Low-working-current-density cyan LED epitaxial structure and preparation method thereof

Abstract

The invention relates to the technical field of semiconductor materials, in particular to a low-working-current-density cyan LED epitaxial structure and a preparation method thereof.The low-working-current-density cyan LED epitaxial structure comprises a substrate, and a buffer layer, an N-type semiconductor layer, a low-temperature stress release layer, a multi-quantum-well light-emitting layer and a P-type semiconductor layer which are sequentially stacked on the substrate; the multi-quantum well light-emitting layer comprises a first light blue light multi-quantum well sub-layer, a second blue light multi-quantum well sub-layer, a third blue light multi-quantum well sub-layer and a fourth light blue light multi-quantum well sub-layer which are sequentially stacked and grown from bottom to top; wherein each sub-layer is of a superlattice structure of an InGaN multi-quantum well layer and a multi-quantum barrier layer, and the barrier heights of the sub-layers decrease progressively in a gradient mode, namely, the high barrier, the middle barrier, the low barrier and the low barrier decrease progressively in sequence. The upper-layer low-potential barrier attracts holes to migrate downwards, and the lower-layer high-potential barrier blocks electrons from leaking, so that space matching of the electrons and the holes is realized, and the performances such as luminous efficiency and yield of the cyan LED chip under low working current density are improved.

Description

Technical Field

[0001] This invention relates to the field of semiconductor materials technology, and in particular to a low operating current density blue LED epitaxial structure and its preparation method. Background Technology

[0002] With the rapid development of emerging wearable and portable technologies, micron-sized LED chips (Micro LED) have garnered significant attention and research from scientific institutions and enterprises due to their promising applications in displays, visible light communication, and biomedicine. Furthermore, Micro LED displays possess superior performance characteristics such as nanosecond (ns) level high-speed response, stable inorganic materials, high luminous efficiency, high reliability, high color purity and contrast, and transparency—features that are unattainable by liquid crystal displays (LCDs) and organic LEDs (OLEDs).

[0003] While Micro LEDs possess many superior characteristics, they also face challenges in manufacturing technology and material and device physics. For example, the problem of decreasing peak external quantum efficiency (EQE) and correspondingly increasing current density as chip size decreases has not been fully resolved, with the operating current density currently around 0.01 A / cm². 2 ~0.5A / cm 2 The efficiency of Micro LEDs in this range remains significantly low. In fact, even standard-sized chips used in general lighting and backlighting applications exhibit relatively low efficiency at this current density. This is because standard-sized chips, in order to balance efficiency and cost, operate at a current density of around 20 A / cm². 2 ~40A / cm 2 The corresponding epitaxial structure design and material growth also aim to improve efficiency under high current density, with peak EQE typically around 1 A / cm². 2 ~4A / cm 2 The study focuses on the current density range, neglecting to consider device efficiency at low current densities. The dominant factors in the light-emitting mechanism of LED devices differ at different current densities, and the corresponding epitaxial layer structure should also vary. For example, in the Micro LED operating range of 0.01 A / cm²... 2 ~0.5A / cm 2At low current densities, the carrier concentration in the quantum well is relatively low, resulting in a small Auger recombination rate. Consequently, the quantum well recombination volume can be reduced, thus decreasing the number of quantum wells and defects, and improving the EQE of the device at low current densities. Simultaneously, at low current densities, electron leakage has not yet occurred or is very low. The electron blocking layer structure not only fails to block electrons but also blocks hole injection, reducing the device's quantum efficiency. Therefore, in-depth mechanistic research, design, and growth of LED epitaxial layer structures under low current density operating conditions are essential key technologies for developing high-efficiency Micro LED devices driven by low operating current densities.

[0004] Traditional visible light LED epitaxial structure designs are based on traditional application scenarios with large chips, high current, and high power. However, Micro LED display applications require small size, low current, and low power. LEDs designed with traditional epitaxial structures can no longer meet the application requirements of Micro LED. Summary of the Invention

[0005] The purpose of this invention is to overcome the shortcomings of the prior art. This invention provides a low operating current density blue LED epitaxial structure and its preparation method. The prepared epitaxial structure can have good electron-hole concentration matching degree under low current density conditions, thereby improving luminous efficiency.

[0006] To address the aforementioned issues, this invention proposes a low operating current density cyan LED epitaxial structure, comprising a substrate, on which a buffer layer, an N-type semiconductor layer, a low-temperature stress relief layer, a multi-quantum-well light-emitting layer, and a P-type semiconductor layer are sequentially stacked. The multi-quantum-well light-emitting layer includes a first light blue multi-quantum-well sublayer, a second blue multi-quantum-well sublayer, a third cyan multi-quantum-well sublayer, and a fourth light blue multi-quantum-well sublayer, which are stacked sequentially from bottom to top. The first light blue quantum well sublayer comprises a superlattice structure in which a first InGaN quantum well layer and a first high barrier layer are periodically and alternately grown from bottom to top. The second blue light multi-quantum well sublayer comprises a superlattice structure in which a second InGaN multi-quantum well layer and a second intermediate barrier layer are grown alternately and periodically from bottom to top. The third blue light multiple quantum well sublayer comprises a superlattice structure consisting of a third InGaN multiple quantum well layer and a third low barrier layer that are periodically and alternately grown from bottom to top. The fourth light blue light multi-quantum well sublayer comprises a superlattice structure consisting of a fourth InGaN multi-quantum well layer and a fourth low-barrier layer grown alternately from bottom to top.

[0007] As an improvement to the above technical solution, the alternating growth cycle number of the superlattice structure of the first InGaN multiple quantum well layer and the first high barrier layer is 1 to 3; the first InGaN multiple quantum well layer is an undoped single-layer structure or a multi-layer structure, the In content is X1, 0.10≤X1≤0.13; the thickness of the first InGaN multiple quantum well layer is 2.05nm to 4.78nm. The number of alternating growth cycles of the superlattice structure of the second InGaN multiple quantum well layer and the second intermediate barrier layer is 2 to 5; the second InGaN multiple quantum well layer is an undoped single-layer structure or a multi-layer structure, and the In content is X2, 0.13≤X2≤0.18; the thickness of the second InGaN multiple quantum well layer is 2.05nm to 4.78nm. The alternating growth cycle number of the superlattice structure of the third InGaN multiple quantum well layer and the third low barrier layer is 2 to 8; the third InGaN multiple quantum well layer is an undoped single-layer structure or a multi-layer structure, and the In content is X3, 0.18≤X3≤0.22; the thickness of the third InGaN multiple quantum well layer is 2.05nm to 4.78nm. The number of alternating growth cycles of the superlattice structure of the fourth InGaN multiple quantum well layer and the fourth low barrier layer is 1; the fourth InGaN multiple quantum well layer is an undoped single-layer structure or a multi-layer structure, and the In content is X4, 0.10≤X4≤0.13; the thickness of the fourth InGaN multiple quantum well layer is 2.05nm~4.78nm.

[0008] As an improvement to the above technical solution, in the multi-quantum-well light-emitting layer, X1=X4 <X2<X3; The growth temperature of the first InGaN multiple quantum well layer is T1, the growth temperature of the second InGaN multiple quantum well layer is T2, the growth temperature of the third InGaN multiple quantum well layer is T3, and the growth temperature of the fourth InGaN multiple quantum well layer is T4, where T1=T4>T2>T3.

