial structure, please refer to [link / reference]. Figure 1 It includes a substrate 100, a buffer layer 200, an N-type semiconductor layer 300, a low-temperature stress relief layer 400, an N-type composite epitaxial layer 500, a multi-quantum well light-emitting layer 600, a P-type composite epitaxial layer 700, an electron blocking layer 800, and a P-type semiconductor layer 900 stacked sequentially.

[0025] Please see Figure 2 The N-type composite epitaxial layer 500 is an Al layer that is periodically and alternately grown. x1 A superlattice layer formed by GaN layer 501 and first GaN layer 502; wherein, the Al x1 The GaN layer 501 has several penetrations through the Al x1 The first V-shaped hole in the GaN layer 501, the first GaN layer 502 fills the first V-shaped hole and is located in the Al x1 On GaN layer 501; The multi-quantum-well light-emitting layer 600 is a periodically alternating layer of In. y1 The superlattice layer formed by the GaN layer and the second GaN layer; The P-type composite epitaxial layer 700 is an Al layer that is periodically and alternately grown. x2 GaN layer 701 and In y2 The superlattice layer is formed by GaN layer 702.

[0026] In this invention, an N-type composite epitaxial layer 500 and a P-type composite epitaxial layer 700 are respectively disposed on the lower and upper sides of the multi-quantum-well light-emitting layer 600, forming a composite structure of N-type composite epitaxial layer 500-multi-quantum-well light-emitting layer 600-P-type composite epitaxial layer 700. This can reduce the stress and defect density of the epitaxial layer material, improve the quality of the multi-quantum-well light-emitting layer 600, enhance the radiative recombination efficiency in the multi-quantum-well light-emitting layer 600, and significantly increase the proportion of photon efferent material in the multi-quantum-well light-emitting layer 600, thereby improving the light extraction efficiency of the chip and thus improving the luminous efficiency of the light-emitting diode.

[0027] The first V-shaped hole is provided in the N-type composite epitaxial layer 500, which can effectively release the mismatch stress caused by lattice mismatch and thermal mismatch between the sub-layers of the epitaxial material, significantly improve the quality of the epitaxial material, and in the process of multiple merging, the dislocation defects in the material will be continuously deflected and merged, reducing the dislocation density of the epitaxial material and improving the quality of the epitaxial material, thereby improving the radiative recombination efficiency of the multi-quantum-well emitting layer 600.

[0028] Preferably, the first V-shaped hole is in Al x1 The first V-shaped holes are uniformly distributed within the GaN layer 501, with a distribution density of 1.28 × 10⁻⁶. 7 / cm 2 -6.79×10 12 / cm 2 The aperture of the first V-shaped hole is less than 2 nm. Controlling the distribution density of the first V-shaped hole can achieve a better balance between dislocation interception and merging. If the distribution density of the first V-shaped hole is too low, it cannot effectively deflect and merge penetrating dislocations extending from the epitaxial layer. A large number of dislocations will directly enter the multi-quantum-well light-emitting layer 600, becoming non-radiative recombination centers and severely reducing the internal quantum efficiency. If the distribution density of the first V-shaped hole is too high, it may lead to local stress concentration, causing microcracks or affecting the continuity of the epitaxial layer. Moreover, at this time, the spacing of the V-shaped holes is too small, and during the merging process, new small-angle grain boundaries or stacking faults may be generated due to lateral growth collisions, introducing new defects and reducing crystal quality. For example, the distribution density of the first V-shaped hole is 1.28 × 10⁻⁶. 7 / cm 2 1.28×108 / cm 2 1.28×10 9 / cm 2 1.28×10 10 / cm 2 1.28×10 11 / cm 2 1.28×10 12 / cm 2 6.79×10 12 / cm 2 However, it is not limited to this. Understandably, the lower limit of the aperture of the first V-shaped hole can be the smallest value less than 2nm that can be achieved by existing technology. For example, the aperture of the first V-shaped hole is 1nm-2nm.