[0009] As an improvement to the above technical solution, the first high barrier layer includes a first Si-doped GaN barrier layer one, a first AlGaN barrier layer two, and a first Si-doped GaN barrier layer three, which are stacked and grown sequentially from bottom to top. The thickness of both the first Si-doped GaN barrier layer one and the third Si-doped GaN barrier layer is 1.8 nm to 6.8 nm, and the Si doping concentration is 1.12 × 10⁻⁶. 17 / cm³~7.98×10 17 / cm³; the content of Al component in the first AlGaN barrier layer II is Y1, 0.02≤Y1≤0.36, and the thickness of the first AlGaN barrier layer II is 1.0nm~5.8nm; The second barrier layer includes a second Si-doped GaN barrier layer one, a second AlGaN barrier layer two, and a second Si-doped GaN barrier layer three, which are stacked and grown sequentially from bottom to top. The thickness of both the second Si-doped GaN barrier layer one and the second Si-doped GaN barrier layer three is 1.6 nm to 6.5 nm, and the Si doping concentration is 1.12 × 10⁻⁶. 17 / cm³~7.98×10 17 / cm³; the content of Al component in the second AlGaN barrier layer is Y2, 0.01≤Y2≤0.18, and the thickness of the second AlGaN barrier layer is 0.8 nm~5.0 nm.

[0010] As an improvement to the above technical solution, the total thickness of the first high barrier layer is 10nm~15nm; The total thickness of the second barrier layer is 7nm~13nm; The thickness ratio of the first InGaN multi-quantum-well layer to the first high-barrier layer is 1:2.5 to 1:5; The thickness ratio of the second InGaN multiple quantum well layer to the second middle barrier layer is 1:2.5 to 1:5.

[0011] As an improvement to the above technical solution, the third low barrier layer is a single-layer or multi-layer structure of GaN, and the thickness of the third low barrier layer is 5.0nm~15.8nm. The total thickness of the fourth low barrier layer is 8 nm to 16 nm. The thickness ratio of the third InGaN multiple quantum well layer to the third low barrier layer is 1:2.4 to 1:4.5; The thickness ratio of the fourth InGaN multiple quantum well layer to the fourth low barrier layer is 1:2.5 to 1:5.

[0012] As an improvement to the above technical solution, the fourth low barrier layer includes a fourth GaN barrier layer one, a fourth AlGaInN barrier layer two, a fourth AlGaInN barrier layer three and a fourth AlGaN barrier layer four, which are stacked and grown sequentially from bottom to top. The thickness of the first fourth GaN barrier layer is 0.6 nm to 5.2 nm; the content of Al component in the second fourth AlGaInN barrier layer is Y. 42 0.01≤Y 42 ≤0.08, the content of In component is X 42 0.01≤X 42≤0.09, thickness is 0.6nm~5.2nm; the content of Al component in the fourth AlGaInN barrier layer is Y 43 0.01≤Y 43 ≤0.08, the content of In component is X 43 0.02≤X 43 ≤0.11, thickness is 0.6nm~5.2nm; the Al content in the fourth AlGaN barrier layer is Y 44 0.003≤Y 44 ≤0.06, thickness is 0.8nm~6.8nm; Specifically, at least one of the fourth AlGaInN barrier layer two, the fourth AlGaInN barrier layer three, and the fourth AlGaN barrier layer four is Mg-doped, with a Mg doping concentration of 2.1 × 10⁻⁶. 18 / cm³~7.9×10 19 / cm³.

[0013] As an improvement to the above technical solution, the content of Al component in the first AlGaN barrier layer 2 is greater than the content of Al component in the second AlGaN barrier layer 2, and the thickness of the first AlGaN barrier layer 2 is greater than or equal to the thickness of the second AlGaN barrier layer 2. The Al content of the second and third AlGaInN barrier layers is the same, and the In content of the second AlGaInN barrier layer is less than that of the third AlGaInN barrier layer.

[0014] Accordingly, the present invention also provides a method for fabricating a low-current-density blue LED epitaxial structure, comprising: Provide a substrate; A buffer layer is grown on the substrate; An N-type semiconductor layer is grown on the buffer layer; A low-temperature stress relief layer is grown on an N-type semiconductor layer; A multi-quantum-well light-emitting layer is grown on a low-temperature stress-relieving layer; A P-type semiconductor layer is grown on a multi-quantum-well light-emitting layer; The multi-quantum-well light-emitting layer includes a first light blue multi-quantum-well sublayer, a second blue multi-quantum-well sublayer, a third cyan multi-quantum-well sublayer, and a fourth light blue multi-quantum-well sublayer, which are stacked sequentially from bottom to top. The first light blue light multi-quantum well sublayer comprises a superlattice structure in which a first InGaN multi-quantum well layer and a first high barrier layer are periodically and alternately grown from bottom to top. The second blue light multi-quantum well sublayer comprises a superlattice structure in which a second InGaN multi-quantum well layer and a second intermediate barrier layer are grown alternately and periodically from bottom to top. The third blue light multiple quantum well sublayer comprises a superlattice structure consisting of a third InGaN multiple quantum well layer and a third low barrier layer that are periodically and alternately grown from bottom to top. The fourth light blue light multi-quantum well sublayer comprises a superlattice structure consisting of a fourth InGaN multi-quantum well layer and a fourth low-barrier layer grown alternately from bottom to top.

[0015] As an improvement to the above technical solution, the fourth low barrier layer includes a fourth GaN barrier layer one, a fourth AlGaInN barrier layer two, a fourth AlGaInN barrier layer three and a fourth AlGaN barrier layer four, which are stacked and grown sequentially from bottom to top. After depositing the fourth AlGaInN barrier layer two and before depositing the fourth AlGaInN barrier layer three, the process further includes: performing N polar annealing in an NH3 atmosphere for a processing time of 8~180s, a processing temperature of 830℃~1150℃, and a processing pressure of 50torr~600torr. After depositing the fourth AlGaInN barrier layer three and before depositing the fourth AlGaN barrier layer four, the process further includes: etching roughening annealing in an H2 atmosphere for a processing time of 5~180s, a processing temperature of 820℃~1080℃, and a processing pressure of 50torr~600torr.

[0016] The implementation of this invention has the following beneficial effects: This invention provides a low operating current density blue LED epitaxial structure, comprising a substrate, on which a buffer layer, an N-type semiconductor layer, a low-temperature stress relief layer, a multi-quantum-well light-emitting layer, and a P-type semiconductor layer are sequentially stacked. First, the electron blocking layer between the multi-quantum-well light-emitting layer and the P-type semiconductor layer is eliminated, thus removing the hole-blocking effect of high barrier layers such as AlGaN / AlInN in traditional structures. Holes in the P-type region can be directly injected into the multi-quantum-well light-emitting layer. Secondly, the multi-quantum-well light-emitting layer includes a first light blue multi-quantum-well sublayer, a second blue multi-quantum-well sublayer, a third cyan multi-quantum-well sublayer, and a fourth light blue multi-quantum-well sublayer, which are stacked sequentially from bottom to top. Four heterogeneous multi-quantum-well sublayers are used, and the potential barrier height of each sublayer decreases in a gradient, i.e., high barrier, medium barrier, low barrier, and low barrier decrease in sequence. The gradient barrier design forms a carrier "funnel effect": the low barrier of the upper layer attracts holes to migrate downwards, and the high barrier of the lower layer blocks electron leakage, realizing the spatial matching of electrons and holes, thereby improving the luminous efficacy, yield, and other performance of the cyan LED chip at low operating current density. Attached Figure Description

[0017] Figure 1 This is a schematic diagram of the epitaxial structure of a blue LED according to an embodiment of the present invention; Figure 2 This is a schematic diagram of the structure of a multi-quantum-well light-emitting layer according to an embodiment of the present invention. Detailed Implementation

[0018] 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 the accompanying drawings.