[0029] Further, please refer to Figure 3 The Al x2 The GaN layer 701 has several penetrations through the Al x2 The second V-shaped hole in the GaN layer 701, the In y2 GaN layer 702 fills the second V-shaped hole and is located in the Al x2 On the GaN layer 701, it can be further deflected and merged continuously during multiple growth processes to release the mismatch stress caused by lattice mismatch and thermal mismatch between the sub-layers of the epitaxial material, reduce the dislocation density of the epitaxial layer material, improve the quality of the epitaxial material, further reduce the in-plane total internal reflection of the semiconductor material, and increase the proportion of photon efflux material in the active region.

[0030] In addition, with several penetrating Al x1 The synergy between the N-type composite epitaxial layer 500 and the first V-shaped hole of the GaN layer 501 can reduce the band bending phenomenon caused by the piezoelectric polarization effect of the InGaN material in the multi-quantum-well emitting layer 600 and the P-type composite epitaxial layer 700, thereby increasing the coupling degree between the electron and hole wave functions in the multi-quantum-well emitting layer 600 and further improving the radiative recombination efficiency in the multi-quantum-well emitting layer 600. Simultaneously, the N-type composite epitaxial layer 500 and the P-type composite epitaxial layer 700 are made of porous AlGaN material, which can reduce in-plane total internal reflection of the semiconductor material, increase the proportion of photon efferent material in the multi-quantum-well emitting layer 600, and further improve the light extraction efficiency of the chip.

[0031] Furthermore, the second V-shaped hole in the Al x2 The second V-shaped holes are uniformly distributed within the GaN layer 701, with a distribution density of 1.59 × 10⁻⁶. 7 / cm 2 -9.68×10 12 / cm 2The aperture of the second V-shaped hole is less than 1.8 nm. Controlling the distribution density of the second V-shaped hole can achieve a better balance between dislocation interception and merging. If the distribution density of the second V-shaped hole is too low, it cannot effectively deflect and merge penetrating dislocations extending from the epitaxial layer. A large number of dislocations will directly pass through the multi-quantum-well light-emitting layer 600, forming strong non-radiative recombination centers, which will seriously reduce the internal quantum efficiency. If the distribution density of the second V-shaped hole is too high, the lateral growth capability of InGaN is weak, and the dense small V-shaped holes are difficult to merge effectively, which can easily leave micro-grooves or unfilled pores on the surface, and instead introduce new scattering centers.

[0032] For example, the distribution density of the second V-shaped holes is 1.59 × 10⁻⁶. 7 / cm 2 1.59×10 8 / cm 2 1.59×10 9 / cm 2 1.59×10 10 / cm 2 1.59×10 11 / cm 2 1.59×10 12 / cm 2 9.68×10 12 / cm 2 However, it is not limited to this. Understandably, the lower limit of the aperture of the second V-shaped hole can be the smallest value less than 1.8 nm that can be achieved by existing technology. For example, the aperture of the first V-shaped hole is 1 nm to 1.8 nm.

[0033] Specifically, the number of periods in the N-type composite epitaxial layer 500 is 2-20; the Al x1 GaN layer 501 is an AlGaN layer without intentional doping, and the first GaN layer 502 is a Si-doped GaN layer that can provide some electrons to the multi-quantum-well light-emitting layer 600. By controlling the doping type and concentration of GaN material in the N-type composite epitaxial layer 500, the distribution and concentration of holes in the multi-quantum-well light-emitting layer 600 can be controlled to improve the matching degree of electron-hole concentration in the region of the multi-quantum-well light-emitting layer 600 and improve the brightness and luminous efficacy of the LED device.

[0034] Furthermore, the Al x1 In GaN layer 501, 0.01 ≤ x1 ≤ 0.30; the exemplary x1 can be 0.01, 0.05, 0.10, 0.15, 0.20, 0.25, or 0.30, but is not limited to these.

[0035] Furthermore, in some specific and preferred embodiments, the Si doping concentration in the first GaN layer 502 is 1.28 × 10⁻⁶. 17 / cm 3 -6.97×10 17 / cm 3 An example of Si doping concentration is 1.28 × 10⁻⁶. 17 / cm 3 2.28×10 17 / cm 3 3.28×10 17 / cm 3 4.28×10 17 / cm 3 5.28×10 17 / cm 3 6.28×10 17 / cm 3 6.97×10 17 / cm 3 However, it is not limited to this.