[0019] See Figure 1 and Figure 2 The embodiment of the present invention shown provides a low operating current density blue LED epitaxial structure, including a substrate 100, on which a buffer layer 200, an N-type semiconductor layer 300, a low-temperature stress relief layer 400, a multi-quantum well light-emitting layer 500 and a P-type semiconductor layer 600 are sequentially stacked.

[0020] The multi-quantum well light-emitting layer 500 includes a first light blue multi-quantum well sublayer 510, a second blue multi-quantum well sublayer 520, a third cyan multi-quantum well sublayer 530, and a fourth light blue multi-quantum well sublayer 540, which are stacked sequentially from bottom to top.

[0021] In this invention, the third cyan multi-quantum well sublayer 530 is used as the light-emitting unit, which is suitable for small-size, low-current-density and low-yield LED epitaxial structures. It significantly improves the quality of the multi-quantum-well light-emitting layer and increases the hole injection efficiency of the P-type semiconductor layer, thereby improving its luminous efficacy, yield and other performance at low operating current densities.

[0022] Specifically, the first light blue multi-quantum well sublayer 510 includes a superlattice structure of a first InGaN multi-quantum well layer 511 and a first high barrier layer that are periodically alternately grown from bottom to top, with a period number of 1-3. For example, 1, 2, and 3.

[0023] Preferably, the first InGaN multiple quantum well layer 511 is an undoped single-layer structure or a multi-layer structure, and the In content is X1, 0.10≤X1≤0.13; X1 is exemplarily 0.10, 0.11, 0.12, 0.13, but is not limited thereto.

[0024] Furthermore, the thickness of the first InGaN multiple quantum well layer 511 is 2.05 nm to 4.78 nm. Exemplary thicknesses are 2.2 nm, 2.7 nm, 3.1 nm, 3.5 nm, and 4.5 nm, but are not limited thereto.

[0025] Preferably, the first high barrier layer includes a first Si-doped GaN barrier layer 512, a first AlGaN barrier layer 513, and a first Si-doped GaN barrier layer 514, which are stacked sequentially from bottom to top.

[0026] Furthermore, the thickness of both the first Si-doped GaN barrier layer 512 and the first Si-doped GaN barrier layer 514 is 1.8 nm to 6.8 nm, and the Si doping concentration is 1.12 × 10⁻⁶. 17 / cm³~7.98×10 17 / cm³; exemplary thicknesses are 2.0nm, 3.5nm, 4.5nm, 6.0nm, and 6.5nm, but are not limited thereto; an exemplary Si doping concentration is 1.2×10⁻⁶. 17 / cm³, 3.5×10 17 / cm³, 5.2×10 17 / cm³, 6.2×10 17 / cm³, 7.8×10 17 / cm³, but not limited to this.

[0027] Furthermore, the Al content in the first AlGaN barrier layer 513 is Y1, 0.02≤Y1≤0.36; exemplary Y1 values ​​are 0.02, 0.05, 0.10, 0.18, 0.27, and 0.34, but are not limited thereto. The thickness of the first AlGaN barrier layer 513 is 1.0nm~5.8nm; exemplary thicknesses are 1.1nm, 2.5nm, 3.7nm, 4.7nm, 5.1nm, 5.7nm, and 5.8nm, but are not limited thereto.

[0028] Furthermore, the total thickness of the first high barrier layer is 10nm~15nm; the thickness ratio of the first InGaN multiple quantum well layer 511 to the first high barrier layer is 1:2.5~1:5; for example, 1:2.5, 1:3, 1:3.5, 1:4, 1:5, but not limited thereto.

[0029] The second blue-light multiple quantum well layer 520 comprises a superlattice structure consisting of a second InGaN multiple quantum well layer 521 and a second intermediate barrier layer, which are periodically alternately grown from bottom to top, with a period number of 2 to 5. An exemplary period is 2, 3, 4, 5.

[0030] Preferably, the second InGaN multiple quantum well layer 521 is an undoped single-layer structure or a multi-layer structure, and the In content is X2, 0.13≤X2≤0.18; X2 is exemplarily 0.13, 0.14, 0.15, 0.17, but is not limited thereto.

[0031] The thickness of the second InGaN multiple quantum well layer 521 is 2.05nm~4.78nm; exemplary thicknesses are 2.05nm, 2.78nm, 3.17nm, 3.77nm, and 4.58nm, but are not limited thereto.

[0032] Furthermore, the second barrier layer includes a second Si-doped GaN barrier layer 522, a second AlGaN barrier layer 523, and a second Si-doped GaN barrier layer 524, which are stacked sequentially from bottom to top.

[0033] Furthermore, the thickness of both the second Si-doped GaN barrier layer 522 and the second Si-doped GaN barrier layer 524 is 1.6 nm to 6.5 nm, and the Si doping concentration is 1.12 × 10⁻⁶. 17 / cm³~7.98×10 17 / cm³; exemplary thicknesses are 1.6nm, 2.0nm, 3.5nm, 4.2nm, 5.7nm, and 6.2nm, but are not limited thereto; exemplary doping concentration is 1.12×10⁻⁶. 17 / cm³, 3.75×10 17 / cm³, 4.68×10 17 / cm³, 5.11×10 17 / cm³, 6.33×10 17 / cm³, 7.15×10 17 / cm³, but not limited to this.

[0034] Furthermore, the content of Al component in the second AlGaN barrier layer 523 is Y2, 0.01≤Y2≤0.18; exemplary values ​​are 0.01, 0.07, 0.12, 0.15, and 0.18, but not limited thereto; the thickness of the second AlGaN barrier layer 523 is 0.8 nm to 5.0 nm; exemplary thicknesses are 0.8 nm, 1.2 nm, 2.9 nm, 4.7 nm, and 5.0 nm, but not limited thereto.

[0035] Furthermore, the total thickness of the second intermediate barrier layer is 7nm~13nm; the thickness ratio of the second InGaN multiple quantum well layer 521 to the second intermediate barrier layer is 1:2.5~1:5; for example, 1:2.5, 1:3, 1:4.2, 1:4.7, 1:5, but not limited to these.

[0036] Furthermore, the Al composition of the first AlGaN barrier layer 513 is greater than that of the second AlGaN barrier layer 523, and the thickness of the first AlGaN barrier layer 513 is greater than or equal to the thickness of the second AlGaN barrier layer 523.

[0037] In this invention, the first high-barrier layer and the second middle-barrier layer have the same structure, both comprising, from bottom to top, sequentially stacked Si-doped GaN barrier layer one, AlGaN barrier layer two, and GaN barrier layer three. First, to enhance electron injection efficiency, the Si-doped barrier layer one, as an n-type doped layer, provides a high-conductivity channel, lowers the electron injection barrier, and makes it easier for electrons to flow from the n-type region to the active layer, improving current spreadability. Second, the AlGaN barrier layer two has a wide bandgap characteristic, reducing excessive diffusion of electrons from the active layer to the p-type region, preventing energy loss and non-radiative recombination. Finally, the Si-doped GaN barrier layer three, through silicon doping, regulates hole transport and works synergistically with the lower layers to balance the concentration of electrons and holes in the active region, reducing electron-hole recombination asymmetry and thus improving luminous uniformity. It also improves the electron-hole matching degree in the third blue-light multi-quantum-well sublayer, increasing the luminous efficacy of Micro LEDs at low operating current densities. Simultaneously, it prevents electron injection into the p-type semiconductor layer, thus preventing electron leakage and improving the yield and other performance characteristics of Micro LEDs.

[0038] The third cyan quantum well sublayer 530 includes a superlattice structure of a third InGaN quantum well layer 531 and a third low barrier layer 532 that are periodically alternating from bottom to top, with a period number of 2 to 8; for example, 2, 3, 4, 5, 6, 7, 8.

[0039] Preferably, the third InGaN multiple quantum well layer 531 is an undoped single-layer structure or a multi-layer structure, and the In content is X3, 0.18≤X3≤0.22; X3 is exemplarily 0.18, 0.19, 0.20, 0.21, 0.22, but is not limited thereto.

[0040] Furthermore, the thickness of the third InGaN multiple quantum well layer 531 is 2.05 nm to 4.78 nm. Exemplary thicknesses are 2.05 nm, 2.75 nm, 3.18 nm, 3.92 nm, 4.23 nm, and 4.78 nm, but are not limited thereto.

[0041] Preferably, the third low barrier layer 532 is a single-layer or multi-layer GaN structure, and the thickness of the third low barrier layer 532 is 5.0nm~15.8nm; exemplary thicknesses are 5.0nm, 6.7nm, 8.8nm, 9.6nm, 12.1nm, 15.7nm, and 15.8nm, but are not limited thereto.

[0042] Furthermore, the thickness ratio of the third InGaN multiple quantum well layer 531 to the third low barrier layer 532 is 1:2.4 to 1:4.5; for example, it is 1:2.4, 1:3.4, 1:3.9, 1:4.1, 1:4.5, but is not limited thereto.

[0043] The fourth light blue quantum well sublayer 540 comprises a superlattice structure consisting of a fourth InGaN quantum well layer 541 and a fourth low barrier layer that are periodically and alternately grown from bottom to top, with a period number of 1.

[0044] Preferably, the fourth InGaN multiple quantum well layer 541 is an undoped single-layer or multi-layer structure, with an In content of X4, where 0.10 ≤ X4 ≤ 0.13; the thickness of the fourth InGaN multiple quantum well layer 541 is 2.05 nm to 4.78 nm. Exemplary values ​​of X4 are 0.10, 0.12, and 0.13, but are not limited thereto. Exemplary thicknesses are 2.05 nm, 2.75 nm, 3.12 nm, 3.54 nm, 4.56 nm, and 4.78 nm, but are not limited thereto.

[0045] Preferably, the fourth low barrier layer comprises a fourth GaN barrier layer 542, a fourth AlGaInN barrier layer 543, a fourth AlGaInN barrier layer 544, and a fourth AlGaN barrier layer 545, which are stacked sequentially from bottom to top.

[0046] Furthermore, the thickness of the fourth GaN barrier layer 542 is 0.6 nm to 5.2 nm; exemplary thicknesses are 0.6 nm, 1.8 nm, 2.4 nm, 2.9 nm, 3.7 nm, 4.2 nm, and 5.2 nm, but are not limited thereto.

[0047] Furthermore, the content of Al component in the fourth AlGaInN barrier layer 543 is Y. 42 0.01≤Y 42 ≤0.08, the content of In component is X 42 0.01≤X 42 ≤0.09, thickness ranges from 0.6nm to 5.2nm. Y 42 Examples of thicknesses include 0.01, 0.02, 0.03, 0.04, 0.05, 0.06, 0.07, and 0.08, but are not limited thereto; examples of thicknesses include 0.6nm, 1.8nm, 2.4nm, 2.9nm, 3.7nm, 4.2nm, and 5.2nm, but are not limited thereto.

[0048] Furthermore, the content of Al component in the fourth AlGaInN barrier layer 3544 is Y 43 0.01≤Y 43 ≤0.08, the content of In component is X 43 0.02≤X 43 ≤0.11, thickness ranges from 0.6nm to 5.2nm. X 43Examples of thicknesses include 0.02, 0.03, 0.04, 0.05, 0.06, 0.07, 0.08, 0.09, 0.10, and 0.11, but are not limited thereto; examples of thicknesses include 0.6nm, 1.8nm, 2.4nm, 2.9nm, 3.7nm, 4.2nm, and 5.2nm, but are not limited thereto.

[0049] Furthermore, the content of Al component in the fourth AlGaN barrier layer 545 is Y. 44 0.003≤Y 44 ≤0.06, thickness ranges from 0.8nm to 6.8nm. Y 44 Examples of thicknesses include 0.003, 0.01, 0.02, 0.03, 0.05, and 0.06, but are not limited thereto; examples of thicknesses include 0.8nm, 1.6nm, 2.8nm, 5.5nm, 6.1nm, and 6.8nm, but are not limited thereto.

[0050] It should be noted that at least one of the fourth AlGaInN barrier layer 2 (543), the fourth AlGaInN barrier layer 3 (544), and the fourth AlGaN barrier layer 4 (545) is Mg-doped, with a Mg doping concentration of 2.1 × 10⁻⁶. 18 / cm³~7.9×10 19 / cm³. An exemplary Mg doping concentration is 2.1×10⁻⁶. 18 / cm³, 3.5×10 18 / cm³, 4.7×10 18 / cm³, 5.8×10 19 / cm³, 6.6×10 19 / cm³, 6.7×10 19 / cm³, 7.3×10 19 / cm³, 7.9×10 19 / cm³, but not limited to this.

[0051] The fourth AlGaInN barrier layer 2 543 and the fourth AlGaInN barrier layer 3 544 have the same Al composition; the In composition of the fourth AlGaInN barrier layer 2 543 is less than that of the fourth AlGaInN barrier layer 3 544.

[0052] First, the first AlGaN barrier layer with a high Al component, i.e., the <513> layer, forms a strong electron barrier, effectively blocking the leakage of electrons to the P-type region. The second AlGaN barrier layer with a lower Al component, i.e., the <523> layer, reduces the hindrance to hole injection. The thickness design ensures the electron blocking effect while optimizing carrier transport. Secondly, a structure with a decreasing barrier height from bottom to top is formed, where electrons are confined near the light-emitting region (GaN multiple quantum well layer), increasing the probability of radiative recombination, and the resistance to hole injection is gradually reduced, improving the carrier concentration matching. Finally, the high Al component layer is located at the bottom, and its characteristic of a smaller lattice constant is used to compensate for the compressive stress of the InGaN quantum well.