[0036] Furthermore, the Al x1 The GaN layer 501 has a growth thickness of 0.2nm-2nm. Exemplary growth thicknesses can be 0.2nm, 0.5nm, 0.75nm, 1nm, 1.25nm, 1.5nm, 1.75nm, or 2nm, but are not limited to these. The first GaN layer 502 has a growth thickness of 0.3nm-5nm. Exemplary growth thicknesses can be 0.3nm, 0.5nm, 0.75nm, 1nm, 1.25nm, 1.5nm, 1.75nm, 2nm, 2.25nm, 2.5nm, 2.75nm, 3nm, 3.25nm, 3.5nm, 3.75nm, 4nm, 4.25nm, 4.5nm, 4.75nm, or 5nm, but are not limited to these.

[0037] Specifically, the number of periods in the multi-quantum-well light-emitting layer 600 is 3-16; wherein, the In y1 The GaN layer is an InGaN monolayer structure or an InGaN multilayer structure without intentional doping, and the second GaN layer is a Si-doped GaN monolayer structure or a GaN multilayer structure.

[0038] Furthermore, the In y1 In the GaN layer, 0.05 ≤ y1 ≤ 0.39. For example, y1 can be 0.05, 0.1, 0.15, 0.2, 0.25, 0.3, 0.35, or 0.39, but is not limited to these values.

[0039] Furthermore, the Si doping concentration in the second GaN layer is 1.5 × 10⁻⁶.17 / cm 3 -8.6×10 17 / cm 3 For example, the doping concentration of Si can be 1.5 × 10⁻⁶. 17 / cm 3 3.5×10 17 / cm 3 5.5×10 17 / cm 3 7.5×10 17 / cm 3 8.6×10 17 / cm 3 However, it is not limited to this.

[0040] Furthermore, the In y1 The GaN layer has a growth thickness of 2.1nm-4.8nm, with exemplary growth thicknesses of 2.1nm, 2.5nm, 3nm, 3.5nm, 4nm, 4.5nm, and 4.8nm, but is not limited to these. The second GaN layer has a growth thickness of 5nm-16nm, with exemplary growth thicknesses of 5nm, 5.5nm, 6nm, 6.5nm, 7nm, 7.5nm, 8nm, 8.5nm, 9nm, 9.5nm, 10nm, 10.5nm, 11nm, 11.5nm, 12nm, 12.5nm, 13nm, 13.5nm, 14nm, 14.5nm, 15nm, 15.5nm, and 16nm, but is not limited to these.

[0041] Specifically, the number of periods in the P-type composite epitaxial layer 700 is 2-30, wherein the Al x2 GaN layer 701 is an AlGaN layer that is not intentionally doped, and the In y2 The GaN layer 702 is a Mg-doped InGaN layer that can provide some holes to the multi-quantum-well light-emitting layer 600. By controlling the doping type and concentration of the InGaN material in the P-type composite epitaxial layer 700, the distribution and concentration of electrons in the multi-quantum-well light-emitting layer 600 can be controlled. Combined with the Si-doped first GaN layer 502, the matching degree of electron-hole concentration in the region of the multi-quantum-well light-emitting layer 600 is further improved, thereby improving the brightness and luminous efficacy of the LED device.

[0042] Furthermore, the Al x2 In GaN layer 701, 0.01 ≤ x2 ≤ 0.27. For example, x2 can be 0.01, 0.05, 0.10, 0.15, 0.20, 0.25, or 0.27, but is not limited to these values.

[0043] Furthermore, the In y2In the GaN layer 702, 0.003 ≤ y2 ≤ 0.09, and the Mg doping concentration is 1.6 × 10⁻⁶. 17 / cm 3 -7.5×10 19 / cm 3 For example, y2 can be 0.003, 0.005, 0.009, 0.01, 0.02, 0.03, 0.04, 0.05, 0.06, 0.07, 0.08, or 0.09, but is not limited to these values; the doping concentration of Mg can be 1.6 × 10⁻⁶. 17 / cm 3 3.6×10 17 / cm 3 5.6×10 17 / cm 3 7.6×10 17 / cm 3 9.6×10 17 / cm 3 1.6×10 18 / cm 3 3.6×10 18 / cm 3 5.6×10 18 / cm 3 7.6×10 18 / cm 3 9.6×10 18 / cm 3 1.6×10 19 / cm 3 3.6×10 19 / cm 3 5.6×10 19 / cm 3 7.5×10 19 / cm 3 However, it is not limited to this.