[0053] The present invention solves the problem that the EQE of the traditional structure is significantly reduced at 0.01 - 0.5 A / cm², eliminates the hindrance of the electron blocking layer to hole injection, and the graded In composition design makes the stress distribution more uniform.

[0054] Preferably, in the multiple quantum well light-emitting layer, X1 = X4 < X2 < X3. The InGaN material in the multiple quantum well light-emitting layer forms an InGaN / barrier layer superlattice structure with an increasing and then decreasing In composition. This structure and process design can effectively reduce the lattice mismatch stress between the third cyan multiple quantum well sublayer and the barrier layer material, improve the crystal quality of the multiple quantum well light-emitting layer at low operating current density, thereby increasing the radiative recombination efficiency of the multiple quantum well light-emitting layer and reducing the operating voltage.

[0055] Furthermore, the growth temperature of the first InGaN multiple quantum well layer <511> is T1, the growth temperature of the second InGaN multiple quantum well layer <521> is T2, the growth temperature of the third InGaN multiple quantum well layer <531> is T3, and the growth temperature of the fourth InGaN multiple quantum well layer <541> is T4, where T1 = T4 > T2 > T3. The growth temperature of the InGaN material in the first shallow blue light multiple quantum well sublayer <510>, the second blue light multiple quantum well sublayer <520>, and the fourth shallow blue light multiple quantum well sublayer <540> in the multiple quantum well light-emitting layer is relatively higher than the growth temperature of the InGaN material in the third cyan multiple quantum well sublayer <530>. When the InGaN material is grown at a high temperature, the atomic mobility is high, and it is more inclined to two-dimensional material growth. The defects in the InGaN material will be significantly reduced, and it is easier to obtain high-quality InGaN material. At the same time, the In composition of the InGaN material in the first shallow blue light multiple quantum well sublayer <510>, the second blue light multiple quantum well sublayer <520>, and the fourth shallow blue light multiple quantum well sublayer <540> is lower than that of the InGaN material in the third cyan multiple quantum well sublayer. The lattice mismatch stress between the InGaN material in the multiple quantum well layer and the GaN material is reduced, and the defects caused by large mismatch stress are reduced, which can significantly improve the quality of the multiple quantum well light-emitting layer. The reduction of defects in the multiple quantum well light-emitting layer is beneficial to increasing the radiative recombination efficiency of the multiple quantum well layer, thereby improving the optical efficiency and yield of the Micro LED at low operating current density and other performance.

[0056] Accordingly, the present invention also provides a method for fabricating a low-current-density blue LED epitaxial structure, comprising: Provide a substrate; A buffer layer is grown on the substrate; An N-type semiconductor layer is grown on the buffer layer; A low-temperature stress relief layer is grown on an N-type semiconductor layer; A multi-quantum-well light-emitting layer is grown on a low-temperature stress-relieving layer; A P-type semiconductor layer is grown on a multi-quantum-well light-emitting layer; The multi-quantum well light-emitting layer includes a first light blue multi-quantum well sublayer 510, a second blue multi-quantum well sublayer 520, a third cyan multi-quantum well sublayer 530, and a fourth light blue multi-quantum well sublayer 540, which are stacked sequentially from bottom to top. The first light blue quantum well sublayer 510 includes a superlattice structure of a first InGaN quantum well layer 511 and a first high barrier layer that are periodically and alternately grown from bottom to top, with a period number of 1-3. The second blue light multiple quantum well sublayer 520 includes a superlattice structure of a second InGaN multiple quantum well layer 521 and a second intermediate barrier layer that are periodically and alternately grown from bottom to top, with a period number of 2-5; The third blue light multiple quantum well sublayer 530 includes a superlattice structure consisting of a third InGaN multiple quantum well layer 531 and a third low barrier layer that are periodically and alternately grown from bottom to top, with a period number of 2-8. The fourth light blue quantum well sublayer 540 comprises a superlattice structure consisting of a fourth InGaN quantum well layer 541 and a fourth low barrier layer that are periodically and alternately grown from bottom to top, with a period number of 1.

[0057] Specifically, the growth temperature of the first InGaN multi-quantum-well layer 511 is 750℃~923℃, and the pressure is 50 torr-360 torr; the first high barrier layer includes a first Si-doped GaN barrier layer 512, a first AlGaN barrier layer 513, and a first Si-doped GaN barrier layer 514, which are stacked sequentially from bottom to top; the growth temperature of the first Si-doped GaN barrier layer 512, the first AlGaN barrier layer 513, and the first Si-doped GaN barrier layer 514 is 825℃-928℃, and the pressure is 50 torr-360 torr.

[0058] The growth temperature of the second InGaN multiple quantum well layer 521 is 735℃~923℃, and the pressure is 50 torr-360 torr; the second intermediate barrier layer includes a second Si-doped GaN barrier layer 522, a second AlGaN barrier layer 523, and a second Si-doped GaN barrier layer 524, which are stacked sequentially from bottom to top; the growth temperature of the second Si-doped GaN barrier layer 522, the second AlGaN barrier layer 523, and the second Si-doped GaN barrier layer 524 are all 825℃-928℃, and the pressure is 50 torr-360 torr.

[0059] The growth temperature of the third InGaN multiple quantum well layer 531 is 720℃~923℃, and the pressure is 50 torr-360 torr; the third low barrier layer 532 is a single-layer or multi-layer GaN structure, and its growth temperature is 825℃-928℃, and the pressure is 50 torr-360 torr.

[0060] Preferably, the fourth low barrier layer comprises a fourth GaN barrier layer 542, a fourth AlGaInN barrier layer 543, a fourth AlGaInN barrier layer 544, and a fourth AlGaN barrier layer 545, which are stacked sequentially from bottom to top.

[0061] The process includes, after depositing the second AlGaInN barrier layer 543 and before depositing the third AlGaInN barrier layer 544, an N-polar annealing treatment is performed in an NH3 atmosphere for 8-180 seconds at a temperature of 830-1150°C and a pressure of 50-600 torr. It should be noted that the rough N-polar surface can reduce the in-plane total internal reflection and light absorption loss of photons in the quantum well, which is more conducive to light extraction and improves the light extraction efficiency. After depositing the fourth AlGaInN barrier layer 3544 and before depositing the fourth AlGaN barrier layer 4545, the process further includes: etching roughening annealing in an H2 atmosphere for 5-180 seconds at a temperature of 820-1080°C and a pressure of 50-600 torr. It should be noted that the H2 etching roughening annealing process decomposes defects such as poor crystal quality and high-In-content In clusters on the material surface, improving the crystal quality of the material. Simultaneously, the roughened surface reduces in-plane total internal reflection and light absorption loss in the semiconductor material, thus improving light extraction efficiency.

[0062] Specifically, the growth temperature of the fourth InGaN multiple quantum well layer 541 is 750℃~923℃, and the pressure is 50 torr-360 torr. The growth temperature of the fourth GaN barrier layer 1 542 is 828℃-935℃, and the pressure is 50 torr-360 torr; the growth temperature of the fourth AlGaInN barrier layer 2 543 is 800℃-935℃, and the pressure is 50 torr-360 torr; the growth temperature of the fourth AlGaInN barrier layer 3 544 is 800℃-935℃, and the pressure is 50 torr-360 torr; the growth temperature of the fourth AlGaN barrier layer 4 545 is 800℃-935℃, and the pressure is 50 torr-360 torr.