[0044] Furthermore, the Al x2 The GaN layer 701 has a growth thickness of 0.15nm-1.8nm. Exemplary growth thicknesses can be 0.15nm, 0.3nm, 0.5nm, 0.75nm, 1nm, 1.25nm, 1.5nm, 1.75nm, and 1.8nm, but are not limited to these. The In... y2 The GaN layer 702 has a growth thickness of 0.28nm-4.7nm, and can be 0.28nm, 0.3nm, 0.5nm, 1nm, 1.5nm, 2nm, 2.5nm, 3nm, 3.5nm, 4nm, 4.5nm, or 4.7nm, but is not limited to these.

[0045] A second aspect of the present invention provides a method for preparing the aforementioned LED epitaxial structure, comprising the following steps: (1) Provide a substrate 100; (2) A buffer layer 200 is sequentially grown on the substrate 100; (3) An N-type semiconductor layer 300 is grown on the buffer layer 200; (4) A low-temperature stress relief layer 400 is grown on the N-type semiconductor layer 300; (5) An N-type composite epitaxial layer 500 is grown on the low-temperature stress relief layer 400; (6) A multi-quantum-well light-emitting layer 600 is grown on the N-type composite epitaxial layer 500; (7) A P-type composite epitaxial layer 700 is grown on the multi-quantum-well light-emitting layer 600; (8) An electron blocking layer 800 is grown on the P-type composite epitaxial layer 700; (9) A P-type semiconductor layer 900 is grown on the electron blocking layer 800; The N-type composite epitaxial layer 500 is an Al layer that is periodically and alternately grown. x1 The superlattice layer formed by GaN layer 501 and first GaN layer 502; the multi-quantum-well light-emitting layer 600 is a periodically alternating In... y1 The superlattice layer formed by the GaN layer and the second GaN layer; the P-type composite epitaxial layer 700 is a periodically alternating layer of Al. x2 GaN layer 701 and In y2 The superlattice layer formed by GaN layer 702; Wherein, the Al x1 The GaN layer 501 has several penetrations through the Al x1 The first V-shaped hole in the GaN layer 501, the first GaN layer 502 fills the first V-shaped hole and is located in the Al x1 On GaN layer 501.

[0046] In some specific and preferred embodiments, the Al x1 The growth temperature of GaN layer 501 is 780℃-980℃, and the growth pressure is 30 torr-360 torr; the growth temperature of the first GaN layer 502 is 800℃-1080℃, and the growth pressure is 30 torr-360 torr. In some specific and preferred embodiments, the In y1 The growth temperature of the GaN layer is 650℃-900℃, and the growth pressure is 30 torr-360 torr; the growth temperature of the second GaN layer is 800℃-980℃, and the growth pressure is 30 torr-360 torr.

[0047] In some specific and preferred embodiments, the Al x2 The GaN layer 701 is grown at a temperature of 780℃-980℃ and a growth pressure of 30 torr-360 torr; the In... y2 The growth temperature of GaN layer 702 is 750℃-1030℃, and the growth pressure is 30 torr-360 torr.

[0048] Understandably, the substrate 100 can be selected from sapphire substrate, silicon carbide substrate or silicon substrate; the buffer layer 200, N-type semiconductor layer 300, low temperature stress relief layer 400, electron blocking layer 800 and P-type semiconductor layer 900 are all grown using existing processes and materials, and will not be further described in this invention.

[0049] The present invention will be further described below with reference to specific embodiments: Example 1 This embodiment provides an LED epitaxial structure, including a substrate, a buffer layer, an N-type semiconductor layer, a low-temperature stress relief layer, an N-type composite epitaxial layer, a multi-quantum-well light-emitting layer, a P-type composite epitaxial layer, an electron blocking layer, and a P-type semiconductor layer stacked sequentially. The N-type composite epitaxial layer is composed of periodically alternating Al layers. x1 The superlattice layer formed by the GaN layer and the first GaN layer has a period number of 10. Among them, Al x1 The GaN layer contains several penetrating Al... x1 The first V-shaped hole in the GaN layer, the first GaN layer fills the first V-shaped hole and is located in Al x1 On the GaN layer, the distribution density of the first V-shaped void is 3.28 × 10⁻⁶. 10 / cm 2 The pore size is 1.5 nm; Al x1 The GaN layer is an undoped AlGaN layer, where x1 = 0.15, Al x1 The GaN layer has a growth thickness of 1.1 nm; the first GaN layer has a growth thickness of 1.8 nm.