[0063] It should be noted that the epitaxial wafer growth method in this invention employs Veeco C4 MOCVD (Metal Organic Chemical Vapor Deposition) equipment. High-purity H2 (hydrogen), high-purity N2 (nitrogen), or a mixture of high-purity H2 and high-purity N2 are used as the carrier gas. The N source is high-purity NH3, the Al source is TMAl (trimethylaluminum), the Ga source is TMGa (trimethylgallium), the In source is TMIn (trimethylindium), the Si source is SiH4, and the Mg source is CP2Mg.

[0064] The present invention will be further described below with reference to specific embodiments: Example 1 This embodiment provides a low operating current density cyan LED epitaxial structure, including a substrate, on which a buffer layer, an N-type semiconductor layer, a low-temperature stress relief layer, a multi-quantum well light-emitting layer and a P-type semiconductor layer are sequentially stacked.

[0065] The multi-quantum-well light-emitting layer includes a first light blue multi-quantum-well sublayer, a second blue multi-quantum-well sublayer, a third cyan multi-quantum-well sublayer, and a fourth light blue multi-quantum-well sublayer, which are stacked sequentially from bottom to top. The first light blue quantum well sublayer comprises a superlattice structure consisting of a first InGaN quantum well layer and a first high barrier layer that are periodically alternating from bottom to top, with a period number of 2. The first InGaN multiple quantum well layer is an undoped single-layer or multi-layer structure, with an In content of X1, X1=0.12, and a thickness of 3.4nm. The first high barrier layer comprises a first Si-doped GaN barrier layer one, a first AlGaN barrier layer two, and a first Si-doped GaN barrier layer three, which are stacked sequentially from bottom to top; the first Si-doped GaN barrier layer one and the first Si-doped GaN barrier layer three have a thickness of 4.3 nm and a Si doping concentration of 4.55 × 10⁻⁶. 17 / cm³; The Al content in the first AlGaN barrier layer is Y1, Y1=0.19, and the thickness is 3.4nm.

[0066] The second blue light multi-quantum well sublayer comprises a superlattice structure consisting of a second InGaN multi-quantum well layer and a second intermediate barrier layer that are periodically alternating from bottom to top, with a period number of 4.

[0067] The second InGaN multiple quantum well layer is an undoped single-layer or multi-layer structure, with an In content of X2, X2=0.16; the thickness of the second InGaN multiple quantum well layer is 3.4nm; The second barrier layer comprises a second Si-doped GaN barrier layer one, a second AlGaN barrier layer two, and a second Si-doped GaN barrier layer three, which are stacked sequentially from bottom to top; the thickness of the second Si-doped GaN barrier layer one and the second Si-doped GaN barrier layer three is 4 nm, and the Si doping concentration is 4.55 × 10⁻⁶. 17 / cm³; the content of Al component in the second AlGaN barrier layer is Y2, Y2=0.1, and the thickness of the second AlGaN barrier layer is 3nm.

[0068] The third blue-light multiple quantum well sublayer comprises a superlattice structure consisting of a third InGaN multiple quantum well layer and a third low barrier layer that are periodically alternately grown from bottom to top, with a period number of 5.

[0069] The third InGaN multiple quantum well layer is an undoped single-layer or multi-layer structure, with an In content of X3, where X3 = 0.2; the thickness of the third InGaN multiple quantum well layer is 3.4 nm. The third low barrier layer is a single-layer or multi-layer GaN structure, and the thickness of the third low barrier layer is 10.4 nm.

[0070] The fourth light blue quantum well sublayer comprises a superlattice structure consisting of a fourth InGaN quantum well layer and a fourth low barrier layer that are periodically alternating from bottom to top, with a period number of 1.

[0071] The fourth InGaN multiple quantum well layer is an undoped single-layer or multi-layer structure, with an In content of X4, where X4 = 0.12; the thickness of the fourth InGaN multiple quantum well layer is 3.4 nm.

[0072] The fourth low barrier layer includes four GaN barrier layer one, four AlGaInN barrier layer two, four AlGaInN barrier layer three and four AlGaN barrier layer four, which are stacked and grown sequentially from bottom to top. The thickness of the first fourth GaN barrier layer is 2.9 nm; the content of Al component in the second fourth AlGaInN barrier layer is Y.42 Y 42 =0.04, the content of In component is X 42 X 42 =0.05, thickness is 2.9nm; the Al content in the fourth AlGaInN barrier layer is Y 43 Y 43 =0.04, the content of In component is X 43 X 43 =0.11, thickness is 2.9nm; the Al content in the fourth AlGaN barrier layer is Y 44 Y 44 =0.04, thickness is 3.8nm; The fourth AlGaInN barrier layer is Mg-doped with a Mg doping concentration of 9.6 × 10⁻⁶. 18 / cm³.

[0073] Its preparation method is as follows: Provide a substrate; A buffer layer is grown on the substrate; An N-type semiconductor layer is grown on the buffer layer; A low-temperature stress relief layer is grown on an N-type semiconductor layer; A multi-quantum-well light-emitting layer is grown on a low-temperature stress-relieving layer; A P-type semiconductor layer is grown on a multi-quantum-well light-emitting layer; The multi-quantum-well light-emitting layer includes a first light blue multi-quantum-well sublayer, a second blue multi-quantum-well sublayer, a third cyan multi-quantum-well sublayer, and a fourth light blue multi-quantum-well sublayer, which are stacked sequentially from bottom to top. In the first light blue light multi-quantum well sublayer; The growth temperature of the first InGaN multiple quantum well layer is T1, T1=830℃, and the pressure is 150 torr; the growth temperature of the first Si-doped GaN barrier layer one and the first Si-doped GaN barrier layer three are both 860℃, and the pressure is 150 torr; the growth temperature of the first AlGaN barrier layer two is 860℃, and the pressure is 150 torr.

[0074] In the second blue light multi-quantum well sublayer; The growth temperature of the second InGaN multiple quantum well layer is T2, T2=800℃, and the pressure is 150 torr; the growth temperature of the second Si-doped GaN barrier layer one and the second Si-doped GaN barrier layer three are both 860℃, and the pressure is 150 torr; the growth temperature of the second AlGaN barrier layer two is 860℃, and the pressure is 150 torr. In the third blue-light multi-quantum-well sublayer; The growth temperature of the third InGaN multiple quantum well layer is T3, T3=770℃, and the pressure is 150 torr; the third low barrier layer is a single-layer or multi-layer GaN structure, and its growth temperature is 860℃, and the pressure is 150 torr.

[0075] In the fourth light blue multi-quantum well sublayer; The growth temperature of the fourth InGaN multiple quantum well layer is T4, T4=830℃, and the pressure is 150 torr; the growth temperature of the first fourth GaN barrier layer is 860℃, and the pressure is 150 torr; the growth temperature of the second fourth AlGaInN barrier layer is 860℃, and the pressure is 150 torr; the growth temperature of the third fourth AlGaInN barrier layer is 860℃, and the pressure is 150 torr; the growth temperature of the fourth fourth AlGaN barrier layer is 860℃, and the pressure is 150 torr.

[0076] Example 2 The difference between this embodiment and Embodiment 1 is that: X1=0.13, X2=0.13, X3=0.18, X4=0.1.