[0050] The multi-quantum-well light-emitting layer is an In-type material grown in a periodic alternating pattern. y1 The superlattice layer formed by the GaN layer and the second GaN layer has a period number of 9; In y1 The GaN layer is not intentionally doped, where y1 = 0.22; In y1 The GaN layer has a growth thickness of 3.5 nm; the second GaN layer has a growth thickness of 10 nm.

[0051] The P-type composite epitaxial layer is composed of periodically alternating Al layers.x2 GaN layer and In y2 The superlattice layer formed by the GaN layer has a period number of 15; Al x2 The GaN layer is an undoped AlGaN layer, where x2 = 0.14; Al x2 The GaN layer was grown to a thickness of 1.0 nm; In y2 In the GaN layer, y2 = 0.05; In y2 The GaN layer was grown to a thickness of 2.5 nm.

[0052] This embodiment also provides a method for fabricating an LED epitaxial structure, including the following steps: (1) Provide a substrate; (2) Buffer layers are grown sequentially on the substrate; (3) An N-type semiconductor layer is grown on the buffer layer; (4) A low-temperature stress relief layer is grown on the N-type semiconductor layer; (5) An N-type composite epitaxial layer is grown on the low-temperature stress relief layer; (6) A multi-quantum-well light-emitting layer is grown on an N-type composite epitaxial layer; (7) A P-type composite epitaxial layer is grown on a multi-quantum-well light-emitting layer; (8) An electron blocking layer is grown on a P-type composite epitaxial layer; (9) A P-type semiconductor layer is grown on the electron blocking layer; In the process of preparing the N-type composite epitaxial layer, Al x1 The growth temperature of the GaN layer is 880℃ and the growth pressure is 200 torr; the growth temperature of the first GaN layer is 940℃ and the growth pressure is 200 torr. During the fabrication of the multi-quantum-well light-emitting layer, In y1 The growth temperature of the GaN layer is 780℃ and the growth pressure is 200 torr; the growth temperature of the second GaN layer is 880℃ and the growth pressure is 200 torr. During the preparation of the P-type composite epitaxial layer, Al x2 The GaN layer was grown at 880℃ under a growth pressure of 200 torr; In y2 The GaN layer was grown at a temperature of 890℃ and a growth pressure of 200 torr.

[0053] Example 2 This embodiment provides an LED epitaxial structure, which is basically the same as that in Embodiment 1, except that: Al x2 The GaN layer contains several penetrating Al... x2 The second V-shaped hole in the GaN layer, Iny2 The GaN layer fills the second V-shaped hole and is located in Al. x2 On the GaN layer, the distribution density of the second V-shaped voids is 4.59 × 10⁻⁶. 9 / cm 2 The aperture is 1.5 nm.

[0054] The preparation method is the same as in Example 1.

[0055] Example 3 This embodiment provides an LED epitaxial structure, which is basically the same as that in Embodiment 1, except that: The first GaN layer is a Si-doped GaN layer with a Si doping concentration of 3.28 × 10⁻⁶. 17 / cm 3 ; The second GaN layer is a Si-doped GaN layer with a Si doping concentration of 4.6 × 10⁻⁶. 17 / cm 3 ; In y2 The GaN layer is a Mg-doped InGaN layer with a Mg doping concentration of 3.5 × 10⁻⁶. 18 / cm 3 .

[0056] The preparation method is the same as in Example 1.

[0057] Comparative Example 1 This comparative example provides an LED epitaxial structure that is basically the same as that in Example 1, except that: Al x1 The GaN layer does not contain several penetrations through Al. x1 The first V-shaped hole in the GaN layer; the first GaN layer is located in Al. x1 On the GaN layer.