[0077] Example 3 The difference between this embodiment and Embodiment 1 is that: X1=0.1, X2=0.18, X3=0.22, X4=0.13.

[0078] Example 4 The difference between this embodiment and Embodiment 1 is that: The thickness of the first InGaN multi-quantum-well layer is 2.05 nm; The thickness of the first Si-doped GaN barrier layer is 6.8 nm, the thickness of the second AlGaN barrier layer is 5.8 nm, and the thickness of the third Si-doped GaN barrier layer is 6.8 nm. The thickness of the second InGaN multiple quantum well layer is 2.05 nm; The thickness of the second Si-doped GaN barrier layer one is 6.5 nm, the thickness of the second AlGaN barrier layer two is 5 nm, and the thickness of the second Si-doped GaN barrier layer three is 6.5 nm.

[0079] Example 5 The difference between this embodiment and Embodiment 1 is that: The thickness of the third InGaN multiple quantum well layer is 2.05 nm, and the thickness of the third low barrier layer is 15.8 nm. The thickness of the fourth InGaN multiple quantum well layer is 2.05 nm, the thickness of the first fourth GaN barrier layer is 5.2 nm, the thickness of the second fourth AlGaInN barrier layer is 5.2 nm, the thickness of the third fourth AlGaInN barrier layer is 5.2 nm, and the thickness of the fourth fourth AlGaN barrier layer is 6.8 nm.

[0080] Example 6 The difference between this embodiment and Embodiment 1 is that: Only the fourth AlGaInN barrier layer is Mg-doped, with a Mg doping concentration of 9.6 × 10⁻⁶. 18 / cm³.

[0081] Example 7 The difference between this embodiment and Embodiment 1 is that: Only the fourth AlGaN barrier layer is Mg-doped, with a Mg doping concentration of 9.6 × 10⁴. 18 / cm³.

[0082] Example 8 The difference between this embodiment and Embodiment 1 is that: The fourth AlGaInN barrier layer 2, the fourth AlGaInN barrier layer 3, and the fourth AlGaN barrier layer 4 are all Mg-doped, with a Mg doping concentration of 9.6 × 10⁻⁶. 18 / cm³.

[0083] Example 9 The difference between this embodiment and Embodiment 1 is that: The growth temperature T1 of the first InGaN multiple quantum well layer is 800℃, the growth temperature T2 of the second InGaN multiple quantum well layer is 830℃, the growth temperature T3 of the third InGaN multiple quantum well layer is 770℃, and the growth temperature T4 of the fourth InGaN multiple quantum well layer is 800℃.

[0084] Comparative Example 1 This comparative example provides a blue LED epitaxial structure, including a substrate, on which 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 are sequentially stacked. The multi-quantum-well light-emitting layer has a periodic structure of alternating InGaN multi-quantum-well layers and GaN quantum barrier layers, with a stacking period of 8. Within a single period, the InGaN quantum well layer has an In content of 0.17%, and the thickness of the InGaN quantum well layer is 3.4 nm; the thickness of the GaN quantum barrier layer is 13 nm.

[0085] The epitaxial structures obtained in the examples and comparative examples were fabricated into 20μm×20μm MicroLED chips and tested at currents of 3μA / 10μA / 30μA. The luminous efficacy improvement, emission wavelength / nm, WD STD (nm) and XRD test results of the epitaxial wafers were measured. The luminous efficacy improvement was calculated based on Comparative Example 1.

[0086] The performance test results are shown in Table 1.

[0087] Table 1 Performance test results of the examples and comparative examples

[0088] Arcsec (002) data can characterize screw dislocations, while arcsec (102) data can characterize mixed dislocations of screw and edge dislocations. The smaller the value of arcsec (002) or arcsec (102), the lower the dislocation density and the better the crystal quality. WDSTD mainly reflects the wavelength standard deviation. The smaller the standard deviation, the more concentrated the chip parameter distribution and the more stable the manufacturing process.

[0089] As can be seen from the above results, the electron blocking layer between the multi-quantum-well light-emitting layer and the P-type semiconductor layer is eliminated in this invention, and the multi-quantum-well light-emitting layer includes a first light blue multi-quantum-well sublayer, a second blue multi-quantum-well sublayer, a third cyan multi-quantum-well sublayer, and a fourth light blue multi-quantum-well sublayer, which are stacked sequentially from bottom to top; and the superlattice structure of each layer is designed with a gradient decreasing barrier height, which significantly improves the crystal quality of the multi-quantum-well light-emitting layer and improves the hole injection efficiency of the P-type semiconductor layer, thereby improving the luminous efficacy and luminous stability of the cyan LED epitaxial structure under low operating current density, making it suitable for small-size, low-current, and low-power cyan Micro LEDs.

[0090] The above description represents the preferred embodiments of the present invention. It should be noted that those skilled in the art can make various improvements and modifications without departing from the principles of the present invention, and these improvements and modifications are also considered to be within the scope of protection of the present invention.

Claims

1. A low operating current density blue LED epitaxial structure, characterized in that, It includes a substrate, on which a buffer layer, an N-type semiconductor layer, a low-temperature stress relief layer, a multi-quantum-well light-emitting layer and a P-type semiconductor layer are sequentially stacked; The multi-quantum-well light-emitting layer includes a first light blue multi-quantum-well sublayer, a second blue multi-quantum-well sublayer, a third cyan multi-quantum-well sublayer, and a fourth light blue multi-quantum-well sublayer, which are stacked sequentially from bottom to top. The first light blue quantum well sublayer comprises a superlattice structure in which a first InGaN quantum well layer and a first high barrier layer are periodically and alternately grown from bottom to top. The second blue light multi-quantum well sublayer comprises a superlattice structure in which a second InGaN multi-quantum well layer and a second intermediate barrier layer are periodically alternating from bottom to top. The third blue light multiple quantum well sublayer comprises a superlattice structure consisting of a third InGaN multiple quantum well layer and a third low barrier layer that are periodically and alternately grown from bottom to top. The fourth light blue light quantum well sublayer comprises a superlattice structure consisting of a fourth InGaN quantum well layer and a fourth low barrier layer that are periodically and alternately grown from bottom to top.

2. The low operating current density blue LED epitaxial structure as described in claim 1, characterized in that, The alternating growth cycle number of the superlattice structure of the first InGaN multiple quantum well layer and the first high barrier layer is 1 to 3; the first InGaN multiple quantum well layer is an undoped single-layer structure or a multi-layer structure, and the In content is X1, 0.10≤X1≤0.13; the thickness of the first InGaN multiple quantum well layer is 2.05nm to 4.78nm. The number of alternating growth cycles of the superlattice structure of the second InGaN multiple quantum well layer and the second intermediate barrier layer is 2 to 5; the second InGaN multiple quantum well layer is an undoped single-layer structure or a multi-layer structure, and the In content is X2, 0.13≤X2≤0.18; the thickness of the second InGaN multiple quantum well layer is 2.05nm to 4.78nm. The alternating growth cycle number of the superlattice structure of the third InGaN multiple quantum well layer and the third low barrier layer is 2 to 8; the third InGaN multiple quantum well layer is an undoped single-layer structure or a multi-layer structure, and the In content is X3, 0.18≤X3≤0.22; the thickness of the third InGaN multiple quantum well layer is 2.05nm to 4.78nm. The number of alternating growth cycles of the superlattice structure of the fourth InGaN multiple quantum well layer and the fourth low barrier layer is 1; the fourth InGaN multiple quantum well layer is an undoped single-layer structure or a multi-layer structure, and the In content is X4, 0.10≤X4≤0.13; the thickness of the fourth InGaN multiple quantum well layer is 2.05nm~4.78nm.