[0058] Comparative Example 2 This comparative example provides an LED epitaxial structure that is basically the same as that in Example 1, except that: an N-type composite epitaxial layer is not provided, that is: An LED epitaxial structure includes a substrate, a buffer layer, an N-type semiconductor layer, a low-temperature stress relief layer, a multi-quantum-well light-emitting layer, a P-type composite epitaxial layer, an electron blocking layer, and a P-type semiconductor layer stacked sequentially. Comparative Example 3 This comparative example provides an LED epitaxial structure that is basically the same as that in Example 1, except that a P-type composite epitaxial layer is not provided, i.e.: An LED epitaxial structure includes a substrate, a buffer layer, an N-type semiconductor layer, a low-temperature stress relief layer, an N-type composite epitaxial layer, a multi-quantum-well light-emitting layer, an electron blocking layer, and a P-type semiconductor layer stacked sequentially.

[0059] Comparative Example 4 This comparative example provides an LED epitaxial structure that is basically the same as that in Example 1, except that: no N-type composite epitaxial layer and no P-type composite epitaxial layer are provided, that is: An LED epitaxial structure includes a substrate, a buffer layer, an N-type semiconductor layer, a low-temperature stress relief layer, a multi-quantum-well light-emitting layer, an electron blocking layer, and a P-type semiconductor layer stacked sequentially.

[0060] Using the same chip process conditions, 10mil×24mil chips were fabricated from the LED epitaxial structures obtained in Examples 1-3 and Comparative Examples 1-4. 300 LED chips were sampled from each example and tested at a current of 120mA. The luminous efficiency improvement rate of each example was calculated compared with that of the LED chip prepared in Comparative Example 4. The specific test results are shown in Table 1.

[0061] Table 1. Test results of the examples and comparative examples

[0062] The results above show that by setting N-type composite epitaxial layers and P-type composite epitaxial layers on the upper and lower sides of the multi-quantum well light-emitting layer, respectively, and setting an open structure in the N-type composite epitaxial layer, the resulting composite structure can reduce the stress and defect density of the epitaxial layer material, improve the quality of the multi-quantum well light-emitting layer, enhance the radiative recombination efficiency in the multi-quantum well light-emitting layer, and significantly increase the proportion of photon emanators in the active region, thereby improving the luminous efficiency of the light-emitting diode.

[0063] The above description is merely a preferred embodiment of the present invention and should not be construed as limiting the scope of the invention. Therefore, any equivalent variations made in accordance with the claims of the present invention are still within the scope of the present invention.

Claims

1. An LED epitaxial structure, characterized in that, It includes a substrate, a buffer layer, an N-type semiconductor layer, a low-temperature stress relief layer, an N-type composite epitaxial layer, a multi-quantum-well light-emitting layer, a P-type composite epitaxial layer, an electron blocking layer, and a P-type semiconductor layer stacked sequentially. The N-type composite epitaxial layer is an Al layer that has been grown in a periodic alternating pattern. x1 The superlattice layer formed by the GaN layer and the first GaN layer; The multi-quantum-well light-emitting layer is an In-type material that is periodically and alternately grown. y1 A superlattice layer formed by the GaN layer and the second GaN layer; The P-type composite epitaxial layer is an Al layer that has been periodically and alternately grown. x2 GaN layer and In y2 The superlattice layer formed by the GaN layer; Wherein, the Al x1 The GaN layer contains several penetrations through the Al. x1 The first V-shaped hole in the GaN layer, the first GaN layer fills the first V-shaped hole and is located in the Al x1 On the GaN layer.

2. The LED epitaxial structure as described in claim 1, characterized in that, The Al x2 The GaN layer contains several penetrations through the Al. x2 The second V-shaped hole in the GaN layer, the In y2 The GaN layer fills the second V-shaped hole and is located in the Al. x2 On the GaN layer.

3. The LED epitaxial structure as described in claim 1, characterized in that, The distribution density of the first V-shaped hole is 1.28 × 10⁻⁶. 7 / cm 2 -6.79×10 12 / cm 2 The diameter of the first V-shaped hole is less than 2 nm.

4. The LED epitaxial structure as described in claim 2, characterized in that, The distribution density of the second V-shaped pores is 1.59 × 10⁻⁶. 7 / cm 2 -9.68×10 12 / cm 2 The diameter of the second V-shaped hole is less than 1.8 nm.