3. The low operating current density blue LED epitaxial structure as described in claim 2, characterized in that, In the multi-quantum well light-emitting layer, X1=X4 <X2<X3; The growth temperature of the first InGaN multiple quantum well layer is T1, the growth temperature of the second InGaN multiple quantum well layer is T2, the growth temperature of the third InGaN multiple quantum well layer is T3, and the growth temperature of the fourth InGaN multiple quantum well layer is T4, where T1=T4>T2>T3.

4. The low operating current density cyan LED epitaxial structure as described in claim 1, characterized in that, The first high barrier layer includes a first Si-doped GaN barrier layer one, a first AlGaN barrier layer two, and a first Si-doped GaN barrier layer three, which are stacked and grown sequentially from bottom to top; The thickness of both the first Si-doped GaN barrier layer one and the third Si-doped GaN barrier layer is 1.8 nm to 6.8 nm, and the Si doping concentration is 1.12 × 10⁻⁶. 17 / cm³~7.98×10 17 / cm³; the content of Al component in the first AlGaN barrier layer II is Y1, 0.02≤Y1≤0.36, and the thickness of the first AlGaN barrier layer II is 1.0nm~5.8nm; The second barrier layer includes a second Si-doped GaN barrier layer one, a second AlGaN barrier layer two, and a second Si-doped GaN barrier layer three, which are stacked and grown sequentially from bottom to top. The thickness of both the second Si-doped GaN barrier layer one and the second Si-doped GaN barrier layer three is 1.6 nm to 6.5 nm, and the Si doping concentration is 1.12 × 10⁻⁶. 17 / cm³~7.98×10 17 / cm³; the content of Al component in the second AlGaN barrier layer is Y2, 0.01≤Y2≤0.18, and the thickness of the second AlGaN barrier layer is 0.8 nm~5.0 nm.

5. The low operating current density cyan LED epitaxial structure as described in claim 4, characterized in that, The total thickness of the first high barrier layer is 10nm~15nm; The total thickness of the second barrier layer is 7nm~13nm; The thickness ratio of the first InGaN multi-quantum-well layer to the first high-barrier layer is 1:2.5 to 1:5; The thickness ratio of the second InGaN multiple quantum well layer to the second middle barrier layer is 1:2.5 to 1:

5.

6. The low operating current density cyan LED epitaxial structure as described in claim 4, characterized in that, The third low barrier layer is a single-layer or multi-layer structure of GaN, and the thickness of the third low barrier layer is 5.0 nm to 15.8 nm. The total thickness of the fourth low barrier layer is 8 nm to 16 nm. The thickness ratio of the third InGaN multiple quantum well layer to the third low barrier layer is 1:2.4 to 1:4.5; The thickness ratio of the fourth InGaN multiple quantum well layer to the fourth low barrier layer is 1:2.5 to 1:

5.

7. The low operating current density cyan LED epitaxial structure as described in claim 6, characterized in that, The fourth low barrier layer includes four GaN barrier layer one, four AlGaInN barrier layer two, four AlGaInN barrier layer three and four AlGaN barrier layer four, which are stacked and grown sequentially from bottom to top. The thickness of the first fourth GaN barrier layer is 0.6 nm to 5.2 nm; the content of Al component in the second fourth AlGaInN barrier layer is Y. 42 0.01≤Y 42 ≤0.08, the content of In component is X 42 0.01≤X 42 ≤0.09, thickness is 0.6nm~5.2nm; the content of Al component in the fourth AlGaInN barrier layer is Y 43 0.01≤Y 43 ≤0.08, the content of In component is X 43 0.02≤X 43 ≤0.11, thickness is 0.6nm~5.2nm; the Al content in the fourth AlGaN barrier layer is Y 44 0.003≤Y 44 ≤0.06, thickness is 0.8nm~6.8nm; Specifically, at least one of the fourth AlGaInN barrier layer two, the fourth AlGaInN barrier layer three, and the fourth AlGaN barrier layer four is Mg-doped, with a Mg doping concentration of 2.1 × 10⁻⁶. 18 / cm³~7.9×10 19 / cm³.

8. The low operating current density cyan LED epitaxial structure as described in claim 7, characterized in that, The content of Al component in the first AlGaN barrier layer 2 is greater than the content of Al component in the second AlGaN barrier layer 2, and the thickness of the first AlGaN barrier layer 2 is greater than or equal to the thickness of the second AlGaN barrier layer 2. The Al content of the second and third AlGaInN barrier layers is the same, and the In content of the second AlGaInN barrier layer is less than that of the third AlGaInN barrier layer.

9. A method for fabricating a low operating current density blue LED epitaxial structure as described in any one of claims 1 to 8, characterized in that, include: Provide a substrate; A buffer layer is grown on the substrate; An N-type semiconductor layer is grown on the buffer layer; A low-temperature stress relief layer is grown on an N-type semiconductor layer; A multi-quantum-well light-emitting layer is grown on a low-temperature stress-relieving layer; A P-type semiconductor layer is grown on a multi-quantum-well light-emitting layer; The multi-quantum-well light-emitting layer includes a first light blue multi-quantum-well sublayer, a second blue multi-quantum-well sublayer, a third cyan multi-quantum-well sublayer, and a fourth light blue multi-quantum-well sublayer, which are stacked sequentially from bottom to top. The first light blue light multi-quantum well sublayer comprises a superlattice structure in which a first InGaN multi-quantum well layer and a first high barrier layer are periodically and alternately grown from bottom to top. The second blue light multi-quantum well sublayer comprises a superlattice structure in which a second InGaN multi-quantum well layer and a second intermediate barrier layer are periodically alternating from bottom to top. The third blue light multiple quantum well sublayer comprises a superlattice structure consisting of a third InGaN multiple quantum well layer and a third low barrier layer that are periodically and alternately grown from bottom to top. The fourth light blue light quantum well sublayer comprises a superlattice structure consisting of a fourth InGaN quantum well layer and a fourth low barrier layer that are periodically and alternately grown from bottom to top.

10. The method for fabricating a low-current-density blue LED epitaxial structure as described in claim 9, characterized in that, The fourth low barrier layer includes four GaN barrier layer one, four AlGaInN barrier layer two, four AlGaInN barrier layer three and four AlGaN barrier layer four, which are stacked and grown sequentially from bottom to top. After depositing the fourth AlGaInN barrier layer two and before depositing the fourth AlGaInN barrier layer three, the process further includes: performing N polar annealing in an NH3 atmosphere for a processing time of 8~180s, a processing temperature of 830℃~1150℃, and a processing pressure of 50torr~600torr. After depositing the fourth AlGaInN barrier layer three and before depositing the fourth AlGaN barrier layer four, the process further includes: etching roughening annealing in an H2 atmosphere for a processing time of 5~180s, a processing temperature of 820℃~1080℃, and a processing pressure of 50torr~600torr.

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