5. The LED epitaxial structure as described in claim 1, characterized in that, The first GaN layer is a Si-doped GaN layer with a Si doping concentration of 1.28 × 10⁻⁶. 17 / cm 3 -6.97×10 17 / cm 3 ; The second GaN layer is a Si-doped GaN monolayer or GaN multilayer structure, with a Si doping concentration of 1.5 × 10⁻⁶. 17 / cm 3 -8.6×10 17 / cm 3 ; The In y2 The GaN layer is a Mg-doped InGaN layer with a Mg doping concentration of 1.6 × 10⁻⁶. 17 / cm 3 -7.5×10 19 / cm 3 .

6. The LED epitaxial structure as described in claim 1, characterized in that, The number of periods in the N-type composite epitaxial layer is 2-20; The Al x1 The GaN layer is an undoped AlGaN layer, where 0.01 ≤ x1 ≤ 0.

30. x1 The GaN layer is grown to a thickness of 0.2 nm-2 nm; The thickness of the first GaN layer is 0.3nm-5nm.

7. The LED epitaxial structure as described in claim 1, characterized in that, The number of periods in the multi-quantum-well light-emitting layer is 3-16; The In y1 The GaN layer is an undoped InGaN monolayer or InGaN multilayer structure, wherein 0.05 ≤ y1 ≤ 0.39; the In y1 The GaN layer thickness ranges from 2.1 nm to 4.8 nm. The growth thickness of the second GaN layer is 5nm-16nm.

8. The LED epitaxial structure as described in claim 1, characterized in that, The number of periods in the P-type composite epitaxial layer is 2-30; The Al x2 The GaN layer is an undoped AlGaN layer, where 0.01 ≤ x² ≤ 0.27; the Al x2 The GaN layer thickness ranges from 0.15 nm to 1.8 nm. The In y2 In the GaN layer, 0.003 ≤ y2 ≤ 0.09; the In y2 The GaN layer thickness ranges from 0.28 nm to 4.7 nm.

9. A method for preparing an LED epitaxial structure as described in any one of claims 1-8, characterized in that, Includes the following steps: (1) Provide a substrate; (2) A buffer layer is sequentially grown on the substrate; (3) An N-type semiconductor layer is grown on the buffer layer; (4) A low-temperature stress relief layer is grown on the N-type semiconductor layer; (5) An N-type composite epitaxial layer is grown on the low-temperature stress relief layer; (6) A multi-quantum-well light-emitting layer is grown on the N-type composite epitaxial layer; (7) A P-type composite epitaxial layer is grown on the multi-quantum-well light-emitting layer; (8) An electron blocking layer is grown on the P-type composite epitaxial layer; (9) A P-type semiconductor layer is grown on the electron blocking layer; The N-type composite epitaxial layer is an Al layer that has been grown in a periodic alternating pattern. x1 The superlattice layer formed by the GaN layer and the first GaN layer; The multi-quantum-well light-emitting layer is an In-type material that is periodically and alternately grown. y1 A superlattice layer formed by the GaN layer and the second GaN layer; The P-type composite epitaxial layer is an Al layer that has been periodically and alternately grown. x2 GaN layer and In y2 The superlattice layer formed by the GaN layer; Wherein, the Al x1 The GaN layer contains several penetrations through the Al. x1 The first V-shaped hole in the GaN layer, the first GaN layer fills the first V-shaped hole and is located in the Al x1 On the GaN layer.

10. The method for preparing the LED epitaxial structure as described in claim 9, characterized in that, The Al x1 The growth temperature of the GaN layer is 780℃-980℃, and the growth pressure is 30 torr-360 torr; the growth temperature of the first GaN layer is 800℃-1080℃, and the growth pressure is 30 torr-360 torr. The In y1 The growth temperature of the GaN layer is 650℃-900℃, and the growth pressure is 30 torr-360 torr; the growth temperature of the second GaN layer is 800℃-980℃, and the growth pressure is 30 torr-360 torr. The Al x2 The GaN layer is grown at a temperature of 780℃-980℃ and a growth pressure of 30 torr-360 torr; the In... y2 The growth temperature of the GaN layer is 750℃-1030℃, and the growth pressure is 30 torr-360 torr.

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